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Option t — No-Action • The strength of this option is primarily low cost The principal weakness of immediate closure without further action is the difficulty in obtaining regulatory approval at this point with the available groundwater data from 1988 to 1994, indicating that groundwater has not been impacted In the previous section, this option received a relatively low numerical rating from technical and administrative implementability considerations and does not appear to be feasible at this time Option 2 — Limited Action -- Groundwater Monitories • The strength of this option includes the protection of groundwater and subsequently the public's health and safety, which is achieved for relatively low ' cost Additional benefits of this option include the continuation of groundwater monitoring, while maintaining flexibility of increasing monitoring frequency, extending monitoring duration, and allowing for further remedial action if monitoring results indicate that groundwater has been impacted The weaknesses of this option include the uncertainty of cost expenditures, and the time required ' to complete final closure This option received the highest numerical rating in the previous season and appears to be feasible Option 3 — Limited Action — Monitoring and Pavement Maintenance • Similar to Option 2, the strength of this option includes protection and flexibility for further action at a reasonable cost The pavement maintenance program provides additional protection by reducing the infiltration of rainwater and potential mobilization of constituents in soils This option scored very high in the numerical rating and appears to be feasible as well Option 4 — In-Situ Biov_entin • This option provides additional treatment of TPH-impacted soils, but will not reduce TPH concentrations of impacted soils to background in a relatively short period of time By enhancing the movement of oxygen within the vadose zone, this technology enhances the biodegradation of TPH by the native population of soil microorganisms without using liquids which would require groundwater 1 extraction The cost of this in-situ technique is intermediate Although not cost- prohibitive, the effectiveness of this option may be limited by the predominantly silty soils on the site Ex-situ bioremediation conducted in 1990 could reduce TPH concentrations in soils to approximately 1,000 mg/kg, pnncipaily because fine-textured soils retained much of the TPH preventing biodegradation This option is considered only marginally feasible because of the time required and the limited effectiveness compared to the substantial costs required to implement this technology sAc127 10 26 DAMES &MOORE