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J. k, QUARTERLY GROUNDWATER MONITORING REPORT FOURTH QUARTER 2002 QUIK STOP MARKET NO. 132 Ox 3559JVEST HAMMER LANE 31Z STOCKTON, CALIFORNIA 1.0 INTRODUCTION ATC Associates Inc. (ATC) is pleased to present this report of the results of the Fourth Quarter 2002 groundwater monitoring conducted at the subject site in Stockton, San Joaquin County, California (Figure 1). The site plan (Figure 2) shows the location of the station building, adjacent streets, monitoring wells, and other site-specific features. '1 The monitoring wells have been sampled quarterly to monitor two shallow groundwater aquifers underlying the site. The program scope of work is as follows: 0 Measure depth of groundwater; • Analyze groundwater samples for select petroleum hydrocarbon constituents; +�t 0 Construct groundwater elevation contour maps within the study area boundaries; and t a Compare current and past data. The existence and degree of petroleum hydrocarbons in the groundwater underlying the site is evaluated by (1) the presence of the free-floating product and (2) laboratory analyses of groundwater samples to evaluate concentrations of total petroleum hydrocarbons as gasoline (TPH-G), and for benzene, toluene, ethylbenzene, and total xylenes (BTEX). Included with this report, in compliance with the July 18, 1997 request of the Regional Water Quality Control Board (RWQCB)-Central Valley Region, are results of analysis for the fuel oxygenates methyl-tert-butyl ether (MTBE) (a non-metallic antiknock and oxygenating compound used in gasoline), di-isopropyl ether (DWE), ethyl-tert-butyl ether (ETRE), tert- amyl methyl ether(TAME), tert-butanol (TBA), ethylene dibromide (EDB), and 1,2-dichloroethane (1,2- DCA) by United States Environmental Protection Agency (USEPA) Method 8260 for samples collected from ten groundwater monitoring wells. As indicated in the RWQCB letter, the purpose of analyzing for these fuel oxygenates is to determine which oxygenated compounds are present, if any, in groundwater. I In a letter to Quik Stop Markets Inc. dated April 27, 1998, the San Joaquin County Public Health Services, Environmental Health Division (PHS-EHD) required sampling of all site wells and analyzing for TPH-G, BTEX, and fuel oxygenates. Previously the PHS-EHD had recommended sampling of monitoring well MW-5 only. 2.0 GROUNDWATER SAMPLING On November 19, 2002, in accordance with ATC's Field Protocol (Appendix A), groundwater samples were collected from on-site groundwater monitoring wells MW-1R, MW-2, MW-3, MW-4, MW-5, and off--site groundwater monitoring wells MW-6, MW-7, MW-8, MW-9 and MW-10. Groundwater purged t„ from the wells and equipment decontamination water was placed in Department of Transportation (DOT) !' Quarterly GW Monitoring Report-4th Qtr 2002 NATC Quik Stop l to.s, 132 Quik Stop Markets, Inc. r 4 I TAdJECTSIOVIK STOP MKTSIOS 13Mepons400213d0[r2002Rp[ ATC Project No.75.62503.3203 February 11,2003 ,, Page 1 of 3