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WASTEWATER RECLAMATION AT ST. CROIX, U.S. VIRGIN ISLANDS By OSCAR KRISEN BUROS A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1975 Saint Croix It's been many things to me but certainly it is an unforgettable Virgin. ACKNOWLEDGEMENTS The author wishes to state his gratitude to: The members of his supervisory committee who originally encouraged him to use this project as a dissertation and have supported him during its completion. The firm and personnel of Black, Crow and Eidsness, Inc., for their complete support and backing during the long period of work in the islands and the preparation of this dissertation. R. David G, Pyne who has given him the aid and advice needed back in the mainland. To the many Virgin Islanders who he has met and worked with during the past four and a half years. To his wife for her patience and encouragement during the project and especially during the writing of this dissertation. To the U.S. Environmental Protection Agency and the Government of the Virgin Islands who funded the project. m TABLE OF CONTENTS ACKNOWLEDGEMENTS ABBREVIATIONS AND SYMBOLS ABSTRACT SECTION I INTRODUCTION II III IV Description of St. Croix Outline of the Wastewater Reclamation Project Dissertation Introduction Early History The U.S. Navy in the Virgin Islands Groundwater on St. Croix Development of the Water Supply PRELIMINARY INVESTIGATIONS OF THE RECHARGE AND STUDY AREA Selection of the Recharge and Study Area Description of the Study Area Golden Grove Recharge Area Negro Bay Recharge Area Hydrological Developments in the Study Area Water and Wastewater Systems on the Island DESCRIPTION OF THE PROJECT FACILITIES Advanced Wastewater Treatment Plant (AWWTP) Recharge Areas MONITORING ACTIVITIES DURING THE PROJECT Water Quality Groundwater Quantity and Movement Advanced Wastewater Treatment Plant Page iii vii X 1 14 24 LITERATURE REVIEW OF THE WATER RESOURCES ON ST. CROIX 25 25 26 28 31 39 51 51 69 79 85 89 92 103 103 128 145 145 149 152 TV TABLE OF CONTENTS (CONTINUED). SECTION Page VI MAJOR PROBLEM AREAS ENCOUNTERED IN THE PROJECT 156 Conceptual 156 Coordinated Planning 157 Changing Conditions 158 Project Location 159 Delays 160 Equipment Outages 160 Natural Disasters 161 Summary 161 VII OTHER ACTIVITIES ASSOCIATED WITH THE WASTEWATER RECLAMATION PROJECT 162 Irrigation 162 Clam Culture 164 Pisciculture 165 Interrelationship 165 VIII RESULTS AND DISCUSSION 166 Water Quantity Changes Due to Recharging 166 Water Quality Changes Due to Recharging 194 IX CONCLUSIONS 209 X RECOMMENDATIONS 211 APPENDIX PART A LOGS OF PROJECT WELLS 226 PART B PRIMARY WELLS—ANALYTICAL DATA 236 PART C SECONDARY WELLS—ANALYTICAL DATA 271 PART D STREAM SAMPLES—ANALYTICAL DATA 294 PART E AWWTP OPERATIONAL DATA 301 PART F SOIL BORING INFORMATION 304 PART G WATER LEVELS IN PROJECT WELLS 307 PART H ENGLISH TO METRIC CONVERSION 339 TABLE OF CONTENTS (CONTINUED). Page REFERENCES 341 BIOGRAPHICAL SKETCH 347 VI PVC Polyvinyl chloride PWD Public Works Department SAR Sodium absorption ratio sec Seconds sq Square Std Dev Standard deviation SVI Sludge volume index TDS Total dissolved solids USDA U.S. Department of Agriculture USGS U.S. Geological Survey V.I. Virgin Islands WAPA Water and Power Authority wk Weeks Well Abbreviations and Symbols A Adventure BMW Bethlehem Middle Works E Envy F Fountain FP Fair Plains G6 Golden Grove GP Grove Place LL Lower Love MB Manning Bay NB Negro Bay P Paradise PW Project well UB Upper Bethlehem viii A Rain gage Public well --pumped ^ Public well --not pumped H Private well --pumped H Private well --not pumped ^ Sampling station on a stream IX Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy WASTEWATER RECLAMATION AT ST. CROIX, U.S. VIRGIN ISLANDS by Oscar Krisen Buros Chairman: Thomas deS. Furman Major Department: Environmental Engineering Sciences St. Croix is the largest island in the Territory of the U.S. Virgin Islands which are located 1,100 miles (1,770 km) southeast of Miami, Florida. The increased water consumption on St. Croix caused by an expanding population and a rising standard of living has seriously depleted the island's limited freshwater reserves. Several seawater desalinization plants have been built on the island to produce potable water but they are very expensive to operate. In order to conserve what water is available the concept of water reuse was proposed in 1968. This developed into a wastwater reclamation project which began work in 1971 to ascertain the technical and economic feasibility of employing wastewater effluent so as to increase the island's freshwater resources. The major use was to be for the artificial recharging of the groundwater. The wastewater reclamation project on St. Croix has demonstrated that it is possible to economically augment the island's freshwater reserves through the use of reclaimed wastewater for the artificial recharge of groundwater. The most successful method of recharge has been with the use of spreading basins in Estate Golden Grove. The project has spanned close to 4-1/2 years and has resulted in the construction and operation of an advanced wastewater treatment plant and recharge facilities which can process up to 0.5 mgd (1,892 cu ni/day). Investigation of the geology, hydrology, and groundwater movement in the area and the compilation of considerable data on treatment plant operations, recharge activity, well water quality, and groundwater quantity has been completed. After numerous delays in the construction of the treatment plant, recharging operations began in February, 1974. During the subsequent 8 months various minor problems in the system were resolved and plant production steadily increased until in October, 1974, it was possible to recharge an average of 1 mil gal/wk (3,785 cu m/wk). The restriction at that point was caused by a lack of wastewater influent. Of the two recharge sites utilized it was possible to eliminate one and focus all attention on the most feasible site at Estate Golden Grove. At the recharge rate used in Golden Grove, no significant adverse effects were observed in the groundwater extracted downstream of the project. There was, however, evidence of a notable increase in available groundwater in the vicinity of the recharge activities. The major problems experienced during the project's operational phase were: 1. The lack of sufficient wastewater for treatment and subsequent recharge. XT 2. The mechanical failure of equipment associated with the treatment process. 3. The transfer, to the central treatment plant, of wastewater containing a high percentage of seawater. This last problem, followed immediately by a record flood on the island, caused the premature termination of the recharge activities in October, 1974. Although the flood damage has been repaired, it is not expected that the saltwater problem will be resolved until the latter part of 1975. At that time it will be possible to resume the artificial recharge activities. Using the present facilities for treatment and recharging it is estimated that recoverable groundwater could be increased by at least 0.3b mgd (1,351 cu m/day) at the recovered water cost of about $2.15/ thousand gal ($0.56/cu m). Although this is considerably higher than the $Q.30/thousand gal ($0.08/cu m) estimated for recovering the limited amount of groundwater, it is much cheaper than the cost of $5. 16/thousand gal ($1.36/cu m) for water produced by the government's desalinization plant on the island and additionally it will provide a dependable source of fresh water for St. Croix. xn SECTION I INTRODUCTION Description of St. Croix St. Croix is the largest of the more than 50 islands and cays which comprise the Territory of the U.S. Virgin Islands. The Virgin Islands are located 1,100 miles (1,770 km) southeast of Miami, Florida, and have been a posses:^, ion of the United States since 1917 when they were purchased from Denmark (see Figure 1). St. Croix is 84 sq miles (217 sq km) in area. It is about 20 miles (32.2 km) long and 6 miles (9.6 km) wide at its broadest point (see Figure 2). A range of low mountains forms a spine along its longer east-west axis. The Northside Range at the western half of the island hugs the northern shore and a flat coastal plain has been formed from the foothills of the range to the south shore. It is on this coastal plain between the two major towns of Frederiksted and Christiansted that the majority of the people of the island live. The island has about 40,000 inhabitants and the major source of employment is in alumina processing, petroleum refining, watch assembling, tourist-related services, or ^jovernment agencies. Agriculture, which used to be the largest source of income on the island, has dwindled considerably in the last decade. The growing of sugarcane has been CN 1X1113 2 t^TlLLEs' u f f^''^''-^-^^^- phased out, leaving beef cattle and dairy products as the major agricultural enterprises. In the latter part of the eighteenth century when agriculture was the only industry, the entire island was divided up into plots of about 150 to 300 acres (61 to 122 ha). Each plot was called an estate and given a name. This system of estate division remains today and forms an important function in the location of any point on the island. These names, such as Golden Grove, Adventure, and Negro Bay, are used throughout this report to aid in the location of areas for those familiar with the island. Water Supply Along with this shift from a rural agricultural -economy towards industrial growth and tourism, there has been a rapid increase in population and a rise in the standard of living. With these changes has come a massive increase in total water consumption. Although each dwelling is still required by law to be constructed so as to catch and store the rainv;ater from its roof as a basic source of water, it has been necessary for the government to augment this supply through a water distribution system. This additional water was originally derived from wells located in the central part of St. Croix, but is now supplemented by large seawater desalinization plants located in Christiansted and mid-island at the Martin Marietta Alumina Company, The combination of rainwater catchments and groundwater could go a long way in satisfying the demand for water on the island, but they are very much dependent on the pattern of weather in the area. c u s- 0) o s- (lOsn3A3T Oiai3IA10I±N310d 3AllV13y (•"OllVdNIVa AlHiNOlAl 1V10± In the past few years this pattern has tended to minimize the benefits to be derived, directly or indirectly, from the rainfall. Figure 3 compares rainfall and the water levels in two wells in central St. Croix over the past 4 years. Although the average rainfall over this short period approaches the norm expected, the distribution of rainfall throughout the individual years has made it difficult for efficient cistern storage and has detrimentally affected the efficient natural recharge of the groundwater. The combination of reduced rainfall, a diminished groundwater supply, and increased individual consumption has caused the demand to exceed the production of water from these traditional sources. Although only about 70 percent of the populace is connected to the public distribution system, it has been necessary to use increasing amounts of desalinized water in the system until presently the groundwater contribution to the total water supply picture is only about 30 percent. The desalinized water for the potable system is produced by two distillation plants, one operated by the Virgin Islands Water and Power Authority (WAPA) and the other by the Martin Marietta Alumina Company. Each provides about 0.65 mgd (2,460 cu m/day) to the system. The average amount of water being distributed in the public system during the spring of 1975 was about 1.8 mgd (6,813 cu m/day). This amount represents the supply and not the demand, as the demand for water exceeds this figure by possibly as much as 30 percent for just the existing hookups. Additionally, in the past year or so at least 14 miles {72.5 km) of water mains have been added to the system. Connections to these new mains have been almost nil as there 10 is insufficient water in the system to properly service any new consumers. It has been quite normal to wait 2 to 3 years for individual homes to obtain permission to hook up to the potable distribution system and even after the connection is made there is no assurance that a steady supply of water will be available. Water Costs As the price of petroleum has increased so has the cost of producing desalinized water, which requires oil-fired boilers to produce the steam used in the distillation process. Since almost two- thirds of the water in the public potable system is derived from distillation plants the aggregate cost has increased drastically. The changing cost to the public system for this water over the past three years is shown in Figure 4. This shows the cost to the government from both the WAPA and the Martin Marietta plants. In June, 1975, the cost of water from these plants was $5. 16/thousand gal ($1.36/cu m) and $6.86/thousand gal ($1.81 cu m) respectively, for an average of 0.75 mgd (2,839 cu m/day). This is compared to the estimated cost of $0.30/thousand gal ($0.08/cu m) for groundwater produced on the island. Although water is sold to the general public for $4.00/thousand gal ($1.05/cu m), which is about ten times the cost in the mainland United States, the government is still losing money in distributing it due to the high proportion of expensive desalinized water used. At present the WAPA is increasing its water supply capacity by the construction of a new 2.25 mgd (8,516 cu m/day) desalting plant s- <u o. 12 (|bB puesnoMVsje||op)is03 39Va3AV 13 which should be on line sometime in the latter part of 1975. Although this could possibly give the island a surplus of water, it is realized that the Martin Marietta Alumina Company will soon be phasing out its sales of water to the government and that in the past the consumer demand has always risen to match the am.ount of water that the government has been able to distribute. Water Reuse With the water supply system based mainly on desalted water, the water is converted from seawater to fresh water at great expense, used once, and then returned to the ocean as wastewater. Not only is it expensive, but also the expansion of the desalination facilities creates a situation where there is a greater dependency upon water from a single source instead of the more versatile multiple-source concept which the island still possesses. If this desalted water could be used once, processed for reuse, and utilized again before being completely degraded by discharge back into the ocean, the cost of the processing between uses should be significantly below the expense currently required to recover fresh water from the ocean by distillation. The potential source of this reusable water, public wastewater flows, receives only primary or no treatment at all before being discharged into the ocean. However, in accordance with the current implementation of federal environmental legislation, it may soon be necessary to provide secondary treatment to all wastes discharged from the island. All of these steps require progressively higher quality effluent, and yery little extra processing is required to adapt these effluents to various water reuse programs on the island. Among these programs would be reuse for agricultural irrigation, pisciculture, groundwater augmentation, fire control, prevention of saltwater intrusion, and various industrial purposes. The idea of wastewater reclamation is not new, the inadvertent reuse of wastewater being rather widespread throughout the United States and the rest of the world. It is a major factor necessitating the treatment of water before distribution to the public. Koenig (1966) in a study of 155 communities in the United States served by surface water found that, including industrial wastewaters, the median reuse factor was about 50 percent. Throughout the world there are areas where deliberate reuse of wastewater is being practiced. These are predominantly in the arid regions where the cost of procuring new water exceeds that of processing wastewater for reuse. Localities in California, Texas, Israel, and South Africa are utilizing wastewater reclamation plants for various purposes. Outline of the Wastewater Reclamation Project Project Description The concept of wastewater reclamation and its subsequent reuse for groundwater recharge on St. Croix has been studied and suggested by the U.S. Geological Survey (Robison, 197?^; Jordan, 1973) and engineering consultants (Engineering-Science Inc., 1968). This report covers a study entitled "Wastewater Reclamation Project on St. Croix, U.S. Virgin Islands," which was sponsored by the U.S. Environmental Protection Agency (EPA) and the Virgin Islands Government, Division of Natural Resources Management. In this project a portion of the flow 15 normally discharged to the sea from the island's new primary treatment plant at Bethlehem Middle Works was used for reclamation purposes. The flow was diverted and processed in an advanced wastewater treatment plant (AWWTP) adjacent to the primary plant. Processing was by biological and physiochemical means and produced a treated wastewater which was conveyed by a force main to recharge areas located about 1-1/4 miles (2 km) away. Here it was stored in a holding tank and introduced into the groundwater aquifers by various methods. This was for the purpose of improving the yield of wells in the area and assisting in preventing further seawater intrusion which threatens Fair Plains, one of the government's major well fields on the island. The project was handled for the government by the consulting engineering firm of Black, Crow and Eidsness, Inc., of Gainesville, Florida. Project personnel worked on the island continuously from April, 1971, to October, 1975, studying the problem, supervising the construction, operating all of the facilities involved, and evaluating the results. Early in the project the recharge sites were located and a study area of about 8 square miles (23 km) was defined, which included the drainage basins where the recharge activities would take place. Wells and surface water throughout this study area were monitored for 2-1/2 years in order to clarify the hydrological characteristics of the region and to establish baseline data for the project before recharging began. The study area is outlined in Figures 2 and 5. The most important portion of the region is shown in detail in Figure 6. 17 19 20 Project Objective The overall objective of this project was to determine the feasibility of increasing the freshwater reserves on St. Croix by the use of wastewater reclamation. This consisted of the artificial recharge of the groundwater on the island using tertiary-treated wastev/ater effluent. The project entailed not only the operation of the treatment and recharge facilities but the study of the wastewater collection system; the geohydrological character of the recharge area and the subsequent water distribution; evaluation of the effects on the groundwater regime; and the costs associated with the production of fresh water in this manner. Project Phases The project was divided into four phases: initiation, investigation, operation, and evaluation. A diagrammatical outline of these phases and their scheduling during the project is shown in Figure 7. Phase 1 - Initiation . This included the discussions and efforts made in formulating a proposal that outlined the steps of the investigation and proposed a budget to match these plans. During this time the grant application and approval were obtained and a contractual agreement between the parties involved was defined and finalized. This phase ended in March, 1971, with the assignment of a full-time engineer to the project who began field work on St. Croix the following month. Phase 2 - Investigation, design, and construction . This phase covered the investigation of the conditions that affect the recharging 22 z S2z Occ <z >i 2< <Z(- ^ <Qa. > Z m LU <(r h- 23 operation and included the selection of the sites for recharging and the area to be monitored during the project. Studies were made of the hydrology, geology, soils, land use, groundwater, and surface water, in the study area. A monitoring program was begun to establish baseline data on water quality and quantity. An advanced wastewater treatment plant (AVfWTP), force main, holding tank, and recharge facilities v/ere designed and constructed. All facilities were tested for operation. This phase was completed in January, 1974. Phase 3 - Operation . Phase 3 began in February, 1974, and consisted of operating the plant and recharge facilities. Improvements and modifications v;ere made to the AWWTP and recharge facilities as required during the operational phase. Recharging operations continued until October, 1974, when they were curtailed due to the high total dissolved solids (IDS) in the incoming wastewater. In November, 1974, the primary plant and wastewater collection network were rendered inoperative by heavy rains and flooding. Also damaged were the recharge facilities in Estate Golden Grove. Repairs to all facilities were completed by May, 1975. However, further recharge operations were restricted by the high IDS in the collected wastewater due to the use of salt water for flushing in the town of Frederiksted. The operational phase of the project ended in May, 1975, with the complete transfer of the project facilities to the Virgin Islands Government, Division of Natural Resources Management. Phase 4 - Evaluation . The data gathered throughout the project were evaluated to determine the actual feasibility of the project, both on a technical and economical basis. This final report 24 contains the results oT the evaluation and contains recommendations for further development of the wastewater reclamation project. Phase 4 was completed in November, 1975, with the completion of this report. Dissertation This dissertation covers the scope of work from phase two through phase four of the project. It includes the investigations, operations, monitoring, and other work necessary in demonstrating and evaluating the feasibility of increasing the water resources on St. Croix by the use of wastewater reclamation. The author was hired by the consulting engineering firm of Black, Crow and Eidsness, Inc. specifically to carry out this project in the Virgin Islands. He moved to St. Croix in April, 1971, and successfully directed the operations on the island until the facilities were turned over to the government in June, 1975. SECTION II LITERATURE REVIEW OF THE WATER RESOURCES ON ST. CROIX Introduction This literature review documents the progress in the study and development of the natural water resources on St. Croix from the time of Columbus through 1975. It discusses the evolution of the water system from open shallow wells to the present work with the reuse of water by wastewater reclamation, which is the subject of this dissertation. To the best of this author's knowledge, this is the most extensive review of literature on the subject of water resources on St. Croix in existence at this time. There is no doubt that there are other documents available that will relate to water resources, in one form or another, that are not included in this review. The absolute dependence of St. Croix on unpre- dictable rains as a major direct source of water in the past has made the Cruzans extremely aware of the importance of fresh water on the island. Presently, many people keep daily rain records and a running tot^l of the year's rainfall so as to guide their consumption of water fr their own cisterns. Judging from this interest in present times ther.: is probably a wealth of unofficial records on rainfall and observations on streamflow, well water quality, and storm runoff 25 26 existing in the form of passing references in letters, diaries, and papers written during the past. Since the water resources on St. Croix were so poorly developed at the time that the United States purchased the island in 1917, there probably were letters or reports to the Danish government with eval- uations and proposals to do something about the lack of a decent v/ater supply. Unfortunately, a considerable amount of public and private documents were destroyed at the time of the island's transfer in 1917 (Lewisohn, 1970) and much of the remainder transferred to Denmark. The literature that is reviewed deals mainly with the time from 1917 to the present when the most intensive activity in actual water resource development took place on St. Croix. Again, other information and documents probably exist on the subject but the literature cited is, in the author's opinion, the most important in guiding and influencing the steady development that has taken place on the island in providing the islanders with a decent, dependable water supply. Early History Virgin Islands historian, Florence Lewisohn (1970), presents the story of western iron's first known concern with water resources on St. Croix. This was in November, 1493, when Columbus made his second voyage to the Americas with a fleet consisting of 17 ships and 1,200 armed men. On November 13, Columbus is believed to have anchored off what is now known as Sugar Bay on St. Croix's north coast. Aside from giving the island its name, Santa Cruz, or the Island of the Holy Cross, he sent men ashore to explore the area and obtain fresh water for the 27 fleet. Salt River, which is actually a freshwater stream, empties into Sugar Bay and it is assumed that the fresh water was obtained there. What is known is the heavy price paid for the water, as in the ensuing contact with the local Carib indians, one of the crew members died after receiving a poisoned arrow in the chest. Columbus and the fleet left soon afterwards without further exploration of the island or its water resources. From that day to the present the freshwater resources on St. Croix have continually played an important role in the development of the island. Substantial settlement of St. Croix did not occur until the early 1700s when, under Danish rule, the island was divided up into estates which were used for the cultivation of sugarcane. Shaw (1933) in his article, "St. Croix: A marginal sugar-producing island," explains that in order to obtain just an average yield of sugarcane, the land requires at least 45 in. (114 cm) of well-distributed rainfall. His study of rainfall records from 1850 to 1930 showed that the annual rainfall was greater than 45 in. (114 cm) for only 43 of the 80 years and noted that generally it was not well distributed throughout the year. He presents a chart showing the rainfall, cane production, and land area under cultivation annually for the 80-year period. The changing sugar yields due to the rainfall, combined with competition from other sugar producers, resulted in alternating cycles of profits and bankruptcies for the plantation owners. The introduction of the sugar beet in the early nineteenth century was a severe blow to St. Croix and it was only during the exceptionally good rainfall years that profits could be made. 28 After the United States purchased the island in 1917, there was an increased effort to revitalize sugar production, but water problems plagued the industry. In 1931 the largest sugar mill on the island, at Bethlehem, went bankrupt after 10 years of extremely dry weather. At this time over 60 percent of St. Croix's population of 11,000 (Lewisohn, 1970) were dependent on agriculture. The decrease in population from 26,600 in 1835 (Johnson, 1936) to 11,000 in 1931 is indicative of the problems on the agriculturally oriented island. The U.S. Navy in the Virgin Islands The United States government has shown interest in the water resource situation in the Virgin Islands from the time of purchase in 1917 to the present. This initially was begun by the Department of the Navy which administered the islands until about 1931. One of the prime reasons for the purchase of the land from Denmark was to keep the islands from falling into German possession if the latter occupied Denmark during World War I. The German-owned Hamburg-American Line already had large docking facilities and a coaling station in neighb ,'ing St. Thomas. Holding the Virgin Islands and nearby Puerto Rico secure was considered vital by the United States for the protection of the Panama Canal. The navy conducted inspections of the Virgin Islands and Puerto Rico relative to the establishment of a large naval base. The rejection of sites in the Virgin Islands for this base was largely dependent on the lack of available fresh v/ater to supply it (Pettigrew, 1921). Lieutenant Pettigrew in 1919 made a report in which he considered the use of shallow wells or the impoundment of surface water in St. Thomas 29 for a water source, but by 1921 he had made measurements of v/ell yields rainfall, and surface runoff and suggested that the Virgin Islands not be considered for a large naval installation. The financial aspect of the problem can be seen in the price of water sold to ships by the West Indian Company Ltd. in Charlotte Amalie, St. Thomas, which was $4. 00/ thousand gal ($1.05/cu m) in September, 1916 (DeBooy and Paris, 1918, p. 269). By 1922 the price charged to U.S. Navy vessels in Charlotte Amalie was up to $6.00/ thousand gal ($1.58/cu m) (Warfield, 1924). In a 1923 report (Bureau of Yards and Docks) to the Secretary of the Navy, it was proposed that a rainwater catchment and storage facility be built to supply 0.3 mgd (1,135 cu m/day) to naval vessels and the town of Charlotte Amalie. The cost of water to be produced from this facility was estimated at $1 .80/thousand gal ($0.48/cu m). Aside from its concern with the small navy base in St. Thomas, the Department of the Navy surveyed conditions in St. Croix and made recommendations for improvements. In June, 1917, less than 3 months after transfer of the islands from Denmark, Surgeon C. S, Butler, USN, wrote a report to the governor of the territory which recommended that sanitation improvements begin in the major towns of Charlotte Amalie in St. Thomas and Christiansted and Frederiksted in St Croix. The governor requested $2 million for this purpose the following month, but no appropriation was made. In August, 1917, Gaylord Church, a civil engineer with the U.S. Navy, submitted a report to the governor of the territory recommending that in St. Croix consideration be given to supplying the town of 30 Christiansted, population 4,500, with a freshwater source derived from shallow wells or an impounding reservoir. While for Frederiksted, population 3,000, he advised an impounding reservoir. For both towns he suggested consideration of the use of salt water for flushing purposes. During that same month a board submitted a report on sanitary conditions in the Virgin Islands. It was the board's stated opinion that "the securing of fresh water in the islands has driven into the minds of the board the conclusion that the standard of civilization is almost dependent upon the amount of fresh water that is used per person" (Bureau of Yards and Docks, 1917). Commander Warfield, USN, reviewed the status of water and sewerage systems in 1924 in a detailed report to the Secretary of the Navy. He noted that in Christiansted only 348 of the 560 houses had guttering to divert water for cistern collection. The total cistern storage capacity of the town was about 1.4 mil gal (5,300 cu m) , He estimated that 60 percent of the inhabitants either drank brackish water from the 124 wells in the town or else depended on obtaining water from neighbors or from government- or church-owned cisterns. He stated that these facilities were insufficient to supply these people during prolonged dry periods. He recommended the construction of additional storage facilities totalling 2.5 mil gal (9,463 cu m) and the development of a drainage basin in the hills above Christiansted for use as a natural catchment and reservoir. In Frederiksted, Cociniander Warfield estimated the town's storage capacity at 0.8 mil gal (3,023 cu m) and suggested that this be increased by 1.8 mil gal {6,813 cu m). He mentions that the town 31 was supplied by rainwater collected in cisterns and brackish water from wells. He recommended as an alternative to increasing storage in town, the impoundment of surface water from either Jolly Hill or Creque Gut. He favored the use of Creque Gut and advised the construction of a 4-ft (1.22 m)-high diversion dam and a 0,5 mil gal (1,893 cu m) storage reservoir with facilities for filtration and chlorination. The Creque Gut project was, in fact, carried out in 1926 with a 60-ft (18.3 m)-high concrete arch dam being constructed with a storage capacity of 9 mil gal (34,065 cu m). Warfield summed up his report by noting that the present system of night soil removal of human wastes in Christiansted and Frederiksted was satisfactory, bearing in mind the economic conditions of the towns. Therefore he recommended that the installation of saltwater flushing and sewer systems be deferred for the present. This lack of flush toilets helps to explain why the planners for water systems in these towns at that time used the figure of 5 to 7.5 gpd/cap (19 to 28 1 /day/cap) for consumption estimates. Naval administration of the island ended in about 1931 when control of the islands was transferred to the Department of the Interior. Groundwater on St. Croix Groundwater has probably been a source of water on St. Croix for hundreds of years. It supplied many of the villages scattered throughout the island. From evidence that remains today these supplies were generally from hand dug shallow wells and water was usually obtained by the use of a rope and bucket. Although the windmill was ^ery cormion 32 in the islands for grinding cane during the eighteenth and nineteenth centuries, only a small percentage of them were used for v;ater purposes. It was not until the 1920s when the fan mill was introduced into the island that wind power was effectively used for pumping water. Groundwater Geology The development of groundwater resources on St. Croix was aided immensely by the observations of geologists concerning the formation and structure of the island. Being off the beaten track, the island did not have a legion of geologists who visited it, but those who did served it well. Cederstrom (1950) covers the work of the early geologists summarizing their findings and giving a rather complete bibliography of their publications which will not be repeated here. One visitor not mentioned by Cederstrom was Taylor (1888) who wrote of his observations of the Danish West Indies and included a short but concise geological description of St. Croix. He also included some temperature data for the islands and presented a table of the mean monthly rainfall in St. Thomas compiled over an 11-year period by a Dr. Hornbeck. The mean annual rainfall from these data was 46.8 in. (119 cm). With the assumption of control over the islands by the United States in 1917, a series of geologists visited the island with the express purpose of studying its potential for groundwater development. Groundwater was desired as a source of water for the inhabitants, the sugar factories, and for large-scale irrigation schemes. In 1919 a geologist from the U.S. Geological Survey, Dr. Thomas W. Vaughan, spent about a month studying St. Thomas, St. John, and 33 eastern Puerto Rico. During that time he made a quick reconnaissance of St. Croix (Vaughan and Kidwell, 1920) to consider the possibility of groundwater on the island. One of Vaughan's most important conclusions was that, based on study and observation, he did not believe that it was possible for groundwater from Puerto Rico to be conveyed under the intervening sea in aquifers so as to be available in the Virgin Islands. Warfield (1924, p. 2) quotes Vaughan on this subject as stating, "Both the composition of these rocks and their geological structure preclude the possibility of their containing supplies of artesian water." Dr. Vaughan went on to mention that the salt content and the extreme hardness of the groundwater in St. Croix rendered it unde- sirable for domestic use and that "all of the waters are of such poor quality for economic purposes that discussion of their merits can only be of a relative value." Dr. James Kemp, a geology professor from Columbia University, visited St. Croix in 1923 to study its geological formations and to try to ascertain what possibilities there were to obtain water from subterranean sources. After his study he reported to the governor (1923) that it was improbable that any deep wells would produce enough water to supply any large-scale irrigation projects on the island, although sufficient water for stock could be developed. More than fifty years have passed since Professor Kemp came to this conclusion, but the author feels it is still a ^jery valid and pertinent observation for present-day planners. 