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Mr. Brendan Kenny October 7, 2020 Page 3 In July 2018, SFPUC responded to the NOV and Order, emphasizing its commitment to rectifying the issues and explaining that it was investigating the cause and means to prevent lamp breaks. Since the response letter to the NOV was sent on July 9, 20182, the SFPUC has voluntarily and timely reported each of the UV lamp breaks, including ones with no sleeve breaks, to the San Joaquin County Environmental Health Department. The SFPUC also indicated that it was working with a consultant to characterize the soil at the grit pond. The SFPUC further explained that it can neither suspend UV treatment operations at the Facility, nor certify absolutely the cessation of discharges related to lamp failure due to the countervailing requirement to maintain continuous primary disinfection of the water. Response Actions Upon receiving the NOV, the SFPUC implemented several response actions. These actions include conducting a root cause analysis, modifying Facility operations, developing an interception plan, and working with the UV system manufacturer to replace existing UV lamps with prototypes and newer designs that the manufacturer believes are more robust, as described in the following paragraphs. Since July 2018, SFPUC staff have been investigating the root cause of the UV lamp breaks along with Calgon Carbon UV Technologies (UV system manufacturer) and Stantec (Facility designer). In August 2019, Calgon's investigation into the unexpected UV lamp breaks not only at the Facility, but also at several other treatment facilities using Calgon systems, concluded that their UV lamps were more prone to breaks in a certain power operating range. The SFPUC immediately decided to re-program the Facility's UV lamp power operating range to reduce the likelihood of UV lamp breaks. The system re- programming was completed in October 2019. The reduction in lamp power at times required more UV lamps to be in operation but did not negatively affect disinfection requirements. In February 2020, Calgon provided the Facility with 10 new prototype UV lamps that the Calgon laboratory had shown to be capable of operating in the original power operating levels. The prototype UV lamps have not broken to date. In November 2018, SFPUC developed and implemented a temporary emergency interception plan for responding to UV lamp break events at the Facility. Under that interception plan, the drain leading downstream from the UV building to the grit pond was plugged, and the water released in response to a UV lamp-break bypassed the Facility's normal drainage system. Water was instead routed into two 20,000-gallon Baker tanks located just south of the a Incidents occurred on 7/2/17,7/17/2018, 12/17/2018, 12/27/2018, 1/4/2019,3/20/2019, 8/5/2019,9/20/19, and 8/24/2020