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Boyett Petroleum,Manteca Third Quarter 2002 Groundwater Monitoring Report Page 4 4.0 MONITORING RESULTS 4.1 FIELD OBSERVATIONS Floating product, sheen, and odors associated with petroleum hydrocarbons were not observed in the 1 groundwater purged from the monitoring wells during the groundwater sampling. The groundwater purged from MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, and MW-9 contained a significant amount of suspended sediment. Field observations are included on the Groundwater Monitoring Field Forms in Appendix B. 4.2 GROUNDWATER ELEVATION CONTOURS On September 30, 2002, Condor representatives surveyed the locations and elevations of MW-1 through MW- 9. The well collars of all the monitoring wells were surveyed relative to an established benchmark in order to comply with California Assembly Bill 2886. The survey data were collected with a Trimble 5700 Centimeter- Level RTK Global Positioning System (GPS) and referenced to the North American Datum of 1983 (NAD83). Current groundwater elevation measurements are referenced to the updated survey data. The current well collar survey data is presented in Table 1, below, and in historical groundwater monitoring data included in Appendix C. IThe water level measurements collected from monitoring wells MW-1, MW-2, MW-3, MW-6, MW-7, and MW-8 on September 26, 2002 generally indicate a general groundwater gradient to the south/southwest. 1 Monitoring wells MW-4 and MW-5 were dry. Historical groundwater gradients reported for the site have been highly variable. Groundwater elevation data associated with the monitoring wells are presented in Table 1, below. Figure 3, Appendix A, illustrates the groundwater elevation contours on September 26,2002. Table 1 Groundwater Elevation Data (September 26,2002) 1 Monitoring Well TOC Elevation' Screened Depth to Groundwater Interval(bgs) Groundwater Elevation' MW-1 36.16 13-33 21.81 14.35 MW-2 35.97 15-25 21.40 14.57 MW-3 36.18 15-25 21.26 14.92 MW-4 3 5.3 8 9-24 DRY NM 1 MW-5 35.93 10-30 DRY NM MW-6 36.07 10-25 22.02 14.05 MW-7 36.42 10-25 21.61 14.81 MW-8 36.43 10-25 21.79 14.64 MW-9 35.95 40-50 21.91 14.04 ITOC Elevation: Elevations are referenced to NAD83 datum by post-processing the base station against the Condor Stockton(CNDR) CORS Station NGS Benchmark HS 4486,elevation 35,03 feet. 'Groundwater Elevation:Elevations are measured from the top of the well casings and are referenced to the benchmark indicated above. All measurements are in feet. NM—Not measured 4.3 LABORATORY ANALYSES The groundwater samples were analyzed for BTEX and selected gasoline oxygenates/additives by EPA Method o2GOD, aild I Fn-kJ uy iviciliuu ou i Sivl. T itc selected oxygenates/additives inciuded methyi tent butyi ether (MTBE), ethanol (EtOH), tertiary-butanol (TBA), di-isopropyl ether (DIPE), ethyl-tert butyl ether (ETBE), tert-amyl methyl ether(TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane(EDB). ' 3 ' �"a CONDOR