SITE INFORMATION AND CORRESPONDENCE_CASE 2

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CENTRAL VALLEY WATER BOA' RESPONSE (SWRCB/OCC File A-1846) -5- PETITIONS FOR REVIEW OF WA'SfE DISCHARGE REQUIREMENTS ORDER NO. R5-2007-0036 (NPDES NO. CA0079154) AND TIME SCHEDULE ORDER NO. R5-2007-0037 CITY OF TRACY, WASTEWATER TREATMENT PLANT CONTENTION B: The Regional Board abused its discretion by imposing mass limits in addition to concentration limits without adequate justification. BODS, TSS, Ammonia, Nitrate, and Nitrite. Mass limitations for BODS, TSS, and ammonia were required in addition to concentration limitations, because these constituents are oxygen demanding substances. Old River from the San Joaquin River to the Delta Mendota Canal is listed on the CWA Section 303(d) list for low dissolved oxygen (DO) and receiving water sampling indicates periods of low DO. Therefore, mass limitations for BODS, TSS, and ammonia were required to limit the oxygen demand on the receiving water. Mass limits were also required for nitrate and nitrite, but this appears to be an error. Therefore, the Central Valley Water Board recommends the State Water Board remand the Tracy Permit for reconsideration of the mass limits for nitrate and nitrite. Mercury. The Delta waterways are listed in accordance with Clean Water Act section 303(d) as impaired for mercury, based on bioaccumulation of mercury in fish tissue. Furthermore, health advisories by the Cal/EPA Office of Environmental Health Hazard Assessment remain in effect for human consumption of fish in the Delta, including Old River at Tracy, due to excessive concentrations of mercury in fish tissue. Reliable monitoring data confirm the impairment. (See discussion of mercury in Response to Contention C.) Central Valley Water Board staff is developing a Methylmercury total maximum daily load (TMDL) for the Delta that proposes methylmercury load reductions for facilities discharging to the South Delta, including Old River. In these situations, the SIP recommends the Regional Board consider whether the mass loading of bioaccumulative pollutants should be limited in the interim to "representative current levels" pending development of applicable water quality standards or TMDL allocation. (SIP, § 2.1.1.) Consistent with this recommendation, an interim effluent mass limitation for mercury of 0.042 pounds/month (as total recoverable) is included in the Tracy Permit. The intent is, at a minimum, to prevent further impairment while a TMDL for mercury is being developed. A mass limit is appropriate for bioaccumulative constituents such as mercury, because any increase in loading to an already impaired water body would further degrade water quality. Copper. The Discharger's-petition states that there is a mass limit for copper. However, the final effluent limitations in the Tracy Permit do not contain a mass limit for copper.