SITE INFORMATION AND CORRESPONDENCE

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INFORMATION— HtET r u` EXXON ^COM PANY U.S.A. _..FORMER.'EXXON .RETAIL SITE 7-3942 GROUND WATER TREATMENT :SYSTEM DISCHARGE"' _ SAN dOAQUIH 'COUNTY . . , . . _.... Exxon Company U.S.A. proposes to discharge treated ground water from the cleanup of an underground gasoline tank leak into injection wells (21,600 gpd)- and the remainder (up to 7200 gpd) into a storm drain tributary to--an .ai al averap r the. Pumped ground water will be treated by passing it through an_n d stripper then serially through two exchangeable activated. carbon units then discharged to e holding tank prior to discharge to the injection wells and storm drain. The activated carbon units are regenerated or disposed off-site The treatment system is designed for a- flow of 20 gpm-.(28,800 gpd)- of.-ground water. The proposed treatment system should be capable of dependably removing petroleum constituents and lead to non-detectable concentrations by current analytical technology. The 30-day Median effluent limitations have, therefore, been set to less-than the limit of detection (0.5 All ) for benzene, ethyl benzene, toluene, and xylene in EPA Method 602; to less-than the limit of detection (50 Erg/1 ) for Total Petroleum Hydrocarbons by EPA Method 8015; and less-than the limit of The detection (1 .0 Erg/1) for lead by furnace atomic absorption spectroscopy. 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. The daily maximum for Total Petroleum i Hydrocarbons is at the taste and odor threshold of 100 Erg/1 . The daily maximum for lead is set at 50 ug/1 , the primary drinking water standard for lead.- Water ead:Water quality objectives adopted pursuant to the Inland Surface Waters Plan are applicable to the discharge. The discharge to surface waters 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 is monthly. If routine monitoring show detectable concentrations of Total Petroleum Hydrocarbons, benzene, toluene,xylene, ethyl benzene, or lead, the frequency of monitoring will be increased to weekly until the constituent(s) concentrations are below detection.