Attachment 2:
Less than 9% Impervious Cover Assessments
06/08/12
Impaired Waters Assessment for
Impaired Waters with <9% Impervious Cover in
Contributing Watershed
Impaired Water Bodies
The list of impaired water bodies covered by this assessment is included in Table 1.
Impairments
Impairments included under this assessment methodology include those typically associated with
storm water runoff from impervious cover. Impairments for specific water bodies are listed in Table
1 for each water body as listed on MassDEP’s Massachusetts Year 2010 Integrated List of Waters
(MassDEP, 2011).
Relevant Water Quality Standards
This assessment covers a wide range of impairments related to a variety of water quality standards.
Relevant Water Quality Standards can be found on MassDEP’s website:
http://www.mass.gov/dep/service/regulations/314cmr04.pdf
Site Description
This assessment applies to the water bodies listed in Table 1. These water bodies are located
across the state and have various impairments that could potentially be related to storm water. They
potentially receive direct discharge from MassDOT urban roadways.
Assessment under BMP 7U
A Total Maximum Daily Load (TMDL) has not been developed for the impairments for the water
bodies listed in Table 1. Therefore, MassDOT assessed these impairments using the approach
described in BMP 7U of MassDOT’s Storm Water Management Plan. As described in BMP 7U’s
Description of MassDOT’s Application of Impervious Cover Method (MassDOT Application of IC
Method, MassDOT 2011), impervious cover (IC) provides a measure of the potential impact of
storm water on many impairments.
MassDOT’s Application of the Impervious Cover Method
MassDOT’s IC Method applies many aspects of USEPA Region I’s Impervious Cover Method
described in USEPA’s Stormwater TMDL Implementation Support Manual (ENSR, 2006) to
MassDOT’s Impaired Waters Assessment Program. The MassDOT IC method assesses potential
storm water impacts on the impaired water and evaluates the impervious cover reduction required
to ensure that storm water is not the cause of the impairments. Consistent with findings of USEPA
and others, when the impervious cover for a watershed exceeds 10% a decline in stream quality
occurs and that severe impairment can be expected when the IC exceeds 25%. Alternatively, the
Center for Watershed Protection states that the influence of IC on the receiving waters when the
Impaired Waters Assessment for Pathogen Impaired Waters
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06/08/12
watershed is in the range of 1-10 percent impervious “is relatively weak compared to other potential
watershed factors”. Therefore USEPA chose a 9% target (1 point less than 10%) as the value at
which storm water impairments are no longer a significant source of pollutants (CWP, 2003).
MassDOT also chose to use the 9% impervious cover target for its IC Method analysis. Additional
information regarding this method is provided in MassDOT’s Application of IC Method document.
Figure 1 illustrates the flow chart steps from the MassDOT’s Application of IC Method document
that are addressed by this assessment. To be conservative, MassDOT did not rule out water
bodies based on the IC value of the total watershed and instead based Table 1 on those water
bodies where the local watershed contributing to the impaired segment (referred to as the
subwatershed in this analysis) is equal to or less than the 9% target (Step 2).
The subwatershed to the impaired water body was delineated using the USGS Data Series 451.
When USGS Data Series did not delineate the subwatershed of the water body under review, the
GIS shapefiles were modified based on USGS topography to add specificity. Impervious cover data
was available as part of the USGS data layers Data Series 451 and MassGIS’s impervious surfaces
data layer. For the water bodies listed in Table 1, MassDOT calculated that each subwatershed
had less than 9% impervious cover. Therefore, as described in the MassDOT IC Method storm
water is not a likely cause of the impairments to these water bodies.
Conclusions
MassDOT has concluded, using the IC Method, that there is no required reduction in impervious
area for the water bodies listed in Table 1 because the percent of impervious cover within the
subwatershed is equal to or less than the 9% maximum IC target. This indicates that storm water
from this watershed is not likely the cause of the impairments. Therefore, further assessment of
these water bodies is not warranted under the Impaired Waters Program.
MassDOT will continue to identify opportunities to implement additional structural BMPs to address
pollutant loading when road work is conducted under MassDOT’s Programmed Projects Initiative
portion of the Impaired Waters Program. Work on programmed projects, which often include
broader scale road layout changes, may provide additional opportunities for construction of new
treatment BMPs. This is consistent with an iterative adaptive management approach to address
impairments. Furthermore, MassDOT will continue to implement the measures outlined in its Storm
water Management Plan (SWMP) to minimize the impacts of storm water from its property.
