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ri r 1 INTRODUCTION This report presents data collected during the first quarter 1999 monitoring period at the USA Gasoline Corporation (USA) Service Station No. 65, located at 2500 West Lodi Avenue, Lodi, California (see Figure 1). Groundwater monitoring consists of measuring depths to water, collecting groundwater samples for subjective laboratory analysis, and evaluating gradient and direction of groundwater flow beneath the site. 2 BACKGROUND The subject site is currently an operating retail gasoline station located on West Lodi Avenue in Lodi, California. During the course of the site assessment programs conducted between 1987 and 1993, a total of 10 groundwater monitoring wells were installed. Historically, all wells have shown petroleum hydrocarbon impact, however monitoring wells MW-1 and MW-5 through MW-7 have had very little impact. Three gasoline UST's and associated piping were removed and replaced on October 6 and 7, 1997. Approximately 500 cubic yards of hydrocarbon-impacted soil were excavated and removed from the site during these activities. • 3 GROUNDWATER GRADIENT AND DIRECTION The first quarteor 1999 groundwater monitoring event at USA Service Station No. 65 was conducted on March 30, 1999. Depth to groundwater measurements at monitoring wells MW-1 through MW-8, S-1 and S-2 were made using an electronic sounding device and recorded on monitoring well data forms (see Appendix A). Locations of monitoring wells are illustrated in Figure 2. Depth to groundwater measurements are summarized in the table. At the time of the first quarter monitoring event, groundwater was first encountered at depths of 35.65 to 37.74 feet below ground surface. March 30, depth-to-groundwater measurements were used in constructing a groundwater contour map (see Figure 2). During the first quarter 1999 monitoring event, groundwater beneath the site generally flowed to the south-southeast with a gradient of 0.003. Field data sheets are presented-in Appendix A. 4 SAMPLING, ANALYSIS, AND MONITORING PROGRAM RESULTS Groundwater samples were collected from ten monitoring wells on March 30, 1999. Sample locations are illustrated in Figure 2. Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHG) by United States Environmental Protection Agency (USEPA) method 8015 and for benzene, toluene, ethylbenzene, and total xylenes (BTEX) and methyl tert-butyl ether (MTBE) by USEPA method 8020. MTBE was confirmed using USEPA method 8260. OAK\S:\USA\00651QTRLY\0o65o 199.DOC\uh:1 1