United States
Environmental Protection
Agency
Total Maximum Daily Loads
THSDLs
TMDL at a Glance
Eagleville Brook Impervious
Cover (1C) TMDL
(approved March 2007)
www.ct.gov/dep/lib/dep/water/tmdl/tmdl_final/
eaglevillefinal.pdf
Factors causing impairment
Aquatic life designated uses impaired due to
a complex array of pollutants transported by
Stormwater
Innovative TMDL Focuses on Impervious Cover to
Address Stormwater Impacts in the Eagleville Brook
Watershed
Like many urban watersheds, the Eagleville Brook watershed in eastern Connecticut
is characterized by a mosaic of hard surfaces, such as parking lots and rooftops, that
do not allow rain to infiltrate. Traveling over these impervious surfaces, large volumes
of rapidly moving Stormwater can carry a complex array of pollutants and cause other
problems, such as streambank erosion and flooding. As shown in Figure 1, urban areas
surround the headwaters of Eagleville Brook, including the University of Connecticut
(UConn) and the Town of Mansfield, Eagleville Brook demonstrated water quality
problems associated with Stormwater runoff from urban impervious surfaces.
The Connecticut Department of Environmental Protection (DEP) conducted
surveys of fish and macroinvertebrate communities. Figure 2 shows how excessive
sedimentation from Stormwater runoff can degrade aquatic habitat. From these
surveys, DEP concluded that Eagleville Brook did not meet the aquatic life
designated use in Connecticut's water quality standards and required a TMDL.
Studies by DEP across small Connecticut watersheds indicate that as little as
11 percent impervious surface has the potential to affect the speed, the timing, and
the quality of runoff to a stream. Parts of the brook's watershed exceed 25 percent
impervious surface.
Sources contributing to impairment
Urban storm water runoff from impervious surfaces.
Impervious cover used as surrogate to address mix
of pollutants and other stressors conveyed by storm
water
Restoration options
Reduce and disconnect impervious cover where
practical; minimize additional disturbance; install
engineered best management practices to reduce
effects of impervious coveron receiving waters
Stakeholder involvement
University of Connecticut, Town of Mansfield,
Connecticut Department of Environmental Protection,
Willimantic River Alliance, local businesses and
watershed residents
Status of waternody
Ongoing implementation
Benefits to stakeholders
Improved water quality and aquatic health,
increased education, access to funding, and effective
partnerships
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To address the aquatic
life impairment, DEP
developed an innovative
TMDL for Eagleville
Brook. Rather than
identifying reductions
in specific pollutants,
the Eagleville Brook
TMDL establishes a
target percentage of
impervious cover (1C) for
the watershed. Although
1C is not the direct factor
causing the impairment,
it is a good indirect, or
surrogate, measure because of the relationship between impervious surfaces and
stormwater-related water quality problems. As stated in the final TMDL report,
the goal of the TMDL is to reduce the effects of Stormwater on aquatic life in
Eagleville Brook. Therefore, future evaluation of the effectiveness of the TMDL
will focus on the health of aquatic life in Eagleville Brook—not on measuring
reductions in impervious cover in the watershed.
Figure 1. Location of the Eagleville Brook watershed.
What is a total maximum daily load (TMDL)?
It is a study or analysis that calculates the maximum amount of a pollutant that a waterbody can receive and still meet
water quality standards. The TMDL establishes a pollutant budget and then allocates portions of the overall budget to
the pollutant's sources. For more information on TMDLs, visit EPA's website at www.epa.gov/owow/tmdl.
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Figure 2. Excessive sedimentation is a contributing cause of degraded habitat
in Eagleville Brook.
How are TMDLs at work in the Eagleville
Brook watershed?
The Eagleville Brook 1C TMDL established a framework
for highlighting water quality concerns and developing
workable solutions. DEP applied the stressor identification
process to examine the relationship between impervious
cover and the adverse effect on aquatic life. This process
enabled stakeholders to see connections between land use
actions and water quality.
Through the TMDL development process, DEP set a
combined load allocation and wasteload allocation of
11 percent 1C for Eagleville Brook. This target represents
a recommended 12 percent 1C threshold target and a
margin of safety of 1 percent 1C. The margin of safety is
intended to account for uncertainty in the analysis.
What is the current status of Eagleville Brook
as a result of the TMDL process?
With approval of the Eagleville Brook 1C TMDL in March
2007, partners are just beginning to implement the
TMDL. Over time, DEP will measure the aquatic diversity
in Eagleville Brook to determine if implementation
efforts are making progress toward restoring the brook's
aquatic life designated uses. Although the ultimate
measure of success is meeting the aquatic life designated
uses, progress toward reducing impervious cover and
mitigating impacts from stormwater runoff can also serve
as an interim measure of TMDL implementation success.
How did local stakeholders benefit from the
TMDL process?
Although it is too soon to measure the water quality
benefits from implementing the TMDL, other benefits
from the TMDL process include the following:
O Increased stakeholder awareness and education.
Through the stressor identification analysis,
stakeholders participating in the TMDL development
process gained a better understanding of the connection
between pollutant loads from impervious surfaces,
the effects of stormwater volume and velocity from
impervious surfaces, and changes to aquatic habitat and
diversity.
O Support for innovative stormwater management
techniques. The innovative approach to the Eagleville
Brook TMDL translates to the consideration and
piloting of innovative stormwater management
techniques that fall under the umbrella of low impact
design (LID). LID techniques under consideration in
the Eagleville Brook watershed include green roofs and
rain gardens. Through the mapping process, DEP and
its partners will identify other potential locations for
innovative stormwater management techniques and
determine the associated cost-effectiveness of these
approaches at priority locations.
O Increased local stakeholder participation
opportunities. The Eagleville Brook 1C TMDL process
has fostered citizen involvement, such as participation
in the streamwalk project sponsored by the Quinebaug-
Shetucket Heritage Corridor Water Subcommittee.
O Increased access to funding. UConn and the Town
of Mansfield are currently using Clean Water Act
section 319 grant funding to create a watershed-based
plan for the Eagleville Brook watershed that will assist
with TMDL implementation. The total project cost is
$349,731, with $200,000 in section 319 nonpoint source
grant funding from DEP and $149,731 in matching funds
from UConn. The project will identify opportunities for
near-term BMP implementation, as well as document
a general methodology by which other regulated
communities and entities can address impervious cover-
based TMDLs. In addition, UConn is implementing a
green roof project at a science building on campus. This
project has a total cost of $83,333,000, with $50,000
in section 319 nonpoint source grant funds from DEP
and $33,333 in matching funds from UConn. DEP
is providing an additional $25,687 for this project to
support more water quality monitoring activities
For more information on the Eagleville Brook 1C TMDL, contact
Chris Bellucci, Connecticut Department of Environmental Protection, Christopher.Bellucci@ct.gov, (860) 424-3735 Q CPA
For more information on the Connecticut TMDL Program, visit '
www.ct.gov/dep/cwp/view.asp?a=2719&q=325604&depNav GID=1654 December 2009
EPA841-F-09-002B
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