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Stockton RWCF, Tertiary Plies, -2- J 14 February 2001 Inspection Report recirculation gate valve is non-disinfected wastewater from Pond 4 and the recirculation ditch. The elevation of this wastewater is typically lower than that in the CCC unless there are conditions such as a low tide as was observed on the morning of 7 December 2000. Once the leaking was discovered, RWCF staff attempted to further close the recirculation gate valve. It was determined that the nut or"stem" on the bottom of the valve was broken and was not allowing the valve to tighten and seat itself as designed. At 0903 the discharge to the SJR was stopped and the siphon box and CCC began to be drained. As the CCC and the siphon box were drained the leakage was observed by RWCF staff from around the top portion of the gate valve at an estimated rate of 20- gallons per minute (gpm). By 1500, the nut on the valve had been repaired and by 1530 treated wastewater was recirculating through the plant. At 1603 a Hazardous Material Spill Report was filed with the Office of Emergency Services and at 1610 the Regional Board was notified by telephone voice mail by Ms. Hinson of the leakage. At approximately 2000 hours on 7 December 2000, discharge to the SJR had resumed. Mr. Von Aspem pointed it out that on 5 December 2000,the Sr. Operator discovered that the siphon valve was opened only one-third of its capacity. If the valve is not opened fully then the elevation of treated wastewater in the CCC may rise to level above normal operating parameters. The siphon valve was fully opened after this discovery and the elevation head of the treated wastewater in the CCC returned to its standard operating height. This would mean that while the siphon valve was only partially opened, the treated wastewater in the CCC was at an elevation which was greater than that on the reverse side of the gate valve. Therefore, Mr. Von Aspem believes that the leaking was not occurring prior to 5 December 2000. Using the initial leakage rate of 20 gpm over a 41-hour period, it is possible that up to 49,200 gallons of non-disinfected wastewater may have leaked into the CCC. However, it is more realistic to consider the that the leaking only occurred during low tides, approximately one-third of the total time of the release or approximately 12 hours, which equates to 14,400 gallons. The incident report stated that the estimated leak rate was 2 gpm, considerably less than the estimate 20 gpm leak rate discussed during the time of my inspection. The incident report estimated that the lower leak rate might have occurred over a 41-hour period resulting in a release of up to 4,921 gallons. The recorded effluent discharge rate during the time of the release averaged approximately 29 million gallons per day. Using either approximation,the dilution of disinfected wastewater to the leaked non-disinfected wastewater is considerable. No receiving water specific sampling and analysis for total coliform organisms was conducted by the Discharger to determine the approximate extent of the release. However, the incident report indicates that analysis of a 24-hour composite sample collected from within the siphon box during the period in question, was well within the NPDES requirements. It is our understanding that the final effluent grab samples are collected within the CCC prior to dechlorination and not from within the siphon box. Mr. Von Aspem and the incident report indicate that a procedural change to the standard operating procedures has been made so that the non-disinfected wastewater will be continually drained to keep its elevation lower than that of wastewater within the CCC. This will effectively prevent any of the non- disinfected pond recirculation water from draining back into the CCC should the valve ever fail again.