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1� <br /> QUARTERLY GROUNDWATER MONITORING REPORT <br /> 1 FOURTH QUARTER 1998 <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 1998 <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 /> • Measure depth of groundwater. <br /> • Sample and analyze groundwater samples for selected petroleum hydrocarbon constituents. <br /> • Construct groundwater elevation contour maps within the study area boundaries. <br /> ' • Compare current and past data. <br /> The existence and degree of petroleum hydrocarbons in the groundwater underlying a site is evaluated by <br /> (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 /> 1998 Fourth Quarter Groundwater Monitoring Report <br /> H:ILEFHUAAN1QLIIKSTOP1132\9aryt-4th.dm[January 2g,1999] <br />