oEPA
United States
Environmental Protection
Agency
EPA Publication Number 905F13001
July 2013
Implementing Stormwater Infiltration
Practices at Vacant Parcels
and Brownfield Sites
U.S. Environmental Protection Agency
Office of Water
Office of Solid Waste and Emergency Response
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 1
Introduction
This document presents information to assist communities, developers, and other stakeholders
in determining the appropriateness of implementing stormwater management practices that
promote infiltration at vacant parcels and brownfield sites.
A brownfield is a property where redevelopment or reuse may be complicated by the presence
(or likely presence) of contamination. Vacant parcels may also be brownfield sites depending
upon their prior use. Redevelopment of brownfield properties is often conducted using
approaches that are specifically designed to reduce or eliminate the human and ecological
health risks associated with these substances. Common risks associated with brownfield sites
include:
Risk To...
Human health
Groundwater
Nearby surface waters or ecosystems
Resulting From...
Direct contact, inhalation, or ingestion
Leaching of a contaminant(s)
Runoff from the site which has picked up
contaminants due to leaching or erosion
Strategies for reducing or eliminating these risks can include removing contaminated soil or
waste materials, treating soils on site, placing a cap or barrier over contaminated areas,
bioremediation, or monitored natural attenuation.
Many urban and suburban communities are required to develop municipal stormwater
management programs to control the discharge of pollutants from their separate stormwater
and sewer systems. These municipal stormwater programs typically require new development
and redevelopment projects to implement best management practices (BMPs) that reduce
pollutant discharges and control stormwater runoff. The specific requirements for each
stormwater program can vary, but many programs require or encourage development projects
to address stormwater runoff through controls that either infiltrate stormwater prior to its
runoff from a property or provide for the detention and treatment of the stormwater before it
is discharged.
Communities seeking to implement sustainable stormwater management frequently use rain
gardens, bioswales, permeable pavement and other practices, often referred to as green
infrastructure, to manage runoff. These stormwater infiltration practices often allow
accumulated runoff water to percolate into the subsoil which reduces stormwater runoff.
Projects that infiltrate stormwater runoff on-site can provide multiple benefits, including
decreased stormwater infrastructure costs, increased groundwater recharge, and decreased
pollutant loads in stormwater runoff.
Vacant or under-utilized parcels may appear to be promising places to locate stormwater
infiltration practices. However, it is important to reconcile the goal of sustainably managing
stormwater with brownfield site considerations. Infiltrating stormwater at sites where there are
contaminants present may mobilize the contaminants and increase the potential for
groundwater contamination.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 2
This document was developed to assist communities, developers and stakeholders in making
decisions about whether to implement green infrastructure infiltration practices at brownfield
sites. With careful site analysis and planning, decision-makers can plan for stormwater
management practices which promote the infiltration of stormwater while minimizing the
potential for mobilizing contaminants.
Stormwater Management Approaches
Stormwater management practices are typically intended to capture, convey (through ditches
or sewers) and in some cases treat stormwater which runs off of roads, parking lots, rooftops,
and other impervious surfaces or areas of active construction in an urban or suburban area.
Stormwater practices may also include storing wet weather flows, for example in a detention
basin, to help prevent localized flooding. In addition, stormwater management approaches may
include green infrastructure practices to trap
IHi ' • ' DT^^^^^^BI^HR!?W\ _U M u U •
pollutants and reduce the amount of m^l\
stormwater to be conveyed and discharged.
Successful implementation of stormwater
management and infiltration practices at
brownfield sites requires careful planning;
stormwater management planning and
implementation should be integrated with
site investigations, state approvals, the
selection of clean-up approaches and
techniques, and the design and engineering
of site improvements. The safe
implementation of stormwater infiltration
needs to be considered during the early
phases of planning for site redevelopment. Locating infiltration practices so that they do not
mobilize contaminants requires a collaborative effort by team members responsible for
delineating and defining the contamination, remedial engineering, site planning, and site
design.
Installation of a subsurface stormwater storage
and infiltration gallery.
When is a vacant parcel or infill redevelopment site a "brownfield,"
where contamination issues need to be considered?