34 Meyerhoff (1927) gave a detailed description of many of the important geological features and formations on St. Croix as part of a large-scale investigation of the Virgin Islands and Puerto Rico by the New York Academy of Sciences in the late 1920s. In 1938 the U.S. Geological Survey sent D. J. Cederstrom to St. Croix where he spent about 5 months studying the island's geology and its relation to groundwater as he assisted the Virgin Islands Company to locate adequate groundwater for one of its sugar mills. Cederstrom subsequently published the information that he gathered in the form of an article on physiography (1941) and a report on geology and groundwater in St, Croix (1950). The latter is the best source of basic information on groundwater for the island. It relates the study of the formations on the island to the existence of ground- water in St. Croix. A detailed geologic map is included in the report, as are numerous observations on wells existing at the time and logs for wells constructed as part of the National Park Service well drilling project during the period 1940 to 1941. One of Cederstrom' s notable contributions to the understanding of groundwater geology on St. Croix was the test hole drilled to a depth of 1,506 ft (459 m) near Fredensborg on the central coastal plain. Drilling was by the rotary clay seal method and the probe penetrated, in this order 25 ft (7.6 m) of alluvial marl, 83 ft (25.3 m) of the Kingshill marl, and was still in the Jealousy formation after 1,398 ft (426.1 m). This test permitted several important geological concepts to be formed; among these were: 35 1. The Kingshill marl is of limited thickness and is underlain by the Jealousy formation. 2. The Jealousy formation, where not weathered, is not a v/ater- bearing strata. Present-day Cruzan well drillers accept this as fact and discontinue drilling once the Jealousy formation is reached. 3. The Jealousy formation is of great thickness even at a short distance from the base of the mountains bordering the the coastal plain. In his article, "Notes on the physiography of St. Croix, Virgin Islands," Cederstrom (1941) discusses the formation of the central coastal plain at length. This is important with regards to groundwater, as the central plain is the source, or potential source, of almost all of St. Croix's public groundwater supply. During the period 1959 to 1951 John Whetten spent 8 months doing geological investigations and other field work on St. Croix which resulted in the publication of his doctoral thesis entitled, "Geology of St. Croix, U.S. Virgin Islands" (1952). This study gives an overall description of the geology of the island with a review of the work which preceded it. Whetten believed that the Jealousy formation, which is a grey montmorillonitic mudstone, was possibly altered volcanic ash that was wind transported from somewhere in the northern part of the Lesser Antilles. This ash filled a graben located in the present central coastal plain. Discussing the Kingshill marl, he mentions that this is apparently a fossil coral reef built between two separate islands which are now the Northside and East End ranges. This formation was 36 followed by general uplift, erosion, and folding actions along with the deposition of the recent alluvial sediments. In brief editorial footnotes in a reprint of another article on St. Croix by Whetten (1968), the editors mention that viork is currently going on to further investigate the interface of the Kingshill marl with the overlying alluvium (Multer and Gerhard, 1974). This will be of interest as this interface is often a productive water-bearing zone and the extent of leakage of water from the alluvium into the marl is a question of importance in understanding groundwater movement on the island. Rainfall Aside from geological theory, information on rainfall has been important in ascertaining the available water which will eventually end up as groundwater. Since the amount of water in a homeowner's cistern is directly proportional to the rainfall, it is not surprising that many Cruzans keep records of the rainfall at their homes. As noted previously Shaw (1933) graphed the annual rainfall from 1850 to 1930. Johnson (1936) presented tables of the monthly rainfall for St. Croix from 1852 to 1936, along with the monthly record of pan evaporation in Christiansted from 1919 to 1935. An isohyetal map of St. Croix is included in a report by Tippetts et al. (1959). This report also includes a hydrograph of the monthly rainfall at Anna's Hope for the years 1920 through 1957, and computes an annuai mean rainfall of 43.31 in. (110.0 cm) for that station. 37 Lawaetz (1974) has taken the rain records from 1872 through 1971 and presented these data as mean monthly rainfall for four 25-year periods. He arrived at a 100-year average of 44.83 in. (113.9 cm). Lawaetz ranked the months as to maximum and minimum rainfall and determined that on a 25-year basis, March had the minimum and September, October, and November had the maximum. Jordan (1973) has graphically displayed the rainfall from 1850 to 1968 in a hydrograph and has shown a plot of the accumulated departure from the mean annual value of 42.45 in. (107.8 cm) for the period. This latter method gives a good indication of the groundwater conditions which depend on the pattern of successive years of rainfall. Bowden (1958) produced a series of rainfall maps which cover St. Croix on a month-to-month basis. These are tied in with rainfall variability curves for rainfall at various locations on the island. He concludes that St. Croix is a dry island and that a water deficit occurs for at least 10 months in a year in most areas due to the high evapo- ration rate. He concludes that the raising of vegetables on a year-round basis would not be possible without supplemental irrigation. The publication lists sources of data for numerous rainfall stations and the years covered by those data. In a study done by Bowden et al . (1970) covering the climate and water balance in the northwest Virgin Islands, the emphasis is on St. Thomas, St. John, and Tortola; but there are some interesting comments on St. Croi . The contention is that in the past the mean rainfall data for the various islands tended to be overestimated. He states that St. Croix's average rainfall should actually be less than 40 in. (101.6 cm), not the 45 in. (114.3 cm) most frequently used. This could be true as the records used are those from the central and eastern portions of St. Croix where most people live. One of the reasons that they live in these areas is that they can get sufficient rainwater to keep a decent water supply in their cisterns and hence one would expect that the rainfall would be higher at these stations. With the problems of drought and too little rainfall in the islands, it is appropriate to note that too much rainfall can also be a burden. Shaw (1932) discusses 1931 as one of the wettest years on St. Croix in which 69.81 in. (177.3 cm) of rain fell. The problem that year was that this excess water created swampy conditions in the Gallows Bay district of Christiansted. This provided a favorable breeding place for anopheles mosquitoes which spread malaria at a tremendous rate through the island. Over 900 cases and 22 deaths from malaria were reported that year, compared to only 15 cases in the previous 12 years. Another visitor who commented on the excess of rain on St. Croix was an anonymous invalid who tried to relieve his chronic respiratory problems by spending the winter in warmer climates. The invalid spent a part of the winter of 1838 to 1839 in St. Croix and subsequently published a book on the experience. He mentions in the book the occurrence of frequent short rain showers, about 4 to 5 times per day, with the intervening periods being filled by scorching sun. Concerning the rain, the invalid commented (An Invalid, 1839, p. 39) "It was generally considered, and I have no doubt correctly too, that exposure either to the sun or rain was dangerous even to the inhabitants. 39 and productive of certain injury to strangers or invalids." This invalid was also fearful of going out at night and soon thereafter departed St. Croix on a brig bound for Cuba. Development of the Water Supply The work of Warfield (1924) in determining the status of the water supply on St. Croix has already been discussed. His recommendations were generally followed by the navy, improving the overall water supply situation to some degree. His work was updated by Johnson (1936) who spent 3 months in St. Croix during 1936. He found that in Christiansted 45 percent of the inhabitants had no cistern^ at all and that during periods of drought 73 percent of the populace lacked a dependable source of water and had to obtain water from neighbors or a municipal cistern. The 16 public wells that were in service at the time were brackish and polluted. He felt that the groundwater quality was apparently degrading due to excess usage for toilet flushing and bathing. During his stay on the island there were 9 cases of typhoid including 3 deaths. He predicated his recommendations for improvements on the basis of a freshwater consumption of 5 gpd/cap (19 1/day/cap), which is the amount set by Dr. Knud-Hansen, Municipal Physician of St. Thomas, as the minimum standard for maintaining health in the Virgin Islanci (Johnson, 1936, p. 10). Johnson recommended the continued reliance on collected rainwater for potable purposes with the expansion of catchment area and cistern storage along with passage of laws to require cisterns in eyery dwelling. 40 He suggested the use of well water only for flushing and bathing. He felt that the Recovery Hill drainage area should be utilized for the impoundment of runoff water which could be used for nonpotable purposes in a separate municipal water system which would be supplemented by seawater as the situation required. Albert Nelthropp, the present Assistant Commissioner of Public Works for the Virgin Islands, related to the author that the separate saltwater system was installed soon after this time. In his opinion the threat of fires in town was a major impetus for its installation. He mentioned that in about 1935 a large fire occurred in a lumber yard located near the corner of Strand and Queen Cross streets which threatened the entire town. The following year a malfunctioning kerosene refrigerator started a serious fire in Government House. Difficulties in getting water to the fire spurred on efforts to install a system of fire hydrants in town. Although money was scarce, labor was abundant and inexpensive. An old cast iron line which was once used to pump sugar juice from the :.;.-inding station at Barren Spot to the Central Mill in Christiansted was dug up and relaid in town. The entire job was done by hand labor and the pipe is still in use in the network today. Generally, seawater has been used in the system. In Frederiksted, Johnson found 8 public wells and 44 percent of the population without cisterns. In droughts, only 23 percent of the population had an assurred adequate supply. At this time Creque Reservoir was the principal source of water for the town. Johnson noted that the reservoir had been drawn empty during past periods of 41 drought; but he attributed this more to wasteful use, rather than leakage of the dam or lack of adequate runoff into the reservoir. However he strongly recommended that weirs be constructed upstream of the reservoir and that measurements by kept on the inflow. He also recommended that the water be chlorinated before distribution to town, so it is probable that Warfield's advice to filter and chlorinate the water had not been followed. Johnson noted that conditions in the Frederiksted area were favorable for wells, although the water would probably be high in minerals and thus probably not suitable for drinking purposes. In the 1930s a homestead program was carried out on St. Croix in which large estates were bought and subdivided into plots of 3 to 10 acres (1.2 to 4.1 ha) for sale to local people. At the same time the federal government created the Virgin Islands Company which attempted to revive the island's ailing sugar industry (Lewisohn, 1970). The result of these acts was to rekindle interest in the exploration for available groundwater, especially since the federal government was heavily financing the work. Cederstrom came to the islands under this program and did his work on groundwater geology in St. Croix, as mentioned previously. In response to a request from the National Park Service, Cederstrom wrote a memo (1940) discussing specific wells existing on homesteads in Whim and La Grange as part of this program. He warned of the danger of overpumping the wells due to potential saltwater intrusion and suggested that many wells be drilled and pumped at a low rate rather than a few pumped at a high rate. In the memo he mentions hearing that "hundreds of 42 barrels of water are being carted daily from the mud hole at Castle Burke," and suggests that a well be installed in the area. He also states that no further wells should be constructed in the homesteads at La Grande Princess, as the groundwater there is already overdrawn and additional pumpage would only be detrimental in its effect. In 1948 the USGS located and supervised the drilling and testing of 19 wells on St. Croix (McGuinness, 1951a). The wells numbered 7, 11, and 13 in the Concordia area were developed for the Christiansted water supply, while the wells numbered 17 and 19 on Mahogany Road were reconstructed for a supply to Frederiksted (Tippetts et al . , 1959). The firm of R. L. Kenan and Associates of Montgomery, Alabama, worked with the USGS on this project. In 1951 McGuinness (1951b) of the USGS advised against any large ground or surface water development until sufficient hydrological data were gathered so as to properly expend any available funds. In 1953, McGuinness briefly reviewed the water resources in the Virgin Islands for the Under Secretary of the Interior and again recommended the collection of data on streamflow, sediment movement, and groundwater availability. In 1958 the consulting engineering firm of Tippetts, Abbett, McCarthy and Stratton, Inc. (TAMS) of New York studied the island and made a report to the government of the Virgin Islands on a potable water supply for St. Croix (1959). Christiansted at this time had as its principal source the 3 wells drilled by the USGS at Concordia in 1949. These were connected to town via a 3.5-mile (5.6 km)-long pipeline. The 43 remainder of the water was supplied by cisterns in town. The Recovery Hill catchment system is not mentioned and presumably was unused by that time. In Frederiksted, the 3 wells along Mahogany Road had become the source of supply replacing Creque Reservoir. In fact the wells used the old 4-in. (10 cm) line, previously used by the reservoir, to convey the groundwater into Frederiksted. The report mentioned that the water from the reservoir had been turbid on occassions and that the reservoir itself had gone dry in times of drought. The Frederiksted distribution system was suspected of having excessive leakage since the apparent demand was considerably above that actually used by consumers. Also discussed in the report is a small well field at Fair Plains near the airport. Of the three wells mentioned, one of them was in use to supply the terminal building. This is p, obably the well presently referred to as GG-7, which is owned by the Virgin Islands Port Authority. No mention is made of the adjacent wells drilled by Cederstrom in Fair Plains. TAMS recommended increased groundwater exploration, investigation of distribution losses, additional cistern storage, and expansion of the saltwater system. It also urged a program of data collection on the streamflow from the Creque, Jolly Hill, Fountain, and Hermitage drainage basins to ascertain whether reliable surface water supplies could be developed in any of those areas. TAMS also proposed that a pipeline be built to connect the Christiansted and Frederiksted systems and the well field at Fair Plains. 44 In 1962 field work was carried out on St. Croix by the USGS (Hendrickson, 1963) as to the potential for increasing the amount of groundwater available for use on the island in its public supply. At this time there were now active five wells at Concordia and three on Mahogany Road. Seven public wells had been recently drilled at Barren Spot but none had been equipped with pumps. As part of the field work, pumping tests were performed on several of these wells. A detailed discussion of the groundwater hydrology in the Barren Spot area was included in Hendrickson' s paper. In January and February of 1962, 4 wells were drilled at Estate Adventure by the government. These wells were tested and the results included in Hendrickson's report. Also discussed was the industrial well field at Golden Grove which supplied the sugar mill at Bethlehem. This field was subsequently abandoned after the mill ceased operations in 1968. The Manning Bay (Fair Plains) well field is mentioned as having a total of 5 wells. A comment by Hendrickson was made about the danger of saltwater intrusion in this area. Apparently what he had mentioned has occurred in the past few years, necessitating the closing down of at least 3 wells in Fair Plains since 1972. During 1963, the consulting firm of Praeger, Kavanagh and Waterbury of New York City began investigations of the groundwater potential in Estates Fountain, River, and Hermitage. These investi- gations were in connection with the development of a resort complex in the area. The major features of the resort would be an 18-hole golf course and several hotels. 45 In the report (Praeger, Kavanagh and Waterbury, 1964) the results of 17 test wells were discussed including construction logs and pumping tests. Indications were that the area studied had the potential for a groundwater recovery of about 0.35 mgd (1,325 cu m/day). Ward and Jordan of the USGS issued a general report on the water resources of the Virgin Islands in 1953. They discussed the relation between the various rock formations in the islands and their potential for yielding or transmitting groundwater. Maps of the islands are included which illustrate this relationship and act as a guide to the well-drilling potential at various locations. They recommended addi- tional groundwater development adjacent to River and Bethlehem guts. Land use and its potential effects on future water resources were briefly mentioned. This theme was later developed into a separate paper by Jordan (1972) entitled, "Land-use effect on the water regimen of the U.S. Virgin Islands." In it he drew a correlation between the amount of runoff of a drainage basin and the percent of forest and brush cover in the basin. He states that the relationship is inverse with the heavy vegetation contributing to the loss through evapo- transpiration. Jordan concluded with the thought that land use in the mountain basins exerts a greater influence on stream discharge than does topography, geology, and even perhaps rainfall. On the same topic Bent Lawaetz (1975) of the V. I. Department of Agriculture also discussed the high loss from trees and added to this idea the theory that the lack of land cultivation for many years has permitted a hard, less porous soil surface to develop which has 46 had an adverse effect on infiltration and percolation of potential groundwater. In 1972, Robison of the USGS made a report on groundwater in central St. Croix. Based on data collected over the years in various studies, he analyzed the potential of the area and presented these ideas in the form of water management alternatives. Among the alternatives suggested were the dilution of brackish groundwater with distilled water, electrodialysis or reverse osmosis of brackish water, and aquifer recharge with treated wastewater. The basis for these alternatives is the premise that there is a large quantity of ground- water of varying quality in the Kingshill marl and its associated alluvium. Robison estimates this to be about 130 billion gal (492 trillion cu m). Whether this estimate is close to the actual amount certainly bears close investigation before proceeding on any extensive projects. A hypothetical system for the recovery of this groundwater was presented in the report. Robison also reviewed the major groundwater sites on the island and mentioned areas for potential groundwater development. Jordan (1973) in his survey of the water resources of St. Croix has gathered together a tremendous amount of information on ground and surface water on St. Croix and presented it in a single report. He has divided up the island into groundwater areas and discusses each one with regard to geology, present use, and potential groundwater exploitation. He has also summarized streamflow data available for River, Jolly Hill, and Creque guts. The careful evaluation of this one table alone is well worth the time of anyone who is considering the use of impoundments for a water supply. 47 Other records of water levels and water analysis of wells throughout the Virgin Islands are contained in a report (Robison et al., 1973) compiled by the USGS. Wastewater Reclamation and Reuse The concept of water reuse through wastewater reclamation for the Virgin Islands was outlined in a report to the government of the Virgin Islands by the consulting engineering firm of Engineering- Science Inc. (1968) of Arcadia, California. The report reviewed the water supply system in the islands and projected future demands for water. It suggested the possible reuse of wastewater for a variety of purposes ranging from industrial cooling to direct potable use. Various alternative treatment processes and distribution schemes with their costs were outlined. The use of treated effluent for groundwater recharge on St. Croix was discussed along with the potential problems from the saltwater systems in use in Frederiksted and Christians ted. Early that same year a representative of the W. G. Ammon Corporation in conjunction with the consulting firm of Reynolds, Smith and Hills, Inc., presented a plan (FWPCA, 1970) that included wastewater reclamation for St. Croix. This was done at a public hearing conducted in the Virgin Islands as part of the national estuarine pollution study. It was suggested that wastewater be processed by distillation for reuse on the islands. Apparently this plan did not progress too much beyond the public hearing stage. A discussion of the concept of v/astewater reuse as a partial solution to the island's water problems was contained in the report, 48 "The U.S. Virgin Islands and the Sea" (Beller et al . , 1970). The report strongly urged that all the potential sources of fresh water be examined and that a long-term water management plan be made for each island. The actual project which would culminate in the reclamation of wastewater on St. Croix began in 1972 with the author beginning the field work on the island. The first interim report on the project was issued in 1971 (Black, Crow and Eidsness, Inc.). The project, which would consist of the artificial recharge of the groundwater with treated effluent, was described and the progress in the selection of recharge areas and background monitoring was noted. In October, 1973, a second interim progress report (Black, Crow and Eidsness, Inc., 1973) was written which reviewed the project up to the completion of the treatment and recharge facilities but before recharging began. Recharge operations took place during 1974 and the results of the project are presented in this dissertation. During the past 3 years the author has presented a variety of papers concerning v/astewater reclamation in general terms and the St. Croix project in particular (Buros and Basiouny, 1972; Buros, 1974a, 1974b, 1974c, 1975a, 1975b, 1975c). The USGS, which has a history of interest in St. Croix's water resources, has suggested the use of wastewater reclamation in 2 of its recent reports. Robison (1972) of the USGS suggested the use of secondary-treated or tertiary-treated effluent for artificial recharge of aquifers by either surface infiltration or direct injection; while in 1973 Jordan 49 recommended the consideration of a system of greenbelts in some of the major alluvial valleys. These areas would be used for water spreading of storm water runoff and treated wastewater effluent. The recharge from the spreading areas would augment the groundwater and could act as a freshwater barrier to protect inland well fields. Surface Water The two surface water projects recommended by Warfield (1924) were constructed on St. Croix. Johnson (1936) has described their construction, capacity, and usage. In 1924 the Recovery Hill reservoir and catchment slab was built above Christiansted. Its closed concrete reservoir had a storage capacity of about 0.9 mil gal (3,406 cu m) and in operation only stored water collected from the adjacent concrete catchment, while permitting the runoff from the 115 acre (46.6 ha) drainage basin to pass on by, through town, and into the harbor. In 1935 all of the collected water at Recovery Hill was being used by the municipal hospital for flushing, scrubbing, etc., and not for the town's drinking purposes. In 1926 a 60-ft (18.3 m)-high concrete arch dam was built across Creque Gut 3.5 miles (5.6 km) northwest of Frederiksted. The impoundment had a storage capacity of about 9 mil gal (34,000 cu m). The v/ater was piped to Frederiksted for use in the public system. Presently in 1975 both of these projects are in disuse although the Recovery Hill area was recently cleared by the Public Works Department and plans are being made by the U.S. Soil Conservation Service to clean the accumulated sediments out of Creque Dam. 50 The prospects and problems associated with surface water impoundment and use on St. Croix have been discussed by numerous investigators (Johnson, 1936; McGuinness, 1951a, 1951b, 1953; Meyer, 1952; Van der Lippe, 1952; Tippetts et al . , 1959; Ward and Jordan, 1963; Bowden, 1968; Jordan, 1972, 1973). The problems include lack of suitable sites, leakage, siltation, high evaporation rates, lack of adequate streamflow, and the necessity to treat the water before potable usage. Reviews of prospective dam sites on St. Croix were made by Meyer (1952) and Van der Lippe (1952). Meyer's study includes logs of test borings made at many of the potential sites. He repeats the common complaint of most investigators coming to St. Croix on water resource projects; that is, the lack of basic data concerning the hydrological cycle. He considered the primary purpose of the dams to retain water for direct use or to aid in groundwater recharge. In the past 30 years about 278 small dams have been built in the territory with the majority of them being on St. Croix (Lawaetz, 1974). These dams have an estimated total storage capacity of over 500 mil gal (1,892 billion cu m) and are used for livestock and some irrigation, while also recharging the groundwater. They have also aided immeasurably in reducing pollution and loss of soil through erosion and sediment movement. The USGS has published (Robison et al . , 1973) the records of the streamflow in various drainage basins on St. Croix during the 1960s. These data include chemical analysis of selected samples of surface water. SECTION III PRELIMINARY INVESTIGATIONS OF THE RECHARGE AND STUDY AREA Selection of the Recharge and Study Area The key decision in the project was the selection of the recharge area. If an unsuitable site had been selected and developed, then the remainder of the effort on the project would have been largely wasted. Therefore the preliminary investigations centered around the selection of a suitable site and the definition of its hydrogeological features. In the selection of the areas which were used for recharging, there were two major constraints involved. The first was financial in that the budget for the project only provided sufficient funds for up to 2 miles (3.2 km) of force main. Thus, the maximum distance of the recharge area from the advanced wastewater treatment plant was predetermined. The second major constraint was that the basic decisions as to the pattern of wastewater interceptors and the location of the central primary treatment plant were made by others before this project was begun. Since the influent for the advanced wastewater treatment plant (AWWTP) would come directly from this primary plant, the location of that plant determined the site of the advanced wastewater treatment plant. 51 52 The budget for development of the recharge areas was based upon the understanding that the land utilized must be obtained at little or no cost. At the time when the original proposal was outlined in 1969, local officials had indicated that there would be little problem in using land at Estate Barren Spot in central St. Croix. This probably seemed natural at the time as the area then consisted of abandoned fields of sugarcane. The recharge areas v/ere proposed for a location which was on alluvial soil and in the same hydrological basin as one of the larger public well fields on the island. However, between 1969 and the start of the project in 1971, the fields in question and almost all of the surrounding land were purchased or optioned by a local developer who began to construct homes on the site. Despite this, it was hoped that perhaps the operation could be handled in certain greenbelt areas within the development which would be beneficial for both the project and the developer. Subsequent negotiations on this subject proved otherwise, as the financial and operational conditions that were suggested by the developer did not appear feasible. The costs would have vastly exceeded the funds available for purchase of the lands and the restrictions would have seriously hindered the success of the project. Investigations were then conducted to find a new site for the recharge operations. One important criterion for the alternative site was that it be located on government-owned or controlled land. This would avoid the necessity for the purchase or lease of the property, and would give the government control over the operation and full possession of the facility upon completion of the project. 