SITE INFORMATION AND CORRESPONDENCE

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Vft,. .� INFORMATION SHEET 5_ CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY treatment facility, and providing a maximum cap on the quantity of these substances which can be discharged within one day. The previous permit required that, whenever a water quality based limitation for BOD of 10 mg/1 was in effect, the limit for TSS also was set at 10 mg/l. The Discharger requested that TSS requirements remain at the technology-based limit during the entire year, and not continue to be decreased to 10 mg/l whenever water quality-based limitations were in effect for BOD, CBOD, or ammonia. Dissolved oxygen in the receiving water can be adequately regulated in the permit with the water quality-based limitations for CBOD and ammonia. Increasing the limitation for TSS to 30 mg/l is consistent with the antidegradation provisions of 40 CFR 131.12 and State Water Resources Control Board Resolution 68-16. Any impact on existing water quality will be insignificant. Total Residual Chlorine (TRC)- The existing permit required effluent not exceed a monthly average TRC concentration of 0.02 mg/l, or a daily maximum concentration of 0.05 mg/l. The proposed permit requires that the discharged effluent not exceed a daily TRC average concentration of 0.018 mg/1 and a monthly TRC average concentration of 0.011 mg/1. The time averaged limitations are proposed rather 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 proposed limitations are based on the receiving water studies conducted by the Sacramento Regional Wastewater Authority for its discharge to the Sacramento River. Sacramento Regional found that these concentrations did not significantly impact aquatic life (although some impacts were noted). The receiving water conditions, including types of aquatic species present, initial dilution of the effluent in the receiving water, and tidal and slack water conditions, are similar for both the Stockton and Sacramento discharges. The Sacramento studies were therefore applied to the Stockton discharge as the best available chlorine toxicity study currently available for Stockton's discharge conditions. A Provision has been added to require the City to operate the siphon discharge shutoff to minimize chlorine discharges to the extent technically and operationally feasible, and to report all TRC concentrations greater than zero 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). The Department of Health Services