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Memorand uiW CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD . CENTRAL VALLEY REGION 3201 S Street Sacramento, California 95816 Phone: 445-0270 TO: Antonia K.J. Vorster FROM: Dan T. Ward Senior Engineer Area Engineer DATE: 10 July 1985 SIGNATURE: _ SUBJECT: SAN JOAQUIN RIVER FISH KILL, CONTINUED This memo updates my memo of 27 June 1985 on the same subject. UPDATE Attached are two tables describing: 1) effluent and river conditions from 17 May to 21 June, and 2 ) detailed effluent and operational data for 19 and 20 June. An analysis of these data as they relate to the fish kill is as follows: 1. The City of Stockton has been violating their chlorine residual require- ments occasionally for the past two months. (See Table 1 ) 2. On 19 June, to prevent further coliform violations , they attempted to achieve breakpoint chlorination. 3. From 1530 on 19 June to 1710 on 20 June the City discharged to the river approximately 25 million gallons of effluent, containing up to 10.5 ppm residual chlorine and with a pH of 3.1 to 4.9. 4. The estimated flow in the river was from 10 to 11 mgd, flowing upstream toward Vernalis. Therefore, treatment plant effluent made up an estimated two-thirds of total river flow. Additional pertinent information is as follows: 1. Chlorination (adding chlorine to wastewater treatment plant effluent) , is the process by which potentially disease-causing microorganisms are killed before the effluent is discharged to a watercourse. After effluent has been chlorinated, some chlorine sometimes remains in solution. This ' residual chlorine' must be removed by dechlorination facilities prior to dicharge. The City' s permit requires the residual chlorine level not exeed 0.02 ppm. 2. Chlorination of the effluent was ineffective for two weeks before the fish kill . This could have been due to high nitrite concentrations, suspended solids concentrations, organic matter concentrations, or other factors. These constituents contribute to chlorine demand. Chlorine demand is defined as the difference between the chlorine applied and the amount of residual chlorine remaining after chlorination. 3. The multi-media filters continue to be out of service. These filters remove suspended solids and therebv reduce chlorine demand.