NCHRP 25-25(92)
Transferability of Post-Construction Stormwater
Quality BMP Effectiveness Studies
Project Objectives
 Identify and review transportation-related BMP
performance monitoring studies and existing BMP
assessment protocols
 Evaluate conditions and factors influencing the
transferability of BMP performance monitoring results
 Investigate the feasibility of establishing a central
repository (BMP Database) for DOT post-construction
stormwater
Transferability of Post-Construction Stormwater Quality BMP
Effectiveness Studies (NCHRP25-25, Task 92)
Report Organization
1. Introduction and Background
2. Survey of State Practices and Literature/Data Review
3. Effect of Geographic and Other Variables on BMP
Performance
4. BMP Effectiveness Standardization Considerations
5. Resources Needed to Develop a BMP Database Portal
for State DOTs
6. Summary and Conclusions
Survey of State Practices and
Literature/Data Review
Existing BMP Acceptance/Assessment Protocols
 Technology Assessment Protocol―Ecology (TAPE)
 Washington Department of Ecology (Active; adopted by many)
 Technology Acceptance and Reciprocity Partnership (TARP)
Protocol for Stormwater BMP Demonstrations
 Endorsed by California, Massachusetts, Maryland, New Jersey,
Pennsylvania, and Virginia (Partnership dissolved, but protocols
still used in many states)
 Environmental Technology Verification (ETV) Program
 EPA Office of Research and Development (Inactive)
 Stormwater Testing and Evaluation for Products and Practices
(STEPP)
 Water Environment Federation (WEF) and American Public Works
Association (APWA) (In development)
TAPE Summary
 Minimum Hydrologic Performance: Capture 91% of long-term runoff
 Five Treatment Categories
 Pretreatment : TSS removal 50% or achieve ≤50 mg/L
 Basic: TSS removal 80% TSS or achieve ≤20 mg/L
 Enhanced: DCu removal 30% or achieve ≤5 µg/L and
DZn removal 60% or achieve ≤20 µg/L
 Phosphorus: TP removal 50% or achieve ≤0.1 mg/L
 Oil: no visible sheen, TPH max ≤10 mg/L, daily average ≤10 mg/L
 Three Designated Use Designations
 General Use Level Designation (GULD)
 Conditional Use Level Designation (CULD)
 Pilot Use Level Designation (PULD)
Note: Capture = Amount of runoff managed for volume and/or water quality
TARP Summary
 General Acceptance Criteria
 A minimum of 15 storm events per monitoring location
 At least 50% of the annual average rainfall sampled for a
minimum of 15 inches of precipitation.
 Average particle size: mean < 100 microns; approximate TSS
distribution: 55% sand, 40% silt, and 5% clay
 TSS influent concentration: 100 – 300 mg/L
 Flows with a range up to 125% of design capacity
 Scour tests
 Participating states have additional requirements
ETV Summary
 A public-private partnership between EPA and nonprofit
testing and evaluation organizations, verified the
performance of innovative technologies
 No longer funded
 Latest protocol (Draft 4.1) was developed in 2002
 Program stopped taking applications in 2013
 Operations concluded in early 2014
STEPP Summary
 On Feb 6, 2014, WEF's Stormwater Testing and Evaluation for Products and
Practices (STEPP) Task Force released a white paper identifying the need
and challenges of developing a national program
 Alternative program structures
 Testing and Evaluation
 Certification
 Regional Standards
 Non-Programmatic Verifications
 Market-Based Verifications
 Alternative funding mechanisms
 Public-private partnership
 Fee-for-service
 Grants
 Subscriber/membership
DOT BMP Certification and Evaluation
Practices
 Caltrans: Uses Stormwater Advisory Teams (SWATs) to evaluate
new technologies submitted; Treatment BMP Technology Report,
updated annually, lists BMP approved or considered for pilot study.
 MassHighway: Acceptable protocols include those from the
Massachusetts Strategic Envirotechnology Partnership (STEP),
TARP, and ETV. Stormwater Policy Handbook updated with
approved BMPs.
 New Jersey: Certification requires verification of pollutant removal
rates by N.J. Corporation for Advanced Technology (NJCAT),
another TARP state, or third party testing organization. Acceptable
BMPs are listed in the NJDEP Stormwater Best Management
Practices Manual.
DOT BMP Certification and Evaluation
Practices (cont.)
