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I I 1 16 QUARTERLY GROUNDWATER MONITORING REPORT SECOND QUARTER 2000 I' QUIK STOP MARKET NO. 132 355 WEST HAMMER LANE STOCKTON, CALIFORNIA 1.0 INTRODUCTION ATC Associates Inc. (ATC) is pleased to present this report of the results of the Second Quarter 2000 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. The monitoring wells have been sampled quarterly to monitor two shallow groundwater aquifers underlying the site. The program objectives are listed below: • Measure depth of groundwater; • Sample and analyze groundwater samples for select petroleum hydrocarbon constituents; • Construct groundwater elevation contour maps within the study area boundaries; and • 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). Also in compliance with the request of the California Regional Water Quality Control Board (RWQCB, State of California, May 2, 1995), we are including reporting of methyl-tert-butyl ether (MTBE) (a non- metallic antiknock and oxygenating compound used in gasoline). In compliance with the July 18, 1997 request of the RWQCB-Central Valley Region, included with this report are results of ii analysis for the fuel oxygenates tert-butanol (TBA), MTBE, di-isopropyl ether (DIPS), ethyl-tert- r 2000 Second Quartcr Groundwater Monitoring Report 1\PLEASANTONTrojectOn Progrms QUIKSTONQS 132(0003)IREPORT51100012ndQtr2o00rpt.doc 1