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CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 3443 Routier Road, Suite A, Sacramento, CA 95827-3098 NOTICE OF PUBLIC HEARING and Cease and Desist Order for CITY OF MANTECA AND CITY OF LATHROP WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY The City of Manteca owns and operates the Wastewater Quality Control Facility that receives wastewater flows from the City of Manteca and some areas of the City of Lathrop. The City of Manteca currently discharges 5.3 mgd of treated domestic and industrial wastewater to 370 acres of farm land for irrigation adjacent to the treatment plant. Excess treated wastewater flows are discharged to the San Joaquin River. The Board is considering the issuance of a Cease and Desist Order pursuant to Section 13301 of the California Water Code ,requiring the City of Manteca and the City of Lathrop Wastewater Quality Control Facility (hereafter Discharger)to cease and desist from discharging wastes in violation of Waste Discharge Requirements Order No. 97-115. The proposed Order alleges that the Discharger has violated, or threatens to violate, its waste discharge requirements. In June 1997,the Discharger was given stricter toxicity effluent limitations than were contained in their previous permit. Since the adoption of Order 97-115 in June 1997 and continuing through March 1998,the Discharger has violated the Order's effluent bioassay requirement, consistently reporting 0 % survival. The Discharger violated the daily minimum survival for any 1 bioassay (less than 70%) and the median survival in 3 or more consecutive tests (90% survival). To lower the ammonia levels in the effluent,believed to be the cause of the problem,Discharger - instituted process modifications to operate the plant in a partially nitrified mode. As a result of these actions,weekly bioassay tests for the months of April and May 1998 were in full compliance with the permit limits. In addition,the Discharger has investigated the use of alternative bioassay test species as allowed by the U.S.E.P.A. Results from two additional bioassay tests for the month of May 1998 were in full compliance with the permit limits. The proposed Cease and Desist Order is necessary to require further investigation of these corrective actions and to determine if these measures will be long lasting and consistent over time.