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r ' 15 • November 1945 AGE-NC Project No 95-0142 ' Page 18 of 19 Because of the relatively low flow rates measured during the SVE pilot test, a unit capable of at least ' 250 scfin will be required for remediation at the site, a thermal oxidation SVE unit would be the most cost-effective choice A 24 to 36 month soil remediation period can be expected ' We recommend the installation of two addtional soil vapor extraction wells within the contaminated soil plume One soil vapor extraction well should be installed southwest of former TK1-90 ' excavation, a second soil vapor extraction well should be installed northeast of the former TK1-90 excavation The SVE well network should include all extraction wells as well as monitoring well MW-4 Proposed locations of the extraction wells are illustrated in Figure 5 ' Twoadditional extraction wells will be required to facilitate ground water remediation at the site see eq gr _ ( , ' Section 9 0 ) one extraction well should be installed northeast of MW-1, a second extraction well should be installed northwest of MW-2 Proposed wells are illustrated on Figure 5 I9.0. RECOMAMNDATIONS FOR REMEDIATION OF HYDROCARBON-IMPACTED GROUND WATER Ground water gradient calculations indicate that MW-4 has remained the down-gradient well since January 1995 As in the three previous sampling events, the highest concentration of dissolved ' hydrocarbons were detected to MW-3, north of the former UST excavations, no hydrocarbons were detected in MW-4 ' Upon careful consideration, an in-situ method appears to be more effective in cost and in operation over the "pump and treat" method Both in-situ methods described in this CAP could be equally effective in remediating the site As with in-situ bioremediation of soil at the site, bioremediation of Iground water are likely to be the more cost-effective However, special monitoring requirements unposed by some regulatory agencies can reduce cost effectiveness Furthermore, it is our experience from dealing with regulatory agencies throughout the State of California that they are apprehensive of approving in-situ ground water bioremediation without conducting a comprehensive pilot test r Combined with SVE, the IAS method "mecharucally/physically" strips hydrocarbons without the raddition of any chemicals or rmcrobe solution into the environment It is a better known and more 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, we recommend the installation of an IAS system for remediation of ground water at the Stockton Plating site A 24 to 30 month remediation period can be expected IWe estimate that the IAS system will require the installation of 9 or 10 spargrng points (wells) four IAS wells should be installed between former UST excavation TK1-90 and MW-4, two IAS wells should be installed northeast of MW-1, two IAS wells should be installed northwest of MW-2, and