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INFORMATION SHEET ORDER NO.R5-2004-0028 15 INFORMATION SHEET ORDER NO.R5-2004-0028 16 CITY OF MANTECA,CITY OF LATHROP AND DUTRA FARMS CITY OF MANTECA,CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY SAN JOAQUIN COUNTY adequately nitrifies and denitrifies the waste stream to protect the beneficial uses of municipal and conditions that are a combination of worst-case observations'using effluent data and using receiving domestic supply. water data(see Table 7). Consistent with 40 CFR section 122.44(d)(vi)(A)and the Basin Plan"Policy for Application of Water Quality Objectives",this Order implements the Basin Plan narrative toxicity 10 Ammonia-Nitrogen objective by applying USEPA's Ambient Water Quality Criteria for the Protection of Freshwater Aquatic Life for ammonia. This Order includes effluent limitations for ammonia,based on the This section provides a detailed discussion and evaluation of ammonia in the effluent. narrative toxicity objective and the USEPA's Ambient Water Quality Criteria for the Protection of Freshwater Aquatic Life. A review of the Discharger's monitoring reports from January 1998 through December 2002 shows an average ammonia effluent concentration of 18 mg/1,a minimum concentration of less than 0.1 mg/l, The acute criterion or criteria maximum concentration(CMC)for ammonia is a fancfion of receiving and a maximum concentration of 43 mg/1. The data indicate very little seasonal fluctuation. Receiving water pH and is stated as a I-hour average concentration. A worst-case scenario occurs when there is water monitoring(R-1)was conducted from January 2002 through December 2002(see Table 4). The little to no dilution of the effluent by the receiving water. This was discussed in the previous dilution receiving water data showed an average of 0.2 mg/1 with a minimum of less than 0.01 mg/1 and a section. Therefore,for the acute criteria,water quality objectives need to be achieved in the effluent at maximum of 1.4 mg/l. the end-of-pipe. As allowed by the TSD,this Order calculates the CMC using critical conditions that are a combination of worst-case observations. The acute criterion for ammonia is determined by 10.1 Toxicity Criteria evaluating the maximum effluent pH at the end of the pipe. The maximum allowable effluent pH is 8.0. The calculated CMC for this condition is 5.6 mg/1 ammonia as N. The maximum effluent The USEPA 1999 Update of Ambient Water Quality Criteria for Ammonia provides the applicable concentration,measured on 15 August 2001,was 42.8 mg/1 ammonia as N. This exceeds the water quality criteria for this pollutant. Ammonia is not a priority pollutant;therefore,USEPA calculated ammonia CMC value. Even using the mean effluent ammonia concentration of 17.7 mg/1 guidance,rather than the SIP,is applicable for reasonable potential and effluent limitation calculations. exceeds the CMC value under worst-case pH conditions. This scenario shows that there is reasonable Section 4.3.3 of the TSD allows the consideration of exposure duration in evaluating toxicity to potential for acute water quality objectives to be exceeded by effluent ammonia concentrations. organisms passing through a mixing zone. When evaluating either an acute or chronic mixing zone for ammonia,the pH of the mixture of effluent and receiving water should be used to determine The receiving water pH and ammonia concentrations were also evaluated to determine if there is appropriate criteria to be applied within that mixing zone. The pH in the mixing zone will be a reasonable potential to cause acute ammonia toxicity,based upon concentrations found in the receiving function of the effluent pH and the ambient dilution water pH being mixed together. The pH is an water. The acute criterion is determined using the receiving water pH. In July 2002,the receiving important factor because toxicity of ammonia increases logarithmically as pH increases. water reached a maximum pH of 9.3,as recorded by the City at the R-1 monitoring site. The receiving water ammonia concentrations determined by the discharger's monitoring during 2002 indicated a 10.2 Consideration of Aquatic Organisms maximum concentration of 1.4 mg/l with an average of 0.2 mg/l. As determined by the TSD approach, the receiving water at times may exceed the CMC for ammonia. The most stringent acute ammonia criteria are applied when salmonoids are present within the water column. The San Joaquin River at Manteca is a migratory path for salmon,and they are likely to be The chronic criterion,or criteria continuous concentration(CCC),for ammonia is a function of both present in the river at any time of the year. The chronic ammonia criteria are most stringent when pH and temperature. For ammonia,the CCC is stated as a 30-day average concentration,with the early life stages(ELS)of aquatic species are present. In response to a request for information highest 4-day average within the 30-day average not to exceed 2.5 times the CCC. As allowed by the regarding the time of year ELS of fish are present in the San Joaquin River near the Deep Water Ship TSD,the CCC is calculated using critical conditions that are a combination of worst-case observations. Channel(DWSC),a Department of Fish and Game memorandum,dated The highest receiving water 30-day average pH was 9.1,observed during June/July 1992 at the DWR 27 February 2001,states ELS of multiple fish and invertebrates species are present in the San Joaquin Mossdale monitoring station. The maximum 30-day average temperature of 25.7 C(78.3 F)was River year-round. Therefore,both acute and chronic ammonia toxicity are based on the assumption observed during July 2002 at the DWR Mossdale monitoring station.The calculated CCC for this that both salmonids and ELS of fishes are present in the San Joaquin River near the Manteca WQCF condition is 0.21 mg/1 ammonia-N. The effluent 30-day average ammonia concentration during that outfall year-round. same period was 14.1 mg/1 ammonia as N and 17.7 mg/1 averaged over the past 5 years. The calculated CCC is exceeded which demonstrates that the 10.3 Reasonable Potential Evaluation effluent has the reasonable potential to cause or contribute to chronic ammonia toxicity in the receiving water. The reasonable potential evaluation shows that the WQCF effluent has reasonable potential to cause or contribute to an in-stream excursion above USEPA acute and chronic water quality criteria for ammonia. This has been demonstrated by determining reasonable potential based on critical EPA Technical Support Document,March 1991,Chapter 3