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• • <br /> INFORMATION SHEET ORDER NO. 97-115 (revised) -6- <br /> CITY OF MANTECA AND CITY OF LATHROP <br /> SAN JOAQUIN COUNTY <br /> • At the location of maximum plume diameter, approximately 98% of the river's cross section would <br /> have ammonia concentrations below acute toxicity levels. <br /> • An aquatic organism floating with the river current would take approximately 72 seconds to pass <br /> through the maximum length of the acute toxicity zone, assuming the river velocity of 0.56 fps. <br /> Chronic Toxicity Mixing Zone <br /> Chronic toxicity calculations used a river pH of 8.3, and a background river ammonia concentration of <br /> 0.07 mg/l. Plant effluent discharge pH was 7.08, and effluent ammonia concentration was 30 mg N/1. <br /> The chronic mixing zone was predicted to be: <br /> • Cigar-shaped plumes emanating from each diffuser port, extending a maximum of 51 feet down <br /> river. The plumes gradually widen as the effluent is mixed with river water to a maximum of 2.6 <br /> feet in diameter. The ammonia concentration decreases along the length of the plume. (Attachment <br /> E) <br /> • The cumulative cross sectional area of the 12 plumes is 63 square feet, and would cover a <br /> maximum of 3.2% of the river's cross sectional area. <br /> • At the location of maximum plume diameter, approximately 97% of the river's cross section would <br /> have ammonia concentrations below chronic toxicity levels. <br /> • An aquatic organism floating with the river current would take approximately 64 seconds to pass <br /> through the maximum length of the acute toxicity zone, assuming the river velocity of 0.56 fps. <br /> Worst Case Mixing Zone—Non-Summer Conditions (October—May) <br /> River flow was assumed to be 1032 cfs. <br /> Acute Toxicity Mixing Zone <br /> Acute toxicity calculations used a river pH of 8.4, and a background river ammonia concentration of <br /> 0.2 mg/l. Plant effluent discharge pH was 7.65, and effluent ammonia concentration was 35 mg N/l. <br /> The acute mixing zone was predicted to be: <br /> • Cigar-shaped plumes emanating from each diffuser port, extending a maximum of 28 feet down river. <br /> The plumes gradually widen as the effluent is mixed with river water to a maximum of 2 feet in <br /> diameter. The ammonia concentration decreases along the length of the plume. (Attachment F) <br />