SITE INFORMATION AND CORRESPONDENCE

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a ' INFORMATION SHEET I ARCO PRODUCTS COMPANY ARCO STATION 434 GROUND WATER TREATMENT SYSTEM DISCHARGE SAN JOAQUIN COUNTY ARCO Products Company proposes to discharge treated ground water from the cleanup of an underground gasoline tank leak into a storm drain which is tributary to South Main Canal in Lodi. The South Main Canal is operated by the Woodbridge Irrigation District. Pumped ground water will be treated by passing it serially through two 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 provides nearly 100% redundancy in the treatment system. The treatment system will initially be designed for a flow of 2 gpm (3000 gpd) ofround 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 ug/1) for benzene, ethyl benzene, toluene, and xylene in EPA Method 602; to less-than the limit of detection (0.05 mg/1) for Total Petroleum Hydrocarbons by EPA Method 8015; and less-tEhan the limit of detection (1.0 µg/l) for lead by furnace atomic absorption spectroscopy. 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, io-luene, xylene, and Total Petroleum Hydrocarbons, the Daily Maximum Effluent Limitation has been set at ten times the detection limit. The daily maximum for Total Petroleum Hydrocarbons is above the taste and odor threshold of approximately 0' .1 mg/1 , however, there is no use of the receiving water for domestic purposes anywhere near the discharge point. The daily maximum for lead is set at 50 Mcg/l , the primary drinking water standard; for lead. 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 constitiuents 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, xylene, ethyl benzene, or lead, the frequency of monitoring will have to be increased to allow determination of compliance with the 30-day limits. Surface water flow from the site is to South Main Canal , which is operated by the Woodbridge Irrigation District.