SITE INFORMATION AND CORRESPONDENCE_1985-2004

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INFORMATION SHEET ORA NO. R5-2004-0028 • 8 CITY OF MANTECA, CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY 6 Thermal Limitations The State Water Resources Control Board(State Board) Water Quality Control Plan for Control of Temperatures in Coastal and Interstate Waters and Enclosed Bays and Estuaries of California(the Thermal Plan) is applicable to this discharge. The Thermal Plan requires that such a discharge: (a) shall not exceed the receiving water temperature by more than 20 °F; (b) shall not create a zone, defined by water temperatures of more than 1'F above natural receiving water temperature which exceeds 25 % of the cross sectional area of the River at any point; and, (c) shall not cause a temperature rise greater than 4 °F above the natural temperature of the receiving waters at any time or place. For the purposes of compliance with the Thermal Plan, the Discharger is considered to be an existing discharger of elevated temperature waste. Monitoring by the Discharger indicates that the 20 degree°F limitation of Objective 5.A.(1)a of the Thermal Plan is occasionally exceeded in winter months when . the receiving water is at its lowest temperatures. Modeling conducted by RMA, subject to the limitations discussed below, indicates that the current and the expanded flows with continuous discharge exceed both the 1 degree and 4 degree requirements of Objectives 5.A.(1)b and 5.A.(1)c of the Thermal Plan. The modeling also demonstrates that a timed discharge,that is, discharging only on the outgoing tide, for the increased flow exceeds only the 4 degree requirement,but not the 1 degree requirement. The Discharger has requested an exception to the 4 degree requirement of Objective 5.A.(1)c of the Thermal Plan which requires that the discharge shall not cause a surface water temperature rise greater than 4 OF above the natural temperature of the receiving waters at any time or place and has also requested a one month averaging period to meet the 20 degree limit of Objective 5.A.(1)a. An exception cannot be authorized at this time due to a number of factors. First, the accuracy of the temperature model results which are the basis for the receiving water limitation violations are questionable due to a lack of site data to calibrate and validate the model, the lack of accounting for atmospheric heat gains and loss from the proposed holding pond and the river, the lack of accounting for tidal cycles and recirculation from the limited model run time, and the lack of accounting for the Brown Sand, Inc. discharge adjacent to the City's discharge. Second, the Discharger has not conducted regular monitoring of temperature at the outfall as required in its previous permit, and the available information is based on a limited data set which correlates the temperature at the plant site and at the outfall. Third, the Discharger has not provided adequate evidence that a 30-day averaging period for Effluent Limitation B.11. will not cause adverse impacts to aquatic life. Finally, the Discharger does not currently have the capability to implement a timed discharge on out-going tides. Effluent Limitations and Receiving Water Limitations are included to require compliance with the Thermal Plan. If adequate information is developed to support exceptions to the Thermal Plan, this Order may be reopened to modify limitations for Thermal Plan compliance.