Residential Stormwater Facilities

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.
• For projects which meet the thresholds above, Full Infiltration or Downspout Dispersion in accordance with the 2012 Washington State Department of Ecology Stormwater Management Manual For Western Washington is required.
• Full Infiltration specifications (BMP T5.10A)
• Downspout Dispersion specifications (BMP T5.10B)
• Treatment of Pollution Generating Impervious Surface (PGIS) in accordance with the 2012 Washington State Department of Ecology Stormwater Management Manual For Western Washington is always required.

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.