SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

RESPONSE TO WRITTEN COMMENTS -19- City Of Stockton-Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting copper and cyanide, based on this method. Tables 11-4 and 11-5, of the tentative permit, have also been modified due to this change. The changes to the tables are not in redline format. Staff s response regarding,the harmonic dilution credit has been addressed above. Stockton Comment No. IV.I (Bvpass Rule Interpretation): The Board has included EPA's bypass rule provision as part of the permit. The City does not object to this provision but we are concerned that the provision be properly applied. RWQCB Response: Finding 3 explains how the treatment processes are currently operated, including periodic operation of the DAF and filters, and no specific flow pattern for the pond system. The bypass provision does not preclude the City from bypassing the tertiary facilities when conditions permit, until 1 January 2003, when Provision 1 requires continuous operation. Stockton Comment No. IV.J (Copper): The tentative order proposes to establish restrictive interim and final effluent limitations for copper based upon the belief that the existing discharge does not achieve applicable dissolved water quality standards by using EPA's default dissolved:total translator, even though the EPA translator does not apply to non-CTR objectives. The tentative order then establishes effluent limitations for copper under the assumption that no dilution was available. This approach is misplaced since the City has provided detailed evaluations demonstrating that dissolved metals levels are well below applicable objectives and that substantial immediate and long- term dilution is available under low flow conditions. The City provided substantial information over the past five years that would allow calculation of a site-specific translator for the San Joaquin River under these conditions. Thus, failure to use the relevant information regarding instream water quality, dilution, and translators caused the establishment of unnecessary and inappropriate limitations. RWQCB Response: The City states, "The Board applies this criteria as if it were an acute objective; it was not part of the CTR and there is no default translator applicable to this objective." Since dilution has not been adequately shown to occur under acute or chronic conditions, the Basin Plan objective must be applied at the end-of-pipe. The EPA default translator was used, because adequate information is not available to determine a site-specific translator. Dissolved and total metals data within the influence of the discharge and within a projected zone where the standards apply is necessary to determine the site-specific translator. The City has submitted metals data for receiving water monitoring stations R-1 and R-7. Station R-1 is 8 miles upstream of the outfall and Station R-7 is 7.3 miles downstream of the outfall. This is well outside the area in which the standard must apply. The City may perform a site-specific metals translator study in accordance with Section 1.4.1 of the SIP and the permit can be reopened to modify the effluent limitations if necessary. The City states, "The Jones & Stokes Report (April 2001) evaluated dilution in the San Joaquin River as a function of effluent flow, net river flow, and tidal conditions. This analysis conformed that initial dilution results in a one-hour dilution factor of 1:1 within 125 feet of the discharge at the maximum flow rate of 55 MGD and a four-dav:. -age dilution", r of 4:1 at average flc v :-onditions. Because the instream data confirm th, _assimilative cc., -uty exists, the permit limit should be