ARCHIVED REPORTS_XR0008606 CASE 1

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INFORMATION SHEET . MOBIL OIL CORPORATION FORMER MOBIL GASOLINE SERVICE STATION 10-NP4 GROUND WATER TREATMENT SYSTEM DISCHARGE SAN JOAQUIN COUNTY Mobil 071 Corporation proposes to discharge treated ground water from the cleanup of an underground gasoline tank leak into a storm drain which is tributary to Sugar Cut, tributary to Old River, near Tracy The storm drain is operated by the City of Tracy. Pumped ground water will be treated by passing it serially through two 1,000-1b exchangeable activated carbon units prior to discharge to the storm drain. The activated carbon units are regenerated or disposed off-site. When breakthrough of the lead carbon unit occurs, the lead unit is removed for regeneration, the trailing unit is placed in the lead position, and a new unit is placed in the trailing position. After some operational experience in determining the time of breakthrough on the lead unit, this procedure provide nearly 100% redundancy in the treatment system. The treatment system will initially be designed for a flow of 3-5 gpm (4200-7200 gpd) of ground water, but could later be expanded to a maximum of 15 gpm (21,600 gpd) if it is found that additional ground water must be extracted to assure containment and cleanup of the ground water plume. The proposed treatment system should be capable of dependably removing petroleum constituents and lead to non-detectable concentrations. The 30-day Average effluent limitations have, therefore, been set to less-than the limit of detection (0.5 pg/1 ) for benzene, ethyl benzene, toluene, and xylene in EPA Method 602; and to less-than the limit of detection (0.05 mg/1 ) for Total Petroleum Hydrocarbons by EPA Method 8015. The Daily Maximum effluent concentrations are established to allow for some effluent quality variation and the false positive analytical results inherent in analyses near the limits of detection. For benzene, ethyl benzene, toluene, xylene, and Total Petroleum Hydrocarbons, the Daily Maximum Effluent Limitation has been set at ten times the detection limit. Water quality objectives adopted pursuant to the Inland Surface Waters Plan are applicable to the discharge. The discharge is considered to be low volume, and therefore, monitoring for constituents with numerical water quality objectives is not being required. The proposed frequency of routine monitoring, quarterly for most constituents, is not sufficient to determine compliance with the 30-day Average effluent limitations. If the initial weekly or routine quarterly monitoring show detectable concentrations of Total Petroleum Hydrocarbons, benzene, toluene, xylenes, or ethyl benzene, the frequency of monitoring will have to be increased to allow determination of compliance with the 30-day limits.