City of Seattle Stormwater Code & Manual Update
Herrera worked with the City of Seattle to update the City’s stormwater code and manual to maintain equivalency with the 2019-2024 NPDES Phase I Permit and Ecology’s 2019 Stormwater Management Manual for Western Washington.
The 2021 Seattle Stormwater Manual update included clarifying design requirements, adding a new BMP for sidewalks and trails (sidewalk/trail compost-amended strip), adjusting the requirements for rainwater harvesting to expand potential applicability in urban areas, updating sizing factors for multiple BMPs, and adding an option for developing a landscape management plan for pollution-generating pervious areas.
Herrera assisted with developing materials and facilitating in-person and virtual public meetings for interested stakeholders (local consultants, contractors, and the general public). The stormwater code and manual were finalized in the spring of 2021 and became effective on July 1, 2021.
Along with the stormwater manual, Herrera updated implementation tools including the On-site Stormwater Management List Approach Calculator, the Pre-Sized Flow Control Calculator (for parcel-based projects with less than 10,000 square feet of hard surface), and the Stormwater Facility Credit Program calculator. The final manual and calculators are available on the City's website.