USVI Public Records

Document text

'J^GERAGHTY & MILLER, INC. Environmental Services Ground Water Engineering Hydrocarbon Remediation Education September 23, 1991 Mr. Leo Francis Commissioner Department of Public Works No. 8 Subbase St. Thomas, U.S. Virgin Islands 00802 Re: Request for Temporary Discharge of Groundwater to Treatment Plant. Dear Commissioner Francis: Geraghty & Miller, Inc. will be conducting a ground-water investigation in the Tutu, St. Thomas area. The investigation work plan is expected to be approved by the U.S. Environmental Protection Agency (USEPA) within approximately two . weeks. Approximately 40,000 to 45,000 gallons of ground-water will be generated during the investigation, primarily during the purging of monitoring wells for sampling and pump testing. The USEPA has indicated this ground water must be handled as a waste. Geraghty & Miller would like to request authorization for a temporary discharge of the generated ground water to the nearest wastewater treatment facility. Ground-water quality sampling of existing wells in the Tutu area has been conducted since September 1990 under the supervision of USEPA and U.S. Virgin Islands Department of Natural Resources (DPNR) representatives. The proposed ground-water investigation will include the installation of ten shallow monitoring wells and seven deep monitoring wells in the Tutu area (see Figure 1). After the monitoring wells are installed, each well will be developed by pumping to improve the efficiency of the well. After well development, the monitoring wells will be purged to remove non-representative ground water prior to two water-quality sampling events. 201 West Passaic Street, 3rd Floor• Rochelle Park, New Jersey 07662-(201) 909-0700-FAX pnn 909-0567/0568 TUT 006 1893 *64917* 64917 GERAGHTY & MILLER. INC. Aquifer testing, consisting of step tests and pumping tests, will be carried out in between the two ground-water sampling events. Based upon a preliminary telephone conversation between Ms. Mary Cornwall, Department of Public Works, and Thomas Danahy, Geraghty & Miller, Inc., we have provided an estimate of our expected discharge volumes and concentrations of volatile organic compounds (VOCs). Table 1 presents a summary of the anticipated ground water discharge volumes. Table 2 presents an estimate of the average VOC concentration that will be present in the generated ground water. The five VOCs listed on Table 2 are the only compounds detected above trace concentrations. The VOC averages were calculated using the maximum values detected in the Four Winds II and Tillett well samples during three sampling events conducted from September 1990 through June 1991. The Tillett well samples have consistently contained elevated VOC concentrations. The Four Winds n and Tillett wells are both situated in the center of the study area. The average of the maximum VOC values for the Tillett and Four Winds II samples (Table 2) is considered to be representative of the average VOC concentrations that would be present in the proposed monitoring well ground water. A field gas chromatograph (GC) will be onsite throughout the investigation, allowing for rapid determination of VOC content of samples. If required, additional laboratory analysis could be performed as confirmation of the field GC results. If necessary, the ground water could be temporarily stored onsite until the analytical results were available. Please let us know if the proposed discharge is feasible. If necessary, pre-treatment (using carbon adsorption or air stripping) may be performed to meet required discharge VOC limitations. TUT O06 GERAGHTY & MILLER. INC. 3 Geraghty & Miller, Inc. and the USEPA would like to finalize the project work plan within the next two weeks. Your timely response to our request would be greatly appreciated. Sincerely, GERAGHTY & MILLER, INC. Thomas V^Danahy enior~Scienti5t/Sroject Manager Daniel A. Nachman Vice President/Project Director c: Julie May Monsanto, USVI-DPNR Sarah Odland, CDM Ana Gloria Ramos, TEIC TVD:nr PRQ1301/092191.1tr TUT 006 1895 Table 2. Average Concentration of Volatile Organic Compounds in Tutu Study Area, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands. Four Winds II Tillett Average VOC Parameter Highest Value* Highest Value* Value 1,2-Dichloroethene 230 400 315 Trichloroethene 21 72 46.5 Tetrachloroethene Benzene Vinyl Chloride 90 ND ND 180 27 17 135 13.5 8.5 All values reported in micrograms per liter (ug/L). Analyses performed using USEPA Method 524.2. High concentration samples were diluted and analyzed using USEPA Method 624. * Highest value detected during three sampling events September/October 1990, February 1991 and June 1991. ND Not detected. PROBOl&vccvo GERAGHTY & MILLER. INC. TUT OO6 .1896 Table 1. Schedule of Ground-Water Discharges, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands. Weeks from Project Start Activity Estimated Volume of Generated Ground Water (gallons) 13-15 17-18 21-22 31-32 Monitoring Well Development Monitoring Well Purging - Sampling Round 1 Step Tests and Pumping Tests Monitoring Well Purging- Sampling Round 2 5,100 2,800 33,100 2,800 Estimated Total 43,800 gallons PRODOl/jbcdwd GERAGHTY & MILLER, INC. TUT 006 1897 DEALERSHIP . / MW-10 X SOIL BORING SHALLOW MONITORING W£LL A DEEPER MONITORING WELL • EXISTING SUPPLY WELL SITE PLAN TUTU SERVICE STATION INVESTIGATION ST. THOMAS, U. S. VIRGIN ISLANDS & M Her. Inc. TUT 006 1898