Joint Regional Water Supply System Joint Transmission Main - Unit 3 Reach 5 Air-Vacuum Valve Relocations

The South Coast Water District proposes to relocate three existing Joint Regional Water Supply System (JRWSS) air-vacuum relief valves that are currently in underground vaults, where they have the potential to flood, to aboveground locations next to or in the vicinity of the existing vaults, consistent with current JRWSS standards. Operations staff would then be able to access the air-vacuum valves for inspection, maintenance, and replacement without entering a confined space. The existing underground vaults and air-vacuum piping connections to the water transmission mains would remain in place. The air-vacuum piping would be extended from the existing water transmission mains, penetrating each vault through a core-drilled hole, and then connected to the new aboveground air-vacuum relief valves. Construction activities at each location would require excavation to a depth of 3 to 5 feet below ground surface and result in a total disturbed area of approximately 300 square feet. All excavation and land disturbance activities would take place within the existing right-of-way of Alicia Parkway in the City of Laguna Niguel (Figure 1, Project Sites) and on land that was previously disturbed to construct the existing pipeline, vaults, and street improvements. We understand that construction would likely occur sometime between April and October 2025. The three vaults would be constructed in sequence with construction periods ranging from three to five days with a maximum of eight trucks required at each site, totaling 20 trips. All three sites will require lane closures and will be scheduled to occur outside of peak commuting hours. The project sites are all within existing roadway with no impact to any trees or other biological resources and would require only shallow excavations (maximum of 5 feet) into previously disturbed soils.