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STAFF REPORT • • 3 SPX CORPORATION MARLEY COOLING TOWER COMPANY GROUNDWATER EXTRACTION AND TREATMENT SYSTEM SAN JOAQUIN COUNTY New Effluent Limits, Hexavalent Chromium, Copper Existing Order No. 93-221 included effluent limitations for hexavalent chromium and copper. These new limits were established in this proposed Order using aquatic toxicity water quality criteria from the CTR, and using reasonable potential and effluent limit calculation methodologies prescribed by the SIP. Considering that the SDC may at times provide little or no assimilative capacity, final water quality based effluent limitations were developed using a steady state model,with no credit provided for dilution. The use of the CTR water quality criteria and new reasonable potential methodologies prescribed by the SIP resulted in changes to limitations in the existing Order-No. 93-221 as summarized below: Effluent Limitations(µg/L, ppb) Maximum Daily Monthly Average Copper: Order No. 93-221 6.5 6.5 Proposed Order 6.5 3.3 Hexavalent Chromium: Order No. 93-221 11 11 Proposed Order 16 8.0 Monitoring data indicates the Discharger is currently capable of meeting the new effluent limitations, with the exception of the new monthly average limit for copper(The exact concentrations of copper in the effluent are unknown, historical data indicates concentrations of copper are reported as less than the laboratory detection limit of 5.0 pg/L, ppb). Current laboratory methods can now detect concentrations of copper to 0.5 µg/L, ppb. A compliance schedule is included in the proposed Order for copper. The Discharger commented that the discharge supports the aquatic habitat between the point of discharge and the Calaveras River, and that the effluent limits should be applied at the point where the SDC reconnects with the Calaveras River, and should then consider appropriate dilution factors. The Discharger does not believe they should be required to maintain an unnatural aquatic environment, and that it is inappropriate to develop limits without consideration of dilution. Deltakeeper commented that the new daily maximum hexavalent chromium limit is less stringent than the previous permit, and that the Discharger must submit justification required by the SIP prior to receiving a compliance schedule for copper. Order No. 93-221 does not provide a basis for the existing permit limits. As noted above, Staff utilized all available relevant data to perform the reasonable potential analysis and calculate effluent limits as prescribed by the SIP in the proposed Order. The l lµg/L,ppb concentrarion limit of Order No. 93-221 is a chronic water quality criteria value which was previously applied as an acute (daily maximum) limit. This oversight has been corrected using the methodologies of the SIP. The monthly average limit proposed by this Order includes a mass limitation, and will result in an overall reduction in the allowable mass emission.