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S E C 0 R • QUARTERLY SUMMARY REPORT First Quarter 2004 Circle K Store #08671 8606 Thornton Road, Stockton, California City/County ID # Stockton County San Joaquin PREVIOUS ASSESSMENT The site is located at 8606 Thornton Road, Stockton, California The site is currently an operating gasoline service station that contains two gasoline USTs, associated product lines, and dispensers In May 1998, product lines and dispensers were upgraded to meet 1998 EPA standards Analytical results from pea gravel samples collected from above the USTs and soil samples collected from the former product line and dispenser excavations indicated the presence of petroleum hydrocarbons in soil beneath the site The results of this work are documented in SECOR's report titled Removal and Replacement of Product Lines and Dispensers, dated July 22, 1998 During product line and dispenser upgrade activities, approximately 21 tons of petroleum-impacted soil were over-excavated from the site and disposed of at Forward Landfill On January 27 and 28, 1999, four groundwater monitoring wells (MW-1 through MW-4) were installed onsite by SECOR The results of this work are documented in SECOR's report titled Well Installation Report, dated March 16, 1999 Since their installation, the four wells have been monitored and sampled quarterly On December 12th through 14th, 2001, one deep soil boring (SB-1) was drilled to an approximate depth of 63 feet below ground surface (bgs) and three additional groundwater monitoring wells (MW-5, MW-6, and MW-7) were installed onsite by SECOR The results of this work are documented in SECOR's report titled Site Assessment Report, dated June 21, 2002 The site is currently monitored and sampled on a quarterly basis During the last quarterly ) groundwater monitoring event conducted on August 13, 2003, maximum concentrations of TPHg and MtBE were reported at 300 ppb and 3,300 ppb, respectively Depth to groundwater at the site ranged from approximately 30 feet below ground surface (bgs) to approximately 37 bgs during 2003 Groundwater flow direction was to the east-northeast at a gradient of 0 001 feet per foot ft/ft during the third quarter 2003 In November 2003, SECOR installed deep well MW-8, MW-9, and MW-10 at the site Petroleum hydrocarbons were not reported in sod and groundwater samples form the new wells Vertical and lateral delineation of the plume has been completed SENSTIVE RECEPTORS SECOR performed a sensitive receptor survey to identify the location of permitted water supply wells within a 2,000-foot radius of the site The sensitive receptor survey consisted of reviewing the California Department of Water Resources (DWR) files for locating water supply wells in the area, contacting the local water purveyor (San Joaquin County), and a conducting a door-to-door • field survey in search of any wells or other sensitive receptors within 1,000 feet of the site Four wells were identified within the surveyed area, one municipal well and three domestic wells The domestic well was identified as Colonial Heights municipal water supply well #3 (Well DW-3)