DETAILS OF SUCCESSDESIGNING AND CONSTRUCTING GREEN

INFRASTRUCTURE TO MAXIMIZE PROJECT BENEFITS

Beyond the Basics Stormwater Management Conference

September 14, 2016

Dan Christian, PE, D.WRE

Tetra Tech

Sustainability Goals

• Triple Bottom Line

• Economic

• Social

• Environmental

• Goals like “14. Enhance

stormwater

management” are easy

• Look for synergistic

opportunities

• Green roof = energy

reduction

• Tree plantings = reduced

energy consumption, etc.

LID Process

• Identify Regulatory Needs

• Conduct Hydrologic and

Geotechnical Survey

• Protect Natural Features

• Use Drainage and Hydrology as

Design Elements

• Establish Clearing and Grading

Limits

• Reduce/Minimize Total and Effective

Impervious

• Select LID Practices

Design Criteria

• Water Quality Treatment Volume

• ~90% non-exceedance, ~1.0 inch rainfall

• Typically focus on runoff retention

• Channel Protection

• Purpose – maintain stable channel hydrology

• Typically designed for 2-year event (3.0 in)

• Commonly volume and peak flow control

• Municipal Sewer Conveyance

• Used to size sewer pipes and open channels

• 5 to 10-year events commonly used (3.7 - 4.2 in)

• Commonly sizing pipes for post-development peak flow

• Local Flood Control

• Manage local drainage to prevent problem flooding

• 25 to 100-year events commonly assumed (5.1 – 6.6 in)

• Commonly detention storage with peak flow limited to pipe capacity

Sizing

• How do you size these things for all the different criteria?

• Hand calculations

• Spreadsheets

• Dedicated hydrologic modeling software

• Calculating complete hydrographs is important

HSPF

WMS

PIHM

CUHP

IWFM

HydroBEAM

CWYET

Final Site Design

• Place practices at the appropriate locations

• Size practices to meet hydrologic design criteria

• Verify that geotechnical and drainage requirements have been met

• Complete designs such as finish details and notes

• Complete the site plans

BIORETENTION PROFILELet’s take a quick sidetrack and look at the typical components of a

bioretention system and example cross sections

Bioretention

Aggregate Reservoir

In situ soil

Choker Course

Planting Soil/Filter

Mulch

Surface storage

Underdrain

Swale - Small

Swale - Large

Parking Lot Swale

Bioretention Parking Lots

Bioretention at Building Sites

Linear Planter - Small

Linear Planter - Large

Planter Box Next to Building

Curb Extension

Neighborhood Scale

BIORETENTION DETAILSNow let’s look a little closer at the component details

Bioretention Engineered System

Soil Media

Temporary

Ponding Area

Cleanout

UnderdrainOverflow

Inlet

On-line

Off-line

Off-line

When full, water backs up on street

and flows down to catch basin

On-line

All runoff enters the bioretention

Outlet

Outlet

Inlet

• Sized to capture design flow

• Location and elevation

• Prevent clogging and sediment accumulation

• Guard against excessive inlet velocities

Inlets

Outlet and Overflow

• Water needs a way to get out

• In-line versus off-line

• Location and elevation

• Mulch and topsoil should

stay in

Outlets

Pretreatment

• Capture large sediment

(sometimes trash and debris)

• Prevent erosion

• Level weir wall

• Options

• Filter strips

• Grass channels

• Sumps

• Hydrodynamic devices

• Screens and baskets

• Design based on dynamic

settling and Stokes Law

Pretreatment

Primary Storage Area

• Level soil surface

• Encourage even

infiltration and

reduce erosion

Sloped Surface• Within each cell:

• Soil and aggregate are level

• Maximizes storage

• Promotes infiltration

• Between cells:

• Separating wall

• Overflow from one cell

cascades to next one

downstream

• Can be constructed as

continuous swale.

• System used for

conveyance, not just storage

• Reduced storage volume.

• Increased likelihood of

surface flooding

downstream.

Sloped Surface

Vegetation

• Water Uptake

• Stabilization

• Impeding Flow

• Filtration

• Infiltration

• Nutrient Uptake

• Toxin Uptake

• Pollutant Breakdown

• Plants for Stormwater Design : Species Selection for

the Upper Midwest, by D. Shaw and R.Schmidt, 2003.

