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' 29 January 1999 AGE-NC Project No 98-0448 ' Page 4 of 5 ' • Between August 1998 and December I998, ground water elevation decreased an average 1 11 feet at the site ' • From September to December 1998, a substantial decrease in dissolved petroleum hydrocarbon concentrations were observed from wells MW-1,MW-2, MW-4A and MW-4B (Table 2) I • Various BTE&X compounds were detected in water samples collected from wells MW-1, MW-2, MW-4A, MW-4B and MW-6 at concentrations ranging as high as 17,000µg/l ' • Concentrations of benzene detected in samples collected from wells MW-1, MW-2,MW-4A and MW-4B were above the State of California Maximum Contaminant Level (MCL) for drinking water of 1 0 ppb ' • MTBE was detected from laboratory analysis (by EPA Method 8260) of MW-413 at a concentration of 1 5µg11 • In September 1998, concentrations of MTBE were detected at MW-2 at a concentration of 690 µg11 (by EPA Method 8020), however, in December 1998, MTBE was not detected above a laboratory reporting limit of 200 µg/l • DIPE was detected from MW-1 and MW-4B at concentrations of 34 Ug/1 and 1 1 µg/l, respectively No other fuel oxygenating compounds were detected from analyzed water ' samples • The elevated concentrations of petroleum hydrocarbons detected in samples collected from ' wells MW-2 and MW-4 indicate that these wells are within or near the dissolved petroleum hydrocarbon "core area" of the plume (Figure 4) • The horizontal extent of impacted ground water has not been delineated to the west or the ' east 5.0 RECOMMENDATIONS Based upon the results of this investigation, AGE recommends • Continued quarterly ground water monitoring The next quarterly monitoring and sampling is scheduled for March 1999 • Preparation of a Work Plan Addendum to assess dissolved petroleum hydrocarbons west- northwest and east-northeast of MW-6 • A Corrective Action Plan (CAP) should be prepared following completion of site I Advanced GeoEn%Pronmenta[,Inc