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I <br /> ° i%6, <br /> 610 Hunter, Stockton <br /> Page 2 <br /> Currently about 35 gallons of groundwater per hour are being extracted from the knock out <br /> tank during operation of the SVE/AS system, from which, ATC calculated in the QMK that <br /> 10. 13 pounds of TPH-g have been removed to date, compared to 8723.29 pounds of TPH-g <br /> removed by the SVE/AS system since it began operation in December 2002. Contaminant <br /> concentrations in MW-1groundwater samples declined from a high of 140,000 micrograms <br /> per liter (ug/1) of TPH-g in December 2002, to 39,000 ug/l in September 2005, a 72.2% <br /> reduction in a 3-year period. At the current groundwater extraction and attenuation rate, <br /> EHD linearly extrapolates a reduction from 39,000 ug/l to 10,864 ug/l in the next 3 years. <br /> Since there is a sunset date of Dec 31, 2010 for the State Clean Up Fund (the Fund), the <br /> existing SVE/AS and supplemental groundwater extraction system may not be sufficient to <br /> remediate the dissolved contamination in time to meet that sunset date, potentially resulting <br /> in un-reimbursed remediation costs after that date. EHD recommends that you evaluate <br /> other remedial alternatives or supplemental strategies for groundwater treatment, such as <br /> increasing the rate of groundwater extraction to increase the vadose zone for soil extraction, <br /> dissolved mass removal, or ozone injection. Please provide the evaluation to EHD in your <br /> next quarterly report (first quarter 2006), or submit a separate proposal for groundwater <br /> clean up to EHD by April 1 , 2006. The report should also include a calculation of the <br /> remaining dissolved contamination mass, if possible an estimate of the flux rate, an <br /> estimated mass removal rate, and an estimate of the time required to achieve closure <br /> conditions utilizing the proposed methodology. <br /> Please feel free to direct any questions you may have to Jeffrey Wong at (209)468-0335. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> o �to rw—� <br /> Jeffrey Wong, Senior REHS Nuel L. Henderson, Jr., PG <br /> LOP/Site Mitigation Unit _ LOP/Site Mitigation Unit <br /> c: Jeanne Homsey - ATC Associates Inc. (ATC) <br /> c:. RWQCB, Central Valley Region — James L. L. Barton, PG <br />