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' Beacon Station No 641 December 8, 1997 Stockton,California Additional Subsurface InvestigaaQR pow with two nested soil vapor extraction wells Soil boring SW-1 was completed as a sparge well 1 The sediments encountered during drilling consisted primarily of silts, sands, and clays The ' sediments were classified using the Unified Soil Classification System (USCS) A copy of the USCS is shown on the Boring Log Symbol Key included with the boring logs in Appendix C The drill cuttings were screened with an OVM, and four soil samples were collected from the stockpiled cuttings, composited at the laboratory, and analyzed for gasoline-range ' hydrocarbons (Table 1) All cuttings generated during this study were stockpiled on and covered with visqueen sheeting until subsequent disposal by Ultramar Monitoring Well Installations - Phase 1 MW-1 , a 2-inch inside diameter (ID) groundwater monitoring well, was constructed in the 10-inch diameter soil boring B-2 The well was completed with 80 feet of schedule 40 polyvinyl chloride (PVC) well screen with 0 020-inch factory-machined slots The bottom of the screened interval, also the total drilled depth of the soil boring, was 80 feet bsg Blank PVC well casing was installed from the top of the screened interval, 60 feet bsg, to the ' surface The annular space opposite the well screen was backfilled with # 3 Monterey sand to approximately two feet above the screened interval A four-foot seal of bentonite was ' then placed above the filter sand and hydrated with approximately ten gallons of fresh water Two soil vapor extraction wells were constructed in the remainder of the boring (VW-1 & iVW-2) tMQgitoring Well Installations - Phase 2 MW-2, MW-3, and MW-4 are 2-inch ID groundwater monitoring wells constructed in 8- inch borings, and for well MW-5 which is a 4-inch ID well constructed in a 10-inch boring Each of the four monitoring wells were completed with 25 feet of schedule 40 PVC well screen with 0 020-inch factory-machined slots The bottom of the screened interval for each ' 1641-13 rpt 5 HORIZON ENVIRONMENTAL INC