NCHRP 25-41 GUIDANCE FOR ACHIEVING VOLUME REDUCTION OF HIGHWAY RUNOFF IN URBAN AREAS August 10, 2016

Today’s Presenters

• Moderator Michael Fitch, Virginia Transportation Research Council

• Guidance for Achieving Volume Reduction of Highway Runoff in Urban Areas Eric Strecker, Geosyntec Consultants Aaron Poresky, Geosyntec Consultants

NCHRP is...

A state-driven national program

• The state DOTs, through AASHTO’s Standing Committee on Research... – Are core sponsors of NCHRP

– Suggest research topics and select final projects

– Help select investigators and guide their work through oversight panels

NCHRP delivers...

Practical, ready-to-use results • Applied research aimed at state

DOT practitioners • Often become AASHTO

standards, specifications, guides, manuals

• Can be directly applied across the spectrum of highway concerns: planning, design, construction, operation, maintenance, safety

A range of approaches and products • Traditional NCHRP reports • Syntheses of highway practice • IDEA Program • Domestic Scan Program • Quick-Response Research for

AASHTO • Other products to foster

implementation: – Research Results Digests – Legal Research Digests – Web-Only Documents and CD-ROMs

NCHRP Webinar Series • Part of TRB’s larger webinar

program • Opportunity to interact with

investigators and apply research findings.

Today’s Presenters

• Eric Strecker and Aaron Poresky, Geosyntec Consultants

NCHRP 25-41

GUIDANCE FOR ACHIEVING VOLUME REDUCTION

OF HIGHWAY RUNOFF IN URBAN AREAS

Various regulatory trends and current motivators towards reduction of surface runoff volume (i.e., volume reduction)

Agencies’ desire to get “out in front” of trends to help inform policy, guide program development and limit unintended impacts

Need for practical guidance that could be adopted or adapted as part of local guidance

IMPETUS FOR PROJECT

NCHRP 25-41 PROJECT GOALS

Provide national-scale guidance on identifying constraints and assessing the feasibil ity of controll ing runoff volumes in the urban highway environment

Identify and/or develop a menu of potentially suitable volume reduction approaches (VRAs)

Provide a framework for selecting and conceptually designing VRAs for specific site and project conditions

Develop simple tools to predict and compare volume reduction performance of VRAs

Guidance Manual (NCHRP Report 802)

Technical Appendices VRA Fact Sheets Infiltration Testing Groundwater Quality and

Water Balance Geotechnical Issues Permeable Pavements

Volume Performance Tool (Spreadsheet) and User ’s Manual

PROJECT OUTCOMES

Project Officer:

Chris Hedges, NCHRP

Project Panel:

Mike Fitch, Chair, Virginia DOT

Brian Beucler, FHWA

David Ahdout, New Jersey DOT

Kristin Schuster, Michigan DOT

Mark Maurer, Washington State DOT

Meredith Upchurch, District of Columbia DOT

Paul Wirfs, Oregon DOT

Scott Taylor, RBF Consulting

Research Team

Geosyntec Consultants, Eric Strecker and Aaron Poresky

The Low Impact Development Center, Neil Weinstein

Venner Consulting, Marie Venner

NCHRP PANEL AND RESEARCH TEAM

High efficiency of pollutant removal compared to many treatment BMPs

Combined benefits of pollution and hydrologic control, plus groundwater recharge where applicable

Effective as an element in a treatment train

VRA = Volume Reduction Approach

WHY VOLUME REDUCTION?

