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• •State of-CaliforniaDepartment of Health Services <br /> • <br /> Memorandum l <br /> To �W David Wang, P.E. Dot` ' August 17, 1989 <br /> Senior Waste Management Engineer Sub'e <br /> � INTERIM GROUNDWATER <br /> TREATMENT SYSTEM DDTC <br /> From <br /> Toxic Substance Control Program <br /> 4250 Power Inn Road <br /> BACKGROUND: <br /> Findings from the Defense Depot Tracys (f)DTC) remedial <br /> investigation have substantiated the presence of industrial <br /> solvents including both trichloroethene (TCE) and <br /> tetrachloroethene (PCE) in the groundwater. Groundwater sampling <br /> has recorded concentrations of TCE as high as 560 parts per <br /> billion (LM - 25/ screened from 8 to 38 feet) and PCE as high as <br /> 340 parts per billion (LM -30/ screened from 10 to 20 feet) . In <br /> an effort to reduce the further degradation of the groundwater, <br /> DDTC has proposed the construction of an interim groundwater <br /> treatment system. The system would greatly reduce further <br /> off-site migration of TCE and PCE until a final remedy could be <br /> implemented. <br /> The Depot submitted its' original proposal for the interim system <br /> in May 1989 . The design criteria was to control highly <br /> contaminated groundwater migrating through a shallow sand zone. <br /> To accomplish this goal, the interim system would consist of an <br /> air stripper capable of treating up to five hundred gallons per <br /> minute, seventeen extraction wells, and six injection wells. The <br /> extraction wells would be placed in two clusters at an <br /> approximate depth of fifty feet, the injection wells would <br /> discharge to a depth of one hundred feet. The targeted cleanup <br /> level set for TCE and PCE treated by the air stripper is one part <br /> per billion. <br /> The regulatory agencies (the Department of Health Services and <br /> the California Regional Water Quality Control Board) expressed <br /> concern over the lack of geologic and hydrogeologic data <br /> supporting the placement of the extraction and injection well <br /> fields. Also of concern was the lack of specific monitoring <br /> requirements for the interim systems performance. These concerns <br /> were expressed at a 6 June 1989 technical meeting and via <br /> subsequent correspondence. Despite the agencies concerns, both <br /> wished to encourage the construction of an interim system. At <br /> the 6 June technical meeting, a revised approach was adopted for <br /> the construction of the extraction and injection wells. The <br /> Depots' contractor, ERC Environmental, would develop criteria to <br />