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r = 2 . 0 GROUNDWATER FLOW DIRECTION AND GRADIENT On April 30, 2002, ASE measured the depth to water in six (6) site groundwater monitoring wells using an electric water level sounder. The surface of the groundwater was also checked for the presence of free- floating hydrocarbons or sheen. No free-floating hydrocarbons or sheen were observed in any of the site groundwater monitoring wells. As requested by the San Joaquin County PHS-EHD, the groundwater sampling was coordinated with the consultants investigating two adjacent properties, the BP Service Station located at 2375 Tracy Boulevard to the west and the former Chevron Station located at 575 Grant Line Road to t h e north. Groundwater elevation data from the three sites are presented in Tables One, Two, and Three. A groundwater potentiometric surface map that includes groundwater elevation data from all of the monitoring wells in the area is presented as Figure 2. The groundwater flow direction is to the northwest with a gradient of approximately 0.0082 ft/ft. This gradient and flow direction are consistent with previous findings. 3 .0 GROUNDWATER SAMPLE COLLECTION AND ANALYSIS Prior to sampling, each monitoring well was purged of three well casing volumes of groundwater using dedicated polyethylene bailers. The parameters pH, temperature, and conductivity were monitored during the well purging. Groundwater samples were not collected until these parameters stabilized. Groundwater samples were collected from each well using dedicated polyethylene bailers. The samples were decanted from the bailers into 40-m1 volatile organic analysis (VOA) vials and pre-preserved with hydrochloric acid. The samples were capped without headspace, labeled and placed in a cooler with wet ice for transport to Kiff Analytical, LLC of Davis, California (ELAP #2236) under appropriate chain-of-custody documentation. Well sampling field logs are presented in Appendix A. The groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPH-G), benzene, toluene, ethyl benzene, and total xylenes (collectively known as BTEX), and fuel oxygenates by EPA Method 8260. Analytical data from the three sites are presented as Tables Four, Five, a n d Six. The certified analytical report and chain-of-custody documentation are included as Appendix B. TPH-G, benzene, and MTBE isoconcentration %6 ' maps are presented as Figures 3, 4, and 5, respectively. Singh's Unocal Service Station Quarterly Report - April 2002 Sampling -2-