There are a number of simple approaches to determine if a property could be characterized as
a brownfield site. The history of prior use is a good indicator of brownfield potential. Prior land
uses and the types of activities that took place on the site are often good predictors of whether
there will be contaminants and/or waste materials in the soil that could complicate the
redevelopment and reuse of the site. The following graphic illustrates the general relationship
between property use/site history and the associated probability of contamination.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 3
Low Probability -^—
of a contaminated site
—». High Probability
of a contaminated site
Park - Farm - Residential - Retail - Commercial - Service Station/Dry Cleaners - Industrial
Past and Present Property Use
Note that while the graphic shows the relative probability that there will be contamination at a
site, each site needs to be considered individually. For example, some land presently used as
park space may have had a different land use in the past. Farming areas may have past
pesticide use or farm waste management issues. A residential lot may have an old oil tank
buried in the yard or area where trash was burned.
Prior uses of a property can and should be identified from a
review of records such as current and past zoning requirements,
title search results, and deed records. Environmental records
related to a specific location (address or area) can be obtained
from the interactive EnviroMapper web site
(http://www.epa.gov/emefdata/em4ef.home) maintained by the
U.S. EPA. The EnviroMapper web site provides access to several
U.S. EPA databases to provide information about environmental
activities that may affect air, water, and land anywhere in the
United States. Maps depicting the locations of environmental
events, contamination, or other concerns also can be generated.
Many states also have environmental records databases that can
provide information regarding potential contamination at
particular properties.
A venf for an underground
storage tank is an indication
that the tank is still present.
A visit to the property can provide information regarding past use and the potential for the
property to be impacted by environmental contamination. Certain features at a property may
be indicators of potential contamination including the presence of:
• Underground storage tank vents or fill ports.
• Monitoring wells.
• Soil piles covered with plastic sheeting or tarps.
• Staining of soils and/or dead vegetation.
• Excavations that are not backfilled with clean
material.
At some properties, contaminated debris may remain
from previously demolished buildings. In such cases, it is
important to obtain records from the demolition to
determine if environmental hazards, such as fuel oil
tanks or lead based paint, were removed prior to the
building demolition.
The identification of the location
and size of the area where
compound concentrations
represent an unacceptable risk is
crucial to the planning of
stormwater management
practices.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 4
The site factors discussed above are typically considered as part of a site investigation (Phase I
and II Environmental Site Assessments) carried out to confirm if the property is impacted from
a prior use(s) or otherwise potentially contaminated.
Importance of Site Characterization
Prior to the initiation of any brownfield site reuse or redevelopment, a site investigation will
normally be conducted to obtain information regarding the property's potential contamination.
Knowledge regarding any potential contamination is needed to plan for any potential
remediation, to make the property safe for occupation, and to address environmental and
possible ecological concerns in a safe and cost-effective manner. Lenders, insurers and State
and federal environmental regulations often require an environmental investigation of a
commercial property at the time of property transfer to identify potential contamination and
the potential environmental and health impacts from any contamination. Environmental
investigations are normally conducted in the following stages:
Phase I Environmental Site
Assessment
Phase II Environmental Site
Assessment
Commonly includes the identification of environmental
concerns through a visual examination of the property,
acquisition and review of historic environmental records and
property use information, property ownership and lien records,
historic aerial photographs, and other records related to the
prior use and ownership of the property.
Conducted to determine if the information and potential
conditions identified in Phase I are evidence of contamination
and if such conditions create an environmental impact. This
phase can include soil borings or test pits to collect samples of
surface and subsurface soils for laboratory analysis. Monitoring
wells can be installed to collect groundwater samples for
laboratory analysis. Environmental impacts are characterized by
size and depth through sampling of subsurface materials and
groundwater.
If contaminant concentrations identified during Phase II
represent an unacceptable risk, a supplemental site assessment
is needed to identify the horizontal and vertical extent of
contamination. Once identified, risks can be further evaluated
along with remedial approaches for site construction to reduce
risks to an acceptable level.
Environmental conditions at brownfield properties need to be well-understood to ensure any
necessary cleanup meets environmental regulatory requirements and to effectively design
remedial efforts (if needed). The identification of the location and size of the area where
contaminant concentrations represent an unacceptable risk is crucial to the planning of
stormwater BMPs. Project stakeholders, regulators and designers need to have access to and
Supplemental Site
Assessment
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 5
evaluate this information in order to plan which stormwater management practices can be
placed at a site.
