Stormwater permits in Mercer Island: fees, timeline & requirements (2026)
Everything you need to know about pulling a stormwater / drainage permit in Mercer Island, Washington — when one is required, what it costs, how long review takes, what documents are required, and which inspections you can expect. Cited to Mercer Island Community Planning & Development.
Free lookup, no account needed — your lot polygon, zoning, setbacks and overlays, cited to Mercer Island's source.
When does drainage work need a permit in Mercer Island?
Ecology's Stormwater Management Manual for Western Washington (SWMMWW, 2024 edition) is the state floor. A municipal stormwater permittee may instead adopt a REGIONAL manual Ecology has determined equivalent, and most do — some counties publish their own, some cities publish their own, and others adopt Ecology's directly. WHICH MANUAL APPLIES IS A PER-JURISDICTION FACT and it changes the numbers: review thresholds for new plus replaced impervious surface and for land-disturbing activity differ between manuals, so read this jurisdiction's own adopting chapter before quoting one. Critical-area and closed-basin parcels get stricter review under every manual.
From Mercer Island's own code
“A. There is hereby created and established, by the adoption of this chapter and the provisions therein, a city storm water management program, hereinafter referred to as "the program." The program shall set forth the primary authority and responsibility for carrying out the Action Agenda for Puget Sound including, but not limited to, responsibilities for planning; establishment of requirements for new development and redevelopment; public education efforts to educate citizens; design, construction, maintenance, administration, operation and improvement of the city's storm and surface water…”Source ↗verified 2026-05-02
Required submittals
- Drainage report (full or simplified)
- Site plan with impervious calc
- BMP / facility detail
- Geotech if infiltration claimed
Inspection sequence
- Pre-construction (BMPs in place)
- Facility installation
- Final stabilization
Contractor specialties needed
General contractor
Who can do this work in Mercer Island?
Kolmo Construction is a licensed Washington general contractor — KOLMOL*753JS, active through April 10, 2027, bonded and insured — working throughout Mercer Island and King County. Kolmo prepares the drawings and submittals, files the stormwater / drainage permit with Mercer Island Community Planning & Development, carries the project through review and inspections, and performs the construction. Call (206) 410-5100 for a Mercer Island stormwater / drainage quote.
Notes & caveats
Issuing body is city public works / county DPER, often parallel to the building permit. On-site infiltration / detention required where infeasible to discharge to municipal storm. Critical-area parcels (steep slope, salmon-bearing watercourse) get more conservative review.
How to apply yourself
- 1. Confirm your parcel's zoning & overlays. Run an address lookup for your Mercer Island stormwater / drainage — we'll pull your specific lot polygon, zoning, setbacks, and any shoreline/ECA/historic overlays.
- 2. Assemble submittals: the 4 documents under Required submittals above.
- 3. Submit through the city portal: Mercer Island Community Planning & Development ↗
- 4. Track review. Respond to reviewer comments promptly.
- 5. Pay issuance fees (Mercer Island's fee schedule sets them) and pick up the permit. Inspection card travels with the job.
Or have Kolmo do it
Kolmo prepares the drawings and submittals, files with Mercer Island Community Planning & Development, handles reviewer comments, and builds the project.
Licensed WA general contractor KOLMOL*753JS · bonded & insured
Stormwater permits in Mercer Island — FAQ
When does drainage work need a permit in Mercer Island?
Ecology's Stormwater Management Manual for Western Washington (SWMMWW, 2024 edition) is the state floor. A municipal stormwater permittee may instead adopt a REGIONAL manual Ecology has determined equivalent, and most do — some counties publish their own, some cities publish their own, and others adopt Ecology's directly. WHICH MANUAL APPLIES IS A PER-JURISDICTION FACT and it changes the numbers: review thresholds for new plus replaced impervious surface and for land-disturbing activity differ between manuals, so read this jurisdiction's own adopting chapter before quoting one. Critical-area and closed-basin parcels get stricter review under every manual.
How much does a stormwater / drainage permit cost in Mercer Island?
Mercer Island's storm drainage review and inspection is billed hourly, $364 at the least (2 hours at $182); a land clearing permit is $214, and grading $285 for 50 to 100 cubic yards and $405 for 101 to 1,000. Wet season construction approval is $1,638 (2026 Fee Schedule).