Hydrologic Assessment Executive Summary
Excerpted from the
Hydrologic
Assessment study, March 2002.
ES.1 Introduction
In 1994, Massachusetts embarked on a new approach to environmental
management -
the Watershed Initiative. Because the initiative involves the state's
coordination of its
decision-making process across regulatory programs, the multi-disciplinary
Basin
Teams were created with the goal of understanding watersheds and
the impacts of
decisions from various regulatory programs. This study was prepared
for and
funded by the Massachusetts Executive Office of Environmental Affairs
on behalf of
the Nashua River Watershed Team in response to DEM RFR #450, as
part of the
Massachusetts Watershed Initiative. The work was completed by Camp
Dresser Mckee
(CDM) in June 2002.
Available water is a critical component for the future
of Nashua River watershed
residents and for protection of aquatic resources. Despite being
in a water-rich
region, many rivers in Massachusetts are severely flow stressed.
This project provides
the foundation on which future water use decisions can be made in
the Nashua River
watershed.
The relationship of water withdrawal and wastewater
discharge and their effect on
river flow is the main objective of this study. In addition, this
report examines the
effects of future population growth and the associated demand for
additional water
supply sources and increase in wastewater flow.
The tasks set forth in this report are similar to
the river basin plans historically
produced by DEM in conjunction with other state and regional planning
agencies.
The findings of this report are intended to be used as a basis for
water management
and wastewater discharge permitting and to assess the potential
impacts to biological
resources of the watershed that may result from consumptive uses
of water.
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ES.2 Watershed
Description
The Nashua River watershed is 538 square miles in area and contains
all or part of 31
communities. Seven of the communities are in New Hampshire and the
remaining 24
communities are in Massachusetts. Figure ES-1 presents the Nashua
River watershed.
The communities include older, urbanized cities such as Leominster
and Fitchburg
and smaller, rural towns such as Ashby and Princeton. The population
of many of the
towns in the watershed is increasing rapidly, with some having growth
rates of 20%
predicted over the next twenty years. Flows associated with Devens
are accounted
for in the flows of the four local communities that make up Devens.
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ES.3 Water Supplies
The headwaters of the Nashua River contain Wachusett Reservoir,
a major water
supply for the metropolitan Boston area. In addition, the City of
Worcester has
several reservoirs in the headwaters of the Nashua River, which
that city uses as
water supply. Nineteen communities in the watershed withdraw water
either from
groundwater wells or from surface water reservoirs for public water
supplies. Future growth in these communities will put greater demand
on the water resources in the Nashua River.
The existing water suppliers withdraw 183 mgd annually
from the groundwater and
surface waters in the watershed, or 25.7 mgd if Worcester's and
MWRA's water
supplies are excluded. The water need for communities with supplies
in the
watershed is forecasted to increase to 187 mgd in the year 2020
or 29.7 mgd if
Worcester and MWRA water supplies are not included.
Currently, 23.8 mgd of water is distributed in water
service areas annually in the
basin by the public water suppliers. This amount is forecasted to
increase to 28.3 mgd
in the year 2020.
The assessment of water conservation by the public
water suppliers found room for
improvement. Two metrics, residential water use of 80 gpcd or less
and unaccounted
for water (UAW) of 15 percent or less, were used to evaluate the
water conservation
programs for each public water supplier. Five out of 25 water suppliers
exceeded the
residential benchmark of 80 gpcd. Eight water suppliers exceeded
the UAW
benchmark of 15%. In most cases, the water supplier explained the
high UAW in the
Annual Statistical Report (ASR) submitted to the Department of Environmental
Protection. Additionally, seven public water suppliers reported
UAW 5% or less,
which is unlikely to be accurate.
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ES.4 Water Supplies
at Risk
An evaluation was performed to identify public water supplies that
are in proximity
to either a Massachusetts Contingency Plan (MCP) site or solid waste
facility. A
ranking system was developed based on the proximity and the risk
posed by the site
to the water supply. Six community water supplies and three non-community
water
supplies were considered to be at risk from either a nearby MCP
site or a solid waste
facility.