 Oregon DOT: Proprietary BMP must have TAPE certification. BMPs
not listed as “preferred” in the Hydraulics Manual must be approved
by Hydraulic Engineering staff.
 Virginia DOT: Evaluation based on TARP protocols and Virginiaspecific requirements. Virginia’s Department of Conservation and
Recreation (DCR) Stormwater Management Handbook lists
approved BMPs.
 Washington DOT: Requires TAPE certification. Acceptable BMPs
listed on the Highway Runoff Manual.
Existing National Scale Stormwater
Databases and BMP Study Clearinghouses
 International Stormwater BMP Database (BMPDB) – relational BMP
design and performance database that is actively populated,
analyzed, and maintained
 National Stormwater Quality Database (NSQD) – land use based
water quality data set that include highway runoff data
 FHWA/USGS National Highway Runoff Database (HRDB) - relational
database focused on highway runoff; used as a preprocessor for the
Stochastic Empirical Loading and Dilution Model (SELDM)
 EPA’s Green Infrastructure Webpage – not a database, but provides
links to databases and BMP performance summary reports and tools
 Center for Watershed Protection (CWP) National Pollutant Removal
Performance Database – focuses on percent removal with limited
BMP design information; database not available online; findings are
primarily disseminated through interpretive reports prepared by CWP
Other Links to BMP Studies and Research
Washington State DOT: http://www.wsdot.wa.gov/Environment/WaterQuality/Research/
Caltrans Monitoring & Research and Applied Studies:
http://www.dot.ca.gov/hq/env/stormwater/special/newsetup/#monitoring
Washington Stormwater Center : http://www.wastormwatercenter.org/
VA Stormwater BMP Clearinghouse: http://vwrrc.vt.edu/swc/index.html
Villanova Urban Stormwater Partnership (VUSP):
http://www1.villanova.edu/villanova/engineering/research/centers/vcase/vusp1.html
North Carolina State University: http://www.bae.ncsu.edu/stormwater/pubs.htm
University of Maryland/ Mid-Atlantic Water Program:
http://archive.chesapeakebay.net/pubs/bmp/BMP_ASSESSMENT_FINAL_REPORT.pdf
http://www.ence.umd.edu/~apdavis/LID-Publications.htm
University of Minnesota: http://stormwater.safl.umn.edu/
University of New Hampshire (UNH) Stormwater Center: http://www.unh.edu/unhsc/
Delaware DOT: https://www.deldot.gov/stormwater/publications.shtml
National LID Clearinghouse: http://www.lid-stormwater.net/clearinghouse/
Green Highways Program: http://www.lowimpactdevelopment.org/green_highways.htm
USGS Transportation-Related Research: http://water.usgs.gov/osw/TRB/index.html
University of Central Florida Stormwater Management Academy: http://www.stormwater.ucf.edu/
Literature Review
Research Category
Number of Studies
Reviewed
Capture Efficiency
5
Climatic and Meteorological Factors
9
Design Variables and Unit Treatment Processes
8
Hydro-modification Performance
3
Long-Term Pollutant Retention
1
Maintenance
9
Runoff Quality Characterization
27
Treatment Trains
1
Volume Reduction Performance
9
Water Quality Performance
44
TOTAL
116
Literature Review (cont.)