53 In selecting an alternate site, the new primary treatment plant was used as a center and all the government holdings within a radius of three miles were determined from tax records. These included territorial government, federal government, and Virgin Islands Port Authority lands (see Figure 8). The current and future uses for the land were determined. Much of the land, although presently not used, was scheduled for develop- ment in the immediate future. A study was then made of the general soil and geological conditions existing at each site. For the soils investigations, two reports published by the Soil Conservation Service of the U.S. Depart- ment of Agriculture (USDA) proved extremely useful. These were: Soils and Their Interpretations for Various Uses, St. Croix. American Virgin Islands (McKinzie et al , , 1965) and Soil Survey, Virgin Islands of the United States (Rivera et al . , 1970). They delineated the soils and their engineering and agricultural uses throughout the island. Their concern has been with the characteristics of the profile of the upper 60 in. (152 cm) of the soil. This layer is of primary interest to the project due to its ability to permit infiltration and percolation of the water to be recharged. An interpretive map in the first publication which was of great value was entitled, "The soil limitations for resi- dences with individual septic tanks." These limitations were based on many of the characteristics such as percolation rate, shrink-swell behavior, depth to water table, etc., that would also apply to the arti- ficial recharge operation. On this map the soil conditions were inter- preted as providing slight, moderate, or severe limitations to the use of individual septic tanks. This information is shown on Figure 9. Areas 55 57 58 showing slight limitation were those considered most suitable for the project, although others were considered. Geological conditions have been characterized by Cederstrom (1950) and Robison (1972) in separate U.S. Geological Survey (USGS) publications concerning groundwater on St. Croix. This geological information, modified by observations in the field, is shown in Figure 10. This was an aid in outlining the possible groundwater flow, the relative subsurface permeabilities and the type of water-bearing formations to be expected. Observations made in the field produced specific information on soil conditions, current land usage, and existing facilities such as wells, roads, available power, etc. Several temporary roads were built and a trailer-mounted boring rig was used to make soil borings at various locations. Samples v/ere evaluated in the field to determine the soil profile. Borings were made at three different depths--4, 7, and 20 ft (1.2, 2.1, and 6.1 m). The resulting 20-foot (6.1 m) holes were used for the placement of piezometric tubes while the 4- and 7-foot (1.2 and 2.1 m) holes were utilized for percolation tests. These latter two depths were selected to give information on percolation capabilities of shallow ponds versus a deeper trench arrangement. The results of the tests were used to indicate the relative capacity for percolation between sites. The data derived from the percolation tests in the four areas--Golden Grove, Negro Bay, Adventure, and Barren Spot--are illustrated in Figure 11 . Three sites were intensively investigated. These were in Estates Adventure, Golden Grove, and Negro Bay. The site at Adventure was discarded due to unfavorable soil conditions. The Negro Bay site 60 62 (li) aovduns oNnoaD Moiaa -i3A3t aaivM 63 indicated some good percolation values and no water table but appeared to contain some hard horizontal rock layers at depths from 8 to 20 ft {2.4 to 6.1 m). The presence of a hard limestone layer is a situation very typical of the Kingshill marls in which this site is located. The Golden Grove site was very similar to the one at Barren Spot. Both are located in alluvial valleys above a major public well field and have relatively equivalent percolation results. However, the groundwater at Golden Grove is closer to the surface than that at Barren Spot. The recharge area finally selected was one which made use of a dual -site concept. Two separate sites were used, one at Negro Bay and the other at Golden Grove. The sites selected were made up of two entirely different soil and geological conditions but are located quite close to each other. This permitted the use of one force main and holding tank to supply both areas with only a slight additional amount of piping. As these two formations comprise the bulk of the geological composition of the coastal plain, the data obtained are quite valuable in planning any expansion of the project to other areas of the island. The Golden Grove portion was the primary site of recharging operations with the Negro Bay area used only for secondary experimentation. The Golden Grove project area is part of a larger parcel owned by the territory which is being developed into a governmental complex. The entire parcel is 94 acres (38 ha) and will ultimately be the site of a large building complex including an adult correctional facility, a juvenile detention center, and the Public Safety Headquarters. At the time of the initial studies the entire 64 area appeared untouched and was overgrown with scrub growth. Presently, the adult correctional facility and the public safety building have been constructed. In using this parcel, the permanent installations involved with the recharging operations were located so that they will not interfere with any of the future buildings planned for the area. This again acted as another imposed restriction in the selection of land for recharging. After extensive discussions, several small areas of the parcel were set aside for project use by Lieutenant Governor Maas who was supervising the development of the parcel at that time. These areas were generally adjacent to the course of a meandering stream. River Gut, which winds through the parcel. The basic geological formation is an alluvial valley with the soil types classified as being in the Coamo, Fraternidad, and Fredensborg series (see Table 1). The actual soil boundaries are not sharp in this area and the existence of some nonconforming lenses in the soil profiles is common. The topographic features in the area where the groundwater recharge operations in Estate Golden Grove will take place are shown in Figure 12. About one mile (1.6 km) down the alluvial valley is the Fair Plains well field which is the major well field on the island with an average production of about 0.24 mgd (908 cu m/day). It is this well field that will be ultimately affected by the recharging operations at Golden Grove. The Negro Bay site consists of about 8 acres (3.3 ha) spread over a slight saddle between two low hills. The underlying formation is the Kingshill marl. The major soils in this area are classified in 65 TABLE 1. SOIL CLASSIFICATIONS IN THE PROJECT AREA Soil Classification Description Aguilita Series Gently sloping to steep, well-drained soils that are shallow over soft limestone or marl. These soils formed in residuum derived from limestone. In a typical profile the surface layer is yery dark grayish brown and light brownish gray gravelly clay loam about 6 in. (15 cm) thick. Below this is mixed very dark grayish brown firm calcareous gravelly clay loam that is 50 to 70 percent lime- stone fragments. The substratum, at a depth of about 10 inches, is mostly soft limestone but contains hard limestone concretions. The soft limestone material can be penetrated with a spade. Drainage is good, and the permeability is moderate. The water table is low. Coamo Series Gently sloping well -drained soils that are deep over volcanic and limestone rocks. These soils occur on alluvial fans and terraces. They formed in sediments derived from these rocks. The sedi- ments range in texture from clay to sand. In a typical profile the surface layer is ^ery dark grayish brown clay loam about 8 in. (20 cm) thick. It contains a few rock fragments. The subsoil is "^ery dark grayish brown and yellowish brown, firm clay. It also contains a few rock fragments. The substratum, beginning at a depth of about 24 in. (61 cm), is yellowish brown, friable, calcareous clay loam stratified with sand and gravel. Fraternidad Series Moderately well -drained soils that formed in clayey sediments derived from volcanic and limestone hills. In a typical profile the surface layer is \-ery dark grayish brown clay about 13 in. (33 cm) thick. Below this, to a depth of about 62 in. (157 cm), is light olive brown calcareous, very firm clay. Drainage is moderately good. Permeability is slow. 66 TABLE 1 (CONTINUED) Soil Classification Description Fredensborg Series VJell-drained soils that formed in clayey, cal- careous sediments over soft limestone or marl. These soils occur near coastal areas, in valleys, and on foot slopes below the limestone hills. In a typical profile the surface layer is very pale brown, very friable, calcareous silty clay loam. At a depth of about 20 in. (51 cm) is a very pale brown, soft marl or limestone. The information for this table was adapted from the publication. Soil Survey, Virgin Islands of the United States - 1970. 68 69 the Fredensborg and Aguilita series (see Table 1). Borings made on the site indicated that a hard layer of limestone existed under most of the area at a depth of 8 to 20 ft (2.4 to 6.1 m). This has a mild anticlinal shape with an axis in a northeasterly direction and a slope of about 3 degrees. Recharging operations took place on the south side of the axis. Work in this secondary site was largely of an experimental nature to see if the marls would have any potential for artificial recharge as they are predominant along the coast of the central plain. Although the major soil types in the area are classified as having moderate to severe limitations for septic tank installations, initial on-site percolation tests produced favorable results. After the selection of the recharge area was accomplished, a study area was defined for the project. This consisted of the surface drainage area both above and below the recharge sites plus some additional area to the south which was thought to be related by groundwater flow. Within the study area, wells were selected for monitoring water quality and water levels. These included wells which were above and below the recharge sites and some which were entirely out of the drainage basin to use as controls. Description of the Study Area The study area is outlined in Figures 8, 9, 10, and 13. Figure 13 shows the area in detail including the existing wells and recharge sites. This study area is about 8 sq miles (20.7 sq km) and consists mainly of the drainage area for an intermittent stream called River Gut. The main portion of this stream, referred to as the East 70 71 Branch, originates from springs located within Fountain Valley and flows south-southeast through the area for a distance of about 6 miles (9.7 km). The northern part of the study area begins at the ridges of the hills which surround Fountain Valley where they delineate the drainage into the valley and downstream through River Gut. The ridge line here ranges from 300 to 1,000 ft (91 to 305 m) in elevation and the slopes fall off sharply to the undulating valley floor. Once south of the line which runs from the villages of Grove Place to Coble, the study area becomes a gently sloping flat plain that continues to the shore about 3 miles (4.8 km) to the south. Low eroded hills on the southern end of the area divert the flow of River Gut slightly to the east as they direct its course through a gap in the hills known as Fair Plains. It is at this gap where one of the government's largest well fields, the Fair Plains well field, is located. The east and west branches of River Gut wind through the study area in a streambed that is generally depressed 2 to 10 ft (0.5 to 3 m) below the land surface. Along its banks are older more established trees which were left untouched during the years of cultivation. A wide variety of trees are represented including, but not limited to, mango ( Mangifera in dica ), hog plum ( Spondias mombin ), West Indian almond ( Terminalia catappa ), royal palm ( Roystonea boringuena ), and licorice ( Pithecellobium saman ). These trees range from 40 to 50 ft (12 to 15 m) in height and tower over the lower scrub growth of the adjacent fields. 72 Visually, the animal density and diversity has appeared low in the study area with the most frequently seen animals being the mongoose ( Herpestes auropunctatus ) and the white-tailed deer ( Odocoileus virginiana ) . Until about 1958 almost all of the flat portions of the study area were used for pasture and for the cultivation of sugarcane by the Virgin Islands Corporation. Aside from the golf course which occupies the upper end of the study area, most of the rest of the land has been allowed to naturally shift from pasture and cane to scrub growth. This process has almost completely driven out the ratoon crops of sugarcane by the rapid growth of Guinea grass ( Pancium maximum ) and the spread of acacia ( Acacia tortuosa ), tan-tan ( Leucaena glauca ), and thibet ( Albizia lebbek ) trees throughout the area. The change in vegetation has been assisted by several fires which often sweep the area during the dry seasons. The main activity in the study area over the past 5 years has been the clearing of land by bulldozing. Generally only a small section of land is affected at a time but probably the whole area has been cleared once and some parts several times. Fires have also occurred in the area during times of drought. These usually will burn entire fields and act as a clearing agent. Regrowth from both causes is rapid and with the proper rainfall the main effects of clearing can disappear within 3 to 6 months. In 1972 a major wastewater interceptor was built alongside the main and west branches of River Gut to serve the village of Grove Place. About the same time a 100-unit multistory housing project, Croixville, was built just north of the Adventure well field and two 73 large governmental complexes, the Public Safety Headquarters and an adult correctional facility, were constructed in Estate Golden Grove. In conjunction with the construction of the correctional facility, about 1,000 ft (305 m) of River Gut was widened, straightened, and the trees removed as part of a flood control plan. Portions of the Golden Grove recharge area have been cleared and planted in Bermuda grass, which gives better service and is easier to maintain than the native Guinea grass. During clearing operations the larger more desirable thibet and licorice trees were preserved on the site. The Negro Bay site, which is on the Kingshill marl, has probably not been used agriculturally for at least 35 years. The soil is not as rich as other parts of the coastal plain and the area had been part of the U.S. Army base during World War II. Here the scrub growth was lower in height but much denser and predominantly in thorn trees such as acacia. The cleared areas have quickly moved to revegetation with Guinea grass. Groundwater Geology Study area . The knowledge of the groundwater geology in the study area is somewhat fragmentary since it depends largely on gathering information through actual coring of the mantle, either for intellectual gratification or the actual construction of a well. This has always been a rather expensive pursuit and currently costs approximately $10/ft ($32.80/m) for a 6-inch (15 cm) uncased hole using a cable tool drilling rig. 74 An interpretive sketch of the geological formations in the coastal plain that probably affect the flow and location of groundwater in the study area is presented in Figure 14. This sketch is based on a variety of source information but most notably on observations by project personnel, Public Works Department v/ell logs, and publications by Cederstrom (1941, 1950) and Whetten (1962). The major portion of the study area is in the coastal plain which gently slopes up from the south shore to the hills of the Northside Range. The geological base for this plain in the study area is the Jealousy formation. Cederstrom (1950) mentions that this is a gray clay, or mudstone, which contains some calcareous conglomerate in its makeup. This formation is referred to locally as blue clay and it has a reputation, not unfounded, for being an impermeable nonwater- bearing strata. Test drillings by Cederstrom found that this formation had a thickness, adjacent to the study area, of over 1,398 ft (426 m) and hence when a local well driller encounters this formation, he generally drills no further. Lying on the Jealousy formation is the Kingshill marl which Cederstrom (1950, p. 21) describes as consisting of "buff-to-white moderately thick bedded limestone, alternating with soft cream or white marl . The limestone portion is generally quite hard while the marl is comparatively soft and easily cut with a knife. The vertical permeability of this formation is extremely low due to the intact limestone layers, while the horizontal permeability can be quite high due to solution cavities or other voids in the formation. 75 On the coastal plain the hills at Jealousy and Lower Love are made up only partially from Kingshill marl while all of the hills south of the Center! ine Road consist of this formation. It probably formed the entire plain but has been eroded by streams and the eroded beds replaced by local alluvial deposition. This can best be seen in the geological cross section of Estate Golden Grove, in Figure 15, where a U-shaped valley has been eroded from the marl and filled with the alluvial clays, sands, and gravels that make up the upper, most recent formation on the plain. This alluvial material becomes thinner as it proceeds northward to the lower slope of the Northside Range. Within the alluvium a number of defined gravelly aquifers exist separated by thicker layers of silty clay. This clayey soil ranges from moderately to highly impermeable, depending on the location. The existence of alluvium is no guarantee of an underlying aquifer, as apparently the deposition of sands and gravels has been nonuniform both horizontally and vertically, which has resulted not only in the lack of aquifers in the alluvium in some locations but isolated sand and gravel lenses in others. As seen in Figure 14 the alluvium and Kingshill marl formations terminate in the north by contact with the Mount Eagle volcanics. Cederstrom (1950, p. 16) mentions that "a large part of the material is volcanic in origin, that much of it is stratified, and that some limestone beds are interbedded with volcanics. Dark fine- grained massive, laminated or slaty rocks, hard thin- to thick-bedded limestone, and spotted or porphyritic rocks are most common." The Mount Eagle volcanics generally yield minor amounts of groundwater in M-O 77 -1W::^''H^'-' 'i^V^^^^^^^p' < zoN CCOX (iONOI1VA3"I3 78- their weathered portions and in the rock fractures and crevices. The Mount Eagle volcanics make up the vast majority of the Northside Range and it is believed that much of the water in the aquifers of the coastal plain has its origin in these hills. The exact structure of the interface, defined by the dashed circle in Figure 14, between the coastal plain and the Northside Range is unknown and merely hypothesized in this sketch. It is certainly a subject worthy of further research efforts on the part of local geologists. Not shown in Figure 14 is the geological structure of Fountain Valley, which is in the northernmost part of the study area and contains the springs which initially supply River Gut. Fountain Valley has an alluvial valley floor but its walls are made up of not only Mount Eagle volcanics but an intrusive igneous rock referred to by Whetten (1968) as Fountain Gabbro. A plan view of the geological formations exposed at the surface in central St. Croix is shown in Figure 10. Naturally the geology of the recharge areas is of great concern to the project since this determines the ultimate disposition of the recharged water after it enters the soil. As was mentioned, two recharge areas were selected which are adjacent to each other but yet geologically dissimilar. One contains alluvial deposits and the other marls. These areas. Golden Grove and Negro Bay, contain the geological formations that make up the vast majority of the land held by the local government and therefore would be available for future groundwater recharge utilization. 79 Golden Grove Recharge Area Using information obtained from old well logs, potentiometric data plus borings, and nev/ wells constructed in the area as part of this project, three diagrams of the assumed geological configuration in the Golden Grove area have been constructed. These are shown in Figures 13, 15, and 16. Basically the area consists of alluvial deposits laid down on top of the Kingshill marl. The alluvial deposit is the one of concern in this area as far as recharging is concerned. As shown in Figure 15 the deposit varies in thickness up to about 70 ft (21.3 m). Its predominant constituent is a montmorillonitic clay which tends to be somewhat impervious. Spaced within the alluvial clays are thin horizontal aquifers of clayey-sandy-gravelly material. These aquifers are usually no more than 2 ft (0.61 m) in thickness and are probably not well interconnected except due to boreholes in the vicinity and possibly at the junction of two streambeds near the Fair Plains well field. Groundwater studies have demonstrated that the potentiometric head throughout the valley reflects the confined condition of the water within the aquifer and does not represent a free mter table. In most of the study area and the island in general, an unconfined water table does not exist. The water in the aquifers moves from northeast to southeast below the recharge area. It must be kept in mind that Figure 14 has the vertical scale exaggerated 15 times for clarity and that the actual slope of the ground surface and aquifers is less than 1 degree from the horizontal. 4-O 81 LUoz< w o < I-zoN oX M IS10I1VA313 cnco 83 o > -I -I m I I F5 t: s < < ;: S f »^ i " I- 2 < ii ii d - o o trt a. > — tj UJ D CC Z O 2 < - X < UJ i^ UJ (/) ta (Ii) NoiiVAana 84 The upper aquifer, in Figure 15, is the aquifer mainly affected by the surface recharge activities in the area. The material between this aquifer and the ground surface tends to be a nonhomogeneous soil with great variations taking place in the soil types across the valley floor. The upper 18 inches of soil is a dark clay with the lower material being lighter in color and containing a higher percentage of silt and sand. This sand is of the silica variety, which is rare on the island since calcareous sand is the predominant form on the shoreline. Several beds of sand have been encountered in the region but unfortunately they were not extensive in area nor is it certain that they are interconnected. The gut which winds through the valley depends on a base flow from springs located at the head of the stream and other areas where the streambed cuts into an aquifer and thus flows when the groundwater level is above the elevation of the bed. The method of recharging proposed in the Golden Grove area was by the use of spreading basins and existing streambeds. The limiting factor was expected to be the permeability of the soil between the recharging activity and the upper aquifer. The bottoms of the spreading basins were therefore excavated below the extremely clayey surface layer to utilize the increased permeability of the lower silty horizons. This scheme did prove feasible and the recharge operations were conducted mostly in the basins. The streambed in the Golden Grove area is below the surrounding land from 2 to 8 ft (0.6 to 2.4 m) and thus somewhat closer to the aquifer in question. Six small check dams 2 to 3 ft (0.6 to 0.9 m) high were constructed in the streambed to hold the 85 recharge water to facilitate infiltration and percolation. Unfortunately the floods in October, 1974, severely damaged all of these check dams before recharge experiments in the streambed could be carried out. Negro Bay Recharge Area The geology of this area consists of calcareous material of various types. Explorations in the recharge area were carried out by shallow borings, to a depth of about 15 ft (4.5 m), and wells were constructed to a maximum of 150 ft (46 m). A hypothesized geological cross section of the Negro Bay recharge area is shown in Figure 17. The surface layer of about 6 to 12 in. (15 to 30 cm) is a dark clay while the subsoil is of a calcareous nature, white to buff in appearance and composed of a combination of a soft pov;derlike material interspersed with cemented nonstratif ied marl. Beginning at about 10 ft (3 m) below grade there are alternate hard and soft stratifications of limestones and marl which continue to a depth of about 150 ft (46 m). Here the Kingshill marl rests on a montmorillonitic mudstone geologically designated as the Jealousy formation and commonly referred to on the island as blue clay. Stratifications within the Kingshill marl in this area are about 2 to 6 in. (5 to 15 cm) thick. The movement of groundwater through the marl is by solution cavities which apparently are rather small, generally having cross sections of no more than about 20 sq in. (129 sq cm). These solution cavities seem to run in specific strata in the formation but are not always interconnected within the same strata. 87 (jONOIiVA3n3 During the summer of 1972 two wells were drilled, PW-2 and PW-3, which confirmed the existence of alternate hard and soft layers within the Kingshill marl. The formation was dry until the drilling operation penetrated a hard limestone layer at an elevation of about 2 ft (0.61 m) below sea level and encountered water. This water proved to be under pressure and rose in the well to about 15 ft (4.6 m) above sea level. The two wells were constructed 250 ft (76 m) apart and encountered water at the same elevation. The groundwater was confined in both cases but production in one well was estimated at a rate of only 2 gpm (0.13 1/sec) while the other produced at about 60 gpm (3.8 1/sec). Currently the latter well is being used by the Virgin Islands' government as part of its public supply. Recharging in the Negro Bay area involved the use of the unconsolidated marls in the upper 10 ft (3 m) of the existing formation. Numerous soil borings were made by the project in this area to map out the extent of the unconsolidated marl and the underlying limestone anticline. Long-term percolation tests indicated that the upper softer marls were capable of receiving large quantities of recharge water. This concept was tested on a full scale with reclaimed wastewater, using surface methods such as spray irrigation and spreading basins. The recharged water from the site was expected to percolate down to the first hard layer about 10 ft (3 m) below the surface which would place it on the south slope of a mild anticline which has a northeasterly axis. Indications v-jere that this hard layer was contiguous and probably impermeable. The water would then mound and be available for recovery. This system would not involve any mixing with the existing groundwater in the area as the groundv;ater is located in strata about 80 ft (24 m) below the surface where it was extremely improbable that the recharged water could reach. Unfortunately the rate of infiltration and percolation of the recharged water in Negro Bay did not prove to be up to expectation and recharging operations were suspended in August, 1974. Hydrological Developments in the Study Area Groundwater In the normal groundwater recharge cycle on St. Croix, the heavier rains occur between August and December; these tend to fill up the aquifers which then slowly empty until the following fall when they are refilled. There is also a short rainy season in the spring and occasionally other times of heavy rains which aid in recharging, but basically the aquifers must depend on these fall rains or any long series of heavy rains which come in a pattern to permit maximum infiltration and minimum runoff to the sea. Large amounts of rain alone are unsatisfactory as much of the water can be lost in runoff. The long-term relationship between the rain pattern and the water levels in some wells in the study area is shown in Figure 3. The groundwater in the study area at Golden Grove is entirely dependent on infiltration possible from a tributary area of about 5.6 sq miles (14.4 sq km). Much of this area is surfaced with tight clays and hence is limited as to its potential for infiltration and permeability. The major aquifers in the Golden Grove area are of gravelly sand with a thickness of less than 2 ft (0.6 m) and an estimated width which varies from 250 to 1,000 ft (76 to 305 m). 90 There are several individual aquifers interspaced by clayey strata. The major recharge activity appears to take place in the area north of Centerline Road after which the groundwater flows south-southeast to the ocean. This water is tapped in numerous places by government and private wells which draw down on the stored water. A measure of the amount of water existing in the aquifer at any time is the potentiometric head on the aquifer at various points along the flow network to the sea. Water level recorders were installed in various key locations along the flow route which monitored the water levels in these wells. Some accuracy is lost in these measurements since the wells generally penetrate, and thus interconnect, more than one aquifer. At the time of the first interim report (Black, Crow and Eidsness, Inc.) in June, 1972, the study area was affected by a surplus of groundwater. This hindered borings and required the formulation of plans to reduce the amount of groundwater in the recharging area to provide capacity in the aquifers to test the feasibility of recharging. Plans to alleviate this situation were carried out, but by the time of the second interim report (Black, Crow and Eidsness, Inc.), in October, 1973, a contrary situation had occurred in that a general deficit of precipitation during the preceding 17 months had produced a circumstance where some of the aquifers were nearly empty and others were producing at a reduced capacity. This deficit condition continued for an additional year and marked one of the worst droughts in recent history. On July 22, 1974, 91 the island v-^as proclaimed a federal drought disaster area. Many wells went dry during this time and others, near the sea, had a significant rise in salt content due to saltwater intrusion. Although the drought condition was alleviated in August, 1974, by the first significant rains in months, it definitely came to a close by November, 1974, when record rains caused severe flooding over large portions of the island. On November 15, 1974, the island was again declared a federal disaster area, only this time it was due to flooding. Half the average annual rainfall was received within a period of 25 days and the soil could not handle the disposal of the water by infiltration. As a result, billions of gallons of water ran off into the surrounding sea. Although some recharge of the aquifers did occur during this period, it was not concomitant with the amount of precipitation experienced. Piezometric levels rose, but in the subsequent 8 months only scant rainfall occurred and the levels rapidly dropped again. By July, 1975, many of the piezometric levels had dropped close to the previous spring's drought level. Although the quick shift from one extreme to another in the water situation v;as caused by an unusual rain condition, the overall long-range pattern of going from a surplus to a deficit of water seems to be a regular, though unpredictable, phenomenon for the island. This points up the utility of having a method of artificial groundwater recharge working on the island which will permit the leveling off of groundwater production at a constant, predictable high rate, regardless of the climatic conditions. 92 Surface Water The only significant surface flow in the study area occurs in River Gut. In general, its base flow is dependent on the groundwater level in the area. Runoff from storms makes up its flow on only a small percentage of its total flow days. However, these runoffs can be quite considerable and only a few days of heavy runoff can represent the majority of the total annual flow. The amount of this runoff contributing to streamflow is dependent on the rainfall pattern, soil moisture, land surface, and vegetation conditions. During 1971 through early 1972 there was a continuous base flow in River Gut as it passed through Golden Grove. But then due to the depressed water table and lack of adequate precipitation, there was no flow in the lower half of River Gut from March, 1972, to October, 1974, with the exception of two days of storm runoff and one week as a result of a broken water main near the Adventure well field. A flash flood occurred in October, 1974, and an even larger flood came again in the following month. A sustained flow followed in River Gut which continued until the latter part of December, 1974. From then until September, 1975, there has been no flow in the streambed in the Golden Grove area. Water and Wastewater Systems on the Island The potable water distribution system on the island of St. Croix has developed in small stages as finances permitted and politics dictated. Its initial function was to service the two towns of Christiansted and Frederiksted and the central sugar factories built at several locations in the island. From this it was expanded or 93 converted to serve the expanding needs of the populace. Currently both tov^ns are supplied with potable water and portions of the central coastal plain are included in the system. The wastewater collection system was relatively simple up to 1970. Both towns collected and discharged their untreated wastewater, via outfalls, into their respective harbors. Inland, most homes used septic tanks while large housing developments employed small package plants with discharge onto the fields or out to sea. In 1966 a consultant surveyed the obvious defects in the existing system and submitted a report and master plan (Camp, Dresser and McKee, Inc.) for the collection, treatment, and ultimate disposal of wastewater on St. Croix. This plan has been followed with only minor deviations and today is well on its way toward completion. Basically the plan called for a single treatment facility on the south shore about midway between Christiansted and Frederiksted. The wastewater from the two towns and the central portion of the island would be transported to this facility by gravity interceptors and force mains, given primary treatment, and discharged to sea via a long ocean outfall. The system and its design are excellent; however, since the designers were apparently neither informed by the local government of its desire for eventual water reuse nor able to foretell the generally unpredictable future on the island, the system was not designed to cope with the complex problem of wastewater reclamation. This fact, combined with the system of water distribution, has caused considerable problems for the reclamation project. The system of water distribution and wastewater collection on the island is crucial to the successful reuse of water on St. Croix. 