SITE INFORMATION AND CORRESPONDENCE_CASE 2

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Response to Written Comment -9- 24 April 2007 City of Tracy WWTP San Joaquin County dichlorobromomethane, and chlorodibromomethane are all based on long-term (70 years of exposure) objectives to protect human health. No justification exists for short- term limits for these constituents. Request: Impose only monthly averages for iron, dichlorobromomethane, and chlorodibromomethane since the objectives for these constituents are set to protect against long term chronic effects. RESPONSE: The effluent limitations for iron are based on the Basin Plan site- specific water quality objectives for the Delta and are expressed as a maximum concentration. Therefore, the effluent limitations for iron are expressed as maximum daily effluent limitations in the tentative Order to implement the objective. Dichlorobromomethane and chlorodibromomethane are priority pollutants. Thus, the SIP governs the calculation of effluent limitations. The effluent limitations for dichlorobromomethane and chlorodibromomethane were calculated in accordance with section 1.4 of the SIP, which contains procedures for calculating maximum daily and average monthly effluent limitations. CITY OF TRACY - NPDES COMMENT #14: Section IV.A.1.d. and Fact Sheet, Page F-54. Temperature. Language was added to clarify that this limitation (i.e. that the "maximum temperature of the discharge shall not exceed the natural receiving water temperature by more than 20°F") derived from the temperature objectives in the Thermal Plan. The Central Valley Basin Plan establishes the threshold for acceptable temperature alterations as "...it can be demonstrated to the satisfaction of the Regional Water Board that such alteration in temperature does not adversely effect beneficial uses." If such demonstration is the result of the study specified on page F-7 of the Fact Sheet, the Permit should state that the subject effluent limitation should and will be modified. Request: Add a reopener provision to Provision VI.C.1. for temperature modifications based on studies conducted by the City. Pages F-9 before Table F-1 and F- 71 should also be amended to reflect changes made to the permit RESPONSE: A new reopener provision has been added to the agenda version of the proposed Order. CITY OF TRACY - NPDES COMMENT #15: Sections IV.A.2.a, 3.a., 4.a., and 5.a., Tables 5-8. Maximum Daily and Mass Limits for BODS and TSS. The Regional Water Board is proposing to add limits based on maximum daily values and mass limits that are more stringent than required by federal law. Regional Water Quality Control Board, Central Valley Region Board Meeting — 3/4 May 2007 Item#17