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INFOICNLkTI0N SHEET ` Y OF STOCKTON USTTN ROAD LANDFILL GROUNDWATER TREATMENT SYSTEM ,.AN JOAQUN COUNTY The City of Stockton discharges treated groundwater from the extraction of groundwater polluted by leakage from the unlined Class III landfill. Polluted groundwater has been detected 1000 feet dovmgradient to the northeast of the landfill. The groundwater treatment system is designed to treat 400 gpm (580,000 gpd) of extracted groundwater. About 305 gpm (440,000 gpd) will be discharged to the north branch of the south fork of Littlejohns Creek tributary to the San Joaquin River. The north branch of the south fork of Littlejohns Creek is an intermittent stream maintained by the San Joaquin County Flood Control District primarily for the drainage of irrigation return flow. Pending expansion of the treatment system and approval by the Executive Officer, this permit allows the discharge flow to be . increased from 0.44 mgd to 0.79 mgd, to allow improved capture of the volatile organic plume being r ernediated. Pumped groundwater is treated by passing it through an air stripper, and then is discharged to a manhole and then to Littlejohns Creek. The stripped air is passed through two exchangeable activated carbon units. Tetrachloroethylene (PCE), 1.1-Dichloroethane, 1,2-Dichloroethane, and Vinyl Chloride have been identified in the groundwater as constituents of concern. In addition, Trichloroethylene (TCE) is a degradation product which may be present. The treatment system should be capable of dependably removing these volatile organic constituents (VOCs) to non-detectable concentrations as determined by is.►Trent analytical technology. Therefore, 30 -day median effluent limitations for individual VOCs are set at less than a practical quantitation limit (PQL) of 0.5 ug/l, with the exception of 1,2-Dichloroethane, which is set at the National Toxics Rule standard of 0.38 µg/l. A daily maximum effluent limitation is set to allow for some effluent quality variation and for the false positive analytical results in analyses near the limits of detection. The daily maximum limit for total VOCs has been set at 1 µg/1 in any single sample. The previous permit contained effluent limitations for benzene, ethyl benzene, toluene, and xylene. These constituents have not been shown to be of concern in the effluent, and have been removed from this permit. Eliminating these effluent limitations is consistent with the antidegradation provisions of 40 CFR 131.12 and S WRCB Resolution 68-16. Any impact on existing water quality will be insignificant. Three species chronic toxicity monitoring is required since the discharge constitutes at least fifty percent of the flow in the receiving water. The monitoring consists of collecting quarterly samples and conducting chronic toxicity tests on 100% effluent as specified in EPA 600/4-91-002, and a full dilution series if toxicity is found. Also, monthly estimates of upstream dilution flow is required. If the chronic toxicity monitoring results indicates that the Discharger may be contributing toxicity to Littlejohn Creek, the Discharger shall submit to the Board for approval a workplan to investigate the toxicity, shall implement the workplan upon approval, and take all reasonable steps to reduce or eliminate the toxicity. The previous permit specified waste discharge requirements for storm water discharges associated with industrial activity in accordance with 40 CFR Parts 122, 123, and 124. This permit does not function as a :corm water discharge permit, and the Discharger must file a Notice of Intent to be covered under '%VRCB Water Quality Order No. 97-03-DWQ, for discharges of storm water associated with industrial 1c;tivicies. PHL:njs Amended 5 June 1998 CS 005431 City of Stockton 190855-0006