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J; Well Installation Report San Joaquin County Environmental Health Department February 17,2006 . Page 2 of 5 investigation Monitoring wells MW-1 through MW-3 were completed to a depth of 91 feet and screened from 71 to 91 feet bsg Monitoring wells MW-4 and MW-5 were each completed to a total depth of 92 feet and screened from 72 to 92 feet bsg Elevated levels of fuel hydrocarbon constituents were detected in the 48 8-foot sample collected from MW-1, the 21 5-foot sample collected from MW-3, and the 36 5- foot sample collected from MW-4 Chemical analyses of all other samples showed low concentrations or concentrations below the laboratory reporting limit In December 1993, Hydro Environmental Technologies Inc (HET) drilled and installed three groundwater monitoring wells (MW-6 through MW-8) Each monitoring well was completed to a total depth of 90 feet and screened from 70 to 90 feet bsg The analytical results indicated all soil samples reported concentrations were below the laboratory reporting limits for petroleum hydrocarbon constituents In December 1994 and January 1995, Brown and Caldwell (BC) drilled and installed one dual completion air sparge/soil vapor extraction well (AS-11SVE-1) and two soil vapor extraction wells (SVE-2 and SVE- 3) Soil vapor extraction well SVE-1 was installed in the same borehole as air sparge well AS-1 to a total depth of 79 feet and screened from 69 to 79 feet bsg Soil vapor extraction wells SVE-2 and SVE-3 were each completed to a total depth of 65 feet and screened from 55 to 65 feet bsg Elevated levels of petroleum hydrocarbon constituents were detected in all the soil samples collected and submitted for laboratory analysis from well bonngs AS-1/SVE-1, SVE-2 and SVE-3 In March 1995, BC conducted vapor extraction and air sparge pilot studies at the subject site Soil vapors were extracted from SVE-2 at flow rates ranging from 20 to 40 standard cubic feet per minute (scfm) at induced vacuums ranging from 64 to 110 inches of water column (inwc) Soil vapors were extracted from SVE-1 at flow rates ranging from 38 to 40 scfm at induced vacuums ranging from 108 to 116 mwc Air was injected into AS-1 at a flow rate of 8 scfm under pressures ranging from 26 to 38 pounds per square inch (psi) Based on the results of the vapor extraction/air sparge pilot studies, it was estimated that each vapor extraction/air sparge well would have an approximate radius of influence of 40 feet In June 2001, Clearwater Group Inc (Clearwater) drilled and installed four groundwater monitoring wells, designated as MW-9 through MW-12 Monitoring wells MW-9 through MW-12 were each completed to a total depth of 65 feet bsg and screened from approximately 40 to 65 feet bsg Elevated levels of fuel hydrocarbon constituents were detected in the 25, 40, and 45-foot soil samples collected from well boring MW-10, and in the 50-foot sample collected from well boring MW-12 Chemical analyses of all other soil samples showed low concentrations or concentrations below the laboratory reporting limit In December 2002, ATC installed five groundwater monitoring wells (MW-13 through MW-17) because existing wells had submerged screens Each of the wells were completed to a total depth of 65 feet bsg and screened between 40 and 65 feet bsg ATC also installed three dual completion vapor extraction/air sparge wells (VEAS-1 through VEAS-3) and one groundwater extraction well (EX-1) for the purpose of conducting pilot study activities Also in December 2002, once the remediation wells were installed, a Vapor Extraction Feasibility Test, Air Sparge Feasibility Test, and an Aquifer Pump Test was conducted Based on the results, ATC recommended the installation of a multiphase extraction system in their Corrective Action Plan, dated February 26, 2003 Site and Area Geologic Materials ' The subject site is located in the San Joaquin Valley, which is a north-south trending basin bounded by the Sierra Nevada Mountain Range to the east and the Coast Ranges to the West Within the Stockton W\RPMS-CAVWorkmgTroiect Files1100966 Stockton 2537 Waterloo RoadVnvestigation