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ES.5 Wastewater
Discharges
Seventeen communities have wastewater collection systems in the
watershed. A total
of 25.0 mgd of wastewater is collected annually in the watershed.
The amount of
wastewater collected is forecasted to increase to 32.7 mgd in the
year 2020. Currently,
four communities export wastewater from the watershed: Ashburnham
and Gardner
(to Gardner's Wastewater Treatment Plant in the Millers River watershed),
and West
Boylston, Holden and Rutland (to Worcester's Upper Blackstone wastewater
treatment plant).
The Nashua River and its tributaries receive the discharge
of wastewater from seven
public wastewater treatment plants. Three wastewater treatment plants
discharge to
the North Nashua River. Wastewater treatment plants also discharge
to the main
stem of the Nashua River.
The North Nashua River is a good example of the impact
of water withdrawal and
wastewater discharge. The headwaters of the North Nashua River contain
numerous
water supply sources, both groundwater and surface water reservoirs.
Water is
withdrawn from these headwater sources and discharged downstream
at the
municipal-owned wastewater treatment plants of Fitchburg and Leominster.
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ES.6 Inflow/Outflow
Analysis
An inflow/outflow analysis for the Nashua River was performed. The
watershed
was divided into 27 separate subareas, which were used to calculate
the water balance
at a small scale. This process was performed to determine areas
of the watershed that
may be subject to diminished river flow, as well as areas that may
have the potential
for additional withdrawal. The 27 subareas have been grouped into
five separate
subwatersheds: the Wachusett, North Nashua River, Squannacook River,
Nissitissit
River, and main Nashua River.
The approach used in the inflow/outflow analysis was
to tally the sources and uses of
water in each subarea. Information was collected on the location
of water supply
withdrawals, water distribution and wastewater collection service
areas, and areas
where wastewater discharge. Annual, August, and winter demand periods
were
evaluated.
Annual 2000
The 2000 annual inflow/outflow analysis shows a net gain of 0.7
mgd for the
Nashua River watershed or a net loss of 156.5 mgd when MWRA's and
Worcester's
water withdrawals are included.
The findings for individual subareas in the watershed
are more telling. Of the 27
subareas in the watershed, only eight have a net gain of flow, and
19 subareas have
a net loss of flow. Of the eight subareas that gain flow, five of
these subareas gain
flow from having a wastewater treatment plant discharge in the subarea.
August 2000
For this scenario, there is a net loss of 1.1 mgd for the Nashua
River watershed or a
net loss of 165.9 mgd if MWRA's and Worcester's withdrawals are
included.
Water withdrawn in August (29.8 mgd) is 3.5 mgd greater than the
average annual
volume (26.3 mgd), primarily to meet the greater summer water demand.
Of the 27 subareas in the watershed, 9 have a net gain of water
and 18 have a loss of
water.
Annual 2020
For this scenario, there is a net gain of 0.3 mgd for the Nashua
River watershed or a
net loss of 157.2 mgd if MWRA's and Worcester's withdrawals are
included.
Water withdrawn (30.0 mgd) predicted in 2020 will increase by 3.7
mgd over the
annual amount withdrawn (26.3 mgd) in 2000 primarily to meet the
increase in
water demand.
Wastewater collection is forecast to increase from
25.0 mgd in 2000 to 29.9 mgd in
2020, an increase of 4.9 mgd.
Of the 27 subareas in the watershed, 9 have a net
gain of water and 18 have a loss of
water.
August 2020
For this scenario, there is a net loss of 1.9 mgd for the Nashua
River watershed or a
net loss of 167.4 mgd if MWRA's and Worcester's withdrawals are
included.
Water withdrawals (34.3 mgd) predicted in 2020 will increase by
4.5 mgd over the
August 2000 withdrawn amount withdrawn (29.8 mgd) in 2000, primarily
to meet
the increase in water demand.
Wastewater collection is expected to increase from
20.3 mgd in 2000 to 24.7 mgd in
2020, an increase of 4.4 mgd.
