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n Joaquin County Public Works - 3 - 9 January 2007 <br />VOCs by less than 50 ug/1. 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 escaping through 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 />