94 The distribution system has a variety of point sources which add water of differing qualities to the system at various locations. Table 2 names these point sources and lists the quantity and quality of the water added to the system. Figures 18 and 19 show the sources of wastewater and outline the relationship between chloride content from these sources and the flows in the entire collection system on the island. Figure 18 shows the situation as it was in June, 1974, when the reclamation project was in operation. At this time only the central portion of the island was contributing wastewater to the treatment plant at Bethlehem Middle Works. This limited area of collection is the reason that the amount of wastewater available for processing in the AVJWTP was so limited during the operational phase of the project. The water used in this area is a combination of groundwater from the Adventure, Barren Spot, and Fair Plains well fields plus some of the desalinized water from the Martin Marietta Company. Additionally, of course, each building in the island supplies collected rainwater from its own cistern. The most serious problem with the reuse of water on the island comes from the total dissolved solids (TDS) in the waste stream. Most notable are the chlorides which affect the taste of the water and its suitability for agricultural purposes. Table 2 shows the great range of chloride concentrations from the various sources. Some of this groundwater for the central area is mixed in the 10 mil gal (37,850 cu m] storage tank at Ksingshill before distribution; but the final chloride content of water used, and hence wa tewater produced, is really a function of the day-to-day production of each source. Figure 20 is a graph of the chloride content of the influent to the AWWTP during the 96 98 MON BIJOU HD FREDENSBURG HD STRAWBERRY HILLHD AUREO DIAZ HEIGHTS HD CENTRAL HIGH SCHOOL 99 TABLE 2. MAJOR WATER SOURCES ON ST. CROIX Average daily Average contribution to chloride ^"'"^^ the water supply content (mgd) (cu m/day) (mg/l) Desalinized water WAPA Stern Rogers plant Martin Marietta Alumina Co. plant Groundwater Fair Plains well field Barren Spot well field Adventure well field Concordia v^ell field Mahogany Road-La Grange well field Rainwater collected in cisterns Total of homes on island (estimate) 0.3 1,135 10 0.74 101 (i/BLu)iM3iN03 aaiaoiHO 102 operational phase of the project. The chloride content ranged from about 300 to 2,500 mg/l during this operational period. Figure 19 shows the relationship of the chlorides in the various sources of wastewater and the flows in the entire collection system which went to the central primary treatment plant in September, 1975. The sources of wastewater have been increased by flows from the town of Frederiksted. Aside from a large increase in wastewater, there was now the addition of about 0.08 mgd (300 cu m) of seawater which is used in Frederiksted for flushing purposes in several of the major housing projects. This collection configuration became effective in October, 1974, with the activation of the wastewater pump- ing station in Frederiksted. The chloride content in the wastewater being processed at the AWWTP increased immediately to about 2,000 mg/l. This made the reclaimed wastewater unsuitable for present reuse purposes. The artificial recharge of groundwater was discontinued while the local government tried to resolve the problem. Although progress has been made towards resolution, the situation still existed in September, 1975. SECTION IV DESCRIPTION OF THE PROJECT FACILITIES Advanced Wastewater Treatment Plant (AWWTP) Purpose The purpose of the AWWTP within the project framework was to upgrade the quality of the wastewater to a level where it could be safely and efficiently used for artificial recharge of the groundwater on St. Croix. Goal The goal of the AWWTP was to produce a clear, odor-free effluent which would be extremely low in organics, suspended solids, and microorganisms. Certain operational guidelines were drawn up and, aside from normal organic reduction, it was desired that the effluent have a turbidity of less than 3 Formazin Turbidity Units (FTUs) and preferably less than 1. At the same time, the effluent should have a free chlorine residual (FCR) after a 30-minute contact time of 1 mg/1 or more, at 1 FTU; and 3 mg/1 or more, at 3 FTUs. The purpose of using these guidelines was two-fold. One was the protection of public health and hence the desire to reduce exposure of the public to possible pathogenic organisms to a negligible degree. Additionally it v;as realized that the soil in the 103 104 main recharge area was predominately clays and silts and that this type of soil could be expected to clog readily if any significant biological activity or mechanical entrapment took place. By adhering to the guidelines, it enabled the project to minimize these problems and efficiently utilize the small amount of land available for recharging. Design Assumptions In the design of the plant, certain assumptions were made. A discussion of the most significant of these follows with pertinent comments on their validity. Assumption 1. The primary plant and the associated wastewater collection system in the western and central portions of the island would be completed and operating with a total flow of about 1 mgd (3,785 cu m/day) by the time the reclamation of wastewater began. In actuality the construction of the plant and interceptor network was delayed at all stages, with the primary plant not being placed in operation until August, 1972, and the important western end of the collection system not being completed until October, 1974. Thus incoming wastewater flows were below expectation during the operational phase of the project. Assumption 2 . The incoming wastewater to the primary plant would have a high biochemical oxygen demand (BOD) and ammonia-nitrogen (NH3-N) content. The local environmental health officials on St. Croix were quite insistent on designing for a high incoming BOD. The basis for this idea, at the time, was quite reasonable. Several package ]05 treatment plants had been recently constructed in the territory to service various large housing developments. Although different types of plants were used, the results were often yery poor as the high organic loading to the plants had caused them to operate badly and, in many cases, such as the package plant at Mon Bijou, to become a community nuisance. This high BOD was the result of low water usage, often only 15 to 40 gpd/person (57 to 151 1/day/person) due to the severe shortage and high cost of fresh water. A health department report (Grigg et al . , 1971) on package treatment plants on neighboring St. Thomas, which has similar water problems, showed a range in BOD of incoming wastewater from 6 to 693 mg/1. Since no interceptors existed at the time of design in the central portion of the island, with the exception of the vicinity of Mon Bijou, opportunities for testing were limited; and in view of the package plant problems, it does not seem like an unreasonable assumption. Samples of the incoming wastewater at the Mon Bijou plant and the Frederiksted pumping station in July, 1971, were analyzed and had a BOD of 1,000 and 260 mg/1, respectively; while the NH3-N level was 90 and 56 mg/1, respectively. For design purposes it was estimated that the BOD to the secondary portion of the plant would range from 200 to 750 mg/1. In actuality at the same time as the design of the AWWTP was taking place, construction began on numerous multistory housing projects in central and western St. Croix. These were completed in late 1973 and had a capacity for about 8,000 residents, which is about 20 percent of the population of the island. A decision was made to connect these units to the public potable water system and in most ]06 cases to supply unmetered water to the tenants as part of the basic monthly rental The result was a tremendous increase in the average water usage and a concomitant reduction in the BOD of the wastewater which entered the collection system from the central and western portions of the island. The mean value of the BOD, determined on a bimonthly basis during 1974, for incoming effluent for the AWWTP ranged from 68 to 140 mg/1. Hence the plant has plenty of excess aeration capacity. Assumption 3 . Surface methods of artificial recharge would be employed. In actuality that is what happened. Assumption 4 . The saltwater flushing system in Frederiksted would be converted to fresh water to avoid contaminating the wastewater to be used for reclamation. In actuality although the local government knew of the situation, steps were not taken to alleviate the potential conflict. Since the Frederiksted wastewater system was not connected to the central collection until October, 1974, there was not really a problem until then. After the connection, due to flooding damage on the Island, no positive action was taken on removing the salt water until a governmental study group was formed by the governor in June, 1975, to look into the problem. It is hoped that this saltwater situation will be resolved during the fall of 1975. Until then, the project cannot use its product water for agricultural irrigation or for groundwater recharge. 107 Basic Design The plant was designed to be an extended aeration activated sludge plant follov^ed by units to permit chemical coagulation, filtration, and disinfection. A block diagram of the plant is shown in Figure 21 and an aerial photo of the facility appears in Figure 22. A list of major components with their specifications is shown in Table 3 while the major design parameters for the activated sludge section are shown in Table 4. These parameters make it apparent that this is basically a standard extended aeration plant, but with a higher volumetric loading and aeration capacity to minimize the size of the aeration tanks. The use of a completely mixed extended aeration plant with sludge recycle gave the facility an inherent ease of operation and the ability to handle moderate shock loads. The prolonged residence time and excess aeration capacity were expected to provide the environment for the growth of nitrifying organisms which would act to convert ammonia compounds to nitrates. This, in curn, would reduce the ultimate chlorine demand at the time of disinfection. After being aerated and continously agitated, the mixed liquor moves from the aeration tanks to a circular clarifier for solids separation, with provisions for a maximum of 100 percent sludge recycling. After clarification the flow goes to a solids contact unit (a reactor-clarifier) where chemical addition facilitates the removal of remaining suspended matter including colloidal mat rial . This chemical, aluminum sulfate (alum), is mixed in the reactor turbine section of the unit. Solids removal is by coagulation and a o 109 C/3< o I-< CE UJ< ~ U-CC iLU -Jlu ujlu"-cl iccO 2 ^ CC LU H- < ^ z ^ H < - < -I CE LU Q- Q- CE a^ o I JL I no (asct^ja'fesygfegtt^ Figure 22. Aerial view of the AWWTP. 11 I— yo O r— Q LO • I— >> CO Q. a> en E a. o i- LO cr> o in CO O r— o o o 1— CO m CO -^ E 113 flocculation, which results in precipitation in the clarifier section and agglomeration aiding filtration in the subsequent sand filters. The filtration unit is composed of two gravity sand filters which operate in parallel. The design filter loading rate is approximately 2.2 gpm/sq ft (90 1/min/sq m) when both filters are in operation. Backwash water is obtained from the chlorine contact chamber and the backwashing is controlled by autoisiatic timers. Detention time is a minimum of 30 minutes in the chlorine contact chamber before the effluent passes over a weir to the v/et well for transfer to the recharge areas by tvio vertical turbine pumps. Special Design Features Certain features were built into the AWWTP to increase its flexibility ano usefulness to the project. The most important of these are discussed in the following paragraphs. 1. The aeration unit is separated into two equal tanks with the water surface of one being 2 ft (0.61 m) above the water surface of the other. This permits the tanks to be operated singly, in parallel, or in series without additional pumping required. 2. There are provisions for bypassing either the solids contact unit, the filter, or both. 3. The effluent from the plant can be directed to either the recharge areas, the head of the primary plant, or into the ocean outfall . 4. The plant is monitored by recording instruments to give a continuous record of the effluent turbidity, conductivity, residual chlorine, and flow. 114 Plant Construction Bids were opened in January, 1972, for the construction of the AVNTP. The award v/as made to the Pizzagalli Corporation of South Burlington, Vermont, and construction began in April, 1972, with a contract completion date of January, 1973. The bid price was $698,400. Although the original structural work on the project proceeded rapidly, there were delays in the fabrication and delivery of some of the proprietary devices for the plant and additional delays on the site involving subcontractors, scheduling, quality control, etc. The plant was provisionally accepted in October of 1973 while final acceptance did not take place until May, 1974. Start-up began during the fall of 1973 with the plant operational by January, 1974. Operation The plant mode of operation was dictated by two important factors: low flows and a low BOD. In early 1974 the flows through the plant averaged less than 0.25 mgd (946 cu m/day) and the influent BODs ranged below 100 mg/1. In order to compensate for this, the AWWTP was operated using only one of the aeration tanks and the aerators were modified to run on automatic timers during only part of the day. Typically the flow from the primary plant followed a daily pattern in which the flow diminished from about 2 AM to 10 AM and then built up rapidly and continued, with oscillations, throughout the day and early evening. This changing flow pattern created problems in the solids contact unit (SCU) in maintaining a chemical sludge blanket in the reaction zone. To correct this problem, the flow pattern was 115 modified by splitting the clarifier effluent and returning a portion of the high flows back to the primary plant. This return flow was ultimately recycled to the AWWTP but delayed in time. This had the effect of clipping the peak flows and augmenting the low flows through the solids contact unit. This steadier flow improved the SCU performance remarkably, but at the sacrifice of a lower influent BOD, by dilution and a reduced production level from the plant. Successful operation of the plant was very sensitive to the food to microorganism ratio as reflected in the organic loading parameter, pounds of BOD applied per pound of solids under aeration (g/g). A comparison of the actual average loading factors with the design parameters is presented in Table 4. This shows the overall organic loading for the operating period remaining wery close to the design factor of 0.13 although the operational data for the plant, as displayed in Table 5, and the Appendix, show changes in both influent organic concentration and the mixed liquor suspended solids (MLSS) concentration in the aeration tank. Operational experience proved that the plant operated best at this loading factor and performance suffered considerably with deviation from this level, especially with a lower loading factor. Thus careful attention had to be paid to the amount of MLSS in the aeration tank compared to the influent BOD. Excess solids were pumped to the unused aeration tank which acted both as a sludge storage facility and an oxidation pond. This method of sludge handling provided a safeguard for plant operation, allowing the addition of microorganisms to the plant at times when, due to upsets, 115 improper operation, or toxic materials, the sludge concentration was reduced in the aeration tank. Nitrification did occur within the secondary units, as shown by the ammonia and nitrate data in Table 5. But this process, especially reinforced by excess aeration and possibly other factors, made solids separation difficult in the clarifier. The amount of aeration was always a compromise between enough to keep the aeration tanks mixed and hold a reasonable dissolved oxygen content but not too much to induce bulking and subsequent excess solids carry-over in the clarifier. The modification of the plant to permit the addition of alum to the effluent of the aeration tanks improved settling characteristics considerably. A dose rate of from 14 mg/1 to 25 mg/1 was found to be effective. While nitrification did reduce the chlorine demand during disinfection, it also created a problem by setting the stage for denitrification in the clarifier. This problem is noted by Sawyer (1967) and Busch (1971) who suggest the expeditious removal of the sludge before it can be buoyed to the surface by entrapped or attached nitrogen gas bubbles. This problem would generally occur in the early morning hours when the flow from the primary plant was reduced. This often permitted the sludge underflow in the clarifier to jam in the telescope valve, if the latter was not set exactly right, causing the sludge to start to build up at the bottom of the tank. This soon was buoyed up and drastically increased the solids loading to the solids contact unit and the filters, g ^^rally clogging the latter. Continuation of this process for any length of time usually resulted 117 TABLE 5. OPERATING DATA FOR THE AWWTP (AVERAGE VALUES FOR THE PERIOD JANUARY TO OCTOBER, 1974) 118 in a serious reduction of MLSS and, in general, unsatisfactory plant performance. In operating the solids contact unit, an alum dose of between 20 mg/1 and 35 mg/1 was found to produce a good sludge blanket. Automatic sludge withdrawal was adjusted to keep the top of the sludge blanket at least 5 ft (1.5 m) from the surface. Alum was used as it was relatively inexpensive, functioned without pH adjustments, was simple in operation, and worked. Some experimentation was made using commercial polymers but the results did not justify the extra cost and problems. While alum worked quite well during the project's operational period, it may be that in the future when the mineral content of the wastewater changes due to shifts in the water source to desalinized water, other coagulants and filter aids will need to be employed. Not only does alum react with the bicarbonate in the wastewater as follows: AlzCSOJa + 6HCO3 -> 2A1(0H)3 + SSO^ + 6CO2 to form a voluminous, gelatinous floe to aid in clarification but it also combines with phosphates in this reaction: Al2(S0j3 + 2PO4 -> 2A1P0^ + 3SO4 Gulp (1971, p. 27) mentions that the "two reactions compete for aluminum ions. At pH values above 6.3, the phosphate removal mechanism is either by incorporation in a complex with aluminum or by adsorption on aluminum hydroxide floe." 119 The pH of the wastewater at the point of alum application was about 7.2. The pH was reduced in the AWWTP by approximately 0.6 units due to alum addition and disinfection. Total phosphorus reduction did occur but the removal rate v/as not consistent. Removals ranged from about 10 to 60 percent within the plant. Phosphorus removal was not a goal of plant design and only occurred as a by-product of clarification. Phosphorus was expected to cause no problems in recharging and would be removed in the upper soil layers by the clays and silts in the area. Disinfection was accomplished by the use of gas chlorination. Originally 150-lb (68 kg) cylinders were used to supply the gas but early in the project this system was converted to 1-ton (908 kg) cylinders. This reduced the cost of the chlorine from approximately $0.50/lb ($0.23/kg) to about $0.25/lb ($0.11/kg). Dosage varied with effluent quality but generally ranged from 20 to 30 mg/1 . This v/as more than was actually needed since a steady rate of chlorine feed was used to maintain the minimum FCR desired at all flow levels. Thus the selected rate chlorinated the high flows and organic surges at the proper FCR and overcnlorinated during the low flows. A programmed proportional feeder could reduce the usage of chlorine considerably. The results of disinfection were excellent, with a reduction of col i form bacteria from a magnitude of 10'^ colonies/100 ml in the AWWTP influent to a value of and occasionally 1 colony/100 ml in the effluent. 120 Plant Production When the interim report for this project was published in October, 1973 (Black, Crow and Eidsness, Inc.), it predicted that it would only be possible to produce a maximum of 750,000 gal/wk (2,839 cu m/wk). This was attributed to the expected low wastewater flows to the primary plant, the pattern of pumping associated with the primary plant, and the lack of personnel to man the AWWTP on a 24-hour basis. This situation would have been substantially improved with the addition of the wastewater flow from Frederiksted but it was decided to continue ahead with the project without waiting for completion of that phase of the wastewater collection system. As it was, work was not completed on the crucial Frederiksted pumping station, whose operation about doubled the flow to the primary plant, until October, 1974. However, by making certain modifications to the basic plant design and operations schedule, it was possible to exceed the estimated maximum production level; and by the time the recharge work was suspended, in October, 1974, the plant was averaging over 1 mil gal/wk (3,785 cu m/wk) and had boosted its maximum daily production to about 300,000 gpd (1,135 cu m/day). This represents effluent actually delivered to the recharge areas. Actual production in sections of the plant was higher. A bar graph showing the actual weekly production and delivery of reclaimed wastewater to the recharge area is shown in Figure 23. These data exclude water produced and not pumped to the recharge area and water used for backwashing. 1.4 1.2 121 < < aiO CC<Xo LU tt 0.8 O O ai ccm>3 0.6 lUQ CC UJ < <3 04 0.2 n F M A M 1 1 n 1 -T: J I J I A TIME-1974 1 I O I N I D I Figure 23. AWWTP production utilized for artificial groundwater recharging. 122 Delivery of water to the recharge areas was halted if the guidelines for turbidity or free chlorine residual were exceeded or if the chloride content exceeded 500 mg/1 to 550 mg/1. Generally the plant operated at a turbidity level of about 1.5 FTU and a FCR of 4 mg/1. Operational Problems Aside from the low flows to the plant, power input problems plagued the plant throughout its operation. Failures in the island's power distribution system are common. The manner in which the power would be cut off to the plant v/ould often cause the control circuits to register an overload and to open their automatic circuit breakers, which required manual resetting. If this occurred on weekends or evenings when the plant was not manned, then the plant would not function properly and production was lost. Difficulties with various pumps posed the next most troublesome problem in the operation of the plant. The reliability of the pumps was probably affected by their remaining idle for a long period of time when the plant was delayed in completion and then operating under a salty tropical condition. More production was lost due to pump difficulties than from any other mechanical cause. Initial troubles centered around the submersible pumps on the influent station. These initially had two manufacturing defects which took considerable time to finally locate. Then one of the pumps had to be completely overhauled due to a seal failure. However for the past 18 months they have been operating without problems. 123 The plant water pump has burnt out once and lost its impeller on another occasion. The vertical turbine effluent pumps had a series of problems during the summer of 1974. The motor on one of the pumps shorted out and required rewinding, and the pump assembly on the other required a complete overhaul. Since these incidents occurred within a few days of each other in July, it adversely affected the plant's ability to transfer treated effluent to the recharge area for about 5 weeks until repairs were effected. The distance from the mainland and the difficulty in obtaining spare parts and service turn a small incident like this into a major problem. An algal problem was experienced in the clarifier, solids contact unit, filters, and chlorine contact chamber. In the clarifier the algae formed on the effluent trough and baffle. This was handled by scrubbing down the affected area twice a week before the algae built up to an unmanageable degree. The problem was severe in the solids contact unit and the final solution was to cover the unit v/ith an opaque polypropylene fabric which was custom-made by a local sailmaker. This has worked excellently and has solved the difficulty. The algal buildup in the filter was controlled by the chlorine in the backwash water and a plywood cover over the splitter box. The direct sunlight on the chlorine contact chamber not only created an algal problem but it caused a higher chlorine demand during the daylight hours. Initially a temporary opaque plastic cover was placed over the chamber but this was later replaced by the construction of a 50 x 20 ft (15 x 6 m) steel building over the chamber. This not only served the purpose of covering the chamber but 124 it provided extra storage room for chemicals (alum) and tools plus an office and shower area for the operators. Plant Expansion The present capacity of the AWWTP is adequate to permit the artificial recharge and recovery of sufficient groundwater to economically justify its operation. If there is a viable market for additional recl.^^imed wastewater and if there is a reliable long-term supply of wastewater of a quantity that merits treatment, then the expansion of the AWWTP should be considered. However extensive capital outlays should not be made on expansion until a reasonable plan has been agreed to for the disposition of the high chloride wastewater from both the Frederiksted and the Christiansted areas. The AWWTP has the capability for inexpensive expansion of capacity built into many of the units, so that outright duplication of the units would not be necessary. The following is a discussion of each major unit operation as it applies to future plant expansion. Influent pumping . This is an item that needs correction immediately. The influent to the AWWTP is erratic due to the diurnal pattern of flows in the interceptors and the nature of the high capacity pumps used in the primary plant lift station. With their present installation the flat rate 350 gpm (22 1/sec), AWWTP influent pumps either do not get enough to pump or cannot handle all that is available from the ocean outfall lin... It is suggested that the present AWWTP lift station be abandoned and the pumps be relocated at the effluent end of the 125 primary clarification basins. These basins will act as large equalization tanks permitting the pumps to deliver a continuous flow to the AWWTP. The proper location of the pumps will allow the rakes to function unimpaired, although the surface skimmers will be inoperative while the level of the tank is below the effluent weir. Certain adverse currents may be induced during low flow operations; but since the product will be receiving additional treatment in the AWWTP, it should not be a great disadvantage. It is suggested that 8-in. (20 cm) cast or ductile iron pipe be used from the pumps to the AWWTP along with throttling valves to adjust the head. This will reduce the friction head over the longer distance so that the original pumps can still be used. It will also provide capacity so that the pumps can be operated at higher rates when desired. When in dual, parallel operation using the new pipeline, it is believed that the present pumps will be able to deliver up to 550 gpm (35 1/sec). The installation of this change now could probably increase the reliable output of the AWWTP by about 0.1 mgd (378 cu m/day). The need to bypass and return a portion of the flow in the secondary clarifier would be largely eliminated. A smooth flow, steady organic loading, and efficient chemical addition could be maintained 24 hours per day. Aeration . The aeration section of the plant is overdesigned for the wastewater now being processed; and by operating both aeration tanks, there should be little problem in handling up to 700 gpm (44 12i 1/sec) both from a hydraulic and oxygen transfer standpoint. This is assuming that the wastev;ater characteristics do not change in the future. Clarification . The design loading is about 540 gpd/sq ft (22 cu m/day/sq m) of surface area in the clarifier. However with the use of coagulants such as alum and the proper operation of the aeration tank, this loading can probably be exceeded without problems. The higher level must be determined by actual experimentation since it will depend on the makeup of the wastewater and the selection and dosage of coagulants used. During plant operations extended trial runs were made adding alum to the effluent from the aeration tank to improve solids separation in the clarifier. This enabled plant personnel to bypass the solids contact unit (SCU) and transfer the clarifier effluent directly to the filters. This eliminates the SCU from use and it could be utilized, with some modifications, as an additional clarifier to work in parallel with the present one. Keeping the same design surface loading rate, this would allow the clarification of an additional 0.2 mgd {757 cu m/day) of mixed liquor suspended solids. However there are some disadvantages to keep in mind- The SCU acts as a backup for the clarifier. If the clarifier malfunctions and permits solids carry-over, the solids are usually handled in the SCU. Without the SCU the solids would rapidly clog the filter. The second major disadvantage is that there are no provisions for surface skimming nor underflow solids return to the aeration tank from the SCU. 127 Filtration . It is doubtful that this unit can increase its production capacity. It is suggested that if additional filtration capacity is needed, another filter unit capable of handling at least 350 gpm (22 1/sec) be purchased and installed. Effluent puirips . To increase production it would be necessary to purchase new pumps with a higher capacity. These could be insLdlled in the same location as the old pumps. These should be selected and equipped with throttling valves so that the rate of discharge can be matched to the production level of the plant. This will prevent the wet well from being emptied too rapidly and thus reducing the cycling of the pumps. The old pumps could be utilized, at a later time, at a booster station to transfer reclaimed water from a storage facility at the Department of Agriculture's Lower Love facility to various points for irrigation purposes. Expansion plan . It is recommended the expansion of plant capacity be carried out in 3 phases. After each phase, performance of the system should be reevaluated and modifications made, as necessary to the next phase. These phases, along with a generalized cost estimate are discussed in the following paragraphs. Phase 1 - 0.5 mgd (1,892 cu m/day) - Move the influent pumps to the effluent end of th? primary settling tanks. Construct the line to transfer the wastewater from the primary plant to the aeration tank. Install throttle valves on the influent and effluent pumps. Expand the recharge area. Estimated cost $30,000. It is suggested that these improvements be made as soon as possible. 