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4 <br /> Mr. Kenneth Earnest <br /> February 23, 1994 <br /> Page 2 <br /> Ground Water Sample Analytical Results <br /> Ground water samples were collected from monitoring wells MW-1 through MW-5 on <br /> October 26, 1993, using the procedures outlined in Enclosure A. Field observations and ground <br /> water sampling documentation are presented in Enclosure B. This ground water sampling event <br /> was witnessed by Mr. Michael J. Infurna, Jr., Public Health Services, County of San Joaquin. <br /> Ground water samples collected on October 26, 1993, were submitted to a state-certified <br /> laboratory for analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and total petroleum <br /> hydrocarbons as gasoline (TPHg). Ground water sample analytical results for the October 26, <br /> 1993, sampling event are compiled in Table 2. Ground water samples were also collected on <br /> November 22, 1993, from monitoring wells MW-1 through MW-5 and submitted for analysis <br /> of halogenated volatile hydrocarbons in accordance with U.S. Environmental Protection Agency <br /> (EPA) Method 601. Copies of the certified laboratory analytical reports from the October 26 <br /> and November 22, 1993, sampling events are presented in Enclosure C. <br /> Discussion <br /> Concentrations of TP-Hg in ground water samples collected on October 26, 1993, ranged from <br /> 130 micrograms per liter (µg11) in a sample collected from monitoring well MW-1 to 9,600µg11 <br /> in a sample collected from monitoring well MW-3. Benzene concentrations ranged from <br /> 0.68 µg/l in monitoring well MW-5 to 3,100 µgll in the sample collected from monitoring well <br /> MW-3. An inferred benzene isoconcentration map based on the October 26, 1993, ground water <br /> sample analytical results is illustrated on Figure 4. <br /> Ground water samples collected on November 22,1993, did not contain detectable concentrations <br /> of halogenated volatile hydrocarbons except for the sample obtained from monitoring well <br /> MW-5. This sample contained 2.6 µg11 of 1,2-dichloroethane. Copies of certified analytical <br /> reports are presented in Enclosure C. <br /> As of the October 26, 1993 sampling event, the installed pump in monitoring well MW-3 has <br /> removed 3,867 gallons of water. <br /> Future Work <br /> Quarterly ground water monitoring will continue on the site. The next sampling event is <br /> scheduled for January 1994. <br /> s <br /> ACTON- <br /> MICKELSON- �,�coas.mi <br /> van DAM,INC. <br /> Consulting Scientists,Engineers,and Geologists <br />