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
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.
EagleuilleBrook-2
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.
Who are the participating stakeholders and
key partners?
Connecticut DEP is responsible for developing TMDLs in the
state of Connecticut. To develop the 1C TMDL for Eagleville
Brook, DEP worked with key stakeholders, including UConn's
Center for Land Use Education and Research (CLEAR).
TMDL implementation, unlike TMDL development, is in the hands of local stakeholders
and partners, depending on the actions recommended by the TMDL. UConn's CLEAR
and the Town of Mansfield are currently engaged in a project funded through a Clean
Water Act (CWA) section 319 nonpoint source grant. Local watershed groups such as the
Willimantic River Alliance, the Quinebaug-Shetucket Heritage Corridor, Inc., and the
Thames River Basin Partnership have also taken an active interest in implementing the
Eagleville Brook TMDL.
How did stakeholders participate in the TMDL process?
The overall TMDL process includes the following elements: CWA section 303(d) listing
decisions, TMDL development, and TMDL implementation. Each element of the TMDL
process provided stakeholders with an opportunity to express concerns and share
information about the water quality problems in Eagleville Brook with DEP and other key
partners. A description of each element of the TMDL process is provided below.
Section 303(d) listing decisions
If a waterbody does not meet water quality standards (i.e., numeric or narrative criteria)
for one or more pollutants, it goes on a state's 303(d) list. Impaired waterbodies on this
list require a TMDL for each pollutant contributing to the impairment. Stakeholders
have the opportunity to provide input during the 303(d) listing process. While assessing
Eagleville Brook, DEP observed low fish population densities and large amounts of
habitat unoccupied by fish. Stretches of Eagleville Brook were almost devoid offish. The
surveys noted that sediment deposition from storm water runoff, as shown in Figure 2,
was affecting in-stream fish habitat. An extensive DEP benthic invertebrate assessment
following the fish surveys concluded that Eagleville Brook did meet the aquatic life
designated use in Connecticut's water quality standards. DEP placed Eagleville Brook on
Connecticut's 2004 list of impaired waterbodies requiring TMDL development.
TMDL development
Although DEP had sufficient information to determine that Eagleville Brook did not
support the aquatic life designated uses, the data did not clearly point to a specific cause
of impairment. As part of the TMDL development process, DEP conducted a Stressor
Identification (SI) analysis to determine the most probable cause. The results of the
SI analysis pointed to a complex array of pollutants transported by stormwater as the
probable cause of the impairment in Eagleville Brook. Because no one pollutant was
responsible for the impairment, DEP identified 1C as a surrogate measure based on the
relationship between impervious surfaces and stormwater quality and quantity. DEP
developed a technical support document that provides the scientific basis for the use of 1C
as a surrogate measure for stormwater related impacts by demonstrating the correlation
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between pollutant loads, stormwater flow, and runoff from impervious surfaces. The
technical support document recommends a target of 12 percent 1C for Connecticut
streams with a watershed size comparable to that of the Eagleville Brook watershed.
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.
DEP conducted an analysis of existing 1C conditions in the Eagleville Brook watershed
using UConn's Impervious Surface Assessment Tool (ISAT). Calculating the existing 1C
conditions in the watershed helped identify the percent 1C reductions needed in specific
locations to achieve the 11 percent 1C target. For example, the TMDL identifies the need
for a 59 percent 1C reduction in one area on UConn's campus to achieve the 11 percent
1C target.
DEP provided several opportunities for stakeholders to provide input on the Eagleville
Brook 1C TMDL, including public meetings and a formal public comment period. DEP
reviewed comments provided by the public on the draft TMDL and prepared a response
to comments document. According to DEP, public feedback on the draft TMDL was
largely favorable, although there were some concerns that an 1C TMDL approach might
restrict future growth and development. DEP reassured the public that this approach
would not focus on removing existing impervious surfaces or prevent future development.
Instead, the goals of the TMDL are intended to promote improved stormwater
management techniques and reduce the effects of stormwater runoff on the watershed.
TMDL implementation
Implementing the Eagleville Brook 1C TMDL involves a four-step adaptive management
strategy. The four steps are as follows:
O Reducing 1C where practical
O Disconnecting 1C from Eagleville Brook
O Minimizing additional disturbances
O Installing engineered best management practices (BMPs) to reduce the quantity and
improve the quality of stormwater runoff.
A CWA section 319 project for Eagleville Brook is designed to take advantage of nationally
recognized UConn expertise in stormwater management, landscape analysis, and land
use planning, including ongoing DEP-UConn partnerships with the Jordan Cove research
project and the Nonpoint Education for Municipal Officials (NEMO) education program.
The goal is to develop a watershed-specific water quality management plan.
As part of this project, UConn, NEMO, and the Town of Mansfield are mapping
potential locations for stormwater improvements and examining cost effectiveness for
recommended BMPs at the mapped locations.
The TMDL development process has influenced the UConn staff involved with the design
and implementation of stormwater BMPs, including the Campus Sustainable Design
Guidelines. The TMDL has also set the stage for efforts to test BMPs within the Eagleville
Brook watershed and measure site-scale results. For example, UConn is piloting a green
roof in one location and identifying other possible locations suitable for this innovative
stormwater management technique and others, such as rain gardens.
The Town of Mansfield has also implemented the Eagleville Brook 1C TMDL through
local land use planning and development reviews. For example, the town requested that
the Environmental Review Team conduct a review and prepare a report for a proposed
off-campus housing project and a small residential subdivision along Eagleville Brook.
EagleuilleBrook-3
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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
EagleuilleBrook-4
SEPA
December 2009 • EPA841-F-09-002A
For more information on the Eagleville Brook 1C TMDL, contact
Chris Bellucci, Connecticut Department of Environmental Protection
Christopher.Bellucci@ct.gov, (860) 424-3735
For more information on the Connecticut TMDL Program, visit
www.ct.gov/dep/cwp/view.asp7a=2719&q=325604&dep Nav_G ID=165 4
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