Section 319
DNPDINT SOURCF PROGRAM SUCCESS STORY
Stakeholders Cooperate to Remove Dam and Restore Stream Hydrology
I , A century-old dam across Black Brook created an impoundment
\J U WU ca||ecj Maxwell Pond, which was a site for ice harvesting, fishing,
swimming and other recreation. Over time, sediment from poorly managed industrial sites accumulated
in the pond, which became stagnant and shallow. As a result, the New Hampshire Department of
Environmental Services (NHDES) added Maxwell Pond to the 2002 Clean Water Act (CWA) section
303(d) list of impaired waters. Stakeholders restored the pond's water quality by reducing upstream
sediment sources and removing the dam. Once Black Brook returned to its free-flowing condition (and
Maxwell Pond ceased to exist and was reclaimed as a segment of Black Brook), the dissolved oxygen
level rebounded and the brook could once again support its aquatic life designated use. As a result of
the improvements, in 2010 NHDES removed the former Maxwell Pond portion of Black Brook from the
state's CWA section 303(d) list of impaired waters for dissolved oxygen.
Problem
New Hampshire's Black Brook flows approximately
seven miles from its headwaters in the town of
Dunbarton to the city of Manchester, where it emp-
ties into the Merrimack River. More than 100 years
ago (circa 1900), Maxwell Pond Dam was construct-
ed across Black Brook in northwest Manchester to
create an ice-harvesting pond (Figurel). When first
created, Maxwell Pond included 5.5 acres of open
water and had a maximum depth of 12 feet.
In the late 1950s, a cement processing plant/sand
and gravel company began operating in the Black
Brook watershed upstream of Maxwell Pond.
Historically, the company stockpiled materials next
to the brook, had poor on-site stormwater controls,
and built undersized culverts at road crossings,
which caused flooding and exacerbated erosion
during storm events. The excessive sediment load
from within the watershed was transported in the
swift flow of Black Brook and then deposited in
Maxwell Pond as the flow decreased within the
impoundment.
By 2002 the pond that had once hosted ice harvest-
ing, skating, swimming, fishing and other uses had
become severely impaired by sediment accumula-
tion. The maximum water depth had diminished
to three feet. Maxwell Pond was warm, supported
excessive aquatic plant growth, and had low dis-
solved oxygen levels. The applicable New Hampshire
water quality standard for dissolved oxygen requires
that Class B waters achieve a 75 percent minimum
Figure 1. Maxwell Pond Dam on Black Brook in
September 2008.
daily average dissolved oxygen saturation and meet a mini-
mum instantaneous concentration of 5.0 milligrams per
liter (mg/L). Maxwell Pond data showed that dissolved oxy-
gen levels violated both the dissolved oxygen saturation
standard (in 10 of 19 samples) and the dissolved oxygen
concentration standard (in 6 of 19 samples). Because the
waterbody did not support its aquatic life designated use,
NHDES added Maxwell Pond to the state's 2002 CWA sec-
tion 303(d) list of impaired waters for low dissolved oxygen
concentration and dissolved oxygen saturation. As a result
of those impairments, along with additional environmental
concerns, recent flooding, and other public safety issues,
the city of Manchester was compelled to repair or remove
the dam.
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Project Highlights
Table 1. Maxwell Pond Data for 20091
Multiple partners began work to restore Black
Brook in 2002. Using EPA CWA section 319 funds,
Trout Unlimited managed a project that studied
the causes of the impairments and considered
strategies for watershed restoration (including dam
removal). The owner of Aggregate Industries imple-
mented sediment control practices and removed
perched, undersized culverts to reduce erosion
upstream of the project site.
In 2006 the city of Manchester administered a
second CWA section 319-funded project to design
and implement the restoration project. The NHDES
Dam Maintenance Section began removing the dam
in February 2009. By mid-
March, Black Brookflowed
freely to the Merrimack
River for the first time
in more than 100 years.
Project partners stabilized
and replanted slopes in
spring 2009 (Figure 2).
Additional water quality,
vegetation, fish population
and physical/hydrological
monitoring are ongoing.
Partners plan to complete
more riparian plantings
and additional streambank
stabilization activities
during 2010.
Figure 2. Same location as Figure 1
showing Black Brook in June 2009
after the dam was removed and
natural gas line relocated.
Results
Removing the dam in 2009 drained Maxwell Pond
and reestablished the free-flowing condition of
Black Brook. Participants in the NHDES Volunteer
Lake Assessment Program and Volunteer River
Assessment Program monitored dissolved oxy-
gen levels before and after NHDES removed the
dam. The data show that the Black Brook riverine
assessment unit (NHRIV700060801-05-02) that
runs through the former Maxwell Pond site now
meets water quality standards for dissolved oxygen
(Table 1). If the data had shown continued dissolved
oxygen problems at the former Maxwell Pond site,
NHDES would have transferred the impairment to
Black Brook. However, because the assessment
unit now meets water quality standards, NHDES has
Sample date
28 Jun09
23Jul09
23Aug 09
18 Sep 09
26 Sep 09
Former Impoundment Site (01A-BKB)
DO (mg/L)
7.60
8.18
7.62
10.55
9.01
DO Saturation (%)
84.5
87.9
90.2
101.9
84.0
1 To meet the water quality standards, the dissolved
oxygen (DO) concentration must be at least 5 mg/L and
the DO saturation must be at least 75 percent.
removed the former Maxwell Pond portion of Black
Brook from the state's 2010 CWA section 303(d)
list of impaired waters for dissolved oxygen. Black
Brook assessment unit NHRIV700060801-05-02
remains on the impaired waters list for mercury,
benthic macroinvertebrate bioassessments and pH.
Partners and Funding
Numerous partners cooperated on the project,
including the city of Manchester, local residents,
local companies, NHDES and EPA. EPA CWA section
319 funds provided $13,350 for the initial study and
$105,000 to administer, plan, document and imple-
ment the project. The city of Manchester, in close
cooperation with NHDES staff, provided project
coordination. The city contributed $40,000. In addi-
tion to the CWA section 319 grants, federal support
came from a $50,000 American Rivers/National
Oceanic and Atmospheric Administration (NOAA)
grant, $10,000 from Trout Unlimited/NOAA funds,
and $64,000 from Gulf of Maine Council/NOAA
funds. State project funding included a $6,000
New Hampshire Corporate Wetlands Restoration
Partnership grant and $25,000 from the New
Hampshire State Conservation Committee. Fairpoint
Communications provided $46,450, and National
Grid provided $149,539 in services to relocate
natural gas and telephone lines affected by removal
of the dam structure. Aggregate Industries provided
$150,000 in services to correct upstream sediment
contribution and fish passage obstructions. Many
others, including local residents, representatives
from New Hampshire Fish and Game, Dubois & King
Inc., Amoskeag Fishways, and state-funded NHDES
staff, provided in-kind services (worth $26,000).
I
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-10-001W
September 2010
For additional information contact:
Barbara McMillan
Watershed Outreach Coordinator
New Hampshire Department
of Environmental Services
603-271-7889 • Barbara.mcmillan@des.nh.gov
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