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^GERAGHTY & MILLER, INC Environmental Services Ground Water Engineering Hydrocarbon Remediation Education March 11, 1992 Commissioner Leo Francis Department of Public Works #8 Sub Base, Crown Bay St. Thomas, U.S. Virgin Islands 00802 Re: Request for Temporary Authorization of Ground-Water Discharge to Sanitary Sewer in the Tutu Area, St. Thomas, U.S. Virgin Islands. Dear Mr. Restovic: Pursuant to our previous correspondence and discussions, Geraghty & Miller, Inc. is formally requesting temporary authorization of a ground-water discharge to the sanitary sewer in Tutu, St. Thomas. Geraghty & Miller will be conducting a ground-water investigation in the Tutu area in accordance with a work plan which has been approved by the U.S. Environmental Protection Agency (USEPA). The objectives of the work plan are to delineate the potential sources, the horizontal and vertical extent, and the potential migration pathways of petroleum hydrocarbon products in soil and ground water in the vicinity of Route 38 within the Tutu Well Site (see Figure 1). The ground-water investigation will include the installation of ten shallow monitoring wells and seven deep monitoring wells. Approximately 45,000 gallons of ground water will be generated during the investigation, primarily during aquifer pumping tests and ground-water sampling. Figure 2 presents the layout of the proposed treatment system. Prior to discharge, the ground water will be treated by airstripping and carbon adsorption to meet federal drinking water standards. Table 1 presents volatile organic compounds (VOC) levels detected during previous sampling rounds of two existing water supply wells (FW n and T-1) located in the center of the Tutu Wells site (see Figure 1). These data represent results from the sampling rounds conducted in September/October 1990, February 1991, and June 1991. The FW n Well and the T-1 Well are expected to be representative of the ground-water concentrations in the Tutu Wells Site. To develop the design basis (worst case) scenario, the 201 West Rassaic Street, 3rd Floor • Rochelle Park, New Jersey 07662 •(201) 909-0700 • FAX (201) 909-0567/0568 TUT OO6 181B *64906* 64906 •GERAGHTY & MILLER, INC. 2 highest concentration of each constituent detected during sampling of the FW n Well and the T-l Well was used as the influent concentration to the air stripper (Table 1) for CASE 1 (Figure 3). Since benzene, toluene, ethylbenzene, and xylenes (BTEX) may be present at higher levels than detected, the concentration of each was increased to 100 parts per billion (ppb) for CASE 2 (Figure 4). This modification provides a degree of conservatism such that if high concentrations of BTEX are present, the air stripper should be adequate to reduce effluent concentrations to discharge standards. Discharge standards shown in Table 2 have been established at USEPA Maximum Contaminant Levels (MCLs), or USEPA Maximum Contaminant Goals (MCLGs). Calculations show that an air stripper tower design having a diameter of 1 foot, a packed height of 8 feet, and an overall height of 14 feet will be adequate to reduce the influent concentration to the required level. The packing used in the design was 1-inch Jaeger Tripacks (typical for a small diameter tower). The limiting constituent establishing the packed height is 1,2-dichloroethene at a level of 400 parts per billion (ppb). The predicted effluent concentrations are presented on Table 3 for the maximum influent concentrations (CASE 1) and modification for BTEX (CASE 2). The air discharge is calculated to be 0.005 and 0.008 pounds per hour (Ibs/hr), respectively, for CASE 1 and CASE 2 on Table 3. Flow rates to the air stripping system are expected to be the highest during aquifer pumping testing (10 gpm). Therefore, a