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i <br /> APR 1 7 2008 <br /> Shaw, Shaw Environmental, Inc. ENVIROAI <br /> �I:Ni� Arf, <br /> P <br /> -- - _ - F'Ri1'117 C"-n <br /> A World ofSolutions", <br /> April 15, 2008 <br /> Mr. James L.L. Barton, P.G. <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive, #200 <br /> Rancho Cordova, CA 95670-6114 <br /> Subject: Response to Comments dated April 1, 2008 on Biosparge Pilot Test Work Plan for <br /> the Transmission Shop Site at 515 W. Charter Way, Stockton, California <br /> Dear Mr. Barton: <br /> On behalf of Mr. Don Rogers, Shaw Environmental, Inc. is pleased to provide the responses to your <br /> comments made on the Biosparge Pilot Test Work Plan for the above-referenced site on April 1, 2008. <br /> Specifically, the responses below address comments (1) through (4). <br /> Response to Comment (1) on Biosparge Well Casing Diameter and Borehole <br /> The proposed biosparge well casing diameter is 1 inch. To comply with San Joaquin County <br /> Environmental Health Department (SJCEHD) requirements for well construction, the nominal borehole <br /> diameter for this test well will be 5 inches. To accommodate the larger borehole diameter, hollow-stem <br /> auger drilling may have to be performed instead. Regardless of the drilling method, the well <br /> construction procedures will conform to SJCEHD requirements. <br /> Response to Comment (2) on Helium Use <br /> The inclusion of helium as tracer gas in an air injection pilot test was to be consistent with generally <br /> accepted industrial practice. However, after further review of the pilot test program and the monitoring <br /> objectives, it was determined that the use of a tracer gas for biosparging would not provide as much <br /> benefit as originally anticipated. Therefore, the plan to include tracer gas monitoring is removed from <br /> the Pilot Test Work Plan. The attached Figure 5A shows the revised biosparge pilot test schematic <br /> diagram. <br /> Response to Comment (3) on Vapor Monitoring <br /> To provide monitoring of the potential vapor migration north of the biosparge test well during air <br /> injection, a 2-inch vapor monitoring well will be installed approximately 8 feet north of the well (within <br /> about 3 feet south of the drapery shop). The attached Figure 4A shows the proposed location of the <br /> new vapor monitoring well. The well will be screened between 10 and 20 feet below ground surface <br /> and constructed of polyvinyl chlorinated (PVC) Schedule 40 casing with a 0.02-inch slotted screen. <br /> 1326 NORTH MARKET BLVD., SACRAMENTO, CA 95834 • 916.565.4358 • FAX 916.565.4356 <br /> I <br />