SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

INFORMATION SHEET DEFENSE DISTRIBUTION REGION WEST TRACY INTERIM GROUND WATER CLEANUP SYSTEM SAN JOAQUIN COUNTY The Defense Distribution Region West (DDRW) Tracy is conducting CERCLA RI/FS activities. Ground water contamination, specifically trichloroethene (TCE) and tetrachloroethene (PCE) , above State and Federal action levels, has been detected. DDRW is planning to implement a CERCLA Interim Remedial Measure (IRM) to control the migration of a portion of the most heavily TCE/PCE polluted ground water along the northwest boundary of DDRW. The extracted ground water 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 ground water cleanup system includes the following: a. The extraction of approximately 120 gpm of contaminated ground water from six extraction wells. The extraction wells will be screened within the uppermost sand and gravel aquifer along the northwest boundary of DDRW. b. The treatment of the extracted contaminated ground water by air stripping. The air stripping tower's hydraulic design capacity is 500 gpm. The system will be capable of achieving a 99.6% 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 ground water (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 ground water 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 (1.0 ppb for TCE and PCE) on the proposed discharge to protect the beneficial uses of the aquifer; (2) an operational requirement on the air stripper to optimize TCE and PCE removal efficiencies to non-detectable levels if practicable, and (3) 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 DDRW ( including the development of a ground water contaminant transport model) . The Order requires the Discharger to conduct an air stripper evaluation study during the start-up and prove-out phase of the IRM system.