design flow of 15 gpm was selected for the air stripping system. The process flow involves discharge from the wells to a feed tank, through the air stripper, carbon adsorption units, discharge line, and finally to the sanitary sewer. Figure 3 shows the process flow for CASE 1 and the discharge rate of the constituents in pounds per hour to the feed tank, atmosphere, carbon adsorption units, and sanitary sewer. Figure 4 shows the same information for CASE 2. The water treatment system will be located at the Esso gasoline station, on Route 38, in the Tutu area (see Figure 2). Construction of the water treatment system is anticipated to start in mid-May 1992. Ground-water will be pumped from proposed Monitoring Wells MW-10 and TUT 006 1819 GERAGHTY & MILLER, INC. MW-10D to determine aquifer characteristics (see Figure 2). Operation of the water treatment system will occur infrequently through November 1992 (see Table 4). At least two samples (one influent sample and one treatment effluent sample) will be collected and analyzed for volatile organic compounds using USEPA Method 524.2 during each operation of the treatment system to document the effectiveness of the treatment system. The temporary discharge piping will be installed in compliance with Occupational Safety and Health Administration (OSHA) regulations. Signs and physical barriers (e.g., caution tape) will be installed as needed to minimize physical hazards associated with discharge piping in pedestrian pathway areas. In addition, discharge piping will be removed from pedestrian pathway areas when the system is not in operation. If you have any questions or require additional information, please call. Sincerely, GERAGHTY & MILLER, INC. Clinton Moffatt Staff Scientist Thomas V. Danahy Senior Scientist/Project Manager Enclosure c: May Cornwall, DPW Mirko Restovic, DPW Ana Gloria Ramos, TEIC CM:(v 4nt0130lHf2AB1192.hr Daniel A. Nachman Vice President/Project Officer TUT OO6 1820 Table 1. 0- r" CO K3 Summary of Detected Concentrations of Volatile Organic Compounds in Ground-Water Samples Collected from September 1990 to June 1991; Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands. CONSTITUENT Vinyl Chloride 1,2-Dfchtoroethene Chloroform Trichloroethene 1,1,2-Trfchloroethene Tetrachtoroethene Benzene Toluene Ethylbenzene Xylene f-1 10/2/90 17J 28QJ R 56J R 120J 32J R R — T-1FR 10/2/90 12J 270J R 47J R 981 26J R R - T-l 2/5/91 7 200J ND 36 ND 100D 27 1 1 - T-l FWn FWIIFR FWn 6/5/91 9/26/90 9/26/90 2/5/91 5 _ _ — 400DEJ 75J 61J 230D 0.9 72DJ 6J 4J 21 4 180DJ 25J 18J 90D 3J - - - 0.8J ND ND ND ND _ _ _ _ pwn 6/5/91 — 130DJ - 12J — 34DJ — ND — - Constituent concentrations in mfcrograms per liter [parts per billion (ppb)]. D Compound was quantified using a secondary dilution by USEPA method 624. E Result is outside calibration range. J Result was detected below the reporting limit or is an estimated concentration. R Result is unusable and rejected. FR Sample ID suffix denotes Field Replicate of previous sample. ND Compound not detected. - Compound not measured. PR01301 -#2/tututb!l.wk3 GERAGHTY & MILLER, INC Table 2. Design Basis Scenario Influent Constituent Concentrations, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands. CONSTITUENT Vinyl Chloride 1,2-Dfchloroethene Chloroform Trfchloroethene 1,1,2-Trichloroethene Tetrachloroethene Benzene Toluene Ethylbenzene Xytene CASE1 MAX INFLUENT CONCENTRATION 17 400 1 72 4 180 32 1 1 — CASE 2 MODIFICATION FOR BTEX 17 400 1 72 4 180 100 100 100 100 MCL/MCLG 2 5 N N 3 N 5 1000(a) 700 10000 CH Constituent concentrations inmfcrograms per liter [parts per billion (ppb)]. N No proposed MCLs/MCLGs. - Compound not measured. (a) Final Rule (effective July 1992). PR01301-*2/tututab.wk3 Q* CO GERAGHTY & MILLER, INC Table 3. Effluent Concentrations for Design Basis Scenario