• Plants for Stormwater Design: Species Selection for

the Upper Midwest, Volume II. By D. Shaw, T.

Randazzo, H. Johnson, R. Schmidt, B. Ashman, 2007.

Ideal Plants – Functional Perspective

• Deep rooting

• Climate and water adaptability

• Overall enhancement of soil infiltration over time

• Tolerant of pollutants

• Targeted pollutant removal

• Habitat value

• Lack of invasiveness

Transpiration Rates of Various Plants

Plant Name Plant Type Transpiration Rate

Perennial rye Lawn grass 0.27 in/day

Alfalfa Agriculture crop 0.41 in/day

Common reed Wetland species 0.44 in/day

Great bulrush Wetland species 0.86 in/day

Sedge Wetland/prairie species 1.9 in/day

Prairie cordgrass Prairie species 0.48 in/day

Cottonwood Tree (2 year old) 2-3.75 gpd/tree

Hybrid poplar Tree (5 year old) 20-40 gpd/tree

Cottonwood Tree (mature) 50-350 gpd/tree

Weeping Willow Tree (mature) 200-800 gpd/tree

Source: Plants for Stormwater Design Volume II by D. Shaw and R. Schmidt (ITRC 2001)

Plant Selection

Consider maintenance

Public PerceptionUnderstanding the “human” side of

new forms of green infrastructure

for Detroit vacant propertieshttp://graham.umich.edu/media/pubs/Det

roit-Green-InfrastructureFactsheet_0.pdf

Cues to Care• Defined edges

• Mowing lawn panels or strips

• Flowering plants, colorful trees,

showy flowers

• Massing and structure

• Trimmed shrubs, plants in rows,

linear planting designs

• Bold patterns

• Color composition

• Wildlife feeders and houses

• Fences, architectural details, lawn

ornaments, pathways

Soil• A special or engineered soil

specified by the particular practice

• Chosen for specific porosity –

infiltration of stormwater

• May have special characteristics to

treat or absorb nutrients and other

pollutants

Soil

• Light fluffy soil for

vegetation

• Avoid excessive

compaction

• Often specialized

• May reuse soil with

amendments

Example Mixesa) 60-70% sand, 15-25% topsoil, 15-25% organic matter (good for growing plants, likely to

leach nutrients)b) 70-85% sand, 15-30% organic matter (likely to leach nutrients, dries out quickly)c) 85-88% sand, 8 to 12% fines, 3-5% organic matter (fines sorb more dissolved

phosphorous and metals, dries out quickly)d) 60-75% sand, min. 55% total coarse and medium sand, <12% fine gravel less than 5 mm,

2-5% organic matter (best for pollutant removal, moisture retention and growth of most plants)

Soil Characteristics

• Porosity: void space of soil

(space for water)

• Infiltration: movement of water

through soil

• Field Capacity: proportion of void

space that stays wet due to

surface tension (i.e. after water

drains by gravity)

• Wilting Point: point at which

plants can no longer withdraw

water fast enough to keep up

with transpirationSource: FISRWG

Infiltration Capacity

• Dry Soils, Little or No Vegetation

• Sandy soils: 5 in/hr

• Loam soils: 3 in/hr

• Clay soils: 1 in/hr

• Dry soils with Dense Vegetation

• Multiply by 2

• Saturated Soils

• Sandy soils: 1 to 4 in/hr

• Loam soils: 0.25 to 0.50 in/hr

• Clay soils: 0.01 to 0.06 in/hr

Source: Rawls, W.J., D.L. Brakensiek, and N. Miller, “Green-Ampt Infiltration Parameters

from Soil Data” J. Hydr Engr. 109:62, 1983), EPA SWMM 5 Users Manual, and FISRWG

42

POROUS PAVEMENTS

Porous Pavements

Aggregate storage

In situ soil

Filter coarse (as required)

Pervious Pavement

Geotextile

Underdrain

Choker coarse or setting bed (as required)

