United States Environmental
Protection Agency New England
Managing Stormwater with Low
Impact Development Practices:
Addressing Barriers to LID
EPA901-F-09-003
Executive Summary
Low Impact Development or LID practices manage
Stormwater by minimizing impervious cover and by using
natural or man-made systems to filter and recharge
Stormwater into the ground. Roads, parking lots, and other
types of impervious cover are the most significant
contributors to Stormwater runoff. There is a direct
relationship between the amount of impervious cover
and the biological and physical condition of downstream
receiving waters.
The goal of LID is to reduce runoff and to mimic a site's
predevelopment hydrology by minimizing disturbed areas
and impervious cover and then infiltrating, filtering, storing,
evaporating, and detaining Stormwater runoff close to its
source. LID practices include measures such as preserving
undeveloped open space, rain gardens, green roofs, porous
pavement, and biofiltration.
LID has a number of advantages over conventional
Stormwater management practices. LID can reduce or
eliminate the need for larger detention ponds and flood
controls. It also reduces pollutant loading to receiving waters
as well as stream bank erosion associated with peak flows
LID also can provide a visual amenity in developments and
allow more flexible site layouts. Finally, LID can cost less
than conventional techniques.
Stormwater and TMDLs
In New England, many streams are impaired by
Stormwater and as a result, a total maximum daily load
(TMDL) water quality study is required. Research has
shown that there is a strong correlation between pollutant
loads, Stormwater flows, and runoff from impervious
cover. Therefore, TMDLs have been developed using
Impervious Cover (1C) as a surrogate parameter for a mix
of pollutants conveyed by Stormwater. Because they
reduce or have the same effect as reducing 1C, LID
techniques and best management practices (BMPs) will
help with the implementation of these TMDLs and result
in restored water quality. Additional information on
incorporating green infrastructure and/or LID concepts
into TMDLs and implementing Stormwater TMDLs can be
found at the following websites.
http://www.epa.gov/owowAtmdl/stormwater/pdf/tmdl lid fin
al.pdf
http://www.epa.gov/region1/eco/tmdl/assets/pdfs/Stonnwat
er-TMDL-lmplementation-Support-Manual.pdf
April 2009
For more information about LID and its many benefits over
conventional Stormwater management, see Incorporating
Low Impact Development into Municipal Stormwater
Programs, on EPA Region 1 's Web site under Stormwater.
This fact sheet seeks to address potential concerns and
barriers regarding LID techniques, compared to
conventional Stormwater management practices.
Cost Concerns
Q. I have heard that LID practices cost more than
conventional methods of Stormwater management.
A. LID can actually cost less than conventional Stormwater
management and be environmentally beneficial. EPA
recently commissioned a detailed study that examined 17
development projects that used LID techniques. The study
compared the actual cost of the LID developments to the
estimated cost of the project using conventional Stormwater
management. The study found that LID can achieve
significant cost savings through reduced grading,
landscaping, paving, and infrastructure costs (curbing, pipes
and catch basins, for example). (LID techniques can also
eliminate or reduce the size of Stormwater structures, which
can provide more open space or buildable lots.) With a few
exceptions, total LID capital costs were lower than
conventional methods, with savings ranging from 15 to 80
percent. The EPA report is titled Reducing Stormwater Costs
through Low Impact Development (LID) Strategies and
Practices, December 2007, EPA 841-F-07-006 For a copy of
the report go to
http://www.epa.gov/owow/nps/lid/costs07/documents/re
ducingstomnwatercosts.pdf
The EPA LID study did not compare maintenance costs, but
another EPA study found that LID has similar maintenance
costs compared to conventional methods. See Page 6-14 of
EPA's 1999 report, Preliminary Data Summary of Urban
Stormwater Best Management Practices, EPA-821-R-99-012
at http://www.epa.gov/OST/stormwater.
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EPA 901-F-Oe-003
Addressing Bafflers to LID
The following is a table from the EPA LID study comparing
the cost of conventional and LID approaches for a number of
the developments in the case study. Note that negative
values denote increased cost for LID design over
conventional developments costs.
