SITE INFORMATION AND CORRESPONDENCE_CASE 2

Home Browse Search

Response to Written Comments -10- 24 April 2007 City of Tracy WWTP San Joaquin County Request: Remove all maximum daily and mass limits for the conventional pollutants, BOD and TSS. RESPONSE: Maximum daily effluent limitations for BODS and TSS are included in the tentative Order to ensure the treatment works are not organically overloaded and operate in accordance with the design capabilities. Regarding mass limitations, federal regulation at 40 CFR 122.45(f)(1) states that "Pollutants limited in permits shall have limitations, standards or prohibitions expressed in terms of mass..." and 40 CFR 122.45(2) states that "Pollutants limited in terms of mass additionally may be limited in terms of other units of measurement, and the permit shall require the permittee to comply with both limitations." Mass limitations for BODS and TSS have been included in accordance with these regulations and are necessary to ensure the treatment works are not organically overloaded and operate in accordance with the design capabilities. Furthermore, BODS and TSS are oxygen-demanding substances, therefore, mass limitations are also necessary to protect the aquatic life beneficial uses of the receiving stream. CITY OF TRACY - NPDES COMMENT #16: Section N.A.1.h. Dissolved Oxygen Limits. The City contends that a dissolved oxygen (DO) limit has not been adequately justified and that the limit was based on historic receiving water data (1998 to 2003), which is too old to rely on. Furthermore, the City contends that since the Permit already includes restrictions on all of the constituents that cause an oxygen demand on the receiving water (e.g., BOD, TSS, ammonia, and nitrogen) and a receiving water limitation requiring that the discharge not cause the concentrations of dissolved oxygen to fall below 5 mg/L in Old River, a DO effluent limit is duplicative, unnecessary, and should be removed. Request: Remove the Dissolved Oxygen effluent limitation. RESPONSE: The Basin Plan contains a numeric site-specific water quality objective for the Delta, in the vicinity of the discharge, that requires that dissolved oxygen concentrations shall not be reduced below 5 mg/L. 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. Based on 556 receiving water samples measured in the vicinity of the discharge from 1998 through 2003, the average DO concentration was 8.8 mg/L, with a maximum and minimum of 14.3 mg/L and 4.6 mg/L, respectively. Effluent DO concentration data is not available. However, the discharge contains constituents that cause an oxygen demand on the receiving water (e.g. BOD, TSS, ammonia, and nitrogen). Since, at times the receiving water does not comply with the Basin Plan's water quality objective for DO, the discharge has a reasonable potential to cause, or contribute, to an in-stream excursion of the DO Regional Water Quality Control Board, Central Valley Region Board Meeting —3/4 May 2007 Item#17