The intent of the Stormwater Management Manual (SWMM) is to incrementally, over time, manage stormwater flows that are currently un-managed. The current definitions of development and redevelopment do not provide clarity on how the manual applies to alterations or expansions to sites and buildings that are significant, but don’t increase the footprint. This includes dormers, ADUs, adding floors to residential, multi-family or commercial developments, etc. Clarity is also needed for repaving where the footprint is not increased and for some sidewalk projects. The following is proposed as interim guidance for determining the application of the Stormwater Management Manual for these types of projects.
If a structure is altered by 500 sq. ft. or more with the intent of creating living/business space (excluding that required for repairs or maintenance as required under Chapter 4) the SWMM will apply, even if the alteration does not affect the ground floor footprint.
- A 900 sq. ft. home adding a 600 sq. ft. second floor would trigger the SWMM.
- A 900 sq. ft. home adding a 300 sq. ft. dormer would not trigger the SWMM.
- Fully removing and replacing a roof would trigger the SWMM.
- A two-story commercial space adding a 550 sq. ft. third floor would trigger the SWMM.
- Interior improvements/remodeling to a basement or existing 2nd floor (attic) would not trigger the SWMM.
If changes to paved or other impervious surfaces expose 500 square feet or more of gravel (regardless of layer name or grade), the SWMM will apply even if the disturbance does not change the footprint. This would exclude grind and overlay projects where asphalt remains and gravels are not exposed. See illustration below.
Though street trees are encouraged as an impervious area reduction technique where it is not feasible for sidewalks to drain into a stormwater facility in the right-of-way, it is not expected that a separate stormwater management facility be constructed to serve sidewalk areas only.
BES would like to introduce their new Major Projects Group Engineer
Adrienne Aiona has been recently hired by the Bureau of Environmental Services as their new “Major Projects Group (“MPG”)” engineer, covering land use and building permit review for large-scale developments like those we have seen in the South Waterfront area and Pearl District. Adrienne has previously worked at BES from 2003 – 2008 in many positions including: Community Watershed Stewardship Program AmeriCorps member; Private Stormwater Facility Maintenance Inspection Program at WPCL; and in the CIP watershed design group. She’s spent the last 7 years in Oakland, CA earning her master’s degree and doing stormwater/restoration engineering design.