ProJ.ct
Convsntlonal
—
cost
(.stlmat.d)
Actual UD
cost
Cost
dlffscsnc
P.rcsntag.
dlf!.rsnos
2 Avenue
SEA Street,
Seattle, WA
$868,803
$651,548
$217,255
25%
Auburn
Hills, WI
$2,360,385
$1,598,989
$761,396
32%
Bellingham
City Hall,
WA
$27,600
$5,600
$22,000
80%
Bellingham
Donovan
Park, WA
$52,800
$12,800
$40,000
76%
Gap Greek,
AR
$4,620,360
$3,942,100
$678,500
15%
Garden
Valley, WA
$324,400
$260,700
$63,700
20%
Kensington
Estates,
WA
$765,700
$1,502,900
($737200)
-96%
Laurel
Springs, WI
$1,654,021
$1,149,552
$504,469
30%
MiliCreek
(per lot), IL
$12,510
$9,100
$3,411
27%
Prairie
Glen, WI
$1,004,848
$599,536
$405,312
40%
Somerset,
MD
$2,456,843
$1,671,461
$785,382
32%
Tellabs
Corporate
Campus, IL
$3,162,160
$2,700,650
$461,510
15%
Cold Weather Issues
Q. Does LID work in New England’s cold weather?
A. Yes. LID practices work in cold and freezing weather. The
University of New Hampshire’s (UNH’s) Stormwater Center
has looked at this issue closely. It carefully monitored the
performance of a number of LID practices in both summer
and winter at its controlled field site in New Hampshire. In its
2007 Annual Report, the UNH Stormwater Center reached
the following conclusion:
All of the LID stormwater approaches we have
monitored—bioretention systems, tree fitter, porous
asphalt parking lot, sand filter and gravel wetland—
demonstrated excellent water quality treatment and peak
flow reduction year round.
The only system that had reduced efficiency in winter was a
vegetated swale. Winter conditions significantly lowered the
swales’ ability to treat water quality and manage water
quantity, likely as a result of icing of the ground surface. This
swale was not a more complex engineered water quality
swale or bioswa!e. Such swales might have better cold
weather performance than a conventional vegetated swale.
The UNH Stormwater Center’s report is at
http:/Iwww.unh.edu/erg/cstev/2007_stormwater_annual_r
eport.pdf
SOur research data tell us that It’s possible to design and
install systems that do an excellent job of treating
pollutants in stormwater, dampening the peak flows of
runoff, and reducing the volume of stormwater through
infiltration, even in cold dimates with poor SOiIS.
- UNH Stormwater Center 2007 Annual Report.
The findings regarding porous asphalt are especially
encouraging. The UNH Stormwater Center found that some
of the highest infiltration rates were in the winter, as opposed
to the summer, because of the larger pore space of the
asphalt in the winter compared to the summer. The center
also found that the porous asphalt required significantly less
salt for deicing than a similar lot paved with conventional
asphalt. The center concluded that porous pavement is a
high-performance stormwater management practice that with
proper design and oversight can be affordable and effective.
For more information on cold weather performance of porous
pavement, see Pervious Pavements: New Findings About
Their Functionality and Performance in Cold Climates,
Stormwater, September 2008. Also, for more information on
permeable pavement, see
http:/Iwww.mapc.org/regionaLplannlng/LID/permeable_p
av lng.html
Hydrodynamic separators, which have been installed in
many New England locations, are small, flow-through
devices that remove sediments and floating oils primarily by
An example of permeable paving. (Source: Silver Lake Project:
Massachusetts Executive Office of Energy and Environmental
Affairs)
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EPA 901-F-09-003
Addressing Barriers to LID
creating a swirling action in the stormwater and by particle
settling. The UNH Stormwater Center data demonstrated that
the performance of hydrodynamic separators was
significantly reduced during cold winter months because of
the increased viscosity of winter stormwater runoff and high
chloride concentrations, which combine to reduce particle
settling velocity. A number of LID practices had better
performance than the separators tested. The center
concluded that hydrodynamic separators are most effective
when used as a pretreatment device for a system that also
includes filtration or infiltration. See pages 22 and 23 of the
UNH Stormwater Center 2007 Report
http:llwww.unh.ed ulerg!cstevl200l_stormwater_annual_r
eport.pdf
Further Information on Contaminated Sites
EPA has prepared two fact she’ets that contain more
information and links to design guidelines for
contaminated sites.
