SITE INFORMATION AND CORRESPONDENCE 2000-2018

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FACT SHEET ORDER NO. 0-031 _ ATTACHMENT C -3 CITY OF LODI WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY It follows from the preceding paragraph that effluent dissolved oxygen content must also be limited to prevent discharges that would immediately place the receiving water at an unacceptable dissolved oxygen level. Therefore, this Order requires an effluent dissolved oxygen concentration to be 5.0 mg/1 or greater when conditions allow and surface water discharge takes place. c) Dilution/Mixing Zones The previous permit provided for a mixing zone for compliance with water quality objectives. The mixing zone extended throughout the entire length of Dredger Cut, approximately 1500 meters, to the confluence with Bishop Cut and White Slough. Order No. 93-030 established effluent limitations for compliance with dissolved oxygen and aquatic toxicity water quality objectives, and for disinfection to protect public health at the edge of this mixing zone. With regard to mixing zones, the Basin Plan states, "...the Regional Water Board may designate mixing zones within which water quality objectives will not apply provided the discharger has demonstrated to the satisfaction of the Regional Water Board that the mixing zone will not adversely impact beneficial uses... In determining the size of such mixing zones, the Regional Water Board will consider the applicable procedures and guidelines in EPA's Water Quality Standards Handbook and the Technical Support Document for Water Quality-based Toxics Control..." The Board finds that, based on water quality evidence and the applicable pro.;edures gt4delines currently available, provisions for a mixing zone by allowing compliance with water quality objectives to be determined at the confluence with Bishop Cut and White Slough should not be continued. Dredger Cut is a dead end slough, with minimal dilution in the vicinity of the discharge. _Results of a study conducted over the previous permit term have shown that the average dilution is 2:1 over a tidal cycle at a location approximately 300 meters downstream of the outfall. This mixing zone covers the cross-sectional area of Dredger Cut. Because available dilution within the mixing zone is negligible, extending for at least 300 meters, the Board will not designate any mixing zone within which water quality objectives will not apply. The elimination of the mixing zone within Dredger Cut requires that this permit apply water quality objectives to Dredger Cut which have nlever been applied to this specific area of the water body. Effluent limitations for lead, zinc, and cyanide, as well as BOD (for compliance with the dissolved oxygen objective) and temperature have been included in this permit, as explained below, based on the application of water quality obi_ctives within Dredger Cut. The Discharger is not currently capable of meeting these effluent limitations. This order provides for a time schedule for meeting the effluent limitations. The time schedule is authorized to be included in this order based on 40 CFR §122.47. The Board considers the elimination of the mixing zone in Dredger Cut for compliance with water quality objectives as a new interpretation of the Basin Plan.