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• Mr George Takemori Project OF90-002 04 <br /> May 30, 1996 <br /> Page 4 <br /> subsurface to regain its original equilibrium The remediation system will be operated in <br /> the second quarter to determine if the soil vapor concentration has increased to make <br /> extraction and treatment of soil vapors economically viable EMCON, in the interim, is <br /> also evaluating alternative techniques to remediate the residual hydrocarbon concentration <br /> in the subsurface <br /> CONCLUSIONS <br /> Dissolved hydrocarbons were detected in groundwater monitoring wells MW-11, MW-13, <br /> and MW-14 However, the laboratory indicated that the chromatogram did not match the <br /> typical gas fingerprint The increased hydrocarbon concentrations un wells MW-11, <br /> MW-13, and MW-14 were higher this sampling event than any historically high levels of <br /> hydrocarbons Based on dechnuig trends in previous sampling events, EMCON believes <br /> that the laboratory results may be erroneous For this reason, EMCON proposes to over- <br /> purge the wells prior to sampling during the second quarter of 1996 in order to remove <br /> any possibility of inadvertently introducing petroleum hydrocarbons Dissolved <br /> hydrocarbons were not detected in the other wells sampled The groundwater flow <br /> • direction has generally been toward the northeast <br /> The cumulative mass of TPHG removed to date is approximately 3,008 pounds (see <br /> Table 2) <br /> WORK GN PROGRESS <br /> Monthly operation and maintenance of the remediation system will be discontinued The <br /> treatment unit will be pulsed as required to remove any accumulation of hydrocarbons <br /> During the second quarter monitoring event, EMCON will overpurge the wells to remove <br /> any inadvertently-introduced hydrocarbons After the second quarter results have been <br /> received, EMCON will evaluate the effects of intrinsic bioremediation at the site With <br /> declining influent concentrations and increased microbial activity, it may be more cost- <br /> effective to discontinue SVE and monitor intrinsic bioremediation Teichert will continue <br /> to perform quarterly groundwater monitoring The next sampling event is tentatively <br /> scheduled for the last week of May 1996 <br /> It is EMCON's understanding that Teichert will submit a workplan to abandon monitoring <br /> wells MW-1, MW-3, MW-4, and MW-5 Once the workplan is approved, Teichert will <br /> contract a licensed well driller to abandon the wells <br /> • <br /> SACNN\PJ"F9MF900020 4HS-95\pas 1 <br />