GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 5
United States
Environmental Protection
Agency
EPA832F12016
Total Maximum
Daily Loads
This factsheet is the fifth in a series of six on integrating green
infrastructure concepts into permitting, enforcement, and
water quality standards actions.
Introduction
Implementing TMDLs with
Green Infrastructure
Watershed Planning
TMDL Case Studies
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Integrating Green Infrastructure Concepts into
Permitting, Enforcement, and Water Quality
Standards Actions
This factsheet is the fifth in a series of
six factsheets in the U.S. EPA Green
Infrastructure Permitting and Enforcement
Series (http://water.epa.gov/infrastructure/
greeninfrastructure/gi_regulatory.
cfm#permittingseriesA This series
describes how EPA and state permitting and
enforcement professionals can incorporate
green infrastructure practices and approaches
into National Pollutant Discharge Elimination
System (NPDES) wet weather programs,
including stormwater permits, Total
Maximum Daily Loads (TMDLs), combined
sewer overflow (CSO) long-term control
plans (LTCPs), and enforcement actions.
This series builds upon EPA's continued
investment in green infrastructure and low
impact development. Existing EPA authority,
guidance, and agreements enable EPA
Regions and state agencies to work with
permittees to include green infrastructure
measures as part of control programs.
For additional resources on green infrastructure,
go to the EPA Green Infrastructure Web
page: http://water.epa.gov/infrastructure/
greeninfrastructure/index.cfm.
Key green infrastructure guidance issued
to date can be found at: http://water.epa.
gov/infrastructu re/green infrastructure/
gLpolicy.cfm.
Introduction
Throughout the U.S., there are many waters listed for water
quality impairments associated with combined sewer
overflows (CSOs), storm sewer overflows (SSOs), and
urban and suburban stormwater discharges. In addition
to delivering pollutant loadings to receiving waters, the
volume and energy of stormwater discharges can cause
physical changes to water bodies. Green infrastructure
practices can be implemented to reduce pollutant loadings
and the volume of wet weather discharges, and help
restore and protect water quality.
The purpose of this factsheet is to describe how Total
Maximum Daily Loads (TMDLs) and TMDL implementation
plans (IPs) can address the hydrological factors that
contribute to impairments by including green infrastructure.
This factsheet also summarizes two case studies to
demonstrate the principles discussed.
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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 5
Implementing TMDLs with Green Infrastructure
Section 303(d) of the Clean Water Act requires States
(and authorized Tribes) to establish a list of waters for
which technology-based effluent limits are not sufficient to
implement water quality standards. After establishing the
303(d) list. States are required to create a TMDLfor each
impaired water body that calculates the maximum amount
of pollutants the water body can receive and still meet
water quality standards. Once these pollutant "budgets"
or allocations are calculated, they can then be translated
into management actions that are implemented through
permitting and/or non-regulatory programs.
Currently there are thousands of 303(d)-listed waters
in the U.S. for stormwater-source pollutants such as
pathogens, nutrients, sediments, and metals. In addition,
many listed waters have degraded habitat and/or impaired
biological communities that are related to changes in
natural hydrology that have occurred as development
hastaken place. Urban and suburban development
often is associated with greater areas of impervious
surfaces, resulting in increased stormwater volumes and
velocities, which are highly erosive and degrade stream
and lake habitats. As land use increasingly becomes more
urbanized, water body impairments from stormwater
sources likely will increase, requiring additional TMDLs.
The following sections discuss how green infrastructure
concepts and practices can be integrated into TMDLs and
TMDL IPs to help restore impaired waters.
Future Growth
EPA's regulations at 40 CFR §130.2(i) and §130.7 define a
TMDL asthe sum of wasteload allocations (WLAs) for point
sources plus load allocations (LAs) for nonpoint sources
plus a margin of safety (MOS) to account for uncertainty.
Mathematically, a TMDL can be expressed as follows:
TMDL
MOS
WLAs are loads allotted to existing and future point
sources, and LAs are loads allotted to existing and future
nonpoint sources plus loads from natural background.