Design Principles for Storm water Management on
Compacted, Contaminated Soils in Dense Urban Areas,
April, 2008:
http:/Iwww.epa.gov!brownfieldslpublicationslswdpO
408.pdf
Case Studies for Storm water Management on
Compacted, Contaminated Soils in Dense Urban Areas,
April, 2008:
http:llwww.epa.govlbrownfieldslpublicationslswcsO
408.pdf
Ground Water Issues
Q. Will LID practices that infiltrate stormwater into
the ground pollute drinking water sources?
A. If properly sited and designed, infiltration practices should
not adversely affect ground water. Data from the UNH
Stormwater Center indicate that infiltration practices remove
pollutants found in urban stormwater below levels of concern
for ground water protection. Furthermore, the benefits of
replenishing ground water supplies for future use and stream
base flow maintenance are substantial.
Depending on local site conditions, infiltration practices
without pretreatment might not be appropriate in areas where
ground water is a drinking water source (such as a zone of
influence of a drinking water well) or in other sensitive ground
water areas identified by a federal, state, or local government
(such as aquifers overlain with thin, porous soils). Also,
infiltrating stormwater runoff from certain land uses or
activities with likely or known exposed contamination should
be avoided, especially in drinking water wellhead protection
areas, unless special precautions are taken Examples of
such hot spot or high load areas include gasoline service
stations, manufacturing facilities that store or handle
hazardous materials, salt storage piles, and brownfield
properties. Contact your local and state regulators, such as
the state drinking water program, to obtain further information
regarding where infiltration may and may not be used.
As for sites with contaminated soils, there are a number of
practices that can successfully manage stormwater and
prevent the mobilization of subsurface contamination. For
example, LID filtration systems can be lined with an
impermeable liner and outfitted with subdrains that discharge
to the surface or away from subsurface plumes. Green roofs
can be installed on the top of buildings to reduce the amount
of stormwater runoff, and stormwater can be captured and
reused for toilet flushing or irrigation.
Q. I have heard that LID infiltration practices are
regulated under the Underground Injection Control
(UIC) program of the federal Safe Drinking Water
Act. Is this true?
A. EPA has clarified that most LID practices are not
regulated under the UIC program In a memorandum dated
June 13, 2008, EPA described the situations where the UIC
program applies to various stormwater infiltration best
management practices (BMPs) Generally, practices such as
rain gardens, bioretention areas, vegetated swales,
stormwater wetlands, and permeable pavement are typically
not regulated under the UIC program. Systems that are
deeper than they are wide or that include a subsurface
distribution system are subject to the UIC program. These
could include infiltration galleries and trenches, drywells, and
some manufactured infiltration systems. Even for infiltration
systems that require UIC permitting, most states have
general permits or expedited permitting for typical road and
parking lot stormwater infiltration systems.
UIC Program Links
For EPA’s June 13, 2008, guidance memorandum, see
http:llwww.ecy.wa.govlprogramslwqlstormwaterlmun
For EPA New England’s UIC program, see
http:llwww.epa.govlregionllecoldrinkwaterlpcgroun
dwater_discharges.html
For New England state UIC program contacts, see
http:/Iwww.epa.gov!regionh!ecoldrinkwater/state.html
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EPA 901-F-09-003
Addressing Bafflers to LID
Public Safety Issues
Q. I am aware that, in some instances, LID calls for
reducing street widths and reduced use of
sidewalks to decrease impervious surfaces. Isn’t
this a threat to public safety?
A. National road design associations and the American
Association of State Highway and Transportation Officials
have thanged their standards to allow reduced roadway
widths. Studies have shown that reduced street widths still
provide all the functions of access, parking, and circulation
for residents and emergency vehicles alike. In fact, some
studies have shown that narrower street widths are
associated with reduced traffic speeds and fewer accidents.
Depending on density, minimizing the use of sidewalks might
help to reduce development costs, increase housing
affordability, and reduce impervious surfaces. Sidewalks can
be limited to one side of a street and incorporate pervious
surfaces such as pervious concrete payers.
A number of municipalities have addressed the concern that
narrow roads cannot accommodate large fire trucks by
eliminating curbing or by reinforcing the street right-of-way so
that emergency vehicles can travel on road shoulders, if
necessary. Permeable pavement can also be used for street
shoulders.