with 1 Foot Diameter Tower and 8 Foot Packed Depth, Tutu Service Station Investigation, St. Thomas, U.S. Virgin Islands. c-i / , CONSTITUENT MAX INFLUENT CONCENTRATION Vinyl Chloride 1 ,2-Dfchloroethene Chloroform Trichloroethene 1,1,2-TrfchIoroethene Tetrachloroethene Benzene Toluene Ethylbenzene Xylene 17 400 1 72 4 180 32 1 1 — CASE1 CASE 2 EFFLUENT % MODIFICATION FOR BTEX EFFLUENT % CONCENTRATION REMOVED CONCENTRATION REMOVED 0.1 4.5 0.0 1.0 03 25 0.5 0.0 0.0 — 99.6 98.9 97.6 98.6 91.5 98.6 98.6 983 98.0 - 17 400 1 72 4 180 100 100 100 100 0.1 4.5 0.0 1.0 03 25 1.4 1.7 2.0 2.0 • 99.6 98.9 97.6 98.6 915 98.6 98.6 983 98.0 98.0 Constituent concentrations in mircogram per liter [parts per billion (ppb)]. Air Stripper: 1 foot diameter, 8 foot packed depth, 14 feet overall height. Flow is 15 gallons per minute (gpm). Liquid Loading Rate is 19.1 gallons per minute per square foot (gpm/sqft). Air to Water Ratio is 30 (volumetric). Air Rate is 60 cubic feet per minute (cfm). Temperature of influent is 845 degrees Fahrenheit (F). Packing is 1 inch Jaeger Tripacks. Limiting compound is 1,2-Dfchloroethene. PR01301-#2/tututbW.wk3 GERAGHTY & MILLER, INC. Table 4. Schedule of Ground -Water Discharges, Tutu Service Station Investigatbn, St. Thomas, U.S. Virgin Islands. Weeks from Project Start (Expected Start Date March 2,1992) Activity Estimated Volume of Generated Ground Water (gallons) 13-15 (July 2 - July 16) * 17-18 (July 30 - August 6) * 21-22 (August 27 - September 3) * 31-32 (November 5 - November 12) * Monitoring Well Development Monitoring Well Purging — Sampling Round I Step Tests and Pumping Tests Monitoring Well Purging - Sampling Round 2 5,900 3,000 33,100 3,000 Estimated Total 45,000 gallons * Dates are approximate. PR01301-#2/sgwd.l23 GERAGHTY & MILLER. INC. TUT 006 1824 LEGEND • SOIL BORING • SHALLOW MONfTORING WELL •• DEEPER MONITORING WELL • EXISTING SUPPLY WELL NOT TO SCALE GERAGHTY 9 MILLER. INC. SITE PLAN TUTU SERVICE STATION INVESTIGATION TUTU, ST. THOMAS, U.S. VIRGIN ISLANDS FIGURE TUT OO6 1825 M.H SCALE **.» 1EGEHD »- SANITARY SEWER UNE - STORM SEWER UNE SANITARY SEWER MANHOLE STORM SEWER CATCH BASIN GKRACBIY 9 lOLLER. INC. TUTU SERVICE STATION INVESTIGATION TUTU. ST. THOMAS. U.S. VIRGIN ISLANDS FIGURE 2 TUT 006 1826 Figure 3. Groundwater Process Flow Diagram for CASE 1, Tulu Service Stalion Investigation, St. Thomas, U.S. Virgin Islands. Feed Tank O-D•D Fee Pum d P Air Stripper IFoot Diameter ———— < Carbon Adsorpfon UnHs Air Discharge to the Atmosphere To Sanitary Sower H C CONSTITUENT Vinyl CMorMe 1^ OfcMoroefcene Chloroform Triehbroehene 1.1.2 Triehtoroeltene TelraeMoroethene Bentene Toluene Ettybenxene Xylene Total o 0.0001 0.003 0.00001 0.00054 0.00003 0.00135 0.00024 0.00001 o.oooot - 0.0053 O 0.0001 0.003 0.00001 0.00053 0.000026 0.00133 0.00024 0.00001 o.oooot •• 0.005 o 0.0 0.0 0.0 0.00001 0.000002 0.00002 0.0 0.0 0.0 •• 0.0003 <: NO NO NO NO NO NO NO NO NO ~ NO Constituent concenkafions In pounds per how (Ibs/hr). Ground water Row b 15 gallons per mtnula (gpm). =™t CD Figure 4. Process Row Diagram for CASE 2, Tulu Service Station Investigation, St. Thomas, U.S. Virgin Islands. Gfotmdwatef Feed Tank r -D— Fcad Puinp Air Sftippw IFool Diameter Cmbon Adsorption Unils Air Discharge to ttie Atmosphere To Sanitary Sewer \ —\ C CONSTITUENT Vinyl CMotkto UDfeMonMlhtfM CWototefiw TltoMoflMVMIM U ,1 Ti tcMorMlhtftt <z> TahMnt Etiytbcnnnt Xytotw Total Consohwfit oofiMfthiitloits In poutxlv pv notif (Ww/nt). Ground watot flow It 15 gnlont ptr mtmil* (Qpfn). \^/ <D 0.0001 0.003 0.00001 0.00054 0.00003 0.00135 0.00075 0.00075 0.00075 0.00075 0.00809 0.0001 0.003 0.00001 0.00053 0.000028 0.00133 0.00074 0.00074 0.00073 0.00073 0.000 0.0 0.0 0.0 0.00001 0.000002 0.00002 0.00001 0.00001 0.00002 0.00002 0.00000 NO NO NO NO NO NO NO NO NO NO NO H- CD W CO