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1 _ CJ 8 Inc. Page Bolo icaC7ecknics 7 City o . f Escalon Project No. 750.3 February 26,2001 2.3 Groundwater Cleanup Alternatives At this time, the groundwater plume does not extend from the contaminant source area of well MW-1 to down gradient well MW-4. The proposed SVE system may be able to reduce the loading to groundwater and a separate remedial system may not be. needed. GTI proposes to defer the treatment of the groundwater plume until after the effectiveness of the vadose remediation is judged. 2.4 Result of Feasibility Study Li As outlined above, excavation and RNA are not suitable for the site. The SVE extraction + wells currently in place have been demonstrated to be capable of removing contaminants from the vadose zone. It is recommended that a Soil Vapor Extraction and Treatment System be installed to accomplish the following goals: - • Remove the elevated.concentrations of BTEX, MTBE and TPH-G in the vadose zone soils. • Stop the•continued leaching of these contaminants from the soil into the groundwater. • Increase the oxygen content in the subsurface so that the rate of biodegradation of these hydrocarbons will increase. 2.5`. Remediation Goals ` In their January 11, 2001, correspondence, SJC-PHS/EHD states that- "San Joaquin County has established that primary and secondary drinking standards, known as maximum contaminant levels, are appropriate cleanup goals, at a minimum, for all contaminated underground storage tank sites within the county". Acknowledging this statement, the goal of the SVE system is to reduce the contaminant loading from the soil to the groundwater t. such that groundwater quality is restored to meet the above criteria. The target zones of the remedial system are those identified as Zones 1 through 3 in g Y g Figure's 3a and 4a. L 3.0 VAPOR EXTRACTION-REMEDIAL ACTION t3.1 Vapor Extraction Wells No�additional vapor extraction wells (VEW) are proposed at this time. Data from the pilot test suggests that the impacted .soils beneath the site are within the demonstrated radius of influence of the four existing vapor extraction wells. All four wells will be used to cycle the r applied vacuum throughout the affected soils. L 3.2. Air Recharge Wells a The existing groundwater monitoring wells and unused vapor extraction wells (those not currently attached to the vacuum) will be used for air-recharge wells by fitting them with breather caps. The breather caps will be constructed so as to not allow rainwater to enter the LTJ wells.