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� 1 STAFF REPORT -5- STOCKTON REGIONAL WASTEWATER CONTROL FACILITY SAN JOAQUIN COUNTY production, sediment oxygen demand, and discharge from the RWCF. Therefore solutions to comply with the DO objectives need to be developed through the TMDL process, which is underway. The BPTCP,Regional Toxic Hot Spot Cleanup Plan proposed how to deal with NPDES permitting during the interim period while the TMDL is developed. The text states in part, "Where dischargers are a significant contributor to the River's DO problem, improvement in the effluent quality may be required prior to completion of a TMDL...However, load reductions from existing dischargers will not be required if satisfactory progress is being made on TMDL development unless it is clear before the process has been completed that the specific load reduction would be required even under the TMDL. It will be assumed that satisfactory progress is being made if the majority of the studies to determine load allocations are underway by December 1999, and it appears likely, that the Steering Committee will recommend a TMDL implementation plan, including load allocations, to the Regional Board staff by the year 2002." The Regional Board found, at its last meeting, that "reasonable progress" is being made. Staff must determine whether load reductions must be required in the permit renewal, or if decisions should be delayed until the TMDL implementation plan is approved. 5. Ammonia/Nitrogen Ammonia has been reported in the effluent and receiving waters. Review of self-monitoring reports by the Discharger and additional ambient data collected by others indicate that a significant amount of ammonia is discharged by the facility from October through March. In addition to considerations with regard to receiving water DO, effluent limitations for near- and far-field toxicity will need to be considered. Staff will need to evaluate the possibility of requiring the Discharger to nitrify the wastewater. Nitrogen in any form can stimulate algal growth, which can contribute to DO problems, so denitrification of the effluent will also need to be considered. 6. Reasonable Potential Analysis Metals, volatile organic compounds, semi-volatile compounds, salts and inorganic compounds, which have been reported by the Discharger, will need to be thoroughly reviewed by staff. An analysis must be performed to determine if any of the constituents have reasonable potential to cause or contribute to a violation of Basin Plan numeric or narrative receiving water objectives, and if effluent limitations for these compounds should be required in the new permit. If the California Toxics Rule (CTR)is adopted, staff will also evaluate the reasonable potential to cause or contribute to a violation of a CTR objective. 7. Mercury Mercury is listed under the Federal 303(d) list as a pollutant causing impairment in the Sacramento-San Joaquin Delta. This listing is based partly on elevated levels of mercury in fish tissue. The discharge must not cause or contribute to an increased mercury level in fish tissue. Mercury has been detected in the effluent of the Discharger and therefore, a mass effluent limitation will need to be considered and developed for the permit. As with the DO