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i Mr. Kenneth Earnest October 5, 1993 Page 2 of San Joaquin. Ground water samples collected on July 27, 1993, were submitted to a state-certified laboratory for analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and total petroleum hydrocarbons as gasoline (TPHg). Ground water samples collected from monitoring wells MW-2 and MW-5 were also analyzed for halogenated volatile hydrocarbons in accordance with EPA Method 601. Ground water sample analytical results for the July 27, 1993, sampling event are compiled in Table 2. Copies of the certified laboratory analytical reports from the July 27, 1993, sampling event are presented in Enclosure C. Discussion Concentrations of TPHg in ground water samples collected on July 27, 1993, ranged from 7,000 micrograms per liter (µg11) a sample collected from monitoring well MW-3 to 190 µg/l in a sample collected from monitoring well MW-4. Benzene concentrations were also highest in the sample from monitoring well MW-3 at 2,300µg11 and were lowest (2.6µg/1) in the sample from monitoring well MW-4. An inferred benzene isoconcentration map based on the July 27, 1993, ground water sample analytical results is illustrated on Figure 4. Ground water samples collected from monitoring wells MW-2 and MW-5 were analyzed for halogenated volatile organics. A sample collected from monitoring well MW-5 contained 1,2-dichloroethane and trichloroethene at concentrations of 0.18 and 0.13 µg11, respectively. A sample collected from monitoring well MW-2 did not contain detectable levels of halogenated volatile organic constituents. Copies of certified analytical reports are presented in Enclosure C. The analytical results of the EPA Method 601 analysis are compiled in Table 3. Future Work AMV is in the process of preparing an Interim Problem Assessment Report/Remedial Action Plan (PAR/RAP) for the site. While additional assessment of the distribution of petroleum constituents in ground water may be necessary, the PAR/RAP will propose remedial measures to remove the residual source of petroleum hydrocarbon constituents from soils underlying the site and.inhibit the migration of ground water containing petroleum constituents. Quarterly ground water monitoring will continue on the site. The next sampling event is scheduled for October 1993. It is recommended that samples collected from monitoring well MW-5 be analyzed for chlorinated solvents in forthcoming monitoring events. �r LRPTOMECD ACTON • MICKELSON • van DAM, INC. Consulting Scientists, Engineers,and Geologists