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WASTE DISCHARGE REQUIREMENTS r CITY OF TRACY WASTEWATER TREATMENT PLANT SAN JOAQUIN COUNTY -2- also concluded that the surface water and groundwater quality had not been adversely affected by the pond releases. 8. The Board, on 9 December 1994, adopted the Third Edition of the Water Quality Control Plan for the Central Vallev Region- Sacramento River and San Joaquin River Basins which contains water quality objectives. These requirements are consistent with that Plan. 9. The beneficial uses of Old River and Delta waters are municipal, industrial, and agricultural supply; recreation; freshwater habitat; wildlife habitat: migration: spawning; and navigation. 10. Effluent limitations, and toxic and pretreatment effluent standards established pursuant to Sections 208(b), 301, 302, 303(4), 304, 307, and 316(a) of the Clean Water Act and amendments thereto are applicable to the discharge. 11. The State Water Resources Control Board Water Qualitv Control Plan for Control of Temperature in Coastal and Interstate Waters and Enclosed Bays and Estuaries of California(Thermal Plan) is applicable to this discharge. 12. The discharge is presently governed by Waste Discharge Requirements Order No. 91-055, adopted by the Board on 22 February 1991. 13. The Department of Health Services has expressed concerns about the protection of public health because the discharge from the City of Tracy is upstream of two major water intake facilities, the Bureau of Reclamation Delta-Mendota Canal and the Department of Water Resources Clifton Court Forebay. The Delta-Mendota Canal is used for drinking water for the City of Tracy and for irrigation of food crops. 14. Federal regulations require effluent limitations for all pollutants that are or may be discharged at a level that will cause or have the reasonable potential to cause,or contribute to an in-stream excursion above a narrative or numerical water quality standard. Based on information submitted by the Discharger as part of the Effluent And Receiving Water Quality Assessment(ERWQA), the Board finds that the discharge does not have a reasonable potential to cause or contribute to an in-stream excursion above a water quality objective. 15. Effluent limits in this permit are based on modeling results of the flow characteristics of Old River. The modeling demonstrates that during low flow periods of Old River approximately 1.0% of its flow consists of the wastewater from the Discharger on a monthly average. Delta Pumping and tidal cycles may,however, result in less dilution for short periods of time which may have significant water quality impacts. The Discharger had been required by Order No. 91-055 to install a flow monitoring device on Old River to help clarify the short term dilution and potential water quality impacts, but the monitoring device was never installed. Additionally,there are proposals to further manipulate surface flows in the Sacramento-San Joaquin Delta in the future which may have an affect on the flows in Old River. If the flow characteristics of Old River are significantly changed, or is found to be significantly different than the flow used to develop permit limits, the permit will be reopened for modification of effluent limits. See Provision F.9 16. The Discharger submitted a Draft Wastewater IDS Study to determine the cause of elevated mineralization in the Discharger's wastewater and proposes an implementation plan for mineralization reduction. The Mineralization Plan has not yet been finalized. This Order