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04 April 2001 AGE-NC Project No 98-0505 ' Page 2 of 5 Field activities were performed in accordance with guidelines for investigation of underground storage tank (UST) sites and sampling ground water rnonitonng wells established by the Regional Water Quality Control Board - Central Valley Region (RWQCB) and by the San Joaquin County ' Public Health Services - Environmental Health Division (PHS-EHD) ' 2 1 MONITORING WELL PURGE PROCEDURES Ground water sampling of the on-site wells was conducted on 01 March 2001 For the sampling event, a Solmst water level meter was used to measure the depth to ground water in the eight monitoring wells relative to the tops of the well casings The ground water elevations and gradient were determined from these data (Table 1) After S�' depth to groundwater measurements, a rnmunum of 3 casing-water volumes was purged from P each well to be sampled using a PVC submersible two-stage pump Approximately six to twenty- four gallons of water were removed from wells MW-1 through MW-8 Temperature, pH and conductivity of purged ground water were measured at 1-to 4-gallon intervals using a Oakton water • analyzer The field data and field sheets are included in Appendix A Purged water was temporarily ' stored on-site in 55-gallon DOT-approved H-17 storage drums pending proper disposal Following purging, the depth to ground water was measured to ensure that a minimum of 80% well-volume recharge had been achieved prior to sampling 2 2 GROUND WATER SAMPLE COLLECTION A water sample was collected from each well using a new, clean, disposable plastic bailer I Immediately upon retrieval,the samples were transferred into three 40-m1 EPA-approved VOA vials containing 0 5 ml 18% hydrochloric acid as a sample preservative The samples were logged on a chaui-of=custody form, stored in a chilled container and transported under chain-of-custody to McCampbell Analytical Inc (MAI), a California Department of Health Services (DHS)-certified laboratory The ground water samples were analyzed for ' • Total petroleum hydrocarbons quantified as gasoline (TPH-g) and diesel (TPH-d) in accordance with EPA Method 8015 Modified, • Volatile aromatic hydrocarbons benzene, toluene, ethylbenzene and total xylenes (BTEX) ' in accordance with EPA Method 8020, and • Oxygenated compounds di-isopropyl ether(DIPE),ethyl tertiary-butyl ether(ETBE), methyl tertiary-butyl ether(MTBE),tertiary-amyl methyl ether(TAME),tertiary butanol(TBA),and ' methanol, ethanol, ethyldibronnde (EDB) and 1,2-dichloroethane (1,2-DCA) in accordance with EPA Method 8260-Modified, respectively Advanced GeoEnvironmental,Inc