Impaired Waters Assessment for Pathogen Impaired Waters
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References
CWP, Center for Watershed Protection. 2003. Impact of Impervious Cover on Aquatic Systems.
Watershed Protection Research Monograph No. 1. Ellicot, MD.
ENSR. (2006). Stormwater TMDL Implementation Support Manual for US Environmental
Protection Agency Region 1. ENSR International & USEPA Region 1, Boston, MA.
Project No.: 10598-001-500. Retrieved from:
http://www.epa.gov/region1/eco/tmdl/pdfs/Stormwater-TMDL-Implementation-SupportManual.pdf
Massachusetts Department of Environmental Protection (MassDEP). (2011). Massachusetts Year
2010 Integrated List of Waters - Final Listing of the Condition of Massachusetts’ Waters
Pursuant to Sections 305(b), 314 and 303(d) of the Clean Water Act. Retrieved from:
http://www.mass.gov/dep/water/resources/10list6.pdf
Massachusetts Department of Transportation (MassDOT). (2011). Description of MassDOT’s
Application of Impervious Cover Method in BMP 7U (MassDOT Application of IC Method).
Impaired Waters Assessment for Pathogen Impaired Waters
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06/08/12
Figure 1 MassDOT's Application of the IC Method
Step 1: Calculate
% IC of Total
Contributing
Watershed
Watershed 9% IC
Stop Analysis
under this
program.
Revisit during
programmed
projects
Watershed > 9% IC
Step 2: Calculate
% IC of
Subwatershed
Subwatershed 9% IC
Stop Analysis
under this
program.
Revisit during
programmed
projects
Subwatershed >
Step 3: Calculate Amount of
Effective IC Reduction Required
in Subwatershed
Step 4: Apply Target Percent Reduction of IC
Needed in Subwatershed to MassDOT ‘s Urban
Directly Discharging Areas
Step 5: Calculate Effective IC
Reduction Credit from
Existing MassDOT BMPs
BMPs Provide Target
Effective IC Reduction
BMPs Do Not Provide Target
Effective IC Reduction
Step 6: Recommend
Additional BMPs to Extent
Practicable to Reduce
Effective IC to Target
Stop Analysis:
Storm Water
from MassDOT is
not causing the
Impairment
Forward Analysis
and BMP
Recommendatio
ns to Designers
for BMP Design
and Permitting
Impaired Waters Assessment for Pathogen Impaired Waters
Page 4 of 5
06/08/12
Table 1. Impaired Waters Addressed by IC Method with <9% IC in Watershed
Waterbody ID
MA35-07
Waterbody Name
Otter River
Impairments of Concern (2010)**
Turbidity, Nutrient/Eutrophication Biological Indicators,
Fishes Bioassessments, Aquatic Macroinvertebrate
Bioassessments
% IC in
Subwatershed
8.0%
MA36-11
Sevenmile River
NA
7.3%
MA36056
Eames Pond
Oxygen, Dissolved
6.9%
MA41-06
Cady Brook
(Low flow alterations*), Nutrient/Eutrophication Biological
Indicators
8.8%
MA81-07
Nashua River
Phosphorus (Total), Aquatic Macroinvertebrate
Bioassessments
8.6%
MA81-19
Squannacook River
NA
5.3%
MA91-08
Mill River
Aquatic Macroinvertebrate Bioassessments
7.6%
MA94-18
Bound Brook
(Fish-Passage Barrier*), Turbidity
5.9%
MA94-28
Aaron River
(Fish-Passage Barrier*), Excess Algal Growth, (NonNative Aquatic Plants*)
5.0%
MA11019
Cheshire Reservoir,
South Basin
(Non-Native Aquatic Plants*), Excess Algal Growth,
(Eurasian Water Milfoil, Myriophyllum spicatum*)
3.6%
MA32021
Congamond Lakes
Oxygen, Dissolved, (Eurasian Water Milfoil,
Myriophyllum spicatum*)
7.7%
MA72122
Uncas Pond
Oxygen, Dissolved, (Non-Native Aquatic Plants*)
7.0%
MA81098