BMP Type
Available Studies from
Literature Search
Bioretention
9
Constructed & Pocket Wetlands
5
Dry Detention Basins
12
Infiltration Trenches/Basins
7
Manufactured Device
17
Permeable Pavement
7
Wet Retention Ponds
10
Sand/Media Filter
14
Vegetated Swales & Filter Strips
19
Wetland Basin/Channel
2
Geographic Distribution of BMP
Performance Studies Identified in Literature
EPA Rainfall Zone Number
Source: NPDES Phase I regulations, 40 CFR Part 122, Appendix E (USEPA 1990)
Studies
Found
Zone 1 - Great Lakes
12
Zone 2 - Northeast
8
Zone 6 - Southwest
7
Zone 3 - Southeast
6
Zone 7 - Northwest
5
Zone 5 - Texas
3
Zone 9 - Rocky Mountain
2
Overview of Studies and Data in the BMPDB
Total number of studies
Total number of transportation-related studies
Total number of states represented
Total number of states represented in
transportation-related studies
Highest number of studies for any one state
Highest number of transportation-related
studies for any one state
Total number of states with no studies
Total number of BMP types in all studies
434
126
23
10
78 (FL)
66 (CA)
27
12
Number of Transportation-Related Studies in BMPDB
State
BMP Type
Bioretention
Dry Detention
Basins
Filter Strips
Manufactured
Device
Permeable
Pavement
Retention Ponds
CA
DE
FL
MD
MN
NC
TX
1
1
34
9
WA
WI
1
5
3
7
1
11
Vegetated Swales
6
2
4
12
2
1
40
1
3
1
3
1
2
6
2
Wetland Basin
1
66
9
9
21
1
2
Wetland Channel
TOTAL
2
1
Sand/Media Filter
Total
VA
1
15
10
24
5
5
2
1
1
8
3
6
24
1
1
126
Effect of Geographic and
Other Variables on BMP
Effectiveness
Overview of Factors Affecting BMP
Performance
 BMP performance is influenced primarily by influent characteristics
and BMP unit operations and processes (UOPs)
 Both of these factors are affected by geographic variables such as
climate, soils, topography, and on-site and surrounding land uses
 Primary UOPs provided by stormwater BMPs include
 Hydrological/Hydraulic: flow attenuation/storage and surface
runoff volume reduction (infiltration)
 Physical Treatment: filtration and settling/sedimentation
 Chemical Treatment: sorption and coagulation/flocculation
 Biological: microbially-mediated transformation and plant uptake
Climate and Hydrology Effects
 Differing rainfall intensity-duration-frequency can affect pollutant
mobilization and hydraulic loading rates
 Differences in evapotranspiration, soil moisture, temperature and
other related factors that affect types and success of vegetation in
stormwater systems
 Temperature can affect viscosity of water which can affect infiltration
rates and particle settling
 Seasonality can affect the growing season, nutrient cycling in
vegetative communities, seasonal groundwater levels, and
decay/decomposition
 Presence or absence of snow and frozen surfaces due to changes in
temperature and differences in snow melt characteristics due to
variations in sunshine, precipitation, temperature, and wind.
Distribution of Average Annual Precipitation
(1981-2010)
Source: PRISM, Oregon State University, 2013
Distribution of Normal Mean Annual
Temperature (1981-2010)
Source: PRISM, Oregon State University, 2013
Median Highway Runoff
Concentrations by EPA Rain Zone
Median Highway Runoff Event Mean Concentration by EPA Rainfall
Zones
Constituent
1
2
3
4
30.7
5
6
7
83.9
81.1
51.3
TSS (mg/L)
134.1
38.9
TKN (mg/L)
2.02
1.81
1.58
1.75
1.03
NOx (mg/L)
0.83
1.43
0.90
0.62
0.26
TP (mg/L)
0.12
0.42
0.09
0.19
0.23
0.12
DP (mg/L)
0.05
0.10
0.04
0.13
0.08
TCu (µg/L)
46.1
18.7
15.9
6.00
28.7
11.0
TPb (µg/L)
12.2
72.3
3.24
58.9
15.5
4.74
TZn (µg/L)
193
108
85
58.8
154
70.1
COD (mg/L)
90.2
133
39.3
57.3
179
66.3
1883
2287
FC (MPN/100 mL)
2095
109
8
101
9
294
Data Source: National Stormwater Quality Database (NSQD) and Highway Runoff Database (HRDB) - Post 1983 data only
TSS Concentrations by Rain Zone
NOx Concentrations by Rain Zone
Total Phosphorus Concentrations
by Rain Zone
Total Copper Concentrations by
Rain Zone
Soils and Topography Effects
 Soils vary in their degree of compaction, hydraulic conductivity, pH,
erodability, particle density/size distribution, cohesion, pollutant
sorption characteristics, and ability to retain water
 All of these factors can affect stormwater runoff composition and