LA Times (June 25, 2015) DWP to unveil plan to capture storm runoff http://www.latimes.com/local/california/la-me-stormwater-plan-20150625-story.html

EXAMPLE VOLUME REDUCTION APPROACHES

Vegetated conveyances

Dispersion (natural, engineered)

Media filter drains

Permeable pavement shoulders

Bioretention without underdrains

Bioretention with underdrains

Inf i l trat ion trenches

Inf i l trat ion basins

Underground inf i l trat ion systems

Volume reduction primarily based on infiltration, supported by evapotranspiration in some VRAs

Available space, set back from roadway and structures

Permeable to moderately permeable soils

Adequate subsurface capacity for additional infiltration

Groundwater table well below infrastructure

Groundwater recharge desirable

Shallower slopes

Absence of soil or GW contamination

Absence of geotechnical hazards

Setbacks from utilities and wells

At or near original grade

Isolated from major sediment sources

Incorporated into conveyance or flow control features

FAVORABLE CONDITIONS/OPPORTUNITIES

Limited space and lack of permeable soils in many projects

Site-specif ic condit ions appropriately inf luence many planning and design decisions

Uncertainty of success unti l implementation

Increasingly, volume reduction is a f irst and mandatory consideration

Limited ful l scale experience with VRAs, part icularly whole l i fecycle costs and maintenance

KEY CHALLENGES

On-site Retention BMPs

Example: Infiltration trench

On-site Biotreatment BMPs

Example: stormwater planter

Subregional/Regional Retention BMPs

Example: groundwater recharge basin

Subregional/Regional Biotreatment BMPs

Example: constructed wetland

Typical BMP selection hierarchy in California and other MS4 permits beginning circa 2009

ORANGE COUNT Y EXAMPLE

C O N TA M I N AT E D S O I L S / P L U M E S , D E P T H T O G W + A / B + N AT U R A L P L U M E S + C O N TA M I N AT E D S I T E S + I N D U S T R I A L L A N D U S E + S T E E P S LO P E S

EVAPOTRANSPIRATION- SPATIAL WATER BALANCE CONSIDERATIONS

Bioretention Areas

Natural Conditions Developed Conditions with VRAs

Imperviousness = 0%

1” Rainfall = 1” Over Pervious Surface Shallow localized ponding

Unsaturated infiltration dominates “Sponge” area ≈ watershed area

Imperviousness = 50%; BMP = 5%

1” Rainfall ≈ 10” Over SCM Concentrated ponding in SCM

Unsaturated and saturated infiltration “Sponge” area = SCM area

GENERAL WATER BALANCE IMPACTS

ET fraction estimated as 83-97% in Southern California Chaparral.1

1 Ng and Miller (1980) Soil Moisture Relations in the Southern California Chaparral. Ecology, Vol. 61, No. 1. (Feb., 1980), pp. 98-107

REGIONAL VARIABILITY IN WATER BUDGET Location: Annual Fluxes: Source: Northwest (Cascade Mountains); The two study watersheds adjoin each other in the upper McKenzie River watershed on the west side of the Oregon Cascades

Runoff and Baseflow = 70%; ET = 30%; Water Storage Change = 0%

Jefferson et. al., 2008

East of the Rocky Mountains Runoff and Baseflow = 27%; ET = 73%; Water Storage Change = 0%

Mill, 1994

Texas Runoff = 12.5 %; ET = 86 %; Recharge = 1.5%

Ward, 1993

South Eastern US: five-state study area (Georgia, South Carolina, North Carolina, Virginia, and Maryland)

Runoff and baseflow = 37%; ET and Recharge = 63%

Rose, 2009

Susquehanna River Basin Runoff and Baseflow = 49%; ET = 51%; Water Storage Change = 0%

Najjar, 1999

The Baptism River watershed in northern Minnesota. The watershed is heavily timbered with both deciduous and coniferous trees.

Runoff and Baseflow = 55% Mohseni & Stefan, 2001

The Little Washita River watershed in Oklahoma. One third of the watershed is cultivated and the rest is either pasture or wooded pasture.

Runoff and Baseflow = 7% ET and Recharge = 93%

Mohseni & Stefan, 2001

North Eastern US Runoff and Baseflow = 55% ET and Recharge = 45%

Church et al. 1995

Southern California Chaparral (average of two years of monitoring)

South facing: Runoff and Baseflow = 3%; ET = 97% North facing: Runoff and baseflow = 9%, ET = 83% and storage change = 8%.

