GSI in Washington State Status and Trends Urban GI Summit February - PowerPoint PPT Presentation

GSI in Washington State Status and Trends Urban GI Summit February 21, 2018 1

Agenda • Regulatory application of Low Impact Development (LID) • LID and Underground Injection Control • Research • Lessons Learned

Minimum Requirement #5 On-site Stormwater Management Employ On-site Stormwater Management In MSW Permit, LID BMPs to addressed on 3 levels: infiltrate, disperse, and • Site & subdivision retain • Development Codes stormwater • Watershed Scale runoff on-site to the extent feasible 3

LID Performance Standard Match post-development discharge durations to pre- developed durations from 8% of the 2-year flow to 50% of the 2-year flow • Pre-development generally a forested land cover 4

LID Std: Control durations from 8% of 2-yr through 50% of 2-year LID Standard MR #5 MR #7 Flow Control Standard 5

List #2 Lawn and • Soil Quality and Depth landscaped areas: Glacial till: high in Same soil with 30% runoff and poor turf compost added. Up to quality 50% less runoff. Turf still healthy 4 years later Photos: UW Test Plots 6

List #2 Roofs: Consider • Full Dispersion or in order listed; Downspout Full Infiltration use first feasible • Bioretention • > 5% of drainage area • Downspout Dispersion Systems • Perforated Stub-out Connections 7

List #2 Other Hard Full Dispersion Surfaces Permeable pavement (driveways, Bioretention roads, patios, walks, parking > 5% of drainage area lot) consider Sheet Flow Dispersion, or in order listed; Concentrated Flow use first Dispersion feasible 8

What happens if all items on list are infeasible? Applicant must show this is true No need for anything from list(s) Must still meet Runoff Treatment and Flow Control 9

MR #5 and Flow Control Exempt Water Bodies Post-Construction Soil Quality and Depth Downspout Full Infiltration, Downspout Dispersion Systems, or Perforated Stub-out Connections Concentrated Flow Dispersion or Sheet Flow Dispersion 10

Underground Injection Control

Research • Washington Stormwater Center • Full Scale Porous Asphalt and Permeable Concrete • Mesocosm BSM • Full Scale Bioretention

GROSS Grants • Redmond • Kitsap County • Tacoma

SAM/Permittee • Bioretention Soil Media • Bellingham Phosphorus free BSM

Lessons Learned • Infiltration isn’t the end of stormwater • May need to temper use (there are places where you can’t do LID) • Local Jurisdictions need freedom to limit where LID is implemented • Need training on non-BMP aspects of LID (Site Planning, trees, etc.)

Questions? 16

Contact Information Douglas C. Howie, P.E. Dept. of Ecology douglas.howie@ecy.wa.gov (360) 407-6444 17