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SITE REMEDIATION AND SUPPLEMENTAL INVESTIGATION PROGRAM ESSO TUTU SERVICE STATION TUTU, ANNA'S RETREAT, ST. THOMAS, U.S.V.I. February 1995 Prepared for: Esso Caribbean and South America 396 Alhambra Circle Coral Gables, FL 33134 Prepared by: Forensic Environmental Services, Inc. 623 North Pottstown Pike Exton, Pennsylvania 19341 TUT OO7 .184.1 *65009* 65009 SITE REMEDIATION AND SUPPLEMENTAL INVESTIGATION PROGRAM ESSO TUTU SERVICE STATION TUTU, ANNA'S RETREAT, ST. THOMAS, U.S.V.I. Eage 1.0 INTRODUCTION 1.1 Preface 1-1 1.2 Site Description 1-3 1.3 Remedial Objectives 1-4 2.0 EXISTING SITE CONDITIONS 2.1 Site-Specific Hydrogeology 2-1 2.1.1 Geology 2-1 2.1.2 Ground-Water Hydrology 2-3 2.2 Vadose Zone Soil Quality 2-5 22.1 Underground Storage Tanks/Pump Island 2-5 2.2.2 North Oil/Water Separator 2-6 2.2.3 Other Potential Source Areas 2-8 2.3 Ground-Water Quality 2-9 2.3.1 North Oil/Water Separator 2-10 2.3.2 Underground Storage Tanks/Pump Island 2-11 2.3.3 Phase-Separated Hydrocarbons 2-12 2.3.4 Regional Ground-Water Quality 2-13 3.0 PROPOSED REMEDIAL PROGRAM 3.1 Conceptual Model 3-1 3.2 Vadose Zone Remediation 3-1 3.3 Saturated Zone Remediation 3-3 4.0 SUPPLEMENTAL 1NVESTIGATION/PRE-DESIGN ACTIVITIES 4.1 Vadose Zone Remediation 4-1 4.2 Saturated Zone Remediation 4-2 S.O IMPT.FMENTATION SCHEDULE 5.1 Tentative Implementation Schedule 5-1 TUT 007 1842 LIST OF FIGURES Following Page 1-1 Area Map 1-3 1-2 Site Map 1-3 2-1 Water Table Elevation Map, Shallow Wells, 4/94 2-3 2-2 Soil Sample Locations, Soil Tech Tank Removal, 6/8/89 2-5 2-3 Soil Boring Location Map 2-6 2-4 Soil Sample Location Map, Oil/Water Separators 2-7 2-5 Ground-Water Isoconcentration Map, Total BTEX in ug/L, 4/94 2-9 2-6 Ground-Water Contaminant Distribution, Chlorinated Compounds in ug/L, 4/94 2-10 3-1 Conceptual Hydraulic Capture Zones 3-3 LIST OF TABLES Following Page 2-1 Summary of Ground-Water Elevation Data 2-3 2-2 Summary of Soil Data, Soil Tech Tank Removal Samples 2-5 2-3 Summary of Soil Analytical Results, BB&L Soil Borings 2-6 2-4 Summary of Soil Analytical Data North Oil/Water Separator 2-7 2-5 Summary of Ground-Water Analytical Results 2-9 2-6 Chlorinated VOC Statistical Analysis 2-13 5-1 Tentative Implementation Schedule 5-1 TUT 007 SECTION 1.0 INTRODUCTION 1.1 Preface Anna's Retreat (Tutu) is located on the eastern end of Saint Thomas, United States Virgin Islands. The Tutu area can be best characterized as a densely populated mixed residential, commercial and industrial area. This history of diverse land use'has exerted significant stresses on the localized ground-water regime (aquifer). The most significant of these stresses is the degradation of ground-water quality as a result of anthropogenic activities (e.g.., residential and commercial septic systems, improper handling and disposal of waste oils/hazardous materials, unpermitted discharges to storm sewers, commercial and industrial operations, etc.). As a result of these variable and widespread sources, the upper Tutu aquifer basin has experienced a cumulative/progressive reduction in regional ground-water quality. The Tutu area of Saint Thomas has been the focus of an ongoing Environmental Protection Agency (EPA) directed investigation subsequent to July 1987. EPA's investigative activities were precipitated as a result of the detection of volatile organic compounds in several potable water wells located within the upper (northern) portion of the Tutu aquifer basin. Specifically, sampling conducted by Weston in July 1987, on behalf of the EPA, identified the presence of synthetic chlorinated organic compounds (halocarbons) and aromatic hydrocarbons at variable concentrations and in sporadic locations within a number of ground-water production wells in the Tutu area. Subsequent to July 1987, periodic water quality sampling of potable wells has been conducted by the EPA. Additionally, site inspections, document reviews, and sampling activities have been implemented in an attempt to identify potentially responsible parties (PRPs). 1-1 TUTURAP2.TUTU#2 In 1992 EPA directed the Tutu Environmental Investigation Committee (TEIC), comprised of Texaco Caribbean, Inc. and Esso Standard Oil, to implement a joint hydrogeologic investigation within the Tutu area. In an attempt to characterize the extent and sources of ground-water contamination, ground-water monitoring wells were installed, soil/ground-water samples were collected, and aquifer hydraulic information was obtained. Findings from this investigation were presented by Geraghty & Miller in a Technical Memorandum (Tech Memo II) dated May 1993. This investigation program represented the first step in the iterative process through which a comprehensive Remedial Investigation/Feasibility Study (RI/FS) for the Tutu area would be developed. To address data voids identified in Tech Memo II, Geraghty and Miller developed elements of a Phase II Remedial Investigation program in 1993. This program was submitted to EPA in December 1993, and subsequently approved and implemented in 1994. Findings of the Phase II /—N Remedial Investigation were presented in draft form in an October 1994 report. In addition to global Remedial Investigation activities, several PRPs have conducted site- specific investigations. Specifically, Esso has commissioned several site investigations of the Tutu service station. These investigations have been implemented in phases and include the following significant tasks: • assessment of soil quality beneath the former location of the site's gasoline storage tanks (samples collected during tank replacement activities 1989); • investigation of the stations subsurface waste oil and oil/water separator piping systems; • determination of environmental conditions adjacent to potential on-site source areas including: the gasoline dispenser island; former location of hydraulic lifts; oil/water separators; and existing gasoline storage tank field; • characterization of hydrogeologic conditions beneath and adjacent to the site; and • determination of ground-water quality on site as well as up- and downgradient of the station. 1-2 TUTURAP2.TUTLW2 1845 This document serves to provide a concise summary of environmental conditions at and proximal to the Esso service station, and to propose a remedial action program in accordance with conditions of the Administrative Order On Consent (AOC) signed by Esso Standard Oil and Texaco Caribbean, Inc. in 1992. The collection and analysis of supplemental environmental data proposed in conjunction with this program will be implemented, to the extent possible, to conform with the EPA approved Quality Assurance Project Plan (QAPP) developed by Geraghty & Miller for Phase I and Phase II Remedial Investigation activities. 