"Future growth allowances" in TMDLs account for
anticipated new or increased pollutant loadings. For
instance, in areas where land use changes are anticipated,
TMDLs can include a reserve for increased loadings
of pollutants caused by land use changes or future
population growth. This reserve can be expressed as a
distinct element in the mathematical expression above, or
included in the WLAs or LAs. For example, if the population
being served by a municipal wastewater treatment plant
is expected to grow, the volume of the discharge from
the wastewater treatment plant (WWTP) would also be
expected to grow. In a case like this, the TMDL might
include a "future growth allocation" for the WWTP
discharge reflecting any additional pollutant loadings
expected as a result of population growth.
A "future growth allocation" can also be included in the
TMDLfor stormwater discharges if significant land use
changes are expected to occur in the drainage area.
For example, if open space and farmland are predicted
to be converted to residential and industrial land uses,
there will be more imperviousness in the drainage area.
The volume of stormwater and the pollutant loadings
for many constituents will likely increase when the
development occurs. In situations such as this, the TMDL
may include a "future growth allocation" reflecting the
expected increases in pollutant loadings from stormwater
discharges.
A "future growth allocation" for stormwater will typically
reflect at least two factors:
1. The anticipated extent of new development (future
growth), i.e., how much land area will convert from open
space or agricultural uses to more intensive land uses.
2. The anticipated design of the new development
areas, i.e., will conventional development practices
be implemented, or will green infrastructure practices
be widely implemented? The future growth allocation
typically can be lower if green infrastructure practices
will be systematically implemented.
In determining a "future growth allocation" for stormwater
in a TMDL, population projections and land use plans
can be used to estimate the future growth, and pollutant
loadings associated with the future development can be
estimated using various modeling tools. Typically, when
green infrastructure practices are implemented, the "future
growth allocation" for stormwater can be lower. If the
"future growth allocation" for stormwater can be reduced
by planning for green infrastructure practices, this may
create more flexibility with regard to other allocations in the
TMDL while still meeting overall pollutant reduction targets.
Implementation Plan
TMDL IPs describe the management actions that can be
adopted to reduce pollutant loadings to meet the water
quality targets identified in the TMDL. Although there are
no federal requirements that IPs be approved by EPA or
included in a TMDL, many States do develop IPs and/or
include some implementation information in the TMDL.
An IP can specifically discuss how green infrastructure
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K:
Effective green infrastructure approaches like rain gardens and swales help protect our waterways for safe recreational uses.
practices can help restore and protect water bodies,
and can identify regulatory, permitting, or non-regulatory
actions or programs to stimulate green infrastructure
implementation. For example, a TMDL's implementation plan
might discuss which stormwater management practices
could be, or are expected to be, implemented to meet the
WLA(s)orLA(s)intheTMDL
ATMDL implementation plan could potentially also identify
the long-term stormwater management controls needed to
restore and protect impaired waters. These controls could
be built into stormwater permits for construction sites and
MS4 permits. The construction general permit for sites
in the Big Darby Creek watershed in Ohio is an example
of an NPDES permitthatwill foster green infrastructure
implementation. The permit includes groundwater recharge
requirements, which will be accomplished in many cases
through use of green infrastructure practices. See:
http://www.epa.state.oh.us/dsw/permits/GP_
ConstructionSiteStormWater_Darby.aspx
An IP can include mechanisms for implementing green
infrastructure practices where they were anticipated in
calculating the "future growth allocation." For example,
local jurisdictions can establish requirements and
standards for green infrastructure implementation in local
codes and ordinances. The Conservation Design ordinance
adopted by the Village of Homer Glen (Illinois) is an
example of a local ordinance thatwill reduce stormwater
volumes and pollutant loads from areas where new
development occurs.
See: http://www.homerglenil.org/Ordinances/OR05-
062ConstructionHours.pdf
Following are two additional examples of IPs which include
green infrastructure components to control pollutant loads:
Machado Lake Toxics TMDL - Machado Lake in Los
Angeles, California is impaired for pesticides and PCBs.
The sources of impairments are primarily stormwater
discharges. Numeric targets have been set for water.
sediment, and fish tissue to protect aquatic life, fishing,
and other recreational uses in the lake. WLAs are mass-
based and established to control the suspended sediment
associated contaminants. The implementation plan
identifies various green infrastructure best management
practices (BMPs) as effective means of controlling the
pollutant loads. The implementation plan notes, "Structural
BMPs may include the placement of stormwater treatment
devices designed to reduce sediment loading, such as
infiltration trenches, vegetated swales, and/or filter strips
at critical points in the watershed. These types of BMPs
generally reduce stormwater velocity, which allows
sediment to settle out and to infiltrate runoff."