More Information on Narrower Streets
American Association of State Highway and
Traneportetion Officials. Guidelines for Geometric Design
of Veiy Low-Volume Local Roads (ADTS 400)
http:llwww.tran.portat lon.org
EPA’s Web site on LID Street Design
hftpllcfpub.eps.govlnpdeslstorniwaterlmenuofbmpsli
nd.x .cfm?act lon=browse&Rbutton .dota ll&bmp=87
ITE Journal. June 1996. A Toolbox Appmach to
Residential Traffic Management
ITE Journal. February 2000. Child Pedestrian Injuries on
Residential Streets: Implication for Traffic Engineering.
Walter M. Kulash. Residential Streets. 3 ed. Urban Land
Institute
Q. Don’t LID stormwater management practices
increase the likelihood of flooding?
A. No. All stormwater systems, whether conventional or low
impact in design, are typically designed to safely convey
large storm flows by including appropriate overflow controls
that bypass the stormwater system to prevent flooding of the
stormwater system. Many LID practices offer the advantage
of reducing the volume and intensity of stormwater runoff,
thereby reducing the scope and capacity of required overflow
controls. LID infiltration and filtration practices also reduce
the likelihood of flooding downstream of the stormwater
controls, thereby reducing the burden on drainage
infrastructure and reducing the potential for sewer overflows.
Q. What about mosquitoes?
A. LID practices mostly process stormwater in the ground or
are designed to completely drain any standing water within
48 to 72 hours. This drainage time prevents mosquitoes from
breeding because mosquitoes need more than three days of
standing water to breed and reproduce.
Low impact cluster design subdivision. (Source: Massachusetts
Executive Office of Energy and Environmental Affairs)
An example of a tree filter. (Source: University of New
Hampshire Stormwater Center)
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A 901-F .OG-003
Addressing Bafflers to LID
Concerns Related to Novelty of LIb
Q. Aren’t LID techniques untested and innovative?
Will I get in trouble if I use something new?
A. LID practices have been used successfully across the
country and in New England. Hard data has been developed
that measures the efficiency of LID and compares LID to
conventional practices. For example, the UNH Stormwater
Center has carefully monitored the water quality treatment
and water quantity control of a number of structural LID
techniques. See its Annual Report for more details. The
University of Connecticut has also analytically compared the
performance of a conventional and LID subdivision. See
http:llwww.Jordancove.uconn.eduljordan_covelpublicati
onslfinal_report.pdf.
Also, many LID techniques are nonstructural, such as
practices that reduce the amount of developed area in a
subdivision. These techniques are tested in that they control
stormwater by mimicking the natural systems.
More lnfonnation on UD Practlc.s
The UNH Stormwater Center has an inventory of real-
world examples of successful and innovative BMP
installations throughout New England. The inventory can
be searched by state or practice. See
http:llwww.erg.unh.edulstormwaterl lndex.asp.
For several LID case studies in Massachusetts, see
httpllwww.mass.govlenvlrlsmartgrowth_toolklt!pag
esISG-CS.html
The University of Massachusetts maintains a database of
verified technical information on innovative stormwater
practices. See http:Ilwww.mastep..n.t
Q. What about the monitoring and maintenance of
LID techniques?
A. Both conventional and LID stormwater treatment facilities
typically require maintenance to ensure that the facility
operates as designed and to prolong the effectiveness of the
systems to treat stormwater. Municipalities should require
maintenance for conventional and LID stormwater facilities.
Each type of facility should have a maintenance plan specific
to that facility and location to account for sites where
sediment and pollutant loading might be especially high.
Maintenance includes items such as sediment removal,
erosion repair, and vegetation pruning. LID techniques do not
typically require specialized maintenance equipment and
may be able to be maintained as part of typical landscaping
activities.
Regulatory arriers -
Q. I’ve heard that local ordinances actually
discourage or can prohibit certain LID practices
and that such ordinances do not allow LID.
A. In some instances, local ordinances and bylaws can
prohibit or restrict certain LID practices, but LID in general is
not prohibited. For example, subdivision regulations might
require curb and gutter conveyance designs. Conflicts may
also exist regarding road widths and parking requirements.
There are, however, a number of tools to help alleviate this
problem. LID practitioners have developed checklists of
municipal regulations that can be barriers to LID so that such
regulations can be modified or repealed. Municipalities can
also provide guidance that LID techniques will be allowed
under waiver, variance, or site plan or special permit review
provisions.
