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INFORMATION SHEET ORDER NO.R5-2004-0028 17 INFORMATION SHEET ORDER NO.R5-2004-0028 18 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 The monthly average receiving water pH and temperature from the Mossdale monitoring station,and The Clean Water Act requires publicly owned treatment works to comply with the secondary treatment ammonia concentrations collected from the R-1 sample location during 2002 were evaluated to and applicable water quality standards existing prior to 1 July 1977. USEPA's regulations state that determine if concentrations have been observed in the receiving water above the chronic criteria. The any NPDES compliance schedule may not extend beyond an applicable Clean Water Act statutory TSD method demonstrated a reasonable potential for the receiving water to exceed the chronic deadline. Therefore,a compliance schedule that extends the date for compliance with water quality ammonia toxicity. The maximum ammonia concentration of 1.4 mg/1 also demonstrates that there are standards that existed prior to 1 July 1977 may not be included in the Order. times when there is no assimilative capacity in the receiving water for additional ammonia. 11 Priority Pollutants 10.4 Effluent Ammonia Limits This section and its subsections discuss how priority pollutants are evaluated against criteria and how Based on the above discussion of reasonable potential,daily and monthly effluent ammonia limitations limitations and interim requirements are developed. are required to protect aquatic organisms from ammonia toxicity. The USEPA TSD recommends that statistical permit limit derivations be used to develop chemical specific limitations for NPDES permits. For priority pollutants,guidance for determining reasonable potential,effluent limitations,and Effluent limitations are calculated as shown in Table 8. Because of the seasonal variation in pH and compliance schedules is provided by the SIP,adopted in March 2000 by the SWRCB. USEPA temperature of the receiving water and the sensitivity of the ammonia criteria to these conditions, promulgated the numeric water quality criteria for priority pollutants with the adoption of the CTR in seasonal limitations are established. May 2000. Table 10 summarizes the priority pollutants of concern and their respective criteria. For the warm weather months from 1 June to 30 September,the maximum permitted monthly average Priority pollutant constituents were analyzed in the effluent and the receiving water(location R-1) effluent pH is 8.0,the maximum historical monthly average receiving water pH is 9.1,the maximum from January 2002 to December 2002. The results of these analyses were evaluated for their historical monthly average effluent temperature is 27.2 F,and the maximum historical monthly reasonable potential to exceed Basin Plan,CTR,or other applicable criteria. Section 1.3 of the SIP average receiving water temperature is 25.7 F. The pH and temperature at the edge of a 4:1 mixing establishes the guidance for reasonable potential analysis. Table 10 summarizes the reasonable zone were estimated utilizing the USEPA DESCON program. These estimations are utilized in Table potential analysis of the detected constituents. 8 to calculate effluent limitations that maintain compliance with chronic aquatic criterion in the receiving water outside of the mixing zone. Effluent limitations compliant with acute criteria for 11.1 Inorganic Priority Pollutants conditions at the end-of-pipe are also determined,but the more restrictive chronic criteria determine the final effluent limitations. Table 8 provides a daily maximum effluent limitation of 4.4 mg/l The inorganic pollutants arsenic,copper and cyanide were found to have a reasonable potential to ammonia as N and a 30-day average effluent limitation of 2.1 mg/l. As defined by the 1999 criteria, cause or contribute to an exceedance of the applicable Basin Plan objectives. Effluent limitations are the 4-day average CCC ammonia concentration shall not exceed 2.5 times the value of the 30-day therefore required for arsenic,copper,and cyanide. CCC. However,considering the maximum daily limitation is less than 2.5 times the CCC in all cases, the 4-day average cannot exceed the maximum daily limitation. Based on the information received from the Discharger,the use of the steady-state model described in Section 1.4B of the SIP was utilized for calculating effluent limitations. Dilution credits are provided For the cool weather months from 1 October to 31 May,the maximum permitted monthly average to the degree indicated in the dilution evaluation(see section 2). The acute and chronic criteria for effluent pH is 8.0,the maximum historical monthly average receiving water pH is 8.5,the maximum copper are a function of hardness. In general,lower hardness values provide more stringent criteria. historical monthly average effluent temperature is 25.2 F,and the maximum historical monthly The hardness value expected to occur at the point in the receiving water where the standard applies,is average receiving water temperature is 19.6 F. The pH and temperature at the edge of a 4:1 mixing considered the design hardness. San Joaquin River hardness data is available at Vernalis,Mossdale, zone were estimated utilizing the USEPA DESCON program. These estimations are utilized in Table and at the Manteca outfall(R-1). The data sets have similar values. There is more river hardness data 8 to calculate effluent limitations that maintain compliance with chronic aquatic criterion in the available over a longer period at Vernalis,therefore,the Vernalis data were used to evaluate receiving receiving water outside of the mixing zone. Effluent limitations compliant with acute criteria for water hardness. In determining design hardness,the Regional Board analyzed the receiving water conditions at the end-of-pipe are also determined. In this case,the more restrictive acute criteria hardness measured at Vernalis during periods when critical low flow was probable(i.e.San Joaquin determine the final effluent limitations. Table 8 show that the acute criteria using the maximum River flow at Vernalis ranging from 800 cfs to 1,200 cfs). The effluent hardness was also utilized for permitted effluent pH of 8.0 provides a daily maximum effluent limitation of 5.6 mg/1 ammonia as N the acute criteria calculations where dilution is not available. and a 30-day average effluent limitation of 2.8 mg/l. Receiving water hardness is generally flow-related with lower flows providing higher hardness values. To determine the design hardness,receiving water hardness and flow data collected from the USGS monitoring station at Vernalis from 1950 through 1999 were evaluated. The dataset was filtered for