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u � RESPONSE TO WRITTEN COMMENTS -33- City Of Stockton-Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting DeltaKeeper Comment No. 6E: Finding No. 30 admits that the State Implementation Plan recommends that the Regional Board should consider whether the mass loading of mercury should be limited to representative, current levels. The Permit must include a mass limit for mercury. The Clean 'Nater Act requires that "[a]ll pollutants limited in permite shall hive limitations, standards or . . prohibitions expressed in terms of mass . . ." with a few, inapplicable exceptions. 40 C.F.R. § 122.45(f). Contrary to Finding No. 30, the Permit fails to contain an effective interim load limit for mercury. It only provides that the Discharger can"bank" increases in mercury loadings until such time as a discharge specific offset program is adopted by the Regional Board. There is no assurance that a mercury bank will ever be implemented. This is effectively an illegal open-ended compliance schedule. RWQCB Response: The permit followed the SIP recommendation to limit the mass loading to current levels pending completion of the TMDL. A mass limitation was included. The permit also requires year-round operation of tertiary filtration, source control, as well as an offset feasibility study. These requirements will reduce the mercury in the discharge pending completion of the TMDL. DeltaKeeper Comment No. 7: A Limit For Toxicity Must Be Included hi The Permit. Finding No. 28 states that the Discharger will be allowed to continue to kill bioassay fish until 1 November 2005. Considering the lack of dilution in the river, toxicity in bioassays can translate into toxicity in the receiving waters. The Clean Water Act and the SIP may allow toxicity to continue under a compliance schedule but the federal Endangered Species Act requires a take permit. Both the San Joaquin River and the Delta are listed under § 303 (d) of the Clean Water Act as impaired because of unknown toxicity. The Tentative Permit proposes to allow additional toxicity in the mixing zone. Under low flow conditions, substantial toxicity is likely to be caused by interactions between the mixture of high temperature, ammonia, low dissolved oxygen, and elevated metal and organic chemical concentrations in the effluent. Extensive toxicity has been identified in the effluent. Fact Sheet at 13.1 and 13.2 40 CFR 122.44(1)(i) states that"[1]]imitations must control all pollutant or pollutant parameters (either conventional, nonconventional, or toxic pollutants)which the Director determines are or may be discharged at a level which will cause, have the reasonable potential to cause, or contribute to an excursion above any State water quality standard, including State narrative criteria for water quality." "When the permitting authority determines....that a discharge causes has the reasonable potential to cause. or contributes to an in-stream excursion above the allowable ambient concentration of a State nume criteria within a State water quality standard for whole effluent toxicity, the permit must contain effluent limits for whole effluent toxicity." 40 CFR 122.44(l)(iv) By definition, an impaired waterbody has no remaining assimil- vc capacity. Mixing zones are not allowed where there ro assimilative capacirr the recei, n f . The SanJoaqui; Ri•;er has no