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San Joaquin County Publi orks - 3 - 9 January 2007 <br /> f <br /> VOCs by less than 50 ug/I. Beneficial uses of groundwater would be impaired at <br /> concentrations much less than 50 ug/I for.many VOCs (i.e. Trichloroethylene Cal/EPA Cancer <br /> Potency Factor, one in million cancer risk is 2.7 ug/I for dinking water) and would require <br /> groundwater remediation. Therefore, a groundwater remediation system should also be <br /> included as part of the cost estimate for corrective action. <br /> North County Recycling Center and Sanitary Landfill <br /> North County Recycling Center and Sanitary Landfill consists of four (4) modules. Modules 1 <br /> and 2 were combined into a single module in 1991. Module 3 was constructed in 1995 and <br /> Module 4 was constructed in 2003. All modules are lined and were constructed with leachate <br /> collection and recovery systems. VOC impacts have occurred in the past and current <br /> monitoring data suggests VOCs continue to impact the vadose zone with sporadic VOC <br /> detects in groundwater. San Joaquin County's "Hypothetical Release Scenario" includes <br /> landfill gas escapingthrough liner penetrations that migrates to groundwater resulting' in low <br /> level VOC impacts. Under this "Hypothetical Release Scenario" San Joaquin County has <br /> proposed as a corrective action a Geoprobe investigation to estimate the location of the <br /> release, and installing nine (9) gas extraction wells including supporting infrastructure. The <br /> estimated cost for this proposed corrective action is $155,484.00. <br /> Staff agrees the "Hypothetical Corrective Action" for the North County Recycling Center and <br /> Sanitary Landfill is an appropriate response under the "Hypothetical Release Scenario" for the <br /> gas release and the costs appear reasonable. For the same reason as stated in the Foothill <br /> Sanitary Landfill comments a groundwater remediation system should be added to the cost <br /> estimate. <br /> If you have any questions please call me at (916) 464-4737. <br /> Todd A. Del Frate <br /> Engineering Geologist <br /> Lower San Joaquin River Watershed <br /> Discharger to Land Unit <br /> cc: Robert McClellon, San Joaquin County Environmental Health Department, Stockton <br />