Ng & Miller, 1980

POTENTIAL HABITAT CHANGES

Dry Ephemeral Stream

Perennial Stream

Infiltration Increased over Natural Levels

EFFECTIVENESS OF VRAS

Storage Volume: How much of the first storm can the VRA capture and manage?

Treatment /Loss Rate: How much of the next storm (and the next and the next…) can the VRA capture and manage?

Emerson, 2008 (Dissertation, Villanova)

Strecker and Poresky, 2009 (Water Report)

Storage volume and loss rate are both important

EFFECTIVENESS OF VRAS

Highway Geometric Design Standards

Vegetation and Landscaping Standards

Drainage and Flood Control

Construction practices conducive to successful VRA installation and long-term operation

OTHER HIGHWAY DESIGN REQUIREMENTS

Hydrology and VRA Design

Infiltration rates

Geotechnical

Hydrogeology

Utilities/ sanitary sewer

Groundwater protection

Pavement design

Vegetation selection and management

Geometric design and

vehicle safety

POTENTIAL INVESTIGATIONS AND DESIGN CONSIDERATIONS/COORDINATION

Effective site characterization

Early identif ication of suitable opportunit ies

Realist ic assessment of constraints and l imitat ions Limits of site

Regulatory limits

Limits of knowledge (e.g., future soil properties following construction)

Selection of VRAs compatible with opportunit ies and constraints Geometric compatibility

Infiltration feasibility

Need for adaptability/resiliency

Tools/framework for evaluating alternatives

KEYS TO ACHIEVING VOLUME REDUCTION

• Is it physically possible to implement a certain VRA based on the site conditions?

Can you do it?

• Would the use of a certain VRA have the potential to result in undesirable physical consequences on the project or the site environs?

Should you do it? If so, how much

should you do?

• Does the cost required to construct the VRA and/or mitigate potential risks posed by the VRA outweigh the volume control benefits it would achieve?

If you do it, do it carefully.

FEASIBILITY AND DESIRABILITY FRAMEWORK

Chapter 1 – Introduction

Chapter 2 – Stepwise Approach for Incorporating Volume Reduction: How to Use This Manual

Chapter 3 - Volume Reduction in the Urban Highway Environment

Chapter 4 – Volume Reduction Approaches

Chapter 5 – Selecting and Applying Volume Reduction Approaches

GUIDANCE MANUAL CONTENTS AND ORGANIZATION

Appendix A – VRA Fact Sheets

Appendix B – Users Guide for the Volume Performance Tool

Appendix C – Infi ltration Rates and Factors of Safety

Appendix D – Water Balance and Groundwater Quality

Appendix E – Geotechnical Considerations

Appendix F – Permeable Pavement Considerations

GUIDANCE MANUAL CONTENTS AND ORGANIZATION

Intended Users

DOT managers Permit writers

Consultants and planners

DOT project staff and design

engineers

Potential Uses

Understanding the technical basis of volume reduction requirements and setting

volume reduction goals

Providing a framework for discussion with regulators about technical feasibility and

