Low Impact Development in Western WA Municipal Stormwater Permits

Transcription

1 Low Impact Development in Western WA Municipal Stormwater Permits USGS Tacoma Office September 19, ttp://

2 Municipal Stormwater Permits Implement Clean Water Act NPDES Program and EPA Stormwater Rules Washington s NPDES program began 2

3 The Municipal Stormwater Permits regulate discharges from municipal separate storm sewer systems (MS4). A Regulated MS4 is 3

4 Western Washington Permitting Strategy Reissued Permits Permits - Phase I and Phase II Permits - Phase I and Phase II Permit Revisions New & Redevelopment Monitoring 4

5 Low Impact Development - LID PCHB rulings Phase I:2008 Western WA Phase II:2009 5

6 LID: A stormwater and land use management strategy that strives to mimic pre-disturbance hydrologic processes of infiltration, filtration, storage, evaporation and transpiration by emphasizing conservation, use of on-site natural features, site planning, and distributed stormwater management practices that are integrated into a project design. From: Low Impact Development Technical Guidance Manual for Puget Sound, January

7 LID addressed at 3 scales Site & subdivision Development Codes Watershed Scale 7

8 Site & Subdivision: Appendix 1 Revises wetland guidance for MR #8: Match pre-project inputs; + 20% daily; + 15% monthly Revises MR #5 to incorporate LID BMPs LID Performance Standard List Option within urban growth areas Feasibility Criteria 8

9 Use List #1 Or Projects subject only to MR #1 - #5 2,000 sq ft > hard surfaces < 5,000 sq ft Meet LID Performance Standard Can t use Rain Gardens; Can use Bioretention Demonstrate compliance with approved models & methods can 9

10 List #1 Lawn and landscaped areas: Soil Quality and Depth (T5.13) Roofs: Consider in order listed; use first feasible Full Dispersion or Full Infiltration (T5.30 or T5.10A) Rain Gardens or Bioretention (T5.14A or B) Downspout Dispersion Systems (T5.10B) Perforated Stub-out Connections (T5.10C)

11 List #1 (continued) Other Hard Surfaces (driveways, patios, walks, parking lot) consider in order listed; use first feasible Full Dispersion (T5.30) Permeable pavement, or Rain Gardens, or Bioretention (T5.15, T5.14A, T5.14B) RG or Bioretention area > 5% of drainage area Sheet Flow Dispersion, or Concentrated Flow Dispersion (T5.12 or T5.11)

12 Project Type & Location Projects Triggering MR #1 - #9 Requirement Development (new or redevelopment) on any parcel inside the UGA, or development outside the UGA on a parcel less than 5 acres LID Performance Standard and BMP T5.13 OR List #2 (applicant option) Development (new or redevelopment) outside the UGA on a parcel of 5 acres or larger LID Performance Standard and BMP T

13 List #2 Same as List #1 with two changes: Rain Gardens not an option Other Hard Surfaces: Permeable Pavement is 2 nd priority Bioretention is 3 rd priority Vegetated roof consideration deleted

14 Manual References a. Site planning requirements (Volume I, Ch. 3) b. BMP selection criteria (Volumes II - V) c. BMP design criteria (Volumes II V) d. BMP infeasibility criteria (Volumes III & V) e. LID competing needs criteria (Volume V) f. BMP limitations (Volume II V)

15 Stormwater Management Manual for Western Washington Edits focus on: LID (Vol. V: Chapters 5 & 7) Revised guidance for designing infiltration facilities (Vol. III, Ch. 3) New & revised source control, construction & treatment BMPs WWHM update and modeling guidance Related LID Technical Guidance Manual update available Nov. 2012

16 LID Performance Standard Match post-development discharge durations to pre-developed (pre-european settlement) durations from 8% of the 2-year flow to 50% of the 2-year flow. 16

17 LID Performance Standard vs Flow Control Standard LID Performance Standard addresses the lower, more frequent stormwater flows (8% of 2-year through 50% of the 2-year) Flow Control Standard addresses the higher, less frequent stormwater flows (50% of the 2-year through the full 50-year)

