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Mr George Takemon Project OF90-002 04 October 25, 1995 Page 4 A reduction in the concentration of TPHG in groundwater in MW-14 was observed during the third quarter 1995 monitoring event This decrease in the concentration of TPHG can be attributed to air sparging in AS-1 Destruction Efficiency During the third quarter 1995, the destruction efficiency of the system has been greater than 99 percent for TPHG and greater than 96 percent for benzene, based on the soil vapor analytical results (see Table 5) The emission rate during the third quarter is calculated to be 0 005 pounds per day (lb/day) and 0 0002 lb/day for TPHG and benzene, respectively The operation of the remediation system is in compliance with the requirements set forth by the S.VUAPCD's Pernut- to-Operate CONCLUSIONS The system was operational for an average of 94 percent and removed approximately 1,270 pounds of TPHG in the third quarter The cumulative mass of TPHG removed to date is approximately 2,438 pounds The concentrations of TPHG and benzene are decreasing, indicating that soil vapor extraction has been effective in removing hydrocarbons from the soil Dissolved hydrocarbons detected in groundwater monitoring well 1l,W-14 decreased substantially since the second quarter monitoring event Dissolved hydrocarbons were not detected in the other wells sampled The groundwater flow direction has generally been toward the northeast Groundwater data is consistent with previous sampling events Because monitoring wells MW-3 through MW-5 are screened above static groundwater and are not potential sources for vapor extraction, EMCON recommends these wells be abandoned by pressure grouting In addition, because the casing in monitoring well MW-1 is damaged, EMCON recommends this well be destroyed In addition, EMCON recommends the addition of nutrients (phosphorus, nitrogen and potassium) into impacted wells to facilitate microbial degradation of petroleum hydrocarbons WORK IN PROGRESS Monthly operation and maintenance of the remediation system will continue Teichert will continue to perform quarterly groundwater monitoring The next sampling event is tentatively scheduled for the last week of November 1995 It is EMCON's understanding that Tetchert will submit a workplan to abandon monitoring wells . MW-1, MW-3, MW-4, and MW-5 Once the workplan is approved, Teichert will contract a licensed well driller to abandon the wells SAC\N PJ010F9010i900020 4DS-95 PAS 1