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WASTE DISCHARGE REQUIREMENTS -11- DEFENSE DEPOT TRACY SAN JOAQUIN COUNTY INFORMATION SHEET DEFENSE DEPOT TRACY INTERIM GROUNDWATER CLEANUP SYSTEM SAN JOAQUIN COUNTY The Defense Depot Tracy (DDT) is conducting CERCLA RI/FS activities at DDT. Groundwater contamination, specifically trichloroethene (TCE) and tetrachloroethene (PCE) , above State and Federal action levels, has been detected. DDT is planning to implement a CERCLA Interim Remedial Measure (IRM) to control the migration of a portion of the most heavily TCE/PCE polluted groundwater along the northwest boundary of DDT. The extracted groundwater will be then be treated and discharged to shallow aquifers utilizing injection wells and/or an existing storm drain holding pond. The main components of the Dischargers' interim groundwater cleanup system includes the following: (a) The extraction of approximately 120 gpm of contaminated groundwater from six extraction wells. The extraction wells will be screened within the uppermost sand and gravel aquifer along the northwest boundary of DDT. (b) The treatment of the extracted contaminated groundwater by air stripping. The air stripping tower' s hydraulic design capacity is 500 gpm. The system will be capable of achieving a 99.8 % removal efficiency. A vapor control unit, utilizing granulated activated carbon, will be used to remove trace organics from the tower' s exhaust air. (c) The disposal of the treated groundwater (approximately 120 gpm) to three shallow aquifer injection wells and/or to the existing storm drain holding pond during the summer months (May through October) . (d) The performance monitoring of the cleanup system to gauge its effectiveness. This includes the installation of five wells to monitor the extraction system, and five wells to monitor the injection system. (e) The assessment of the effect of this interim groundwater cleanup system on ground water contamination, including the development of a numerical ground water contaminant transport model . This Order establishes (1) discharge prohibitions and effluent limitations on the proposed discharge to protect the beneficial uses of the aquifer; (2) discharge specifications on the various phases of the IRM to ensure the operational effectiveness of the system (including influent, effluent and well monitoring programs) ; and (3) technical report submittal requirements to document the effectiveness of the IRM and its potential application to other areas at DDT ( including the development of a groundwater contaminant transport model ) .