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i t r i10 INTRODUCTION ' This report presents data collected during the fourth quarter 1999 monitoring event 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. 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 underground storage tanks 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 fourth quarter 1999 groundwater monitoring event at USA Service Station No. 65 was conducted on December 19, 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 Table 1. ' At the time of the fourth quarter monitoring event, groundwater was first encountered at depths of 39.19 to 40.87 feet below ground surface. During the fourth quarter 1999 monitoring.event, ' groundwater beneath the site generally flowed to the south-southeast and southwest with a gradient of 0.002 and 0.004 foot per foot, respectively (see Figure 2). Field data sheets are presented in Appendix A. ' 4 SAMPLING,LING, ANALYSIS, AND MONITORING PROGRAM ' RESULTS Groundwater samples were collected from 10 monitoring wells on December 19, 1999. Sample ' locations are illustrated on Figure 1. Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHG)by United States Environmental Protection Agency (USEPA) method 8015; for benzene, toluene,ethylbenzene, and total xylenes (BTEX) and methyl tert-butyl ether (MTBE) by USEPA method 8020; and for oxygenates (tert butyl alcohol (TBA), MTBE, ethanol, diisopropyl ether, ethyl tert butyl ether, and tert amyl methyl ether) using USEPA Method 8260. ' SACH\\SACRFPI\COMMON\Consulting\data�Sharcd\Projects\PJ7\79Z065.bs.doc-00\it:1 IT CORPORATIon 1