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Problem Assessment Work Plan } I 4 CWS—Multi-Campus Regional Center January 23,2003 Page-7. i a short duration, as described. Once completed in the described time frame, only the site monitor wells will be present on-site. No other obvious impacts to the site will be present. {{ Alternative two includes soil vapor extraction (SVE) and groundwater pump and treat, which will be { combined to reduce residual contamination in soil and groundwater at the source area. The vapor extraction system will remove soil vapors from soil in the area of the former tank excavation. Soil vapors will be removed from the subsurface through SVE wells and combusted in a thermal oxidizer. Condensate from the 1 extraction system will be processed through activated carbon canisters used for the groundwater pump and treat system and released to the sanitary sewer. An SVE pilot test will be required to determine the number and location of SVE wells needed to remove the hydrocarbons in the soil. Groundwater will be extracted from wells to be installed to a depth of approximately 65 feet;bgs. Groundwater will be pumped at a rate to capture the plume and to draw down the aquifer in the vicinity of the wells to a depth of approximately 55 feet bgs. This will enable the SVE system to:draw hydrocarbon ' c yapors from the previously saturated soils, thus enhancing the effectiveness of the SVE'in remediating the :1 site. An aquifer pump test will be required to determine the number and location of wells and the pumping j rate deeded to accomplish the desired results. Extracted groundwater will be processed through carbon ti t. I canisters and released to the sanitary sewer. This alternative is justified because it will reduce the level of V,t contamination in the soil and groundwater to minimize the potential impact to the beneficial use of groundwater. The time to arrange logistics and complete the remediation is estimated to be 18 to 24 months. I During the SVE and pump and treat remediation, a moderate amount of site disruption will be necessary. The SVE and carbon treatment equipment will be housed in a small fenced area. All piping for the system it :will in closed trenches. The remediation equipment will typically be continuously noisy. t The no action alternative would involve no active remediation efforts. The subsurface contamination would ! be allowed to degrade naturally in place. The plume could be monitored to evaluate mobilization of contaminants. This alternative may be justified because the source of contamination is relatively isolated (under an asphalt cap) and of moderate concentration, such that it may not pose a significant threat'to the public from the potential pathways of direct inhalation. Risk Based Corrective Action(RSCA), including :Tier II analyses (involving additional site sampling), would be required, however, to evaluate the risk'to the public from site contamination- Time for remediation by this method could take decades and would require ;,continued quarterly monitoring until closure is received. 6.2 COMPARATIVE COST ANALYSIS I Preliminary'cost estimates for the first and second alternatives are presented in Table' C and Table Din. ..Appendix B. These are general estimates for comparison purposes only and are not based on actual monitoring and reporting requirements, which may change with conditions. The accuracy of these estirnates should be considered no better than within 25-50% of the true costs. Estimated costs for soil' over- excavation and removal are approximately $583,000. Estimated costs for the SVE and,groundwater pump and treat alternative are approximately $304,000. There are no remediation costs associated with the no action alternative other than RSCA and possible additional monitoring costs associated with intrinsic bioremediation testing, etc. x t F I - " I ! , « CONDOR