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0 <br /> INFORMATION SHEET <br /> CITY OF MANTECA AND CITY OF LATHROP <br /> WASTEWATER CONTROL FACILITY <br /> ORDER NO. 97-115 (revised) <br /> SAN JOAQUIN COUNTY <br /> The City of Manteca and City of Lathrop (hereafter Discharger) is currently governed under Board <br /> Order No. 97-115,NPDES No. CA0081558, adopted 20 June 1997. The Discharger has requested <br /> this Order be revised. <br /> The City of Manteca owns and operates the wastewater control facility that receives wastewater flows <br /> from the City of Manteca and some areas of the City of Lathrop. The City of Manteca is responsible <br /> for the operation and discharge from the treatment plant, while the City of Lathrop is only responsible <br /> for its portion of the wastewater collection system, and for compliance with any restrictions imposed <br /> by the City of Manteca. <br /> The City of Manteca currently discharges 5.3 mgd of treated domestic and industrial wastewater at <br /> agronomic rates to 210 acres of farmland owned by the City adjacent to the treatment plant, and 160 <br /> additional acres leased by the City with the excess flows discharged to the San Joaquin River. The <br /> flows to agricultural land are required to be maximized to limit the discharges to surface waters. <br /> The existing design flow of the treatment plant is 6.95 mgd. Order No. 97-115 allowed for a plant <br /> expansion up to 8.11 mgd to accommodate population growth. The Discharger is in the process of <br /> completing design work for the expansion, which will have a design flow of 9.87 mgd. <br /> The existing treatment process consists of raw influent bar screening, flow metering and grit removal, <br /> followed by primary sedimentation, biofiltration, conventional activated sludge and secondary <br /> sedimentation. The plant's secondary effluent is agronomically reclaimed. Excess effluent is <br /> chlorinated, dechlorinated and discharged to the San Joaquin River. <br /> Order 97-115 contains stricter toxicity effluent limitations than those contained in the Discharger's <br /> previous permit. Since the adoption of Order 97-115 in June 1997, the Discharger has periodically <br /> violated the Order's effluent bioassay requirement. A toxicity identification evaluation report (TIE) <br /> determined the toxicity was caused by ammonia in the treated effluent. <br /> The Discharger's wastewater effluent normally contains ammonia concentrations between 10 mg/1 <br /> and 25 mg/l,with a 5-year high of 37.2 mg/l. Effluent ammonia concentrations are dependent on the <br /> time of the year, effluent flow, wastewater temperature and the mode of plant operation. Ammonia is <br /> acutely toxic to aquatic life at concentrations found in the Discharger's effluent. <br /> On 30 April 1999, the Regional Board adopted Cease and Desist Order(CDO) No. 99-051 to <br /> investigate and implement methods to bring the discharge into compliance with effluent limitation <br /> C.5 (acute toxicity). The CDO required the Discharger to identify and implement changes at the <br />