SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET $ CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY mercury in fish tissue). Mercury was found at concentrations greater than 0.012 µg/l at every sampling station. Results make it appear that the mercury problem is ubiquitous throughout the receiving water during the winter period. However, the accuracy of mercury analyses at the low regulatory levels can be questionable without implementing 'clean technique' for sample collection, handling, and analysis. Therefore, this Order requires additional study to assess whether the levels of mercury in the discharge causes or contributes to an in-stream excursion above a water quality objective. If the discharge causes or contributes to an in-stream excursion above a water quality objective, then the City must submit information to calculate an effluent limit. Finally, the permit can be reopened to include the effluent limit. Chronic Toxicity Requirements The Basin Plan requires that there be no toxics in toxic amounts. This Order implements the Basin Plan by prohibiting toxic pollutants to be present in the water column, sediments, or biota in concentrations that adversely affect beneficial uses; that produce detrimental response in human, plant, animal, or aquatic life; or that bioaccumulate in aquatic resources at levels which are harmful to human health. The Order requires effluent chronic toxicity testing to be conducted as specified in the Monitoring and Reporting Program, according to standard EPA protocol. If the testing indicates that the discharge causes, has the reasonable potential to cause, or contributes to an in-stream excursion above a water quality objective for toxicity, the Discharger must conduct a Toxicity Reduction Evaluation (TRE). The Order can be reopened and a chronic toxicity limitation or specific chemical toxicant included. Additionally. if a chronic toxicity water quality objective is adopted by the State Water Resources Control Board, this Order may be reopened and a limitation based on that objective included. This Order requires the frequency of testing to be 4 times per quarter, four quarters per year. This frequency is reasonable, as other discharge with similar discharge flows, and more available dilution conduct tests at this frequency. After 16 tests are completed in accordance with this Order, which meet all test acceptability criteria, the frequency shall be reduced to one test per quarter, four quarters per year. The effluent discharge is typically started and shut down several times over the course of a month. The chronic toxicity test requires that test water be renewed several times over the course of the test. In order to ensure the test can be completed in the event of a plant shutdown, this Order requires that sufficient renewal water be collected at the beginning of the test and at each renewal.