desirability

Scoping the analyses necessary for incorporating VRAs into the project design

process

Understanding potential design implications of volume reduction goals

Refining project-specific estimates of achievable volume reduction

Conducting site assessment and feasibility analyses

Prioritizing, selecting, and applying VRAs

Plan

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Mana

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STEPWISE APPROACH FOR INCORPORATING VOLUME REDUCTION

Step 1 Establish Volume Reduction Goals

Step 3 Identify Potentially Suitable VRAs

Step 4 Prioritize VRAs from Screened Menu

Step 2 Characterize Project Site and Watershed

Step 5 Select VRAs and Develop Conceptual Designs

Manual Reference Example Stepwise Process

Step 1 Establish Volume Reduction Goals

Step 3 Identify

Potentially Suitable VRAs

Step 5 Select VRAs and

Develop Conceptual

Designs

Step 2 Characterize

Project Site and Watershed

Understand regulatory context

Identify resource protection needs

Understand factors influencing volume

reduction

Conduct preliminary screening of applicability

Develop preliminary site

plans

Select VRAs

Develop conceptual

designs

Estimate performance and cost; compare to

goals

Identify highway and project type

and related factors

Obtain available information and coordinate with

applicable parties

Conduct site assessments

1.2 and 3.1 – Regulatory Setting 3.2 – Key Factors in Volume Reduction 3.3 – Urban Highway Types 3.4 – Site Assessment

3.4 – Site Assessment 4.0 – Volume Reduction Approaches Appendix: VRA Fact Sheets 5.2 – Initial Screening to Identify Potential VRAs

5.4 – Conceptual Design Development 4.4 – Additional Resources for VRA Design and Maintenance Information

3.2 – Key Factors in Volume Reduction 3.3 – Urban Highway Types 3.4 – Site Assessment

Refin

e goa

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Step 4 Prioritize VRAs from Screened

Menu

Consider additional factors to differentiate between potentially

suitable VRAs

Weight and score factors to identify high

priority VRAs

5.3 – Prioritizing Approaches from Screened Menu of VRAs

Conduct preliminary screening of

feasibility and desirability

Overall stormwater management objectives: Manage pollutant loads Maintain recharge Control hydrologic impacts

Regulatory context: Absolute volume reduction

requirements vs. Volume reduction to MEP

vs. Opportunistic volume

reduction

STEP 1: ESTABLISH VOLUME REDUCTION GOALS

Topography and Drainage Patterns

Off-Site Drainage and Adjacent Land Uses

Soil and Geologic Condit ions

Groundwater Considerations

Geotechnical Considerations

Existing Uti l i t ies

Harvested Water Demand Assessment

Responsible Agencies and Other Stakeholders

Watershed-based and Other Joint Planning Opportunit ies

STEP 2: SITE ASSESSMENT ACTIVITIES

Planning Phase Assessment

Where within my project area are VRAs potentially feasible?

What VRAs are potentially suitable for my project?

Design Phase Assessment

What design parameters should I use to design volume reduction facilities?

Is the design safe? How does the design mitigate unacceptable levels of risk?

Is the design protective of potential unintended consequences for other media?

STEP 2: SITE ASSESSMENT ACTIVITIES

Larger area of interest

More focused area of interest

More efficient methods and

analyses

More rigorous

methods and analyses

Appendix C – Infi ltration Rates and Factors of Safety

Appendix D – Water Balance and Groundwater Quality

Appendix E – Geotechnical Considerations

SUPPORTING APPENDICES

STEP 3: IDENTIFY POTENTIAL VRAS

Site Design / Project Type Site Characteristics Watershed

Characteristics

Evaluate VRA Applicability [Section 5.2.2)

Which VRAs are potentially applicable for the project?

Evaluate Feasibility

and Desirability

(Section 5.2.3]

Which VRAs are potentially feasible and desirable for the project?

Early Identification of VRA Opportunity Locations

Develop Drainage, Grading, and Util ity Configurations to Accommodate VRA Opportunity Locations

Limit Footprint of Disturbance

Minimize Non-Essential Impervious Surface

Conserve and/or Amend Topsoil

SITE DESIGN APPROACHES

Looped Interchanges

Diamond Interchanges

Irregular ROW

Shoulder Outside of Clear Zone

Shoulder Inside of Clear Zone or Breakdown Lane

Median or Inside Breakdown Lane

VRA FACT SHEETS (APPENDIX A)

