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-4- <br /> FACT SHEET ORDER NO. -00-031 <br /> ATTACHMENT C <br /> CITY OF LODI <br /> WHITE SLOUGH WATER POLLUTION CONTROL PLANT <br /> SAN JOAQUIN COUNTY <br /> d) Disinfection <br /> The designated beneficial uses of Dredger Cut, White Slough and Bishop Cut include contact <br /> recreation and irrigation. Effluent limitations for disinfection are based on available dilution in the <br /> receiving water, in order to protect contact recreation as a beneficial use of the water. Discharge <br /> limits for disinfection have previously been applied at the confluence of Dredger Cut and White <br /> Slough, since it was assumed that body contact water recreation does not occur within Dredger Cut, <br /> and that greater than 20:1 dilution was available at the confluence. Dredger Cut has been required <br /> to be posted as a wastewater disposal area since the last permit renewal. Current information <br /> available indicates that the previous dilution estimate was not accurate, and that less than 20:1 <br /> dilution exists at the confluence of Dredger Cut and White Slough. The California Department of <br /> Health Services (DHS)recommends treatment levels to protect public health from both body <br /> contact water recreation and food crop irrigation. The DHS, in general, recommends that, in cases <br /> where relatively undiluted wastewater discharges are permitted to agricultural drains and creeks that <br /> have been identified by the Board to have beneficial uses of body contact water recreation or <br /> irrigation of vegetables and food crops where the vegetables or fruit may come in contact with the <br /> treated wastewater, then the wastewater should be adequately oxidized, coagulated, filtered, and <br /> disinfected. The wastewater should be considered adequately disinfected if: <br /> 1) The chlorine disinfection process provides a CT (residual chlorine concentration times <br /> modal contact time) value of not less than 450 milligram-minutes per liter at all times, <br /> r <br /> with a modal contact time of at least 90 minutes, based on peak dry weather design <br /> flow; and <br /> 2) The median concentration of total coliform bacteria measured in the disinfected effluent <br /> does not exceed an MPN of 2.2 per 100 ml utilizing the bacteriological results of the <br /> last seven days for which analyses have been completed and the number of total <br /> coliform bacteria does not exceed an MPN of 23 per 100 ml in more that one sample in <br /> any 30 day period. No single sample should exceed an MPN of 240 per 100 ml for total <br /> coliform bacteria. <br /> In accordance with the general recommendations of the DHS, and the specific comments received <br /> in regard to this facility, this permit contains a time schedule to require a higher level of treatment <br /> for disinfection. <br /> The Board has considered the factors specified in Water Code Section 13263, including considering <br /> the provisions of Water Code Section 13241, in adopting the coliform limitation in the proposed <br /> waste discharge requirements. In a letter from the City of Lodi (dated 24 February 1999) to the <br /> Regional Water Quality Control Board, the city provided a cost estimate of between $10 to <br /> $15 million dollars to design and construct the proposed disinfection. To date, there has been no <br /> elaboration or refinement of this rough estimate. <br /> Staff finds, that these requirements are necessary to protect the beneficial uses of Dredger Cut, <br /> Bishop Cut, and White Slough, including public health impacts of recreational uses and irrigation <br />