United States
Environmental Protection
Agency
EPA/600/R-15/219
October 2015
www2.epa.gov/water-research
Green Infrastructure for Stormwater
Control: Gauging Its Effectiveness with
Community Partners
Office of Research and Development
Water Supply and Water Resources Division
\
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EPA/600/R-15/219
October 2015
Green Infrastructure for Stormwater Control:
Gauging its Effectiveness with Community Partners
Summary of EPA GI Reports
Prepared by
Matthew Hopton, Ph.D.
Michelle Simon, Ph.D., P.E.
Michael Borst
Ahjond Garmestani, Ph.D., J.D.
Scott Jacobs
Dennis Lye, Ph.D.
Thomas O'Connor, P.E.
William Shuster, Ph.D.
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Water Supply and Water Resources Division
Edison, NJ
Cincinnati, Ohio
Taylor Jarnagin, Ph.D.
U.S. Environmental Protection Agency
Office of Research and Development
National Exposure Research Laboratory
Environmental Sciences Division
Research Triangle Park
Raleigh, NC
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ABSTRACT
This document is a summary of the green infrastructure reports, journal articles, and conference
proceedings published to date. It is our intention to update this summary as we have more
information to share and when relevant publications are completed. The Environmental
Protection Agency's Office of Research and Development has an ambitious research agenda to
continue quantifying the performance of green infrastructure during the next five years. This
report contains the synopses of the significant findings, lessons learned, and guidance to
communities based on a number of research efforts that included one roof downspout
disconnection, three green plus one conventional roof, two rain garden and bioretention, and two
permeable pavement research efforts across eight EPA regions. Some of the research addressed
water quality changes, such as bacteria, chlorides, solids, nutrients, and metals through
individual storm control measures. Others studied the aggregate hydrologic response from a
collection of green infrastructure storm water control measures over areal spaces of one to 100
acres over a period of one to seven years. One study focused on the impact of development due
to the conversion of farm to suburbs for ten years. In addition to the green infrastructure
performance studies, twelve sites were systematically characterized for disturbed urban soil
infiltration rates. While this is the most comprehensive summary of the Office of Research and
Development's research efforts to date, the findings of the research for the next five years will
greatly increase our ability to apply green infrastructure.
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DISCLAIMER
The U.S. Environmental Protection Agency, through its Office of Research and Development, funded and
managed, or partially funded and collaborated in, the research described herein. It has been subjected to
the Agency's administrative review and has been approved for external publication. Any opinions
expressed in this document are those of the author(s) and do not necessarily reflect the views of the
Agency, therefore, no official endorsement should be inferred. Any mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
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ACKNOWLEDGEMENTS
The authors of this report appreciate the assistance of Dr. Roberta Campbell and Ms. Josephine Gardiner
provided in generating this document and to Dr. Ariamalar Selvakumar and Mr. Jason Berner for their
thorough and speedy reviews. This research would not have been possible without the cooperation and
support of the communities and various entities and staff within the communities.
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TABLE OF CONTENTS
ABSTRACT 2
DISCLAIMER 3
ACKNOWLEDGEMENTS 4
TABLE OF CONTENTS 5
LIST OF ABBREVIATIONS 7
LIST OF ABBREVIATIONS, CONTINUED 8
LIST OF TABLES 9
LIST OF FIGURES 9
EXECUTIVE SUMMARY 10
Introduction 10
Infiltration 15
Hydrology 16
Water Quality 17
Place-based 17
Guidance for stakeholders and decision makers 18
Future needs (i.e., new questions, where our knowledge is lacking, etc.) 19
Community Access/General Interest 19
Summaries of Specific Research Efforts and References 22
Region 2 - Edison, NJ 22
Region 2 - New York, NY 26
Regions - Clarksburg, MD 29
Regions - State College, PA 31
Region 4 - Louisville, KY 35
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Region 5 - Cincinnati, OH 38
Region 5 - Cleveland, OH 41
Regions - Detroit, MI 43
Region 6 - Austin, TX 45
Region 7 - Kansas City, MO 47
Region 7 - Omaha, NE 51
Regions -Denver, CO 52
Region 9 - Phoenix, AZ 55
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LIST OF ABBREVIATIONS
ASCE American Society of Civil Engineers
BACI Before-After-Control-Impact
BMP Best Management Practices
GATE Cities and the Environment
CN Curve Number
CRADA Cooperative Research and Development Agreement
CSO Combined Sewer Overflow
CSPA Clarksburg Special Protection Area
DEP Department of Environmental Protection
DOI Digital Object Identifier
EEC Edison Environmental Center
EISA Energy Independence and Security Act
EO Executive Order
EPA Environmental Protection Agency
ET EvapoTranspiration
GI Green Infrastructure
HSPF Hydrological Simulation Program Fortran
JAWRA Journal of the American Water Resources Association
KCMO Kansas City Missouri University
KCWSD Kansas City Water Services Department
LID Low Impact Development
LiDAR Light Detection and Ranging
mm millimeter
MSD Metropolitan Sewer District
NPDES National Pollutant Discharge Elimination System
NYC New York City
ORD Office of Research and Development
PA Porous Asphalt
PC Pervious Concrete
PICP Permeable Interlocking Concrete Pavement
RARE Regional Applied Research Effort
RWH Rain Water Harvesting
SCM Storm Control Measures
SSC Suspended Solids Concentration
SSURGO Soil Survey Geographical
SUDS Sustainable Urban Drainage Systems
SUSTAIN System for Urban Stormwater Treatment and Analysis Integration
SWMM StormWater Management Model
TC Total coliform
TDR Time Domain Reflectometers
TSS Total Suspended Solids
U.S. United States
USGS United States Geological Survey
UV Ultraviolet
VELMA Visualizing Ecosystems for Land Management Assessment
VMC Volumetric Moisture Content
WQ Water Quality
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LIST OF ABBREVIATIONS, CONTINUED
WSUD Water Sensitive Urban Design
WWF Wet Weather Flow
XPSWMM XP' s StormWater Management Model
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LIST OF TABLES
Table 1 13
Table 2 14
LIST OF FIGURES
Figure 1. Map of EPA ORD green infrastructure research sites (2015) 15
Figure 2. Twelve cities located in each of the major soil orders were sampled to characterize altered
urban soils 16
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EXECUTIVE SUMMARY
Introduction
ORD has worked with numerous U.S. communities to study how green infrastructure
(GI) can be utilized to improve the performance of currently failing wastewater systems, and to
understand better the co-benefits of this approach to water management and related social,
economic, and environmental ramifications. The American Society of Civil Engineers (ASCE)
evaluated the water infrastructure and gave the U.S. a grade of D - because most of our water
infrastructure is nearing the end of its useful life.: Further, EPA has issued 849 combined sewer
overflow (CSO) permits2 that have aggressive deadlines to reduce CSO events that will be very
expensive ($187.9B in the next 20 years) to achieve.3 As communities develop land and alter
land use, difficulties associated with managing stormwater can be expected to increase.
"Gray" stormwater infrastructure is designed largely to move stormwater away from the built
environment, whereas GI reduces the quantity and treats stormwater on site while delivering
many other environmental, social, and economic benefits.4 EPA recommends that communities
use GI whenever or wherever it can be effective and economically advantageous for aging water
infrastructure upgrades.5 This document is a brief summary of EPA's Gl-related research efforts
and the results to date from these studies. More detail can be found in the references listed at the
end of each summary. The research efforts are grouped by EPA Region and community. Each
1 American Society of Civil Engineers http://www.infrastructurereportcard.org/drinking-water/ accessed 7/20/2015
2 EPA's Report to Congress on Implementation and Enforcement of the CSO Control Policy
http://water.epa.gov/polwaste/npdes/cso/upload/csortcappsd s.pdf accessed 7/2/2015
3 Water Environment Federation http://www.wef.org/WaterProtectionReinvestmentAct Summary 080112 accessed
7/21/2015
4 http://water.epa.gov/infrastructure/greeninfrastructure/gi why.cfm accessed 7/21/2015
5 EPA
http://YOsemite.epa.gov/opa/admpress.nsf/3881d73f4d4aaaOb85257359003f5348/5390e840bfOa54d785257881004f9
6dl IQpenDocument accessed 7/20/2015
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summary introduces the collection of papers, a brief description of the research performed, the
research questions asked, and insight from the results of the research.
To manage stormwater in densely-populated and developed areas, civil engineers have
focused on gray infrastructure to manage stormwater and efficiently move it offsite. They have
sized and designed gray infrastructure (e.g., pipes, tanks, pumps, etc.) for centuries and have
become very comfortable with such technologies. However, the U.S. has far less engineering
experience with GI technologies as compared to traditional "gray" infrastructure and there has
been a push to utilize "green" technologies because they can be less impactful to the
environment and may be economically advantageous to communities (i.e., lower installation and
maintenance costs). Moreover, GI may be less disruptive to the hydrologic cycle because the
intent often is to infiltrate the stormwater rather than move it offsite. Individual GI stormwater
control measures (SCMs)6 (e.g., disconnection of roof down spouts, rain gardens, green roofs,
detention ponds, permeable pavement, etc.) have only been analytically studied for the last
twenty years and studies measuring the aggregated response of many SCMs over large areas and
for multiple years are extremely rare. The overarching goal of EPA's GI research is to quantify
the reduction in stormwater runoff and resulting changes in water quality and other
environmental, economic, and social benefits, and to obtain engineering cost and design data.
EPA is examining the costs of design, installation, operation, maintenance, and
replacement for GI with the intent to develop objective data that communities can use when
6 Storm Control Measures (SCMs). Many EPA documents use the term "Best Management Practice (BMPs)" for GI
and Low Impact Development (LID). There has been some reluctance from the regulated community, academics,
and even regulators to continue to use the term owing to the fact that the specific term "Best" implies a high level of
expected performance. Some have referred simply to stormwater management practices. The National Research
Council proposed the term stormwater control measures (SCM). However, as the Clean Water Act (CWA (1977)
specifically refers to "Best Management Practices," BMPs will be the legal name until the CWA is either amended
or superseded. EPA web pages still refer to BMPs.
