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04 January 2002 <br /> AGE-NC Project No. 95-0100 <br /> Page 3 of 4 <br /> at the site decreased an average 0.45 feet between the July and November 2001 ground water <br />' monitoring events. The groundwater flow direction for the sampling event was inferred to be toward <br /> the northwest at an average gradient of 0.01 feet/feet. Data from MW-4 was not used to determine <br /> ground water gradient, as this well is screened at a deeper interval than the other wells. Figure 3 <br /> illustrates the contoured ground water elevations. <br />' 3.2. GROUND WATER ANALYTICAL RESULTS <br />' During the sampling event MTBE was detected in MW-1 and MW-3 by EPA method 8020 at 80 <br /> micrograms per liter (µg/l) and 27 µg/l, respectively. MTBE was confirmed in each sample by EPA <br /> method 8260 Modified at concentrations of 95 µg/1 and 31 µg/l, respectively. No other fuel <br /> oxygenates were detected at or above laboratory reporting limits in the ground water samples. <br /> Analytical results of ground water samples are summarized in Table 2. Copies of the laboratory <br />' reports (McCampbell Analytical Laboratory ID 82822 to 82827), quality assurance and quality <br /> control (QA/QC) data and chain-of-custody fortes are in Appendix B. <br /> lie 4.0. SUMMARY AND CONCLUSIONS <br /> Based on the findings of this and previous investigations, AGE concludes the following: <br /> • The ground water flow direction was toward the northwest during the November 2001 <br /> sampling event. <br /> • MTBE was detected in samples from monitoring wells MW-1 and MW-3 at concentrations <br /> ' as high as 95 µg/l. <br /> • The MTBE concentrations exceeded the State of California maximum contaminant level <br /> (MCL) of 13 gg/l in the water samples collected from wells MW-I and MW-3. <br /> 1 The lateral extent of MTBE-impacted ground water has been defined. <br /> 5.0. RECOMMENDATIONS <br /> Based—n the results of this investigation, AGE recommends that quarterly tiionitoring be continued. <br /> The next monitoring and sampling event should be conducted in January 2001. <br /> ' A work plan to abandon domestic well DW-1 has recently been approved by San Joaquin County <br /> PHS-EHD. AGE anticipates the work will be performed by March 2002. <br /> ' Advanced GeoEnvironwental,Inc. <br />