Is Infiltration Appropriate?
Stormwater management approaches that include infiltration need to be carefully evaluated
when being considered for a brownfield site, or potentially contaminated property. The
following questions can be used to help determine if infiltration or other stormwater
management approaches are appropriate for a specific brownfield property. To summarize key
steps in the decision-making process, a decision tree is presented near the end of this
document. A detailed environmental site investigation, as described above, should be
completed to identify the location, limits and contaminants in soil and groundwater so the
questions below can be answered and the decision tree can be used effectively.
1. Is a LNAPL, DNAPL, biodegradable waste, or teachable contaminant source
present at the site?
A light non-aqueous phase liquid (LNAPL) is a
liquid that has a density less than water, allowing
it to float on groundwater (e.g., diesel fuel). A
dense non-aqueous phase liquid (DNAPL) is
denser than water, allowing it to sink or move
downward through the groundwater table (e.g.,
tetrachloroethylene). LNAPLsand DNAPLsare
considered substances that tend to flow though
subsurface soils and are often the source of soil or
groundwater impacts at a brownfield site.
Because LNAPLs and DNAPLs are independently
mobile and can produce multiple hazards, the use
of infiltration or stormwater management
practices in close proximity to LNAPLs or DNAPL
contaminated areas should generally not be
considered. Areas of the site that do not contain
LNAPL or DNAPL can be considered for infiltration
only if the proposed infiltration will not move or
spread the LNAPL or DNAPL. More information
concerning LNAPLs can be found at:
http://www.epa.gov/wastes/hazard/correctiveaction/curriculum/download/lnapl.pdf.
U.S. EPA has developed a Synthetic Precipitation Leaching Procedure (SPLP) (USEPA Method
1312) to simulate the leaching of compounds from contaminated soil and certain wastes as a
result of precipitation infiltrating the ground surface. The SPLP test can be conducted on
samples of soil or other materials from a brownfield site (e.g., debris). A defined amount of the
material is mixed with laboratory grade water in a rotary agitator for a period of 18 hours. At
the end of mixing, the water portion of the mixture is extracted for laboratory analysis to
identify the resulting concentration in the leachate. These leachate concentrations or SPLP
Illustration of a release from a gasoline storage
tank with LNAPL floating on the groundwater
table.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 6
results are then compared to groundwater quality, surface water quality or to applicable site
specific clean-up standards (compound concentrations that represent acceptable risk). If the
SPLP result identifies compound concentrations in the leachate that are less than the clean-up
standard, stormwater most likely can be infiltrated through the material as long as there were
sufficient SPLP tests to properly characterize the material from a leachability standpoint.
Contaminants that are leachable or water soluble generally present relatively greater risks as
compared with some other categories of contaminants, because the contaminants can be
mobilized relatively easily through the soil from infiltrating stormwater and impact
groundwater. Other contaminants, such as many metals, can bind to the soil and may be less
likely to be mobilized by infiltrating stormwater. In considering whether infiltration practices
are appropriate at a particular site, the nature of the contaminants present should be evaluated
to assess if the contaminants are likely to be mobilized by the water moving through the soil. If
there are leachable or water soluble contaminants present on a site, it is usually not advisable
to locate infiltration practices over or near the contaminated areas. Volatile organic
compounds, phenols, and herbicides are classes of compounds that are often highly water
soluble.
Biodegradable waste materials (e.g., garbage) often produce gases and leachates that impact
soil and groundwater. The rate in which leachates and gases are produced from biodegradable
materials often is increased by the application of water. Therefore, stormwater management
practices that promote infiltration are generally not advisable at sites where there are
biodegradable materials in the ground.
Remedial measures are often planned at brownfield sites to prevent leachable or water soluble
contaminants from spreading and impacting groundwater and/or surface waters. A common
approach is to apply an impervious cap over the contaminated area. Other approaches include
using the building footprint or impervious areas such as parking lots to prevent infiltration.
Also, vertical barriers can be installed to prevent lateral groundwater flow and spreading
leachable or water soluble compounds. If these or other remedial measures are planned,
infiltration practices should only be considered if they do not negatively impact the operation
of remedial measures proposed for the site (see question 5, below).
2. Is groundwater beneath the property impacted or could it become
impacted?
