SITE INFORMATION AND CORRESPONDENCE 1980-1999

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within the range of all Central Valley ESUs of chinook salmon and steelhead trout,the Sacramento splittail, and the threespine stickleback. (Draft Biological Conference Opinion,page 181). B. The Permit Must Include A Water Quality Mass-Based Limit For Chlorine. There is a conflict between the Tentative Permit and the Information Sheet with respect to chlorine. The Tentative Permit includes a chlorine limit of 0.01 mg/1 (10µg/1) as a weekly average and 0.019 mg/1 (19}10) as a daily average. However,the information states that the Order contains effluent discharge limitations for total residual chlorine of 0.01 mg/l as a weekly average, and 0.019 mg/1 as an hourly average based on the ambient criteria to protect aquatic life. There is an obvious conflict between the Tentative Permit and Information Sheet. Our review of available data indicates that a proposed effluent limit for chlorine of 0.018 mg/l (19 µg/1) as a daily average would allow far higher hourly peaks and have significant impacts beyond those reported in the Tentative Permit. A chlorine daily average of 0.019 mg/1 would allow a conservative estimated hourly peak of at least 0.45 mg/l, (450µg/1)based on 24 one-hour samples or a peak of 2.73 mg/l (2,730 gg/1)based on ten-minute samples. EPA ambient water quality criteria development document(EPA 440/5-84-030) for chlorine shows that acute toxicity values range from 28 µg/1 for daphnia magna to 710 µg/1 for the threespine stickleback. The species mean acute value for rainbow trout was 61 µg/1. EPA recommends that freshwater species should be adequately protected if chlorine does not exceed 19 µg/1 more than once every three years on the average. The EPA Development Document for Ambient Water Quality Criteria states that if criteria are exceeded more than once in three years, irreparable harm will be done to aquatic life in receiving streams. The recommended exceedance frequent of three years is the EPA's best scientific judgment of the average amount of time it would take an unstressed system to recover from a pollution event in which exposure to chlorine exceeds the criterion. Stressed systems would be expected to require more time for recovery. A discharge of 0.45 mg/l (450µg/1) would exceed the LC50 for numerous fish and invertebrate species in addition to benthic organisms. It would equal EPA's recommended level of 19 µg/1 (one hour average, discharged once every three years) which is necessary for maintenance of a healthy stream even if the daily peak was maintained at 19 µg/1. It would also exceed the DFG's recommended limit of 0.02 mg/l (20µg/1) as a daily maximum. Finding 22 states that"Dredger Cut is a dead end slough,with minimal dilution in the vicinity of the discharge" and"[b]ecause available dilution within the mixing zone is negligible, and the mixing zone extends for at least 300 meters,the Board will not designate any mixing zone within which water quality objectives will not apply." The removal of chlorine is a fairly simple process. The Tentative Permit must contain chlorine concentration limits of).019 mg/l (19 µg/1) as DeltaKeeper,Tentative NPDES Permit,Lodi, 17 December 1999,Page 3.