128 Phase 2-0.75 mgd (2,725 cu m/day) - Install an additional 350 gpm (22 1/sec) gravity filter. If the clarifier cannot handle the new load, then repipe the solids contact unit in parallel. Install effluent pumps with a capacity of 700 gpm (44 1/sec). Expand recharge areas. Estimated cost $70,000. Phase 3 - 1 mgd (3,785 cu m/day) - Install an additional clarifier, new influent pumps, and expand the recharge area. Make general plant improvements to handle higher loading. Estimated cost $140,000. Recharge Areas The development of the recharge facilities took place in stages during the construction and operational phases of the project. The initial fe.:ilities developed covered those types of surface recharge methods which appeared to offer the most promise as far as recharge in the existing soil strata was concerned. As noted previously, it was expected that the AWWTP would produce about 750,000 gal/wk (2,840 cu m/wk) in the period following start-up and the recharge facilities were sized to handle this capacity. As operations continued and information was collected, the data were evaluated and the facilities were modified, expanded, or phased out as the situation dictated. The original recharge facilities consisted of spreading basins, spray irrigation, and spreading in a dry streambed. All of these facilities were built with flexibility to permit modification to ensure maximum efficiency. 129 Although the effluent from the AWWTP was conveyed to the recharge areas in a permanent ductile iron force main, the final portion of the piping from the force main to the basins, etc., employed portable aluminum and PVC pipe so that changes could be readily made by project personnel with a minimum of effort and expense. As discussed in the section on preliminary investigations, recharge was planned to take place in two separate areas. Golden Grove and Negro Bay, which were geologically different but located very close to each other and hence easily served by the same force main and storage tank. Golden Grove was to be the major facility, with the Negro Bay site to be used for secondary experimentation. As part of the final selection and location process for the recharge sites, a series of wells were drilled in the two areas to further define the geological strata. The logs of these wells and a chart of the soil borings appear in the Appendix and the well locations are shown on Figure 6. Three of these nine wells, PW-1, PW-2, and PW-4, were transferred to the Public Works Department (PWD), which activated them for use in its potable water system. At the time of drilling and initial pump tests these wells had a demonstrated aggregate total capacity of about 100 gpm (6.31 1/sec). This addition of approximately 140,000 gpd (530 cu m/day) to the potable water system was meant to aid the PWD in building up its freshwater reserves so that it would be able to switch the saltwater flushing system in Frederiksted to fresh water when the town's wastewater was diverted to the new primary ty^eatment plant at Bethlehem Middle Works. 130 However as drought conditions persisted on the island, the yield of the wells decreased to approximately 60 percent of their initial rates. Still, this would be sufficient production to allow substitution of potable water for salt water in Frederiksted where the saltwater usage is approximately 75,000 to 80,000 gpd (284 to 302 cu m/day). The active project well in Negro Bay, PW-2, was located where it should not, due to the geology of the area, be affected by the recharging operations at the Negro Bay site. However the two wells in Golden Grove, PW-1 and PW-4, should be affected to some degree by the recharge operations in that area. PW-1 was located approximately 200 ft (61 m) from the edge of the nearest spreading basin, while PVi-4 was about 300 ft (91 m) from the same basin. Although the wells were hydrologically upstream of the recharge site, they were expected to extract a small diluted portion of the artificially recharged water. The recharging was also expected to increase the yields of these wells since water was being added to one of the aquifers being pumped. This increase, however, would not necessarily be directly and entirely from the recharged water but most probably would be due to a combination of recharge flows and impounded aquifer flows resulting from the damming up of the aquifer by the artificial mound created at the recharge site immediately downstream. The recharge areas were developed and constructed within the project by renting heavy equipment for the earth-moving portions and performing the minor work remaining using project personnel. The development and operation of the two areas are described in the following discussion. 131 Golden Grove Recharge Area Description . The Golden Grove recharge area consists of six spreading basins and six small check dams in the adjacent riverbed. A sketch of the facility is shown in Figure 24 and an aerial photograph showing a portion of the basins is seen in Figure 25. The six spreading basins were constructed with a total bottom area of about 45,000 sq ft (4,180 sq m). During construction the upper layer of the soil was removed in each case to expose the more porous lower horizons. Due to the extremely clayey soil between the upper aquifer and the one immediately below it, the upper one acts as a conduit to move the new water horizontally with minimal leakage between the two. Bermuda grass was developed in the recharge basins and surrounding areas. This grass was selected as it is tolerant to a high level of dissolved solids and is quite resistant to dry periods, prolonged flooding, and heavy traffic. The grass aids in stabilizing the soil, reducing erosion while creating root channels to encourage infiltration and percolation. Due to normal uptake and metabolism, a portion of the nutrients contained in the recharged water is incorporated in the plant material. This low grass is easily cut, harvested, and mechanically removed from the recharge area. This effectively removes some of the nutrients from the system. No definitive studies were undertaken on the nutrient uptake by the Bermuda grass but the grass grew luxuriantly during a time of severe drought on the island. Water was brought to each spreading basin by a 4-in. (10 cm)- diameter aluminum irrigation pipe. The water was discharged into the 132 To NEGRO BAY V^ F-ROMl . \^WLLLF METER -^1^ \\ |i^ TO —< STORAGE TANK Figure 24. The Golden Grove recharge area. 133 FEET 50 100 METERS 6 10 20 30 Figure 24. (Extended) 135 iJb basin by impinging it upon a splash block and a pile of large stones. This dissipated the energy in the water so that it could enter the basin without eroding the bottom. Each pond was first tested for a short period to ascertain its relative ability for infiltration and percolation. After this, two ponds were selected to determine how long the wet cycle of operation could be extended without a noticeable drop in infiltration efficiency. During recharging operations the selected basin, or basins, were filled to a height of 3 to 3.5 ft (0.9 to 1.1 m). Then the flow to the pond was adjusted to maintain the same water depth. This meant that the water was entering the pond at the same rate that it was being lost by infiltration and evapotranspiration. It proved relatively easy, in practice, to hold the depth to within 0.5 ft (0.15 m) through the use of adjustable valves at the force main standpipes. The results of the operation are outlined in the section on results and discussion. The work using the check dams in Golden Grove was scheduled to begin in November, 1974. Unfortunately recharge operations were suspended due to the high TDS of the wastewater and the floods during that month; therefore no data were collected on that phase of the project. Design considerations . One of the best guides to the design and operation of a groundwater recharge system using wastewater effluent is a report entitled "Soil Mantle as a Wastewater Treatment System" by McGauhey and Krone (1967). This was based on considerable experience with septic tank studies and was broadened to include other 137 soil-oriented treatment systems involving wastewater. Aside from an extensive literature review and discussion of the the theoretical aspects of the subject, the authors present some recommendations for the design and operation of an engineered soil system. As part of these recommendations they developed eight criteria for optimizing such a system. These criteria from the report (McGauhey, 1967, p. 144) are quoted below; and following each one is a discussion of its application to the system constructed in Golden Grove on St. Croix. In reviewing these criteria and subsequent discussions it must be kept in mind that they were developed for a soil-aquifer system which was meant to act as a treatment process for wastewater. In the St. Croix project the soil-aquifer system is meant to be a treatment process only in the sense of a polishing of the extensive processing that has already taken place in the AWWTP. The system also acts as a safety barrier against any occasional deficiencies in the treatment process. Hence it is expected that the soil system will reduce nutrients and remove most organics, bacteria, and viruses but it is not to be expected to bear the brunt of the oxidation and filtration processes that a system using settled wastewater or septic tank effluent might experience. " Criterion 1 : The infiltrative surface should be no less permeable than any undisturbed parallel plane within the system." As part of the construction of the basins the upper, less permeable, layer was removed to expose a more permeable soil horizon. Soil borings in the area indicate that permeability does not decrease below the newly exposed horizon before the upper aquifer is reached. 138 " Criterion 2 : The soil surface should be managed in such a manner as to disperse clogging material." One of the suggestions made by McGauhey and Krone was to grow vegetation on the areas to provide root channels and expand the soil. This was done using Bermuda grass which additionally stabilized the banks of the basins to permit foot traffic and incorporated a portion of the applied nutrients in their plant material for removal by harvesting. " Criterion 3 : There should be no abrupt change in particle size between coarse trench fill or surface cover material and soil at the infiltrative surface." Since the existing soil structure is the infiltrative surface, this is no problem as no larger material, such as gravel, is applied to this surface. " Criterion 4 : The infiltrative system should provide a maximum of sidewall surface and a minimum of bottom surface." The use of a basin design entirely violates this criterion. The cost of construction, ease of maintenance, and simplicity in operation were deciding factors in selecting spreading basins over trenches. Additionally the use of vegetation for dispersing any clogging material (Criterion 2) and nutrient uptake can be maximized with the basin configuration. " Criterion 5: Continuous inundation of the infiltrative surface must be avoided," By using a system design, such as the one in Golden Grove, containing many basins, the flow can be diverted to any of the basins, allowing some to be utilized while others are allowed to dry out. i39 Successful management of the facility depends on having sufficient basin area so as to provide for alternative loading and drying cycles during operation. The area required in the future has been reevaluated on the basis of the results obtained and is discussed under the section on monitoring activities, " Criterion 6 : Aerobic conditions should be maintained in the soil system." This is to promote aerobic metabolism of the soil biota to prevent the buildup of undesired anaerobic by-products such as clogging slimes or taste and odor-causing compounds. This can be maintained in several ways. The first is to use alternate loading cycles, wet and dry, in the operation of the spreading basins. Another is to remove the water accumulating in and above the aquifer under the spreading basin as rapidly as possible so as to prevent the groundwater mound from building up until it reaches the bottom of the basin. The section on recommendations for future development covers this situation. " Criterion 7 : The entire infiltrative surface should be loaded uniformly and simultaneously." Since the bottom area of the spreading basins is the primary infiltrative surface, it will be loaded rather uniformly as the bottoms are relatively level. The sidewalls, however, are loaded differentially, but they do not contribute as much to the total recharge effort. " Criterio n 8: The amount of suspended solids and nutrients in the applied water should be minimized." 140 The design of the treatment process for this project was oriented towards a high reduction of suspended solids and organic material. The problem of a mat forming on the surface of the soil and clogging the pores did not manifest itself to any noticeable extent in the project during normal operations. Nutrients were not fully removed in processing at the AVIWTP, with ammonia generally converted to the nitrate form and the phosphates only partially removed. Undoubtably the growing and harvesting of Bermuda grass in the spreading basins aided in the removal of additional nutrients while the soil itself is capable of handling phosphate removal. Negro Bay Recharge Area Description . In the Negro Bay area two types of recharge methods were tested: spreading basins and spray irrigation. A sketch of the facilities is shown in Figure 26. The spray irrigation portion consisted of a gently sloping (0.031) field 250 ft by 250 ft (76 m by 76 m). The water was transferred from the permanent standpipe to the field by 4-in. (10 cm) aluminum irrigation pipe. In the spray area grids containing 8 spray heads each were set in the field. The feed in the grid loops was by 2-in. (5 cm) PVC pipe. The spray heads were Rainbird 30 B-TNT with an 11/64 x 3/32 nozzle that was rated for a 92-ft (28 m) diameter circular spray pattern at 40 psi (258 kg/sq cm) with an individual feed of about 7 gpm (0.44 1/sec). These spray heads v;ere placed on 2.5-ft (76 cm) risers at 60 ft x 60 ft (18 m x 18 m) spacing. The actual rate of surface loading was about 2 gpd/sq ft (0.08 cu m/day/sq m). 142 «f»#^e# 143 The normal mode of operation was to run the entire system 3.5 to 13 hours at a time with the total loading ranging from 0.3 to 1.1 gal/sq ft (0.012 to 0.044 cu m/sq m). Higher loading than this caused surface runoff and erosion of the soil. The entire area was seeded with Bermuda grass which, due to the poor soils in the area, did not fill out as thickly as it did in the Golden Grove spreading basins. The results of the tests were not encouraging. Water did not build up in the various piezometric tubes installed in the area. If the spraying time or amount of water applied at a single time was increased, runoff occurred. The rate of application was far below that of the ponds. What apparently occurred is that the soil moisture in the upper layer was increased during spraying periods; but in the periods between spraying, the water was removed by evapotranspiration aided by the capillary nature of the marly soil which acted as a wick for the water incorporated in the soil. To decrease erosion a better vegetative cover could have been developed by leaving more of the clayey soil on the surface. However this would also act as a further barrier to the infiltration of water applied by spraying. The two spreading basins in the Negro Bay section were run on an alternating wet and dry cycle. Each pond has an average bottom area of about 2,500 sq ft (232 sq m). The ponds are built on a slight slope so that the water depth is limited by the downslope side. The marls neither lend themselves well to the construction of berms around the ponds nor to stabilized banks as do the soils in Golden Grove. Erosion of the sidewalls contributed to the plugging of the bottom surface of the bas-^ns. 144 Each pond was initially run on a constant-head basis where the ponds were filled to a certain depth and then the flow was throttled down to try to maintain that depth. This was not satisfactory over a long-term basis as the ponds took so little water that the setting had to be too low for effective operation. The average percolation rate based on bottom area was so low that work in the Negro Bay area was suspended and the remaining efforts were applied in the Golden Grove area. SECTION V MONITORING ACTIVITIES DURING THE PROJECT As part of the project an extensive monitoring program was established to provide data for a "before, during, and after" look at the various parameters that might be affected by the recharge operations. It was desired to carefully monitor surface and groundwater quality and quantity in the study area and, in addition, monitor the operation of the AWWTP. Water Quality A water quality laboratory was established within 3 months of project operation on St. Croix. This vjas first located in the field office, then in laboratory space donated by the Martin Marietta Alumina Company, and finally in February, 1973, in the permanent laboratory which was constructed as part of the AWl^TTP facility. The number of parameters analyzed was increased as laboratory facilities improved. Initially a chemist was brought in from the mainland to do the work and to train local people for the work so that he could phase himself out. In addendum No. 1 of the original project proposal (FWPCA- 1970), a list of analyses to be performed during the project was noted and is as follows: Chemical oxygen demand 145 146 Biochemical oxygen demand Total nitrogen Ammonia nitrogen Nitrite nitrogen Nitrate nitrogen Phosphate Total organic carbon Chloride Col i form To these tests were added those for alkalinity, calcium, and total hardness plus operational tests for the AVJWTP. All of these analyses were performed on St. Croix with the exception of the total organic carbon and total nitrogen measurements which were performed in the Black, Crow and Eidsness laboratory in Gainesville, Florida. A survey of the entire study area was made and wells, both public and private, were selected for monitoring purposes. These were located above and below the theorized groundwater flow at the proposed recharge areas. Only active wells were selected for water quality monitoring purposes. These were wells that were being actively pumped, thus assuring a fresh sample of the groundwater for analysis. Additionally sampling points were selected along the course of River Gut where surface water could be sampled. These sampling stations are shown on Figure 13. To avoid needless duplication of sampling and analysis, the selected wells were divided into two groups, primary and secondary, with the primary wells being considered the most important. 147 A sampling schedule (see Table 6) was then devised which included all of the sampling stations and all of the analyses scheduled in a systematic fashion that included all of the sampling points in a full analytical time cycle. These time cycles were 4 weeks in length and permitted the chemist time to sample and perform the analyses with a minimum of storage time, and sufficient extra time to maintain the laboratory, prepare reagents, and do the necessary paperwork associated with the laboratory. In sampling, problems were encountered throughout the project. The greatest was in simply obtaining the samples. Most wells had no provision for sampling taps and these had to be added where permissible so as to sample the water before it was mixed in a storage cistern. Often it was not possible to add these taps, or if they existed, they sometimes were removed at a later time by the owner or alterations were made to the premises which then prevented access to the taps. One has to keep in mind that sampling has continued at some stations for over 4 years. It was easy to install taps on most of the government-owned wells but these were soon discovered by people who used them during dry periods to either fill up drums of water to take home to fill their cisterns, to provide water to wash cars, or both. This abuse of the government wells often provoked the Public Works Department to remove the sampling taps altogether. The wells that were drilled adjacent to the Golden Grove recharge area for the purpose of monitoring the changing water levels during recharging were also sampled. Since these had no pumps installed nor easily available power; they were simply dipped, using a 148 cr o >1 c •a: SS1W Qoa 003 d moi N-^ON >^:H.ULLB>|L\/ UjnLD[B3 SSBUpjBH s9p!.aoLi]3 UJJ0J.L[03 OOi 009 003 d LP^Oi N-^ON /C:tLULLe>ILV mnpi.B3 ssaupjBH aDue:^Dnpuo3 OLj-pads sapijomo (M) S9[duiBS UaiBMS^SBM (S) S3[dlllBS ua:^BM /jBpuooas (d) saLdiuBS ja:jBM A'UBUJLJcl /"BQ ON >|aaM 333: 333: 2 3: 3: 3: H- u- s: 1— 3: »- I I 5^ I "P 149 project-constructed torpedo sampler. Despite being dipped a few times at each sampling, this was obviously an inferior method of sampling and the data obtained from these wells should be viewed with this in mind. The water quality data for the project are presented in tabular form in the Appendix. Groundwater Quantity and Movement A study of groundwater quantity and movement was made using water level data from wells selected in the study area. These v^/ells were generally inactive nonpumping wells on public and private property. Water level recorders were placed on a series of wells to ascertain what continual variations took place while other wells were simply measured by taping at regular intervals. Since a free water table does not exist in the study area south of the Centerline Road, these water levels represent the potentiometric surface of the groundwater rather than the actual depth of the aquifer. Aside from these data, additional information on the potentiometric surface was gathered by installing small diameter, 3/4- in. (1.9 cm) PVC, tube wells in the vicinity of the proposed recharge area. Holes for these wells were dug using a 4-in. (10 cm) soil boring rig with an auger bit. This gas-powered drilling rig was mounted on a trailer which could be moved rapidly from site to site. Although the rig could drill holes quickly in the tight clayey soil, it could not penetrate far below the existing water in the soil as the sides of the holes in the vicinity of the water would collapse as the sectioned auger was being removed to clear the hole. Since all of the 15 holes were drilled during a period of excess groundwater in the area, the resultant tube wells were not deep enough to be usable during the extended period of dry v;eather that occurred during the last 2.5 years of the project. Additionally the majority of the tube wells downstream of the recharge area were destroyed during the construction of the adult correctional facility. Most of the tube wells upstream of the recharge area were lost in two fires which swept the area and those that survived went down to the blades of a large government- owned cane cutter which made intermittent unpredictable forays into the area to cut forage for the island's cattlemen. However, the tube wells did furnish useful information in initially calculating the flow pattern of groundwater in the area, which aided in the final placement of the recharge structures. Moreover the actual boring of the holes produced valuable data on the soil horizons in that part of the study area. The water level data for wells in the study area are presented in graphical form in the Appendix. Rainfall Data Initially three recording rainfall gages of the weighed bucket type were installed in various parts of the study area to collect rainfall data. On the aggregate this data collection system was not even a moderate success. The gages suffered from mechanical breakdown, human abuse, and animal interference. The clock portion of the gages continually broke down. Repairs were difficult to procure on the island and the replacement 151 spring-driven clocks cost close to $100 each. Several replacements were purchased but they soon failed in operation. Additionally, the rain gages seemed to exude a magnetic pull for human curiosity and at two of the locations the security lock was frequently twisted off the case and the gage thoroughly examined. At the Negro Bay location the gage was located adjacent to a government well and was repeatedly broken into to obtain the bucket, which apparently was used in conjunction with the v^ell to wash cars. Another problem was animal interference, which at the Bodkin location above Fountain Valley, took the form of the gage being used as a rubbing post by cattle. There was also the general problem of the local tree lizards, Anolis acutus, which would occasionally be found living in the gage. This selection of dwelling place was no doubt accidental on their part and probably the result of falling through the narrow funnel-shaped opening which directs the rain to the weighing bucket. Once trapped inside, the lizard would repeatedly jump on the recording needle, thus distorting the recording. They would eventually die, attracting large numbers of ants who would invade the gage to consume the body. The only gage remaining after the first 3 years was the one installed at the fire station in Grove Place. This gage remained relatively unscathed but has suffered from numerous and continuous clock failures. Fortunately, the U.S. Department of Agriculture maintains a rain gage at Bethlehem Upper Works, which is on the eastern edge of the study area on a hill just above the Golden Grove recharge area. This 152 gage, v/hich is protected and attended daily, has produced far more reliable information and its data have been used in this report. Advanced Wastewater Treatment Plant The operation of the advanced wastewater treatment plant v/as monitored as to flow, power consumed, chemicals used, influent and effluent quality, etc. This work was performed by both the plant operators and the project chemist. The sample log pages displayed in Figures 27 and 28 show how the various plant functions were recorded. These logs required a fair portion of the operator's time to complete every day; but in filling them out and examining the various recorded data that had to be entered into the log, he obtained a better understanding of the plant's operation. The effluent flow chart. Figure 27, was especially helpful in recognizing small problems in operation before they became major disasters. The operating data for the plant have been statistically analyzed and presented in the Appendix of this report. 154 ^ 155 A n V A M C p ! ,V /v: r pw fl T £ f T^rArMr DhTt [^/.<vV7f] r PLANT- 'jT,'<Rnj.< y\9r,iM r.ufi^ir,': // ' 'v-rr 1 I— ! "A" FLOUJ OfNTK r^ I 278| «""»"•-"» I >T I—tr^ _J * ft^WVW-TP '-••1^^^38gl_^eVc7~<. > T' lL .^ .^ — -ip- — — — >- iK r»u» "%<H^ ^lO'- .-lirt/t. y isjtoo\ To '".Ccrf*»&0 33rC00 TKtO A>U>»TI> SECTION VI MAJOR PROBLEM AREAS ENCOUNTERED IN THE PROJECT As in any large undertaking, there have been a considerable number of problems that have occurred during the course of the project. The vast majority of these were solvable as the project progressed. Some of them required minor changes in the direction of the project while others caused considerable delay in the completion of the project itself. The following is a discussion of some of the major problem areas within the project that became apparent as the work proceeded. Conceptual The reuse of water cannot be treated as an isolated event in the water resource plans of an area. The concept must be integrated into both the water supply and wastewater treatment systems. However this project was, by definition and funding, an experimental facility built to determine whether the concept was feasible. Thus major changes in the existing system and future construction could not really be expected until the feasibility was proven. This meant that the concept of reuse had to be fitted into a system that was basically designed without that idea in mind. Since St. Croix has a variety of water sources, ranging from distilled to brackish to seawater, that feed into the wastewater system at different 156 em 157 points; it makes it essential to coordinate the entire operation. Hence certain problems were already built, or designed, into the syst and either had to be compensated for during the project or will require modification in the future. The most notable problem resulting from this conceptual gap is the high chloride level of the incoming wastewater. In order for project operations to proceed at all, a chloride level of up to 500 mg/1 had to be tolerated and used for recharge purposes. This was the result of the brackish well water that was being used in the section of the island whose wastewater supplied the project. Even more critical is the use of seawater for fire and flushing purposes in the towns of Christiansted and Frederiksted. It was the connection of the wastewater collection network of Frederiksted, with its salty wastewater, to the central primary treatment plant that finally closed the project down in October, 1974. Although the problem in Frederiksted will be resolved, at least temporarily, in the fall of 1975, the potential chloride problem posed by the connection of Christianst to the system in 1977 lies ahead. Coordinated Planning There are numerous agencies within the territorial government which have an interest and responsibility for the production, distribution, and usage of public potable water plus the collection, treatment, and disposal of the island's wastewater. This split responsibility has caused confusion and occasional problems in fulfilling the project goals. 158 Changing Conditions Under actual field conditions on a project of this magnitude and time span, unwanted changing conditions had to be accepted. Many of these changes would not be tolerated in a laboratory operation where it is desirable to hold conditions the same while varying selected parameters, preferably one at a time. There were four main areas where these changing conditions caused problems. Weather Several extreme, and unseasonable, variations in the amount of precipitation occurred during the project. This resulted in excess groundwater during the exploratory and design phase. Then an extreme deficiency occurred during the recharge operations. The operations were finally terminated by record rains and floods that severely damaged the facilities. This has been followed by another unusual and extended drought period. These swings have affected the quality of wastewater received, the well yields, aquifer conditions, and surface- water activity. Water Sources The changing production levels of the various sources of water on the island affected the quality of the subsequent wastewater to a large extent. This is especially true in the western portion of the island where any reduction in the production of desalinized water from the Martin Marietta plant meant an immediate increase in the proportion of brackish well water used. This had an effect on the quality of water produced at the reclamation plant due to the change in the mineral content of wastewater received. 159 Construction Activity This activity occurred both in the drainage areas tributary to the recharge area and those associated vnth the wastewater collection system. In the immediate area, the construction of a large penitentiary complex adjacent to the recharge area resulted in the loss of a large number of piezometers and the use of a portion of the streambed that had been planned for recharge operations. The large amount of public housing constructed during project development which contributed its wastewater to the interceptor system changed the expected character of that wastewater. All during the project the interceptor system was being expanded. This meant that the volume of wastewater was increasing and changing as areas with different water sources were sev/ered. Groundwater Extraction The quantity of groundwater removed from the study area was varied to meet local demand or to inversely match the output of the desalinization plants. The project had no control, besides suggestive, over the operation of these wells. Project Location It was implicitly assumed that the reclamation plant would be located adjacent to the newly constructed central primary treatment plant on the island. This latter facility v;as located on the island with hydraulic transport and outfall disposal characteristics in mind. This location, along with the funding limitations in constructing a force main, restricted the choice of recharge areas. 160 Delays The wide scope of the project made it extremely vulnerable to delays due to complications in some stage of either this project or one of the many other activities that affected this project. The most significant delays are discussed in the following paragraphs. The completion of the interceptor sewers was delayed in schedule, which greatly reduced the amount of wastewater that the project had available to process and reuse. This delay has to be weighed against the benefit of not completing the Frederiksted pumping station on time. It permitted the operation of the recharge phase without the flow of salt water that accompanied the Frederiksted wastewater. The construction of the AWWTP was delayed due to shipment and procurement problems with some of the proprietary devices, problems with subcontractors, and construction difficulties. The shipment of spare parts for the repair of equipment was often delayed during plant operation. The customs status of the territory and the distance between the mainland United States and the Virgin Islands caused numerous difficulties in obtaining spare parts and manufacturers' service. Airfreighting of shipments was no guarantee that they would arrive in a reasonable time. Most spare parts were unavailable locally. Equi pment Out ages Problems were experienced with several pieces of equipment in the AWWTP. These were mainly pumps which required numerous repairs. 