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considering implementation of GI. To help communities make this decision, EPA is developing
models, such as SWMM, VELMA, and HSPF, and Decision Support Tools, such as the National
Stormwater Calculator, to predict the performance of GI. Communities rely on these models and
tools to help them make what can be multibillion dollar decisions. For example, Kansas City,
MO designed its $10 million 100-acre Middle Blue River pilot on SWMM predictions and,
based on the performance of this 100-acre pilot, it will design its $2 billion, 20-year consent
decree sewer upgrade.7 EPA's stormwater modeling tools are very sophisticated, but EPA will
continue to develop and improve some of these models through validation using field data at
large spatial scales in an effort to assist communities in making sound decisions.
Presented in Table 1 are ORD GI projects with completed publications (i.e., reports and
journal articles). ORD intends to update this document as more information becomes available
when additional results are published. Some of ORD research sites such as Cincinnati,
Cleveland, Detroit, Louisville, Edison, and Camden, are still active.
GI can be applied to new or retrofit instillations. The U.S. is a demographically and
geographically diverse country, and as the map (Fig. 1) and the tables (Table 1 and 2)
demonstrate, EPA has just started to examine the performance and effectiveness of GI under all
the different demographic and geographic conditions throughout the U.S. Eventually, EPA
hopes to provide information useful to communities of all sizes (i.e., population and area) and in
all climatic regimes.
7 Kansas City Water Services Department (KCWSD). 2013. Final Report Kansas City Overflow Control Program
Middle Blue River Green Solutions http://www.burnsmcd.com/Resource_/PageResource/Overflow-Control-
Program-Assistance/Final-Report-Kansas-City-Overflow-Control-Program-Middle-Blue-River-Basin-Green-
Solutions-Pilot-Project-2013-ll.pdf
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Table 1. EPA has a number of community-based research efforts, each utilizing different GI
SCMs, and of various sizes, in an attempt to quantify changes to stormwater runoff due to GI.
Number of Individual SCMs Evaluated Per Location
Location
Edison, NJ
New York, NY
State College, PA
Clarksburg, MD9
Louisville, KY
Cincinnati, OH
Cleveland, OH10
Detroit, MI
Austin, TX
Kansas City, KS
Denver, CO
Dis-
connection
166
1
Rain
Gardens
2
82
12
78
Green
Roofs
I8
1
6
1
Bio-
Retention
51
Permeable
Pavement
3
14
2
2
Tree +
Infiltration
Planters
32
8 The Edison Roof was not a green roof but a conventional roof. ORD characterized the water quality of the roof
runoff of a conventional roof for comparison to a possible future green roof.
9 Role of Urbanization
10 Demolished Building
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Table 2. EPA has a number of community-based research efforts, each utilizing different GI
SCMs, and of various sizes, in attempt to quantify changes to water quality in stormwater runoff.
Water Quality Parameters Studied
Location
Edison, NJ8
New York, NY
State College, PA
Clarksburg, MD11
Louisville, KY
Cincinnati, OH
Cleveland, OH12
Detroit, MI
Austin, TX
Kansas City, KS
Denver, CO
Dis-
connection
Bacteria
Rain
Gardens
Nutrients
Nutrients
Metals,
PAHs,
Total
Suspended
Solids, E.
coli
Nutrients,
Metals,
Total
Suspended
Solids
Green
Roofs
Nutrients,
Metal
Nutrients
Nutrients
Nutrients
Bio-
retention
Nutrients,
Metals,
Total
Suspended
Solids
Permeable
Pavement
Chlorides,
Nutrients,
Metals,
Total
Suspended
Solids
Nutrients
Tree
Planters
Nutrients
11 Role of Urbanization
12 Vacant lots
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w York, NY
idison, NJ
Clarksburgh, MD
500 1000
2000
^m Kilometers
Figure 1. Map of EPA ORD green infrastructure research sites as of 2015.
Infiltration
A major site-specific property of GI often is the ability to infiltrate water. EPA's
National Stormwater Calculator uses the USDA's SSURGO Soil database13 to look up the
infiltration rates of soils but this database contains undisturbed soils. However, many urban soils
have been disturbed, altered, or relocated and most urban soils have been compacted which
reduces their ability to infiltrate water. To understand how soil in urban systems perform when
used in GI implementation, each of the major soil orders in the continental U.S. and Puerto Rico
have been characterized. To date, EPA has systematically measured the infiltration rates and
13 http://www.ncgc.nrcs.usda.gov/products/
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characterized the soils in 12 cites (Portland, ME; Camden, NJ; Atlanta, GA; New Orleans, LA;
Detroit, MI; Cleveland, OH; Cincinnati, OH; Omaha, NE; Junction City, KS; Phoenix, AZ;
Tacoma, WA, and San Juan, PR). In addition to these cities, EPA has measured the urban soil
infiltration rates at many of their research sites, including Edison, Cincinnati, Louisville, and
Kansas City. ORD has studied GI sites located in densely urban, suburban, and more natural
sites.
Soil Assessment Status
..
500
Mumrto-a
Figure 2. Twelve cities, representing each of the major soil orders, were sampled
to characterize altered urban soils.
Hydrology
Most of the GI research efforts studied the hydrology of specific types of low impact
development (LID) SCMs, such as green roofs or permeable pavement. Much of the data
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collected to date can be used to determine the maximum amount of rain specific SCMs can
completely infiltrate, and, conversely, what it cannot. Furthermore, these data can be used to
calibrate and validate the SWMM LID modules to help figure out when and where the models
work best and caveats to consider when using the models. The Cincinnati, Louisville, and
Kansas City GI research efforts have investigated the performance and effectiveness at a
watershed scale by examining the response of numerous LIDs rather than focusing on the
performance of one individual type of SCM.
Water Quality
The Edison, Cincinnati, Louisville, and Kansas City research efforts investigated nutrient
effects but also metal and total suspended solids reductions through permeable pavement, rain
gardens, and bioretention SCMs. Most of the GI water quality (WQ) data collected at
municipalities have significant variance in the inlet, outlet and percent removal event mean
concentrations. Statistical analyses of these data are often hampered by the fact that only a few
samples could be collected or where experimental replication is not feasible or within budget.
The Edison data set has higher numbers of samples with statistically comparable values for
chloride, metals, and nutrient data.
Place-based
Place-based field research requires a time commitment as collaborations are established,
baseline measurements are recorded, GI is installed, and storm events are monitored. Given
adequate time, these studies can be used to quantify the performance and effectiveness of GI and
used to improve models and help communities make decisions. Working with municipalities
offers many opportunities for synergistic monitoring and advancement of GI implementation for
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EPA. However, there can be coordination challenges when construction schedules are delayed
and Federal contracts end.
The field-based research efforts performed to date have been very insightful, but are just
beginning to examine all of the variation and diversity of stormwater management conditions in
the U.S. EPA is gaining a better understanding of the intricacies of stormwater management and
that there is not a one-size-fits-all solution.
Guidance for stakeholders and decision makers
GI research is a long-term, complicated, and expensive undertaking and EPA is working
intensely to understand better how the different types of GI perform under different
environmental settings and to provide a better estimate of expected results from its use.
Stakeholders and decision makers need to understand that there are different levels of
performance and effectiveness that can be achieved from GI and that there are solutions that can
be implemented at multiple spatial scales and in multiple configurations. Ideally, EPA will
provide case studies as examples for communities of similar social, economic, demographic, and
geographic characteristics to help them identify options for dealing with stormwater
management. Communities need to recognize that GI provides a number of ecosystem services
that are not restricted solely to stormwater management and they should consider these as well
when deciding which GI SCMs to use. Although many of the challenges and resulting solutions
are generalizable, each community deals with issues that may be unique to them and they must
use the best available information to address and resolve these issues.
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Future needs (i.e., new questions, where our knowledge is lacking, etc.)
Although EPA is gaining a better understanding and appreciation of GI for stormwater
management, quite a few knowledge gaps need to be filled to provide information that is more
useful for communities. Because the U.S. is so diverse and the number of GI SCMs are great,
EPA needs to determine how repeatable the performance and effectiveness of certain practices
are in different climatic regimes. Specifically, much of the EPA GI research has been in the
eastern U.S., in wet (i.e., mesic) climates. EPA ORD has not examined arid or semi-arid regions
nor does EPA have an understanding of the benefits and drawbacks of infiltrating more
stormwater. There could be water quality and water quantity effects and these need better
understanding. Ideally, EPA will provide models that have been fully validated and that clearly
express the strengths and weaknesses of different GI types, and where they work best so
communities can use the information to make sound decisions and better manage their systems.
This will require additional research in areas of the country that have largely been ignored. The
issue is further complicated by a changing climate and resulting nonstationarity (i.e., past climate
conditions are not a predictor of future climate conditions) and EPA research needs to help
communities prepare for an uncertain future.
Community Access/General Interest
One of the more problematic issues any new concept or practice faces is the evolution of
the terminology associated with it. As the topic of watershed drainage and its connection to
stormwater management is increasingly discussed by researchers and decision-makers alike,
new, multi-worded terms can muddle communication and slow development. Another area with
room for improvement lies in the lack of integration between urban design and the developing
field of urban ecology. Traditionally, environmental consultants, who generally do not conduct
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scientific research, are providing outdated and non-site-specific information to city planners,
designers, and engineers. This leaves out important ecological-specific research an urban
ecologist could provide. Thirdly, there are many socio-economic and political barriers and
benefits to GI as an alternative to gray infrastructure-based stormwater management. These
papers address the complexities and opportunities regarding the increased interest and
implementation of GI systems as sustainable solutions to stormwater management.
The scope of the papers listed in this section is conceptual and broad, meant to
encompass the challenges and potential opportunities of implementing any kind of GI into any
type of urban environment. Case studies in Cleveland and Milwaukee are provided as examples
to help explain how stakeholders can overcome barriers to GI application. Questions of how to
translate new and often localized terminology for use in larger scale applications, and ways to
integrate urban ecological research directly into the planning process were also asked.
