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California- regional Water ,.i Quality Corgi► Board Central Valley Region Linda S.Adams Karl E. Longley,Sr1). PE. (hair Secreta,v for Sacramento .11ain Orrice l.inyrocvnecnol 11020 Son Cenlrr Uricc 42 \rm,bl Prnreaion 00. Rnnrhu Cunlo,a. Chli�miarrrnrlN Phone 19161 464-3291 .11\19161 464-4(,45 rhe ari,•p,.ti,., hltp://e , oaterbourds ca.g,,, antral,allc• . 29 January 2007 Mr. Mark J. Madison JAN 3 l 2007 Director of Municipal Utilities ENVIROi'dMENT 2500 Navy Drive PERMIT/SERVICES jH Stockton, CA 95206 PROPOSED PROCESS CHANGE, CITY OF STOCKTON WASTEWATER TREATMENT FACILITY, WASTE DISCHARGE REQUIREMENTS (WDRs) ORDER NO. R5-2002-0083 (NPDES CA0079138), SAN JOAQUIN COUNTY On 22 January 2007, OMI Thames Water, the contract operator for the City of Stockton, wrote the Regional Water Board a "Notification of Process Change" in which it proposed to remove the existing facultative ponds from online duty and to place them into a stand-by mode. The letter discusses advantages of the process change in terms of factors such as ammonia removal, nitrification, and turbidity but does not discuss the potential impacts on the discharge temperature. The letter further states that the City will commence the process change on 1 February 2007 unless the Regional Water Board objects to the process change. In May 2006, to comply with Provision G.15 of WDRs Order No. R5-2002-0083 requiring evaluating the effect of a thermal temperature discharge on migrating fish, the City submitted a report entitled Potential Thermal Effects of Stockton Regional Wastewater Control Facility Discharge on Migrating Fish in the San Joaquin River. The study measured changes in river temperature resulting from wastewater treatment facility discharge. The study concluded that the discharge does not provide a temperature impact on migrating fish because the 30-day residence time in the 630-acre stabilization ponds adjusted the discharge to ambient temperature. Therefore, taking the ponds out of service could cause the City to be in immediate violation of temperature limitations and could subject the City to potential enforcement actions. Provision BA.c., Standard Provisions and Reporting Requirements for Waste Discharge Requirements, 1 March 1991 (Standard Provisions), requires the submittal of a Report of Waste Discharge at least 180 days before making any material change in the discharge It further defines a material change as significantly changing the method of treatment. Therefore, prior to instituting any material process changes, the City must submit a Report of Waste Discharge to comply with Provision B.4.c. of Standard Provisions. The Report needs to outline how the process change will impact compliance with permit requirements, including temperature, such that violations do not occur. California Environmental Protection Anenc•r pia Recycled Paper