Decisions regarding the appropriateness of implementing infiltration practices at a brownfield
site must take into account if there are contaminants present on the site (question 1) and
whether the groundwater beneath the site is contaminated. In some cases, groundwater under
a site can be contaminated, even if those contaminants are not present on the site. This can
happen for example when activities or site conditions at an upgradient property caused the
groundwater to become contaminated.
Generally speaking, if the groundwater beneath a site is known to be contaminated, it is not a
good idea to implement infiltration practices at the site. The movement of contaminants in
groundwater can be accelerated by an infiltration practice potentially resulting in
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 7
environmental impacts to neighboring properties. However, there could be situations where
infiltration practices can be implemented, depending upon the specific circumstances, including
the compounds and concentrations present in a groundwater plume. An example might be a
situation where natural attenuation has been selected as the appropriate strategy for dealing
with a groundwater plume with a low concentration of contaminants where there is little
potential for off-site migration. Relatively clean rain water infiltrating down to the groundwater
may have the effect of speeding up the natural attenuation process.
Following is a specific example when it could be a good idea to implement stormwater
infiltration practices even though there is identified groundwater contamination in the area:
Stakeholders from a watershed partnership met with agency and city staff for an
update on the cleanup of the Superfund sites, an area-wide groundwater
problem that covers many square miles in the watershed. In response to
questions about the impacts stormwater infiltration could have on the ongoing
Superfund cleanup, Superfund and city staff pointed out that in some areas of the
watershed stormwater infiltration and the resulting acceleration of pollutant
mobilization would be beneficial for the groundwater cleanup if the pollutants
are mobilized within the zone of influence of extraction wells used for
groundwater remediation.
Close coordination between those considering infiltration projects and those managing the
groundwater remediation is necessary to determine if/when an infiltration project may be
beneficial. Situations where infiltration could aid in the remediation of certain contaminants in
some environments should be discussed with EPA and/or the state remediation program.
When evaluating a site to determine if stormwater infiltration practices may be appropriate, it
is important to consider whether or not groundwater is contaminated on an adjacent property
and whether that property is located upgradient from the parcel where green infrastructure is
being considered. Contamination from an upgradient property may eventually travel to the
parcel. Decisions about whether to infiltrate stormwater when there is known groundwater
contamination in the area should be made carefully on a case-by-case basis, taking into account
the type of contaminants and whether infiltrating stormwater will affect environmental or
human health risks.
Other appropriate stormwater practices can be designed that provide filtration (treatment)
benefits and promote evapotranspiration, but not allow for infiltration. This topic is further
discussed in the section below titled, "Stormwater Management without Infiltration."
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 8
3. Are areas or parts of the property not
impacted?
Often the entire brownfield property is not impacted or
problematic material can be relocated to create an area
that is not impacted by contamination. In planning to
implement stormwater management at a brownfield site,
the volume, location and thickness of contaminated areas
should be reviewed. If an area of the site is not impacted or
can be remediated to remove the contaminants, it may be
appropriate to plan infiltration practices in such areas (see
example at right). At this case study site, impervious
surfaces - barriers to exposure and to limit downward
movement of contaminants in the soil as a result of rainfall
and infiltration - are placed over the areas with
contamination and green infrastructure practices are
located in other uncontaminated areas of the site.
4. Are there State standards I can refer to as a
guide in making decisions about infiltration
practices?
Many states have developed soil concentration standards
for various compounds for the soil to groundwater leaching
pathway. See for example Tablesl and 2 below. Standards
are continuously being updated and vary from state to
state. Where soil standards/criteria have been established,
such standards can be helpful in evaluating whether
infiltration practices may be suitable at a particular site.
However, it should be noted that in most cases the standards were developed based on typical
rainfall amounts entering the soil profile. The standards as established generally do not take
into account the relatively larger amounts of water that would move through the soil if
infiltration practices are installed.
Parking - Earner to
Exposure to
Contaminated Soil
Rain Gardens Swale
Example redevelopment plan using
green infrastructure while placing
barriers over contaminated soils.