There are a number of model ordinances that expressly
require LID and other practices that reduce storrnwater runoff
both during construction and post-construction. A good
number of municipalities have enacted regulations that
reduce storrnwater pollution. Municipal stormwater regulation
is also a requirement for some municipalities under EPA’s
Phase II Stormwater regulations.
An example of a rain garden.
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EPA 901-F-Oø-003
Addressing Bafflers to LID
Websltes Relevant to Regulatory Bafflers
For checklists of potential LID barriers in existing
regulations, see the following websites:
Center for Watershed Protection
http:Ilwww.cwp.orglResourc._Ubrary/Center_Doc
slSWlpcguldancelTool4.pdf
Massachusetts Metropolitan Area Planning Council
httpllmapc.org!reglonalpIannlngIUDIUD_cod.s.h
tml
For model ordinances that promote LID and runoff
reduction, see the following websites:
Massachusetts Model LID By-Law
http!!www nass.govI.nvlrIsmart_growth_toolkft/p
agesl8G-bylaws-lldhtml
New Hampshire MOdel LID By-Law
http:lldes.nh.govlorgan lzat lon!dlvlslona!water!wmb
IreppllnnovatlveJand_us. ,htm
Q. What about individual house lots?
A. In many areas, individual house lots are the predominant
land use, and their stormwater contributions cannot be
ignored. Luckily, LID can be used to infiltrate roof and
driveway runoff with drip line trenches, rain barrels, and rain
gardens. The University of Maine Cooperative Extension has
an excellent guide for installing rain gardens that can be found
at http://www.uri.edulcelhealthylandscapesl27O2.pdf
Additional Resources
This fact sheet is one of a series of four prepared by EPA Region 1.
The others are listed below and are available on the EPA Region 1
website. http:llwww.epa.govlregionllnpde&storTnwater
• Funding Stormwater Programs
• Incorporating Low Impact Development into Municipal
Stoirnwater Programs
• Restoring Impaired Waters: Total Maximum Daily Loads (TMDL)
and Municipal Stormwater Programs
For other EPA and non-EPA Web sites, see the following:
EPA’s National LID website
http:/lwww.epa.govlowow/npsl lid
A compilation of a number of resources, with links, a literature
review, fact sheets and technical guidance. This site includes a
national menu of BMPs.
EPA’s New England Stormwater page
http:/lwww.epa.govlreg lonlltoplcslwater/stormwater.html
Includes information, resources, links and contacts.
The Massachusetts LID Toolkit, Metropolitan Area Planning Council
http://www.mapc.org/lld.htrnl
Includes fact sheets on Low Impact Site Design, roadways and
parking areas, permeable paving, bioretention, vegetated swales,
filter strips, infiltration trenches and dry wells, cisterns and rain
barrels, and green roofs.
Center for Watershed Protection website
http://www.cwp.org
A nonprofit organization that provides technical tools for protecting
water resources.
Low Impact Development Center website
http:llwww.lowlmpactdeveloprnentorg
This is a nonprofit organization that promotes proper site design that
replicates preexisting hydrologic site conditions. The Web site
contains a variety of technical resources and case studies regarding
LID.
The University of New Hampshire Stormwater Center
http://www.unh.edulerg/cstevl lndex.htm
The center serves as a technical resource for stormwater
practitioners by studying the design, water quality and quantity, cost,
maintenance, and operations of stormwater management systems.
Contacts
EPA New England
Myra Schwartz
Schwartz. myra( epa qov
617-918-1696
Ray Cody
Cody. Ray epa.qov
617-918-1366
JM
I L .1
I 1i
— , IIU H_
An example of a biofilter in Portland, Maine. (Source: University
of Southern Maine, Portland)
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General Disclaimer: References in this fact sheet to
any non-federal product, service, or enterprise do not
constitute an endorsement or recommendation by the
EPA.
Information Disclaimer: The information provided in
this fact sheet is only intended to be general summary
information to the public. It is not intended to take the
place of written laws, regulations, permits, or EPA
policies.
Website Endorsement Disclaimer: This fact sheet
provides links to non-EPA websites which contain
additional information that may be useful or interesting
and are consistent with the intended purpose of this
fact sheet. References in these websites to any
specific commercial product, process, service,
manufacturer, or company does not constitute its
endorsement or recommendation by the EPA. The
• EPA is not responsible for the contents of non-EPA
websites, and cannot attest to the accuracy of these
websites.
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EPA 901 -F-09-003
Addressing Barriers to LID
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