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Valley Water Treatment page 2 Corrective Action Plan GPE Project No.480.3 .December 12,2006 In 1987, a former underground gasoline tank was removed under County supervision and low levels of petroleum hydrocarbons leaked to impact the soil. On March 9, 2005, Geo-Phase Environmental issued a document entitled Report - Soil Borrow .Installation 612 N. Buena Vista Avenue, Stockton CA regarding the installation of several Geo-Probe soil borings that documented the presence of gasoline hydrocarbons in the soil and groundwater in the area of the former tank. On December 1, 2005, four monitoring wells were drilled and constructed as directed by the San Joaquin County Environmental Health Department. This work was described in a document entitled Report, Soil -Boring .Installation & Moaitorin Well Constructiona, Former Valley.. Water Treatment dated March 14, 2006. Since then, the only site activity has consisted of quarterly groundwater monitoring. Since then, the groundwater has been monitored on a quarterly basis. 3.0 FEASIBILITY STUDY Prior to making the decision to mitigate the gasoline release by means of soil excavation, several possible remedial methods were evaluated to assess their relative likelihood of achieving an adequate level of contaminant reduction and the cost effectiveness. The following points summarize the methods considered: Natural Attenuation While the active remedial investigation commenced relatively recently, the gasoline release was originally discovered about 18 years ago. Clearly, 18 years of natural degradation have failed to adequately mitigate the soil and groundwater contamination. It is therefore unlikely that additional time will degrade the gasoline sufficiently for closure in any reasonable period. In the mean time, annual groundwater monitoring costs of about $10,000 would be incurred. Soil Vapor Extraction Soil Vapor Extraction (SVE) can be effective in mitigating gasoline releases in cases where a fair degree of permeability exists in the subsurface and where most of the contaminant mass lies in the vadose zone. Based on boring logs, it appears that an adequate degree of permeability exists, but depending on the variability in groundwater elevation, the bulk of the contaminant mass may lie below the water table, thus reducing the effectiveness of the remedial system. 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295