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t <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> ORDER NO. 99-051 <br /> REQUIRING THE CITY OF MANTECA AND CITY OF LATHROP <br /> WASTEWATER QUALITY CONTROL FACILITY <br /> TO CEASE AND DESIST <br /> FROM DISCHARGING CONTRARY TO REQUIREMENTS <br /> The California Regional Water Quality Control Board, Central Valley Region, (hereafter Board) finds: <br /> I. The City of Manteca wastewater treatment plant treats the flows from the City of Manteca and <br /> certain areas of the City of Lathrop. The City of Manteca is solely responsible for the wastewater <br /> treatment facility. <br /> 2. The Board, on 20 June 1997, adopted Order No. 97-115 (NPDES NO. CA 0081558) which <br /> prescribes requirements for an average discharge of 53 million gallons per day (mgd) of treated <br /> combined domestic and industrial wastewater to land and partially to surface water. The City of <br /> Manteca and the City of Lathrop(hereafter Discharger) were both named as dischargers on Order No. <br /> 97-115. Land disposal of effluent is maximized by seasonally discharging effluent at agronomic rates <br /> to existing City-owned irrigation fields and other leased property. Excess flows are discharged to the <br /> San Joaquin River. <br /> 3. The Board, on 24 July 1998, adopted Cease and Desist Order No. 98-169 which directed the City <br /> of Manteca and the City of Lathrop to implement a permit compliance workplan. The plan included <br /> identification and implementation of changes required at the wastewater treatment plant to ensure <br /> reliable compliance with Waste Discharge Requirements Order No. 97-115. The plan was to include <br /> evaluation of treatment options and any other measures which would ensure compliance, including, <br /> but not limited to, changes in test species to include rainbow trout in addition to the permitted <br /> fathead minnow, and consideration of effects of the acutely toxic discharge on ambient waters and <br /> beneficial uses. The above stated plan included a time schedule with full continuous compliance <br /> with Order 97-115 by 1 December 1998. <br /> 4. The City of Manteca and the City of Lathrop proceeded with the necessary work to comply with <br /> Order 98-169 and the time schedule. The Discharger for the past several months has been <br /> investigating the use of rainbow trout as an alternative species to the permitted fathead minnow for <br /> use on the 96 hour bioassay. The bioassay test results showed fathead minnows could tolerate total <br /> ammonia concentrations greater than 10 mg/1 while rainbow trout could not tolerate ammonia <br /> concentration above 20 mg/l. While operating the plant in a partial nitrification mode it has been <br /> found to be possible to maintain a constant effluent ammonia concentration of less than 20 mg/l, but <br /> extremely difficult to maintain a constant effluent ammonia concentration of less than 10 mg/l. <br /> Furthermore, comments from the U.S. E.P.A. state that they do not support the proposed change in <br /> test species to rainbow trout, a less sensitive species. The Discharger has for the present time <br /> withdrawn its request to use rainbow trout in the 96 hour bioassay. <br /> 5. The 24 July 1998 staff presentation, for the adoption of Order 98-169, noted "If major plant <br /> modifications are found to be necessary,the Cease and Desist Order will be brought back to the <br />