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INFORMATION SHEET ORI&NO. R5-2004-0028 21 CITY OF MANTECA, CITY O LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY less than 10 values, the maximum effluent concentration and a 3.11 multiplier(from Table 5-2 of the TSD)provides the estimated maximum levels. The calculations of the allowed dilution are shown in Table 12 which: (1) summarizes the monitoring data for the human carcinogens that have reasonable potential to exceed human carcinogen criteria; (2) summarizes the statistics used in calculating the estimated maximum concentration; and, (3) determines the amount of dilution that would be required to meet the applicable human-carcinogen criteria. Final effluent limitations are calculated and summarized in Table 13. 11.2.3 Ability to Meet Effluent Limitations and Interim Requirements Based on historical effluent data, the WQCF can meet the effluent limitations for dibromochloromethane,bromodichloromethane, 2,4,6-trichlorophenol, and bis(2-ethylhexyl)phthalate. Additionally,because the plant will install a UV disinfection system by 1 February 2009,the THM constituents are expected to decrease significantly. Section 1.4.2.2.B of the SIP requires, among other things, that when a mixing zone/dilution credit is granted, the permit must specify the point in the receiving water where the applicable criteria/objectives must be met. The Discharger has not performed such an analysis over a variety of now conditions. However, considering the long-term averaging period for human carcinogens, the infrequency of critical conditions and worst-case effluent concentrations, and the fact that there are no drinking water intakes for numerous miles down- or up-stream of the discharge, the Regional Board finds the lack of a detailed mixing zone study is not significant enough to postpone the imposition of final effluent limitations for dibromochloromethane,bromodichloromethane, 2,4,6-trichlorophenol and bis (2-ethyhexyl)phthalate. 11.2.4 Receiving Water Monitoring for Human Carcinogen Priority Pollutants Receiving water monitoring of human carcinogens is required to provide assurance that water quality criteria are being met downstream of the discharge and that the beneficial use of municipal supply is being protected. Although a mixing zone analysis has not been performed to delineate the specific boundaries of the mixing zone for human carcinogens,the samples collected at the existing R-1 and R- 4 receiving water monitoring locations should provide adequate information to demonstrate compliance with water quality criteria. 11.3 Bioaccumulatives Based on information submitted by the Discharger, the Regional Board concludes that the discharge contains mercury. The Delta waterways are listed in accordance with Clean Water Act Section 303(d) as impaired for mercury based on bioaccumulation of this pollutant in fish tissue. The CTR contains criteria for mercury. The CTR criteria,however, do not address bioaccumu abutithe Th ever, WQCF effluent contains detectable levels of mercury below CTR priority pollutant the bioaccumulation rates in fish tissue used to calculate the CTR water quality criteria are based only on a laboratory derived bioconcentration factor that considers organism uptake from water only and does not consider the contribution from the organism's food source. Therefore,the CTR criteria are