Porous Pavements

Source: American Concrete Pavement Association, 2006

Typical system with underdrain Rock trench along pavement edge

Open trench along pavement edge Rock trench extending beyond pavement

Asphalt

• Installed with standard HMA paving

equipment and no special training

• Mix Design is required

• Binder Content 5.0 - 6.5%

• Air Voids ≥ 18%

• Drain down ≤ 0.3%

• Evaluate for Moisture Susceptibility

• Typical cross-section

• 2 to 4-inch asphalt layer

• Choker course, 1 to 2 inches thick

composed of 0.5-inch diameter stone

• Aggregate subbase, thickness varies

Porous Asphalt Pavements for Stormwater

Management: Design, Construction and Maintenance

Guide. Information Series 131. National Asphalt

Pavement Association (NAPA). 2008.

Concrete

• Pervious designed as regular concrete pavement, but has lower strength• Ranges from 400 psi to 4000 psi

• Strength decreases linearly as void ratio increases

• 15% to 20% void ratio can result in 7-day compressive strengths of 2900 to 3300 psi

• ACPA PerviousPave software for design www.acpa.org/perviouspave/

• Most “car traffic only” pavements are 6 inches of pervious concrete

• Use certified professionals (list available on nrmca.org)

• Water content is critical to success

• Cover during curing

Illinois Ready Mixed Concrete Association, Pervious Concrete.

http://www.irmca.org/site/page23.aspx

National Ready Mixed Concrete Association. Pervious Concrete.

http://www.perviouspavement.org/

FHWA www.fhwa.dot.gov/pavement/concrete/pubs/hif13006/index.cfm

Other Aggregate Based Paving Systems

• Flexi®-Pave (kbius.com)

• Filterpave® (http://filterpave.com)

• Glass (recycled) or aggregate

• elastomeric binder

• PorousPave

(www.porouspaveinc.com )

• Recycled tires, aggregate and

urethane binder

• Sidewalks, driveways, play areas,

parking lots

• Gravel Driveway

• and many more…

Open-Jointed Paving Blocks

• Water drains between pavers

• Concrete and clay materials

• Typical cross-section

• Paver stone

• Bedding course 1 to 2 inches thick,

typically ASTM No. 8

• Aggregate subbase, thickness varies,

typically ASTM No. 57

• Edge restraints are required

Interlocking Concrete Pavement Institute

www.icpi.org

Brick Industry Association

www.gobrick.com

Open-Celled Paving Grids

• Similar design and installation as the open-jointed paving blocks

• Pavers contain large openings

• Voids filled with various materials

• Concrete blocks

Plastic Geocells and Porous Turf

• Various manufacturers

• Vertical load supported by honeycomb structure

• Void space typically filled with granular material

• May be vegetated

Working on slopes

• Pervious concrete successfully

used on 16% slopes

• Asphalt surfaces <= 5% (NAPA

recommended)

• Check Dams or Soil Berms

• Terrace the bottom

COMMON DETAILSBioretention and

Porous Pavement

working from the bottom up

Supported Sides

Supported Sides

• Compact materials under

sidewalk and roads

• Light fluffy soil in bioretention

Aggregate Storage

• Can be used to increase storage

volume

• Open graded aggregate

• Load bearing

• Crushed concrete

• increases pH for years

• impedes vegetation growth

• Steffes R., Laboratory Study of the

Leachate From Crushed Portland

Cement Concrete Base Material, Iowa

DOT. MLR-96-4. September 1999.

Aggregate

• Water storage reservoir

• 30 to 40% void space

• Level bottom surface to

promote even infiltration

Other Types of Storage

• Manufactured

devices

• Plastic and

CMP arches

• Pipes

• Precast

concrete boxes

• Etc.

Filter or Choker Layer• Challenges

• Often specified wrong

• Common failure point of system due to clogging

• Information Needed• Grain size analysis of in situ soil

• Required drainage rates (permittivity of filter)

• Geotextiles (filtration, separation, stabilization, permanent erosion control, and silt fence)

• Aggregate Filter

• 𝐷15, 𝐶𝑜𝑎𝑟𝑠𝑒 𝑆𝑢𝑏𝑙𝑎𝑦𝑒𝑟 ≤ 5 ∗ 𝐷85, 𝑆𝑒𝑡𝑡𝑖𝑛𝑔 𝐵𝑒𝑑

• 𝐷50, 𝐶𝑜𝑎𝑟𝑠𝑒 𝑆𝑢𝑏𝑙𝑎𝑦𝑒𝑟 ≤ 25 ∗ 𝐷50, 𝑆𝑒𝑡𝑡𝑖𝑛𝑔 𝐵𝑒𝑑

• AASHTO Standard Specification for Geotextile Specification for Highway Application. M 288-06. 2011.

