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1 <br /> 'I <br /> . QUARTERLY GROUNDWATER MONITORING REPORT <br /> FOURTH QUARTER 1999 <br /> QUIK STOP MARKET NO. 132 <br /> 355 WEST HAMMER LANE <br /> STOCKTON, CALIFORNIA <br /> 1. INTRODUCTION <br /> ATC Associates Inc. (ATC) is pleased to present this report of the results of the Fourth Quarter 1999 <br /> groundwater monitoring conducted at the subject site in Stockton, San Joaquin County, California <br /> (Figure 1). The site plan (Figure 2) shows the location of the station building, adjacent streets, <br /> monitoring wells, and other site-specific features. <br /> The monitoring wells have been sampled quarterly to monitor two shallow groundwater aquifers <br /> underlying the site. The program objectives are listed below: <br /> I • Measure depth of groundwater; <br /> • Sample and analyze groundwater samples for select petroleum hydrocarbon constituents; <br /> • Construct groundwater elevation contour maps within the study area boundaries; and <br /> • Compare current and past data. <br /> I <br /> The existence and degree of petroleum hydrocarbons in the groundwater underlying the site is evaluated <br /> by (1) the presence of the free-floating product and (2) laboratory analyses of groundwater samples to <br /> evaluate concentrations of total petroleum hydrocarbons as gasoline (TPH-G), and for benzene, toluene. <br /> ' ethylbenzene, and total xylenes (BTEX). Also in compliance with the request of the California Regional <br /> Water Quality Control Board (RWQCB, State of California. May 2, 1995), we are including reporting of <br /> methyl-tert-butyl ether (MTBE) (a non-metallic antiknock and oxygenating compound used in gasoline). <br /> In compliance with the July 18, 1997 request of the RWQCB-Central Valley Region, included with this <br /> report are results of analysis for the fuel oxygenates tert-butanol (TBA), MTBE, di-isopropyl ether <br /> (DIPS), ethyl-tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) by EPA Method 8260 for <br /> samples collected from all seven ground%vater monitoring wells. As indicated in the R%VQCB letter, the <br /> I'•"Pnunh c)„seer Grn nd,,ITer SI,m6lnnn�HrP,ni <br /> II l.I'I R S.l i.'IJI a KST(JP'13_p`h <br />