SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET -3- CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY than an instantaneous limit because the City's continuous (instantaneous) monitoring system coupled with the continuously varying nature of treatment plant operations would produce numerous violations of the instantaneous limitation. Many of these "violations" are of short duration due to a siphon discharge shutoff control system, have low TRC concentrations, and are not believed to be a significant threat to water quality. The City has not yet submitted final chlorine excursion information However, based on the similarities in the equipment used by the Sacramento Regional Wastewater Treatment Plant, the effluent limitations are based on those in the permit issued to Sacramento Regional County Sanitation District. Stockton should be able to achieve similar limitations with its equipment. A Provision has been added to require the City to operate the chlorine residual control system and the siphon discharge shutoff to achieve the lowest chlorine residual level technically and operationally feasible, and to report all non-zero TRC concentration detected in the effluent (on a daily basis), as part of the Monitoring and Reporting Program. Total Coliform- Previous effluent limitations for total coliform organisms were set at 23 MPN/100 ml (monthly median), and 500 MPN/100 ml (daily maximum). However, with the river model information recently submitted, it has been determined that dilution available is less than 20:1. There is also water contact recreation in the vicinity of the discharge during the summer. Guidelines established by the Department of Health Services recommend that, under these conditions, effluent contain a median MPN of coliform organisms that does not exceed 2.2/100 ml. Therefore, this Order contains monthly median and daily maximum total coliform limits of 2.2/100 ml and 23/100 ml, respectively, from I May through 30 September, and monthly median and daily maximum limits of 23/100 ml and 500/100 ml, respectively, during the rest of the year. Ammonia- The river model contained information that indicates there is a potential for ammonia toxicity in the receiving water during the winter due to the discharge. This Order requires the City to monitor ammonia in both the effluent and receiving water, as well as conduct effluent chronic toxicity bioassays. The permit may be reopened and the effluent limitations modified as necessary to address toxicity issues. Temperature- The permit contains effluent and receiving water temperature limitations which are contained in the Thermal Plan. Because the City believes it is unclear how natural receiving water temperature (not already affected by other dischargers) is determined and the City does not