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performing the remedial soil excavation, the gasoline level measured at monitoring well <br /> MW-1 ranged between 20 mg/L and 61 mg/L. The averaged contaminant level for <br /> samples collected between August 1994 and June 1998 is 52 mg/L. This average value <br /> ' indicates a gasoline mass of approximately 14 Kg, or nearly 4.8 gallons. This mass is <br /> believed to be conservative since the average contaminant level has been applied to the <br /> ' entire plume volume. Thus the actual value was likely to have been lower than that <br /> calculated. <br /> Following the remedial soil excavation, ground water contaminant levels at MW-IA, the <br /> replacement well for MW-1, have shown a significant decrease. These decreases include <br /> a 97% reduction in gasoline levels, and an 99% reduction in benzene levels. Using the <br /> ' ground water analytical data obtained in March 2004, and the same contaminant plume <br /> volume, a mass of 0.23 Kg as gasoline, or approximately 0.08 gallons remain. Once <br /> again, this estimate is considered to be very conservative and the actual residual mass is <br /> believed to be lower than presented here. <br /> A dramatic improvement was noted in ground water contaminant levels immediately <br /> ' following the completion of the remedial excavation. This can be attributed to the <br /> removal of the source of continued ground water contamination. Quarterly sampling <br /> ' events conducted in December 1998, March and June 1999, and March 2004 indicate a <br /> continuation of the reduction in contaminant levels at MW-1A. These data indicate that <br /> natural degradation is occurring, likely accelerated by the addition of ORC during <br /> backfilling of the remedial excavation. Reductions observed between the September <br /> 1998 and March 2004 sampling events indicate a decrease of more than 77% in gasoline <br /> and benzene levels. These reductions are in addition to the reductions observed <br /> immediately following the remedial excavation. Since the ORC was anticipated to have <br /> been exhausted within six months of its installation, the reductions observed since March <br /> 1999 are more likely the result of indigenous organisms, volatilization, or other natural <br /> ' factors. <br /> ' 14.0 SITE REMEDIATION <br /> ' A remedial soil excavation was performed in July and August, 1998. Approximately <br /> 1,522 cubic yards of gasoline contaminated soil were excavated and aerated on-site. <br /> ' Following the remedial excavation, Oxygen Release CompoundO (ORC) was added to <br /> the backfill material to aid passive in-situ remediation. A total of 510 pounds of ORC <br /> was placed into the excavation below the anticipated high ground water elevation. <br /> 1 <br /> American Geological Service,Inc. <br /> CA95DE-029 16 <br />