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Department of Toxic Substances Control <br /> Maureen F. Gorsen, Director <br /> Linda Adams 8800 Cal Center Drive Arnold Schwarzenegger <br /> Agency Secretary Sacramento, California 95826-3200 Governor <br /> Cal/EPA /� <br /> �ECE V EDD <br /> JUL 0 9 2008 <br /> July 8, 2008 ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Mr. Maurice Benson <br /> Defense Logistics Agency <br /> Defense Distribution Depot San Joaquin, <br /> Sharpe Site <br /> P O Box 960001 <br /> Stockton, California 95296-0250 <br /> COMMENTS ON THE DRAFT HYDRAULIC FRACTURING AND INJECTION OF EHC <br /> PILOT STUDY WORK PLAN, FOR DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN <br /> COUNTY (DDJC), SHARPE SITE, LATHROP, CALIFORNIA <br /> Dear Mr. Benson: <br /> The Department of Toxic Substances Control (DTSC) received the above-mentioned <br /> work plan on June 9, 2008. The work plan discusses the proposed injection of redox <br /> compound (EHC) consisting of carbon substrate combined with zero-valent iron into the <br /> saturated soil matrix using hydraulic fracturing to target the highest concentrations of <br /> Trichloroethene (TCE) in groundwater in the Central Area at site P-5A. <br /> The EHC fieldwork proposes a total of nine cone penetrometer test (CPT) locations for <br /> groundwater sampling and soil matrix analysis; three CPTs pre-fracture to define TCE <br /> concentrations and lithology, two CPTs at three months post-fracture, two CPTs at <br /> six-months post-fracture, and two CPTs at 12 months post-fracture for monitoring the <br /> contaminant concentrations and redox potential. <br /> In addition to the proposed CPT sampling, the work plan proposes the installation of two <br /> dual-nested monitoring wells to be located in the B-zone aquifer in low to moderate <br /> permeability soils. One dual-nested well will be located within the fracture area <br /> approximately seven feet from the fracture borehole with the other well located <br /> downgradient and outside the radius of fracture. <br /> DTSC has reviewed the above-mentioned pilot study work plan and has the following <br /> comments: <br />