1.2 Site Description The Esso Tutu station is located adjacent to the Four Winds Plaza on Smith Bay Road (Route 38), south of the intersection with Route 384 (Figure 1-1). The station presently operates as a gasoline retail facility, but in the past also conducted limited vehicle maintenance and repair activities. Gasoline at the station is stored in two on-site underground storage tanks (USTs) located in the southeastern corner of the property (Figure 1-2). The USTs are each 10,000-gallon capacity and contain regular unleaded and super unleaded product. Gasoline is dispensed to vehicles from the pump island located approximately 50 feet north of the USTs. Structures on the service station property include a service building, an enclosed garage/storage area, two open garage areas, and a garage enclosed by a steel cage (Figure 1-2). The service building is located in the central portion of the site and is used for the storage of station records and retail products (one-quart oil cans, windshield fluid, etc.). Also within the building are vacant rooms which had previously served as vehicle maintenance bays prior to termination of repair activities and building renovations. The enclosed garage/storage area (located in the southern portion of the site) is currently used for the storage of supplies and equipment related to ongoing environmental studies. Materials contained within this area include a ground-water treatment system, health and safety equipment, 1-3 TUTURAP2.TUTU#2 . TUT OO7 1846 EPA REGION II SCANNING TRACKING SHEET DOC ID # 65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 1-1 AREA MAP (Page: TUT 007 1847) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 1-2 SITE MAP (Page: TUT 007 1848) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 and sampling tools. The enclosed garage/storage area is locked and secured to prevent public access. Open garages (including the caged garage) are present at the Esso Tutu station in the southwestern corner of the site. The open garage areas, which are not currently used by Esso Tutu personnel, had previously served as vehicle repair bays and/or storage areas. Within these areas are two abandoned subsurface oil/water separators, designated as the "south oil/water separator" and the "north oil/water separator". Historically, the north oil/water separator received waste oil generated in the service bays previously located in the existing service building. The south oil/water separator received both waste oil and storm water generated in service bays previously located along the southern and western boundaries of the site. 13 Remedial Objectives The primary objectives of the proposed remedial action program have been developed in accordance with the 1992 Administrative Order On Consent and include the following: • remove phase-separated hydrocarbons, if any, from the saturated zone; • abate residual sources, to the extent feasible, in the unsaturated zone that are or might have an impact on ground-water quality; and • capture and remediate, if feasible, the soluble-phase aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylene) and semi-volatile compounds emanating from the subject property. TUTURAP2.TUTU#2 fy-j- 1-4 T*i *.._ OO7 SECTION 2.0 EXISTING SITE CONDITIONS Investigative studies at the Esso Tutu station have characterized site environmental conditions in both the vadose and saturated zones. Specifically, the following studies have provided quantitative information regarding site conditions: • UST replacement activities performed by Soil Tech, Inc. and documented in "Final Report, Lab Analysis of Soil for Tank Replacement", dated January 1990. • Site characterization activities conducted by Blasland, Bouck & Lee (BB&L) during the period of November 1993 through April 1994. • Remedial investigation activities performed by Geraghty & Miller from February to May 1994. Presented below is a summary of the physical and chemical characteristics of subsurface soils and ground water at the Esso Tutu site as defined in the above-referenced studies. 2.1 Site-Specific Hydrogeology 2.1.1 Geology The geologic sequence at the Esso Tutu station, from the ground surface down, consists of fill and unconsolidated Quaternary deposits, overlying volcanic units of Mesozoic and Cretaceous age. The fill material at the Esso Tutu station varies in thickness from 2-3 feet at the northern property boundary to approximately 8-10 feet in the southern portion of the site. This layer consists primarily of a fine sand /silt/clay matrix surrounding angular rock fragments. In certain areas, such as the southwestern corner of the site, in the vicinity of the open garages, the fill material incorporates cobbles and boulders. 2-1 TUTURAP3.TUTU#2 TUT 007 1S50 Beneath the fill are unconsolidated Quaternary alluvial and colluvial deposits and weathered bedrock. These sediments range in thickness from two feet in the northern portion of the site to approximately 6-8 feet in the southwestern corner of the property. The Quaternary deposits can best be characterized as a poorly sorted mixture of clay, sift, sand, gravel and cobbles. This material was derived from upland areas and transported to the valley by gravity and surface runoff. Lying beneath the Quaternary deposits is a zone of weathered bedrock (saprolite) that grades into competent rock. The weathered bedrock is composed of dense silt and clay, and in some instances has retained original structure and fracture fabric. Bedrock in the vicinity of the Esso Tutu station consists of two volcanic formations: the Water Island Formation and the Louisenhoj Formation. The Water Island Formation is composed primarily of basaltic flows and breccias. It is unconformably overlain by the Louisenhoj Formation which consists of pyroclastic to ep»W»*tie <u»gite aadesite tuffs and breccias. Locally, the base of the Lcpiseshog:-.Formation consists of the Cabes Point Conglomerate, which contains welt rottndii SB* well sorted pebfetes and cobbles or the older Water Island Formation (Dqiwe%1959 and 1966). Stratographic infonrortWli obtained at the Esso Tutu site awHeaSes that depth to competent bedrock varies from five feet along the northern property boundary to 18 feet in the southwestern portion of the site. Because geologic logs of the area do not differentiate between the two bedrock units, and since the contact between the two formations is ill-defined in the study area, to date, it has not been definitively concluded whether the shallow bedrock beneath the Esso Tutu station is the Water Island or the Louisenhoj Formation. 2-2 TUTURAP3.TUTU*2 .y-j- O07 2.1.2 Ground-Water Hydrology Site hydraulic conditions have been ascertained through the collection and evaluation of data from shallow and deep monitoring wells installed at, and proximal to, the Esso Tutu station. Specifically, two depth intervals have been studied: a shallow interval (10-35 feet) and a deep interval (65-85 feet). Ground-water elevation data and field observations indicate that the shallow portion of the aquifer is present under unconfined conditions. Depth to the water table beneath the Esso Tutu site ranges from 11 feet to 20 feet , with ground water generally flowing to the south- southeast under a gradient of 0.025 (Table 2-1, Figure 2-1). An area of perched ground water is present in the southwestern portion of the site, in the vicinity of the north oil/water separator and well SW-7. This perched zone is likely manifested by a permeability gradient between fill material and saprolite strata. Depth to water in the perched zone, as measured in well SW-7, is approximately 9 feet. Information from geologic logs and pumping tests conducted in the Tutu area indicate that the 65-85 foot interval represents a deeper zone within the water table aquifer, not a separate water bearing system. Ground-water flow in the 65-85 foot interval is generally to the south under a gradient of 0.04. Depth to ground water in monitoring wells screened in this deeper zone ranges from 12.21 feet (DW-2) to 24.80 feet (MW-12D). Vertical hydraulic gradient information obtained from three shallow/deep well clusters proximal to the Esso Tutu station (MW-8/ DW-1, SW-6/DW-2, and MW-10/MW-10D), suggest a slight downward gradient ranging between 0.0035 to 0.01. The vertical gradient of ground- water flow at each well cluster was calculated by dividing the difference of the water level elevation in the well cluster by the vertical separation of the mid-points of the well screens (or open rock intervals). 