FULL CYCLE BIORETENTION Sustaining Performance Over Decades - - PowerPoint PPT Presentation

FULL CYCLE BIORETENTION Sustaining Performance Over Decades

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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

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Upcoming Webcasts

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Wednesday, March 15:

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2017

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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

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

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

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

Bioretention: How it Works

11

Key Bioretention Design Elements

• Ponding area
• Filter media
• Pea gravel
• Overflow
• Vegetation
• Optional:

– Underdrain + stone – Infiltration sump

12

Evolution of Bioretention

• 1992: PG County Design Specification
• 1996: CWP Design of SW Filtering Systems
• 2000: MD Stormwater Manual
• 2008: Baywide Design Specification
• 2009-2013: Bay State Stormwater Manuals
• 2017: ????

Going Beyond the 2008 Bay-wide Design Specification

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

Full Cycle Bioretention

1.Monitoring 2.Assessment 3.BMP Design 4.Construction 5.Inspection 6.Maintenance

• 7. Makeover

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
• ver entire cycle
• 4. Be properly constructed and established
• 5. Inspect using visual indicators
• 6. Use landscape contractors to maintain function
• ver time
• 7. Perform a “make-over” when functions diminish

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?

Performance: Runoff Reduction

• Runoff Reduction (RR) is most important
• utcome 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

Maximizing Runoff Reduction

Underdrain system with Internal Water Storage Vegetation

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

Key Pollutant Removal Factors

• Bioretention is effective in removing range
• f pollutants, including toxics, bacteria

and nutrients

• Next generation design should be capable
• f meeting load removal targets
• Media and vegetation matters
• We are not achieving denitrification

reliably

PON

DON

NO3

NH4

NO3

DON

NO3

MI MINERALIZATION AM AMMONIFICATION NIT NITRIFICATION

NO3

DE DENITRIFI FICATION

N2

Standard Bioretention

PB

No mechanism for full N removal in the standard bioretention design

Source: Allen Davis

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

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

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

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

Performance Issues Observed in Field

28

General Performance Problems with Bioretention (n = 40)

8% 8% 15% 18% 18% 23% 25% 33%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Clogged Soil Media Inappropriate Media Excessive Vegetation Sediment Deposition Short-Circuiting of Treatment Inadequate Vegetation No Pre-Treatment Need Maintenance

Source: CWP (2008) James River Basin

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

Bioretention Inlet Failures

30

31

Filter Bed Failures

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

Severe

32

Bioretention with really large CDAs appear prone to failure

Knucklehead designs

FEEDBACK BREAK

Full Cycle Bioretention

1.Monitoring 2.Assessment 3.BMP Design 4.Construction 5.Inspection 6.Maintenance

• 7. Makeover

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

• r makeovers at individual sites

Performance Targets

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)

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?

• 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

Feasibility & Testing

Bioretention and Karst

• Larger CDAs (20,000 sf)
• Geotechnical work

shows bottom invert is more than 2’ from bedrock

• CDA is a stormwater

hotspot Smaller CDAs (< 0.5 acre) Geotechnical datashows soil column at least 3 feet above bedrock Practice has an underdrain Relax surface ponding and soil media depths

No Liner Liner

• 3. 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.

Upgraded Design Criteria

• 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 non-

erosive levels in the bioretention filter bed that receives them

• 2. Provide more maintainable

landscaping options Problem: no one is sure what the real landscaping

• bjectives 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

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)

• 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?

Sizing/Storage for Treatment Volume (Tv)

𝜽 = 0.25 𝜽 = 1.0 𝜽 = 0.40

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

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”

50

* Note: This a rhetorical question, no need for you to answer it

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

• 4. Require Internal Water Storage Zone

Source: www.bae.ncsu.edu/stormwater

Boosts performance with little or no increase in construction cost

• 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

Bottom of ED Pond Dry Swale

• 6. Supplemental Design Criteria for

Bioretention Areas that Receive Concentrated Flows

FEEDBACK BREAK

• 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

Construction Methods

Bioretention Components: What You Can See

Side Slopes Filter Bed Vegetation Outlet Inflow

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

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

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

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

Focus on the Initial Landscape Phase

• 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 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

1 2 3 4 5

Ongoing Inspections

See CSNs “Bioretention Illustrated” in the Resources Section

Visual Indicator Approach

• Simple visual indicators to rapidly

investigate bioretention function

• Used during routine maintenance visits,
• ngoing 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

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

Routine Regulatory Inspection

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

• Routine maintenance is

critical to sustain functions

• ver 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

Routine Maintenance

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

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

But You Need To Keep It Looking Good!

Fixing Small Problems Before They Become BIG

• 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

Bioretention Makeovers

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

Makeover Retrofits

• Bay communities can get

nutrient credit now for replacing organic rich media with current media spec in their older bioretention areas (circa 1995-2010)

• Credit may be granted for

replacing the current media

• f recently installed

practices with PED media

PED Retrofit of Bioretention Area

Soil Media With Reactive Amendments

CSN Report on PED Crediting Recommendations Expected 4/2017

FEEDBACK BREAK

Webcast Resources

www.chesapeakestormwater.net

• 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

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 !

Evaluation

https://www.surveymonkey.com/r/full-cycle-bioretention