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4 <br /> 2 . 0 GROUNDWATER FLOW DIRECTION AND GRADIENT <br /> On April 27, 2004, ASE measured the depth to water in six site <br /> groundwater monitoring wells using an electric water level sounder The <br /> surface of the groundwater was also checked for the presence of free- <br /> floating hydrocarbons or sheen No free-floating hydrocarbons or sheen <br /> were observed in any of the site groundwater monitoring wells As <br /> requested by the San Joaquin County PHS-EHD, the groundwater sampling <br /> was coordinated with the consultants investigating two adjacent <br /> properties, the former BP Service Station located at 2375 Tracy Boulevard <br /> to the west and the former Chevron Station located at 575 Grant Line Road <br /> to the north Groundwater elevation data from the three sites are <br /> presented in Tables One, Two, and Three <br /> A groundwater potentiometric surface map that includes groundwater <br /> elevation data from all of the monitoring wells in the area is presented as <br /> Figure 2 The groundwater flow direction is to the northwest with a <br /> gradient of approximately 0 011 ft/ft This gradient and flow direction are <br /> consistent with previous findings <br /> 3 . 0 GROUNDWATER SAMPLE COLLECTION AND ANALYSIS <br /> • Prior to sampling, each monitoring well was purged of three well casing <br /> volumes of groundwater using dedicated polyethylene bailers <br /> Groundwater samples were collected from each well using dedicated <br /> polyethylene bailers <br /> The samples were decanted from the bailers into 40-m1 volatile organic <br /> analysis (VOA) vials and pre-preserved with hydrochloric acid The <br /> samples were capped without headspace, labeled and placed in a cooler <br /> with wet ice for transport to Kiff Analytical, LLC of Davis, California (ELAP <br /> #2236) under appropriate chain-of-custody documentation Well sampling <br /> field logs are presented in Appendix A <br /> The groundwater samples were analyzed for total petroleum hydrocarbons <br /> as gasoline (TPH-G), benzene, toluene, ethyl benzene, and total xylenes <br /> (collectively known as BTEX), and fuel oxygenates by EPA Method 8260 <br /> Analytical data from the three sites are presented as Tables Four, Five, a n d <br /> Six The certified analytical report and chain-of-custody documentation <br /> are included as Appendix B An isoconcentration contour map of methyl- <br /> tertiary butyl ether (MTBE) concentrations is presented as Figure 3 <br /> Singh's Unocal Service Station Quarterly Report — April 2004 Sampling <br /> -2- <br />