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RESPONSE TO WRITTEN COMMENTS -30- City Of Stockton-Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting RWQCB Response: The permit does not represent a taking of listed species. Effluent limitations are applied without dilution credit for constituents with acute and/or chronic toxicity criteria. New treatment processes are required, as well as source control for several pollutants, and a toxicity reduction evaluation. In addition it requires the City to assess the thermal impacts of its discharge and - includes a reopener to incorporate new requirements as appropriate. The federal Endangered Species Act does not apply to the action of the Regional Board. It applies only to federal actions. DeltaKeeper Comment No. 4: A"Worst Case"Hardness Value Must Be Used. RWQCB Response: DeltaKeeper states, "Ambient constituent concentrations maybe high during high Tows. For example, in July 1995, the ambient concentration of copper was 7,u g/1 at a hardness of 38 mg/1. The river exceeded both the CCC and CMC. Consequently, there was no remaining assimilative capacity." The ambient concentration of dissolved copper was non-detect (<1.0 µg/1) in July 1995. The total copper concentration was 7 µg/1. Since the CCC and CMC are dissolved standards, the receiving water did not exceed the CCC or the CMC. DeltaKeeper states further, "On 8 September 1998, hardness was 69 while flow was measured at 2,200 cfs. We see little justification for using a hardness value of 107 mg/l." If a hardness of 69 mg/1 was used, then you must consider the higher river flows, the dilution would exceed 25:1. Section 11.3.1 of the Fact Sheet adequately explains the rationale for determining the design hardness and why the design hardness of 107 mg/l is protective of receiving water beneficial uses. DeltaKeeper Comment No. 5: The Proposed Permit "Backslides"From Previous Permits. The CBOD limit represents a"backsliding" from previous permits. Staff is aware of the change from BOD to CBOD in the last Permit that failed to account for organic nitrogen. RWQCB Response: The proposed permit doesn't contain an effluent limitation for organic nitrogen. However, the amount of total oxygen demanding substances allowed to be discharged has been significantly reduced. During the fall and winter months, the RWCF discharges ammonia in excess of 20 mg/1. The proposed permit limits the effluent ammonia to 2 mg/l, as a monthly average, and 5 mg/j, as a daily maximum. Additionally, the requirement to construct tertiary filtration will likely reduce effluent CBOD and total suspended solids. Thus, the proposed permit contains effluent limitations for oxygen demanding substances that are more stringent than has previously been adopted, and is in compliance with the federal regulations, 40 CFR 122.44(1)(2)(ii). However, in order to further address your comment, the proposed Monitoring and Reporting Program has been updated to include effluent monitoring of organic nitrogen to determine if additional limitations are needed. DeltaKeeper Comment No. 6A: Diazinon: The Reasonable Potential Analysis found reasonable potential to exceed criteria. The calculated effluent limit in the Fact Sheet is an Average Monthly Effluent Limit of 0.047 µg/l and a Maximum Daily Limits of 0.061 µg/1. Inexplicably, a daily maximum concentration limit for diazinon of 0.1 µg/1 is included in the Permit. RWQCB Response: The interim effluent limitation for diazinon was calculated in accordance with Section 2.1 of the SIP. As the criteria for diazinon were released in March 2000 after the Basin Plan narrative toxicity criteria were issued, the Basin Plan allows for a compliance schedule of up to ten