18 Combined Std: Control durations from 8% of 2-yr through 50-year LID Standard MR #5 Flow Control Standard MR #7 18

19 Background for LID Performance Standard USEPA & Other States: Single event methods Target: Retain the X-year, 24-hour storm event West. Wash: Continuous runoff methods Target: Match the volume of runoff from the historic land cover for the entire runoff file Alternate: Match a greater portion of the historic flow duration curve Both: Would be an improvement for the beneficial uses Demand use of LID except on rapidly draining outwash

20 Consequences of Performance Standard & List Option More water infiltrating than under historic conditions - loss of vegetative land cover, especially trees Potential for more instances of: - down gradient resurfacing - basement infiltration & utility issues - long ponding times: health consequences - groundwater contamination Risk to be shared between surface & ground waters

21 3 levels Site & subdivision Development Codes Watershed Scale

22 LID Local Development Codes Make LID the preferred and commonly used approach for site development Minimize impervious surface Minimize native vegetation loss PSP Integrating LID into Local Codes Guidebook 22

23 Adopt new site & subdivision stormwater codes LID- Timelines Phase I: June 30, 2015 Phase II: December 31, 2016* Review and revise developmentrelated codes, rules & standards Phase I: June 30, 2015 Phase II: December 31, 2016* * Or GMA update deadline, whichever is later

24 3 levels Site & subdivision Development Codes Watershed Scale

25 LID Watershed Scale Planning Objective Identify a stormwater strategy (ies) that would result in hydrologic and water quality conditions that fully support existing uses and designated uses throughout the stream system

26 LID Watershed Scale Planning Phase I County selects a watershed and leads a planning process Select watershed by Oct. 31, 2013 Submit scope of work by April, 2014 Submit final plan by Oct. 1, 2016

27 Proposed watersheds Streams impacted by development & retain anadromous fish Targeted to accept significant growth > 10 sq. mi. MS4 service area Watersheds proposed in Phase I permit

28 Swamp Creek Jurisdictions: Snohomish County King County Bothell Kenmore Brier Mountlake Terrace Lynnwood Everett

29 Planning Process Baseline assessment Mapping Continuous Runoff Model Calibration Predict future hydrologic, biologic, and WQ Conditions Evaluate strategies to meet WQ Standards Implementation Plan and Schedule Public Review and Comment 29

30 LID Watershed Scale Planning Phase II Municipalities Planning Responsibilities Provide WQ and flow records Provide maps Participate with strategies development Provide monitoring locations

31 Juanita Creek - King Co. Stormwater Retrofit Plan Highly impervious Low B-IBI scores Goal: Improved Water Quality and flow conditions supportive of aquatic beneficial uses (e.g., fish) 31

32 32

33 Basis for evaluating strategies Water Quality Standards exceedences & Pollutant Load Reductions B-IBI scores estimated by regression relationships with stream hydrologic metrics Frequency of gravel disturbance 33 Juanita Creek Stormwater Retrofit Plan HSPF calibrated to the basin

34 Low Pulse Count Low Pulse Duration High Pulse Count High Pulse Duration High Pulse Range Flow Reversals Hydrologic Metrics Used TQMean R-B Index Peak 2-yr: Winter Baseflow 34

35 Juanita Creek Stormwater Retrofit Plan Compared 7 mitigation scenarios to forested condition baseline, including: Ecology Flow Control Ecology Flow Control & Wet ponds Ecology LID, Flow Control, Treatment Stds LID to 40% and 80% of impervious area LID to 80% of impervious area & 3 reg. ponds Cisterns (2.5 feet of storage) 35

36 Juanita Creek Stormwater Retrofit Plan Result: Ecology LID, Flow Control, & Treatment strategy the only option to achieve the goal B-IBI score > 35 (min. necessary for salmon) Achieves most water quality standards Estimated Present Worth Cost: $1.4 billion 36

37 Lessons learned from Juanita Creek Stormwater Retrofit Plan In already developed watersheds, the cost of meeting the federal and state objectives of restoring designated and beneficial uses is very high In mostly undeveloped watersheds, requiring all projects meet the LID performance standard, the flow control standard, and treatment standards might be successful in protecting beneficial uses. In partially developed watersheds, the updated requirements AND significant retrofitting will be necessary 37

38 Implication Municipalities (inside UGA where developers will frequently choose the LID list option) with partially developed basins will have to do more than just apply the new requirements to prevent beneficial use degradation 38

39 Questions? 39

40 Thank you!