As the topic of watershed drainage develops and evolves and GI becomes a more
standardized practice, it is important for end-users of this information to understand the
terminology and exactly what is being discussed. The ecological implications of urban
development are also an important product of both urban and GI design and should involve
direct urban ecological research. It is also essential to note that it is still possible for stakeholders
to see the value of GI, and to implement GI as a method of stormwater management, even in the
face of a combination of financial, administrative, political, and technical challenges.
Due to a conscious effort to use GI as a tool for the mitigation of stormwater overflows,
communication, stakeholder involvement, and accuracy of ecological impact assessments are
integral to laying a promising foundation for the future of GI methods.
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Background Literature
Felson, A, M Pavao-Zuckerman, T Carter, F Montalto, W Shuster, N Springer, E Stander, and O
Starry. 2013. Mapping the design process for urban ecology researchers. Bioscience
63(ll):854-864.
Fletcher, TD, WD Shuster, WF Hunt, R Ashley, D Butler, S Arthur, S Trowsdale, S Barraud, A
Semadeni-Davies, J-L Bertrand-Krajewski, PS Mikkelsen, G Rivard, M Uhl, D Dagenais,
and M Viklander. 2014. SUDS, LID, BMPs, WSUD and more - The evolution and
application of terminology surrounding urban drainage. Urban Water Journal: 1-18.
http://dx.doi.org/10.1080/1573062X.2014.916314
Keeley, M, A Koburger, D Dolowitz, D Medearis, D Nickel, and WD Shuster. 2013.
Perspectives on the use of green infrastructure for stormwater management in Cleveland and
Milwaukee. Environmental Management 51:1093 -1108.
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Summaries of Specific Research Efforts and References
Region 2 - Edison, NJ
The Edison Environmental Center (EEC) is a U.S. EPA facility in Edison, New Jersey.14
This site acts as a test bed for equipment and techniques before implementing them in field
settings where EPA has less control over the location. With ownership of the facility, EPA can
construct experimental GI SCMs to test different design features and include replication to
increase statistical power. There are four GI systems at EEC from which research results have
recently been published: permeable pavement systems, bioinfiltration areas, rain gardens, and
cisterns.
In a retrofitted one-acre parking lot, EPA installed three common permeable pavement
types [permeable interlocking concrete pavement (PICP), pervious concrete (PC), and porous
asphalt (PA)] in 140-ft long head-to-head parking rows designed to receive run-on from the
upgradient impervious hot-mix asphalt driving lane. A primary goal of this research was to
evaluate the effect that permeable pavement type had on the infiltrate water quality composition
and hydrologic response when all three were exposed to the same conditions and rainfall events.
Eight journal articles and one EPA report have been produced on GI research conducted
at the Edison Environmental Center (EEC) with most publications describing results associated
with the permeable pavement systems. Hydrologic performance outputs have evaluated surface
infiltration capacity, surface clogging dynamics, and evaporation. Surface infiltration capacity
was statistically different by pavement type (PC - 4,800 cm/h; PICP - 2,100 cm/h; and PA - 150
14 This facility provides an added level of safety and control for research activities. There is no concern for
vandalism or theft, and areas can be blocked to conduct tests on pavement surfaces.
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cm/h), but each could sufficiently infiltrate runoff from the most extreme rainfall intensity if the
surface was not clogged. Based on visual observations, surface clogging occurred as sediment
from the drainage area was transported with run-on onto the permeable pavement surface and
blocked the pore space.
Embedded soil moisture sensors [time domain reflectometers (TDRs)] in the open-graded
aggregate below the permeable pavement surface documented this observation through remote
monitoring techniques. A water balance of captured infiltrate from lined permeable pavement
sections was calculated, and it showed that evaporation from permeable pavement systems was
measurable, albeit small (about 5% on an annual basis), and that the PC surface had more
evaporation than the other two surfaces.
Published water quality performance reports are limited to chloride, but results associated
with other sampled stressors are in press (nutrients and pH) or under production (metals and
semi-volatile organic compounds). Chloride concentrations in the infiltrate approached 10,000
mg/L for the rain event that immediately followed a snow event where de-icing salt was applied.
Chloride persisted in the infiltrate year round, and it remained above the chronic toxicity
threshold for freshwater aquatic life (230 mg/L) into April. A power regression with cumulative
rainfall since the previous storm event best described the chloride flush through the permeable
pavement system.
A portion of impervious asphalt from this parking lot and the roof from an adjacent
building drain into six bioinfiltration areas that were constructed side-by-side with three different
ratios of drainage area to bioinfiltration surface area to test the effect of size on hydrologic
performance. Embedded soil moisture sensors in the six bioinfiltration areas with three different
sizes demonstrated that infiltration was concentrated near the inlet. These results, in
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combination with meteorological observations and plant size measurements, demonstrated that
shrubs closest to the inlet correlated with larger growth patterns than the shrubs farther from the
inlet primarily because the closer shrubs received substantially more runoff. Runoff provides a
source of water and nutrients and both are essential for plant growth.
A set of eight mesocosm15 rain gardens were constructed with a partial factorial design to
test whether any of the four design treatments (size, presence of a carbon source layer, vegetation
type, and drainage configuration) influenced nitrogen fate in underdrain effluent. Collected
stormwater runoff from a parking lot at the neighboring community college was used to simulate
two event sizes. Lastly, a cistern was installed to provide water for cooling water tower usage
and other non-potable uses. The rain water capture and use research was not designed with
replication but was a research opportunity to monitor use from a system specifically installed to
address Section 438 of the Energy Independence and Security Act of 2007 (EISA) and the
presidential Executive Order (EO) (no. 13148, "Greening the Government through Leadership in
Environmental Management" issued 4/21/2000) to improve environmental performance.
The eight mesocosm rain gardens illustrated that the presence of an internal water storage
zone significantly reduced combined nitrate and nitrite mass, but it significantly increased
ammonia quantity. Overall, there was no significant difference in total nitrogen quantity for the
presence or absence of an internal water storage zone, and the additional carbon source layer did
not have a significant effect on nitrogen removal.
The use of collected roof runoff and condensate recovery led to a substantial reduction of
potable water used for cooling tower makeup water during the warmer months. There was an
average annual 8.3% decrease in potable water usage, in addition to measures to decrease potable
15 Four were 4255 L in volume and the other four were 2785 L.
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water usage previously instituted. The primary source of contamination in roof runoff appears to
be atmospheric, as rainwater concentrations were correlated with most observed constituents in
the roof runoff. There were some building material components (i.e. copper gutters and
galvanized sheet metal), which contributed to the significantly larger observed copper and zinc
runoff concentrations, respectively.
As guidance for stakeholders and decision makers, site-specific conditions will govern
maintenance frequency for permeable pavement systems. The permeable pavement site at the
EEC, with a limited sediment supply, has been in operation for more than 5.5 years without
needing maintenance to alleviate surface clogging. Surface clogging begins at the upgradient
edge (impervious surface/permeable pavement interface) and progresses downslope, so this
mechanism should be considered when selecting locations to manually test surface infiltration
rates for considering when maintenance is needed. The surface of the PC has demonstrated
significant unraveling, however, this observation has not been included in a publication or report.
When bioinfiltration areas are oversized, it increases the likelihood that vegetation planted
farthest from the runoff source will experience water-deficit stress, which could limit growth,
cause mortality, or necessitate additional maintenance (i.e., irrigation and fertilization), so
bioinfiltration design should consider plant placement and species selection relative to the
proximity of the runoff source.
Future needs associated with this research include: (1) exploring the fate of stressors as
water percolates to groundwater, (2) evaluating fate of microorganisms in permeable pavement
systems, (3) determining an efficient method to identify where manual surface infiltration tests
should be conducted in order to evaluate maintenance needs, (4) finding more suitable uses for
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harvested rainwater, and (5) evaluating long-term water quality data from the permeable
pavement research site to determine if there are seasonal effects of changes with age.
References
Borst, M and RA Brown. 2014. Chloride released from three permeable pavement surfaces after
winter salt application. Journal of the American Water Resources Association 50(1):29-41.
http://onlinelibrary.wiley.com/doi/10.1111/jawr. 12132/full
Borst, M, AA Rowe, EK Stander, and TP O'Connor. 2010. Surface Infiltration Rates of
Permeable Surfaces: Six Month Update (November 2009 through April 2010). U.S.
Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio,
Report No. EPA/600/R-10/083.
http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1008CH4.txt
Brown, RA and M Borst. 2013. Assessment of clogging dynamics in permeable pavement
systems with time domain reflectometers. Journal of Environmental Engineering
139(10): 1255-1265. http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE. 1943-
7870.0000734
Brown, RA and M Borst. 2014. Evaluation of surface infiltration testing procedures in
permeable pavement systems. Journal of Environmental Engineering 140(3):04014001.
http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE.1943-7870.0000808
Brown, RA and M Borst. 2015. Quantifying evaporation in a permeable pavement system.
Hydrological Processes, (available online ahead of print).
http://onlinelibrary.wiley.com/doi/10.1002/hyp.10359/full
Gilchrist, S, M Borst, and EK Stander. 2014. Factorial study of rain garden design for nitrogen
removal. Journal of Irrigation and Drainage Engineering 140(3):04013016.
http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000678
O'Connor, TP and M Amin. 2015. Rainwater collection and management from roofs at the
Edison Environmental Center. Journal of Sustainable Water in the Built Environment
1(1):04014001. http://ascelibrary.org/doi/abs/10.1061/JSWBAY.0000792
Stander, EK, AA Rowe, M Borst, and TP O'Connor. 2013. Novel use of time domain
reflectometry in infiltration-based low impact development practices. Journal of Irrigation
and Drainage Engineering 139(8):625-634.
http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000595
Region 2 - New York, NY
This Region 2 Regional Applied Research Effort culminated in an ORD final report on
the topic of green roofs (EPA 2014). This report documents the quantity and quality of runoff
from a suite of urban green roofs located in New York City (NYC). An overall research goal
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was to assess green roof performance on actual urban rooftops, which have lower and more
typical runoff dimensions to drains and are subject to more realistic urban environmental
conditions (i.e., light, wind and rain shadows), as opposed to test plots at academic research
campuses or laboratories. The urban green roofs were located throughout NYC representing
three of the five boroughs (The Bronx, Manhattan, and Queens). All of the areas monitored
drained to combined sewers, so reductions in roof runoff theoretically should help reduce CSO's.