16] During the periods when these pumps were out of service, the production of the AWWTP was reduced, often to no usable output at all. Natural Disasters Flooding occurred on the island during October and November in 1974, seriously damaging the recharge facility and necessitating extensive repairs to the basins, roadways, and pipelines. The floods also damaged the primary treatment plant and many of the major wastev;ater interceptors so that the amount of wastewater supplied to the AWWTP was severely restricted for several months and that which was received was difficult to handle due to the high percentage of clay it contained. Summary Despite all of these problems experienced during the project and all those that will occur during its future operation, the economics of the system will make it worthwhile to continue. The cost of fresh water is too high on St. Croix to use it only once and throw it away. SECTION VII OTHER ACTIVITIES ASSOCIATED WITH THE WASTEWATER RECLAMATION PROJECT Although the purpose of the project was to determine the feasibility of artificial groundwater recharge, it did encourage other uses for reclaimed wastewater. The purpose of this was two-fold; first, to explore alternative uses for water reuse. This is especially important if these alternative uses can replace potable water, which is both expensive and in short supply on the island. Secondly, it was a means of encouraging community-wide interest and support for the idea of wastewater reclamation and water reuse. If another organization or agency actually worked with water reuse and was successful, then it could mean more support for the continuance of the project once the local government assumed operations. The project personnel were successful in encouraging other people to experiment with the reclaimed water and several of these activities are discussed below. Irrigation One of the biggest hindrances to the development of a sound agricultural industry on St. Croix, in the area of fruits and vegetables, is the lack of water. A large amount of water is needed in agriculture to counteract the excessive evapotranspiration rate 162 163 caused by the high ambient temperature and steady tradewinds. Only a week without water can severely damage many vegetable crops on the island. Rainfall has traditionally been extremely unreliable in its time patterns on the island. The rainfall pattern in the last three years has been such that a vegetable enterprise without supplemental irrigation would have faced disaster. Unfortunately, the potable water is too expensive, at $1 ,300/acre-ft ($1.05/cu m), to be used; the groundwater is limited in quantity; and in many areas the groundwater's sodium absorption ratio (SAR) and/or chloride content is too high for prolonged use. Reclaimed wastewater with a controlled SAR and chloride level could be used, in many cases, for agricultural irrigation. Initial uncontrolled experiments were carried out in this area by personnel at the AWWTP in growing ornamental plants and vegetables in a small nursery. Chlorinated effluent from the AWWTP was used for the necessary irrigation. This was an extremely effective public relations feature for the project. If visitors could not fully comprehend the workings of the biological and chemical treatments going on within the AWWTP, they could easily appreciate the profusion of flowers and vegetables that were grown with the finished product. This was especially true since the rest of the island was parched and brown due to one of the longest droughts in recent times. This created sufficient interest that a cooperative venture by the V.I. Extension Service and the V.I. Experiment Station financed and built a 3,000-ft (915 m) spur line that will permit the transfer of reclaimed viastewater directly to the St. Croix campus of the College of the Virgin Islands. There it will be used for research 164 into the uses and effectiveness of irrigation under the subtropical conditions existing in the territory. This research activity was halted due to the high chloride content in the wastewater but is expected to resume in the fall of 1975. Clam Culture Using the nutrients available in the wastewater effluent from the AWWTP, a project to culture freshwater clams ( Rangia cuneata ) has been started. This project is under the direction of the biological oceanography section of the Lamont-Doherty Geological Observatory of Columbia University. It has a facility on St. Croix which has been conducting research on the use of ocean nutrients for production of shellfish for the past 6 years. The clam operation is quite similar in that it utilizes the nutrients remaining in the wastewater effluent to grow algae which are fed to clams. Presently the clam-raising facilities, which are actually large chemostats, have been constructed on the grounds of the AWWTP and began operations in August, 1975. The first phase consists of stabilizing the algal growth in the chemostats. Extensive preliminary tests have already been run at the Columbia University laboratory in St. Croix to select the algae strains to be used and to approximate the growth rate to be expected. The ultimate purpose of the clams will be to use them for a protein source for poultry on the island. When the clams reach the desired size, both the meat and shells will be ground up and the mixture fed to chickens. 165 Pisciculture This project also uses the nutrients in the effluent of the AWWTP to grow algae. In this case it will be used to grow Talapia aurea which are a freshwater herbivorous food fish. This project is sponsored primarily by the V.I. Agricultural Experiment Station. Four ponds have been constructed in the vicinity of the recharge area in Estate Golden Grove and fish are being raised in one of them. Each of these ponds has a capacity of about 0.1 mil gal (380 cu m). The fish will grow in cages suspended in the water. The effluent from the ponds will be used for irrigation purposes. It is proposed that these fish will be used for human consumption. Interrelationship In addition to these three activities involving water reuse that have been developed in cooperation with the wastewater reclamation project, other projects have been suggested by local groups and citizens interested in utilizing this valuable resource. Many of these additional suggestions require further definition and sound financing. The local government, in cooperation with the Water Resources Research Center in St. Thomas, is developing better guidelines and regulations applicable to wastewater reclamation and reuse. Since water is precious in the territory, all of these activities help to complete the water resources picture on St. Croix. SECTION VIII RESULTS AND DISCUSSION Water Quantity Changes Due to Recharging Infiltration and Percolation A key factor in the economic success of a surface method of artificial recharge is the rate of infiltration. This determines the land area required per unit of recharged water. On the Virgin Islands land is expensive, averaging about $10,000/acre ($4,050/ha). In comparing the rates of infiltration between the 8 basins as shown on Figure 29, it is apparent that there is a distinct difference between the rates in the 2 basins in Negro Bay and the 6 basins in Golden Grove. The sustained infiltration rate in Negro Bay was less than 5 gpd/sq ft (0.2 cum/day/sq m) while infiltration rates in the Golden Grove basins ranged from 10 to 28 gpd/sq ft (0.4 to 1.1 cu m/ day/sq m). Negro Bay . In the Negro Bay area, which is located on the Kingshill marl, two methods of surface recharge were tried: spray irrigation and spreading basins. Neither method of surface application proved to be sufficiently successful to warrant further investigations. The spray irrigation was limited in the rate and extent of application by surface runoff on the spray area. The spray area was constructed on a location with a gentle slope of about 0.031. The water 166 168 (il bs/pd6) NOIlVHllldNI dO 3iVa 169 was applied at the rate of approximately 2 gpd/sq ft (0.08 cu m/day/sq m) and once the loading reached about 0.4 to 0.6 gal/sq ft, (0.016 to 0.024 cu m/sq ni), any additional water would tend to runoff down the slope causing soil erosion. This meant that spraying periods were limited to between 5 and 7 hours in a 24-hour period if erosion was to be controlled. During the intervening drying period, evapotranspiration, through the vegetation and the capillary action of the marl, removed the water in the upper soil horizons. The result was no net gain in water entering the marl formation. One of the main reasons for this infiltration problem is the structure of the upper soil horizon in the spray area. Covering the actual marl formation is a cap of soil approximately 8 in. (20.3 cm) thick. All but 2 to 3 in. (5 to 7.6 crO of this clayey organic material was removed and windrowed to prepare the area for surface application. It was realized that when wet the clay would swell and tend to be impervious. However, this upper top soil was necessary to serve as a base for growing grasses. The grasses would aid in preventing soil erosion while at the same time they would remove a portion of the nutrients in the applied effluent. Adjacent to the spray area (see Figure 26) two spreading basins, basins 7 and 8, were each operated for approximately 2 weeks. The resulting sustained rate of infiltration was less than 4 gpd/sq ft (0.16 cu m/day/sc m). This was a better infiltration rate than for the spray irrigation site, but it v;as nc . high enough when compared to the rates in Golden Grove to justify continued operation. Additionally, the banks of the marl basins were unstable when wet. The fine material from the banks was eroded to the bottom of the basin, which contributed to the 170 sealing of pore spaces in the exposed marl. Marl, by itself, v/ill support only sparse vegetation to a very limited degree so the use of grass for stabilization was not possible. In summary the results of the work in Negro Bay shov;ed that artificial recharge by spray irrigation or spreading basins in that area was not justified when compared to the alternative available. This alternative is in Golden Grove where the sustained recharge rates are 4 to 7 times higher and hence the land area required would be proportionally less. Recharge operations in Negro Bay were abandoned in August, 1974, and all subsequent efforts were concentrated on the Golden Grove facility. Golden Grove . This recharge area, which is located in an alluvial valley, was in operation from February through October, 1974. All the recharging v;ork in this area was accomplished by the use of spreading basins. The resulting rates of infiltration for the various basins are shown in Figure 29. These data show a high sustained rate for infiltration and percolation for all of the basins with the minimum rate being in the order of 11 gpd/sq ft (0.45 cu m/day/sq m). The best infiltration rate was encountered in operating basin 5 which had a maximum sustained rate of infiltration in the range of 25 gpd/sq ft (1 .0 cu m/day/sq m). The rate of infiltration is a function of both the soil structure on, and immediately below, the bottom of the basins and the inherent ability of the underlying formation to conduct the percolating water away from the vicinity. If the underlying formation will not remove the introduced water at the same rate that it is being applied, then ponding will occur. 171 In order to test the long-term ability of the underlying formation to handle recharging, basin 2 was operated continuously for 60 days. A sustained decline in infiltration rate v^as not apparent until the final 10 percent of the run. By that time a cumulative loading of about 660 gal/sq ft (26.9 cu m/sq m) had been applied to the basin for a total flow of about 6.6 mil gal (24,981 cu m). Basin 5 was also operated for an extended period of time to test its capabilities. After a dry cycle of 125 days the basin was operated at a high rate of loading for 18 days. During this time the rate of infiltration averaged about 22 gpd/sq ft (0.9 cu m/day/sq m) compared with 11 gpd/sq ft (0.45 cu m/d.,y/sq m) for basin 2 discussed in the preceding paragraph. The total loading for the run was about 400 gal/sq ft (16.32 cu m/sq m). The infiltration rate dropped off drastically during the final portion of the run and there were indi- cations of ponding at that time. These were manifested by some dampness at the bottom of the adjacent structure, basin 6. The decrease in infiltration rates which occurred in both basins 2 and 5 could be caused by clogging of the soil in the basin due to deposition of suspended solids and/or biological growth; or, to the mounding of the water table to the point where it reached the bottom of the basin. Based on observations, examination of water level information, and comparison of infiltration rate data, it is believed that clogging of the soil was involved in both cases but that the mounding water level under the basins also played a part. This is especially true in the case of basin 5 during its final extended run. The clogging condition of the soil due to deposition of organic suspended solids and biological activity is readily reversed by a 72 period of drying so that stable aerobic conditions are restored to the upper soil horizons. This permits aerobic metabolic activity to occur in that area. The low turbidity and organic content of the v/astewater effluent used in this recharging reduced considerably the potential suspended solids involved in mechanical entrapment, while also reducing the food available for microbial growth. In order to continue the long periods of inundation which are vital to the economics of the recharge operations, it is important to continue the operation of the AVIWTP so that the present low levels of turbidity and organic content are maintained, or reduced. The short span of recharge operations in 1974 did not permit sufficient data to be collected to determine the most efficient time period to use for either the inundation of the ponds (wet days) or the intervening drying period (dry days). It will probably take sevei il years of operation and careful monitoring to correctly arrive at the answer. It is likely that there will be different values for each pond due to the difference in underlying strata. For the present, however, operations should be carried out on the basis of 10 wet days, followed by 5 dry days. This will give a complete cycle of 15 days for which an average value for the entire cycle of 8 gpd/sq ft (0.33 cu m/day/sq m) can be used for loading purposes. When operations are renewed then these figures can be updated as experience dictates. Groundwater Movement in the Golden Grove Area St. Croix's physiography in general and stratigraphy in particular create some problems for the groundwater hydrologist. The island's groundwater situation is studied most easily on a broad plane where generalizations can be made on well yields, aquifer flows, and transmissibil ity. The USGS has done this in useful reports such as those recently published by Jordan (1973) and Robison (1972). These reports combined collected data to present an overall view of the groundwater potential on the island. As the area of study in St. Croix is reduced to a single drainage basin, or portion thereof, the difficulties involved in accurate analysis can increase drastically. This project has intensively studied the portion of River Gut where it passes through Golden Grove. The area of interest is the alluvium in the valley into which the artificially recharged water is introduced. Information about the alluvium has been gained mainly by soil borings, well construction, pumping tests, water level monitoring, chemical analysis of water samples, and field observations. The results of all of these investigations have shown that this area is one of extreme complexity when studied as a separate small system. The alluvium is of recent geologic origin and its placement has been a result of years of deposition of material weathered from the basin's surrounding hills. This was deposited by both normal stream sediment transport and by occasional turbulent flooding conditions. The result has been a formation of an alluvial material which is generally heterogeneous and anisotropic in character. It is estimated that field permeability (K^) values for the alluvium range from 0.01 to 10,000 gpd/sq ft (0.0004 to 410 cu m/day/sq ft) and vary in both horizontal and vertical planes. While all of the material will conduct water to some extent, the main aquifers composed 174 predominately of sand and gravel conduct the major portion of the flov;. Based on borings, well construction samples, and observations, these aquifers are neither consistent in thickness, material content, nor horizontal extent. Their thickness ranges from 0.5 to 15 ft (0.15 to 4.57 m) but generally in the order of 1 to 2 ft (0.3 to 0.6 m) thick. Pumping test analysis . Pumping tests were performed on selected wells in the area. However, analyzing the data to provide valid, meaningful results as to permeability (K), transmissibility (T), and the coefficient of storage (S), for each well is not possible to any reasonable degree of accuracy. The reason for this is that many of the assumptions on v/hich the accepted theories and calculations for these parameters are based are not valid in the situation at hand. Of the 7 assumptions listed by Kruseman and DeRidder (1970, p. Ill) v;hich are basic to any conventional analysis, 3 of them cannot be fulfilled. These are: 1. The aquifer has an apparently infinite areal extent. 2. The aquifer is homogeneous, isotropic, and of uniform thickness over the area influenced by the pumping test. 3. Prior to pumping, the piezometric surface and/or phreatic surface are (nearly) horizontal over the area influenced by the pumping test. In the first assumption, the aquifers in Golden Grove have a very real boundary situation where the horizontal extent of the aquifer varies from only 200 to 1,200 ft (60 to 365 m). In the second assumption the aquifer is not homogeneous, isotropic, or uniform in thickness. As for the final assumption, the potentiometric surface slopes steeply at the rate of 50 to 70 ft/mile (10 to 13 m/km) within the alluvium. Aquifers in the recharge area . There are a number of aquifers in the alluvium, some of which are shown in Figures 15 and 16. They are not necessarily connected horizontally, and isolated sand and gravel lenses are not uncommon. Precise knowledge of the strata can only come from additional deep borings; the more borings the better will be the knowledge of the area. However based on borings and well logs avail- able, information on recharge rates and water levels, observations in the field, and engineering judgment; certain tentative conclusions can be made as to the nature of the water-bearing strata in the vicinity of the recharge area. These conclusions are discussed in the following paragraphs. There are one and possibly two main aquifers that transmit the major portion of the groundwater in the upper aquifers through the recharge area. The theorized location of these aquifers is shown on Figure 30. The field permeability (K^) value in the most porous section of the main aquifer is in the range of 3,000 to 7,000 gpd/sq ft (122 to 285 cu m/day/sq m). This was determined by approximating the system during recharging as a constant head parameter. The resulting K^ value checks with the range of K values for aquifers with sands and gravels given by Todd (1959, p. 53) and Davis and DeWiest (1966, p. 164). The average temperature of groundwater on St. Croix is about 27° C which decreases viscosity and increases the K by approximately 33 percent (Todd, 1959, p. 51). o i-o 177 178 It is believed that a portion of the main aquifer was partially exposed during the excavation of the new stream channel recently constructed just south of the adult correctional facility. Based on the recharge operations, it is estimated that the major aquifer below the basins has a main transmitting area of approximately 600 sq ft (55 sq m). This aquifer traces the course of an old streambed across the area. Basins 1, 4, 5, and 6 are located wholly, or in part, over the probable location of the main channel. Basin 2 is interconnected to it by a thinner sand lens. The nature of the interconnection of basin 3 is not clearly understood due to its limited period of recharging. None of the project wells are located within the main channel in Golden Grove since its presence was not suspected until after the wells were con- structed. Wells PW-7 and PW-8 are apparently isolated from the main aquifer while wells PW-5 and PW-6 are connected to it via sand lenses. Wells PW-1 and PW-4 are located on either side of the main aquifer but are probably connected to it by a thin transverse aquifer which continues north underneath the stream. Water level response to recharging . An examination of the water levels in the various wells in the area compared with the rainfall and periods of artificial recharge reveals many points of interest. In Figure 31, the general water levels during 1973 dropped due to the lack of sufficient natural recharge from rainfall. Both vjells GG-3 and GG-5 are upstream of the recharge area. GG-3 was selected as the control well since activity in the recharge area did not appear to affect it. After recharging began in 1974, GG-5 was almost immediately 179 ELEVATION 42.4 E, LU \-< § 1.0 Q aiO §0.5 o LU cc GOLDEN GROVE 1973 JAN I FEB I MAR I APR ' MAY I JUN ' JUL I AUG I SEP I OCT NOV > DhC; 22 JAN I FEBC^mAr i ApS^TlJiAY r JUN I JUL I AUG SEP I OCT ' NOV 1 DEC Figure 31. Comparison of wells GG-3 and GG-5, 1973-1974. 130 affected, as can be seen in Figure 31. The flattening of the slope of this well beginning in March was due to the hindrance of the normal flow in the upper aquifers due to the recharge water added to the same aquifer. Figure 32 compares the immediate boundary wells on the approaches to the recharge area with a well, PW-8, within the area. GG-13 is 1,500 ft (425 m) north of the area. A-18 is 3,700 ft (1,130 m) northwest of the recharge area at the upper end of the aquifer which flows under the basins. GG-3 is in the same general aquifer system as A-18 and 1,300 ft (400 m) upstream of the basins. The lack of activity in these boundary wells indicates that outside influences sue'- as rainfall are not disturbing the groundwater system. Hence the reaction of PW-8 is, in fact, caused by the artificial recharge operations taking place within the localized area of Golden Grove. Figure 33 is significant in two ways. First it shows the extent of water level alterations caused by recharging, as measured in wells in the vicinity of the basins during 1974. Well PW-6 is plotted along with control well GG-3. During 1975, when no recharging took place, the rainfall during the first 7 months was very similiar to that of the previous year. Again PW-6 and GG-3 are plotted and it should be noted that they move almost in unison. The inference is that this is the pattern that the water levels would have taken during 1974, had arti- ficial recharge not taken place. The second manner in which Figure 33 is significant is in the response that PW-6 exhibits when recharging is switched from the eastern to the western basins during the first week in April, 1974. Whereas PW-6 responded almost immediately to recharge in the eastern basins, there 181 iU) SIIBM IMI n3A3n a3iVAA O rt CO «- CN fO 00 I •a: (leB jiui) aaivAA a3oavHD3a 182 JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG SEP OCT NOV DEC cc n HJmi f""" nj[j: -ELEVATION 46.7 n- PW-6 6 - ^*- _j z 14^ cc 111 18 H 22 GOLDEN GROVE 1975 JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG ' SEP ' OCT NOV DEC TIME Figure 33. Comparison of wells GG-3 and PW-6, 1974-1975. 18: was a delay of approximately 15 days before it responded to the operation of basin 4. This delay is attributed to the initial slaking of the soil and filling of the pore space combined with the hydraulic travel time from the basin to the monitor well. This response pattern is repeated in the latter part of August with a similiar switch from an eastern to western basin. The response of PW-8 to recharging (see Figure 34) is indicative of a well which is located within a sand lens that is not interconnected to the aquifer carrying the major portion of flow from the basins. The lens is, however, adjacent to the eastern basins. The response of PW-6 to recharging appears to demonstrate that it is in a sandy lens which is interconnected to the lower part of the main aquifer area. The interconnection is hydraulic and does not consist of water flowing rapidly through the lens. PW-7 is isolated from the basins and main aquifer area. Its water level variations are damped out considerably and they depend on seepage through a less porous soil. Recharged water entering the u,. '^r aquifer system from the basins moves laterally through the aquifers in a general east-south- easterly direction. As the water moves ^ong the aquifer it satisfies the storage demand of any of the unsaturated soil in the vicinity. The main lateral velocity is believed to be in the range of 15 to 25 ft/day (4.6 to 7.6 m/day) in the vicinity of the recharge area while under the direct influence of basin loading. When the groundwater mounding under the basin subsides, and/or if the aquifer dimensions increase substantially, the velocity decreases considerably. 184 li) s"n3w\ iMi laAai aaivM (•u!) invdNivy (i^s 1!^) aaivM a3DavH03a 18; A generalized view of the changing potentiometric surface in the Golden Grove area during the entire period of the project can be seen in Figures 35 and 36. Groundwater Augmentation by Artif ic ial Recharge By ccinparing two identical sections of the groundwater system, one without and the other with artificial recharging, an approximate idea of the net effect of recharging can be ascertained. Only the imme- diate area containing, and adjacent to, the spreading basins is considered in this analysis. Once the artificially recharged water has entered the groundwater aquifers and starts its horizontal flow, it is considered as normal groundwater, subject to the same losses that existed without th- project. Figure 37 shows two typical vertical sections of the Golden Grove valley. Each section has the important water inputs and outputs, one section with and the other without a recharge operation taking place. By comparison, the major changes will be in the addition of recharge water and the subsequent increase in flow in the aquifer. Increased consumptive losses will be the added evaporation from the shallow water-filled basin. It can also be expected that evapot .ans- piration will be increased to some degree in the immediate area due to the additional water available for this either in the aquifer or in the percolating water forming the mound underneath the basin. Percolation between aquifers is believed to be minimal, based upon drilling observations, but might increase with the increased hydraulic head available beneath the inundated basins. However, since extraction of groundwater will take place from all the aquifers in the alluvium. 187 o CCoX (l0l3A31 V3S 3A08V NOIlVA3n3 189 (Jl) n3A3T V3S 3A0aV NOI±VA3n3 the transfer of water between them will not change the ultimate amount of product. Thus the major new loss to the recharged system is in the added evapotranspi ration due to the available moisture in the pond and soil. Meyer (1952) reported that the average annual evaporation from an open pan in the Anna's Hope area, in central St. Croix, over a 10-year period was 70.2 in./yr (177.8 mm/yr), which averages about 0.19 in. /day (4.87 mm/day). This is probably high for the basins due to the rapid turnover of water and consequently its lower temperature. This also neglects the evapotranspiration. that no longer occurs from the soil covered by the water in the basin. Increased evapotranspiration for the sections shown in Figure 37 may be approximated by the difference between Bowden's (1968) highest and lowest monthly evapotranspiration estimates for the Kingshill area adjacent to Golden Grove, which come to 0.12 in. /day (3 mm/day). This represents the possible rise in evapotranspiration due to the increased availability of water in the area which, according to Meyer, is a prime factor to be considered. For the largest basin, basin 4, this means a possible total added evapotranspiration loss of about 1,500 gpd (5.5 cu m/day) which may be compared to the average daily infiltration for this basin of approximately 125,000 gpd (473 cu m/day). This represents a loss of about 1.2 percent of the influent to the basin after initial slaking of the soil has taken place at the beginning of every inundation. Other losses do occur, but these are common to both naturally and artificially recharged water in the aquifers. Probably the largest loss of this sort in Golden Grove is that due to the evapotranspiration Figure 37. Water balance in Golden Grove with and without artificial recharging. 192 NORMAL GROUNDWATER CONDITION EVAPOTRANSPIHATION FROM TREES LVAPOTRANSPI RATION FROM SOIL AND GRASS LEAKAGE POSSIBILITY OF INCREASED EVAPOTRANSPIRATION DUE TO MORE AVAILABLE GROUNDWATER , EVAPOTRANSPIRATION FROM SOIL AND GRASS ARTIFICIAL RECHARGING OF THE GROUNDWATER AQUIFERS AND INTO MARLS 193 involved with the large deep-rooted trees adjacent to River Gut. These trees are protected by Virgin Islands law; and although they supply shade, a windbreak, and soil stabilization along the stream bank, they do extract an undetermined quantity of water from the soil. Attempts of quantifying the amount has not been overly successful. One recent researcher. Rex Meyer (1952, pp. 23-26), discussed transpiration at length in a Department of the Interior report and finally commented that "the difference in plant species and climatic conditions on the island of St, Croix makes it imprac- ticable to apply transpiration ratios determined elsewhere on similiar plants to the vegetation on the island." He concluded his section on transpiration by saying that "it is not possible with the available data to make a reliable estimate of transpiration in any part of St. Croix." This investigation could not improve on this statement but strongly recommends that local research efforts be made in this direction in the future. It is possible that increased soil moisture caused by recharging would increase consumptive use by these trees. Groundwater extraction efficiency will play a large part in the ultimate economies of the water reuse system. Fortunately the ground- water geology of Golden Grove as portrayed in Figure 15 keeps the groundwater flow within defined bounds where it is relatively easy to tap and withdraw with a minimum of loss. However, the aquifer is thin and in some areas in Golden Grove it is limited in its transmissibility. The entrance losses from these thin alluvial aquifers into the vjell casing generally would limit the extraction by individual well to about 20 to 30 gpm (1.3 to 1.9 l/sec). 