2-3 TUTURAP3.TUTU#2 TUT OO7 1852 TABLE 2-1 SUMMARY OF GROUND-WATER ELEVATION DATA TUTU AREA MONITORING WELLS Tutu Esso Service Station St. Thomas, USVI Top-of Casing Elevation (ft) Ground-Water Elevation (ft) Ground-Water Elevation (ft) 'Corrected ground-water elevation as a result of NAPL presence. "Elevation measurement is approximate. No ground water elevation level has been calculated. Top-of-casing elevations are referenced to Mean Sea Level (MSL). Elevations from MW-9 through MW-12D and all CHT wells were obtained between April 7 and April 11, 1994. EPA REGION II SCANNING TRACKING SHEET DOC ID # 65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-1 WATER TABLE ELEVATION MAP SHALLOW WELLS, 4/94 (Page: TUT 007 1854) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 Single-well hydraulic conductivity tests indicate that the permeability of the shallow fracture system below the Esso Tutu station ranges from 1.55 x 10"4 ft/min to 4.61 x 10"6 ft/min. Calculated hydraulic conductivity values for the deep fracture system at well location DW-1 was 1.01 x 10"5 ft/min. Specific results from these tests are presented below: Monitoring Well Calculated Hydraulic Conductivity SW-1 5.47 xlO"6*/™,, SW-3 4.61 xlO'6^ MW-8 1.55xl0^ft/min DW-1 1.01xlO'5ft/min The range in calculated hydraulic conductivity values is consistent with field observations and geologic conditions. Field data obtained during well development, ground- water sampling, and slug testing indicated that recharge to monitoring wells SW-1 and SW-3 was extremely slow. In comparison, data from MW-8 indicated that ground-water recharge in this portion of the aquifer is greater, confirming the higher calculated hydraulic conductivity value. This degree of variability in aquifer permeability is common in bedrock media, where ground-water flow is restricted primarily to fractures, bedding planes, and formation contacts. Monitoring wells which intersect portions of the bedrock that are highly fractured can exhibit greater permeability (all other parameters held constant). The site-specific slug test data indicate that the fracture density in the southern portion of the service station site is low, thereby restricting ground-water flow downgradient from the station property. Hydraulic conductivity data, in conjunction with ground-water gradient information, indicate that ground-water velocity in the area of the Esso Tutu station is relatively slow. Averaging the hydraulic conductivity for the shallow monitoring wells, and assuming an effective porosity of 0.15, produces a calculated ground-water velocity of 0.013 feet/day (4.7 feet/year). 2-4 TUTURAP3.TUTU#2 TUT OO7 .1855 2.2 Vadose Zone Soil Quality Soil quality investigations have been performed at the Esso Tutu station to characterize vadose zone conditions proximal to suspected source areas. A total of 59 samples have been collected during these studies and submitted for laboratory analysis. Based upon these data, two areas within the unsaturated zone at the Esso Tutu station have been identified as a residual source for VOC contamination: 1) the area west of the north oil/water separator; and 2) proximal to the underground storage tanks and pump island. All remaining'areas of the site, including those adjacent to the south oil/water separator, subsurface waste oil/storm water piping, and the former hydraulic lift/automobile repair areas demonstrated non-detectable to very low levels of target constituents, and do not warrant additional investigation or remediation. 2.2.1 Underground Storage Tanks/Pump Island Analytical data characterizing vadose zone soils in the vicinity of the gasoline USTs and pump island were obtained by Soil Tech in 1989 (concurrent with UST replacement activities) and BBL in 1993. Soil Tech obtained 13 samples from the UST excavation during the removal and subsequent installation of new tanks (Figure 2-2). Data from the 13 samples indicated the presence of aromatic hydrocarbons and select semi-volatile organic compounds (Table 2-2). Aromatic hydrocarbons were observed at their highest concentrations in samples obtained from the floor of the excavation, generally at a depth of 11-12 feet below grade (the approximate top of competent bedrock). Samples collected from excavation sidewails demonstrated non-detectable concentrations of BTEX constituents. Semi-volatile organic compounds including naphthalene, fiuorene, and phenanthrene were detected in the UST excavation at concentrations ranging to a maximum of 45 mg/Kg. The spatial 2-5 TUTURAP3.TUTU#2 TUT Q07 TABLE 2-2 SUMMARY OF SOIL DATA SOIL TECH TANK REMOVAL SAMPLES June 8,1989 Tutu Esso Service Station St. Thomas, USVI TP-1 TP-2 TP-3 TP-4 TP-5 TP-6 TP-7 TP-8 TP-9 •9 J TP-10 | TP-11 TP-12 ;-x-x-x-x-x-x-x-x-x*x-Xtt-x-x-x*x-X':-x-x*x-x*x-x-x-x-x-:-:*X'X-x-x*x^ :x:x:X:::X:X.x:x:xa::x:x:x::.ra^ TP-1 3 Benzene <0.006 <0.028 0.23 J 0.002 J 1.1 <23 <0.006 0.093 <0.006 0.003 J <0.006 <0.006 <0.006 Toluene <0.006 <0.028 5.2 <0.006 <0.72 180 <0.006 <0.029 <0.006 <0.006 <0.006 <0.006 <0.006 Ethyl benzene <0.006 <0.028 2.1 0.005 J 55 0.005 J 0.52 <0.006 0.009 <0.006 <0.006 <0.006 Xylenes <0.006 1.6 E 31 E <0.006 <0.72 540 0.3 E 0.22 <0.006 <0.006 <0.006 <0.006 <0.006 Acetone <0.012 <0.057 0.014 <47 0.029 <0.057 0.005 J <0.012 <0.012 <0.012 0.11 2-Butanone Naphthalene <0.012 <0.057 0.4 BJ 3.6 BJ 19 B <0.012 <0.057 <0.012 0.005 J <0.012 <0.012 0.004 J ND ND 32 E ND 9 45E 0.3 J 1.1 ND 0.19 J ND ND ND 2-Methylnaphthalene 0.11 J 0.68 J 45 E ND 43E 1.1 0.14 J 0.18 J ND ND ND Acenaphthene ND ND 0.4 J ND ND ND ND ND ND ND ND ND ND Fluorene ND 0.18 J 1.4 ND ND 1.7 0.29 J 0.29 J ND ND ND ND ND Phenanthrene ND 0.12 J 1.1 ND 0.37 J 1.3 0.16 J 0.18J ND ND ND ND ND Anthracene ND ND 0.13 J ND ND ND ND ND ND ND ND ND ND Fluoranthracene ND ND 0.12 J ND ND 0.16 J ND ND ND ND ND ND ND Pyrene ND ND 0.21 J ND ND 0.25 J ND ND ND ND ND ND ND DI-n-Butylphthalate 0.069 BJ ND ND ND ND ND ND ND 0.063 BJ 0.094 BJ ND 0.033 BJ 0.04BJ Butylbenzylphthalate ND ND ND ND ND ND ND ND ND 0.31 J ND ND ND Bis (2-Ethylhcxyl) Phalate 0.28 BJ ND 0.4 BJ ND 0.11 BJ 0.38 BJ ND ND ND 0.36 BJ ND ND ND Lead ND ND 0.2 ND ND 0.1 ND ND ND ND ND ND ND Arsenic ND ND ND ND ND ND ND ND ND ND ND ND ND Chromium ND ND ND ND ND ND ND ND ND ND ND ND ND Selenium ND ND ND ND ND ND ND ND ND ND ND ND ND 00 O! •--J Notes: ND = Not Detected E = Estimated value above instrument calibration range B = Compound detected in blank J = Estimated value below minimum detection limit TPH = Total Petroleum Hydrocarbons EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-2 