Lewis County, WA Environmental Rules: Stormwater Management (2026)
Key Facts
- Storm Drainage Approval
- required before permits issue
- Trigger threshold
- 5,000+ sq ft new impervious surface
- Small single-family homes
- exempt under size thresholds
- Plans require
- Washington-licensed civil engineer's stamp
- Performance surety
- $1,000 per disturbed acre
- Appeals
- go to Lewis County hearing examiner
Summary
Development in unincorporated Lewis County that adds 5,000 square feet or more of impervious surface, or any subdivision, needs Storm Drainage Approval under LCC § 15.45.090 before a building or subdivision permit can issue. The Public Works Administrator reviews plans stamped by a licensed civil engineer, and small single-family lots under set impervious-surface thresholds are exempt.
The provisions of this Chapter shall apply to all site development activities requiring building, mobile home placement or flood damage prevention reviews and/or permit approvals under Title 15 LCC and to subdivisions approved under Title 16 LCC, within the bounds of unincorporated Lewis County. No site development activities requiring said Titles 15 or 16 LCC reviews or approvals shall be initiated prior to issuance of Storm Drainage Approval unless exempt under LCC § 17.45.100 ... Lewis County shall approve, conditionally approve, or disapprove stormwater plans and facilities for the following activities, unless exempted in LCC § 17.45.100: ... All construction, including remodeling, reconstruction, and new construction which add five thousand (5,000) square feet or more of impervious surfaces, including gravel parking areas. ... Individual single family residences that do not exceed 5,000 square feet of impervious surfaces for lot sizes less than 0.77 acre, or fifteen percent (15%) of impervious surfaces to lot size for lot sizes greater than or equal to 0.77 acre.
Full Breakdown
030 bars starting that work before Storm Drainage Approval issues, unless the project is exempt. 090 lists what triggers review: all long subdivision plats, qualifying short plats, all construction, including remodeling, reconstruction, and new construction which add five thousand square feet or more of impervious surfaces, including gravel parking areas, and any development that changes a discharge point or increases runoff velocity, quantity, or pollution. 77 acre. 110 requires storm drainage and detention plans to carry the stamp of a Washington-licensed civil engineer experienced in hydrology or hydraulics, though a homeowner just over the exemption threshold may file a simpler Abbreviated Storm Drainage Plan without an engineer's seal.
The Director of Public Works, as Administrator, reviews and approves or denies submittals within 30 days, using the state Department of Ecology's Stormwater Management Manual as the technical guideline for adequacy. Decisions, including denied variances, can be appealed to the Lewis County hearing examiner.
Violations & Fines
Failing to meet Chapter 15.45 obligations lets Lewis County draw on the developer's performance guarantee: for a single-family site under five acres of disturbance, the Administrator can enforce the recorded Performance Covenant under § 15.45.420(3), billing the applicant for costs and placing a lien if unpaid; for sites of five acres or more, § 15.45.430 lets the county draw on a Performance Surety set at 125 percent of stabilization costs or $1,000 per disturbed acre, whichever applies.
Frequently Asked Questions
When does a Lewis County project need Storm Drainage Approval?
Is my new house exempt from stormwater review?
Does my stormwater plan need an engineer's stamp?
What happens if my site work violates the stormwater chapter?
Sources & Official References
Other rules in Lewis County
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