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temporary condition Groundwater analytical data in support of this temporary condition from MW-I and MW-7 indicates that once these wells were purged and sampled a few times, the TPHd concentrations declined to non-detectable levels Since groundwater is not impacted, intrinsic bioremediation of groundwater is not currently active However, the data indicates that conditions are very good (sufficient DO, sulfate, and nitrate) for natural biodegradation Hydraulic Conductivity Testing RTD conducted hydraulic conductivity testing using six of the seven onsite groundwater monitoring wells The testing consisted of either specific capacity testing, which includes pumping each well at a constant discharge rate until a stable drawdown is achieved, or slug testing Generally, slug testing is better suited for hydraulic conductivities less than 5-feet/day due to swift water level recovery For higher hydraulic conductivities, specific capacity testing is used Based on field observations, RTDs certified hydrogeologist determined that the shallow screened wells (except for MW-4, which did not have a sufficient water column to perform hydraulic testing) would respond well to slug testing and the deeper screened wells were better suited to specific capacity testing The data collected for this task is used to estimate hydraulic conductivity values at each well location The slug test data was analyzed using the method developed by Bouwer and Rice, 1976 The specific capacity data was analyzed using the method contained in Driscoll, 1986 Table 2 summarizes the results of the hydraulic conductivity testing at the subject site The slug test plots and review of the analysis is contained in Appendix B The calculated hydraulic conductivity values were very different for the deeper screened and shallow screened wells The average hydraulic conductivity of the shallow screened wells is approximately 0 8-feet/day and of the deeper screened wells is approximately 45-feet/day The results for the shallow screened wells are consistent with the boring logs developed for the site (silty sand), however, the results for the deeper screened wells are not generally consistent with the boring logs, except for MW-5 The boring logs for MW-6 and MW- 7 indicate that the wells are screened silt and clayey silt This inconsistency may be due to the fact that soil samples were not collected from 70- to 90-feet, and sandy units may have been encountered, but not identified, or the deeper screened wells may be hydraulically connected via sand pack above the screen with the sand and gravel unit from 40- to 65-feet Given that it is suspected that there may be a hydraulic connection through the sand pack, immediate destruction of the deeper screened wells is strongly recommended The results of the hydraulic conductivity testing indicates that groundwater yields from both shallow screened and deeper screened zones would be in excess of 200-gallons per day Because the deeper screened wells do not appear to be constructed appropriately, and due to the extreme fluctuations in the water table elevation, an efficient groundwater extraction system is not practical nor feasible at this site However, since groundwater is not impacted or threatened, groundwater remediation is not necessary EVALUATION OF REMEDIATION OPTIONS As part of the feasibility study evaluation, RTD has considered options, including 1) impacted soil removal 2) intrinsic bioremediation, and, 3) groundwater pumping Based on all of the information gathered at this site and based on RTDs feasibility study, the most cost effective and feasible remediation option was the removal of impacted soil Applicable cleanup levels for this remediation option is the residual saturation of the remaining petroleum hydrocarbons such that these constituents do not dissolve into groundwater The results of groundwater monitoring conducted from October 1994 through December 1995 shows that the selected remediation option was successful in preventing dissolution of petroleum hydrocarbons into groundwater The DO measurements indicate that natural biodegradation is likely reducing the remaining soil impacts - 8 -