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Mercer Island staff outline stormwater maintenance and new NPDES requirements
Summary
City stormwater staff reported routine maintenance, inspection numbers and 2025 illicit discharge counts, and summarized new NPDES permit requirements including a stormwater management program for existing development, a tree‑canopy goal and a dumpster‑lid behavior campaign.
City stormwater staff presented an annual maintenance and National Pollutant Discharge Elimination System (NPDES) update to the Mercer Island Utility Board on March 10.
Brian Harvickson, right‑of‑way and stormwater manager, provided system totals and recent activity: 357 outfalls to Lake Washington, 5,801 public catch basins (5,540 inspected during the last two‑year cycle), 83 miles of stormpipe, 13 miles of open ditches and nine miles of open watercourses. Harvickson said the city hauled about 175 cubic yards of decanted sump material over the last year and tests decant water quarterly under its permit with King County wastewater.
Harvickson described routine maintenance techniques—jet cleaning, vacuum/vector services, CCTV inspections and targeted repairs timed to align with roadway overlays—and gave examples of field discoveries that led to repairs paid for by responsible parties when possible. Staff also detailed spill responses, saying vehicle leaks and paint spills are common; the city recorded 33 reported illicit discharge events in 2025 and reports responses to the Department of Ecology as required.
Stormwater quality technician Deqa Roble summarized new NPDES requirements that the city is implementing in the second year of the permit cycle. Changes include a stormwater management program for existing development (SMED), a city tree‑canopy goal to support stormwater objectives, a municipal street‑sweeping program and a behavior‑change campaign targeting business practices (the “dumpster lid” campaign). Roble said the city is implementing a source‑control inspection program to visit 12 businesses per year, re‑inspect noncompliant sites and escalate enforcement when necessary.
Board members asked whether businesses were receptive; Roble said outreach has been largely well received and enforcement is progressive: education and reinspection precede fines in the current program design. Staff said they will continue evaluating equipment and technology improvements (flow meters, pipeline condition reading software) and training staff to improve inspection and repair capacity.
The board thanked staff for the report. There was no action required.
