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URS Ms Vickie McCartney, REHS Page 2 San Joaquin County Environmental Health Department ARCO 2186 borings (B-3, B-7, and B-8) were converted to dual-completion vapor extraction wells (VW-1 through VW-3, respectively) October 1996 EMCON supervised the drilling of one vertical soil boring (B-9) B-9 was subsequently converted to monitoring well MW-4 • June—July 1999 Two 10,000-gallon and one 8,000-gallon double-walled fiberglass gasoline USTs, associated dispensers, and piping were removed from the site Two 20,000-gallon USTs were installed in the same cavity as the former USTs Pinnacle Environmental Consultants conducted compliance soil sampling activities for the tank pull Analysis of compliance soil samples indicated that total petroleum hydrocarbons as gasoline (TPHg), benzene, and methyl tertiary butyl ether (MtBE) contamination were present in the soil The excavation areas were backfilled with pea gravel • August 1999 The IT Group (IT) conducted a soil and groundwater assessment that Included two cone penetrometer test (CPT) borings (CPT-2 and CPT-3) on the eastern edge of the site and one CPT boring north of the site (CPT-1) Benzene and MtBE were detected in groundwater samples from CPT-2 No petroleum hydrocarbon compounds were detected in the groundwater samples collected from CPT-1 or CPT-3 September 2000 Delta Environmental Consultants (Delta) conducted an SVE test at the site Three separate 4-hour tests were conducted Soil vapors were extracted from wells VW-IA, VW-2A, and VW-3A The tests Indicated that extraction of soil vapors from these wells at 9 to 10 cubic feet per minute (efm), with 50 to 100 Inches of water column, resulted in a radius of influence between 34 and 45 feet The initial hydrocarbon mass extraction rates were calculated to be between 1 10 and 3 88 pounds of TPHg per day C August 2001 Delta Installed three groundwater monitoring wells (MW-5, MW-6, and MW-7) MW-5 is east of the site on American Street MW-6 and MW-7 are in Oak Park, across Alpine Avenue, to the northwest and northeast of the site ASSESSMENT ACTIVITIES AND FINDINGS In the letter from SJCEHD dated November 17, 2003 (Attachment A), an additional Investigation was requested to assess the vertical extent of petroleum hydrocarbon Impacts near the site USTs One deep onsite groundwater monitoring well (MW-8) w s installed in the dominant downgradient direction from the UST cavity (east-northeast) to assess the }t� l extent of petroleum hydrocarbon- Impacted groundwater beneath the site Og as VE well (VWt a installed to complete the SVE well (AW- t network at the site One AS well installed for use in conjunction with the site SVE wells in an AS/SVE pilot test A work plan for the pilot test will be prepared for submittal to SJCEHD The following paragraphs present a discussion of drilling and well installation, the subsurface conditions encountered, monitoring well development, well sampling and surveying, soil analytical data, groundwater analytical data, and soil and wastewater disposal • K MprocessV5 BP ARCO\0218612004 AssessmentlReport 04 doc