This report presents analysis of water benefits from an array of observed green and
control (non-vegetated) roofs throughout NYC. Water quantity and water quality were measured
in the runoff of green and control roofs. The sites were located on a variety of buildings and
represent a diverse set of available extensive green roof installation types, including vegetated
mat, built up, and modular tray systems. Plant types on individual roofs were also different.
This work confirms that deploying green roofs on existing buildings can reduce the
negative impacts of urban wet-weather flow (WWF), including water quality and water quality
impacts in an urban environment. Findings for water quantity performance demonstrate that the
modular tray system captured the lowest percentage of precipitation among all green roof
systems for storms 0-20 mm in depth but was the highest for storms above 30 mm. Multi-year
predictions indicated that on an annual basis, the built up system will retain the most rainfall,
then followed by the modular tray system, and then the vegetated mat systems. The Natural
Resources Conservation Service curve number (CN) method could not capture observed relative
differences between the retention performances of the built up, modular tray and mat systems in
different storm categories. Individually, the vegetated mat systems had 62% and 42% overall
rainfall retention respectively, whereas the built up system had 56% and tray system 59%. The
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estimated long term rainfall capture of the system was between 37-60% for vegetative mats, 49-
66% for built up, and 47-61% for trays.
Water quality monitoring indicated that the green roofs neutralized the acid rain as the pH
of runoff from green roofs was consistently higher than that from the control roofs and
precipitation with observed average pH's equal to 7.28, 6.27, and 4.82 for the green roofs,
control roofs and precipitation, respectively. In general, observed nitrate and ammonium
concentrations were lower in green runoff than in control roof runoff, with the exception of
runoff from the built up system, which had higher nitrate concentrations than the control roof
runoff. Overall, total P concentrations were higher in green roof runoff than control roof runoff.
Micronutrients and heavy metals were detected either at very low concentrations or not at all.
While there appears to be more chemical constituents present in green roof runoff than
control roof runoff, there is an overall reduction in the volume of runoff from green roofs. Thus,
the total mass of nutrient runoff from green roofs is less than that from non-vegetated roofs. As
a result, the water quality benefits of green roofs are favorable in urban environments. The
projected annual mass loading per unit rooftop area of nitrate, ammonium, and total phosphorous
discharging from all five green roofs was considerably less than that from their respective control
(non-green) roofs, due to the ability of green roofs to retain precipitation. Thus, green roof
implementation could improve urban stormwater and subsequently urban receiving water quality
if achieved at large areal scales. The green roofs of this study were all built on existing
structures, so results of this study could be used for further retrofitting of existing structures with
green roofs.
The continued monitoring of the urban green roofs that were part of this effort (funded as
a Region 2 RARE award) will provide additional data needed to understand the evolving
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performance of urban green roofs with age, as well as the role of seasonality in green roof
hydrology. Other recommendations for further study include undertaking relative cost-benefit
analysis of green roofs versus other stormwater management technologies, more research
experiments considering driving factors for water control such as substrate depth and water
holding capacity, and continued studies that will optimize design with respect to maintenance
and performance.
References
EPA. 2014. Culligan, P, T Carson, S Gaffin, R Gibson, R Hakimdavar, D Hsueh, N Hunter, D
Marasco, W McGillis, and TP O'Connor. 2014. Evaluation of Green Roof Water Quantity
and Quality Performance in an Urban Climate. U.S. Environmental Protection Agency,
Office of Research and Development, Cincinnati, Ohio, Report No. EPA/600/R-14/180.
Region 3 - Clarksburg, MD
This work is from the Clarksburg Monitoring Partnership, a collaborative research effort
in the Clarksburg Special Protection Area (CSPA) in Montgomery County, Maryland. This
effort is a partnership among the U.S. EPA; the U.S. Geological Survey, Eastern Geographic
Science Center (EGSC); and the Montgomery County Department of Environmental Protection
(DEP) along with other research partners. This ongoing research is focused on the use of high-
resolution mapping of urban development using repeat acquisitions of digital orthoimagery and
Light Detection And Ranging (LiDAR) data, high resolution mapping of SCMs and Best
Management Practices (BMPs), streamflow and precipitation monitoring, and in-stream and in-
pipe biological and water quality assessments.16
16 EPA http://www.epa.gov/esd/land-sci/clarksburg01-05.htm.
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This research is meant to evaluate the effectiveness of the County's Phase II BMPs
implemented as a part of the Chesapeake Bay Watershed Implementation Plan for the National
Pollutant Discharge Elimination System (NPDES) stormwater rules for municipalities with less
than 100,000 people.17 This research uses a Before-After-Control-Impact (BACI) study design
to evaluate BMP performance over time during the construction (sediment control) and post-
construction (stormwater control) phases of urban development.
The CSPA is one of four Special Protection Areas in Montgomery County. Clarksburg is
a rapidly developing area where the County is undergoing urbanization in a "town center"
pattern; concentrating development in a relatively small area of high density residences,
businesses, services, infrastructure, and amenities while maintaining intact riparian buffers,
agriculture, and forest patches to the greatest extent possible. The County uses adaptive
management; where lessons learned from one development are applied to later development
plans.
The Phase II BMPs investigated in the research are a mixture of gray infrastructure18 and
Green BMP Treatment Trains and are found in areas of higher development density whereas GI
is more prevalent in areas of lower density development. Distributed BMPs are used to retain
and infiltrate stormwater runoff rather than centralized retention basins.
In spite of the best efforts of the County, monitoring results in the first watershed
developed in the CSPA show a major impact from the development during the construction
phase. Lessons learned to date include the need for greater sediment control and more rapid
http://www.mde.state.md.us/programs/Water/StormwaterManagementProgram/Pages/ProgramsAVaterPrograms/sed
imentandstormwater/storm_gen_permit.aspx.
18 http://water.epa. gov/infrastructure/greeninfrastructure/gi_what.cfm
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conversion of BMPs from construction phase to post-construction phase during the development
process. Future development plans also call for both reducing the intensity of development and
limiting development in headwater stream areas to try to protect water quality and stream biota
(see Annual Reports listed below). Future monitoring will reveal the extent to which water
quality and stream biota recover towards pre-construction levels in areas already built-out and
whether the adaptive management implementation of previous lessons learned will help to
mitigate the impacts of future development. Our plans are to maintain the monitoring work long
enough to see changes that occur during long time scales.
References
Hogan, DM, ST Jarnagin, JV Loperfido, and K Van Ness. 2014. Mitigating the Effects of
Landscape Development on Streams in Urbanizing Watersheds. Journal of the American
Water Resources Association (JAWRA) 50(1): 163-178. DOT: 10.1111/jawr. 12123 <
http://onlinelibrary.wiley.com/doi/10.1111/jawr. 12123/full >
Jones, DK, ME Baker, AJ Miller, ST Jarnagin, and DM Hogan. 2014. Tracking geomorphic
signatures of watershed suburbanization with multitemporal LiDAR. Geomorphology
219:42-52. DOT: 10.1016/j.geomorph.2014.04.038.
Loperfido, JV, GB Noe, ST Jarnagin, and DM Hogan. 2014. Effects of distributed and
centralized stormwater best management practices and land cover on urban stream hydrology
at the catchment scale. Journal of Hydrology 519(C):2584-2595. DOT:
http://dx.doi.org/10.1016/jjhydrol.2014.07.007.
Montgomery County Special Protection Area Annual Reports:
http://www.montgomerycountymd.gov/dep/water/special-protecti on-areas.html#reports.
Region 3 - State College, PA
This Region 3 RARE research culminated in an ORD final report on the topic of green
roofs (Berghage et al. 2009). The work for this research was carried out by the Penn State Green
Roof Center of The Pennsylvania State University at University Park, PA. Specifically, this
research investigated the design specifications and materials of green roofs used as stormwater
control devices. This research was meant to gather field performance data from side-by-side
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structures to provide performance data for stormwater control by green roofs for both water
quantity and quality. Six small-scale buildings were tested in agricultural fields which allowed
for unobstructed wet weather data collection. Additionally this research explored
evapotranspiration (ET), drought limitations, and long term maintenance needs due to exposure
to acid rain. For these additional studies, controlled test bed systems were located in the Penn
State Horticultural Science greenhouses while additional testing of media acidification was
conducted in the laboratory.
The experimental design used small-scale buildings exposed to the local weather in an
attempt to gather data of variance for effects of different roof type and to determine whether
statistically significant differences could be described for any given rain event. Key parameters
monitored included real time flow and grab sample pollution assessment. The grab samples
were analyzed for conductivity, turbidity, pH, nutrients, and trace metals. In a controlled
environment (i.e., greenhouse test bed systems), weighing lysimeter studies were conducted to
obtain background information and to demonstrate the differences in water storage, and retention
and detention characteristics of the media, with and without the presence of plants, and drought
studies. The laboratory study used accelerated aging to determine the effects of acid rain on the
length of life for the roofs.
Collected field data indicated that a 3.5 - 4 inch deep green roof can retain 50% or more
of the annual precipitation in the Northeast. Replicated data from this study provided estimates
of expected differences in performance from identical green roofs. Green roof runoff reduction
was consistent during the warm summer months (almost no runoff) but was variable during
winter months when runoff from the buildings varied in some storm events from 80% for one
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building to 100% for others. Flow rates were reduced in runoff from green roofs until the
systems were saturated at which point runoff flow roughly equaled the rate of precipitation input.
Establishment of plants on Green roofs (first year only) in Region 3 may require
supplemental irrigation. Plants increase the transport of moisture through the soil medium when
compared to unplanted medium. This finding will need to be incorporated into green roof
modeling. Pennman-Monteith ET prediction equations can describe water loss from planted
green roofs.