Partridge Pond
Aquatic Plants (Macrophytes), Turbidity, (Non-Native
Aquatic Plants*)
3.4%
MA93080
Upper Banjo Pond
Turbidity, Aquatic Plants (Macrophytes)
0.4%
*Non-pollutant according to MA DEP 303d Year 2010 Integrated List of Waters
**Impairments listed on the MA DEP 303d Year 2010 Integrated list of Waters
Impaired Waters Assessment for Pathogen Impaired Waters
Page 5 of 5
PHILLIPSTON
WINCHENDON
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
TEMPLETON
MA DOT Urban Area Roads
ASHBURNHAM
¯
Otter River
MA35-07
Town Boundaries
5,500
2,750
0
MA35-07
Otter River
GARDNER
June 2012
HUBBARDSTON
WESTMINSTER
5,500
ft
NEW
BRAINTREE
OAKHAM
Subwatershed
RUTLAND
NORTH
BROOKFIELD
Impaired Water Body Being Assessed
SPENCER
Impaired Water Body
Impaired Stream Being Assessed
ile
enm -11
Sev MA36
er
Riv
Impaired Stream Segment
PAXTON
MA DOT Roads
MA DOT Urban Area Roads
¯
Town Boundaries
Eames Pond
MA36056
EAST
BROOKFIELD
5,500
2,750
0
5,500
ft
MA36-11 and MA36056
Sevenmile River
and Eames Pond
LEICESTER
HOLDEN
June 2012
CHARLTON
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
Cady Brook
MA41-06
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
4,000
2,000
0
¯
DUDLEY
STURBRIDGE
SOUTHBRIDGE
MA41-06
Cady Brook
June 2012
4,000
ft
Nashua
Riv
MA81-0 er
7
DUNSTABLE
Subwatershed
PEPPERELL
Impaired Water Body Being Assessed
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
6,500
3,250
0
¯
6,500
ft
TOWNSEND
MA81-19 and MA81-07
Squannacook River
and Nashua River
GROTON
Squan
na
River M cook
A81-19
June 2012
AYER
SHIRLEY
LUNENBURG
WEST
NEWBURY
NEWBURY
ROWLEY
GROVELAND
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
Mill River
MA91-08
Impaired Stream Being Assessed
Impaired Stream Segment
GEORGETOWN
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
4,000
2,000
¯
0
MA91-08
IPSWICH
Mill River
BOXFORD
June 2012
TOPSFIELD
4,000
ft
HULL
COHASSET
k
roo
nd B 18
u
o
B
94MA
SCITUATE
Subwatershed
Impaired Water Body Being Assessed
Aaron River
MA94-28
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
4,000
2,000
0
¯
4,000
ft
MA94-28 and MA94-18
NORWELL
Aaron River and
Bound Brook
HINGHAM
June 2012
HANOVER
DALTON
CHESHIRE
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
LANESBOROUGH
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
Cheshire Reservoir,
South Basin MA11019
3,750
1,875
0
¯
MA11019
Cheshire Reservoir
(South Basin)
PITTSFIELD
June 2012
3,750
ft
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
SOUTHWICK
Congamond
Lakes
MA32021
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
2,500
1,250
¯
0
MA32021
Congamond Lakes
June 2012
2,500
ft
NORFOLK
FRANKLIN
Subwatershed
Impaired Water Body Being Assessed
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
Uncas Pond
MA72122
2,500
1,250
¯
0
MA72122
Uncas Pond
WRENTHAM
June 2012
2,500
ft
GARDNER
WESTMINSTER
Subwatershed
Impaired Water Body Being Assessed
Partridge
Pond
MA81098
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Town Boundaries
2,500
HUBBARDSTON
1,250
¯
0
MA81098
Partridge Pond
June 2012
2,500
ft
GLOUCESTER
Subwatershed
Impaired Water Body Being Assessed
GLOUCESTER
Impaired Water Body
Impaired Stream Being Assessed
Impaired Stream Segment
MA DOT Roads
MA DOT Urban Area Roads
Upper
Banjo Pond
MA93080
Town Boundaries
2,500
1,250
¯
0
MA93080
Upper Banjo Pond
June 2012
MANCHESTER
2,500
ft