UOPs within BMPs
 Soils that are more easily erodible by wind can be blown onto
impervious surfaces resulting in increased TSS levels and
associated pollutants in runoff
 Steeper slopes increase the velocity of runoff and the mobilization of
pollutants
Traffic Volumes and Adjacent Land Uses Effects
 Traffic volumes and adjacent land use activities can directly influence
the quantity and quality of stormwater runoff influent to a BMP
 Concentration of TSS, TKN, NOx, TP, TCu, TPb, and TZn tend to
increase as the average annual daily traffic (AADT) increases, but
TSS and TP correlations to AADT are weak
 High traffic volume areas are typically in highly urbanized areas, so it
is difficult to determine whether pollutant concentrations are due to
traffic or adjacent land uses or both
 Pollutants without a significant source from vehicular or road
construction materials are likely more affected by adjacent land uses
Median Runoff Concentrations by AADT
Constituent
TSS
(mg/L)
TKN
(mg/L)
NOx
(mg/L)
TP
(mg/L)
TCu
(µg/L)
TPb
(µg/L)
TZn
(µg/L)
COD
(mg/L)
FC
(MPN/100mL)
Medians (90%Confidence Intervals) by AADT Category
0 - 30K
44.0
(36.3 - 52.0)
1.03
(0.85 - 1.18)
0.24
(0.20 - 0.29)
0.12
(0.10 - 0.13)
9.81
(8.20 - 11.00)
4.85
(3.51 - 5.56)
55.0
(48.48 - 62.50)
49.3
(43.0 - 54.0)
5,418
(300 - 13,000)
30 - 90K
63.5
(53.9 - 67.0)
1.66
(1.50 - 1.75)
0.66
(0.60 - 0.71)
0.18
(0.15 - 0.19)
21.2
(17.03 - 22.00)
9.13
(7.33 - 10.88)
113
(100.00 - 125.00)
108
(84.5 - 118.5)
No Data
90K +
100
(91.4 - 107.0)
2.15
(1.96 - 2.39)
1.10
(0.85 - 1.18)
0.24
(0.22 - 0.26)
48.5
(43.00 - 52.00)
30.5
(25.95 - 34.50)
217
(200.0 - 235.90)
95.8
(86.0 - 107.3)
1,735
(1,200 - 2,300)
Data Source: National Stormwater Quality Database (NSQD) and Highway Runoff Database (HRDB) - Post 1983 data only
TSS vs. AADT
NOx vs. AADT
Total Copper vs. AADT
Comparison of Highway Runoff Quality to
Other Land Uses
Constituent
Median EMCs by
AADT Category
Median EMCs by Land Use
90K +
100.0
Commercial
Industrial
Residential
TSS (mg/L)
0 - 30K
44.0
Open
Space
60.0
78.0
61.0
63.0
TKN (mg/L)
1.03
2.15
1.34
1.20
1.29
0.76
NOx (mg/L)
0.24
1.10
0.54
0.65
0.65
0.47
TP (mg/L)
0.12
0.24
0.21
0.22
0.27
0.19
TCu (µg/L)
9.81
48.55
15.00
18.00
12.00
9.50
TPb (µg/L)
4.85
30.48
12.24
16.09
8.67
10.00
TZn (µg/L)
54.98
217.41
120.00
154.00
74.00
70.00
COD (mg/L)
49.3
95.8
62.4
54.0
50.0
29.2
FC (MPN/100mL)
5,418
1,735
3,300
2,100
7,000
4,100
Data Source: National Stormwater Quality Database (NSQD) and Highway Runoff Database (HRDB) - Post 1983 data only
Effluent vs. Influent Concentrations
 Effluent concentrations of most BMPs and pollutants are statistically
correlated with influent concentrations, but many of the correlations
are weak due to high variability in stormwater data sets
 Effluent more correlated to influent concentrations for dissolved
constituents than particulate-bound constituents
 BMPs that include large wet pools or filtration media tend to be less
sensitive to influent quality than those that do not
 Detention basins show a relatively strong influent/effluent correlation
for most pollutants (rho>0.5), while bioretention cells typically show
weak influent/effluent correlation for most pollutants (rho≤0.5)
TSS Influent/Effluent
Regression Curves
Regression equations developed for NCHRP Report 792 (Taylor et al., 2014) from data from the
BMPDB
NOx Influent/Effluent
Regression Curves
Regression equations developed for NCHRP Report 792 (Taylor et al., 2014) from data from the
BMPDB
Total Phosphorus
Influent/Effluent
Regression Curves
Regression equations developed for NCHRP Report 792 (Taylor et al., 2014) from data from the
BMPDB
Total Zinc
Influent/Effluent
Regression Curves
Regression equations developed for NCHRP Report 792 (Taylor et al., 2014) from data from the
BMPDB
BMP Study Transferability Considerations
 Environmental conditions, site characteristics, and BMP design
features should be evaluated.
 Relative importance of each of these can vary significantly
depending on the pollutant, BMP type, and potential data application.
 Climate may be the most important considerations due to the
potential affect it can have on both influent quality and BMP
treatment processes.