• Departments of the Army and the Air Force. Engineering Use of Geotextiles. TM 5-818-8, AFJMAN 32-130. 1995.

• Franks, C., A. Davis, and A. Aydilek. Geosynthetic Filters for Water Quality Improvement of Urban Storm Water

Runoff. ASCE Journal of Environmental Engineering. 2012.

• US Department of Agriculture, NRCS National Engineering Handbook Part 633. Chapter 26 Gradation Design of

Sand and Gravel Filters. 1994

Choker Layer

• Separation layer

between soil and

aggregate reservoir

• Material may be

aggregate or geotextile

Underdrain

• Optional based on infiltration capacity of in situ soil

• Purpose to ensure drainage

• 4-inch diameter or larger

• Types• Rigid PVC

• Flexible HDPE

• SmartDrain(www.smartdrain.com)

• May be paired for redundancy

• Clean-out fittings

• 45 deg bends

• Anti-seep collar, trench dam, clay dam

• Outlet is commonly used to control allowable discharge rate• Orifice end plate

• Valve to allow for flow adjustments

• Upturned elbow• Enhance nutrient removal

• Increase retention depth

Underdrain

• Location and elevation

• May connect to valve

Bioretention Areas(Determine BMP Function and Configuration)

Underdrain Outlet

Trench Dam, Anti-seep Collar, Clay Dam

• Keep retained water where

intended

• Water follows path of least

resistance

• Use along underdrain pipes

• Clay (Bentonite), plastic, concrete,

steel, etc.

Anti-seep collar

Photo: Liberty Nature Preserve

Anti-seep collar

Photo: Liberty Nature Preserve

Source:

The bottom• Level bottom preferred

• On slopes terrace the bottom or

use check dams / baffles

• In situ soil below stormwater

practices typically do not (should

not) be compacted before placing

aggregate and/or soil overtop

• Loosen and scarify soils

• Before planting

• Before placing aggregate or soil layer

Bottom

• Level bottom surface to

promote even infiltration

Hydraulic Restriction Layer

• 30 mil PVC Liner (ASTM D-7176)

• Concrete

• Clay (Bentonite)

Impermeable Liners

• Groundwater Recharge Zone

• Soil contamination is expected or present

• Karst geology presents risk of sinkhole formation

• Runoff from a stormwater hotspot

• Within 100 feet of a water supply well or septic drain field

• Within 10 feet of a structure/foundation

• Infiltrated water may interfere with utilities

• Requires an underdrain

WRAPPING UP DESIGN

Layout the BMPs

Locate Utilities

Common Design Mistakes

• Not understanding the tributary area (size and surface coverage)

• Inadequate inlet

• Sloped surface resulting in reduced infiltration and erosive velocities

• Wrong mulch, floats away and clogs the outlet

• Lack of pretreatment

• No soil tests

• Poor plant selection

• Overly complex

• No maintenance plan

• Wrong geotextile specified

CONSTRUCTIONPlanning

Typical Construction Sequencing

• Preconstruction Meeting

• Planning – schedule, RFIs, submittals,

• Site Preparation – major demolition and

excavation

• Concrete Work

• Hydraulic Controls – hydraulic restrictions,

drainage layer and underdrains

• Bioretention - media barrier, soil,

vegetation, mulch, and energy dissipation

• Porous pavement – aggregate and

pavement

• Testing

Construction Sequencing

Roadside rain garden construction

followed by adjacent retaining wall

construction

• Spoils from retaining wall construction

should not have been placed on rain

garden

• Protection of rain garden should have

occurred

• Improvement to sequence possible?

• Identified at preconstruction meeting?

