SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Californi.-rlegional Water Quality Cor`rol Board `i' z, ; x �7 Central Valley Region Linda m S.Adas Arnold , ,rS a w ltv, v Karl E. Longley-, SeD, P.E., Chair Schwarzenegger Fnr;r�ranemul (Nil'e17701' Pruiecrron OC f 14 200911020 Sun Ccnler Drive#200. Rancho C'ordo%a.California 95670-6 1 1 4 /� Phone(916)464-3291 •FAX(916)464-4645 ENVIRONMENT HEAM http iw�c�� N%aterboards.ca Ro%/central%alleN PERMIT/SERVICES TO: File: Chevron #9-6171 FROM: Jim Barton 6633 Pacific Avenue Engineering Geologist Stockton, San Joaquin Co. UST Unit 2 DATE: 6 October 2009 SIGNATURE: i SUBJECT: UST CASE CLOSURE, CHEVRON #9-6171. 6633 PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY(CASE # 390054). Site Background Chevron #9-6171 (Site) is currently an operating Chevron-branded service station located on the southwest corner of Pacific Avenue and Benjamin Holt Drive in Stockton, San Joaquin. County. The Site is south of the Lincoln Village Shopping Center (Attachment 1). There were two reported underground storage tanks (USTs) releases at the site, one in December 1986 and the second in December 1997. On 12 December 1986, three unspecified volume gasoline USTs and one 550 gallon waste oil UST were removed from the site and replaced with double-walled fiberglass tanks by Chevron (Attachment 2). The case file and available documents do not include a more detailed description of the USTs or their condition upon removal. Maximum confirmation soil sample results from the UST removal were total petroleum hydrocarbons as gasoline (TPHg), 84 milligrams per kilogram (mg/kg); and benzene, 1.7 mg/kg. Immediately following the removal. one groundwater monitoring well (MW-1) was installed to a depth of 52 feet below ground surface (' bgs). MW-1 soil boring concentrations were non-detect for petroleum hydrocarbons with elevated detection limits. A grab groundwater sample analysis, taken from the open boring prior to installing MW-1, reported TPHg, 990 micrograms per Liter (ug/L); benzene, 32 ug/L; toluene, 47 ug/L; and xylenes, 43 ug/L. Subsequent sampling events were attempted in January 1987 and February 1987; however, MW-1 did not have sufficient water to collect a groundwater sample. Between June and August 1990, four additional monitoring wells (MW-2 through MW-5) were installed and screened from approximately 50' to 70' bgs. Petroleum hydrocarbons were not initially detected in soil sampled from MW-2 through MW-5, however, 1 ,2-dichloroethane (1 ,2-DCA) was reported at 7 ug/L in groundwater sampled from MW-5. Tetrachloroethylene (PCE) and 1,2-DCA were reported as the only components in the TPHg (150 ug/L) detected in groundwater in December 1990. The nearby Lincoln Village dry cleaners release is discussed in the March 1991 monitoring report as the probable source of the PCE and 1 2-DCA found in groundwater at the USTs site, as quarterly monitoring California Environmental Protection Agency v��