Of the 27 subareas in the watershed, 9 have a net
gain of water and 18 have a loss of
water.
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ES.7 Subarea Flow
and Stream Flow
The average August and 7Q10 flows, for existing and future scenarios,
were
compared with predicted virgin flows in order to approximate the
level of stress of
each subbasin. DEM guidelines, as described in the draft memorandum:
Stressed
Basins in Massachusetts (Office of Water Resources, February 26,
2001) were followed
to estimate the stress level of each subbasin.
The DEM has defined three hydrologic stress classifications:
- High-Stress: net outflow equals or exceeds estimated
natural August median flow
- Medium-Stress: net outflow equals or exceeds estimated
natural 7Q10 flow
- Low-Stress: no net loss to the sub-basin.
Based on these classifications, the stress levels
for each subarea were determined for
existing conditions (year 2000) as well as predicted conditions
in the year 2020.
Following the DEM stress classification
system
One subarea-Flag Brook-is predicted to be highly stressed (net withdrawals
exceeding median August flow) in the Nashua River Basin under either
existing
condition. Additionally, Monoosnoc Brook is predicted to be highly
stressed in the
future (2020).
Seven subareas are predicted to have medium stress
under existing conditions (net
outflow equal/exceeding natural 7Q10): Quinapoxet River 2, Wachusett
Reservoir,
Monoosnoc Brook, Falulah Brook, Fall Brook, Wekepeke Brook, and
Mulpus Brook.
In the future (2020), Quinapoxet River 1 and Catacunemaug Brook
are expected to
be added to the medium stress list.
It is important to note that a large number of the
subareas predicted to have some
form of stress also contain multi-month reservoirs. These reservoirs
are capable of
storing large flows in the spring and holding them for use during
low flow periods in
late summer. Because of the stored volume, the impact of large demands
in these
basins may not be as great as the stress-classification system implies;
it is possible that
normal low flows are still being released from these reservoirs.
To properly determine the stress levels in these basins, a more
detailed study of each subarea is
required.
Because the Wachusett watershed is highly managed
for the Worcester and MWRA
withdrawals, these withdrawals were not considered in the evaluation
of stress in the
Wachusett Watershed-a much more detailed analysis would be required
to evaluate
their uses. Instead, the calculations were based on other uses of
water in the
watershed, particularly withdrawals by Holden, Rutland, Princeton,
Sterling, and
West Boylston. Based on these withdrawals, three of the four subareas
in the
Wachusett Watershed were calculated to have medium-stress in the
future.
This definition of stress is for water supply purposes. Stress can
also be induced on
aquatic life from poor water quality, loss of habitat, and for flow
reductions less than
those defined above.
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ES.8 Recommendations
The findings indicate that 11 of the 27 subareas in the Nashua River
watershed are or
will be either high stressed or medium stressed under the DEM classification
system.
The stressed subareas are predominately in the Wachusett and North
Nashua
subwatersheds. The following is recommended for the stressed subareas:
- More detailed inflow/outflow analysis to assess
the water balance of the multi-month reservoirs.
- Critical review of any additional water supplies
that may be sought in the stressed subareas.
- Emphasis on development and implementation of water
conservation plans for communities with supplies in the stressed
subareas, especially for those
communities that do not meet the benchmark levels.
- Assessment of aquatic habitat impacts from worsening
flow stresses.
- Critical review of any additional sewering in the
basin, especially sewering that moves water out of a stressed
subarea or out of the basin.
- Wastewater reuse or artificial recharge of wastewater
discharges should be
considered for any WWTP expansion in stressed subareas.
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Additional detail
for most impacted sub-basins
Quinapoxet River
(upper reaches - from the Quinapoxet Reservoir up)
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Quinapoxet sub-basin is currently
under a medium level of stress. With continued withdrawals over
the next 20 years, the entire Quinapoxet sub-basin will be experiencing
flow stress. The upper reaches as defined above will remain under
"medium stress". The lower reaches (remaining portion
discharging directly to Wachusett reservoir) will also be under
medium stress.