Construction Planning

• Expect more Requests for Information

• Submittals commonly requested for:

• Aggregates

• Geotextiles

• Liners

• Soil media

• Mulch

• Vegetation

• Construction specifications should be specific

• Verify available materials – up to one month

lead time

• Order and stockpile materials where possible

Organic Matter

Material

Aged bark fines, hardwood chips,

leaf litter, or similar plant-derived

organic material. Studies have also

shown newspaper mulch to be an

acceptable additive (Kim et al.

2003; Davis 2007). Organic matter

should not include animal manure

or by-products.

Infiltration Rates 0.5 to 6 in/hr (1-2 in/hr

recommended for comprehensive

pollutant treatment and hydrologic

benefit; Hunt et al. 2012)

pH6 to 8

Cation Exchange

Capacity (CEC)Greater than 5 milliequivalents

(meq)/100 g soil

Phosphorus Total phosphorus should not

exceed 15 ppm

Substitutions and Certifications

• Check and certify before accepting

• Shop drawing submittals for all critical

components

• Watch out for substitutions (e.g. plants)

Is it washed? As-Built Certification

Drainage Area• Practices are sized for the drainage area

• Know the intended drainage area

• Field changes may necessitate design changes

Tributary Drainage Area

Bioretention

Curb Extension

Construction Equipment

75

Effects of

Compaction on

Infiltration Rates

• Decreased infiltration

• Decreased root growth

• Increased runoff

Source: Pitt R., S.E. Chen, S. Clark

75

2.40.260All other clayey soils (compacted and dry, plus all wetter conditions)

1.59.818Noncompacted and dry clayey soils

1.31.439Compacted sandy soils

0.41336Noncompacted sandy soils

COVAvg Infil (in/hr)

Number of tests

Source: R. Pitt, S.E. Chen, S. Clark

75

CONSTRUCTIONSoil Erosion and Sedimentation Control

Soil Erosion during Construction

• Keep soil erosion sediment off

• Aggregate storage reservoirs

• Planting soil

• Permeable pavements (all types)

• Bioretention is designed to work AFTER

construction is completed and the

watershed is STABLE

• Do not install if exposed soil is obvious

or surrounding drainage is not stabilized

• Use standard erosion and sedimentation

control measures to stabilize disturbed or

potentially erosive surfaces for onsite

and potential offsite sources

Not Protected Protected

Protect BMPs During Construction

December 09, 2014 LID Operation and Maintenance 79

CONSTRUCTIONGrading, Demolition, Excavation and Utilities

Concrete Work

Site Grading

• Protect Key Hydrologic

Features

• Areas of natural hydrologic

function

• Possible areas for

infiltration

• Establish Clearing and

Grading Limits

• Define the limits of clearing

and grading

• Minimize disturbance to

areas outside the limits of

clearing and grading

Footings, Retaining Walls, Structures

Inlets and Outlets

CONSTRUCTIONSubgrade Preparation

Protect Subgrade for Infiltration

• Consider leaving last 6 inches of soil in the base

• Finish excavation after concrete work complete

• Recommended in areas where fine sediment can clog the subgrade

NEVER Compact the Subgrade with Heavy Equipment

Soil Conditioning

Soil Conditioning• Create an environment where water can

infiltrate

• Favorable environment for plants to succeed

• Begins to restore soil structure & ecology

Source: Tyner 2009

Subgrade

compaction

Minimum

subgrade

treatment

Specification

Low Scarification Loosen the top 6 to 9 inches of subgrade using the teeth of an excavator

bucket (or comparable).

Low-Medium Ripping Using a subsoil ripper or metal bar, rip the subgrade to a depth of 9 to 12

inches, every 3 feet (on center).

High Trenching Excavate 1-foot-deep by 1-foot wide trenches into the subgrade, every 6

feet (on center). Fill the bottom of the trench with one-half inch of coarse

sand, and top off trench with washed aggregate (No. 57 stone or

comparable).

