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Mr. Brendan Kenny October 7, 2020 Page 2 Background Information The Facility, located at 9000 W Vernalis Road in Tracy, California, provides primary disinfection of Hetch Hetchy water before it enters the Bay Area and is delivered to the SFPUC's 2.7 million water customers. Primary disinfection is accomplished by the UV light treatment process and chlorination which allows the SFPUC to maintain compliance with requirements of the Safe Drinking Water Act. Hetch Hetchy water passes through four or more reactors (twelve reactors maximum) at the Facility each equipped with 9 UV lamps. Each UV lamp contains a very small amount of mercury. Between September 2016 and August 2020, there were intermittent UV lamp breaks at the Facility. Consistent with the Facility's design, which serves to protect the system downstream and isolate water affected by the lamp break, a UV lamp break will result in the release of approximately 11,000 gallons of water from the reactor containing the broken lamp. Any water released as a result of a UV lamp break will flow onto the UV reactor room floor and into a trench drain that routes the water by gravity out of the building and into grit basin number 1 (grit pond).' The SFPUC analyzed the mercury levels in this water and sediments in 2018-2019 before the Baker tanks were installed. Since September 2016, there have been 16 UV lamp breaks at Tesla, 12 with lamp and sleeve breaks and 4 with sleeves intact. Mercury in UV lamp breaks with sleeves intact was contained within the lamp structure. Each time a UV lamp break involving a sleeve break occurred, the immediate actions included containment, clean-up, and disposal of the waste at an authorized and permitted location. Furthermore, water sample analytical results and disposal records were sent to the San Joaquin County Department of Environmental Health after each UV lamp break. UV lamps that broke with sleeves intact were placed in sealable plastic bags, double bagged and disposed of as hazardous waste. The Facility retains hazardous waste manifests onsite. In June 2018, the Regional Board issued an NOV and a California Water Code section 13260 Order to the SFPUC requiring submittal of a report of waste discharge. The NOV and Order alleged that the discharge of mercury into the grit pond "would qualify as a designated waste under section 13173(b) of the California Water Code." The NOV and Order further alleged that "SFPUC has and continues to violate section 13260 of the California Water Code (CWC) for the discharge of waste without WDRs." The Regional Board directed the SFPUC to submit: (1) a Cease Discharge Certification; and (2) a Report of Waste Discharge. ' More detail about the UV lamp break events and a schematic of the Facility are included in the memorandum prepared by McCord Environmental,dated June 2020,on pages 4-8.