Geometric Siting Opportunity VRA

01

Veg

etat

ed

Conv

eyan

ce

VRA

02

Disp

ersio

n

VRA

03

Med

ia Fi

lter D

rain

VR

A 04

P

erm

eabl

e Sh

ould

ers

VRA

05 B

iore

tent

ion

w/o

unde

rdra

in

VRA

06 B

iore

tent

ion

with

und

erdr

ain

VRA

07

Infil

tratio

n Tr

ench

es

VRA

08

Infil

tratio

n Ba

sins

VRA

09

Infil

tratio

n Ga

llerie

s

Medians X X X X X X

Shoulders, including breakdown lane and area within Clear Zone (less than approx.15% or 6H:1V)

X X X X X X

Shoulders, outside of Clear Zone (less than approx.15% or 6H:1V)

X X X X X X X

Moderately Steeper Shoulders (steeper than approx.15% or 6H:1V but less than approximately 25% or 4:1)

X

ROW Locations with Limited Uses (i.e., wide spots, irregular geometries)

X X X X X X X X

Adjacent Natural Areas X

Looped Interchange Medians X X X X X X X X

Diamond Interchange Medians X X X X X X X X

Low Traffic Areas - Maintenance Yards, etc. X X X1 X X X X X

GEOMETRIC SITING OPPORTUNITIES

STEP 3 (CONTINUED): EVALUATE FEASIBILITY AND DESIRABILITY

Site Design / Project Type Site Characteristics Watershed

Characteristics

Evaluate VRA Applicability [Section 5.2.2)

Which VRAs are potentially applicable for the project?

Evaluate Feasibility

and Desirability

(Section 5.2.3]

Which VRAs are potentially feasible and desirable for the project?

INFILTRATION FEASIBILITY AND DESIRABILITY CATEGORIES

Category 3: Infiltration not Recommended/Allowed

Category 1: Full Infiltration

Category 2: Marginal/ Partial Infiltration

• Consider VRAs that provide full infiltration • Conduct more rigorous site-specific analysis as part of design

(and potentially construction) to confirm that full infiltration is feasible and desirable

• Include provisions to allow designs to be adapted to Category 2 if actual conditions different than planned.

• Select VRAs that provide opportunity for partial infiltration and supplemental discharge

• Design VRAs to be adaptable for range of actual conditions

• Do not use infiltration • Consider VRAs based on harvest and use (limited feasibility

for DOTs) and/or ET

VRA

Total Relative Volume

Reduction Potential

Relative Portion of Losses to

Deeper Percolation in

Typical Conditions

Relative Potential to

Infiltrate More than

Natural

Possible to Adapt for Marginal Conditions?

VRA 01 Vegetated Conveyance L/M L/M L/M Yes, inherent VRA 02 Dispersion M/H L/M L/M Yes, inherent VRA 03 Media Filter Drain M/H L/M L/M Yes, by design VRA 04 Permeable Pavement M/H M/H M/H Yes, by design VRA 05 Bioretention w/o underdrain H M/H M/H No VRA 06 Bioretention with underdrain M/H M/H L/M Yes, by design VRA 07 Infiltration Trenches H H M/H Not easily VRA 08 Infiltration Basins H H M/H Not easily VRA 09 Infiltration Galleries H H M/H Not easily

SUMMARY OF VOLUME REDUCTION MECHANISMS AND ADAPTABILITY

STEP 4: PRIORITIZE VRAS

Screened List of Potential VRAs

Prioritize Approaches from Screened Menu of VRAs [Section 5.3]

Relative O&M Impact to Agency Relative Cost Relative Reliability

and Safety

Screened and Prioritized VRAs

Relative Performance

Routine Maintenance Activities VRA

01

Veg

etated

Co

nvey

ance

VRA

02

Disp

ersio

n

VRA

03

Med

ia Fil

ter D

rain

VRA

04

Per

meab

le Sh

oulde

rs VR

A 05

B

iorete

ntion

w/o

unde

rdra

in VR

A 06

B

iorete

ntion

with

un

derd

rain

VRA

07

Infilt

ratio

n Tr

ench

es

VRA

08

Infilt

ratio

n Bas

ins

VRA

09

Infilt

ratio

n Ga

llerie

s

Mowing

Maintain Level Spreading Functions

Landscaping and Weeding

Routine Woody Vegetation Management

Sediment Removal/ Management

Vacuum Sweeping

Trash and Debris Removal

Erosion Repair

Rodent Hole or Beaver Dam Repair

Fence or Access Repair

EXAMPLE COMPARISON TABLE: ROUTINE MAINTENANCE BY VRA

Key: Primary maintenance activity; Minor maintenance activity; may not apply in some cases or may be limited; Not usually applicable