See: http://www.waterboards.ca.gov/losangeles/
board_decisions/basin_plan_amendments/
technical_documents/79_New/2010_1122/final_
staff%20report.pdf
Los Angeles River Bacteria TMDL - The Los Angeles River
in California is impaired for bacteria, and this TMDL sets
California's bacterial indicator standards for E. coli as
the numeric targets. The implementation plan includes
multiple Gl approaches. BMPs such as retention, filtration,
bioretention, and biofiltration are identified as methods to
reduce pollutant loads. The implementation plan states,
"Local, on-site, or subwatershed-based projects may be
placed in parks, public land, vacant property, and other
open spaces within the Los Angeles River Watershed....
The types of projects could vary significantly, but would
generally focus on multiple benefits including water
quality improvements, water conservation (either reduced
water use or local recharge), and potentially recreation
or aesthetic benefits." The plan estimates that 406 million
gallons of water per day (MGD) could be managed by
implementation of infiltration projects.
See: http://www.waterboards.ca.gov/losangeles/
board_decisions/basin_plan_amendments/
technical_documents/80_New/LARiverFinal/Staff%20
Report%20LAR%20Bact%2015Jul10%20final.pdf
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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 5
Watershed Planning
In some cases, watershed organizations, municipalities, or
regional planning agencies may develop watershed plans
to restore and/or protect waters. Watershed plans that are
developed or implemented with Clean Water Act Section
319 funds to address 303(d)-listed waters must include at
least nine minimum elements.
See http://www.epa.gov/EPA-WATER/2002/August/
Day-26/w21652.htm.
One of those nine elements is a description of the
management measures that will need to be implemented
to achieve target load reductions (as well as to achieve
other watershed goals identified in the watershed plan).
Where there are wet weather-related pollutant loadings
or other impacts from stormwater (eroded stream
channels, imbeddedness in the substrate), watershed
plans can identify opportunities to use green infrastructure
approaches to restore and protect water quality and
aquatic habitat.
TMDL Case Studies
Supplement 2 of this fact sheet series (see [link]) provides
information on two case studies where the hydrology of the
watershed was specifically addressed as part of the TMDL:
the Olentangy River (Ohio) and Barberry Creek (Maine).
The Olentangy River TMDL identifies the management of
stormwater quantity and quality in developing areas as
an important step to preserving natural stream function
through channel protection, and restoring stream habitat in
agricultural areas. Several sections of the TMDL describe
implementation of green infrastructure measures to
restore/maintain natural hydrology.
The Barberry Creek TMDL addresses the problem of metals
from stormwater runoff through the reduction of impervious
cover. The implementation plan contains discussion of
green infrastructure practices including general stream
restoration techniques, disconnection of impervious
surfaces, and conversion of impervious surfaces to
pervious surfaces.
Vegetated riparian zones act as a living filter, removing excess
nutrients, sediment, and other contaminants from stormwater runoff.
Photo courtesy of USDA NRCS
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Green Infrastructure Permitting and Enforcement Series
This series on integrating green infrastructure concepts into
permitting, enforcement, and water quality standards actions
contains six factsheets plus four supplemental materials
that can be found at http://water.epa.gov/infrastructure/
greeninfrastructure/gi_regulatory.cfm#permittingseries.
Factsheets
1. Potential Challenges and Accountability Considerations
2. Combined Sewer Overflows
3. Sanitary Sewer Overflows
b. Stormwater
5. Total Maximum Daily Loads
6. Water Quality Standards
Supplemental Materials
1. Consent Decrees that Include Green Infrastructure Provisions
2. Consent Decree Language Addressing Green for Grey
Substitutions
3. Green Infrastructure Models and Calculators
b. Green Infrastructure in Total Maximum Daily Loads (TMDLs)
United States
Environmental Protection
Agency
For additional resources on green infrastructure,
goto the EPA Green Infrastructure Web page:
http://www.epa.gov/greeninfrastructure/.
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