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f i 4 t. 2 Soil contamination will be remediated by extraction of vapors from existing wells ATR-2, ATR-3, ATR-4, ATR-5, TEX-1, and VES-1 through VES-7, all of which are screened across the capillary fringe. Well locations are shown on Figure 2. Extraction of vapors from these wells will be monitored and varied as necessary. Lithology The upper 20 feet consists of silts and clays with zones of fine to medium sand. From 20 feet to approximately 30 feet, the lithology consists of fine to medium sand with minor coarse { sand and fine gravel lenses identified in some of the boreholes. Soil Vapor Extraction On December 16, 1991, Brown and Caldwell Consultants (BC) performed a series of pilot tests using existing monitoring wells ATR-2, ATR-3, ATR-4, and ATR-5. The results of this test indicate that vapor extraction is a feasible alternative and volumetric flow rates between 20 and 40 cubic feet per minute (cfm) can be obtained from each well. A wide range of TPH concentration can be expected in the extracted vapor: from 23,000 micrograms per liter (pg/1) in ATR-3 (near the UST) to 640 pg/l in ATR-2. Data generated during the pilot test are provided in Appendix A. a { Wells ATR-2, ATR-3, ATR-4, and ATR-5 are approximately 25 feet deep and constructed of 4-inch- diameter Schedule 40 polyvinyl chloride(PVC)casing with 20 feet of 0.02-inch slotted well screen. The well screen extends from approximately 5 feet below ground surface (bgs) to 25 feet bgs. Well TEX-1 is approximately 40 feet deep and constructed of 6-inch-diameter PVC casing with 30 feet of 0.02-inch wire wrapped well screen. The well screen extends from 5 feet bgs to 35 bgs. The vapor extraction casing in wells VES-1 through VES-7 is constructed of 2- inch-diameter PVC with the screened intervals extending from approximately 5 feet below ground surface to 12.5 to 14.5 feet below ground surface. The sparge well casing in wells VES-1 i through VES-7, S-1, S-2, and S-3 is constructed of 1-inch PVC casing with the screened interval extending from approximately 27 to 30 feet. r Vapors will be extracted at a rate of 0 to 30 cfm from the vapor extraction wells using a vacuum blower located at the treatment compound. Each well will be connected to an extraction and treatment system by below ground PVC piping. Figure 2 shows the layout of the existing and proposed piping system and treatment area. Soil Vapor Treatment A vapor extraction and treatment system (VETS) has been designed based on the pilot test results. In the VETS, the extracted soil vapor will be treated by a King Buck and Associates catalytic oxidizer, or equivalent unit. The unit will have a nominal capacity of 100 cfm and consists of a vacuum/compression unit, electrical preheater, catalytic oxidizer, and operating 3 controls. The system will be powered solely by electricity and designed for continuous services. The unit will rest on a concrete pad located in the treatment area as shown on Figure 2. The unit can be shut down four ways: (1) a thermal cutoff switch in the catalytic oxidizer which is triggered if temperatures exceed 1300° F; (2) a pressure shutoff located in the influent piping E "Q3WC,\7403&U0R7W403.0I.R•1 - QMS-P52"