Screened and Priortized VRAs (From Section 5.2 and 5.3)

Analyze Volume Reduction Performance

and Cost (5.4.3, 5.4.4, 5.4.5)

Compare Performance and Cost to Project Goals

Develop Initial Conceptual Designs (5.4.2)

Develop Volume Reduction Design

Goals Not Met

Goals Met

Adapt Conceptual Design and/or Goals,

as needed (5.4.6)

Other Guidance Manual content: Introduction to

Volume Performance Tool and potential uses

Options for increasing performance and/or reducing costs

STEP 5: DEVELOP AND EVALUATE CONCEPTUAL DESIGN

Consider sensitivity to key parameters

Checklists and Worksheets Site assessment Suitability screening Feasibility screening VRA prioritization

Conceptual Design Tools Volume Performance Tool Conceptual design schematics Whole lifecycle cost forms

PRACTICAL TOOLS FOR DOT USERS (AND OTHERS)

Based on long term VRA performance of 344 rain gauges Uses pre-calculated

nomographs from SWMM modeling to optimize tool performance Provides planning level long

term hydrologic VRA performance without the need for more detailed long-term modeling

Can simulate treatment train performance

VOLUME PERFORMANCE TOOL

Inputs Location-specific climate data Tributary data (area, % impervious, Soil

type) Specific VRA data (type and design

attributes specific to that VRA)

Resul ts Baseline Average Annual Runoff

Volume with no VRAs Reduction in Runoff Volume Captured, Treated, and Released Runoff Volume Bypassed

VOLUME PERFORMANCE TOOL

Olympia, WA Nomograph Providence, RI Nomograph

Two nomographs generated by the tool showing the same VRA and tributary area in different locations

Behind the scenes:

PROJECT LOCATION TAB

Navigation Bar

Project-specific Information

Climate Region Select

Precipitation Gage Select

344 climate divisions supported for the conterminous US; allows adjustment for climate variations within division

PROJECT DESIGN TAB

Tributary Area Input Parameters

VRA DESIGN

VRA design parameters

Embedded schematic to explain VRA design

parameters Option to add second VRA in treatment

train

Overall approach: Enter parameters to describe location, watershed and VRA obtain near real-time estimate of volume performance and capture efficiency

Average long term estimates: Volume Reduction Capture Efficiency Bypass

Reported as volume per year and relative percentages

VOLUME PERFORMANCE SUMMARY

SENSITIVITY ANALYSIS

Select VRA design parameters and define sensitivity

bounds

Tool generates “bow-tie plot” to compare sensitivity of key parameters

Many factors influence the feasibil ity, desirability, and effectiveness of volume reduction and selection of VRAs

A defined process can help organize activities and produce consistent/defensible decisions

Adaptability and resil iency in BMP selection is important where there is increasing pressure to achieve volume reduction in marginal environments

Volume performance tool allows evaluation of effectiveness and sensitivity

KEY OUTCOMES/FINDINGS

NCHRP 25-51: Limitations of the Infiltration Approach to Stormwater Management in the Highway Environment

Build upon previous research: Volume reduction (NCHRP 25-41) Whole lifecycle cost and performance (NCHRP 25-40) Ultra-urban BMPs (NCHRP 25-31)

Incorporate field-scale case studies/lessons learned

More in-depth research into limits, particularly in the highway prism

Identif ication and evaluation of more adaptable/resil ient design and construction approaches

More detailed investigation and design guidance

FUTURE WORK