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FACT SHEET ORDER NO. R5-2002-_ -34- <br /> CITY OF STOCKTON <br /> REGIONAL WASTEWATER CONTROL FACILITY <br /> SAN JOAQUIN COUNTY LATE REVISIONS <br /> for these pollutants. If the monitoring shows a reasonable potential to cause or contribute to an <br /> exceedance of a water quality objective, this Order may be reopened to consider incorporation <br /> of appropriate effluent limitations. <br /> 11.4 Human Carcinogens <br /> 11.4.1 Effluent Limitations for Human Carcinogenic Priority Pollutants <br /> The effluent limitation calculation procedures, in Section 1.4 of the SIP, allow for the granting <br /> of a dilution credit, in this case, 10:1 based on the harmonic mean of the SJR flow UVM data <br /> and the permitted discharge flow (see Section 8.8 of this Fact Sheet). However, the Regional <br /> Board finds that granting of this dilution credit would allocate an unnecessarily large portion of <br /> the River's assimilative capacity for these constituents and could violate the Antidegradation <br /> Policy. Instead, effluent limitations have been developed based on the amount of dilution that <br /> would be required, not to exceed 10:1 such that receiving water concentrations for these <br /> constituents would be met when effluent concentrations are at estimated maximum levels as <br /> determined by the US EPA methodology in Section 3.3.2, pg. 52 of the TSD. <br /> Table 11-4: (1) summarizes the monitoring data for the human carcinogens that have <br /> reasonable potential to exceed human carcinogen criteria; (2) summarizes the statistics used in <br /> calculating the estimated maximum concentration; and, (3) determines the amount of dilution <br /> that would be required to meet the applicable human-carcinogen criteria. Aa� <br /> in the b using <br /> the saFne-R+ethed-as_-spee4f1ed <br /> . <br /> 14 <br /> . The <br /> negative dilution credits shown in Table 11-4 for dibromochloromethane, <br /> bromodichloromethane, 1,1-DCE, PCE and bis (2-ethyhexyl)phthalate, are the result of <br /> arithmetic mean background concentrations of these constituents that are greater than the <br /> criteria value. For the constituents where dilution credits could be determined (chloroform, <br /> dichloromethane, and TCE), final effluent limitations where calculated and are summarized in <br /> Table 11-5. In those cases where the mean background concentrations exceeded criteria, daily <br /> and monthly effluent limitations cannot be calculated, then interim limitations must be <br /> developed. The interim maximum daily effluent limitation is performance-based and is equal <br /> to the adjusted estimated maximum effluent concentration (Table 11-5). <br /> 11.4.2 Ability to Meet Effluent Limitations and Interim Requirements <br /> Based on historical effluent data, the RWCF should be able to meet the limitations for <br /> chloroform, dichloromethane, and TCE. Dichloromethane and TCE have not been detected in <br /> the effluent and chloroform has been detected in 8 of 11 samples. The statistical TSD <br /> aapnroaeh for calculatinv the estimated maximum effluent concentration results in a very hi <br /> gh <br /> estimate for chloroform due to a small dataset and high coefficient of variation (0.97) Using a <br /> conservative coefficient of variation value of 0.6 which is suggested for small datasets, the <br /> estimated maximum effluent concentration is less than the daily maximum efflue— , <br /> Therefore, it is rg iable -_ssume that the RWCF-in meet the ,,`,N. chlorofo >ns. <br /> T-r'icco rtc--alf}�tg- nFn cF, r'WC ceetieii 1 324 and 13 <br /> ., <br /> b <br />