SOIL SAMPLE LOCATIONS SOIL TECH TANK REMOVAL, 6/8/89 (Page: TUT 007 1858) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18TH FLOOR NEW YORK, NY 10007 distribution of semi-volatile organic compounds mimicked that identified for BTEX constituents. Due to the limited thickness of unconsolidated deposits, if any, and the proximity of the water table beneath the present/former location of the USTs, no vadose zone remediation is proposed for this area. Rather, remediation in this area will be facilitated through hydraulic control and aqueous- phase treatment. Soil sampling activities conducted by BBL in 1993 incorporated the drilling of three soil borings (SW-1 through SW-3; Figure 2-3) and the collection /analysis of four discrete soil samples. Results of the volatile organic analyses (Table 2-3) indicated thai BTEX constituents were present in shallow soils adjacent to the dispenser island (sample SW-3, 0-2 feet). Total BTEX constituents were identified at concentrations ranging from 0.066 mg/Kg (benzene) to 1.7 mg/Kg (xylene). However, the 6-8 foot sample interval of boring SW-3 did not demonstrate detectable levels of aromatic compounds, indicating that the vertical extent of impacted soil in this area is limited to shallow depths. Samples obtained from soil borings SW-1 (8-10 feet) and SW-2 (6-8 feet) demonstrated the absence of BTEX constituents, thereby confirming the laterally confined nature of aromatic hydrocarbons detected by Soil Tech in the UST area. Chlorinated volatile organic compounds were not detected in any of the samples collected by Soil Tech during UST replacement activities or in the soil boring samples collected by BBL. 2.2.2 North Oil/Water Separator Soil quality proximal to the north oil/water separator was characterized through the collection of samples in 1993. Analytical data obtained during this investigation demonstrated the presence of soils impacted by volatile organic compounds and base neutral constituents. Data 2-6 TUTURAP3.TUTU#2 TUT OO7 1B5C? TABLE 2-3 SUMMARY OF SOIL ANALYTICAL RESULTS BB&L SOIL BORINGS Tutu Esso Station St. Thomas, USVI Bis (2-ethylhexyl) phthafate I?"o Note*: MA - Not Analyzed Volatile organic analysis conducted using EPA Method 8240; base neutrals analyzed by Method 8270; TPH analysis by Method 8015 (GC-FIO). EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-3 SOIL BORING LOCATION MAP (Page: TUT 007 1861) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18TH FLOOR NEW YORK, NY 10007 indicate that impacted soils were limited to the area immediately surrounding the former north oil/water separator effluent pipe. Volatile organic compounds were detected at their highest concentrations in samples SS-1, SS-3, SS-7 and SS-8, all collected from the eastern portion of the effluent pipe excavation (Table 2- 4 and Figure 2-4). Compounds detected at the highest concentrations included toluene, ethylbenzene, and xylenes, with a maximum reported total aromatic hydrocarbon concentration of 142.3 mg/Kg. Other volatile organic compounds detected in this area included 1,2-dichloroethene, trichloroethene, tetrachloroethene, and 1,1,1-trichloroethane. "The highest reported individual concentration was 3.2 mg/Kg of 1,2-dichloroethene at a depth of three feet in sample SS-3. Data indicate that the extent of BTEX and chlorinated volatile organic compounds is limited to the area adjacent to the western end of the north oil/water separator. Although the vertical extent of BTEX impacted soil is not completely defined, data obtained from sidewalls of the trench (which extended to a depth of approximately five feet) demonstrate a significant decrease in concentration and therefore a limited lateral distribution. Data from samples SS-4, SS-5 and SS-6 (Figure 2-4) all demonstrated BTEX levels significantly lower than the maximum concentrations reported. Analytical data also indicated that the horizontal and vertical extent of chlorinated volatile organic contamination is substantially defined. Samples SS-1 and SS-6 (separated by a distance of approximately 15 feet), both demonstrated the absence of chlorinated volatile organics, thereby defining the eastern and western extent of chlorinated impact. Samples SS-4 and SS-5 (separated by a distance of approximately 5 feet) substantially define soil impact south and north of the former north separator effluent pipe, respectively, with reported concentrations of individual chlorinated compounds less than 0.15 mg/Kg. Sample SS-1, obtained at a depth of 9 feet, demonstrated non- detectable levels of chlorinated compounds. 2-7 TUTURAP3,TUTU#2 TUT Q07 TABLE 2-4 SUMMARY OF SOIL ANALYTICAL DATA NORTH OIL/WATER SEPARATOR Tutu Esso Station St. Thomas, USVI 1,1,1-Trichloroethane 1,2-Dichlorobenzene mg/kg NA 2.8 0.84 <2 <0.38 <0.77 1.4 Naphthalene mg/kg NA 29 11 22 <0.38 19 23 Fluorene mg/kg NA 3.4 1.4 2.6 <0.38 1.4 1.6 Phenanthrene mg/kg NA 9.7 4.5 8.1 <0.38 4.3 6.1 Anthracene mg/kg NA <2.4 0.92 <2 <0.38 <0.77 1.2 Fluoranthrene mg/kg NA 3.1 1.2 2.4 <0.38 1.1 1.5 Pyrene mg/kg NA 15 6.5 9 <0.38 5.7 8 Benzo (a) anthracene mg/kg NA 5.8 2.3 4.3 <0.38 2.1 2.8 Chrysene mg/kg NA 5.1 3.6 <0.38 1.9 2.4 Bis (2-ethylhexyl) phthalate mg/kg NA 19 8.3 11 <0.38 6.7 9.2 Di-n-octyl phthalate mg/kg NA <2.4 <2 <0.38 <0.77 <0.77 Benzo (b) fluoranthrene mg/kg NA 6.1 3.8 <0.38 2.5 Benzo (a) pyrene mg/kg NA 3.2 0.97 <2 <0.38 0.88 1.1 Benzo (ghi) perylene mg/kg NA 7.7 1.6 3.4 <0.38 1.4 1.9 Gasoline Range mg/kg NA 5,000 3,000 3,000 <8 4,000 5,000 Kerosene Range mg/kg NA <4,000 <1,000 <1,000 <8 <1,000 <1,000 Diesel Range mg/kg NA <4,000 <1,000 <1,000 <8 < 1,000 <1,000 Notes: NA= Not Analyzed Volatile organic analysis conducted by EPA Method 8240; base neutrals analysed by EPA Method 8270; TPH analysis conducted by Method 8015 (GC-FID). TUT OO7 1863 EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-4 SOIL SAMPLE LOCATION MAP OIL /WATER SEPARATORS (Page: TUT 007 1864) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 Laboratory data demonstrate the presence of semi-volatile organic compounds and total petroleum hydrocarbons (TPH) in soils west of the north oil/water separator (Table 2-4). The presence and distribution of semi-volatile compounds and TPH mimics that of the aromatic compounds. In general, the highest levels were reported in the eastern portion of the excavation, at a depth of 3 feet. Samples collected at greater depths, and at locations more distant from the separator, contained lower levels of target constituents. Laboratory fingerprinting for TPH indicated the presence of gasoline-range hydrocarbons at concentrations ranging from below detection (SS-6) to 5,000 mg/Kg (SS-3 and SS-8). Kerosene range hydrocarbons and diesel range hydrocarbons were not detected in any of the soil samples. 