194 Based on operating results and engineering judgment, the best mode of operation of the recharge facility in the future is to plan to extract 85 percent of the recharged water in the immediate area of the spreading basins. The remainder should be permitted to flow down the aquifer to be used to protect the Fair Plains well field from further saline degradation. The pumping at the Fair Plains well field can then be adjusted to a rate that will efficiently remove the groundwater without permitting a decrease in overall water quality in the area. Water Quality Cha n ges Due to Recharging Negro Bay The operations in Negro Bay did not affect the underlying groundwater to any detectable degree. The two reasons for this are first, little, if any, recharged water reached the marl -limestone interface that was located 15 ft (4.6 m) below the area. This was due to the low rate of infiltration and percolation combined with the high rate of evapotranspiration. Second, even if water did arrive at this interface, it would need to penetrate approximately 60 ft (18 m) of horizontally layered limestone which is above a confined aquifer. The early termination of operations in Negro Bay combined with the physical difficulties mentioned above essentially preclude the possibility that recharged water reached the aquifer. Golden Grove The water artificially recharged into the Golden Grove area had only a minor effect on the groundwater quality in that basin. In 195 order for the monitoring to be valid, only continuously pumped wells were considered in the final evaluation of the project's effects. Monitor wells . Due to their location the key wells considered for monitoring the recharge operations were GG-8 and FP-8, downstream of the recharge area, plus PW-1 and PW-4 immediately upstream of the basins. The changing chloride content of these wells was judged to be significant as chloride in groundwater is essentially a refractory substance. As such it is not likely to undergo changes due to bio- logical or physiochemical effects such as phosphates, nitrates, ammonia, and degradable organics can, which is why chlorides are often used as a tracer. A change of chloride content is possible in the wells if water with a different chloride concentration joins or replaces the existing water source. This would be the case in the pumping wells being monitored when the artificially recharged water, with a different chloride content, moves through the aquifer and encounters them. A graph of the chloride content for these wells and the recharged water is shown in Figure 38. Wen A-16 . Figure 38 compares the chloride levels with the rainfall and the quantities of recharged water used during 1974. Well A-16 is a control well and is located above the recharge area at the head of the alluvial valley at Adventure. The location of this well is such that it cannot be affected by the recharging. The changes in chloride content shown for A-16 are those normally experienced by wells in the area. Well PW-1. Well PW-1 is located about 200 ft (61 m) upstream of the edge of basin 1. By examination of Figure 38 it is apparent 197 (i/6uj)s3aiaoiH3 I"!! mvjNiva (ib6 ijuj) aaxv/M aaoavHoaa 198 that the recharging affected the chloride content in both June, to a slight degree, and again in September and October. Both of these times were periods when either basins 1 or 2 v;ere in operation. We can expect that the rapid increase during September and October could have been higher had the water added to the aquifer by heavy rainfall in August not occurred. An apparent rise in nitrates from 5.4 mg/1 to 6.7 mg/1 also occurred at this time but it cannot be substantiated as there is insufficient background data on this well. A pump was not installed on PW-1 until January, 1974, so the data available are limited. Well PW-4 . Well PW-4 also showed some indications of a chloride rise but it was minor. Although this well is only 300 ft (91 m) from basin 1, it is believed that the intervening aquifer structure is connected only in an indirect manner. The water from this well was reduced in chloride concentration during November due to the heavy rains and flooding which naturally recharged the soil over the entire area. Well GG-8 . Well GG-8 is located about 1,500 ft (460 m) downstream of basin 6. The water from this well generally has a chloride content higher than the artificially recharged water. However, this well, like many others on St. Croix, derives its water from more then one aquifer. The method of well drilling on the island is such that it is not possible to separately test the aquifers encountered for water quality. However from field observations and tests made while drilling, indications are that the water in the different aquifers is often of sharply varying chemical character. Thus changes in chemical characteristics in a well water are often caused simply by a variation in the contribution to a well that each aquifer makes. Indications are that the recharge water 199 is probably increasiiig the chloride content in an aquifer which normally acts as a source of dilution water for well GG-8. The reaction to the early recharging operations is delayed in time due to the rate of flow of the recharged water from the basins to the well itself. The effect of the later periods of recharge are obscured by the heavy rains that occurred in the fall. This well water has had a trend toward increasing chloride content since sampling began in 1971. The mean chloride values for 1S71, 1972, and 1973 are 426, 453, and 507 mg/1 , respectively. The variation in the other parameters for water from that well fell within a standard deviation of past performance and cannot be considered significant. Well FP-8. Well FP-8 is located approximately 3,300 ft (1,000 m) downstream of basin 6 when measured along the assumed course of the main aquifer. It is likely that FP-8 receives water from both the River Gut and the Bethlehem Gut drainage basins. FP-8 is probably v/ell 45a referred to by Cederstrom (1950, p. 68). This well was drilled to a depth of 225 ft (68.6 m) through the alluvium and marl and 17 ft (5.2 m) into the Jealousy formation. Cederstrom reports (1950, p. 84) that the chloride content in 1940 was 510 mg/1. In 1971, 1972, and 1973 the mean chloride content was 640, 649, and 670 mg/1, respectively. Inspection of Figure 38 shows some indication of increasing chlorides in FP-8 during the latter part of 1974. Although it could be due to the recharged water it cannot, with certainty, be said that this is the cause for the increased chloride content. The water in the Fair Plains well field has been undergoing a general increase in chlorides over the past few years. During 1974, 3 out of the 9 wells in Fair Plains 200 were abandoned due to excess TDS. The water in ttie adjacent well, FP-7, showed a continuous increase in chlorides from 1973 up to September, 1974. This may have had an influence on FP-8. The other chemical and biological parameters monitored in the water from the wells did not show significant changes during this period. Had the recharging operations continued longer and/or the floods not occurred, then it is possible that additional changes in the groundwater might have occurred. With many of the parameters measured it is likely that the concentration of the substance in question underwent changes during the recharging operations. A basic discussion of changes which can occur appears in several reports concerning land disposal of waste- water (iMcGauhey and Krone, 1967; Driver et al . , 1972). In the following paragraphs several of the most important parameters are discussed with relation to their possible fate in the soil system. This discussion is only a summary and the references cited can be consulted for greater detail. Nitrates . The average nitrate nitrogen concentration measured in the recharge water during the period of January through October, 1974, v/as 12.9 mg/1 . The groundwater in the area of the recharge basins has a natural concentration that ranges between 3 and 7 mg/1. Nitrates are not readily absorbed by the soil and thus tend to move through the soil in solution. Reduction in concentration can occur by plant uptake and denitrification (Murrmann and Koutz, 1972, p. 71). A report sponsored by the Corps of Engineers (Driver et al., 1972), mentions that the removal of nitrogen by denitrification is dependent on the soil type and length of inundation of infiltration ponds with 20 clay soils and long inundation times promoting nitrogen removal. Based on plotted data (Driver et al . , 1972, p. 93), a 10-day inundation period would remove about 35 percent of the applied niti^ogen. Nitrate uptake by plants will occur most rapidly during the dry period of the wet-dry cycle when plant growth is the most rapid in the basins. Uptake will be limited to the amount of nitrates available in the soil moisture remaining after recharging has ceased. During operation of the project the grass in the basins was frequently mowed and removed from the area. It is probable that a combination of these two mechanisms reduced the nitrate level in the applied recharge water in Golden Grove. The chief concern with nitrates is to keep the level in water consumed by the public to below 10 mg/1 as NO3-N. This is to prevent the occurrence of methemoglobinemia in infants. Dilution of the water pumped from municipal wells in the recharge area with other sources of water contributing to the island's water supply maintains an acceptable nitrate concentration in the water supply. Ammonia. The average ammonia-nitrogen concentration in the applied recharge water was about 7 mg/1 during the period of January through October, 1974. The normal concentration in the groundwater in Golden Grove ranges up to about 0.5 mg/1. Ammonia at a neutral pH, 6 to 7, is readily adsorbed onto clay soil particles (Murrmann and Koutz, 1972). This will act to hold the ammonia for use by plants at a generally slower rate of uptake. The effluent used in recharging generally had a pH between 5.5 and 7.0. The rapid growth of vegetation on the basins between inundation periods 2o: followed by raov/ing and harvesting should continue to remove ammonia from the system. Phosphorus . The average concentration of all forms of phosphorus in the applied recharge vjater v;as about 9 mg/1 as P during the period January to October, 1974. The normal concentration in the groundwater in Golden Grove ranges up to about 0.1 mg/1. Phosphorus acts similarly to ammonia and is adsorbed in the soils especially on clay particles which are prevalent at the recharge site. The phosphorus will also be utilized by vegetation in the area and can be removed from the system through plant harvesting. Col i forms . The level of standard coliforms in the applied effluent was very low due to the effective disinfection process at the AWWTP. The effectiveness of soils in removing bacterial pathogens is documented and discussed in detail by McGauhey and Krone (1957, pp. 70-78) and in a recent report issued by the Corps of Engineers (Driver et al . , 1972, pp. 49-55). These reports mention the mechanisms of mechanical filtration and adsorption along with natural dieback of pathogens in the soil. These are especially effective in clayey and silty soils which predominate in Golden Grove. The background data on all of the public wells in the study area show a substantial level of coliforms in many of the wells. The operation and sanitation of these wells was not under project control during this study. Many public wells on St. Croix were not sealed properly to prevent surface leakage and contamination until rather recently. Disinfection of the wells before, or during, operation is generally not practiced. Under these conditions it is not possible to correlate recharge operations with any change in coliforms in pumping 203 wells in the area. Based on the disinfection practices used and the literature cited, it is highly doubtful that any bacterial contamination of the pumping wells did, or will, occur due to recharging operations in Golden Grove. BOD, COD, and TOC. The water applied to the recharge basins had an average BOD of 11-5 mg/1 and a COD of 30 mg/1. The ability of a soil system to reduce this oxygen demand caused by organics is discussed in many reports (McGauhey and Krone, 1957; Driver et al . , 1972; Broadbent, 1973). The organic loading from the AWVJTP effluent on the soil system was low. Evidence of increased organic concentrations in the monitored wells was not apparent and it is likely that the organic content was diminished due to oxidation. In studying the results of the analysis of the monitoring wells in the study area for BOD and COD, as presented in the Appendix, two facts must be kept in mind. The first is that BOD and COD measurements at a low level of to 20 mg/1 are not very dependable since any minor contamination, or laboratory error, will dramatically affect the results. The second problem is that all of the pumping public wells monitored are equipped with a vertical turbine pump whose shaft bearings are lubricated by dripping oil down the space between two concentric shafts in the well. This oil, up to about 0.5 gal /month (2 1 /month), accumulates and floats on the surface of the water inside the well. Depending on the level of the water in the well in relation to the pump, this oil can be intermixed with the water and pumped out of the v-^ell in varying con- centrations. This, then, also has noticeable effect on TOC measurements taken on samples. Due to the circumstances of pump start-up and throttling required for the homogenation and entrance of the oil into the pumped water, it will happen at irregular times without necessarily a definite pattern being detected. Summary of water quali ty changes . The previous paragraphs have reviewed the possible reasons behind the water quality changes observed in the monitored pumped wells in the study area in the vicinity of the recharge facilities. Other wells closer to the spreading basins were also sampled and tested for the same parameters during recharge operations. These were wells PW-6, PW-7, and PVJ-8. The primary purpose of these wells was to monitor water level information and hence they were not equipped with pumps. Samples were obtained by the use of a torpedo sampler. Although the sampler was filled several times before taking a sample for labo- ratory analysis the procedure did not cause much movement of water within the 8-in. (20 cm) well casing. The monthly data for the analysis of the samples appear in the Appendix. The data do not show the changes, especially in chloride concentrations, that could be expected. This is probably due to two reasons. First the wells are believed to be located in sand lenses which are not directly connected to the main flow path of groundwater through the area. Second the wells were not pumped so that a continuous interchange of water could occur in the wells. Had continuous pumping occurred, the location of the wells away from the main path of flow would probably have been less significant. As it is, the data are included only for general background information for future studies. 205 Water Quality 1n Future Operations Once the problem of saltwater flushing in Frederiksted is resolved the artificial recharge operations can resume. If, at that time, the distribution of potable water is planned so as to transfer the low TDS desalinized water to the western end of the system, then it will result in the collection of wastewater with a low chloride concentration. Judging from the anlysis of wastewater from villages served wholly be desalinized water (Black, Crow and Eidsness, Inc., 1973, pp. 3-12), it can be expected that the wastewater will have a chloride content of about 100 to 150 mg/1 . The use of processed effluent with a low level of chlorides for recharge operations in Golden Grove should eliminate the chloride problems experienced during the project's operations in 1974. With proper extraction control, it could lead to partial restoration of the Fair Plains well field. AWWTP Operations The operations of the AWWTP was discussed in detail in the earlier sections. The data obtained from the operation havc- been tabulated and presented in a statistical format in Tables E-1 and E-2 of the Appendix. The production of the plant which was used for recharge purposes is shown in Figure 23 and the average operating parameters in Tables 4 and 5. These data cover the period January through October, 1974. January marked the beginning of normal operation after the start-up phase. The project ceased recharge operations during the last week 205 of October due to the high TDS wastewater, while at the same time the heavy rains began to affect the plant performance due to excessive inflow. In early November, 1974, the flooding on the island damaged portions of the interceptors so that much of the influent to the plant consisted of the streamflow from Bethlehem Gut. During subsequent repairs of this interceptor and the one to Frederiksted, which took place over the following 6 months, flows were interrupted and/or bypassed so that normal operation of the AWWTP was not possible. In view of this, the data presented are limited to the period stated. Cost Factors Cost factors, based on the operation of the AWWTP and the recharge facilities, have been projected for the production of artificially recharged groundwater. These data are shown in Table 7 and include treatment in the AWWTP, recharge operations, and ground- water recovery by wells. Cost factors are presented for production at the present design capacity of 0.5 mgd (1,890 cu m/day) and also for expanded operation at the level of 0.75 mgd (2,840 cu m/day) and 1 mgd (3,785 cu m/day). The information upon which the costs are determined is presented in the table along with the assumptions used. If circumstances, assumption,, or prices change; then the cost factors can be restructured within the table to arrive at a revised unit cost. A large percentage of the total cost of reclaiming water is centered around secondary treatment. At present only primary treat- 207 ment is used by the government before discharge of wastewater into the sea. If secondary treatment were required, then the cost of this portion of the facility could, in a large part, be allocated to sanitation instead of reclamation. Only the additional costs of tertiary treatment and recharging could be directly attributable to reclamation. This would then decrease the unit cost considerably in an accountant's view, although the government would continue to pay the total cost. However with secondary treatment of all waste- water before reclamation or discharge to the sea, the economies of scale would begin to reduce the unit cost of production. This is especially true in the matter of labor where the difference in staffing between a 1 mgd (3,785 cu m/day) and a 5 mgd (18,925 cu m/day) plant would not be significant. This is especially true if the recommendation to combine the management of the primary and reclamation plant is followed. 208 TABLE 7. PROJECTED COSTS FOR THE PRODUCTION AND RECOVERY OF RECLAIMED WASTEWATER BY GROUNDWATER RECHARGE AV/V/TP Proclaction Capacity 0.5 mgd 0.75 mgd 1.0 mgd (1 ,890 cu m/day) (2,840 cu m/day) (3,785 cu rn/day) PRODUCTION-ANNUAL COSTS* I. Depreciation (20 yr straight line) iniliatcost $800,000 Phase 1 improvements! 30,000 Phase 2 improvementsf 70,000 Phase 3 improvementsf 140,000 Total Depreciation II. Maintenance and repair III. Labor Project director © $20,000/yr Plant superintendent © 15,000/yr Operator, chief SECTION IX CONCLUSIONS It is economically feasible to use reclaimed wastewater to artificially recharge the groundwater on St. Croix. However, it can only be accomplished successfully at carefully selected areas on the island. A site in the alluvial valley at Estate Golden Grove was demonstrated to be highly suitable for recharge by the use of spreading basins. With the AWWTP operating at design capacity of 0.5 mgd (1,892 cu m/day) and allowing for down time and losses in groundwater recovery, it will be possible to recover potable groundwater for a cost of about $2.15/thousand gal ($0.57/cu m). With expansion of the existing plant and recharge areas to a capacity of 1 mgd (3,785 cu m/day) the cost can be reduced to about $1 .64/thousand gal ($0.43/cu m). It is not economical to artificially recharge and recover any of the subsequent groundwater from the marl formation in the recharge area in Estate Negro Bay on St. Croix. Infiltration and percolation rates were too low and evapotranspiration rates were too high to warrant further efforts in this type of soil structure. With the existing AWWTP it is possible to treat the incoming wastewater, as it was constituted during the 8 months of recharge 209 activity, so that with normal operation the effluent will have a turbidity of less than 3 Formazin Turbidity Units (FTUs) and a free chlorine residual of over 3 mg/1 , after a 30-minute contact time. The use of a high quality effluent for artificial recharge in the recharge basins in Estate Golden Grove will permit the operation of the basins with a minimum of odor or algae problems and a high rate of infiltration into the soil. The average sustained rate of infiltration experienced in the Golden Grove basins was about 14 gpd/sq ft (0.57 cu m/day/sq m) on a wet cycle basis. The recharging activities which took place in Golden Grove and Negro Bay, during the period of project operations in 1974, did not significantly affect the water quality of any pumped well in the area. SECTION X RECOMMENDATIONS Continue the Project The reclamation of wastewater for artificial groundwater recharge should be continued on St. Croix. It has proved to be an economically feasible enterprise and should be a benefit to the island not only for groundwater augmentation but other uses as well. Strengthen the Organization The entire reclamation project is of sufficient importance and complexity that it requires careful organization and staffing to ensure its future success. If the operation continues within the Division of Natural Resources Management, it should be organized with one person having the responsibility for operations, monitoring, distribution, and coordination with other agencies. This person should be an engineer with experience and/or training in both the fields of water supply and wastewater treatment. He should probably hold the title of Assistant Director. There should continue to be a separate superintendent for the AWWTP since this, in itself, is a full-time job. The AWWTP and recharge facility must be adequately manned. It presently is understaffed and will not be able to sustain full production for wery long without additional staff. 211 212 Coordination with other departments and individuals concerned with the reuse of water is vital to the efficient utilization of this resource. The program of expansion and promotion of water reuse for beneficial purposes must continue to stress the multiuse concept of the project. Coordinate Future Planning The concept of the reuse of water must be incorporated into all aspects of planning for water supply and wastewater collection on St. Croix. Although it may not be advantageous to recycle all of tlie water on the island, all new water and wastewater installations and changes, both public and private, must be reviewed as to their effect on the reclamation project. A master plan for water management on St. Croix, which will be published about March, 1976, will aid in this evaluation process. Control Saltwater Usage The use of seawater as a source of fire and flushing water must be carefully evaluated since its use is not compat;'jle with the reclamation of wastewater at a reasonable cost. It must be remembered, though, that salt water is a \/ery inexpensive source of water. The complexity and expense of attempting to eliminate all saltwater discharges to the wastewater collection system on the island may not be commensurate with the benefits derived from a 100 percent reuse capability. At the present time, it is recommended that the saltwater usage in Frederiksted be eliminated by the direct use of fresh water in the saltwater system. This will require about 0.08 mgd (300 cu 213 m/day) of fresh water. This v/ill permit the use in the AWWTP of at least 0.5 mgd (1,892 cu m/day) of low chloride wastewater for reclamation purposes. The additional fresh water produced through artificial recharge and recovery can be returned to the system to make up the flushing water. This will permit the reclamation project to operate until about June, 1977, when the wastewater interceptor system is completed to Christiansted and the wastewater containing salt water from Christiansted will be delivered to the central treatment plant on the south shore. If, by approximately June, 1976, plans for the elimination of all the salt water in the Christiansted area have not been finalized and agreed to in plan and principle by the Public Works Department, V.I. Housing Authority, and the owners of the major hotels, condominiums, and restaurants using salt water, then it is doubtful that the wastewater coming from the area can be used for reclamation purposes and without further modifications the project would probably be shut down again in 1977. The unilateral prohibition of saltwater usage in the avea without an immediately available, cheap alternative would probably create an extremely negative reaction against the concept of water reuse. Split the Wastewater Flow at the Primary Plan t If the salt water cannot be eliminated from the Christiansted area, then it is recommended that a new pumping station be built adjacent to the collection structure at the primary treatment plant. This pumping station would pick up a percentage of the wastewater entering the structure from the central and western portions of the 214 island before it is contaminated by the salty wastewater from Christiansted. The pumping station would then transfer the wastewater directly to the AWHTP with provisions for screening and degritting enroute or via one of the primary settling tanks. In the latter case, the primary facility would need to be altered to permit the splitting of flows within the plant so that the high and low TDS wastewaters could be treated separately. With this plan, reclamation efforts could be continued and expanded to the capacity of the influent available. If successful extended operation at that level indicated that the usage could be expanded to efficiently utilize most of the wastewater from Christiansted; then careful, coordinated plans could be made and carried out to initiate the needed changes to smoothly incorporate this additional supply into the water reuse system. Promulgate Regulations Concerning Reuse As soon as practicable, the proper territorial agency or agencies should promulgate regulations specifically governing the use of reclaimed wastewater for groundwater recharge, agricultural irrigation, and any other activity involving water reuse. These would provide guidelines for the planners and operators associated with the facilities. f^onitoring Future Operations Monitoring in the study area should be continued. This should include chemical and biological analysis and the gaging of water levels in selected wells. A thorough review of the type of analyses run should be made and modified where appropriate. It is suggested 215 that BOD and COD measurements of the wells be suspended and that, at a minimum, all the tests covered in the proposed new EPA drinking water standards (Environmental Protection Agency, 1975) be instituted. Disinfection of Recovered Water All water extracted from the Golden Grove well field in association with the recharge operation should be monitored and thoroughly disinfected, as a safety precaution, before distribution. The Fair Plains collection tank and pumping station should be the focal point for monitoring, disinfection, and distribution of this water. The two direct taps onto the force main connecting the Golden Grove well field to the Fair Plains tank should be either disconnected or altered in a way that will assure proper disinfection of any water used. These two taps feed the adult correctional facility and the Public Safety Headquarters. The disinfection operation at Fair Plains must be carefully monitored to ensure that it is being carried out properly at all times. Consideration needs to be given to the installation of a gas chlorinator instead of the current dry chemical chlorinator system. Prohibit Industrial VJastes Industrial wastes should not be added to the wastewater ultimately used for reclamation purposes unless they have been carefully analyzed and evaluated. This is to ensure that no harmful exotic substances are introduced into the reuse system. Monitor Coagulants' Effectiveness The effectiveness of using aluminum sulfate as a coagulant and filter aid should be continually monitored as the project continues. The projected changes in the major water source in the western portion of the island from groundwater to distilled water may have a detrimental effect on the alum reaction. Other chemicals, including polyelectrolytes, may be required in the future. Any chemicals employed should be approved by the EPA for water treatment usage. Improve Groundwater Recovery The existing recharge facilities were not intended to maximize the recovery of recharged water. Additional groundwater extraction facilities should be constructed in Estate Golden Grove to facilitate this. The emphasis should be on the removal of the groundwater from the upper aquifer which is the one being artificially recharged. Figure 39 is a sketch of the Golden Grove recharge area and shows the stages of well field development that should take place both now and in the future. The first stage of development consists of at least 12 wells located within the recharge area. These are located so as to permit rapid removal of water from under the scattered recharge basins. The second stage is planned to coincide with the expansion of the recharge basins as shown in Figure 40. A feature of this second- stage development will be a horizontal collection system constructed along the northwest property boundary. At this point the upper aquifer is close enough to the surface to permit excavation and 217 TO NEGRO BAY METER - FROM RECLAMATION PLANT -*- Figure 39. Future well field development in the Golden Grove recharge area. 218 UU.. FEET 50 100 METERS 10 20 30 Figure 39. (Extended) 219 TO NEGRO BAY METER FROM THE NEGRO BAY WELL FIELQ. H \v I \-\— FROM RECLAMATION »' TO FAIR PLAINS PLANT -*^ V STORAGE TANK Figure 40. Future expansion of the spreading basins in the Golden Grove recharge area. 220 FEET 50 100 METERS 10 20 30 Figure 40. (Extended) 221 installation of the necessary collectors. A sketch of this system is shown in Figure 41 All extraction facilities, wells, or collectors should be located so as to maintain the minimum 50 ft (15 m) horizontal distance between the wells and the recharge facilities as required by the V.I. Division of Natural Resources Management (Stolz, 1975). Expand the Recharge Area in Golden Grove Expansion of the spreading basins should take place as shown in Figure 40. The area suitable for surface methods of recharging is rather limited in size and expansion in Estate Golden Grove beyond the areas shown will probably be uneconomical. Improve the Performance of the AWWTP The performance and production of the AVJWTP would significantly improve if a steady flow rate to the plant could be maintained. This can be accomplished by relocating the influent pumps from the present wet well to the primary clarifier along with the installation of a new, larger diameter pipeline. This is described in detail in the section on project facilities under ,'ie subheading Plant Expansion . The majority of the work can be accompli shed by local government personnel and the materials required would cost less than $10,000. It is urged that this change be instituted as soon as possible. Consider AWWTP Expansion The present plant and installed equipment have the capability to permit considerable expansion of plant capacity with a relatively 222 150 ft (46 m) , H* -^ H EXISTING WELL ^ APPROX. 15 ft (4.6 m) V ^ HORIZONTAL COLLECTORS -vEXISTING UPPER AQUIFER WIDTH OF EXCAVATOR BUCKET h< *- UNDISTURBED SOIL °-.V;;.;o-_ CLEAN 'l,'-^ .-V.?: 9. GRAVEL i. TWO SHEETS OF HEAVY TAR PAPER '' '''"".'.'•.* •*-' * ' t '* • > •'• '° '. ^ ", V- '^ '•S-^\^f^^'.r:/-^'i^'^^':^-\^^--:^^y existing :'p. •.;';, -"'»;-'o\» -.*-'/.' : **"\'o'- "/• !• ' r{i•:^::\:?::.^}•l.:('•^•^^i^\v:^'r^':i aquifer .•'.'."';".'• 8-in. |20cm)PVCPIPE SLOTTED ON TOP EVERY 4-ln. (10 cm) undisturbed SOIL SECTION A-A Figure 41. Proposed horizontal wells. 223 low amount of capital investment. However expansion should only be carried out if there is full utilization of the present production and a reasonable prospect for the use of additional reclaimed water. Plant expansion is discussed in further detail in the section, Description of the Project Facilities. Expand Local Research Research projects on water reuse as they apply to conditions within the territory should be encouraged. The newly established Water Resources Center at the College of th-; Virgin Islands should take a leading role in directing and funding this research. Some of the following are suggested topics for research. 1. The long- and short-term effects on the various local soils as the result of using reclaimed wastewater for recharge and irrigation purposes. 2. The fate of nutrients, organics, and microorganisms in reclaimed wastewater as it moves through the various types of local soils. 3. Viral studies in the reclaimed wastewater and recovered groundwater. 4. The uptake of nutrients, heavy metals, microorganisms, etc., in local plant materials as a result of the use of reclaimed wastewater for irrigation purposes. 5. Quantification of the loss of groundwater by the transpiration of subtropical vegetation in the territory. 6. Evaluation and revisions, where necessary, of regulations and guidelines governing the use of reclaimed wastewater. 224 7. Investigation of the economics and feasibility of using reverse osmosis to convert tertiary-treated wastewater into potable water. Redu ce Costs The best method to reduce costs would be to combine the staffs of the adjacent primary treatment plant with that of the AWWTP. The present arrangement where each plant has a separate staff is an inefficient use of manpower and equipment. Combining them under one government agency with one head would reduce overall labor costs and permit coordinated operation to the benefit of the wastewater reclamation project. Consult the EPA It is strongly recommended that the Government of the Virgin Islands consult with, and adhere to advice from, the EPA concerning the EPA's current philosophy and regulations concerning vastewater reclamation. These consultations should include a review of the Virgin Islands' regulations concerning all aspects of water reuse, both present and future; the monitoring of wastewater reclamation operations; the placement and operation of recovery wells in the vicinity of artificial recharge areas; the treatment, distribution, and ultimate use of the recovered groundwater derived from wastewater reclamation schemes; and the operation of any other types of reclamation projects in the territory. APPENDIX PART A LOGS OF PROJECT WELLS Part A contains the drilling logs of the nine wells which were constructed as part of the project. 