Field water quality data (e.g., pH, conductivity, color, and nitrate) from green versus non-
green roofs were measured and compared statistically. Results demonstrated that green roofs
may reduce certain pollutants (e.g., acid precipitation and nitrate), but that it may increase
loadings directly related to these planted systems (e.g., phosphorous, potassium, calcium, and
magnesium). The laboratory test of the pH buffering capacity of the planting media suggest that
the green roof media can buffer acid precipitation for approximately 10 to 15 years, after which
it may be necessary to amend the media with lime to maintain the pH buffering capacity.
Green roofs can be incorporated with other GI SCMs and should be included in a
municipal stormwater plan. For suburban or agricultural areas, additional green roof runoff
treatment may be as simple as directing the downspouts to grass-covered areas (vegetated filter
strips or swales) or collecting green roof runoff in rain barrels to be used for irrigation, but this
may not be practical for urban areas where there is limited room for stormwater controls. For
urban areas that have combined sewers, green roofs should be viewed as a benefit due to the
volume reduction to the combined system and the delay in time to peak.
Directly discharging green roof runoff to a receiving water is not recommended due to
the increased levels of phosphorous, potassium, calcium, and magnesium. Due to variability in
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results, a conclusion from this study was that continued sample collection and analysis is
warranted. Further testing of materials used for green roof construction and planting should be
conducted to determine loadings coming from roofs as well as other constituents from
atmospheric deposition and building materials for standard roofing. Modeling loadings for green
roofs for watershed management requires additional monitoring with full-scale roofs or multiple
roofs in an urban setting. The drought studies indicated some potential limitations without the
use of irrigation.
Green roofs need to be tested in other climates so that further design specifications on
plant mixtures, media depth and amendments, and potential irrigation requirements can be
determined. Other climatic conditions should also include year-to-year or long-term studies, as it
seems very likely that in dry years the green roof runoff would be far less than in wet years.
Additional weighing lysimeter studies should be conducted to identify more plant species
suitable for green roofs, especially varieties that are drought resistant and require minimal
nutrient supplements. The effects of green roof runoff discharge on receiving waters or the
potential for additional treatment of green roof discharge were not addressed, and these should
be addressed in future studies.
References
Berghage, RD, D Beattie, AR Jarrett, C Thuring, F Razaei, and TP O'Connor. 2009. Green
Roofs for Stormwater Runoff Control. U.S. Environmental Protection Agency, Office of
Research and Development, Cincinnati, Ohio, Report No. EPA/600/R-09/026, February
2009. http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1003704.txt
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Region 4 - Louisville, KY
The Louisville and Jefferson County Metropolitan Sewer District (MSD) entered into a
consent decree with U.S. EPA, U.S. Department of Justice, and Kentucky Department for
Environmental Protection to limit CSOs. In one of the combined sewer systems, CSO Basin
#130, a GI approach was determined to be more cost-effective than the gray alternative to meet
the CSO targets outlined in MSD's long term control plan. EPA-ORD entered into a
Cooperative Research and Development Agreement (CRADA) with URS Corporation and MSD
to monitor and evaluate the individual performance and collective effectiveness of GI practices
installed in this basin. The basin is 17 acres of mixed residential and commercial areas in the
Butchertown section of Louisville, Kentucky, and the design included: 14 permeable pavement
systems, 28 tree boxes, and 4 infiltration planters installed along the public right-of-way.
During the design and planning stages, the municipality (MSD) hoped the monitoring and
research program could address: (1) how often maintenance is needed for the permeable
pavement surfaces, (2) the lifetime of the system before complete replacement is needed, (3) if
implemented at other locations across the city, should the GI design or placement strategy
change to improve performance, and (4) if the design meets the CSO frequency and volume
reduction targets. These concerns are shared by many communities, so our research attempted to
address these knowledge gaps.
To address the first three concerns, a series of embedded sensors (soil moisture, water
level, temperature) within the SCMs to study the infiltration and exfiltration dynamics of the
system and evaluate how they changed with age. Most of the GI practices were not installed
until 2013, so the fourth concern is still under investigation.
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Based on monitoring results from the first two permeable pavement strips that were
installed in December 2011, three journal articles have been published to date. One article
highlights how installing soil moisture sensors [time domain reflectometers (TDR)] in the open-
graded aggregate below the pavers can be used to monitor remotely the progression of surface
clogging. This installation proved to be a useful monitoring technique to address the question
about maintenance frequency. The second article highlighted the results from multiple pressure
transducers installed in wells along the length of the system. Analyzing the rates at which water
accumulated and drained provided insight on how infiltration and exfiltration processes changed
with time. With respect to the exfiltration rate, there was a significant reduction after the first
few events and through the first thirteen months. The decrease was attributed to fine sediment
on the double-washed aggregate.
Attempts to model the hydrologic performance of this system in EPA SWMM using the
measured water levels to calibrate the model were made, but this task demonstrated that the
treatment of exfiltration by this model did not accurately represent exfiltration processes for a
long, narrow, and deep geometry. Exfiltration was treated as a constant flux on the bottom area
only, which is a similar method as in other common hydraulic models. In this system, the water
drawdown rate decreased considerably with less water because the hydraulic head and exposed
sidewall area were smaller. Alternate ways to model the lateral exfiltration processes were
pursued, and a unit process model was developed and reported in the third paper to include and
quantify lateral exfiltration. The unit process model also included a function to represent
changes in surface infiltration through clogging based on the results from the embedded sensors
that measured the progression of surface clogging.
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As a result of this research, guidance for stakeholders and decision makers can be
provided for permeable pavement placement, remote monitoring strategies to predict
maintenance needs, construction materials that have a negative effect on performance, and the
benefits of a specific system geometry. Surface clogging is accelerated when sediment and
organic material are present in the drainage area, so in an effort to limit the maintenance
frequency, permeable pavement systems should not be sited in areas with unstable drainage areas
and surrounding deciduous vegetation. Soil moisture sensors (TDRs) installed in the open-
graded aggregate of storage gallery proved to be an effective remote monitoring technique to
determine maintenance needs. The fine particle size material (a.k.a., fines) present in double-
washed aggregate (about 2% by mass) resulted in significant reductions in exfiltration rate
during the first 13 months of monitoring. While this is clean by industry standards, the demand
for these applications is not large enough to reduce the fines percentage, so a reduction in
vertical exfiltration capacity should be considered in systems with deep aggregate layers. Even
though the subsoil at the first two monitored sites was clayey and the average infiltration rates
were 0.08 and 0.38 cm/h, the storage gallery and trench nearly drained completely during the
time between typical events because of the specific geometry of the system - long, narrow and
deep. In this type of geometry, most of the exfiltration was determined to be lateral through the
exposed sidewalls.
Future needs associated with this research topic are to: (1) explore lateral exfiltration in
more depth, (2) evaluate the collective effects of GI on sewer flow rates on a larger scale, (3)
evaluate whether the decrease in exfiltration rate continues with time and whether it is
hydrologically meaningful, and (4) investigate the interaction of the exfiltrating water with
existing groundwater.
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References
Brown, RA and M Borst. 2013. Assessment of clogging dynamics in permeable pavement
systems with time domain reflectometers. Journal of Environmental Engineering,
139(10): 1255-1265. http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE.1943-
7870.0000734
Brown, RA and M Borst. 2015. Evaluation of surface and subsurface processes in permeable
pavement infiltration trenches. Journal ofHydrologic Engineering 20(2):04014041.
http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE.1943-5584.0001016
Lee, JG, M Borst, RA Brown, L Rossman, and MA Simon. 2015. Modeling the hydrologic
processes of a permeable pavement system. Journal ofHydrologic Engineering, (Just
Released), 04014070. http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE. 1943-
5584.0001088
Region 5 - Cincinnati, OH
Consent decree settlements for violations of the Clean Water Act increasingly include
provisions for redress of combined sewer overflow activity through hybrid approaches that
incorporate the best of both gray (e.g., high-rate treatment plants, storage tunnels) and green
techniques (e.g., plant-soil systems like rain gardens, green roofs, pervious pavement systems).
Research was undertaken to help determine the most cost-effective, least-invasive method for
introducing GI into local communities where stormwater management is an issue. One six-year
study assessed the potential impact of distributed GI placed on a number of residential lots
within the same watershed. Various water quality and stream biota measurements were taken
three years before and three years after the GI technologies were applied, and the results were
compared to see if stormwater management at the parcel level can provide effective mitigation of
combined sewer overflows. The resulting papers focus on the economic, social, and
environmental factors surrounding the implementation of GI at the residential parcel level as a
tool for stormwater management.
Many of these studies were conducted within the Shepherd Creek Watershed of
Cincinnati, Ohio. The central motivating question was whether stormwater management at the
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parcel level is an effective strategy in mitigating sewer overflows and promoting stream health.
Researchers gauged the willingness of the community to participate in a GI installation program-
namely a reverse auction for the planting of rain gardens and the introduction of rain barrels on
residents' properties. The Shepherd Creek study found that the GI implemented in this
watershed did contribute to ecosystem services such as flood protection, water supply, and
increased water infiltration. It also provided benefits to the local residents, and reduced the need
for larger, more expensive centralized retrofits.
If this strategy is found to be a viable way to manage stormwater runoff and a similar
program attempted elsewhere, it may be beneficial to note a few key factors. First, while there
was indication that education alone may be enough to motivate residents to install GI, research
determined an auction promoted more participation than education alone, and at a cheaper per
unit control cost than a flat stormwater control payment plan. Second, a relatively small
monetary incentive can successfully entice homeowners to accept stormwater management
technologies on their property. Third, as participants share their experiences, neighbors may
become more willing to trust parcel-level stormwater management programs such as the one
conducted in Shepherd Creek.
The majority of GI research in Cincinnati evaluated infiltration-based stormwater
management strategies, but researchers also studied the distribution of urban trees and associated
impacts on stormwater runoff. Trees complement infiltrating GI by intercepting incoming
rainfall and preventing it from contributing to stormwater runoff. Researchers found that public
trees in the Cincinnati area provide substantial stormwater benefits, but these benefits vary
significantly according to community forestry practices at the municipal level. Proactive
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management of public trees can override other drivers of unequal tree distribution within cities
such as race or income.
