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CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD AMENDMENT OF WASTE DISCHARGE REQUIREMENTS -2- CENTRAL 2- CENTRAL VALLEY REGION RESOLUTION NO.R5-2005-0110 CITY OF MANTECA RESOLUTION NO.RS-2005-0110 WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY AMENDING WASTE DISCHARGE REQUIREMENTS ORDER NO.R5-2004-0028 5. The effluent limitations for bromodichloromethane and dibromochloromethane included in NPDES NO.CA0081558 Order No.R5-2004-0028 were based on treatment plant performance prior to converting to full CITY OF MANTECA nitrification. With the significant increase in the formation of disinfection byproducts after WASTEWATER QUALITY CONTROL FACILITY upgrading the WQCF to operate in full nitrification mode,the Discharger is unable to comply SAN JOAQUIN COUNTY with the effluent limitations. 6. Due to the significant change in wastewater treatment,and based upon new water quality information,the Discharger,in a letter dated 20 April 2005,requested that the effluent The California Regional Water Quality Control Board,Central Valley Region,(hereafter Regional limitations for bromodichloromethane and dibromochloromethane be modified based upon Board)finds: current treatment plant performance. 1. On 19 March 2004,the Regional Board adopted Waste Discharge Requirements(WDR)Order 7. This Resolution amends WDR Order No.R5-2004-0028 by increasing the effluent limitations No.R5-2004-0028,NPDES No.CA0081558,prescribing waste discharge requirements for the for bromodichloromethane and dibromochloromethane based on re-calculated dilution credits City of Manteca,City of Lathrop,and Dutra Farms at the Wastewater Quality Control Facility using new effluent data collected while the WQCF was operating in full nitrification mode(see (WQCF)in San Joaquin County. For the purposes of this Resolution,the City of Manteca is Table 16). The re-calculated dilution credits for bromodichloromethane and hereafter referred to as"Discharger." dibromochloromethane(see Table 15)are 63:1 and 82:1,respectively,which are less than the maximum allowable human health dilution of 222:1 for the San Joaquin River. Therefore,the 2. The Discharger owns and operates a wastewater collection,treatment,and disposal system,and increased effluent limitations do not allocate the full assimilative capacity of the receiving provides sewerage service to the City of Manteca and the City of Lathrop. Land disposal of water and are more stringent than water quality-based effluent limitations. Based on the effluent is maximized by discharging effluent at agronomic rates seasonally to existing sample results in the effluent,it appears the Discharger can meet these new limitations. In City-owned property. Excess flow of treated municipal wastewater receives chlorine addition,the Discharger is installing ultraviolet(UV)disinfection by April 2007. Once disinfection and dechlorination prior to discharge to the San Joaquin River. operational,the use of chlorine for final effluent disinfection will be eliminated and the 3. Finding 31 of WDR Order No.R5-2004-0028 specifies the allowable dilution for human formation of disinfection byproducts will be reduced significantly. Consequently,the effluent health-based criteria,including bromodichloromethane and dibromochloromethane. Finding 31 concentrations of bromodichloromethane and dibromochloromethane will decrease. states,"A steady state analysis utilizing the harmonic mean flow at Vernalis provides a dilution 8. Sections 402(o)(2)(33 U.S.C.section 1342(o)(2))and 303(d)(4)(33 U.S.C.section 1313(d)(4)) of 222:1. The Regional Board is not required to grant a mixing zone or allocate the full of the Clean Water Act(CWA)and federal regulations at40 CFR section 122.44(l)prohibit assimilative capacity of the receiving water. For limitations based on these human health backsliding in NPDES permits. These anti-backsliding provisions require effluent limitations criteria,dilution is limited to the amount required to maintain compliance." In WDR Order No. in a reissued or amended permit to be as stringent as those in the previous permit,with some R5-2004-0028,the dilution credits granted for bromodichloromethane and exceptions where limitations may be relaxed. As discussed in Finding 7,the increased effluent dibromochloromethane were 11.5:1 and 8.9:1,respectively,and were based on treatment plant limitations for bromodichloromethane and dibromochloromethane are based on new performance,resulting in effluent limitations more stringent than water quality-based effluent information and are more stringent than water quality-based effluent limitations. Therefore,the limitations. Since the effluent limitations were based on treatment plant performance,the relaxation of the effluent limitations for bromodichloromethane and dibromochloromethane is Regional Board found the Discharger was able meet the effluent limitations. consistent with the anti-backsliding requirements of the CWA and federal regulations and is 4. The WQCF has historically operated in a non-nitrifying or partial nitrifying mode,which also consistent with the antidegradation provisions of 40 CFR section 131.12 and State Water typically produced an effluent with elevated levels of ammonia. Chlorine,when combined Resources Control Board Resolution No.68-16. Any impact on existing water quality will be with ammonia,creates chloramines,which are effective and stable disinfectants. In November insignificant. Furthermore,this Resolution adds a provision to allow Order No.R5-2004-0028 2003,the treatment process was converted to full nitrification mode to reduce ammonia. to be reopened to modify the effluent limitations for bromodichloromethane and Without ammonia in the effluent,organochloramines are formed,which are less effective dibromochloromethane after installation of UV disinfection facilities. disinfectants than chloramines. Consequently,more chlorine is required for disinfection, 9. The Discharger historically utilized drying beds to dewater biosolids with final disposal on land increasing disinfection byproducts,including bromodichloromethane and adjacent to the WQCF. Monitoring and Reporting Program(MRP)Order No.R5-2004-0028 dibromochloromethane. requires biosolids monitoring pursuant to 40 Code of Federal Regulations(CFR)Part 503 for