SITE INFORMATION AND CORRESPONDENCE_1985-2004

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Staff Report City of Manteca and City of Lathrop Wastewater Quality Control Facility mixing zones,revisions to this permit require monitoring of the river for ammonia downstream of the acute and chronic mixing zones. If acute toxicity is found 40 feet beyond the discharge point or chronic toxicity is found 51 feet beyond the discharge point, then this Order will be reopened and effluent limitations added or amended for ammonia toxicity. • This permit allows a change in Effluent Bioassay testing. This permit allows dilution of the effluent with San Joaquin River water, in performing the bioassay testing,to better simulate the actual toxicity occurring in the receiving water. The City has found through studies that fish survive the 96-hour static bioassay and they are able to achieve full compliance with the acute toxicity requirements of their permit when their effluent ammonia concentrations are maintained at 10 mg/1 or less. In order to maintain continuous ammonia level of 10 mg/1 or less, the plant effluent must be diluted with River water at a ratio of 2.8 parts of river water to 1 part of plant effluent. This change in their bioassay effluent limitation testing protocol is proposed in the revised permit. TIME SCHEDULE The following time schedule was prepared by the Board's staff with concurrence from the City of Manteca to achieve full compliance with their NPDES permit. Task Due Date Workplan for measuring river flow velocity prior to 1 June 2001 1 May 2000 Workplan for receiving water sampling investigation to confirm 1 May 2000 CORMIX model predictions Submit technical report on storage pond holding capacity 1 July 2000 Conduct receiving water sampling investigation 1 August 2000 Submit results of the confirmation study to the Board 15 September 2000 Construct diffuser 1 June 2001 Construct river velocity station near point of discharge 1 June 2001 Diffuser fully operational 1 December 2001