SITE INFORMATION AND CORRESPONDENCE_CASE 2

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Response to Written Comments -15- 24 April 2007 City of Tracy WWTP San Joaquin County Executive Officer, this Order will be reopened to modify the effluent limitations for the applicable inorganic constituents. Request: Change "may be reopened" to "will be reopened." RESPONSE: We cannot guarantee that the Order will be reopened. However, we will make every effort to reopen and modify the Order based on available staff resources. CITY OF TRACY - NPDES COMMENT #25: Provision VI.C.1.h., and Fact Sheet, Page F-72, Paragraph VII.BA.h. Human Health Dilution Credits. It is unclear why this needs to be a provision in this permit. The Antidegradation Policy does not require that permits be reopened upon implementation of new treatment technologies to lower effluent limits to meet the new performance levels. If harmonic mean levels are set to implement the existing water quality objectives, those same levels would apply despite the new technology. Request: Remove Provision VI.C.f.h. and Paragraph V1I.B.1.h. in Appendix F as not required, inconsistent with law, and unnecessary. RESPONSE: In the tentative Order, the maximum allowable human health dilution credit is 20:1. However, the granting of the entire human health dilution credit could allocate an unnecessarily large portion of the receiving water's assimilative capacity for human carcinogens and could violate the Antidegradation Policy. In previous NPDES permits, the Regional Water Board has developed effluent limitations for human carcinogens based on the amount of dilution that would be required, such that water quality objectives in the receiving water would be met when effluent concentrations are at estimated maximum concentrations. However, since the City is making upgrades to the facility, some of which could significantly increase the formation of chlorinated by products, using the current plant performance to calculate the necessary dilution credit could result in effluent limitations for dichlorobromomethane and chlorodibromomethane that could not be met after the facility upgrades. Therefore, at this time the tentative Order would allow the entire human health dilution credit. However, because the permit could then allocate an unnecessarily large portion of the assimilative capacity for human carcinogens, the tentative Order includes a reopener to lower the dilution credit based on the performance of the upgraded facility. CITY OF TRACY - NPDES COMMENT #26: Provisions VI.C.3.a. and b. Pollution Prevention Plans. The City contends that the proposed insertion of the words "and implement" should be rejected as contrary to law. Words such as "conduct," "implement," and "implementation" related to a Pollution Prevention Plan (PPP) is Regional Water Quality Control Board, Central Valley Region Board Meeting — 3/4 May 2007 Item#17