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QUARTERLY GROUNDWATER MONITORING AND SAMPLING REVIEW QUARTERLY GTS MONITORING AND SAMPLING REVIEW 4614 W TURNER RD. , LODI PAGE 2 Following the initial excavation, 15 soil borings were drilled, between May 15 and June 2 , 1989 Laboratory results of soil analyses determined the presence of petroleum hydrocarbons in concentrations exceeding 100 mg/kg in the area surrounding the tank excavation After completion, 10 of the borings were converted to groundwater monitoring wells (Figure 2 ) Initial sampling of the wells indicated the presence of benzene in concentrations above the DHS Maximum Contaminant Levels (MCL 's ) for drinking water in three of the wells . In the fall of 1992 , a groundwater treatment system was installed in MW 1 . A report on the installation of this system has been submitted to San Joaquin Public Health Services and to Central Valley Regional Water Quality Control Board. Groundwater and Groundwater Treatment System (GTS) Monitoring and Sam 1p__ink_ Results from earlier quarterly samplings have been submitted in previous reports The quarterly sampling covered in this report was conducted by Caltest Analytical Laboratories . The results of the findings are summarized in the following sections . Groundwater levels are presented in Table 1 . Analytical results are presented in Table 2 Copies of the laboratory reports are presented in Attachment I . SECOND QUARTER 1994 - Sampled on May 10 , 1994 ' Groundwater levels and samples were obtained from monitoring well #3 , #6 , and #7 at the site Monitoring Well 1 has been converted into an extraction well . MW-9 was damaged in 1990 and cannot be sampled The remaining wells were not scheduled to be sampled during this round of sampling. The influent and effluent to the GTS were also sampled Groundwater levels at the three points average 16 . 57 feet below the surface This represent an average drop of 2 44 feet from the fourth quarter of 1993 , which was the last time all three wells were measured No contaminants were detected in the three wells tested In the Groundwater Treatment System (GTS) , 13 0 ppb Benzene, 7 8 ppb Ethylbenzene, 3. 7 ppb Toluene, 37 ppb Xylene and 140 ppb TPHg were detected in the influent ( formerly MW 1) . No contaminants were detected in the effluent from the GTS.