Infiltration Testing• During Construction

• Infiltration rate of in situ native soil

• Bottom of excavation

• Purpose: if not testing during design phase, provides

measured infiltration capacity of soil

• Immediately After Construction

• Purpose: baseline measurement for future comparisons

• Vegetated Areas

• Permeable Pavements

CONSTRUCTIONHydraulic Controls

Dams, baffles, hydraulic restriction layers, reservoirs, underdrains

Hydraulic Restrictions

Underdrain

• Pipe orientation

• Clean washed aggregate

• Pipe material and bends (45 deg)

• Trench dam / anti-sep collar

• Connections

Failure 1: Slotted pipe

with dirty drainage

aggregate

Failure 2: ‘Burrito-

wrapped’, 2 layers over

top, slowed flow

Photo credit: Andy Szatko

Underdrain Connection

CONSTRUCTIONBioretention

Inlets

• Proper elevation grading is paramount

• Practice design, drainage area and runoff volume are intricately linked

• Field changes may require design changes

• Inlets must let water in

Pretreatment

Inlet from street lower than

weir around sediment trap

Level Spreader

Weir not constructed level,

concentrates flow

Bioretention Soil

• Inspect Media

Bioretention Soil Placement

• Install in 6 to 12 inch lifts. Scarify the top of each lift before placing next lift.

• Compact each lift

• Soak with water, gently tamp or boot

• 80 to 85%

• Compaction Test Methods

• Bulk Density. Critical bulk density are different for each soil texture.

• Standard Proctor ASTM D 698. Readings are impacted by soil organic matter. Root growth impeded at 90%.

• Penetration Resistance Method. Not very accurate. 75-250 psi target. Root growth impeded at 400 psi..

• Where travel over installed soil is unavoidable, limit paths and scarify soil driven on

• If soil placed loose expect about 10% consolidation

Bioretention Surface Sloped

Unprotected During Construction

Notice drift on outlet

because surface is clogged

Infiltration Testing• During Construction

• Infiltration rate of in situ native soil

• Bottom of excavation

• Purpose: if not testing during design phase, provides

measured infiltration capacity of soil

• Immediately After Construction

• Purpose: baseline measurement for future comparisons

• Vegetated Areas

• Permeable Pavements

Storage Volume of Practice

• Drainage area equates to a volume of runoff

• Build practices to meet design volume

Category % of Design

Volume

% of Practices

in Category

Severely Undersized <-25% 28%

Moderately Undersized -25% to -10% 22%

Adequate -10% to 10% 17%

Moderately Oversized 10% to 25% 17%

Severely Oversized >25% 17%

Assessing the Accuracy of Bioretention Installation in

North Carolina (2011) B. Wardynski and W. Hunt.

Reference Elevation

• Fixed elevation

• Level

• Stable

• Grade from

• Intentional

• Maintenance friendly

CONSTRUCTIONPorous Pavement

Clean Washed Stone

Source: NCSU BAE

No. 57 No. 2

Aggregate

• Compact

• Surface graded smooth

• Angular not natural rounded

stone

Aggregate

• River rock

• Rolls

• Won’t compact

Transition Strip

Elevation

Pervious Concrete

• Inspect the mix when delivered

• Certified professional

• Test batch and panel

Pervious Concrete

Too wetToo dry

Pervious Concrete Placement

• Covered for 7 to 14 days to cure properly

Pervious Concrete Curing

Porous Asphalt

• Different mix design

• Same construction equipment

Wrong binder

Permeable Interlocking Pavers

• Setting bed

• Cut to fit

• Compact in place

• Fill joints

Washed No. 57 Stone

Pea Gravel

Pavers

Sequence

• Dirt can be removed

• Asphalt cannot

PARTING THOUGHTS

Michigan Ave, Lansing MI

• This garden holds the 25-year storm event

• 75% decrease in average annual runoff

• 2007

• Ultra-Urban

• 5-ft wide planter box style bioretention

• 30 bioretention gardens

• 7,631 square feet

• 4.1 acre tributary area

• 4 blocks, both sides

• ADA compliant

• Adaptable to community needs

Maine Mall Road, Portland ME

• 0.35 miles long

• AADT 16,750 vehicles per day

• Design hourly volume – 2412

• Percent heavy trucks – 5%

• Open graded friction course

• Asphalt treated permeable

pavement

• Reservoir stone 50 year storm

volume

• 2009

QUESTIONS AND

DISCUSSIONS

Daniel P. Christian, PE, D.WRESenior Project Manager, Water Resources

Dan.Christian@TetraTech.com517.316.3939