SITE INFORMATION AND CORRESPONDENCE_FILE 2

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13975 Hwy. 88 -2- 11 December 1998 Lockeford, San Joaquin County The site is underlain by sandy silt from surface grade to approximately 8 feet bgs,and with poorly graded fine to medium grained sand units from 8 to 27 and 42 to 55 feet bgs. Silty clay is identified from 27 to 42 feet bgs and gravelly sand to sandy gravel is present from approximately 55 to 80 feet bgs. Soil boring logs and corresponding soil sampling results indicate that the highest concentrations of soil contamination coincide with the lower permeability silt zones located between 28 and 38 feet bgs in SB-9 and clay and clayey sand zones located at 30 and 35 feet bgs respectively, in MW-2. Groundwater contamination was identified during the initial site investigation activities conducted during June 1987. On 21 November 1994, an extended purge was conducted on MW-2,using a submersible pump,in an attempt to remove impacted groundwater. Only 200 gallons of water were removed from the well during the approximately 7 hour groundwater extraction test. Groundwater sampling activities conducted between June 1987 and May 1998 have shown a significant decrease in contaminant concentrations at the site. Between May 1995 and May 1998 (the past five groundwater sampling events)TPHg and BTEX constituents were detected above laboratory reporting limits in one well only,MW-2, during the 8 July 1996 sampling event, (TPHg at 230 pg/L and benzene at 4.1 µglL). A limited vapor extraction pilot test was conducted on 22 November 1994. A regenerative blower was connected to the outlet for the piping system below the USTs, and air was extracted for approximately 90 minutes. Two air samples were collected,at 15 and 90 minutes, during the vapor extraction test, and analyzed for TPHg and BTEX. Xylenes were detected in the 15-minute sample at 0.088 ppm, and TPHg and xylenes were detected in the 90-minute sample at 10 ppm and 0.26 ppm,respectively. A regional water well survey was conducted for wells located in the vicinity of the site. Two wells, which are City of Lockeford municipal water supply wells,were identified within the 2,000-foot search radius. Lockeford Supply Well#4 is located 1,200-feet northwest of the site,has a total depth of 445 feet bgs, and draws wafer from a minimum depth of 244 feet bgs. Lockeford Well#2 (Tower Well),is located approximately 1,900-feet southwest of the site,has a total depth of 310 feet, and draws water from a minimum depth of 126 feet bgs. The depth to groundwater has been reported between 61 and 75 feet bgs during the past 9 years, which corresponds with the gravelly sand to sandy gravel zone. - Groundwater below the site generally flows toward the south to southwest with a calculated hydraulic gradient between 0.003 and 0.0075 ftfft. Two dry wells (French drains)were referenced in the Closure Summary Report,prepared by Advanced Geo-Environmental (AGE). The dry well were located at the south and east comers of the site, and provided drainage for run-off and wash-down from the product dispenser area These wells were destroyed in July 1987, During my 3 November 1998 telephone conversation with Mr. Kevin McGibben of AGE,he attributed the soil contamination near MW-2 and SB-9 to either the wash down of contamination into the former dry wells or to a product dispenser leak.