Table I: Generic Leach-Based Soil Values for Organic Chemicals
Ohio EPA Derived Leach-Based Soil Values
Chemical
(Organics)
Benzene
Toluene
Ethylbenzene
Total Xylenes
Styrene
Naphthalene
n-Hexane
Soil Type 1
(mg/kg)
0.017
6.8
12
156
0.46
0.27
121
Soil Type II
(mg/kg)
0.0090
4.1
7.9
96
0.37
0.28
111
Soil Type III
(mg/kg)
0.015
7.7
16
191
0.62
0.36
104
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 9
Methyl Ethyl Ketone
Phenol
Carbon Tetrachloride
1,2-Dichloroethane
1,1,1-Trichloroethane
Vinyl Chloride
1,1-Dichloroethene
c/s-l,2-Dichloroethene
trans- 1,2-Dichloroethene
Trichloroethene
Tetrachloroethene
1.8
1.1
0.25
0.0030
1.2
0.0090
0.28
0.12
0.41
0.036
0.15
1.8
1.1
0.25
0.0020
0.74
0.0050
0.10
0.070
0.23
0.023
0.11
1.8
1.2
0.28
0.0030
1.3
0.012
0.24
0.12
0.40
0.048
0.27
Table 2: Generic Leach-Based Soil Values for Inorganic Chemicals
Ohio EPA Derived Leach-Based Soil Values
Chemical
(Inorganics)
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
Leach-based Value
for sources > % acre
(mg/kg)
3.6
3
56,000
57
21
56
89
12
182
2.15
3120
1.5
130
44,000
Leach-based Value
for sources< % acre
(mg/kg)
7.2
6
110,000
114
42
113
178
23
363
4.3
6240
3.0
65
88,000
Notes on Tables 1 and 2:
1. Source: http://www.epa.ohio.aov/portals/30A/ap/docs/sec-a-att.pdf
2. mg/kg -milligram of compound per kilogram of soil (by dry weight). Soil Type I is clean sand and gravel. Soil Type 11 is silty sand. Soil
Type III is till/clay.
3. Values provided are examples only. Check the applicable requirements and criteria in your State. To learn more about practices in other
states, the following website provides links to State brownfield programs: http://www.epa.aov/brownfields/state tribal/state map.htm.
4. Risk-based models/calculations can be used in some situations to provide information for decision-making about clean-up and re-use of
brownfield sites. See for example http://www.deq.state.ok.us/factsheets/land/SiteCleanUp.pdf and/or
http://www.nj.gov/dep/srp/guidance/rs/igw intro.htm. Appropriate soil concentrations are calculated using standardized equations or models
taking into account site-specific information. In certain situations allowable soil concentrations are calculated using computer models
designed for modeling vadose zone contaminant migration based on relatively more extensive site-specific information on soil types, site
conditions, and local climate. One of the factors normally considered in a risk-based model/analysis is the likelihood that groundwater could
become contaminated. A model/analysis will oftentimes use regional rainfall data and site and soil characteristics to evaluate if it is likely
contaminants will leach and groundwater could be at risk. It may be possible to adapt these methods to evaluate if implementation of
infiltration practices at a brownfield site will pose a significant risk to groundwater resources. In adapting a model/method for this purpose, it
will be important to take into account the fact that more stormwater would be draining through the soil if there are engineered infiltration
practices, vs. what amounts would be draining through the soil just from precipitation falling on the site.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 10
So/7 vapor extraction system schematic.
5. Will infiltration interfere with required remediation?
Decision-making about infiltration practices at a brownfield property should take into account
any remedial actions planned for the site. For example, vertical barriers planned to keep
contamination from moving laterally could be negatively impacted by installing infiltration
practices nearby and increasing the pressure differential on the side where infiltration is
increased. Increased hydraulic pressure on a vertical barrier could increase leakage through the
barrier and reduce the effectiveness of the
barrier overtime.
Stormwater infiltration practices could in some
situations also interfere with a soil vapor
extraction system (SVE, see
http://www.epa.gov/oust/cat/svel.htm or
http://www.frtr.gov/matrix2/section4/4-7.html).
Such systems are commonly installed to reduce
the vapor pressure beneath buildings to evacuate
any vapor risk that may be caused by
contaminants beneath the building. Increased
infiltration can increase the moisture content of
the vadose zone, raise the groundwater table,
and reduce the size of the vadose zone. These
changes can prevent the SVE system from operating properly and may result in high volumes of
condensate from the vapor collected, which is commonly contaminated and requires proper
handling, treatment and disposal.
