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RESPONSE TO WRITTEN COMMENTS -36- City Of Stockton - Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting ammonia. EPA concurs with the methodology staff used in the selection of pH values both for the determination of reasonable potential and for the establishment of WQBELs. We share your concern regarding the effects of the plant's high ammonia concentrations in driving down dissolved oxygen in the receiving water. High nitrates may also contribute to low DO values. EPA encourages a close review of the study required under Provision G.14. The time schedule of less than 5 years to meet WQBELs for CTR constituents is consistent with the SIP. The time schedule for WQBELs established from a new interpretation of the Basin Plan narrative criteria is consistent with the Basin Plan allowance for compliance schedules. EPA is also pleased to see that a pollution prevention program and offset program are required to be developed for those pollutants which may be contributing to water quality impairment, but for which reduction at the source or through offsets is more economical than through additional treatment (TDS, pesticides, mercury, etc.). Finally, the receiving water monitoring program, and the addition of monitoring station R-2A will be of tremendous benefit in determining water quality impacts associated with the discharge. RWQCB Response: Comments are noted. NATIONAL MARINE FISHERIES SERVICE COMMENTS NMFS Comments: The NMFS submits this letter in support of the tentative order. This facility apparently needs an upgrade in treatment technology to protect beneficial uses, including the protection of salmonid fish species listed as threatened or endangered. The requirements will result in significant improvements to water quality in the Stockton area of the San Joaquin River. Eliminating impacts caused by elevated ammonia should be particularly beneficial to these fish. We are pleased to see the Board acknowledge that the nitrification process may increase nitrate concentrationsin the discharge, and that denitrification should be examined. The requirement to treat the effluent to Title 22 tertiary standards should also benefit the fish species we manage. The loading of metals and organic contaminants that are sorbed to particles in the discharge will be reduced. Efforts to upgrade treatment processes at municipal wastewater treatment plants throughout the Central Valley Region have not gone unnoticed by the NMFS, and we anticipate that this process will make rapid improvements to water quality conditions. Thank you for your continued efforts in protecting and improving water quality and restoring endangered and threatened salmonids. RWQCB Response: Comments noted.