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WASTE DISCHARGE REQIOMENTS ORDER NO. R5-2004-002* -22- CITY OF MANTECA, CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY Agriculture, Food and Agriculture Organization of the United Nations—Irrigation and Drainage Paper No. 29, Rev. 1 (R.S. Ayers and D.W. Westcot, Rome, 1985). Molybdenum was not monitored in the effluent or in the receiving waters. Because of the uncertainty associated with the lack of monitoring, additional studies of this constituent are warranted to more thoroughly evaluate reasonable potential for this constituent to exceed criteria. MRP No. R5-2004-0028 specifies monitoring for this pollutant. If the monitoring shows a reasonable potential to cause or contribute to an exceedance of a water quality objective, this Order may be reopened to consider incorporation of appropriate effluent limitations. 52. Carbofuran: Carbofirran was detected in the effluent and receiving water at concentrations greater than the OEHHA criterion of 1.7 ug/l. Because the data was greater than the method detection limit but less than the laboratory's reporting limit,the data was flagged as "detected but not quantified". Additional monitoring is required. If the monitoring shows a reasonable potential to cause or contribute to an exceedance of a water quality objective, this Order maybe reopened to consider incorporation of appropriate effluent limitations. 53. Acute Bioassay: The new USEPA test procedure for acute bioassays (EPA-821-R-02-012,Fifth Edition, October 2002) constitutes a more stringent acute toxicity limitation. The finding for ammonia indicated that there is a reasonable potential for the RWCF effluent to cause or contribute to an in-stream excursion above acute and chronic water quality standards for ammonia. To comply with the acute toxicity requirement of this Order and to comply with the Basin Plan narrative toxicity objective,the Discharger must reduce effluent ammonia concentrations to comply with the new effluent limitations by 31 March 2004. Monitoring Reporting Program No. R5-2004-0028 allows the bioassay to be modified to eliminate ammonia- related toxicity until 31 March 2004, at which time the Discharger shall be required to implement the test without modifications to eliminate ammonia toxicity. The time schedule is authorized to be included in the Monitoring and Reporting Program based on 40 CFR § 122.47. 54. Chronic Bioassay: The Discharger shall conduct the chronic toxicity testing specified in the Monitoring and Reporting Program. If the testing indicates that the discharge causes,has the reasonable potential to cause, or contributes to an in-stream excursion above the water quality objective for toxicity, the Discharger shall initiate a Toxicity Identification Evaluation (TIE)to identify the causes of toxicity. Upon completion of the TIE, the Discharger shall submit a workplan to conduct a Toxicity Reduction Evaluation(TRE) and, after Regional Board evaluation, conduct the TRE. This Order will be reopened and a chronic toxicity limitation included and/or a limitation for the specific toxicant identified in the TRE included. Additionally, if the State Board adopts a chronic toxicity water quality objective, this Order may be reopened and a limitation based on that objective included. DISSOLVED OXYGEN ISSUES 55. The dissolved oxygen(DO) objectives applicable to the San Joaquin River areas follows: a. The Basin Plan prescribes a minimum DO concentration in the San Joaquin River of 5.0 mg/l. This standard is applicable throughout the year.