In general, management of environmental systems is complicated by uncertainty in the
constituent factors and processes that comprise an ecosystem. Regardless of the scale of
investment in environmental management, uncertainty remains. Uncertainties in the efficacy of
GI for CSO control arise from non-linearity in fluxes among the different parts of the hydrologic
cycle and spatial and temporal thresholds in potential ecological response. These studies point to
the need for further research to identify the minimum effect thresholds and restoration
trajectories for retrofitting catchments to improve the health of stream ecosystems.
References
Berland, A and ME Hopton. 2014. Comparing street tree assemblages and associated
stormwater benefits among communities in metropolitan Cincinnati, Ohio, USA. Urban
Forestry & Urban Greening 13:734-741. doi: http://dx.doi.Org/10.1016/j.ufug.2014.06.004.
Berland, A, K Schwarz, DL Herrmann, and ME Hopton. 2015. How environmental justice
patterns are shaped by place: Terrain and tree canopy in Cincinnati, Ohio, USA. Cities and
the Environment (GATE) 8(1): Article 1.
Kertesz, R, O Odom Green, and WD Shuster. 2014. Modeling the hydrologic and economic
efficacy of stormwater utility credit programs for U.S. single family residences. Water
Science & Technology 70.11:1746-1754. doi:10.2166/wst.2014.255.
Mayer, AL, WD Shuster, JJ Beaulieu, ME Hopton, LK Rhea, AH Roy, and HW Thurston. 2012.
Building green infrastructure via citizen participation - a six-year study in the Shepherd
Creek (Ohio, USA). Environmental Practice 14:57-67.
Odom Green, O, WD Shuster, LK Rhea, AS Garmestani, and HW Thurston. 2012.
Identification and induction of human, social, and cultural capitals through an experimental
approach to stormwater management. Sustainability 4(8): 1669-1682.
DOI:10.3390/su4081669.
Roy, A, L Rhea, A Mayer, W Shuster, J Beaulieu, M Hopton, M Morrison, and A St. Amand.
2014. How much is enough? Minimal responses of water quality and stream biota to partial
retrofit stormwater management in a suburban neighborhood. PLoS One 9(l):e85011.
Roy AH and WD Shuster. 2009. Assessing impervious surface connectivity and applications for
watershed management. Journal of the American Water Resources Association 45(1): 198-
209.
Shuster, WD, R Gehring, and J Gerken. 2007. Prospects for enhanced groundwater recharge via
infiltration of urban stormwater runoff- a case study. Soil Water Conservation 62:129-137.
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Shuster, WD, D Lye, A De La Cruz, LK Rhea, K O'Connell, and A Kelty. 2013. Assessment of
residential rain barrel water quality and use in Cincinnati, OH. Journal of the American
Water Resources Association 49:753-765. DOT: 10.1111/jawr. 12036.
Shuster, WD and L Rhea. 2013. Catchment-scale hydrologic implications of parcel-level
stormwater management (Ohio USA). Journal of Hydrology 485:177-187.
http://dx.doi.org/10.1016/jjhydrol.2012.10.043
Thurston, HW, MA Taylor, WD Shuster, AH Roy, and M Morrison. 2010. Using a Reverse
Auction to Promote Household Level Stormwater Control. Environmental Science Policy
13:405-414.
Region 5 - Cleveland, OH
Each of these papers address one or several dimensions of the role of GI in sustainable
urban stormwater management. Current consent decree settlements for violations of the Clean
Water Act increasingly include provisions for redress of combined sewer overflow activity
through hybrid approaches that incorporate both gray (high-rate treatment plants, storage tunnels,
etc.) and green techniques (plant-soil systems like rain gardens, green roofs, pervious pavement
systems, etc.). The overall questions that addressed are: 1) can GI be integrated into an urban
setting, 2) how to design, monitor, and maintain the GI, and 3) can GI performance for
stormwater management, and ecosystem services provided be assessed?
Through 2017, the GI retrofit of a neighborhood in Cleveland, Ohio (Slavic Village
Community Development Corporation area) will be studied. Ongoing hydrological and
ecological monitoring provides feedback on the impact of GI implementation. This work centers
on managing the urban landscape for water conservation and storage, developing a role for
community engagement and renewal, and moving forward a comprehensive management
strategy for the stabilization and restoration of urban ecosystems. One important aspect of this
work is that it is conducted in an environmental justice community. Attempts to account for
these unique social and economic factors into the GI implementation process to achieve overall
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integration with environmental management will be made. To this end, the research is dependent
upon collaboration with the Cleveland Botanical Garden, Slavic Village Development
Corporation, Northeast Ohio Regional Sewer District, the City of Cleveland, Region 5, and Ohio
State University.
It is possible to develop effective integrated green approaches at the site scale to improve
the integrity of local hydrologic cycles, reduce runoff that reaches the sewer system, and reduce
risk of combined or septic sewer overflows. The specific management approach includes rain
gardens and using specific landscape hydrologic measurements (made in 2010, 2011 by ORD) to
determine the utility of vacant lots to act as passive GI. These data can be used to prescribe
management for these lots at a level which will make them both cost effective and provide
detention for stormwater abatement.
In general, management of environmental systems is complicated by uncertainty in the
constituent factors and processes that comprise an ecosystem. Regardless of the scale of
investment in environmental management, uncertainty remains. Uncertainties in the efficacy of
GI for CSO control arise from non-linearity in fluxes among the different parts of the hydrologic
cycle and spatial and temporal thresholds in potential ecological response. Further, rapidly-
changing social dynamics of a diverse, post-industrial urban setting under financial austerity
contribute political and social uncertainty. Adaptive management provides a framework that
explicitly accounts for these sources of uncertainty, and a recent paper (Shuster and Garmestani
2015) details our collaborative efforts to date in Cleveland, Ohio.
References
Jacobs, S, B Dyson, W Shuster, and T Stockton. 2013. A structured decision approach for
integrating and analyzing community perspectives in re-use planning of vacant properties in
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Cleveland, Ohio. Cities and the Environment 6( 1): 11.
http://digitalcommons.lmu.edu/cate/vol6/issl/ll
Rhea, LK, WD Shuster, R Losco, and J Shaffer. 2014. Data proxies for assessment of urban soil
suitability to support green infrastructure. Journal of Soil and Water Conservation,
69(3):254-265. doi: 10.2489/jswc.69.3.254
Shuster, WD, A Barkasi, P Clark, S Dadio, P Drohan, B Furio, T Gerber, T Houser, A Kelty, R
Losco, K Reinbold, J Shaffer, J Wander, and M Wigington. 2011. Moving beyond the
udorthent - a proposed protocol for surveying urban soils to service data needs for
contemporary urban ecosystem management. Soil Survey Horizons 52:1-8.
Shuster, WD, C Burkman, J Grosshans, S Dadio, and RJ Losco. 2014. Green residential
demolitions: Case study of vacant land reuse in storm water management in Cleveland.
Journal of Construction Engineering and Management 141(3):06014011.
10.1061/(ASCE)CO. 1943-7862.0000890
Shuster, WD, S Dadio, P Drohan, R Losco, and J Shaffer. 2014. Residential demolition and its
impact on vacant lot hydrology: Implications for the management of stormwater and sewer
system overflows. Landscape and Urban Planning. 25:48-56. DOI:
10.1016/j.landurbplan.2014.02.003
Shuster, WD and AS Garmestani. 2014. Adaptive exchange of capitals in urban water resources
management - an approach to sustainability? Clean Technologies and Environmental Policy
DOI 10.1007/sl0098-014-0886-5.
Shuster, WD, MA Morrison, and R Webb. 2008. Front-loading urban stormwater management
for success - a perspective incorporating studies of retrofit low-impact development. Cities
and the Environment 1 (2): 8.
Shuster, WD, B Newport, B Furio, N Cantello and S. Ellis. 2011. APPENDIX 3, To Consent
Decree, United States and State of Ohio v. Northeast Ohio Regional Sewer District (N.D.
Ohio), Green Infrastructure Requirements.
Shuster, WD, B Newport, B Furio, M Klingenstein, N Cantello, and S Ellis. 2011. APPENDIX
4, To Consent Decree, United States and State of Ohio v. Northeast Ohio Regional Sewer
District (N.D. Ohio), Requirements Applicable to Proposals for Green for Gray Substitutions.
Shuster, W.D. and A.S. Garmestani. 2015. Adaptive exchange of capitals in urban water
resources management - an approach to sustainability? Clean Technologies and
Environmental Policy 17: 1393-1400.
USEPA. 2013. On the Road to Reuse: Residential Demolition Bid Specification Development
Tool. EPA 560K13002, September. 81pp. http://www2.epa.gov/large-scale-residential-
demolition/road-reuse-residential-demolition-bid-specification-development
Region 5 - Detroit, MI
Although the importance of urban soil interpretation has been recognized for many years,
anthropogenic soils have been delineated as simply urban- or made-land on most soil survey
maps. There is a significant lack of information regarding the composition of these soils and
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how they have been altered over time. It is important to gain better understanding of these soils
so that currently unused spaces like vacant lots can be revitalized and used as natural resources
for urban agriculture, GI, etc. The paper referenced in this section argues that anthropogenic
soils found on vacant urban land can be mapped, even at the scale of a single lot.
The soil survey took place on a <0.1 ha vacant lot in Detroit, Michigan. The lot was
formed circa 1998 by the demolition of a wood-frame home from the 1920s in an urban
residential setting. The research set out to conclude whether or not there is a mappable pattern of
anthropogenic polypedons19 against the alternative that the distribution is random, as well as
provide an answer to the possibility of piecing together the history of urban soils and reclaiming
them to suit current stormwater management needs. The type of GI used would be determined
once the composition and content of the soil was known.
