FULL CYCLE BIORETENTION Sustaining Performance Over Decades

Transcription

1 FULL CYCLE BIORETENTION Sustaining Performance Over Decades

2 Welcome to the Webcast To Answer a Poll Question Simply select the preferred option. For those viewing this session alongside several colleagues, respond in a manner that represents your organization as a whole. We ARE Recording this Session All comments and questions will be recorded and included in the archives. We will notify you as soon as the recording and related resources are loaded on the web. We Appreciate Your Feedback Fill out our evaluations our funders need to hear it!

3 Let s Get Interactive Today! We want to get your feedback on how to perfect bioretention, so please submit your comments in the chat box located to the left of the slides. We will read and respond to as many comments as possible during our three feedback breaks today We want to acknowledge insights provided by Ted Scott, Dave Hirschman, Shannon Lucas and many local practitioners in the Bay watershed last year * Although any really bad ideas you hear today are the sole responsibility of CSN

4 Chesapeake Bay Stormwater Training Partnership To learn how you can have access to: FREE Webcasts Free design, inspection & maintenance workshops Intensive stormwater seminars Direct On-site technical assistance Self guided web-based learning modules Visit:

5 Upcoming Webcasts Wednesday, March 15: Users Guide to Urban BMPs in the Chesapeake Bay Thursday, March 30: New Crediting Approaches: Impervious Cover Disconnection and CMAC Thursday, April 20: Fall Leaf Collection and Street Nutrient Loads Register here:

6 2017 Help us recognize the best BMP installed in the Chesapeake Bay Watershed Voting opens February 27 th! Check the finalists:

7 Poll Question #1 Tell us a little about yourselves who are you representing today? Local government Private sector Regulatory agency Non-profit Academia Other tell us in the chat box

8 Poll Question #2 Tell us how this webcast is relevant to you: I design bioretention projects I am involved in bioretention construction or landcaping I inspect or maintain bioretention I am a planner and use BMPs to account for load reductions I am a researcher I am generally interested in the topic Other

9 Poll Question # 3 How satisfied are you with the typical bioretention area installed in your community? Very satisfied Satisfied, but see a few problems Not satisfied, see a lot of problems Very dissatisfied No opinion

10 Today s Agenda Evolution of bioretention practice What we have learned in the last five years The Full-Cycle Approach: Applying it to the next generation of the bioretention practice Audience feedback

11 Bioretention: How it Works 11

12 Key Bioretention Design Elements Ponding area Filter media Pea gravel Overflow Vegetation Optional: Underdrain + stone Infiltration sump 12

13 Evolution of Bioretention 1992: PG County Design Specification 1996: CWP Design of SW Filtering Systems 2000: MD Stormwater Manual 2008: Baywide Design Specification : Bay State Stormwater Manuals 2017:????

14 Going Beyond the 2008 Bay-wide Design Specification

15 Why are we revisiting bioretention? Now the #1 BMP installed in the Bay State design specs are 5 to 10 years old Flood of new research in the last 5 years Critical feedback from inspectors and maintainers Many older BR projects are no longer meeting intended functions

16 Full Cycle Bioretention 1.Monitoring 7. Makeover 2.Assessment 6.Maintenance 3.BMP Design 5.Inspection 4.Construction

17 What is the Full Cycle Approach? 1. Establish minimum performance objectives for the practice 2. Ensure the practice is feasible for the site 3. Meet design criteria to maintain performance over entire cycle 4. Be properly constructed and established 5. Inspect using visual indicators 6. Use landscape contractors to maintain function over time 7. Perform a make-over when functions diminish

18 What have we learned in the past few years? Research on bioretention performance Runoff reduction Pollutant removal BR components that influence performance (+/-) Operational experience What design elements are most problematic? What steps in the cycle are most critical? What is a sustainable plant community?