2.2.3 Other Potential Source Areas As the above-referenced data indicate, residual contamination remains in the vadose zone soils adjacent to the north oil/water separator and the dispenser island. In addition to collecting environmental samples in these areas, discrete soil samples were collected adjacent to the south oil/water separator (Sample SS-9, Figure 2-4) and beneath the former location of the hydraulic lifts/automobile repair area (Samples SB-1, SS-la and SS-2a, Figure 2-4). As demonstrated in Table 2-3, the five soil samples collected from these locations were characterized by the absence of volatile organic compounds. Sample SS-9 did demonstrate a minor concentration of one semi-volatile compound (0.94 mg/Kg of Di-n-octyl phthalate) and the 10 - 12 and 12-14 foot sample intervals from SB-1 were characterized by gasoline range TPH concentrations of 400 and 70 mg/Kg, respectively. It is important to note that the TPH concentrations decreased with increasing depth at SB-1. Based upon field observations and these empirical data, the south oil/water separator, as well as the former hydraulic lift and automobile repair areas, were eliminated as potential sources for ground-water contamination. 2-8 TUTURAP3.TUTU#2 JUT OO7 1865 23 Ground-Water Quality Data regarding the presence and spatial distribution of soluble-phase contaminants in ground water proximal to the Esso Tutu station were obtained from on-site and adjacent monitoring wells. Specifically, wells SW-1, SW-2, SW-3, and SW-7 (Table 2-5, Figure 2-5) are located on site immediately adjacent to potential source areas. Shallow well MW-8 and deep well DW-1 are positioned along the upgradient property boundary of the Esso Tutu station. In addition, five shallow and two deep wells (located within 100 feet of the station property) were incorporated into the monitoring array to evaluate the potential for ground-water quality impact resulting from operation of the Esso station. These wells, and their locations relative to the station property are summarized below: Well Designation Relative Location CHT-2 southwest and downgradient of both the north and south oil/water separators CHT-3 south and immediately downgradient of the USTs CHT-4 northwest and upgradient of the site CHT-7D south and downgradient of the USTs MW-9 southwest of the north oil/water separator and due west of the south oil/water separator M W-10 south and downgradient of the USTs M W-1OD south and downgradient of the USTs Based upon analytical data obtained from a total of IS monitoring wells sampled by BBL (April 1994), and confirmed through Phase II RI sampling by Geraghty & Miller (June 1994); a commingled aromatic hydrocarbon plume exist straddling a perched water zone and the shallow portion of the aquifer beneath and immediately adjacent to the Esso Tutu station. 2-9 TUTURAP3.TUTU#2 TUT 007 1866 TABLE 2-5 SUMMARY OF GROUND-WATER ANALYTICAL RESULTS Tutu Esso Service Station and Adjacent Areas St. Thomas, U.S.V.I. SW-1 5W-2 SW-3 SW-4 sw-s SW4 SW-7 DW-1 DW-2 Benzene pg/L 3700 1400 550 J 12000 10000 J <5 <5 <5 160 99J <5 <5 Toluene pg/L 1800 1800 360 J 3400 3200 J <5 <5 <5 16 <100 <5 Ethylbenzene pg/L 2000 1000 <1000 2200 4100 J <5 <5 <5 110 <100 Xvtenes (total) pg/L 8100 4000 1800 J 10300 22000 J <5 <5 <5 171 82 Methyl Terl Butyl Ether ugA. 42000 52000 35000 J 110000 89000 J 10 6.3 J <5 <50 <50 1600 1500 J 19 16 J 21 19 J TCE ug/L <250* <250' <1000" <250* <1000* <5 4J <5 2J <5 <5 <100 15 10 J 5J PCE pg/L <250* <250* <1000* <250" <1000* 18 15 J 4J <5 <100 62 42 J 14 18 1.2-DCE (total) pg/L <250* <250* <1000* <250* <1000* 46 38J 4J <5 <5 <100 130 92 J 33 43 Vinl Chloride pg/L <500* <500' <1000' <500* <1000* <100 j iBtiljg Gasoline Range mg/L 120 25 NA 310 NA NA NA NA NA NA NA Kerosene Range mg/L <4 <4 NA <40 NA NA NA NA <4 NA NA NA Diesel/02 Range <4 NA <40 NA NA NA NA <4 NA NA NA Naphthalene ug/L 60 <100 1300 1000 J 60 96J Fluorene pg/L <4 <2 40 40 J <2 <2 <2 4J <2 Phenanthrene pg/L 40 32 J <2 <2 <2 3J <2 <2 Anthracene pg/L <50 <2 Pytene Mg/l <2 8J <2 <2 <2 2J <2 Chrysene pg/L 9J Benzo(a)pyrene pg/L 0.3 0.7 <50 0.3 Benzofg, h, ijperylene pg/L 1.4 <50 <5 1.4 c Benzo(b)fluoranthrene pg/L 2.1 <50 0.5 Calcium mg/L 39.5 NA 14.3 J 91.3 86.2 J NA 44.6 NA 52.9 NA 85.7 85 82.5 J 48.5 45 NA 242 Iron mg/L 5.7 MA 14.1 98 108 NA 5.1 NA 18.6 NA 20.3 J 17.5 14.8 J 222 1.1 NA 3.1 Total Suspended Solids mg/L 120 NA 284 2820 324 NA 117 NA 182 NA 159 260 783 18 NA 15 Carbon Dioxide mg/L 835 1190 NA 1020 NA 533 NA 543 NA 752 NA 858 NA 566 NA 577 NA Dissolved Oxygen mg/L 7.6 3.2 NA 5.2 NA 2.4 NA 9.5 NA 2.7 NA NA NA 1.9 NA -- TABLE 2-5 (continued) SUMMARY OF GROUND-WATER ANALYTICAL RESULTS Tutu Esso Service Station and Adjacent Areas St. Thomas, U.S.V.I. CHT-2 CHT-3 CHT-4 CHT-7D MW-8 MW-9 MW-10 MW-10D MW-12D Analytical Parameter | Units 4/11/94 4/11/94 6/1/94 4/11/94 4/11/94 6/2/94 4/7/94 6/3/94 4/7/94 4/8/94I 4/8/94 D J 5/31/94 4/8/94 I 5/31/94 4/8/94 5/20/94 Benzene UO/L 1900 1700 <5 <5 <5 11 <5 <5 <25 <5 <5 Toluene ug/l <5 <50 180 <5 <5 <25 <5 <5 Ethylbenzene MO/L <5 1500 1800 <5 <5 <5 39 <5 <25 <5 <5 o-Xylenes van. <5 1153 2000 <5 <5 <5 <5 <5 <25 <5 Methyl Tert Butyl Ether ng/t 870 15000 13000 14 28 J 10 17 J 450 420 430 340 J 130 170 J 39 360 J TCE pg/L <5 <50* <100* 16 14 10 10 J <5 14 12 18 J 11 14 J <5 9J PCE <5 <50* <100* 50 50 36 32 38J <5 22 19 34J 39 48J <5 33J 1,2-DCE (total) ng/t <50* <100* 150 140 91 89 88J <5 57 51 76 J 100 110 J <5 67 J Vinyl Chloride pg/L <100* <100* 17 16 <25 Gasoline Range mg/L 69 NA NA NA 5.1 NA NA NA Kerosene Range mg/L NA <4 NA NA NA NA NA DieseW»2 Range Naphthalene mg/L NA NA NA NA NA pg/L 260 310 NA Fluorene MBA <2 6J <2 <2 <2 Phenanthrene pg/L <2 4J <2 <2 <2 <2 <2 <2 <2 Anthracene pg/L <20 Pyrene H8A <2 <20 <2 <2 <2 <2 ' <2 <2 Chrysene pg/L <20 Benzo(a)pyrene pg/L <20 <2 Benzo(fl.h,i)perylene PQfl- <20 Benzo(b)fluoranthrene <20 <3^tilit:V^ttt:Cnit«»«)aty::;ig Calcium mg/L MA NA NA NA 44 NA 60.8 NA NA NA 31.2 NA 38.6 NA 30.6 Iron mg/L MA NA NA NA 0.1 NA 49.7 NA NA NA 1.4 NA 0.6 NA 0.3 Total Suspended Solids mg/L NA NA 12300 NA NA NA 478 NA NA NA 45 NA NA Carbon Dioxide mg/L 623 834 NA 552 523 NA 572 NA 640 511 551 NA 516 NA 40 NA Dissolved Oxygen mg/L 2.1 NA 2.9 3.4 NA NA 1.9 2.1 NA 2.5 NA 4.7 NA NA = Not Analyzed R = Rejected J = Estimated Value 'Elevated chlorinated organic detection limit as a result of aromatic hydrocarbon concentrations. H- CO TABLE 2-5 - ADDENDUM SUMMARY OF GROUND-WATER QA/QC SAMPLES APRIL 1994 H-ill 0- ••0 Tutu Esso Service Station and Adjacent Areas St. Thomas, U.S.V.I. Addendum Analytical Parameter Benzene Toluene Ethylbenzene o-Xylenes m&p-Xylenes Methyl Tert Butyl Ether TCE PCE 1,2-DCE (total) Vinyl Chloride Total TB Units (4/8/94) (4/14/94) TB EB EB Bailer Pump pg/L pg/L pg/L pg/L pg/L pg/L pg/L pg/L pg/L pg/L <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 Gasoline Range Kerosene Range Diesel/#2 Range mg/L mg/L mg/L Naphthalene Fluorene Phenanthrene Anthracene Pyrene Chrysene Benzo(a)pyrene Benzo(g,h,l)perylene Benzo(b)fluoranthrene Calcium Iron Total Suspended Solids Carbon Dioxide Dissoived Oxygen pg/L pg/L P9/L pg/L pg/L pg/L pg/L pg/L pg/L NA NA NA NA NA NA <A NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA <50 <5 <5 <1 <3 NA NA NA NA NA NA NA NA NA mg/L mg/L mg/L mg/L mg/L NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-5 GROUNDWATER ISOCONCENTRATION MAP TOTAL BTEX IN UG/L, 4/94 (Page: TUT 007 1870) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 Aromatic hydrocarbons and semi-volatile compounds emanate from the area of the north oil/water separator; and the vicinity of the pump island. Table 2-5 summarizes ground-water analytical data, while maps depicting the distribution of aromatic hydrocarbons and synthetic chlorinated compounds are presented as Figures 2-5 and 2-6, respectively. 