The results suggest that anthropogenic soils on vacant urban land are mappable, even at
the scale of a single vacant lot. The soils approximated an anthrosequence, a related group of
profiles whose characteristics differ mainly because of anthropogenic activity. This
anthrosequence can be used to characterize the map unit composition of native soil-urban land
complexes found on vacant property produced by building demolition. However, a more
complete picture of urban soils via Order 1 surveys would help define the characteristics of
anthrosequences in other urban settings and inform decisions regarding the implementation of
19 polypedon - Two or more contiguous pedons, which are all within the defined limits of a single soil series.
pedon - A three-dimensional sampling unit of soil, with depth to the parent material and lateral dimensions great
enough to allow the study of all horizon shapes and intergrades below the surface.
soil series - The basic unit of soil mapping and classification, comprising soils all of which have similar profile
characteristics and developed from the same parent material.
All above definitions from Micahel Allaby. A Dictionary of Ecology. 2004. Encyclopedia.com.
http://www.encyclopedia.com.
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GI, or other revitalization projects, allowing a city and its community members to reclaim
unused vacant lots and give them a purpose.
References
Howard J and Shuster WD. 2015. Experimental Order 1 Soil Survey of Vacant Urban Land,
Detroit, Michigan. Catena 126:220-230. http://dx.doi.Org/10.1016/j.catena.2014.ll.019
Region 6 - Austin, TX
Water scarcity is being felt in parts of Region 6 due to the historic drought conditions and
an increasing population. Alternative water sources, such as harvested rainwater, are becoming
more important and Region 6 has seen an increase in the number of potable rainwater harvesters.
There is also growing interest in the U.S. regarding rainwater harvesting systems (RWH) that
incorporate minimal treatment. Treatment can be expensive, and both residential and
commercial rainwater harvesters might be interested in minimal-treatment systems because of
the associated savings. Many rainwater harvesters also wish to avoid the use of chemicals, such
as chlorine, that add off-flavors or odors to the water. EPA will require data about (1) risks
associated with using untreated or minimally treated rainwater produced commercially or
residentially, and (2) risks will depend upon exposures occurring during the ultimate use of the
rainwater such as irrigation, drinking, or other indoor household usage (e.g., laundry, bathing).
It is commonly thought that microbiological quality of harvested rainwater poses a
greater potential human health hazard as compared to the physical/chemical quality. The
objectives of this study were to: 1) identify the composition of the microbial community in
untreated or minimally treated harvested rainwater and 2) quantify the impact of typical
residential treatment (e.g., filtration and disinfection) on the microbial community.
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Six residential RWH systems, located in close proximity to one another (within a 1-km
radius) in the central Texas area, were selected for this study. Site 1 performed batch-
chlorination in the cistern, sites 2-5 used ultraviolet (UV) light, and site 6 had no disinfection.
Sites 1-5 used their treated rainwater for potable (e.g., drinking) and non-potable uses (e.g.,
laundry), and site 6 used the water only for non-potable purposes. All the UV sites (sites 2-5)
had either roof-wash filters (which are placed between the gutters and the first cistern such that
collected water is filtered before entering the cistern) or recirculating filters (which are sand
filters through which the cistern water is occasionally passed). In particular, site 5 operated its
recirculating filter once per day. Four sites had first-flush diverters, which divert a fraction of
the initial rainfall to a separate system (e.g., pipe or bath) because the first-flush tends to have
higher contaminant concentrations as compared to subsequent volumes of harvested rainwater.
Each of the tested systems had two filters between the cistern and tap, but the nominal pore size
varied.
RWH systems that are located geographically close to one another will not necessarily
have similar water qualities in their cisterns. Neither will those systems necessarily yield similar
treated water quality, even if they have similar treatment processes in place.
Although Escherichia coli and Eenterococci generally are preferable to total coliform
(TC) as indicator bacteria in environmental applications, none of these appears to be a proper
indicator for the microbiological quality of harvested rainwater. TC, E. coli, and Enterococci
were often absent from the treated rainwater, even though substantial concentrations of the
potential human pathogens Legionellapneumophila, Myobacterium avium, M. intmcellulare,
Aspergillusflavus, A.fumigatus, or A. niger were present.
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The observed log-removals of HPC, L. pneumophila, M. avium, M. intracellulare, A.
flavus, A.fiimigatus, and A. niger by filtration and UV disinfection were less than expected based
on previous laboratory studies. A careful study of the performance of commercially available
UV lamps for residential-scale disinfection is needed. Operators of individual, residential RWH
systems might require additional operation and maintenance training to achieve reliable
treatment of rainwater, such that the quality is similar to that of community water systems.
Federal water quality regulations do not exist for potable RWH systems at individual
residences in the U.S. Consumers of harvested rainwater might incur health risks by indoor
domestic use of harvested rainwaters, if those waters are not suitably treated. For individual
residences, disinfection with ultraviolet (UV) light is the most common disinfection strategy
(70%), while chlorination is used in a smaller number of systems (8%). With respect to
filtration, most of the potable RWH systems surveyed used cartridge filters (48%) or activated
carbon filters (39%). However, the treatment efficacy of individual RWH systems is not well
documented, especially for the removal of potential human pathogens, such asL.pneumophila.,
Mycobacteria spp., and Aspergillus spp., and more research is needed in these areas.
References
Lye, D. (submitted). Harvested rainwater quality before and after treatment in six full-scale
residential systems. PLoS One.
Region 7 - Kansas City, MO
In 2010, Kansas City, MO (KCMO) signed a consent decree with EPA on CSO. The
City decided to use adaptive management in order to extensively utilize GI in lieu of, and in
addition to, gray structural controls. KCMO installed 130 GI SCMs—primarily bioretention
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units—in a hundred acre-pilot; one of the largest retrofitted areas in the U.S. in 2012. EPA's
Office of Research and Development (ORD) partnered with KCMO to conduct extensive
monitoring to quantify the performance of the pilot area. The study focused on the long-term
monitoring efforts to quantify GI performance at two scales: site scale (individual SCMs) and
pilot (100 acre) scale.
Site-scale elements of the GI research included stormwater monitoring systems at eight
individual SCMs (rain gardens, bioretention cells, and smart drains) in the pilot area. Parameters
measured by deployed monitoring systems included inflow, infiltrated volume, bypassed flow,
and drawdown times. In addition, a subset of SCMs is being monitored for water quality
(loading reduction) parameters including particle size, bacteria, nutrients, and metals. EPA also
collected sewershed flow data before and after GI installation, and performed evaluations of land
use, soil infiltration, drainage areas, and individual bioretention unit performance. The titles of
the comprehensive reports written on this study are listed in the references.
This work was performed in the Marlborough neighborhood along the Middle Blue River
in Kansas City, MO. This historically African-American community was established in 1945.
The neighborhood requested that the streets be lined with curbs and gutters to prevent standing
water that had traditionally been present after heavy rains. KCWSD installed the curbs and
gutters as well as relined the aging sewer system. Both of these actions resulted in higher sewer
flow than before the research started. KCWSD installed 67 rain gardens, 5 bioretention cells, 2
cascades, 1 bioswale, 11 curb extensions with rain gardens, 24 curb extensions with below grade
storage, 19 bioretention with below grade storage, 1 gravel parking space, 4300 linear feet of
porous concrete, 1100 linear feet of pervious paver sidewalk, and 90 pervious
sidewalk/infiltration galleries. In addition to the GI installed, KCWSD installed larger
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underground pipes with an additional storage volume of 288,000 gallons which is directly
connected to the sewer system.
However, in spite of system upgrades which resulted in higher sewerflow, ORD
measured a 32% decrease in sewerflow before versus after GI installation which is consistent
with the SWMM model results presented by KCWSD. KCWSD predicted that the peak flow
would reduce by 76%. ORD is interested in seeing the resultant drop in CSO. While these data
are extremely variable, water quality analyses showed around a 50% reduction in all measureable
parameters TSS, SSC, turbidity, nitrate, and phosphate.
This was a challenging effort. There were numerous entities involved in the research:
EPA ORD, EPA Region 7, Kansas City Water Services Division, EPA Contractors Tetra Tech,
University of Missouri-Kansas City, University of Alabama-Tuscaloosa, KCWSD Contractor
Burns and McDonald, KCWSD Contractor URS, Corporation, KCWSD's GI Designer. The
research started in 2008 and ORD finished collecting data in 2013. The design portion of the
research effort was two years longer than anticipated and there was a drought in 2012, right after
the GI was installed resulting in another year for measurement. Many of the original EPA ORD,
EPA Region 7, KCWSD, and contractors who started the research retired before its conclusion.
This was a field scale effort which experienced many problems typical for a practical
application:
1. Originally, it was intended to compare the 100-acre GI pilot to an 87-acre control area under
the same rain fall conditions. There were many problems with the measurement of sewerflow in
the control area and it was not possible to get useable results. The analyses presented in this
report were based on before and after results for the pilot area.
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2. Before GI was installed, KCWSD relined the sewers in the pilot areas which resulted in an
increase sewerflow, which was not expected.
3. The pilot area Marlborough neighborhood requested that KCWSD install curbs and gutters to
prevent standing water from remaining on homeowner's lawns. The installed curbs and gutters
directed more stormwater into the sewers than before the GI was installed.
4. Once all GI was installed in 2012, Kansas City suffered a drought. ORD extended the
research period for another year beyond its original intention.
5. The water quality sampling equipment from one of the five individual BMPs selected for
analysis was accidently destroyed by the solid waste collection system.
The soil infiltration was much higher than expected and the BMPs worked extremely
well. The fact that BMPs had little overflow resulted in a smaller than anticipated dataset to
analyze water quality. However, in spite of system upgrades which resulted in higher sewerflow,
ORD measured a 32% decrease in sewerflow before versus after GI installation which is
consistent with the SWMM model results presented by KCWSD. KCWSD predicted that the
peak flow would reduce by 76%. ORD is interested in seeing the resultant drop in CSOs.
References
EPA. 2011. Report on Enhanced Framework (SUSTAIN) and Field Applications for Placement
of BMPs in Urban Watersheds. U.S. Environmental Protection Agency, Washington, DC,
EPA 600/R-l 1/144, November. http://nepis.epa.gov/Adobe/PDF/P100DEWI.pdf.
