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RESPONSE TO WRITTENCMMENTS -21- City Of Stockton -Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting City fully complies with Basin Plan thermal requirements, the City should conduct a study regarding whether or not the current Basin Plan requirements are sufficiently protective. The City objects to this requirement as legally and technically unsupported. As part of the existing permit, the City was required to evaluate its thermal impact on the San Joaquin River. That study, hereby incorporatedby, reference, submitted to the Board in 1996 and accepted, found that the City's discharge met all Thermal Plan requirements. The Order does not comply with Water Code section 13267. RWQCB Response: Water Code section 13383 authorizes the Regional Board to require dischargers subject to NPDES permits to, among other requirements, sample effluent, retain records, and provide other information as reasonably required. The requirement to conduct a thermal study is consistent with Section 13383. It is also consistent with Water Code section 13267. Stockton submitted a report in December 1995 which provided estimates, based on model results, that the City could comply with all Thermal Plan requirements. However, the study did not address slack tides, and evaluated temperature impacts at R-2 and R-8, receiving water monitoring locations located a great distance from the outfall. These facts, as well as the current state of knowledge regarding dilution and tidal flow at the outfall, would render those conclusions much less certain. In addition, the Thermal Plan does not protect aquatic life from high temperature wastewater being discharged to an elevated temperature river. The discharge of effluent with an elevated temperature may adversely affect Chinook salmon or other migrating fish. The Basin Plan narrative toxicity water quality objective prohibits the discharge of toxic constituents in toxic amounts. The requirement to study the potential impacts to the fishery associated with the discharge of effluent with an elevated temperature is reasonable and appropriate given the evidence in the record. No change was made as a result of the comment. Stockton Comment No. IV.O (Acute WET Testing): The proposed permit seeks to prevent future pH adjustment as part of the acute toxicity testing under the belief that low pH violates instream objectives because dilution is not available. As noted earlier, significant dilution is available, and lower pH readings from the effluent do not cause instream exceedances. Therefore, this restriction regarding the acute WET procedures should be deleted. RWQCB Response: The Regional Board has not approved the City's water quality models. Detailed comments on the models are found in Attachments A, B, and C. The City has not adequately shown that dilution is available. Therefore, due to the impaired condition of the receiving water and the low flows measured at the Stockton UVM during above average wet years, dilution has not been granted in the tentative order. The issue of pH adjustment is also addressed above in Stockton comment N.F. V. New Water Quality Objective for Groundwater Stockton Comment No. V. (New Water Oualitv Objective for Groundwater): The groundwater limitations are inconsistent with the Porter-Cologne Act and the Basin P?-n. The ponds will inevitably ha% an effect on any unc in.- groundwater, whereas Qroulidwe 2r 1 Cation F.2. would apparently provide that the dischai may not cause any statistical increase in Sutuents