SITE INFORMATION AND CORRESPONDENCE_CASE 2

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Response to Written Comments -8- 24 April 2007 City of Tracy WWTP San Joaquin County by the State, except when State regulations contain criteria which are more stringent for a particular parameter and use, or except as provided in footnotes p, q, and x to the table in paragraph (b)(1) of this section." Neither this federal regulation nor the SIP specify that the State's objective be a site-specific objective, merely that the State's objective be in effect. The numerical copper objective in Table III-1 of the Basin Plan was legally adopted by the Regional Water Board, approved by the State Water Board and USEPA, and is therefore in effect until modified or withdrawn by a subsequent formal rulemaking (e.g., a Basin Plan amendment). According to Sections 13263 and 13377 of the California Water Code, the Regional Water Board is required to implement the Basin Plan, including water quality objectives contained therein, when adopting waste discharge requirements and NPDES permits. One cannot directly compare the CTR criteria with the Basin Plan site-specific objective, because the CTR includes separate criteria for acute and chronic aquatic toxicity, whereas, the site-specific objective is expressed as a single maximum concentration. For a meaningful comparison, water quality-based effluent limitations (WQBELs) were first developed based on each water quality objective/criterion and then compared. For the CTR criteria, WQBELs calculated using section 1.4 of the SIP result in an average monthly effluent limitation (AMEL) of 9.1 pg/L and a maximum daily effluent limitation (MDEL) of 14 pg/L (total recoverable). For implementing the Basin Plan's numeric site-specific objective for copper, the Regional Water Board's practice is to only require a MDEL, which would result in a MDEL of 10.4 pg/L (total recoverable). The MDEL based on the CTR criteria (14 pg/L) exceeds the MDEL based on the Basin Plan site-specific objective for copper (10.4 pg/L). Therefore, it is necessary to set the MDEL at 10.4 pg/L to implement the Basin Plan site-specific objective for copper. However, an MDEL of 10.4 pg/L exceeds the AMEL based on the CTR criteria (9.1 pg/L). Therefore, to protect against chronic aquatic toxicity in the receiving stream, it is also necessary to include an AMEL of 9.1 Ng/L. The City requests that a reopener provision be included in the proposed Order to allow the permit to be reopened to amend the final limits based on the WER or BLM adjustment. The proposed Order already includes reopener provision VI.C.1.g., which addresses WEIR studies. Reopener provision VI.C.1.a. allows the permit to be reopened based on new information, which would include any studies provided by the City regarding the BLM. CITY OF TRACY - NPDES COMMENT #13: Provision IV.A.1.a., Table 4. Human Health-based Limits. The tentative permit improperly includes maximum daily limits to implement human-health based water quality objectives. The limits for iron, Regional Water Quality Control Board, Central Valley Region Board Meeting — 3/4 May 2007 Item#17