SITE INFORMATION AND CORRESPONDENCE_CASE 2

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J Response to Written Comments -6- 24 April 2007 City of Tracy WWTP San Joaquin County potential to cause or contribute to an in-stream excursion above a level necessary to protect aquatic life. The agenda version of the proposed Order was corrected to show the RPA using the actual MEC rather than the projected MEC to be consistent with the RPA procedures required by the SIP. The aluminum effluent limitations are not more stringent than required under federal law. The calculation of the aluminum effluent limitations are based on the procedures set forth in Section 5.4.1 of TSD for aquatic life protection. The acute (1-hour) and chronic (4-day) aquatic toxicity criteria are converted to average monthly and maximum daily effluent limitations. Based on the statistics, it is possible to calculate an average monthly effluent limitation that is lower than the chronic criterion. The procedures for calculating water quality-based effluent limitations are described in detail in the Fact Sheet (Attachment F, WQBEL Calculations, Section IV.C.4.d.) The City also objects to the use of the USEPA National Recommended Water Quality Criteria (NRWQC) for aluminum as the basis for effluent limits. The City has not provided information specific to Old River that demonstrates that the NRWQC for aluminum are not applicable. In the absence of such information, the Regional Water Board must rely on the national criteria to prevent toxicity to aquatic life from aluminum. The national criteria were developed based on scientific studies that concluded that aluminum is toxic to aquatic life at specified concentrations. Since the discharge contains aluminum it is necessary to assure that the discharge does not result in toxicity. The narrative toxicity objective from the Basin Plan is applicable to the discharge. Aluminum is a toxic constituent of the discharge. Applying the narrative toxicity objective using the USEPA National Recommended Water Quality Criteria for aluminum is consistent with state policy, the Policy for Application of Water Quality Objectives in Chapter IV (beginning on page IV-16.00) of the Basin Plan. With respect to narrative objectives, the Regional Water Board must establish effluent limitations using one or more of three specified sources, including EPA's published water quality criteria. [(40 CFR 122.44(d)(1)(vi)(A), (B), or (Q. The City points out that the NRWQC for aluminum, Criteria Continuous Concentration, contains a footnote that states, 'USEPA believes that use of Water-Effects Ratios might be appropriate because: (1) aluminum is less toxic at higher pH and hardness but relationship not well quantified; (2) aluminum associated with clay particles may be less toxic than that associated with aluminum hydroxide particles; (3) many high quality waters in U.S. exceed 87 ug/L as total or dissolved." Based on this information, the City requests that the NRWQC for aluminum be adjusted based on the pH and hardness of Old River prior to performing the reasonable potential analysis. However, USEPA states that the relationship Regional Water Quality Control Board, Central Valley Region Board Meeting— 3/4 May 2007 Item#17