SITE INFORMATION AND CORRESPONDENCE_CASE 2

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1140 Response to Written Comments -5- 24 April 2007 City of Tracy WWTP San Joaquin County "(1) If the Discharger monitors pH continuously, pursuant to 40 CFR §401.17, for pH effluent limitations under continuous monitoring, the Discharger shall be in compliance with the pH limitation specified herein, provided that both of the following conditions are satisfied: (i) the total time during which the pH values are outside the required range of pH values shall not exceed 7 hours and 26 minutes in any calendar month; and (ii) no individual excursion from the range of pH values shall exceed 60 minutes." Request: Add the requested language related to compliance with the pH Limits. RESPONSE: Continuous pH monitoring is widely used by POTWs and is necessary to ensure proper operation of the Facility. Furthermore, the proposed Order includes instantaneous maximum and minimum effluent limitations for pH, which require continuous monitoring for compliance determination. The proposed compliance determination language is not appropriate for the City's discharge. The effluent limitations for pH in the proposed Permit are water quality-based effluent limitations necessary to protect the beneficial uses of the receiving water. The regulations cited in the City's comment are not applicable to the discharge. These regulations are for effluent limitations that have been set in accordance with effluent limitation guidelines (ELGs). ELGs are technology- based effluent limitations and are used for setting effluent limitations for non- municipal dischargers. CITY OF TRACY - NPDES COMMENT #11: Section N.A.1.a., Table 4, Aluminum Limits. The City asserts that the reasonable potential analysis for aluminum was conducted incorrectly using a Projected Maximum Effluent Concentration (MEC) of 140 pg/L under the TSD instead of the actual MEC of 74 pg/L as required under the SIP. The City also asserts that the US EPA chronic guidance criteria for aluminum of 750 pg/L (CMC) and 87 pg/L (CCC) used in the reasonable potential analysis is inappropriate and should be replaced by the secondary MCL values of 1000 and 200 Ng/L. Request: Redo Reasonable Potential Analysis using the actual MEC instead of a calculated, projected MEC. If an effluent limit is retained, impose limits no more stringent than 1.0 mg/L as a monthly average and 0.2 mg/L as a weekly average, which represent the MCL values. If this were done, the permit would contain a WQBEL for aluminum, but a compliance schedule and interim limits would no longer be necessary. RESPONSE: The actual maximum effluent concentration (MEC) for aluminum was 140 pg/L from a sample collected on September 1, 2005. Both the MEC and the maximum receiving water concentration for aluminum exceeds the water quality objective. Therefore, aluminum in the discharge has a reasonable Regional Water Quality Control Board, Central Valley Region Board Meeting—3/4 May 2007 Item#17