Whatcom County Code Chapter 20.80.630 determines when a stormwater facility is required for development projects within the Lake Samish, Lake Padden, Birch Bay, or Drayton Harbor watersheds (which are Stormwater Special Districts). These thresholds are:
New construction or remodels that increase impervious surfaces by more than 500 square feet
Renovation projects where the estimated cost of the work exceeds 50% of the assessed value of the existing structure.
The 2012 Washington State Department of Ecology Stormwater Management Manual For Western Washington is a technical document. If your project requires the use of this manual, consultation from a Licensed Civil Engineer may be required.
For stormwater facility requirements in Lake Whatcom, and for areas outside of the Stormwater Special Districts, please see the separate stormwater-related websites for these areas.