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Olivarez Property/aka Skip's Service page 2 <br /> 300 S. California Street, Stockton May 5, 2011 <br /> The EHD has started an evaluation of the current groundwater pump and treat action (GWE) <br /> but needs additional information to complete the evaluation. The EHD directs you to submit the <br /> following information: <br /> 1. an estimate of the pre-remediation and post-remediation sorbed and dissolved <br /> contaminant masses; <br /> 2. an estimate of the GWE mass extraction rate (pounds or gallons of contaminant per <br /> day); <br /> 3. an evaluation of what portion of the residual contaminant mass may still be susceptible <br /> to GWE; <br /> 4. an analysis of the contaminant concentration and distribution data and the effect of the <br /> GWE operation on it; <br /> 5. an evaluation of the current GWE system that discusses historical granular activated <br /> charcoal (GAC) use and cost and projected GAC replacement and costs. The EHD has <br /> concerns that high concentrations of petroleum are overwhelming the treatment system <br /> and may not be providing the most cost-effective remedial method. Please include <br /> recommendations to either continue GWE with GAC as the most cost-effective remedial <br /> action or a provide a recommendation to modify or replace it; and <br /> 6. an evaluation of the effectiveness and costs of a pre-treatment system, such as an air <br /> stripper or a thermal unit, that could reduce the petroleum concentrations of the <br /> extracted groundwater prior to it being treated with GAC. <br /> Please modify the current monitoring well sampling frequency so that monitoring wells MW-1 R, <br /> MW-5, MW-8S, MW-10, MW-11, and extraction well EW-1 are sampled semi-annually, during <br /> the first and third quarters. All other monitoring wells are to remain on the previously approved <br /> schedule. <br /> You may contact Michael Infurna at (209) 468-3454 if you have any questions. <br /> Michael J. Infurna Jr., RENS Nuel C. Henderson Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: James Barton, CVRWQCB <br /> Michael Vlach, Foothill Engineering, 8442 Story Ridge Way, Antelope CA 95843 <br /> Mark Owens, SWRCB-Clean Up Fund <br />