19 Performance: Runoff Reduction Runoff Reduction (RR) is most important outcome in bioretention design Infiltration, evapotranspiration and extended filtration can reduce annual runoff volume by 40 to 70%, depending on underlying soils Internal water storage zone design can further boost RR in bioretention areas

20 Maximizing Runoff Reduction Vegetation Underdrain system with Internal Water Storage

21 Plants and Runoff Reduction While direct plant uptake does not contribute much to pollutant removal, they are essential for runoff reduction and practice sustainability: The evapotranspiration pump Dense root networks maintain media porosity Plant detritus is carbon source for denitrification and enhanced microbial growth Existing adjustor curves can estimate how increased runoff reduction improves pollutant load removal in bioretention areas

22 Key Pollutant Removal Factors Bioretention is effective in removing range of pollutants, including toxics, bacteria and nutrients Next generation design should be capable of meeting load removal targets Media and vegetation matters We are not achieving denitrification reliably

23 Standard Bioretention PON DON NO3 NH4 DENITRIFICATION PB DON MINERALIZATION N2 AMMONIFICATION NITRIFICATION NO3 NO3 No mechanism for full N removal in the standard bioretention design Source: Allen Davis

24 Media Matters Current media recipe meets performance objectives Research shows nutrient removal can be boosted when PEDs are added to the basic bioretention media recipe The removal boost is usually greater for TP than TN On the other hand, low or even negative nutrient removal has been reported for media recipes that rely on compost or fast-decomposing organic matter

25 Vegetation Matters Vegetative cover is important both above and below ground The root network enhances microbial activity in the media to transform nutrients and maintain its hydraulic performance Plant detritus is the long term carbon source needed for denitrification Periodic harvesting may help with nutrient removal from system. Need more research on best plant species for bioretention

26 Critical Design Elements for Better Performance Positive Factors Media Internal Water Storage Zone Plant cover and root depth Neutral or Negative Factors Mulch Plant uptake (not much) Ponding volume

27 Problems Encountered in the Field Poor inflow Poor internal geometry Questionable value of mulch Big drainage areas = more problems Filter bed failures Scrubby plant community

28 Performance Issues Observed in Field General Performance Problems with Bioretention (n = 40) Need Maintenance 33% No Pre-Treatment Inadequate Vegetation Short-Circuiting of Treatment Sediment Deposition Excessive Vegetation 25% 23% 18% 18% 15% Inappropriate Media Clogged Soil Media 8% 8% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Source: CWP (2008) James River Basin 28

29 Most of our current inlet designs don t work well in the real world and actually create much of the maintenance burden associated with bioretention We have a goldilocks problem when it comes to managing such a small elevation drop, especially from curb cut inlets

30 Bioretention Inlet Failures 30

31 Filter Bed Failures 31

32 Mulch is an expensive permanent cover that is real hard to maintain because it floats Severe 32

33 Bioretention with really large CDAs appear prone to failure

34 Knucklehead designs

35 FEEDBACK BREAK

36 Full Cycle Bioretention 1.Monitoring 7. Makeover 2.Assessment 6.Maintenance 3.BMP Design 5.Inspection 4.Construction

37 Bioretention need to be managed over decades Every step in the bioretention management cycle is important to keep them working Some key steps: Confirm underground features during construction Establish successful plant community Operate regular seasonal maintenance regime Use triggers to compel non-routine maintenance or makeovers at individual sites

38 Performance Targets

39 Targets for Bioretention Performance Bioretention areas should consistently achieve the following over their entire life-cycle Runoff Reduction: Reduce half of the stormwater volume going into the bioretention area, from on an annual basis Pollutant Load Removed 90%: sediment 75%: toxins, bacteria and trace metals 50%: nutrients (N and P)

40 More Bioretention Performance Targets Plumbing that can last at least a decade without failing (e.g., inflows, underdrains) Sustainable plant community that improves practice function and creates legit habitat Reasonable routine maintenance burden that can be mostly handled by trained landscape contractors Others?