The planning and design of infiltration and Stormwater management practices needs to be
integrated with the overall site design and remediation planning at a brownfield property.
6. How does the site interact with other
sites or land uses nearby?
Some brownfield sites are located near sensitive
areas such as wellhead (public water supply)
protection zones, rivers, lakes, fens, or wetlands.
Where a site is near an area that is relatively
more sensitive in terms of potential health risks
or ecological risk, the need to protect these areas
should be considered in making determinations
about implementation of infiltration practices.
For example, at a site immediately upgradient of
a wetland or fen that is dependent on shallow
groundwater inputs, an extra margin of safety
may be appropriate in deciding whether to
implement infiltration practices.
Too much Stormwater routed into a forested
wetland can harm the trees. Implementing
infiltration practices upstream of the wetland may
help protect it. (photo credit: Center for Watershed
Protection)
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 11
Land use and site activities in or near areas where stormwater will drain to infiltration practices
also should be evaluated. Some post-redevelopment land uses or site activities may present
relatively greater risks than others. For example, if stormwater will be running off from a
nearby gas station or industrial loading area and potentially draining to an infiltration practice,
implementing the infiltration practice in this situation could present relatively greater risks to
groundwater. Runoff from potentially contaminated areas should be routed to appropriate
stormwater facilities which may include oil and water separators and other treatment facilities
which do not encourage infiltration. Implementing an infiltration practice where the run-on
may include dissolved contaminants is not advisable.
Understanding how the site will be redeveloped or reused in the future may affect decision-
making regarding when infiltration may be appropriate or where practices should be located.
For example, if the site will be used for above-ground petroleum storage tanks and dispensing
fuel, this future use of the site should be taken into account in the evaluation of the
appropriateness of implementing infiltration practices. For situations where there are above-
ground tanks a spill prevention, countermeasure and control (SPCC) plan may be needed. SPCC
plans provide for secondary containment and/or operational procedures and precautions to
ensure that a spill is prevented and controlled in the event of a release. Installing infiltration
practices in areas that could be impacted by a potential release, as identified in a SPCC plan, is
generally not recommended.
Stormwater Management without Infiltration
When contaminants are present but at concentrations sufficiently low that they do not
adversely affect site re-uses or cause risks to public health, stormwater management
approaches that filter or treat stormwater, or which store and reuse stormwater, may be more
appropriate vs. infiltration practices. In situations where infiltration would not be advisable, site
planning and alternative BMP designs often can be used to achieve stormwater management
goals.
There are many methods to incorporate
stormwater management at a brownfield site
without directly infiltrating stormwater into
the underlying soils. Typically a green
infrastructure practice with plants, e.g., a rain
garden, is used as a bioretention or
bioinfiltration practice. The stormwater is
treated or filtered by the soil and the plants,
some water goes back into the air through
evapotranspiration, and most of the water
infiltrates into the soil. An alternative design
that can be used when there is contamination
present in subsoils is a rain garden with an
impermeable liner and an underdrain or
overflow pipe to convey excess water to a
Rain Garden with liner and underdrain. Designs such
as this allow for filtration and evapotranspiration, but
prevent infiltration into subsoils.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 12
nearby storm sewer or point of discharge. This type of practice can be thought of as
biofiltration. The plants and soil perform filtration and treatment functions, some
evapotranspiration will occur, and the water that is conveyed to the sewer system or receiving
water is cleaned. However, the water will not infiltrate through the contaminated soil toward
the groundwater.
Green roofs and cisterns for rainwater harvesting can also be used at sites where there are
contaminants of concern in the soil. These stormwater management practices help reduce the
amount of runoff soaking into the ground or running off site, and can provide corollary benefits.
For example, green roofs can help reduce urban heat island effects, and because they serve as
an insulation layer can help reduce energy costs for a building. Using a cistern can provide
water conservation benefits; stormwater that is collected during rain events can be used during
dry weather periods to irrigate lawns and gardens, thereby helping to conserve potable water.
Summary
Stormwater infiltration practices can provide important benefits where implementation of such
practices is feasible and environmentally protective. Benefits can include decreased stormwater
infrastructure costs, increased groundwater recharge, and decreased stormwater runoff.
