Kennewick, WA Environmental Rules: Stormwater Management (2026)
Key Facts
- Design storm event
- 25-year, 24-hour storm
- Governing manual
- SMMEW (Ecology, 2004 or later)
- Retention requirement
- Onsite retention and disposal required
- Enforcement authority
- Public Works Department
- Civil penalty range
- $100–$5,000 per day
Summary
Kennewick requires new development to design stormwater facilities under the state's Stormwater Management Manual for Eastern Washington, retaining and disposing of runoff onsite for the 25-year, 24-hour storm event.
The City formally adopts the Stormwater Management Manual of Eastern Washington. All design, construction, and post construction management of erosion and sediment control and storm drainage facilities shall be in accordance with Appendix 1 of the NPDES Stormwater Permit... (1) Stormwater shall be retained and disposed of onsite meeting the volume determined by the Soil Conservation Service (SCS) Type 1A storm design method for the 25-year 24-hour frequency.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 19 Update 2).
Full Breakdown
KMC 14.28.045 adopts the Stormwater Management Manual for Eastern Washington for all design, construction, and post-construction erosion, sediment, and drainage work. New development must retain and dispose of stormwater onsite, sized to the SCS Type 1A 25-year, 24-hour storm, and must show it can handle a 100-year event with onsite pooling. Routing runoff to a regional facility or surface water is allowed only if the Public Works Director finds onsite infiltration infeasible: for reasons like shallow groundwater, impermeable soil, or proximity to a hazardous site.
Violations & Fines
Public Works enforces stormwater design under KMC 14.28.046, following Chapter 14.29's illicit-discharge process: escalating from warnings to civil penalties of $100 to $5,000 per day of violation.
Frequently Asked Questions
Does Kennewick require stormwater retention on my property?
Can I just pipe stormwater to a ditch or the river instead?
Sources & Official References
Other rules in Kennewick
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