 Land use and AADT should also be considered, but only for those
BMPs and pollutants which are strongly tied to land use and where
effluent concentrations are correlated with influent concentrations.
 Soils should be assessed, particularly if evaluating volume loss or
potential sources of nutrients, but other characteristics may be more
important with regard to study transferability
BMP Effectiveness
Standardization
Considerations
Recommended Standardized BMP Study
Reporting Protocols
 International Stormwater BMP Database (BMPDB) is recommended as
the DOT BMP study database due to its comprehensive design and
long-term successful operation and maintenance:
 Peer reviewed BMP monitoring and reporting protocols
 Already contains xxx DOT BMP studies
 Public access to the underlying data as well as interpretive reports
 Managed by Water Environment Research Foundation with major
support from FHWA
 BMPDB reporting protocols and tools can be easily adapted/adopted to
meet DOT needs:
 Additional metadata
 Transportation web-site portal
 DOT specific interpretive reports
Recommended Standardized BMP Study
Reporting Protocols
 Every BMP study should report, at a minimum:
 Test site (location, climate, BMP type, etc.)
 Watershed (drainage area, land use characteristics, number of
lanes, AADT, etc)
 BMP design and maintenance (features, dimensions, activities, etc.)
 Monitoring program (study design, monitoring locations, equipment,
QA/QC, etc)
 Monitoring data (precipitation, flow, influent, and effluent by discrete
storm event)
 Construction, maintenance, and monitoring costs are also
recommended
Current General Structure of the BMPDB
Roadway-Specific Additional Metadata Recommendations
 Roadway type
 Average ROW width

 Description of adjacent land use 
and whether there is commingled
flow

 Road shoulder condition

 Monitored traffic lanes
 Lane widths

 Curb presence and type
 Vegetation clear zone maintained 
adjacent to pavement
 Road cross-section type Drainage
system type
Highway mile post
Roadway maintenance
practices/frequencies
Surface pavement type
Date of last resurfacing and
surfacing material and sealants
used
Deicing events/dates
Use of studded tires
Scope of Work and Resources
Needed to Develop BMP
Database Portal, Add Data
Elements, and Prepare
Interpretive Reports for State
DOTs
Potential Scope of Work
 Phase 1 – Enhance Database and Develop DOT Portal
1.1 - Advisory Panel Meeting/Kickoff
1.2 - Communication and Training Promoting Use of the Database,
Basic Website Updates, Administration and
Coordination/Communication with Data Providers
1.3 - Update Web-based Retrieval and Analysis Tools
1.4 - Enhancements/Maintenance to Database Structure, Data Entry
Spreadsheets, and User's Guide
 Phase 2 – Expand Database and Prepare DOT-focused Reports
2.1 - New BMP Data Entry & Upload: includes new studies and may
include expanded data sets/backfilling for existing studies
2.2 - Special Data Analysis Reports (Pollutant Categories or
Advanced Analysis Reports; other Special Reports)
Estimated Budget and Schedule
Phase 1
Task 1.1
Task 1.2
Task 1.3
Task 1.4
Phase 1 Subtotal
$15,000
$15,000 to $20,000
$15,000 to $20,000
$5,000 to 10,000
$50,000 to $65,000
Phase 1
Task 2.1
Task 2.2
Phase 2 Subtotal
$20,000 to $30,000
$25,000 to $35,000
$45,000 to $65,000
Total Budget
$95,000 to $130,000
Weeks from Notice to Proceed
1.1 Advisory Panel Meeting/Kickoff
1.2 Communication, Training, and Outreach
1.3 Update Web-based Retrieval and Analysis Tools
1.4 Enhancements to Database Structure
2.1 New BMP Data Entry and Upload
2.2 Special DOT Data Analysis Reports
Summary and Conclusions
Summary and Conclusions
BMP performance monitoring studies are concentrated in certain
parts of the nation
Most states do not have established BMP monitoring and reporting
protocols, but most states have a mechanism for accepting new
treatment technologies
Climate and land use/AADT are the most important factors to
consider with regard to BMP study data transferability
BMPDB is currently the most appropriate national-scale database
that is actively maintained, populated and analyzed with public
access to the underlying data as well as interpretive reports
BMPDB enhancements have been recommended to better support
DOT objectives, including DOT specific metadata, a DOT “portal” to
the BMPDB for customized data retrieval and analysis options
Questions?