EPA. 2015. Kansas City Middle Blue River Green Infrastructure Pilot Proj ect Summary Report. In EPA
Review.
Kansas City Water Services Department (KCWSD). 2013. Final Report Kansas City Overflow
Control Program Middle Blue River Green Solutions
http://www.burnsmcd.com/Resource_/PageResource/Overflow-Control-Program-
Assistance/Final-Report-Kansas-City-Overflow-Control-Program-Middle-Blue-River-Basin-
Green-Solutions-Pilot-Project-2013-ll.pdf
Pitt, R.; Talebi L. 2014. Modeling of Green Infrastructure Components and Large Scale Test
and Control Watersheds. 218 pages. Appendices 193 pages.
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Tertra Tech. 2011. National Demonstration of the Integration of Green and Gray Infrastructure
in Kansa City, Missouri. A Pre-performance Summary Report. 9/30/2011. 98 pages.
Tetra Tech. 2013. Advanced Drainage Concepts for Using Green Solutions for CSO Control.
2012 Summary Progress Report. 63 pages.
Region 7 - Omaha, NE
Many cities with CSO controls often experience pollution of streams, lakes, and other
natural bodies of water when, in a rain event, the system is overwhelmed and is forced to
discharge untreated wastewater through CSOs. This research looks at the combined potential of
the best of both green and gray infrastructure methods in retaining and/or slowing the movement
of stormwater before it adds to the CSS. A hybrid approach with green and gray infrastructures
playing to their respective strengths may also allow for downsizing or elimination of some
ageing gray infrastructure CSO controls. This paper details a field deployment to Omaha, NE in
order to characterize soil taxonomic and hydraulic properties of vacant lots, park land and other
transitional and mostly abandoned areas in order to assess their potential for the installation of
GI.
Parcels, mostly vacant lots and parks, were selected for assessment by City of Omaha
wastewater officials in areas where the local sewershed may benefit from additional detention
capacity. This research sought to determine the soil taxonomic and hydraulic properties of urban
soils in the greater Omaha area, as well as their potential to be used as an effective stormwater
management tool. Types of GI that would be considered here include any infiltration-based GI
such as rain gardens, in combination with gray infrastructure such as cisterns.
In conducting this and related research it has been found that obtaining site specific soil
data is an important first step before any decisions are made as to what can be done to the green
space. The site specific soil characteristics are often very different from what is described on
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generalized, regional tables and interpolated datasets. This is especially true in highly disturbed
urban areas where soils were either not mapped or only minimally so.
The beginning of more research to come, this study supports the idea that a hybridized
system utilizing both green and gray infrastructure methods with the goal of reducing sewer
overflows is the most efficient and cost-effective alternative to managing stormwater runoff both
in the short and long term. Incorporating GI techniques, such as rain gardens, into a stormwater
management plan not only lessens the stress on the current, ageing infrastructure, but is overall a
more sustainable and aesthetically pleasing option.
Looking ahead, the issue of maintaining these GI SCMs once they are installed, needs to
be addressed. While municipal budgets are often stretched and there is little time for inspection,
post-construction monitoring to determine if the GI works effectively and appropriate operation
and maintenance should be conducted to ensure design effectiveness and otherwise guide
corrections. This field protocol will be a model for other deployments and soil assessment
studies in looking for suitability for the implementation of future GI research.
References
Shuster, WD and S Dadio. 2014. Soils Investigation for Infiltration-based Green Infrastructure
for Sewershed Management (Omaha NE). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/2014/063.
http://nepis.epa.gov/Exe/ZyPDF.cgi/P100KHY2.PDF?Dockey=P100KHY2.PDF
Region 8 - Denver, CO
This Region 8 RARE research culminated in an ORD final report on green roofs (EPA
2012). This green roof research was performed in an applied urban field condition of the rooftop
of EPA Region 8 Headquarters in downtown Denver, CO with supplemental plant and drought
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studies performed at Colorado State University in Fort Collins, CO. Due to the porous and well-
drained nature of the typical growing medium used in extensive green roof systems, the success
or failure of an extensive green roof is primarily dependent on a plant species' ability to grow in
the media. These challenges are intensified for extensive green roofs on buildings in areas
characterized by high elevation and semi-arid climate as typified by the environment of the Front
Range of Colorado. Success of an extensive green roof is primarily dependent on plant species'
ability to survive the low moisture content of the growing medium. Plants adaptable to dry,
porous soils are primarily used in extensive green roof applications. Although Sedum species,
which are succulents, have dominated the plant palette for extensive green roofs, there is
growing interest in expanding the plant list for extensive green roof systems, especially using
native species.
Prior to this study, green roof plants had not been scientifically tested for long term
survivability and adaptability in the Front Range of Colorado. The low annual precipitation,
short periods of snow cover, low average relative humidity, high solar radiation (due to
elevation), high wind velocities, and predominantly sunny days all add up to challenging
growing conditions for many species of plants. Plant studies of individual plants, mixed
plantings and drought studies were performed. Amendments (i.e., zeolite), to traditional green
roof media was tested to see if this benefited the green roof plants. Additionally, overwinter
damage to the initially installed drip irrigation system allowed for comparative performance to
overhead drip irrigation system.
The plant studies revealed, plant cover increased for all six species during the first
growing season. Subsequently, one species was removed from analysis in the second season due
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to the low overwintering rate (12.5%). Four of the five remaining species also exhibited
decreased plant cover due to winter dieback, but survived through the second season.
In terms of plant cover, five of the six species evaluated in this study appear to be
appropriate for use in extensive green roof applications. In the mixed study of eight species, at
the end of the study, the two native species that had higher plant cover than the others. Similar
to the individual plant studies, there were overwintering declines though competition may have
also determined success and reduction of species plant cover.
Four growing media amendments were evaluated based on plant taxa growth
performance. The greatest increase in plant cover from the addition of zeolite was seen in
mixtures with 33% and 66% zeolite.
In the drought study, fifteen plant taxa were evaluated for response to gradual and long-
term drying of the porous extensive green roof growing medium; despite differences in dry
down, the succulent species maintained viable foliage for over five times longer than the
herbaceous species. Additionally, the revival rates of the succulent species were nearly double
those of the herbaceous species.
Volumetric moisture content (VMC) data were collected throughout the study and the
overhead rotary irrigation system delivered a more consistent amount of water throughout the
green roof as measured by instantaneous VMC. Less irrigation was applied in the second year
with the spray irrigation than in the first year with the drip irrigation system. Year to year, for
the months July through September, there was 10% more rainfall in the second year (i.e., 97 mm
compared to 88.1 mm), but there was 32% less irrigation required (i.e., 200 mm compared to 270
mm). Overall, the overhead rotary irrigation increased biomass and plant cover.
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Due to the success of some native species in these experiments, the use of native plants
for green roofs should be pursued though finding adequate supplies may be an issue. In the arid
west, green roofs will most likely require supplemental irrigation. Due to the quick draining
nature of the green roof media and shallow rooted nature of most green roof plants (especially
during establishment), drip irrigation should not be used for green roofs.
Based on the diverse effects observed in this study due to changes in irrigation regime
and interaction effects with zeolite amendments, future studies should look at root growth in
addition to top growth of plants. The low overwintering success or eventual die-off of several
species in the study and overall winter dieback of most of the observed species may be an
indication of desiccation of roots due to limited snow cover. An additional limited irrigation
regime during winter months may improve plant survival in green roofs in arid regions.
Additional studies should be performed with other zeolite mixture ratios, additional native plant
species and mixture of species should be tested. Due to the need to irrigate in the arid west,
determining the cost effective benefits of green roofs beyond stormwater management needs to
be qualified for this GI practice to be more accepted in this area of the country.
References
EPA. 2012. Klett, JE, JM Bousselot, RD Koski, and TP O'Connor. 2012. Evaluation of Green
Roof Plants and Materials for Semi-Arid Climates. U.S. Environmental Protection Agency,
Office of Research and Development, Cincinnati, Ohio, Report No. EPA/600/R-12/592.
http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100FS5E.txt
Region 9 - Phoenix, AZ
Many cities with CSO often experience pollution of streams, lakes, and other natural
bodies of water when, in a rain event, the system is overwhelmed and is forced to discharge
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untreated wastewater through CSOs. By studying the soil morphology and correspondent
hydrologic data in the Phoenix area, this research was aimed at assessing the potential for
residential parcels and desert parks to be used as a tool in managing stormwater flows and
mitigate untreated runoff. This paper details a field deployment to Phoenix, AZ the purpose of
which was to characterize soil taxonomic and hydraulic properties of Aridisol pedons found in
desert parks and residential parcels, as well as a few dual-purpose park-stormwater retention
basins in order to assess their stormwater retention potential.
This research effort looked at two sites located in the outlying native Sonoran Desert that
have not been subject to direct anthropogenic disturbance, four residential lots representing a
range of neighborhoods and landscapes, and three stormwater retention basins that also serve as
recreational fields and feature turfgrass that is maintained and utilized throughout the year. This
study sought to determine whether the Aridisol soils found in the greater Phoenix area are
effective for retaining stormwater, especially those whose soil structure has been affected by
anthropogenic change. Specifically, the focus was on the use of retention basins and other
infiltration-based GI.
The resulting hydropedological data indicate that the infiltration performance of retention
basins is low, probably due to the development of finer surface soils and compaction. Taken as
an aggregate, these findings also suggest that residential yards may have sufficient infiltration
capacity to detain the runoff volume that they produce. Proper maintenance and clearing of
accumulated, fine-textured sediments within any retention basin used for the purpose of
stormwater management may result in an increase in infiltration and overall a more efficient and
impactful system.
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Our limited number of hydropedological assessments indicate a potential for stormwater
management via infiltration into urban Aridisols, although further study is needed to develop
finer scale mapping of soil hydrology in this arid conurbation.
References
Shuster, WD, S Dadio, C Burkman, S Earl, and S Hall. 2015. Hydropedological assessments of
parcel-level infiltration in an arid urban ecosystem. Soil Science Society of America Journal
79:389-406. doi:10.2136/sssaj2014.05.0200.
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