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Utility board hears stormwater operations update and new NPDES requirements
Summary
City stormwater staff told the Mercer Island Utility Board about routine maintenance, inventories and a new NPDES permit (2024–2029) that adds requirements for managing existing development, tree-canopy mapping, a behavior-change campaign focused on Watershed Basin 7, and a source-control inspection program.
Mercer Island Utility Board members heard a detailed report on stormwater operations and new National Pollutant Discharge Elimination System (NPDES) permit requirements during their meeting.
Brian Hertvigsen, the city’s stormwater and right-of-way manager, told the board the system “is a system that transports all the surface water through a series of conveyance systems eventually into Lake Washington because we are an island in the middle of Lake Washington.” He said the system includes 357 outfalls to the lake, 5,565 catch basins (17 more than at the last review), about 83 miles of piped conveyance, 13 miles of open ditches and 9 miles of open water courses.
Hertvigsen described the city’s maintenance program: routine pipe-camera inspections and jet cleaning, use of a contracted Vactor service to remove sediment from catch basin sumps and ponds, decanting and testing liquids sent to King County’s wastewater system, and a quick spill-response program that uses portable spill kits and the…
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