226 227 TABLE A-1. LOG FOR PROJECT WELL NO. 1 (PW-1) 2 228 TABLE A-2. LOG FOR PROJECT WELL NO. 2 (PW-2) Thickness Depth of Elevation Description of strata strata* of stratat ft ft ft Kinghill marl Topsoil White stratified limestone (dry) White limestone, very hard layer Encountered water just below hard layer White limestone stratified Casing perforations: 1 1/2 slots/ft 3 1/2 slots/ft 2 77 229 TABLE A-3. LOG FOR PROJECT WELL NO. 3 (PW-3) Description KinqshiH marl Topsoil White stratified limestone White limestone, yery hard layer Encountered water just below hard layer White limestone soft Jealousy Formation Blue clay Thickness Depth of Elevation of strata strata* of stratat ft ft ft 2 230 TABLE A-4. LOG FOR PROJECT WELL NO. 4 (PW-4) Description Thickness of strata ft Depth of strata* ft Elevation of stratat ft Alluvium Silty clay Silty clay with angular gravel Sandy clayey gravel Gravel , encountered water Sandy gravel Clay with some gravel Clay, yery hard layer at depth 27-28 ft Sandy clay with a trickle of water Sandy gravel trace clay (water bearing) Clay trace gravel Clay, hard layer Kingshill marl White soft marl White stratified limestone White soft marl 5 231 TABLE A-5. LOG FOR PROJECT WELL NO. 5 (PW-5) 232 TABLE A-6. LOG FOR PROJECT WELL NO. 6 (PW-6) Description Thickness Depth of Elevation of strata strata* of stratat ft ft ft Alluvium 233 TABLE A-7. LOG FOR PROJECT WELL NO. 7 (PW-7) Description Thickness Depth of Elevation of strata strata* of stratat ft ft ft Alluvium Clay Clayey sand Sandy clay Gravelly clayey sand Sandy clay, sticky Sandy silty clay, sticky Casing perforations; 234 TABLE A-8. LOG FOR PROJECT WELL NO. 8 (PW-8) Thickness Depth of Elevation Description of strata strata* of stratat ft ft ft 5 235 TABLE A-9. LOG FOR PROJECT WELL NO. 9 (PW-9) Description Alluvium Clay trace sand Clayey sand trace gravel Clayey sand Sandy clay Thickness of strata ft Depth of strata* ft 15 17 20 Elevation of stratat ft 41 34 32 29 Casing - The elevation 29 to 41, an 8 in. steel casing is used. This is slotted 10 shots/ft in its upper 6 ft. Above this is a 2 in. galvanized pipe which goes to the surface. At the connection of the two is a con- crete seal. The purpose of the well was to test the feasibility of an injection well . Well location: Golden Grove Date drilled: August 1973 Casing used: See above Ground elevation: 49 ft First encountered water at elevation: No flow encountered The well was moist but had no water in August 1973. The static water level in February 1975 was at elevation 33 ft. Feet X 0.3048 = meters *Depth to bottom of strata. tElevation of the bottom of the strata. PART B PRIMARY WELLS—ANALYTICAL DATA Part B contains monthly data on the analysis of water samples taken from the primary wells monitored during the project. 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I I I til I III II II 0000 000 00 ooco 0000 000 00 0000 00 o -^ 000 CN tT O (N -^f ON -^ \0 -^ C4 -^ r- 00 I Tj- c^ cs a^ ** ooorrco 00000 CO'f oOCNt^ (NOj CN 0> O O .-A O I - r- I I r- 00 1 00 r~ r-; (N a\ 00 f *^ 2: 00 r- 00 I r- I— 3 00 <N CN W CN StsS CM <M <NCS CS U3 252 c ^ o o " o o 2 irt o u z _ 5 E X E U _ o E O ° -c - § t O >— O ^ <N O VV VV V .— o o , o »— o VVV V V VV o CO -^ r- o '^o Ko KD r— CO \£> r^ o O T— o o o o o o o o o* a\ en CN \^w-i(N. mr--»^i^ u^inu^t V- • V VV VVV vv o o ao <N o o o o" o o o 1 o o o o I q I o q q o I o d o d d d d d o o o o do' d d d d d o o o o o o O O I I o o o o o I q q q q q q q odd d d d d d c:> a q q d d o 1 o q CN O O O 00 1 00 I o I « I OO G G O <D OO oooo oooo oooo oooo oooo o CN^"^ VOOO «iDtNQO en r^ vo I vo "q- vfi t yj U5 I r— «3 tf >— (N CS m CN (71 '^ O I CN CS I I CO •<)• I CN CN O I I O I— I 0^ I CM I (N OOOO OOOO CN CN CN CN CN OOOO OOOO ° P. '*. *. (n* rn" CN CN OOOO OOOO -r o -c q. CN CS CN CN CN OOOO tn u-i »/^ "1 _ < (JO O Z Q r- ^D o o o o CO in (i-i VD -£ (/> o^ oooo o o U3 00 I o oooo 5 < S ^i< 253 'III c/l U (J •IS! CI I i II O O C\ H E I I : I I j I I I : I II Tf a\ ^£) I i ! Ill : I 1 ! 1 1 ill t I t I I VV ; I I ill II I I i I 111! Ill II I I I I ill II KS, ^ O m m u-1 o r- CO 00 00 oo 00 00 I : o o o o o o *^. I o o o o o o o Z _ X E oO O 00 (N I i I I III II Z _ O E O E o 254 -o O c c t: o o to u U Z _ z _ i ^ C3 ™q _ o E u "MM |6J •> E o ^ C ra (J ^ en 255 '', a o 'c i -2 o o 2 l\ <y> U U O 1 <N A II ! I I I I I I t I 111 ill III vv I I : I : II! I I I I 111 II ill! . I z _ I E ! I I I I ^^Tj- .— CNt— CNt— t— T— — III 1 o o o o o o °. ° ° ' '^. -! o o o o" o o o d o o o a. 00 mmo r^in "<!,r?S I I I I I I m fi TT m m mo m | r- <N oo o'o'o oo o oo III I III! I vvv vvv I I ooV O E o^8 = E (J E u « _ o E O I- 5 E (J t" I I I I I Tf * I I I I I I I I I \0 O O Om CMCNO O-^ OOtNCN'* ooo^ o o o o o o o oooo oooo ooo oo oooo ,— -^ooo oovDya-^i- co^o o\ CN CN CN (N (NO* <N O -^ O 00 ON T CS ^ V- CN CS — C-< fN ^fO 0^*0000 VDOO*^ OO VO r-- CN 00 ^ U3 o OOOO oooo oo 256 -o O c c It: o O "^ -x -^ '^ Z _ O E O _ o 3: E O _ O "a <-> E u I- n E U ° a. V V WW 257 ! "2 E S E z _ £ E O E O E O _ o = E O O _ O E O lit: i s a " « g ™o SI I II 1 ! ! ' I ; II I I I I I I i 1 ! ! ! I 11 1111 I I I I I > I fS VO C7\ o o m o V vvvv ! Ill U3 O O <N ; o o o o o o o . ~ ~ dd odd o a o oo ooo o C O * g ^ ! ?. o o ooo o o V V vvv o o o ooo ,— o o o I ; o o 1 o o -- d => ° N*^ V V V II '^1 oooo o oo oooo ri- 00 oi -a- •* O 00 St "* ^ ^ "^ ^^ o o ooo o o •<)<»• ^ cs * ^ O O O r- O O Tf -^ O -* o o * -^ s— T— o I oooo r- O I O 00 CN U3 VO Ti- u-i ui r- CN CN <N <N 00 »0 CN 00 O -si- fN ^ "^ oooo OOOO m oo CN \£i TJ- cs r4 r^ O CN CN ^ -^ (N fN <N CN tN E (J -iio OOOO o oooo o o oooo o o CTi 00 00 00 CO CO ooo oooo ° £ oooo CN (N CN (N oo r- r-^ Ov CN CN rJ en CN <N ooo oooo < 1/1 o z o J2,£s< s— <ui ozQ ill S < 5 2-5 o2 i/i o u o o o o 258 O O .' I kO I I ! 1 ! vvvv ' ' v<7V • vvv vv vv V vv vv CN r-- o o o o o *^ ^ "-l R odoo oo oo 1 o o o o o ! o o o" o o o o CO ^ CM o o o o o o o o o o o o C\ 'C- o d d d _ ^ ^ ,_ o d d d o o o o o o d d vv OO oooo ogo o o I o. ° °. °. °. °. ° od ddo'd ooo ^ vvv oooo 3: E U I VD I t CN ^00 o Zq oooo 00 oooo oooo oooo oooo oooo s -sSi 00 CO I I _ o ^ fN r— *0 t— <N 00 ^ CN CN CN CN \£l r~ »— 00 00 00 00 1 1 00 00 I o o r~ CM CN CN Ci CN CN CN oooo f— CN 000 oooo 00 oooo o o , _ o ta r- vo ly^ vo • o oooo oooo oooo CN CN CN oooo 00 3 '3 2 <yi O z a — L. 'S. < c ^ o o (fl — — o 1/1 (J u 0\ U-. 1 I V 259 z _ z _ 2 E 1 o 260 c ^ o o 2 "5 o 2 Z _ 3C E _ o E O _ O E O E o V o o o o d d o o o o o o o o o o o o o o o o o o o c^ — ^ m m \ Ill irt o o o « 261 2 _ 5 E T- (N f*% o _o U -Si" 3: E u 3|8 E o H _2 E o ^ -i: « ° I™ o o o o |-~ I t TT o o o o o o cs o 00 00 CN CN 262 il -S S I E o o 2 o o o o o o 1 I I I : II I Z _ 2 _ O E O _ o = E (J E (J II I II I I I I II I II III I : : 1 I 11 I I I I I I I I I II III VV ' V III t II I I I I I I I I I II I II 1 i t I i I I I 1 I I I I I CO O -^ 'T oooo o oo oooo U-l -^ tr (N 00 <N U-, o «; '^. ""; *. o o oooo 3 TO 3 O 263 a o c r- O O O V vv VVV ' V V vv • V fn CM CO tT CN o t^. r4 o o o *^ '^, ^. *-*. "-^ o o o o o o o o 0\ T-^ \0 O O ( I O O O O I c o o o o o o o o o o o o P-I Tj- VD Ol Ti- <N o cr. »- r- r- OC I I o o ,— 1— CM CN o o o o o o o o O O O O o o o V vv V V o o o O O O I O I O I O O I I o o o o o o c o o o Ti- •* en ^ o - o = 6(3 r- <N VO "t CM O Ol 00 ^£» vo ^m M I I rj 00 vo o _ o E (J oooo oo oooo oooo oooo oooo oooo o E U "too OOCN OC^O tN (N O 00 «J3 VO r- r-- OO rr a\ >n .— »— ^ *- 1— cs _ O E U 00 rJ- O r- CN CN CN 2 S^P OO-C oOCTi ^tfSoo 1(N^(N trjCN ^MOO tj- tN 'I- 00 O "^ "^ VO ^ m <» m 00 I I o r~ I w o en I '- oooo oooo O^ v^ 0_ O VO O-l U1 TJ- OOOO o o <Q G r- ^ r^ C-4 oooo en m ' en 5Z^< ^ o z. a -Zi 264 o o S2 I Z _ X E z _ O E E o ,_ O E O E u ° -c « ° E V ^ ' ' ' ' V • "vvv v' "^""v r- m r-~ MS o o o o o o o o o o o o I t r I I .o cm" ' iX ^* r-' ^ ^ * ^ f^ o ^ o o oooo oooo oo oo o o oooo o o -^ ^ "^ *^ "^ , S2 O (N (N CO CO ^ m o^ '^ (N CO 00 ^ m en t~, v£) I VD OOOO OOOO OOOO CO rJ 'Xt OO "<* cn s^ o w^ OOOO o o o o i/^ in «^ r- oooo OOTO cr\ o 1— r- 265 ^ S £ E c *t: o o 2 o o 2 1/) U (J H E 266 •a o 'c c ^ o o 2 o o ° o ^ z _ 3: -E u _ O e o -. _ o o "a" a 2 n "S s " o H^ Eo I™ 0000 0000 r- r- O C\ O I O 0000 a o -^ G 5^^< 267 •a 268 ^5 §o "> u o z _ 1 E z _ O E o - o 3: E o , _ o E u t- « E (J > E u 269 -a o c: c ^ o o 5 -^s •;; o 2 E Z _ o Z o E ij (J -I V vv OO ^ CN 0\ vO I >- I 00 '^ en cs d d I I I oooo o oooo 270 -3 o 'E c ^ o O :: o o2 vn U (J O ^ V V PART C SECONDARY WELLS—ANALYTICAL DATA Part C contains monthly data of the analysis of water samples taken from the secondary wells monitored during the project. Data for the period April through September, 1975, are furnished through the courtesy of the Caribbean Research Institute of the College of the Virgin Islands. 271 272 t. S- O) I— (O O - E -O 4- C c •- o o IB 1— 1— O +-> O O I— CO O (-J O •— O ^CVIO C\JC\I «;J-^lCVJ o o o o I CM ir> o I CTi en cvj ^ ^ ir> o o o o I UD CM OvJ I r~. 1— CO ^ Lf) LD I VD ID <£> CM O I CTi cn 00 en o CO oo m CO «d- o OD o o O kO CM CM o en r~. en LT) "=1- ^ ^J- o o o o 00 CM CM O eO t^ CO CM ^ UJ LfJ LO CXD CO ^O CO (X) O CO CO CO CM CO CO 273 TJ E to S_ S- dJ r— (O O -r- E -O I*- C C -r- O O (O I— I— O +-> O O r— 00 O O <NJ C\J I O liD VO lO 00 cr> cn I CO t^ cri r~~ *x> «;( 1^ «^ "^ "=1- ^ «* o o VO CO U3 <X> Csl O r^ tn Lf) Ln ^ «d- ^ «3- CD O to O O O lo CO CO r-~ CO ID o s^ ^ «* "d- «a- "nT CO oooo oooo oooo oooo ooo O «^ I C^J O OJ Od CM o 00 I 1— 00 r~~. ID CO IT) VD LD ID O C30 CM ^ O O O O CO o 2 S 5i! vD o oo 00 CM cr. r-. ^ CM r-- S S J?} 00 00 ^ CT) 00 CO 00 O O O 'c^ CM ^ CM >=3- LO O C^ UD ^ 00 O O O CM O S S S^ ^^ r— r^ ^ o CO CTi 1X5 r^ 00 cn co <^ CO </> (/) I/) (O r— <D (O C I— O -(-> -D -^O O S- CD n3 H- fO E O CX3 CM "d- 00 O O CM ^ LO I o 00 00 lo in cTi r- I o cj^ CO cn 1 O O 00 00 CO o O CM O CM CM r^ O O CTl CD 1— O oooo O O lO (X5 o o LT) cn CO CO O O CM r^ r— 1— 1 •a x: -!-> C E (O o ^ (J OOOO OOOO oooo oooo CTli—CMr— oooo o o o o o o oooo oooo oooo oooo ooo oooo ooo Lf> O O O O O Lf) LOinvOWD lOUDU3^i^ VOVO VOU3U3W3 LftVOVDin lO«3tO gill iggg §1 §§§i iiil P.I . ,— I— I— CM CM C X3 5- C ro <U fO 3 •-3 u- s: o r— CD CL+J > O 3 3 0) (J o ai "-o cc t/i o z: Q c s_ s- >, ^ 2: <: s: c I— cn Q- 3 3 3 0) '-D ""D <: CO 274 (/5 T3 e to S- S- Q) r- (O O -r- E C -r- O O (O r- 1— O 275 -a E 1/5 S- S- 0) r- (O o •- E -O If- c c -r- o o rO r- I— O 4-> O O 1— 00 u o C>d I CO I CO O o .— o ICXJ'^O «d-CM CSJCOIOO IViOVOr- Or- CT>a3IVg C\J CO ^ IX) Lf) CTl <a- r— ^3- «:3- «* "^ 276 IT3 O -r- E -O 4- C C -r- O O (O 1— 1— o +-> O O r- CO O 277 to ^^ S- S- (U r— (T3 O -r- E -o <+- c c -^ o o rO 1— I— O +J O O I— CO 278 -O E i/> S- S- QJ •— fO O •"- E -O 4- C C •>- O O (O r— r— O -t-> O O r— CO o cj <r> 279 1/1 ~^ S- J- (U — 03 O •>- E -O H- C C -r- O O rtj 1— I— O +-> O O ^ O O O O 1— o cy> <Ti ^ ^a- CO CO to vjD O CO Ln «* •a- "5J- ^ CM O LO 00 o o r^ «* VO <£> LO W3 o ^ o CM o o CM O O 00 o Ln CM CM CO I— LO in «* 1-n CO Od CM to r— I— 00 r-~- cr> cj^ m (/) i/l I/) to I— O) (O C I— o -•-> -o ^-<-> O S- C7) rtJ H- re) E O o o o o CO CO cri o r- o o r- CO CO CO CM O l/l CM 3 O -o x: 4J C E (O o o o o o o o o o o o o o o o o o o o o o O O O LO ^ CM CM CM r-^ r^ ^ CM CO CO CO CO o o o r^ "^ "^ CM CO LD 3 rj 3 OJ C J3 S_ fO O) n3 --D U- 2: 280 T3 E l/l S- S- 0) >— (D O -r- E -O 4- C C •!- O O (O I— r— O +-> O O I— 00 O O a-> 281 to ^ S- S- <U r- (O O •>- E "O 't- C C T- O O fO 1— I— O -l-» O O r— 00 (J C_) o o o o o o o O CT> O CX3 CO CTi CO VO m <^ LO Lf) LO LT) O O I— Osl O O CM CO CO 00 r-- r-~ LO Lft ID LO «;?• CM I VO o o o o r— <U <^ (O C r— O (-> X) "^O O S- CD n3 I— lO E o oooo oocM ^oiD«=r <T>0«*"d- OOCVJCn CMCvjrOCM I— CMCMCM 1— CMr— CMCMCMCM oooo o o o CO CD CTi (T> O O O CM CM I— '— CM CM CM OOOO O O CM CM O CO CO C» CM CTi ^ ^ ^ «* CO <:!- CO OOOO O O O OOOO O O ^ VO ^ «d- ^O CXD VD ^ «> ft M A « fv #t CM CM CM CM CM CM CM OOOO O O O o o ^ CO cr> CT» 00 LO in Lo < ^ ^ ^ CM VO CM <^ CTl CT> 1— CTi U3 ID CO 00 I— I— ^ t— ^ =!- ^ «* O I O I r— I O I OOOO o o o «!3- O O O O O O «;! 00 CX) "^ r^ *£) «:*• « .t •s ». « .. ». CM CM CM CM CM CM CM >, C r- cn rO 3 3 3 2: --D O <C CL+J > OJ O O 00 O Z O O CD O I— «a- ID CO in uo uo ir> (O OJ to 3 O Li- 5: "^ 000 ID cn r— LO ID r-^ 1— en Q.4J 3 3 OJ O -D <; 00 O CM ID •=!- O r- en o CO ID U-) ID ID oooo CO O CO CM •^ (D ^ ID CM CM CM CM O <D CM CTl «;! r— C7» CM CM CM r— CM CO VO O — 00 r-^ «* CO ^ * «a^ ^ OOOO OOOO ID <D Lf) «D CM CM CM CM O O O 00 CM O 1— O 10 VO <D ID C ^ S- C ro O) n3 3 •-0 u- s: "-O 282 1/5 ~^ -O E t^ S- S- <U I— (O O •- E T3 <4- C C -r- O O fO f— >— O +J O O I— I/} O O 283 C -r- O O <a .— r— o CO*"©' 284 S- S- OJ — <i3 o -r- e C -^ O O I <x) CO I CM CO CO CO OO CO CO ^ CO CM U3 CO «* LO CO CO CO CO 1 CO <JD I LO r— CO CO o o o o o o o o I CO O CM I o C30 r-^ CM 1— I CM O 00 00 <^ O CO <=! o I— CO 00 CM CM .— I— CM U3 VO CM CM <:}• «;*• r^ LO 1— I— CTi r^ r». r- r— CM CM •— •— " 285 286 1/1 -^ -a E 1/1 s- S- O) r— (o o •>- E "O 4- c c •!- o o rtJ I— •— o 4-> O O r— ro 287 to ^-^ T3 E t/l S- S- QJ — ro O •>- E -O *+- C C -r- O O (O 1— 1— O m 288 a 4- c c •<- o o (T3 r— I— O CO 289 to --^ O E to S- S- OJ r— n3 O -r- E -O M- C C -r- O O (O I— 1— o 4-> O O r— t/0 u o oo O O ^ O O •— n3 290 i- S_ CU r— to o ••- B "O 4- C c •.- o o IT3 1— I— O +-> O O I— t/0 O CJ 0«*0 r— O^Oi— oooo o I CO O I O I o O O UD ^ O r— O I— CsJ CM ID Lf) in Lf) in csj o CO vn OJ CM CM I— in in in in •IJ- CO o ix> o O I— CM in in in CM CM r^ CO 1— I— ^ in in ooo oooo oooo oo oooo oooo O "vj- CM ^ o r- CM cri CO r^ «=1- «;J- oo CM oo tin <:3-OCM^ CM^ ^COCVJ I inoio icn inioooco — o ocMin i voiocri oo OOOOCMCM «^0O «a-0O0O OOOOCM o ^ CO o o CO CM 00 "sr 00 CM oo CM CM CM ^ O CM 00 291 to "^^ -a E I/) s- S- O) >— (O o •>- E T3 4- C C •!- O O fO I— 1— O -(-> O O I— CO O O •r-oj O TJ J= -M cere O O C\J 00 UD CO LT) CvJ in uo Lf) IT) .cj-Otd"'^ OO"^ OCO IPO CNJLOOOi— I— C\JC\J "^Oli LDLDLDLD LOLniO LOLf) LO o o o o oj 00 "^ <Nj «a- CO o O^ lO U3 O CM O CO 1— I— r- CM 1— CM I— o o o o 292 S- S- <U — (O O -r- E "O 4- C C -r- O O ro r— I— O 4-> O O I— t/5 O (_) CM CVJ O ^ 293 « O ••- E C -r- o O 00 1— I o O O CM O CM lO ^J- ^ ^ CO Lf) 1— m cn LO LO Ln in un in «=l- o o o o O O O O «d- U3 >X) 1— 1— «d- 00 CM I— CM CM CM CM CM CM CM CM O O <X3 O 00 00 O CO «d- O CM 00 00 * CM CM CM CM I— I— I— to to r— <U O i- CD (O O O 00 O CM ^ ^D ^ ID < O 1— O US «^ ^ ^ LO «* «;f CO .,— PART D STREAM SAMPLES—ANALYTICAL DATA Part D contains monthly data of the analysis of surface water samples taken from the stream referred to as River Gut. Data for the period April through September, 1975, are furnished through the courtesy of the Caribbean Research Institute of the College of the Virgin Islands. 294 295 ro O 296 o 297 > 298 CDr- O cnCJ B o 299 o +-> •i-IN O +-> ^.Ln O 1/5 C\J 3 O "O -c »-> 1 "* O 00 OJ 00 CM UD I <£> 00 CT> LT) lO CO 1— ^ CM I— CM CM CO CO o o o o O C3 O O "d- lo o CO o CO CM 1— CM en CM CO CO CO CO CO <- «d- o o o o u3 ID CO LO CM r^ r^ en o CM I— I— r— 1— CM CM CM CM CM O CD 00 r— Lf) cn 00 r^ cn cm cm CM cm (/) m 300 +J TJ >— O •i-<N CJ > E •r- O O CO o r^ 00 r~~ o CX3 o lO CO cvj ^ o o o o CM CVJ CM CO C\J CO 00 «* CJ r- r— 1— i£i VO I CO O CO r— CO I to CO ^ o o o o o PART E AWWTP OPERATIONAL DATA Part E contains a statistical presentation of the operational data from the AWWTP for the period January through October, 1974. 301 302 r- oi ^ CN CN vO -^ ^ VO -^ -— 00 ^n o CN m m (N fo o o o I O O O I o (N r-- oo 00 a^ (^ CM xr CN vo Tj- Tj- fS rrj r^ so vn 0\ ^T ,2 c; ^ r^ <N r- -— O "^ r- O *^ r*^ r*^ vO GO (N CN ^ CO O r- vo cN <N r- C4 \0 <D t~ '^ o o m — VO O 00 ON O O r- O O O "£> -^ O O CT\ 00 O -^ O -^ O O 0\ "* o o vo r^ CO r^ 00 vo o o O cr\ CN O 00 ^ X c o o in *rt 00 »/^ »X o r^ *o C>* »- r- p- »— o\ \o i/^ O ^ r'* *ij-* iX TT vO ro .- CS (N »— <N O E z O <N V lO 00 O 0^ ^ ro 00 oo r^ U3 CO at o CN tc *A ro O f'. w ^ a> e- * c Q . o. J c Q =- o ^ „ 3 -I tJ 3 o 3 J S -o E -2 ^S 303 o _ o O <T» ^ -^ O CN VO »— O O OO t— i/^ cr. m w^ OO 'T ^^ C\ rj r- o c% o o * 1^ >- .- o .- o vo vo en m m a\ CM 1— t— o o o I O <N r- 1- O O O I TJ- •^ 0> f*^ O O O I CN * m o r^ Tj- tn »— V£) -^ ON ^ O >! VO <N VO p^ PART F SOIL BORING INFORMATION Part F contains a figure sfiowing the driller's logs of the soil borings taken in the Golden Grove area. 304 305 DESCRIPTION GC Clayev gravels, poorly gr»dsd gravel sand- clay mixtures. SM Silty i»nds, poorly graded sand-silt mixturHS. SC Clayey sands, poorly graded sand-clay mixiurei ML (nnrganic silt^ and vory fine sands, rock flour, jilty, Of clayey fine sands wilh slight plasticity. CL Inorganic clays of low-to-medium plasticity, gravelly clays, sandy clays, silty clays, lean clays. CH Inorganic clayi nf high plasticity, fat clays. ^ SURVEY IV10NUMENT Yellow Marl Limestone Figure F-1. Soil boring locations in Golden Grove. 306 15^ _POTENTIOMETBIC "head, fall 1971 ' BORING NUMBER PIA P2A Ed UNIFIED SOIL CLASSIFICATION SYSTEM USED Figure F-1. (Extended) PART G WATER LEVELS IN PROJECT WELLS Part G contains graphs of the water levels in various wells in relation to the amount of rainfall. 307 308 so- ys £76U z UJ LJJ 70 ^ 68 111 -i 66 CC tii64 <S 62 60 5S 601— 58 A-15 1971 JAN I FEB I MAR I APR I MAY 1.fVi p Jl JUN I JUL EH 2k ffl M m'^ A ¥ Jl.= Mkf. NOV I Lfl: FEB I MAR I APR I MAY I JUN JUL I AUG SEP OCT NOV I DEC TIME Figure G-1. Water levels in well A-15, 1971-1972. 309 57|- 55 53 -^ rffL r 1 1 I Lri h n Jl AR I APR ' MAY ' JUN ' JUL NOV DEC JAN FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG TIME Figure G-2. Water levels in well A-15, 1973-1974. 310 3< Figure G-3. Water levels in well A-15, 1975. 311 62 312 fmt|^rfi[iLi|kJ| n -rfi JAN FEB MAR APR MAY JUN JUL AUG SEP OCT TIME NOV DEC Figure G-5. Water levels in well A-18, 1973-1974, 313 42 40 JAN ^EB MAR APR MAY JUN JUL JUN JUL TIME K z < -2 -1 AUG SEP OCT Figure G-6. Water levels in well A-18, 1975. 314 88 86 §84 Z 2 82 H > 80 LU uj 78 UJ-74 A-19 1971 i^Jl^tfl[Tflr>|h^ irinp-n 1 Oil II -1 JAN ' FEB ' MAR ' APR MAY JUN JUL AUG SEP OCT NOV DEC TIME Figure G-7. Water levels in well A-19, 1971 315 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 48 46 44 42 40 38 36 34 32 30 28 26 -7 316 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC -6 < U. 3< ifl1]rf][]|1 n rf]Jml Jhpf^ .jfhJI FEB MAR APR MAY JUN JUL TIME K AUG SEP OCT NOV DEC Figure G-9. Water levels in well GG-3, 1974-1975, 317 50 48 318 48 46 *^44 Z 2 42 I- > 40 LU ixi 38 ^36 ai -J 34 CC UJH 32 < ^ 30 TOP OF CONCRETE BASE - EL 53 8 GG-5 1971 JAN ' FE JAN ' FEB ' MAR ADD < RJIA^ APR ' MAY II IM ' II II JUN ' JUL 1 4li< z 3< CC Ok -2 OCT NOV DEC ^ 36 Ol -" 34 CC UJ I- 32 -A mm APR MAY JUN J_. tp JUL AUG H, fly z 3< CC - 2 in NOV DEC TIME Figure G-11. Water levels in well GG-5, 1971-1972. 319 FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG SEP TIME Figure G-12. Water levels in well GG-5, 1973-1974. 320 28 26 TOC OF CONCRETE BASE - EL 63 8 I JAN 1 FEB I MAR I APR I MAY I JUN ' JUL ' Al TIME AUG ' SEP ' OCT ' NOV ' DEC 3< CC Figure G-13. Water levels in well GG-5, 1975. 321 18 - ^14 <12 > _|10 Hi > UJ Ul 4 TOP OF CASING -EL. GG-7 1971 M pM I rf%p\ i- TfW, p J-L FEB MAR APR MAY JUN JUL 32 Mi -2 SEP OCT NOV DEC "^ 4 UJ ^ H -A nil^ rn al mj ^^ 14 < u.Z < 3 CC iR FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TIME Figure G-14. Water levels in well GG-7, 1971-1972. 322 Figure G-15. Water levels in well GG-7, 1973-1974. 323 18 £16 014 TOP OF CASING - EL. 39 4 GG-7 1975 11^,-nElf nrljjyj JipPk ^ K z JAN FEB MAR APR MAY JUN JUL AUG SEP CXJT NOV DEC TIME Figure G-16. Water levels in well GG-7, 1975. 324 Figure G-17. Water levels in well GG-13, 1973-1974. 325 TOI- OF CASING- EL 87 IJAN I PER I MAR I APR I MAY I JUN > JUL ' -2 -3 -? 4 < LU2 < -6 -7 JAN I FEB ' MAR I APR I MAY I JUN I JUL ' AUG ' SEP i OCT ' NOV ' DEC TIME Figure G-18. Water levels in well GG-13, 1975. 326 JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL AUG SEP OCT 18 16 Sl4 Z <>10 UJ _i UJ 8 _l > 6 UJ ^0 NB-3 1975 3< I JAN 1 FEB I MAR ' APR ' MAY ' JUN ' JUL ^ -2 -1 AUG ' SEP ' OCT ' NOV ' DEC TIME Figure G-19. Water levels in well NB-3, 1974-1975. 327 38 36 ^34 ZO 32 UJ 26 > <5 20 18 16 TOP OF CONCRETE PUMP BASE - EL. 53.2 PW-1 1973 JAN I FEB ^ rfl^rlJliJlhm J : l\R 1 APR ' MAY I JUN I JUL < LUz 3< a: SEP OCT _b=.Ul NOV DEC 38 36 ^34 Z 2 32 I-<> LU 30 m 28 ^26 UJ -J 24 cc LU < ^ 20 18 16 PW-1 1974 M. cca I I ill. FEB ' MAR h">-J1 n ADO ' MA\ .j£L APR ' MAY ' JUN JUL TIME 1 < Li.z 3< CC 1 ha Figure 6-20. Water levels in well PW-1, 1973-1974. 328 38 36 ^ 34 Z 2 32 I- > 30 UJ LU 28 m 26 UJ -" 24 cc UJ t- 22 < 5 20 18 16 TOP OF CASING - EL, 80 5 PW-3 1973 < u.Z 3< CC -2 :i£] riTLr. &R I APR ' MA MARl^APR ' MAY ' JUN ' JUL IN IJ 1. lOa. mlL Figure G-21 . Water levels in well PW-3. 1973-1974. 329 TOP OF CASING - EL 80.5 I lAM I cm I MAR I APR I MAY ' JUN ' JUL Ir < U.Z 3< -2 -1 JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG^ SEP ' OCT NOV DEC ' TIME Figure G-22. Water levels in well PW-3, 1975. 330 38 36 ^34 ZO 32 H-< 30 LU ^28 UJ26 > LU _J24 OC tii22 <5 20 18 16 TOP OF PVC CASING - EL 66,6 PW-5 1973 mA. M I PFR T JAN I FEB -rTi [ffLr AR 1 APR ' MA ^1 J IIN TJl MAY I JUN I JUL 1\ -fi L NOV DEC z 3< JAN I FEB ' MAR ' APR ' MAY ' JUN ' JUL AUG ' SEP ' OCT ' NOV DEC TIME Figure G-23. Water levels in well PW-5, 1973-1974. 331 Figure G-24. Water levels in well PW-5, 1975. 332 38 36 334 Z <> 30 UJ -I UJ 28 -I lU>26 UJ TOP OF CASING -EL. 51.0 -7 PW-6 1973 IflLii. JAN FEB Icq rrf)-.r. ll£ MAR APR MAY JUN JUL IH -J< u. La SEP OCT NOV DEC Figure G-25. Water levels in well PW-6, 1973-1974. 333 -7 -6 -4. 38 334 43 335 TOPOf CASINO - EL, 47.4 — PW-7 1975 fl-fll,n[]lnrfl Brf^ iL JL mJ{ ' ^N I FEB I MAR 1 APR ' MAY I JUN ^ JUL ' JAN I FEB 3< CC -2 JUN f" JuL" ' AUG I SEP T~ OCT ' NOV ' DEC TIME Figure G-28. Water levels in well PW-7, 1975. 336 ^Figure G-29. Water levels in well PW-8, 1973-1974. 337 TOP OF CASING - EL. 49 6 4 < < 3 OC -2 Figure G-30. Water levels in well PW-8, 1975. 338 FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 48 46 ^44 Z <>40 oi I" 38 ui>36 Hi .34 i r 'so 28 26t| PW-9 1975 5'-^ C 4< u.Z < JAN FEB ii^^^jl.H]i1J JM fk jlf]H MAR APR MAY JUN JUL TIME K AUG SEP OCT NOV DEC Figure G-31 . Water levels in well PW-9. PART H ENGLISH-TO-METRIC CONVERSION In recognition of the advance of the United States to the metric system, the text of this dissertation is written with metric equivalents following the English units of measurement. To avoid confusion and space problems some of the tables and illustrations do not have these equiva- lents. The following table is a list of English units used and their metric equivalents to assist in making individual conversions. The standard abbreviations for the respective units are used. 339 340 rABL: H-1. ENGLISH -TO-METRIC CONVERSION English unit Multiplier Metric unit acre 0.405 ha acre-ft 1,233.5 cu m cu ft 0.028 cu m ft 0.3048 m gal 0.003785 cu m gal 3.785 1 gpd/sq ft 0.0408 cu m/day/sq m gpm 0.0631 1/sec hp 0.7457 kw in. 2.54 cm lb 0.454 kg mgd 3,785 cu m/day mile 1.61 km sq ft 0.0929 sq m sq in. 6.452 sq cm sq miles 2.590 sq km REFERENCES An Invalid, 1839. A Winter in th e West Indies and Florida . New York: Wiley & Putnam. Beller, W. S., Adams, A. A. et al . , 1970. "The Virgin Islands and the sea." Preprint manusci^ipt of a citizen's group report to the governor. St. Thomas: Office of the Government Secretary. Black, Crow and Eidsness, Inc., 1972. 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''Utilization of wastewater for beneficial purposes." h\: Virgin I slands Agriculture a nd Food Fair-- 1975. D. Padda, ed., St." Croix: VM". Department of Agriculture. Buros, 0. K., 1975b. "Water resource planning and wastewater reclamation in the Virgin Islands." A paper presented at the Workshop on Augmenting the Virgin Islands Water Supply sponsored by the Water Resources Research Center. St. Thomas, Virgin Islands. May 9, 1975. Buros, 0. K., 1975c. "Wastewater reclam.ation in St. Croix." A paper presented at the WPCF 48th Annual Conference. Miami Beach. October 5-9, 1975. Buros, 0. K. and Basiouny, F. M. , 1972. "Wastewater reclamation." A paper presented at the Florida AWWA-FPCA 23rd Annual Conference. Daytona Beach. October 29-November 2, 1972. Busch, A. W., 1971. Aerobic Biological Treatment of Wasc e Waters . Houston: Oliodynamic Press. Butler, C. S., 1917. "Report to the Governor of the Virgin Islands." June 9, 1917. St. Thomas: U.S. Naval Station. 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The Virgin Islands O ur New Po ssessions and the Br itis h Islands ." Phi 1 adel ph'i a : Li ppi ncott Company. Driver, C. H., Hrutfiord, B. F., et al., 1972. "Assessment of the effectiveness and effects of land disposal niethcdologies of wastewater management." Wastewater Management Report 72-1. Corps of Engineers. Department of the Army. Engineering Science, Inc., 1968. "Water reclamation for the U.S. Virgin Islands." Arcadia, California: Engineering Science, Inc. Environmental Protection Agency, 1975. "Environmental Protection Agency--Interim primary drinking water standards." Federa l Register , Vol. 40, No. 51, March 14, 1975, 11990-11998. FWPCA, 1970. Application for Class II Demonstration grant entitled "Wastewater Reclamation at St. Croix, U.S. Virgin Islands." Federal Water Pollution Control Administration, Atlanta, Georgia. Grigg, D. I., Shatrosky, E. L., and Van Eepoel , R. P, 1971. "Operating efficiencies of package sewage plants on St. Thom,as, V.I., August-December, 19/0." Government of the Virgin Islands Water Pollution Report No. 12. St. Thomas: Caribbean Research Institute. Hendrickson, G. E., 1963. "Ground water for public supply in St. Croix Virgin Islands." U.S. Geological Survey Water-Supply Paper 1663-D. Johnson, A. F., 1935. "Water supply for the towns of Christiansted and Frederiksted, St. Croix, Virgin Islands of the United States." Santa Fe, New Mexico: U.S. Bureau of Reclamation. Jordan, D. G. , 1972. "Land-use effect on the water regimen of the U.S. Virgin Islands." USGS Prof. Paper 800-D. Jordan, D. G. , 1973. "A survey of the water resources of St. Croix, Virgin Islands." USGS Caribbean District open-file report, San Juan. Kemp, J. F., 1923. "Report to H. H. Hough, Captain, U.S.N. , Governor, Virgin Islands." April 6, 1923. St. Thomas: U.S. Naval Station, Koenig, L., 1966. "Studies related to market projections for advanced waste treatment." FWPCA Publication No. WP-20 AWTR-17. Cincinatti: FWPCA. 344 Kruseman, G. P. and DeRidder, N. A., 1970. Analysis and Evaluation ol_Py!IipJj:'5_JeiL.Data.- Wageningen, The Netherlands: International Institute for Land Reclamation and Improvement. Lawaetz, B., 1974. "Rain Water." In: Virgin Island s Agri culture and Food Fa ir— 1974 . D. Padda, ed., St. Croix: V.I. Department of Agriculture. Lawaetz, B,, 1975. "Why the streams don't run an^iriore." In: Virgin Islands Agriculture and Food Fair . D. Padda, ed. ,Tt. Croix: V.I. Department of Agriculture. Lewisohn, F., 1970. St. Croix Under Seven Flags . Hollywood, Florida: Dukane Press. McGuinness, C. L., 1951a. "Memorandum concerning hydrological studies needed in the Virgin Islands with an addendum on Puerto Rico." USGS Caribbean District open-file report, San Juan. McGuinness, C. L., 1951b. "Additional water development on St. Thomas, V.I. with an addendum on St. Croix." USGS Caribbean District open-file report, San Juan. McGuinness, C. L., 1953. "Summary of the water resources of the Virgin Islands." USGS Caribbean District open-file report, San Juan. McKinzie, W. E., Scott, B. F., Rivera, L. H., 1965. Soi ls and Their Interpretatjons_f_or_ V arious Uses, St. Cro ix. Anier i c an Vi"rg7n" J-'^^a^ds . Spartanburg, South Carolina: Soil Conservation Service. McGauhey, P. H. and Krone, R. B., 1967. "Soil mantle as a wastewater treatment system." SERL Report No. 67-11. Berkeley: University of California. Meyer, R. R., 1952. "Geology and hydrology of dam sites on the Island of St. Croix, Virgin Islands." USGS and the Office of Territories, Department of the Interior. Meyerhoff, H. A., 1927. "The physiography of the Virgin Islands, Culebra and Vieques." J_n: NewJ(oH^ca^demx_of_Sci ences , Sc i ent i f i c Survey of Puev-to Rico and the ^'^-^^^^^j^JJi^^IHil Vol. 4, part 2 . Multer, H. G. and Gerhard, L. C, eds., 1974. Guidebook to t he Geology aiTd_Ecology of Some _ Ma ri ne an d T err e^t r iai E'nvironm e n t s ', St. ^I°i2i^-il:.JlraJii _LsJ ands_. Special Pu'bTi c^at i oTTNoTT. ~ Christiansted: West Indies Laboratory, Fairleigh Dickinson University. 345 Murrmann, R. P. and Koutz, F. R., 1972. "Role of soil chemical processes in reclamation of V'/astewater applied to land." hi: "Wastewater management by disposal on the land." Cold Regions Research and Engineering Laboratory Special Report 171. Hanover, New Hampshire: Corps of Engineers, U.S. Army. Pettigrew, R. L., 1919. "Engineering features of various sites for a first class naval base in the Virgin Islands and Eastern Puerto Rico." August 1, 1919. St. Thomas: U.S. Naval Station. Pettigrew, R. L, 1921. "Water supply for Naval Base of St. Thomas." Report to the Commission on Navy Yards and Naval Stations, January 13, 1921. St. Thomas: U.S. Naval Station. Praeger, Kavanagh and Waterbury--Engineers, 1954. "Evaluation of underground water supply--St. Croix development, St. Croix, Virgin Islands." Report to the Fountain River Co., December 10, 1964. New York: Praeger, Kavanagh and Waterbury— Engineers. Rivera, L. H., Fredrick, W. D., et al., 1970. Soil Survey, Virgin Islands of the United States . Washington: Soil Conservation Service. Robison, T. M., 1972. "Ground water in central St. Croix, U.S. Virgin Islands." USGS Caribbean District open-file report, San Juan. Robison, T. M., et al . , 1973. Water Records of the U.S. Virgin Islands 1962-69 . Department of the Interior, USGS. Sawyer, C. N. and McCarty, P. L., 1967. Chemistry for Sanitary Engineers . New York: McGraw-Hill Book Company. Shaw, E. B., 1932. "St. Croix's rainiest year causes an epidemic of malaria." Science 76:566-567. Shaw, E. B. , 1933. "St. Croix: A marginal sugar-producing island." Geographical Review 23:414-422. Stolz, S. B., 1975. "Water quality management, new Golden Grove well field St. Croix." Letter to K. Euros (Black, Crew and Eidsness, Inc.) July 7, 1975. Christiansted: Government of the V.I., Division of Natural Resources Management. Taylor, C. E., 1888. Leaflets from the Danish West Indies. London: W. Dawson and Sons. Tippetts, Abbett, McCarthy, and Stratton, Inc., 1959. "Potable water supply for St. Croix, Virgin Islands." New York: Tippetts, Abbett, McCarthy, and Stratton, Inc. Todd, D. K., 1959. GroujTdJ*^er_J^ydrpJ_02X. New York: John Wiley & Sons, Inc. 346 Van der Lippe, P., ]952. "Report on the study of economic feasibility of damsites on the Island of St. Croix, Virgin Islands of the United States." U.S. Bureau of Reclamation. Vaughan, T. W. and Kidwell, C. H. , 1920. "The ground water resources of the West Indian Islands, Saint John, Saint Thomas, Culebra, and Vieques, and the eastern end of Puerto Rico." A report to the Commission on Navy Yards and Naval Stations. Washington: USGS, Department of the Interior. Ward, P. E. and Jordan, D. G., 1963. "Water resources of the Virgin Islands, a preliminary appraisal, 1963." USGS Caribbean District open-file report, San Juan. Warfield, R. M., 1924. "Report on water supply, Virgin Islands." A report to the Secretary of the Navy, March 29, -1924. Washington: U.S. Navy. Whetten, J. T., 1962. Geo logy of St. Croix, Virgin Islands . Princeton University Ph.D. dissertation. Ann Arbor: University Microfilms. Whetten, J. T., 1958. "Field guide to the geology of St. Croix, U.S. Virgin Islands." lr]_: Guidebook to the Geo logy and Ecology of Some Marine and Terrestrial Environments", St. Croix, U.S. V irgin Islands . Multer, H. G. and Gerhard, L. C, eds. 1974. Christiansted: West Indies Laboratory, Fairleigh Dickinson University. BIOGRAPHICAL SKETCH Oscar Krisen Buros (Kris) was born in White Plains, New York, where he resided until completing high school. Following graduation he attended the Colorado School of Mines for one year and then served in the U.S. Navy for four years as an electronics technician on board an ocean minesweeper. He completed his undergraduate work in civil engineering at Washington State University following which he worked as a field engineer for Chicago Bridge and Iron Company on various construction jobs in the western United States and Alaska. In 1965 Kris embarked on an extensive trip abroad to study the culture, economy, and customs of various underdeveloped areas in the world. The trip spanned three years and about sixty countries. Notable events during the trip included crossing the Sahara Desert with Arab date traders; surviving the sinking of a riverboat on a tributary of the upper Amazon in which tv/enty-five people drowned; journeying from London to Vladivostok by railway; and traveling the overland route from Nepal to Europe via the Khyber Pass. In 1968 he returned to Washington State University and earned a master's degree in sanitary engineering. This was followed by further graduate studies at the University of Florida's Department of Environ- mental Engineering, where he completed the ccurse requirements and preliminary examination for the Ph.D. in 1971. 347 348 From that time to the present Kris has been employed by the consulting engineering firm of Black, Crow and Eidsness, Inc., of Gainesville, Florida, where he holds a position as a senior engineering specialist. Since April, 1971, he has lived on the island of St. Croix in the U.S. Virgin Islands where he has worked on various engineering problems including a wastewater reclamation project which is the subject of his dissertation. Since moving to the Caribbean, he has married the former Sheila Ann Fullam who was a music teacher at a private school on St. Croix. On the island Kris is active in the Virgin Islands Conservation District and serves on the advisory board of the Water Resources Research Center for the Caribbean Research Institute in St. Thomas. I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. idward .Ef/Single/ Professor of / Env/i'ronmental Enqineerina Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertauion for the degree of Doctor of Philosophy. wCmVo><' /C\ mM:' R. S. Sholtes, Adjunct Associate Professor of Environmental Engineering Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Arnold S. Bleiweis Associate Professor of Microbiology I certify that I have read this study and that in niy opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. /A^ ^:^?^^ K. Paul H, Smith Professor of Microbiology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. ^1'^~^^<Sd ek^y^ "1tx-\^^^(?i Thomas deS. Furman Professor of Environmental Engineering Sciences This dissertation was submitted to the Graduate Faculty of the College of Engineering and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. November, 1975 Dean, Graduate School 3 1262 08666 266 4