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• <br /> • <br /> The City would be willing to forego discharges to Dredger Cut from May 1 S through <br /> September 15 while the Basin Plan Update process is continuing in regard to the issues of <br /> disinfection and effluent dominated receiving waters. <br /> Comment 4. Discharge Limits for Orbanoclilorine Pesticides <br /> The City objects to the effluent limitations for organochlorine pesticides set forth in Section B.1 <br /> of the permit. The detailed bases for the City's objections are provided in the enclosed comments <br /> provided by Hall &Associates Exhibit 2. <br /> In particular, the tentative discharge requirements contain a new lower limit for Lindane based on <br /> language added to the Basin Plan in 1977 specifying no detectable concentrations of chlorinated <br /> pesticides. The detection limit has dropped substantially since 1977, resulting in significantly <br /> lower discharge limits than originally intended. The cost and attainability of this objective thus <br /> was not evaluated during the adoption of the Basin Plan. Based on an initial survey of four <br /> available labs, the quoted best detection limits varied from 0.025 to 0.25 ug/L, with a median of <br /> 0.1 ug/L. The labs said they could achieve lower detection limits for relatively pure water, but <br /> not for wastewater because of interference from other residual constituents. The detection levels <br /> listed in the pesticide data previoi;sly submitted to the Regional Board were the best achievable <br /> with relatively pure water and were not adjusted for interference from wastewater residual <br /> constituents. The lab which performed those analyses is no longer in business. <br /> Based on the quoted laboratory detection levels, we propose that Lindane concentrations in <br /> effluent be limited to non detect at 0.1 ug/L or to average annual background Lindane <br /> concentration, whichever is higher. An alternative would be to perform a study of the receiving <br /> waters to better characterize effluent and background concentrations of Lindane while the <br /> Regional Board revises the effluent limitations for pesticides to be consistent with federal water <br /> quality criteria guidance for pesticides through the Basin Plan update process. <br /> Comment 5. Dilution and Mixing Zone <br /> In the Water Quality Impact report authored by Gary Litton and Jason Nikaido of the University <br /> of the Pacific, the dilution at location D-1 was calculated to average 2.0 over low and high tide <br /> cycles using specific conductivity data and model simulations. It should be noted that plant <br /> effluent is not discharged directly into Dredger Cut, but into an isolated discharge channel <br /> approximately 20 feet wide by 900 feet long which empties into Dredger Cut at the confluence <br /> with Highline Canal. The end of this channel is only a little over 100 feet,from D-1 at the bridge <br /> near the west end of Dredger Cut rather than the 300 meters listed in the Tentative Discharge <br /> Requirements. <br /> Setting chronic toxicity standards based on dilution at D-1 would be protective of essentially all <br /> of the main Dredger Cut channel and Highline Canal. The narrow discharge channel to the east <br /> of Highline Canal could be subject to higher concentrations of constituents, but this is a very <br /> small amount of water and is not used for irrigation, recreation or fishing. We propose that acute <br /> toxicity requirements continue to be applied at the end of the discharge pipe and that dilution at <br /> D-1 be applied for any chronic toxicity limits. <br /> tentcomments%05 Exhibit 1 Page 4 12/17/99 <br />