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EDMUND G. BROWN JR. <br />GOVCRNOF <br />�(l� VVV �L�4`e MnrTRew RooFlouez <br />C 1 L I I D P N 1• �/ SECRETARY FOR <br />EP 232013 ENVIRUNMENThL PFUTEGTIUIJ <br />Water Board _ EW�_�^'M�ar <br />Central Valley Regional Water Quality Cor�f/.TEI <br />20 September 2013 <br />Sergio Morescalchi <br />Environmental Business Manager <br />Atlantic Richfield Company <br />P.O. Box 1257 <br />San Ramon, CA 94583 <br />Staff of the Regional Water Quality Control Board, Central Valley Region (Regional Water <br />Board) have reviewed the 6 August 2013 Pulsed Extraction From Well GW -4 for the Applied <br />Aerospace Structures Corporation facility in Stockton (Report), prepared on your behalf by <br />Parsons. Atlantic Richfield has been remediating a release of volatile organic chemicals <br />(VOCs) at the site including trichloroethene (TICE) by operating a groundwater extraction and <br />treatment system since 1999. The groundwater extraction system has been effective at <br />containing the VOC plume, and off-site monitoring wells are now below Maximum Contaminant <br />Levels for all compounds. However, recovery of VOCs has diminished from over 20 pounds per <br />year to about 1 pound per year. The Report provided the results of a pulsed pumping study <br />conducted at Applied Aerospace (site) to determine if pumping at intervals could enhance the <br />rate of contaminant recovery. <br />The Report shows that the concentration of total VOCs in the extracted water increased from <br />about 50 ug/l to 64 ug/l. Figure 2 also shows that the higher concentrations occurred during the <br />higher groundwater levels. The Report concludes that the higher concentrations result from <br />mobilization of TICE from areas of the aquifer that have been dewatered by pumping. However, <br />The Report concludes that pulsed pumping is not efficient at removing VOCs because the <br />increased concentration of recovery does not compensate for the time the system is not <br />pumping. <br />Regional Water Board staff conclude that the groundwater extraction system may be over - <br />pumping the aquifer. Enhanced recovery may result from decreasing the pumping rate, <br />allowing some of the aquifer to recover and mobilizing TICE from the soil. Therefore, Regional <br />Board staff request that a second study be conducted, decreasing the pumping rate to <br />determine if there is an optimal pump rate that can be maintained with increased concentration <br />of TICE, thereby enhancing the efficiency of the system. Decreased pumping rates may also <br />make operation of the system more economical with lower energy costs and sewerage fees. <br />Please submit a work plan to perform a study by decreasing the pump rate from the extraction <br />wells in a step -wise manner, documenting the concentration of the extracted groundwater. <br />Regional Board staff appreciate Atlantic Richfield's progress at cleaning up the groundwater at <br />this site and bringing the site closer to closure. <br />KARL E. LONGLEY SGD, P.E., CHAIR I PAMELA C. CREEDON P.E., BCEE, EXECUTIVE OFFICER <br />11020 Sun Center Drive #200, Rancho Cordova, CA 95670 Iwww.Waterboards.ca.gov/centralval lay <br />REC•CLED PAPER <br />