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REGIONAL BOARD RESPONSE (SYVRCB/OCC FILE A-1483) -2- PETITION FOR REVIEW OF WASTE DISCHARGE REQUIREMENTS ORDER NOS. R5-2002-0083 AND R5-2002-0084 CITY OF STOCKTON REGIONAL WASTEWATER CONTROL FACILITY The City filed a petition with the State Board requesting review of their previous NPDES permit, Order No. 94-324. The State Board, in Order WQ 96-09 remanded the previous permit to the Regional Board to re-evaluate the flow conditions in the SJR due to changes brought on by adoption of the Bay-Delta Plan and revise effluent limitations accordingly. In adopting Order No. R5-2002-0083, the Regional. Board has addressed the issues raised in State Board Order WQ 96-09. The Regional Board has evaluated all available information and has determined that dilution should not be granted for most constituents. BACKGROUND The RWCF is owned and operated by the City, and treats domestic and industrial wastewaters servicing a population of roughly 300,000. The RWCF consists of a secondary treatment facility, which has a design average dry weather flow(ADWF) of 42 million gallons per day (mgd) and a tertiary treatment facility, which has a design ADWF of 55 mgd. The RWCF treats approximately 34 million gallons of wastewater per day on an annual average. The RWCF accepts wastewater from approximately 40 significant industrial users, which amounts to 5.3 mgd or approximately 16 percent of the facility's yearly average flow. The RWCF secondary treatment facility provides wastewater treatment consisting of screening, grit removal, and primary sedimentation, followed by high rate trickling filters and intermediate settling basins. Additional treatment is obtained by piping the wastewater under the San Joaquin River(SJR) to the tertiary treatment facility which consists of approximately 630 acres of unlined facultative oxidation ponds, followed by dissolved air flotation(DAF), mixed-media filters and chlorination/dechlorination facilities. The DAF and filters are typically operated during peak algal production periods. The tertiary treatment plant has the ability to operate intermittently by using the ponds to store wastewater. Sludge is treated by anaerobic digestion, dewatered by belt-press and removed by a private contractor for off-site use. The City is in the process of a staged expansion of the secondary treatment facility. The expansion includes construction of additional anaerobic sludge digesters, improvements to the sludge management system, supervisory control and data acquisition (SCADA) improvements, biotower improvements, construction of additional primary sedimentation and other ancillary improvements. The expansion will increase the secondary design ADWF to 48 mgd when completed. Wastewater is discharged through a single outfall to the SJR approximately 1.5 miles upstream of the Stockton Deep Water Ship Channel (DWSC). The SJR has a strong tidal influence in the vicinity of the RWCF discharge. The tides typically cause null and reverse flows daily. The flow reversals are strongest at low net flows,but occur at net flows as high as 3000 cfs. Because the SJR is tidal, the flow of diluting water vanes with the tidal cycle. As net river flows drop toward 3000 cfs, at some point in the tidal cycle the incoming tide balances against the outgoing river flow resulting in river flow stagnation and very little dilution of effluent. Below a net river flow of 3000 cfs, the direction of the river flow reverses with incoming tides resulting in periods of time during each tidal cycle with zero net river flows. Additionally, with flow reversals, some volume of river water is multiple dosed with the effluent as the river flows back and forth past the discharge point.