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�Sr rl Z T ii SECOR www secar com INTERNATIONAL 3017 Kilgore Road Suite 100 S E C ® R INCORPORATED Rancho Cordova CA 95670 916-861 0400 TEL 916-861 0430 FAX f ' September 22, 2003 Ms Lori Duncan S E P 2 9 2003 San Joaquin County Environmental Health Division 304 East Weber Avenue ENVIRORMENT HEALTH Stockton, California 95202 PERMIT/SERVICES Re Remedial Well Installation and Start-up Report ARCO Station 44932 16 East Harding Way Stockton, California SECOR Project No 77BP 64932 03 0936 Dear Mrs Duncan SECOR International Incorporated (SECOR) has prepared this letter on behalf of Atlantic Richfield Company to document the installation of remedial wells and start-up of the groundwater extraction and soil vapor extraction remedial systems at the site referanced above (Figure 1) SECOR installed five groundwater extraction wells (EW-2 through EW-7), one soil vapor extraction well (SVE-2), and started the groundwater extraction/soil vapor extraction system at the site Work was performed in general accordance with SECOR's Problem Assessment Report, dated August 29, 2002 and •� approved by the San Joaquin County Environmental Health Division (SJCEHD) in a letter dated November 7, 2002 (Attachment 1) SITE BACKGROUND The various environmental assessments completed at the site are summarized below A table summarizing well construction details Is Included as Table 1 A site plan showing well locations Is included as Figure 2 Between May 25 and June 9, 1999, Gettler Ryan Construction of Dublin, California removed three 10,000-gallon double-walled fiberglass LISTS and enlarged the excavation to accommodate the larger new USTs Approximately 631 tons of soil was over-excavated from the UST complex Over- excavation of the UST complex was completed and samples were collected on June 9, 1999 Six samples collected from the excavation at approximately 19 feet bgs One sample contained TPHg and MtBE at concentrations of 1 02 mg/kg and 0 579 mg/kg, respectively No benzene or fuel oxygenates were detected in any other samples from the over-excavation During the facility upgrade, approximately 150 tons of soil was over-excavated from the product line and dispenser areas TPHg was reported in three of the six samples collected from beneath the former facilities at a maximum concentration of 5,430 mg/kg Benzene was reported in two samples at a maximum concentration of 10 6 mg/kg MtBE was reported in two samples at a maximum concentration of 55 5 mg/kg This work was summarized In SECOR's report titled Soil Sampling During USTs, Product Line, and Dispenser Removal Activities dated December 10, 1999 In August 2000, four groundwater monitoring wells (MW-1, MW-2, MW-3, and MW-4) and one vapor extraction well (SVE-1) were installed at the site Groundwater samples collected from these wells were reported to contain TPHg, benzene, and MtBE MW-4 contained maximum concentrations of • 166,000 ug/L, 10,500ug/L, and 708,000 ug/L, respectively Other detected constituents included TAME, 1,2 DCA, TBA and EtBE This work was summarized in SECOR's report titled Site Assessment Report dated November 6,2000