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WASTE DISCHARGE REQU&MENTS ORDER NO. R5-2004-002*, -11-
<br /> CITY OF MANTECA, CITYATHROP AND DUTRA FARMS
<br /> WASTEWATER QUALITY CONTROL FACILITY
<br /> SAN JOAQUIN COUNTY
<br /> application, in studies, and in monitoring reports, the Regional Board finds that the discharge
<br /> does have a reasonable potential to cause or contribute to an in-stream excursion above a water
<br /> quality standard for aluminum, ammonia, arsenic, chlorine, copper, cyanide,bis(2-
<br /> ethylhexyl)phthalate, bromodichloromethane, dibromochloromethane, electrical conductivity,
<br /> iron, manganese, MBAS,mercury, nitrate, nitrite,pH, temperature, total dissolved solids and
<br /> 2,4,6-trichlorophenol. Final effluent limitations and/or interim performance-based effluent
<br /> limitations and interim requirements with compliance schedules for the pollutants listed above
<br /> are included in this Order. In addition,this Order contains provisions that:
<br /> a. Require the Discharger to conduct a study to provide information as to whether the levels
<br /> of dioxins in the discharge cause or contribute to an in-stream excursion above a water
<br /> quality standard, including Basin Plan numeric or narrative objectives;
<br /> b. If the discharge has a reasonable potential to cause or contribute to an in-stream excursion
<br /> above a water quality standard,requires the Discharger to submit information to calculate
<br /> effluent limitations for those constituents; and
<br /> C. Allows the Regional Board to reopen this Order and include effluent limitations for those
<br /> constituents.
<br /> On 10 September 2001, the Executive Officer issued a letter, in conformance with California
<br /> Water Code Section 13267,requiring the Discharger to prepare a technical report assessing water
<br /> quality. This Order is intended to be consistent with these requirements in requiring sampling for
<br /> dioxins to determine the full water quality impacts of the discharge. The technical report
<br /> requirements are intended to be more detailed, listing specific constituents, detection levels, and
<br /> acceptable time frames and shall take precedence in resolving any conflicts.
<br /> 30. As stated in the above Finding, the USEPA adopted the NTR and the CTR, which contains water
<br /> quality standards applicable to this discharge. The SIP contains policies and procedures for
<br /> implementation of the NTR and CTR. The SIP, Section 2.2.1, requires that if a compliance
<br /> schedule is granted for a CTR or NTR constituent,the Regional Board shall establish interim
<br /> requirements and dates for their achievement in the NPDES permit. The interim limitations must
<br /> be based on current treatment plant performance or existing permit limitations, whichever is
<br /> more stringent; include interim compliance dates separated by no more than one year, and; be
<br /> included in the Provisions. The interim limitations in this Order are based on the current
<br /> treatment plant performance. In developing the interim limitation, where there are ten sampling
<br /> data points or more, sampling and laboratory variability is accounted for by establishing interim
<br /> limits that are based on normally distributed data where 99.9% of the data points will he within
<br /> 3.3 standard deviations of the mean(Basic Statistical Methods for Engineers and Scientists,
<br /> Kennedy and Neville, Harper and Row). Therefore,the interim limitations in this Order are
<br /> established as the mean plus 3.3 standard deviations of the available data. Where actual
<br /> sampling shows an exceedance of the proposed 3.3-standard deviation interim limit, the
<br /> maximum detected concentration has been established as the interim limitation. When there are
<br /> less than ten sampling data points available, the Technical Support Document for Water Quality
<br /> Based Toxics Control((EPA/505/2-90-001) TSD)recommends a coefficient of variation of 0.6
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