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01 June 1999 AGE-NC Project No 95-0137 Page 25 of 26 ' Remediation of impacted ground water should be conducted concurrently with soil remediation to prevent re-contamination of remediated soil In-situ air sparging combined with soil vapor extraction appears to be a viable alternative for remediation of both soil and ground water in the vicinity of the ' former UST location Ground water monitoring at the site indicates that MW-8, located near the domestic well on the ' Jimco site, is the down-gradient well High concentrations of dissolved hydrocarbons have been consistently detected in wells MW-2, MW-3 and vapor extraction wells VW-1 and VW-2 Ground water in the vicinity of monitoring wells MW-2, MW-4, VW-1 and VW-2 (the former UST area) ' is characterized by TPH-g TPH-d ratios ranging from 0 702 to 1 852, the ratio in the area of MW-3 is 0 104 Ground water in the former UST area may be more effectively addressed by IAS, while ground water in the vicinity of MW-3 may be more effectively addressed by attempting to stimulate ' bioremdiation through sparging to increase dissolved oxygen concentrations Combined with SVE, the IAS method"mechamcally/physically"strips volatile hydrocarbons from ground water without the addition of any chemicals or microbe solution into the environment IAS is a widely accepted method of volatilizing hydrocarbons As IAS has few, if any, adverse environmental effects, it is likely to be more readily approved for implementation by regulatory agencies Based upon these considerations and the presence of relatively sandy soil at the Ripon site, AGE recommends installation of an IAS system for remediation of ground water in the former UST ' area An 12 to 18 month remediation period can be expected to be required to reduce volatile and light-end hydrocarbon concentrations by 80 % or to near State of California drinking water standards A sparging/extraction system may also have a secondary effect of bioventing impacted ' soil, increasing the oxygen concentrations available for biologic processes, thereby possibly increasing the natural degradation rate AGE recommends addressing ground water impacted primarily by TPH-d by encouraging biodegredation by increasing dissolved oxygen concentrations This can be accomplished by installation of sparge points for slow sparging If a discharge permit can be procured from the ' CVRWQCB, infection of additional bacterial inoculum and nutrients would stimulate the process ' Ground water remediation alternatives, estimated durations and associated costs, as applied to the whole site, are summarized on Table 8 A Remedial Action Work Plan detailing the proposed installation and operation of the SVEIIAS system should be prepared This work plan should include ' the installation of sparging points and extraction wells Air should be supplied to each of the IAS points via underground piping by a compressor or blower-driven IAS unit capable of approximately 10 to 15 psi to each sparging well at a rate of 4 to 6 scfm Adi,anced GeoEmironmental,Inc