41 Feasibility & Testing Bioretention is popular because it is widely feasible at most sites (esp. when underdrains are used) Some existing testing and feasibility requirements in SDM might even be relaxed Simple cores to define excavation conditions vs. more detailed infiltration tests (for UD) Shallower setbacks to water table Area-based karst liner rules

42 Bioretention and Karst No Liner Smaller CDAs (< 0.5 acre) Geotechnical datashows soil column at least 3 feet above bedrock Practice has an underdrain Liner Larger CDAs (20,000 sf) Geotechnical work shows bottom invert is more than 2 from bedrock CDA is a stormwater hotspot Relax surface ponding and soil media depths

43 3. Upgraded Design Criteria Upgraded Design Criteria 1. Standard bioretention inflow methods 2. Provide more maintainable landscaping options 3. More guidance on stormwater routing in bioretention areas 4. Require internal water zone 5. Revamp design criteria for internal geometry 6. Supplemental criteria for bioretention retrofits in dry ponds, dry swales and sand filters.

44 1. More reliable inflow method Create a standard BR inflow method that works and can be easily cleaned Precast concrete curb cut inlet apron that prevents erosion at the entry side slope and: Reduces incoming flow velocities to nonerosive levels in the bioretention filter bed that receives them

45 2. Provide more maintainable landscaping options Problem: no one is sure what the real landscaping objectives are for bioretention and what maintenance regime is needed to sustain them Solution: Provide a range sustainable landscaping templates that are easy to maintain and require less mulch Support a mow-able meadow landscape option Perennial seed mixes specifically formulated for bioretention areas

46 Advantages of the Mowable Meadow Option Mowed 2X/year Attracts pollinator and birds Seeding rapidly achieves high plant cover Lower construction cost (no plants) Lowest cost maintenance Conceals trash and debris No mulching needed Visually attractive Landscaping crews know how to maintain

47 Mulch-less Landscaping Options (w/0 a lot of pretty flowers) 47

48 3. Routing Stormwater through Bioretention Need more standardized guidance on: Increasing bioretention footprint beyond the media surface area Engineering assumptions for routing stormwater through bowl, media, rock, water layer, and underlying soil Do we really need to specify a max ponding volume more than six inches?

49 Sizing/Storage for Treatment Volume (Tv) η = 1.0 η = 0.25 η = 0.40 Treatment Volume (Tv) = (ponding* x 1.0) + (soil x 0.25) + (gravel x 0.40) Dry/Water Quality Swale Ponding = Storage behind check dams Some State-Specific Sizing Methods Apply

50 Am I crazy or not*? I never see a completely full bowl volume, unless it has failed. Hard to fill the bowl given the fast infiltration rate for bioretention media 6 12 * Note: This a rhetorical question, no need for you to answer it 50

51 Allow Larger Ponding Footprint to Get Extra Storage for Quantity Control 50% increase if ponding is 6 or less 25% increase if ponding is between 6 and 12 Additional Surface Ponding Additional Surface Ponding

52 4. Require Internal Water Storage Zone Boosts performance with little or no increase in construction cost Source:

53 5. Revamp Criteria for Internal Geometry Dispense w/ pretreatment for BR areas with a CDA of less than 1 acre Sideslopes: shift to 4:1 from current 3:1 Provide more definitive flow path criteria

54 6. Supplemental Design Criteria for Bioretention Areas that Receive Concentrated Flows Bottom of ED Pond Dry Swale

55 FEEDBACK BREAK

56 Construction Methods Craft a better construction sequence to prevent failures (especially underground ones) Provide quality control to only accept functional bioretention projects in the community Be able to ensure landscaping is properly established

57 Bioretention Components: What You Can See Outlet Vegetation Side Slopes Filter Bed Inflow

58 Concentrate Construction Inspection on What You Can t See After it is Built Filter Media Pea Gravel or Filter Cloth Overflow Perforated Underdrain in Stone Stone Sump

59 Detailed Construction Sequence #1 Preconstruction material submittals Media, stone, geotextile, matting, seed, etc #2 Mark Utilities and Stakeout #3 Ensure E&S Measures are installed #4 Verify the actual contributing drainage area boundaries