2.3.1 North Oil/Water Separator The distribution of aromatic hydrocarbons associated with the north oil/water separator is characterized by the presence of BTEX, MTBE and select semi-volatile organic compounds. Data from SW-7 demonstrate the presence of BTEX constituents at individual concentrations ranging from a minimum of 16 ug/L (toluene) to a maximum of 230 ug/L (xylene). MTBE was detected at a concentration of 1,600 ug/L in well SW-7. Semi-volatile compounds detected in this well included naphthalene, phenanthrene, pyrene, and chrysene. Naphthalene was detected at the highest concentration (60 ug/L), while the remaining semi-volatile compounds were present at concentrations equal to or less than 4 ug/L. Although soluble-phase aromatic hydrocarbons are present in the ground water proximal to the north oil/water separator, data from adjacent wells indicate that the spatial distribution of the plume is limited, confined primarily to the perched water zone proximal to SW-7. Total BTEX concentrations at wells CHT-2 and MW-9, both located 20-30 feet southwest of SW-7, were less than or equal to 50 ug/L. Additional data from wells CHT-2 and MW-9 has demonstrated the absence of semi-volatile compounds, with the exception of fluorene (5 ug/L at MW-9), and a significant decrease in MTBE concentrations. Ground-water quality data obtained from SW-7 (screened in the perched water horizon) by BBL, and subsequently by Geraghty & Miller, have demonstrated the absence of chlorinated volatile organic compounds (Table 2-5). These data indicate that chlorinated compounds present 2-10 TUTURAP3.TUTU#2 TUT OO7 1871 EPA REGION II SCANNING TRACKING SHEET DOC ID #65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 2-6 GROUNDWATER CONTAMINANT DISTRIBUTION CHLORINATED IN UG/L, 4/94 (Page: TUT 007 1872) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 in soils in the vicinity of the north oil/water separator have not impacted the saturated zone. Chlorinated compounds were absent in well MW-9, while ground water obtained from well CHT-2 demonstrated a concentration of 1,2-dichloroethene of 6 ug/L (Figure 2-6). It is important to note that 1,2-dichloroethene was detected in well CHT-4 (located upgradient of wells CHT-2, MW-9, and the Esso station) at a concentration of 150 ug/L. 23.2 Underground Storage Tanks/Pump Island Similar to the distribution of aromatic hydrocarbons observed proximal to the north oil/water separator, soluble constituents detected in the vicinity of the site underground storage tanks and dispenser island were characterized by the presence of BTEX, MTBE, and PAHs. Based upon the observed spatial distribution and constituent concentration gradients, it has been concluded that this plume originates from the area adjacent to the dispenser island. The highest concentrations of total BTEX constituents (27,000 ug/L) was detected in well SW-3, located immediately downgradient of the dispenser island. Concentrations of total BTEX constituents decreased south of the dispenser island with the downgradient extent of the plume defined by the absence of aromatic hydrocarbons in monitoring wells MW-10 and MW-10D (located approximately 50 feet south of the Esso Tutu property line and USTs). MTBE was detected in monitoring wells proximal to the USTs and pump island with reported concentrations ranging from 42,000 ug/L (SW-1) to 110,000 ug/L (SW-3). Similar to the BTEX distribution, data regarding MTBE concentrations demonstrated a significant decrease in concentration south (downgradient) of the dispenser island. Of the 18 monitoring wells sampled by BBL, four demonstrated the presence of semi- volatile organic compounds (SW-1, SW-3, SW-7, and CHT-3, Table 2-5). Semi-volatile organic compounds detected included naphthalene, fluorene, phenanthrene, anthracene, and pyrene. Of 2-11 TUTURAP3.TUTU#2 TUT OO7 1873 these compounds, naphthalene was detected at the highest concentration (1300 ug/L in well SW- 3), the remainder of the compounds were detected at concentrations less than, or equal to, 40 ug/L. Ground-water samples from wells CHT-2, SW-2 and MW-10 demonstrated the absence of semi-volatile compounds, thereby defining the spatial distribution of ground-water quality impact from these compounds. These data indicate that the aromatic and semi-volatile constituents exhibit a consistent spatial distribution, confirming a common source area. Ground-water analytical data demonstrated the absence of chlorinated organic compounds in both on-site and off-site monitoring wells positioned downgradient of potential VOC source areas on the Esso service station (Figure 2-6). Specifically chlorinated compounds were not detected in well MW-9 (downgradient of the north oil/water separator and immediately adjacent to the south oil/water separator), well SW-7 (immediately downgradient of the north oil/water separator), and wells SW-1, SW-2, and SW-3 (downgradient of the dispenser island and USTs). 2.3.3 Phase-Separated Hydrocarbons Phase-separated hydrocarbons have been detected sporadically on and immediately adjacent to the Esso service station property. Geraghty & Miller detected floating product in monitoring wells MW-9 and MW-9S during the period September through November 1992. Specifically, well MW-9 was characterized by a product sheen on only one occasion, while well MW-9S demonstrated the presence of phase-separated hydrocarbons on four occasions (September 17, September 28, October 28, and November 16, 1992), ranging in thickness from a sheen to 0.11 foot. Subsequent measurements in these two wells have demonstrated the absence of a free-floating product layer. Monitoring well SW-7, located on the station property, has also sporadically demonstrated the presence of phase-separated hydrocarbons. This well exhibited 2-12 TUTURAP3.TUTU#2 TUT OO7 1874 the presence of 0.01 foot of product on December 20, 1993 (shortly after installation); two subsequent measurements demonstrated the absence of phase-separated liquids in this well. Floating product has not been detected at any of the remaining on-site monitoring wells. 23.4 Regional Ground-Water Quality As previously stated, chlorinated compounds were not detected in ground-water samples collected downgradient of potential VOC source areas on the service station property. In contrast, chlorinated compounds have been detected in the regional ground-water flow field both upgradient and downgradient of the service station (Figure 2-6). The most important characteristic with regard to the presence of these compounds in the environment, is the consistency in their absolute concentrations and relative weight percent ratios upgradient and downgradient of the Esso service station property. Tetrachloroethene (PCE), trichloroethene (TCE), and 1,2-dichloroethene (DCE) demonstrate consistent concentrations and relative weight percent ratios in monitoring wells north (upgradient) and south (downgradient) of the service station. For example absolute concentrations of PCE, TCE, and DCE in wells CHT-4 and CHT- 7D (Table 2-6) are almost identical, as are the relative weight percent ratios of the individual constituents. If a statistical comparison is made between the relative weight percent ratios of PCE, TCE and DCE for those wells upgradient and downgradient