SITE INFORMATION AND CORRESPONDENCE 1980-1999

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FACT SHEET, ATTACHME* • -3- WASTE DISCHARGE REQUIREMENTS ORDER NO. 2000-**** CITY OF LODI WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY c) Dilution/MixingZones A report submitted by the Discharger titled, "Water Quality Impact Report, White Slough Water Pollution Control Facility", dated October 1998, evaluates the dilution in the receiving water below the discharge. The report indicates that the average dilution 300 meters below the discharge point, where Dredger Cut meets Highline Canal, is 2:1, over a tidal cycle. From the discharge point to Highline Canal, a distance of 300 meters, there is negligible dilution. At the confluence with White Slough at receiving water monitoring location R-2, a distance of about 1500 meters from the discharge, the average dilution is 4:1. The study also indicated that the predominant direction of flow from Dredger Cut is to the north channel of White Slough. For purposes of establishing effluent limitations, the Board may designate mixing zones within which water quality objectives will not apply provided the Discharger has demonstrated that the mixing zone will not adversely impact beneficial uses. For aquatic life objectives, the acute averaging period is one hour, and the chronic.averaging period is 30 days. Given the tidal cycle, there may be negligible dilution throughout Dredger Cut on an hourly basis, and negligible dilution for at least 300 meters over the longer term. These mixing zones are not limited to a small zone of initial dilution in the immediate vicinity of the discharge, and therefore relaxation of receiving water standards within the mixing zone is not allowed in this permit. d) Disinfection The designated beneficial uses of Dredger Cut,White Slough and Bishop Cut include contact recreation and irrigation. Effluent limitations for disinfection are based on available dilution in the receiving water, in order to protect contact recreation as a beneficial use of the water. Discharge limits for disinfection have previously been applied at the confluence of Dredger Cut and White Slough, since it was assumed that body contact water recreation does not occur within Dredger Cut, and that greater than 20:1 dilution was available at the confluence. Dredger Cut has been required to be posted as a wastewater disposal area since the last permit renewal. Current information available indicates that the previous dilution estimate was not accurate, and that less than 20:1 dilution exists at the confluence of Dredger Cut and White Slough. The California Department of Health Services (DHS)recommends treatment levels to protect public health from both body contact water recreation and food crop irrigation. The DHS recommends that, in cases where relatively undiluted wastewater discharges are permitted to agricultural drains and creeks that have been identified by the Board to have beneficial uses of body contact water recreation or irrigation of vegetables and food crops where the vegetables or fruit may come in contact with the treated wastewater, then the wastewater should be adequately oxidized, coagulated, filtered, and disinfected. The wastewater should be considered adequately disinfected if: 1) The chlorine disinfection process provides a CT (residual chlorine concentration times modal contact time) value of not less than 450 milligram-minutes per liter at all times, with a modal contact time of at least 90 minutes,based on peak dry weather design flow; and 2) The median concentration of total coliform bacteria measured in the disinfected effluent does not exceed an MPN of 2.2 per 100 ml utilizing the bacteriological results of the last seven days for which analyses have been completed and the number of total coliform