60 Construction Sequence (continued) #5 Excavate to Reduce Compaction #6 Reach Correct Invert Elevation and Protect Bottom Porosity #7 Tie into Storm Drain System (under drains or overflow) #8 Install filter fabric (on sides only) #9 Install Under drain and lay Down Stone Layers (IWS) #10 Add Filter Media # 11 Lay Down Surface Layer and Stabilize Slopes # 12 Plant and Maintain Vegetation

61 Inspect Critical Construction Elements at the Right Time Make sure you have a checklist or data collection form to check: Under drain and stone installation Inlet and outlet elevations Curb cut elevations Side-slope stability Quality of filter media Quality of stone and underdrain Final ponding depth

62 Focus on the Initial Landscape Phase Landscaping contract covers first year after installation Regular watering first few months Spot re-seeding Remove and replace dead plants Repair erosion on side-slopes Perform final inspection at end of establishment phase Usually extends 6 to 12 months after installation Developer or builder responsible for this first year of maintenance

63 Ongoing Inspections See CSNs Bioretention Illustrated in the Resources Section

64 Visual Indicator Approach Simple visual indicators to rapidly investigate bioretention function Used during routine maintenance visits, ongoing inspections Indicators trigger a punch list of maintenance tasks to restore function More severe cases trigger an in depth forensic investigation to fix the problem

65 More on Visual Indicators Goal: Evaluate individual bioretention areas in 20 minutes or less How: Follow a prescribed sequence to assess performance and functionality by using numeric triggers to grade visual indicator as scoring Pass, Minor, Moderate or Severe Result: Use of a tablet tool to develop a punch-list of tasks to follow-up on to bring the BMP up to speed

66 Routine Regulatory Inspection Ensure BMP is properly maintained and functioning; Develop a punch list of needed maintenance tasks Tool: Visual Indicators NOTE: Method should be used to quickly evaluate practice during each routine maintenance visit as well MS-4 Permit Once ever 1-5 years Trained person

67 Routine Maintenance Routine maintenance is critical to sustain functions over decades Routine maintenance costs less in the long term Can be done by trained landscape contractors Expect areas to lose major function at practices that are not been maintained for 3 years or longer

68 The Routine Maintenance Regime Seasonal maintenance (quarterly) Scheduled routes and production oriented Set crews with light equipment Trained landscape contractors Can flag failing facilities for more intensive investigation

69 Basic Quarterly Maintenance Regime Maintain landscaping (mow, thin, split, prune, reinforce, manage weeds and invasive plants, harvest, as needed Remove trash and debris Clear obstructed inlets, repair erosion or remove sediment Rake mulch, de-cake or add mulch, as needed Stabilize any erosion in filter bed and side-slopes Report any severe problems that warrant an FBI

70 But You Need To Keep It Looking Good! Fixing Small Problems Before They Become BIG

71 Bioretention Makeovers A makeover is essentially a complete re-build of an existing bioretention area to: Restore lost function Increase nutrient reduction This entails replacement (or recycling) of all of its design components Plants Media Stone Drainage

72 Makeover to Recover Function Many of legacy bioretention areas have lost or are losing their enough runoff reduction, water quality or landscaping functions (e.g., 1995 to 2015) Expect areas to lose significant function if they have not been maintained in three or more years Need specific and numeric indicators to trigger when an individual bioretention area has lost enough functions to require a makeover

73 Makeover Retrofits Bay communities can get nutrient credit now for replacing organic rich media with current media spec in their older bioretention areas (circa ) Credit may be granted for replacing the current media of recently installed practices with PED media

74 PED Retrofit of Bioretention Area CSN Report on PED Crediting Recommendations Expected 4/2017 Soil Media With Reactive Amendments

75 FEEDBACK BREAK

76 Webcast Resources Bay Design Specs (VA, DC, DE and NCSU) Bay State Stormwater Compliance Spreadsheets Advanced Bioretention Design Webcast Bioretention Illustrated Bioretention Maintenance and Inspection Videos More Archived Webcasts on Bioretention

77 Evaluation Please take a few moments to answer our 6 question survey to help us better serve your needs in our webcast series. We use this information to report it to assess our work, your needs and to report it to our funders for future webcasts!