of the service station, an excellent correlation is observed which exhibits minimal variability (e.g., 0.05 for PCE and 0.05 for DCE). These data indicate that there is no statistical increase in the concentration of chlorinated volatile organic compounds downgradient of the Esso station when compared to regional ground-water quality. TUTURAP3.TUTU#2 2-13 TUT OO7 1875 oo TABLE 2-6 CHLORINATED VOC STATISTICAL ANALYSIS Tutu Esso Service Station St. Thomas, USVI CHT-4 (upgradient) CHT-7D (downgradient) MW-8 (upgradient) MW-10 (downgradient) MW-10D (downgradient) Average Relative Weight % Coefficient of Variability Tetrachloroethene Concentration (ug/L) 50 50 32 22 39 Relative Weight %• 23.1 24.5 24.6 23.6 26 24.4 0.05 Trichloroethene Concentration (ug/L) 16 14 9 14 11 Relative Weight % 7.4 6.9 6.9 15.1 7.3 8.72 0.41 1,2-Dichloroethene Concentration (ug/L) 150 140 89 57 100 Relative Weight % 69.5 68.6 68.5 61.3 66.7 66.92 0.05 H- 0? SECTION 3.0 PROPOSED REMEDIAL PROGRAM 3.1 Conceptual Model Based upon available, site-specific, empirical soil and ground-water quality data, remedial activities at the Esso Tutu station are presently anticipated to incorporate the following objectives: • remove phase-separated hydrocarbons, if any, from the saturated zone; • abate residual sources, to the extent feasible, in the unsaturated zone adjacent to the dispenser island and north oil/water separator; and • capture and remediate, if feasible, the aromatic hydrocarbons emanating from the dispenser island and north oil/water separator. Although the collection of supplemental design data is required through on-site pilot testing, the current conceptual design of the remedial action program incorporates soil vapor extraction to address potential residual source areas in the vadose zone, and a combination of air sparging and fluid extraction to capture and mitigate the presence of dissolved and phase- separated hydrocarbons from the saturated zone. Final design specifications may vary pending results from pre-design studies (Section 4.0) and initial system operation. 3.2 Vadose Zone Remediation As previously noted, the absence of a significant quantity of unconsolidated deposits and the proximity of the water table preclude vadose zone remediation in the former/present location of the site USTs. The conceptual plan for remediating soils in the vadose zone adjacent to the north oil/water separator and dispenser islands employs soil vapor extraction. Although pilot tests have not been completed to date, physical characteristics of both the subsurface materials 3-1 TUTURAP4.TUTU#2 TUT CO 7 1877 and site contaminants indicate that vapor extraction will prove to be an effective vehicle for reducing contaminant concentrations. The vapor extraction system will be used to treat soils in- situ, eliminating physical and logistical concerns associated with excavating soils proximal to, or beneath, building structures. It is anticipated that horizontal extraction trenches/piping, as opposed to vertical extraction wells, will be installed in the two areas demonstrating soil impact. One extraction trench will most likely be installed within the existing excavation adjacent to the north oil/water separator. This trench will likely extend to a depth of six to seven feet below grade and maintain its present length. The trench will be lined with a perforated PVC pipe and backfilled with crushed stone. A solid section of PVC pipe will extend to the ground surface to facilitate the connection of the drain pipe to a vacuum manifold. The surface of the trench will be sealed with a layer of asphalt to eliminate short circuiting of the vapor extraction system. A soil vapor extraction trench, installed adjacent to the gasoline dispenser island, will be constructed in a similar fashion. It is presently anticipated that this trench, at a minimum, will extend the length of the dispenser island at a distance of approximately ten feet from, and parallel to, the island. The two extraction trenches will be connected to a centralized vacuum pump via solid PVC piping installed below grade. A moisture "drop out" or extraction vessel will be utilized to eliminate water and paniculate damage to the vacuum pump. It is anticipated that treatment of the off-gas will be required initially. This treatment will most likely be provided through portable vapor phase carbon canisters, pending review of pre-design data, applicable regulations, and discussions with Department of Planning and Natural Resources (DPNR ). Based upon preliminary information obtained from DPNR, construction and operation of a vapor extraction system will require two permits: 1) an Earth Change Permit, to facilitate the installation of subsurface piping; and 2) an Air Discharge Permit or de minimis waiver. 3-2 TUTURAP4.TUTU#2 UT 0O7 1878 System effectiveness monitoring will be provided through periodic influent and effluent sampling, as well as the collection of in-situ soil samples at the point in time at which the system influent concentrations exhibit an asymptotic minimum. The specific schedule for collection of monitoring samples will be developed subsequent to completion of pilot scale testing. 3.3 Saturated Zone Remediation It is presently anticipated that the saturated zone remediation system will incorporate the extraction of ground water from three areas utilizing four existing monitoring wells (MW-9, SW- 7, SW-1 and CHT-3). Based upon available aquifer hydraulic data, each extraction well will be pumped at a rate of 0.50 - 1.0 gallons per minute (gpm). Extraction of ground water at a rate of 0.50 - 1.0 gpm will produce a capture zone which extends an estimated 20 to 30 feet in a lateral direction and approximately ten feet downgradient (downgradient stagnation point from each recovery well). The combined effect of withdrawing ground water from these four wells is presently anticipated to establish hydraulic control over the distribution of aromatic and semi- volatile constituents emanating from the Esso Tutu station (Figure 3-1). Increased accuracy regarding the dimensions of the true capture zone will be possible subsequent to the implementation of a short duration pumping test in several of the identified wells. Based upon available liquid level data, it is not anticipated that the volume of phase- separated hydrocarbons, if present, will justify the installation of a dedicated/automated NAPL extraction system. Liquid level measurements will be obtained from site monitoring wells on a periodic basis to evaluate the presence/absence and accumulation rate of phase-separated hydrocarbons. Initially, any accumulation of NAPL will be manually extracted from both monitoring and/or recovery wells through hand bailing. Hydrocarbon product will be stored on site in a fifty-five gallon drum for eventual off-site disposal. 