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STAFF REPORT CITY OF STOCKTON The City has had various equipment failures since 1979. Most pertinent to the fish kill are failures of the tertiary filters and the chlorine and pH con- tinuous monitoring devices. The tertiary multi-media filters broke down in the summer of 1983, and have not operated since. In an inspection on 30 July 1985, staff was told by City staff that the two continuous monitoring devices were operational for a short period of time after installation but were either shut down or broke down shortly thereafter. The City has been, since that time, analyzing for chlorine every two hours as a normal operational practice. THE FISH KILL OF 19 and 20 JUNE 1985 In April 1985 the City began having problems with high levels of coliform bacteria in their effluent. From 1 April 1985 to 17 June 1985, the City violated the daily maximum coliform limit 11 times, and in June violated its 30-day median coliform limit. The City attempted to resolve the coliform violations by increasing the chlorine dosage. This was not completely effec- tive, so on 19 June 1985 the City increased chlorine dosage and instituted "breakpoint chlorination" (see Attachment B). It is very difficult to control the reaction which occurs in "breakpoint chlorination" to achieve and maintain a specific chlorine concentration, and therefore it is not a desirable mode of operation. The City was unable to continuously monitor the chlorine concentration in the effluent because the continuous chlorine monitoring facility had not been functional for many years (we now understand the City is taking steps to repair them) . The City has inadequate dechlorination facilities to handle the high concentration of chlorine which was discharged on 19 and 20 June (improvements are now underway) . During the evening of 19 June, and the early part of 20 June, for 24 hours, chlorine concentrations in the effluent reached as high as 10 ppm. The pH of the effluent was measured at 3.1 to 5.4. These are violations of the requirements ' limitations of 0.02 ppm chlorine and minimum 6.5 pH respectively (see staff memo's Attachment C). On June 19 and 20, an estimated 5,000 catfish were killed in the San Joaquin River ,just below the City' s outfall . The Department of Fish & Game believes the fish kill occurred due to the high free residual chlorine and low pH in the City's effluent (see Attachment D for their detailed report) . The City could have discontinued the discharge to the river at any time by turning a valve, thereby using their ponds for temporary storage. The City knew that high concentrations of chlorine and low pH were present in the effluent within 2 hours of the start of breakpoint chlorination. The discharge continued for approximately 24 hours. The City was requested by Board staff, on 21 June 1985, to use any of their resources to stop violating and to stop causing the conditions which caused the fish kill . There was at least two days