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INTRODUCTION GHH Engineering, Inc. (GHH)is currently providing JAMAR Oil Distribution(JAMAR) professional engineering services to assist them with environmental issues pertaining to their site located at 4075 East Main Street, Stockton, California, as shown on Figure 1. Mr. Jay McIlrath has authorized GHH to prepare this Second Quarter 2003 Groundwater Monitoring Report and Additional Assessment Report(QMR/AAR)for the site. This report has been prepared for submittal to the San Joaquin County Environmental Health Department(County), the lead regulatory agency overseeing environmental issues at the site. This QMR/AAR documents the May 19-23, 2003 installation of one on-site extraction well(EW- 1) and two sets of off-site, clustered, monitoring wells (MW-6A, MW-6B and MW-7A, MW-7B), (See Figure 2). The monitoring wells were installed to further define the downgradient extent of impacted groundwater. The extraction well was installed for use in an aquifer performance test (APT) which was conducted at the site on May 22, 2003. Results of the APT and accompanying slug tests are included in this report. A Sensitive Receptor Survey(SRS) was also performed by GHH during May 2003 and the results of that SRS are included in this report. In addition, this QMR/AAR documents the second quarter 2003 groundwater monitoring event, which was conducted on May 29, 2003 and included all five new wells. BACKGROUND AND SITE HISTORY Site Description The site is currently an Exxon retail gasoline service station that is located on the northwest corner of East Main Street and Oro Avenue at 4075 East Main Street, Stockton, CA. A rectangular office/store building is located near the center of the property. The property is asphalt paved except in the area of the pump dispenser islands where it is paved with concrete, and the northern portion of the site where there is a strip of dirt. The site contains one underground storage tank (UST) and two dispenser islands as shown in Figure 2. The UST is a split 20,000 gallon tank that stores 12,000 gallons regular unleaded gasoline and 8,000 gallons premium unleaded gasoline. No diesel fuel tanks have been located on this site. An underground waste oil tank(300 gallon) located behind the store building to the north and a 500 gallon underground kerosene tank were removed in 1995. The waste oil tank had reportedly been filled with diesel fuel for testing purposes approximately three times since installation. Three previous UST's that stored unleaded regular, leaded regular, and unleaded premium gasoline were removed in 1998. The location of the former waste oil tank and the previous UST's are shown on Figure 3. Geology and Hydrogeology Geologically, the property is underlain by the Quaternary Modesto Formation and the deeper Quaternary Riverbank formation, both of which consist mainly of arkosic alluvium derived �, predominantly from erosion of the Sierra Nevada.Mountains to the east.