3-3 T. TUTURAP4.TUTU#2 ~ ' °°7 J.S79 EPA REGION II SCANNING TRACKING SHEET DOC ID # 65009 DOC TITLE/SUBJECT: TUTU WELLS SUPERFUND SITE FIGURE 3-1 CONCEPTUAL HYDRAULIC CAPTURE ZONES (Page: TUT 007 1880) THIS DOCUMENT IS OVERSIZED AND CAN BE LOCATED IN THE ADMINISTRATIVE RECORD FILE AT THE SUPERFUND RECORDS CENTER 290 BROADWAY, 18™ FLOOR NEW YORK, NY 10007 Extracted ground water will be pumped from the extraction wells to an on-site treatment system. The treatment system will consist of an air stripper and liquid-phase granular activated carbon (GAC) canisters, and will be installed in a secured building, located along the southern perimeter of the site. Preliminary designs indicate that the air stripper will be one foot in diameter, have a packed height of approximately 8 -10 feet, and an overall height of approximately 14 feet. Ground-water effluent from the air stripper will be passed through two GAC canisters prior to discharge. The canisters, each 55 gallons in size, will be used as polishing devices to ensure that discharge requirements are satisfied. This treatment technology has been utilized successfully at the site to treat ground water generated during well development and sampling activities performed as part of the RI, and has demonstrated the ability to reduce volatile organic compound concentrations below Federal Drinking Water Standards. At present, it is expected that treated ground water will be transferred, via an underground pipe, to the storm sewer, located approximately 80 feet west of the treatment area. Based upon preliminary discussions with DPNR, the Department of Public Works (DPW), and the Water and Power Authority (WAPA), treatment and discharge of extracted ground water will require the following permits: 1) a NPDES permit; and 2) a utility connection permit. The necessity to obtain an air discharge permit, as opposed to a de minimis waiver, will be evaluated based upon influent data obtained during proposed pump testing activities. The primary purpose for incorporating air sparging into the proposed remedial action program is to increase dissolved oxygen concentrations within the contaminant plume boundaries, thereby stimulating biodegradation of hydrocarbon compounds. It has been demonstrated that biodegradation is one of the most effective and efficient means of achieving mass reduction of soluble-phase aromatic hydrocarbons. The primary mechanism for the breakdown of hydrocarbons is aerobic degradation, therefore the limiting factor, with respect to the rate of biodegradation, is the amount of dissolved oxygen available for microbial activity. Numerous case studies have TUTURAP4TUTU#2 TUT 007 1881 demonstrated the dramatic impact that elevating dissolved oxygen concentrations can have on the time required to reduce plume mass. It is presently anticipated that air sparging will be conducted in wells either upgradient and/or adjacent to the proposed recovery wells (e.g., SW-2, SW-3, and MW-9S). 3-5 TUTURAP4.TUTU#2 .... .._ 'UJ 007 1832 SECTION 4.0 SUPPLEMENTAL EWESTIGATION/PRE-DESIGN ACTIVITIES Supplemental data collection activities will be required to formulate detailed design specifications for both the ground-water withdrawal and soil vapor extraction programs. It is important to note that these data are not required to determine if these technologies will effectively abate the presence of volatile and semi-volatile organic compounds at the site. Soil vapor extraction and ground-water sparging/extraction have been proven successful and efficient with respect to removing the same contaminants from a large number of analogous sites. Supplemental data regarding soil vapor extraction rates, ground-water extraction rates, vapor and liquid-phase influent concentrations, zones of capture, and mass loading rates are required to more accurately design a cost-efficient treatment system. 4.1 Vadose Zone Remediation Requisite activities related to the final design of the unsaturated zone remediation program will involve vacuum tests at well locations SW-3 and SW-7 to measure air flow rates, document areas of influence, and quantify influent concentrations. Data from these two wells will be utilized to size a vacuum blower and estimate vapor phase carbon saturation rates. The vacuum tests will involve the application of negative pressure to each extraction well, while monitoring the pressure differential in adjacent monitoring wells. It is estimated that a series of step tests will be performed with varying degrees of vacuum exerted on either well SW-3 or SW-7. Each step test will last approximately one hour. Tests will be terminated when data indicate that a steady-state pressure distribution has been obtained. Test results will be utilized to determine optimal extraction rates and predict radii of influence. Vapor samples will 4-1 TUTURAP5.TUTU#2 . ...-, 1.883 TUT 00/ be collected for subsequent laboratory analysis to quantify the concentrations of organic constituents in the influent gas stream. 4.2 Saturated Zone Remediation The primary activity required to develop a final design for the ground-water extraction and air sparging system is the completion of a series of 2-4 hour step pumping tests. Data from these tests will be used to quantify aquifer characteristics such that an effective and efficient system can be designed to establish hydraulic control in the area of the aromatic hydrocarbon and semi-volatile organic contamination. The step tests will be performed at monitoring wells SW-1, SW-7, and MW-9. It is expected that 2-3 tests will be conducted at each well, with extraction rates ranging from 0.25 gpm to 1.0 gpm. Tests will be performed sequentially so that stresses to the saturated zone can be isolated. In addition, the aquifer will be allowed to recover to 80% of its original elevation prior to commencement of the subsequent tests. Data obtained from the aquifer tests will be analyzed using one or more of the methods described by Theis (1935), Cooper and Jacob (1946), and Boulton and Streltsova (1976). The data will be evaluated to determine the capacity of the aquifer to yield water and to define sustainable extraction rates for operation of the ground-water collection system. Other than the collection of supplemental data regarding the concentration of dissolved oxygen and carbon dioxide from select site monitoring wells, no additional data is required to develop and implement an air sparging system. 4-2 TUTURAP5.TUTIM2 TUT OO7 1884 SECTION 5.0 IMPLEMENTATION SCHEDULE 5.1 Tentative Implementation Schedule Based upon our present understanding of site conditions, and assuming that unexpected delays are not encountered as a result of: agency review (EPA and DPNR); permitting; off-site access; weather; or procurement of equipment, a tentative schedule has been developed for the implementation of the remedial action program at the Esso Tutu station (Table 5-1). 5-1 TUTURAP6.TUTU#2 cH TABLE 5-1 Tentative Implementation Schedule Tutu Esso Service Station St. Thomas, USVI Task EPA Review of Site Remediation/Supplemental Investigation Report Scheduling of Supplemental Data Collection Activities Implementation of Supplemental Data Collection Activities Z" '»* Laboratory Analysis of Site Samples Final Design of Ground-Water/Vapor Extraction Systems EPA Review of Final System Design Specifications and Proposed Monitoring Schedule Procurement of Applicable and Appropriate Permitts Procurement of Equipment Scheduling of System Installation Installation of Remediation Systems System Startup and Calibration Initial Phase of System Operation and Monitoring Total Estimated Schedule (Weeks) Time in Weeks (Following Submittal of Report to EPA) 4 3 2 2 4 4 8* 8* 3 3 1 2 36 * - Tasks implemented concurrently