Infiltration can be considered at infill redevelopment sites, vacant parcels, and brownfield sites,
but care must be taken to evaluate the potential for stormwater infiltration to mobilize
contaminants and contaminate groundwater. The decision tree presented on the following
page is a graphical representation of the process for evaluating the potential to implement
infiltration practices at a vacant parcel or brownfield site.
The identification of the location and size of the area where contaminant concentrations
represent an unacceptable risk is crucial to the application of stormwater BMPs. The prior uses
of a site and other information gathered through site assessments can provide valuable
information for making decisions about the site suitability for infiltration practices. Where
contaminants were or are present, soil testing can provide another layer of information
valuable for decision-making.
Successful implementation of stormwater management and infiltration practices at brownfield
sites requires careful planning. Stormwater management planning and implementation should
be integrated with site investigation, State approvals, the selection of clean-up approaches and
techniques, and the design and engineering of site improvements. Locating infiltration practices
so that they do not mobilize contaminants requires a collaborative effort by team members
responsible for delineating and defining the contamination, remedial engineering, site planning,
and site design. At sites where infiltration practices are not advisable, it may be possible to use
green infrastructure practices such as green roofs and biofiltration designs to manage
stormwater and also protect groundwater.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 13
Decision Flowchart for the Use of Stormwater Infiltration at Brownfield Sites
IsaLNAPL, DNAPL, biodegradable waste or
leachable contaminant source present at the
site?
Are the contaminants at the site leachable or
water soluble based on SPLP testing?
Will infiltration
interfere with required
remediation?
\f
Are parts of the
property not
impacted?
Isgroundwater
beneath the property
impacted (is there
evidence of
ground water
contamination)?
Infiltration of
Stormwater can be
considered in
unimpacted areas of
the property (soil and
groundwater) where it
will not .a"ect
impacted areas
•
Infiltration of
Stormwater should
not be considered as
part of the
Stormwater
management
approach
Infiltration can be
considered as a
Stormwater
management
approach at this site
Evaluate if infiltration of Stormwater
will accelerate the migration of
contaminants to off-site properties
Is the site near ecological or sensitive receptors? If so,
include Stormwater management design in ecological or
sensitive area risk assessment or remedial plan to ensure
sensitive or ecological receptors are not adversely impacted
Is a spill containment plan required as part of site reuse? If
so, design Stormwater management and infiltration
facilities so they are hydrauli call'/separate from spill
containmentfacilities including potential overflow from
spill containment areas.
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Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield Sites Page 14
Resources
National Resources Conservation Service (NRCS), "Soil Quality Indicators: Infiltration," USDA
Natural Resources Conservation Service. January 1998.
Natural Resources Conservation Service (NRCS), "Soil Quality Indicators," USDA Natural
Resources Conservation Service. June 2008.
Southeast Michigan Council of Governments and Michigan Department of Environmental
Quality, "Low Impact Development Manual for Michigan -A Design Guide for Implementers
and Reviewers" (see "Implementing LID in Special Areas"), SEMCOG 2008.
U.S. EPA, Design Principles for Stormwater Management on Compacted, Contaminated Soils in
Dense Urban Areas, http://www.epa.gov/swerosps/bf/tools/swdp0408.pdf
U.S. EPA, Case Studies for Stormwater Management on Compacted,Contaminated Soils in Dense
Urban Areas, http://www.epa.gov/swerosps/bf/tools/swcs0408.pdf
U.S. EPA, When are Stormwater Discharges Regulated as Class V Wells?
http://www.epa.gov/ogwdw/uic/class5/pdf/fs uic-class5 classvstudy fs storm.pdf
U.S. EPA, Brownfields and Urban Agriculture: Interim Guidelines for Safe Gardening Practices.
http://epa.gov/brownfields/urbanag/pdf/bf urban ag.pdf
University of Louisville, Sustainable Water Management on Brownfields Sites.
http://louisville.edu/cepm/publications/practice-guides-l/PG32%20-
%20Green%20lnfrastructure%20on%20Brownfields.pdf/view
EPA Publication Number 905F13001
This document was developed by U.S. EPA staff and Tetra Tech, Inc. working under a contract
with U.S. EPA.
Cover Image: Rendering of possible green infrastructure implementation at a vacant land parcel
in Milwaukee. Rendering courtesy of City of Milwaukee and Conservation Design Forum.
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