Medium stress means that the net 7Q10 outflow from the sub-basin
equals or exceeds the estimated natural 7Q10. 7Q10 is the lowest
consecutive 7 day streamflow that is likely to occur in a ten year
period in a particular river segment.
High stress means that the net average August outflow
from the sub-basin equals or exceeds the estimated natural August
average flow.
For the Upper Quinapoxet:
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.275 MGD (million gallons/day) and the existing 7Q10 is (- 0.718
MGD). In other words if the Quinapoxet had never been developed
0.275 MGD should be passing through during a seven day 10
year low. However, the real seven day 10 year low is (- 0.718
MGD) meaning it would be drawing from the aquifer for the
discharge.
The calculated average August virgin flow 3.460 MGD and the existing
average August flow is 2.467 MGD a deficit of about 29%
The calculated 2020 average August virgin flow remains the same
3.460 MGD and the 2020 average August flow is 2.078 MGD a
deficit of about 40%
For the Lower Quinapoxet
(below the Quinapoxet Reservoir): which is currently considered
under "low stress"
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.567 MGD (million gallons/day) and the existing 7Q10 is 0.188
MGD. In other words if the Quinapoxet had never been developed
0.567 MGD should be passing through during a seven day 10
year low. However, the real seven day 10 year low is 0.188
MGD.
The calculated average August virgin flow 7.123 MGD and the existing
average August flow is 6.744 MGD a deficit of about 5%.
The calculated 2020 average August virgin flow remains the same
7.123 MGD and the 2020 average August flow is 6.230 MGD a
deficit of about 15%. Putting the lower Quinapoxet into a category
of "medium stress"
Wachusett Reservoir
(see above note about reservoir operations)
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Wachusett sub-basin is currently
under a medium level of stress. With continued development and withdrawal
pressures, the sub-basin will continue as "medium stress"
by the year 2020. It should be noted that while there is a minimum
flow requirement for discharge over the Wachusett Dam, local and
regional water suppliers need to recognize the importance of continuing
demand for supply on the reservoir
This means that the net 7Q10 outflow from the sub-basin equals or
exceeds the estimated natural 7Q10. 7Q10 is the lowest consecutive
7 day streamflow that is likely to occur in a ten year period in
a particular river segment.
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.357 MGD (million gallons/day) and the existing 7Q10 is 1.824
MGD. In other words if the Wachusett had never been developed
0.357 MGD should be passing through during a seven day 10
year low. However, the real seven day 10 year low is 1.824
MGD. Note, the Massachusetts Water Resources Authority is required
to maintain a minimum release of about 1.8 MGD over the Wachusett
Dam.
The calculated average August virgin flow 4.485 MGD and the existing
average August flow is 2.181 MGD a deficit of about 51%.
The calculated 2020 average August virgin flow remains the same
4.485 MGD and the 2020 average August flow is 1.621 MGD a
deficit of about 64%.
Flag Brook (see
above note about reservoir operations)
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Flag Brook sub-basin is currently
under a high level of stress, and will continue a high level of
stress into 2020.
This means that the net average August outflow from the sub-basin
equals or exceeds the estimated natural August average flow.
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.689 MGD (million gallons/day) and the existing 7Q10 is (-3.935)
MGD. In other words if Flag Brook had never been developed
0.689 MGD should be passing through during a seven day 10
year low. However, the real seven day 10 year low is (-3.935)
MGD meaning it would be drawing from the reservoirs and aquifer
for the discharge.
The calculated average August virgin flow 4.255 MGD and the existing
average August flow is (-0.369) MGD a deficit of over 109%.
The calculated 2020 average August virgin flow remains the same
4.255 MGD and the 2020 average August flow is (-0.818) MGD
a deficit of over 120%.
Monoosnoc Brook
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Monoosnoc sub-basin is currently
under a medium level of stress, but it is bordering on a high level
of stress. Looking ahead to the year 2020, the Monoosnoc is placed
under a high level of stress.
This means that the net 7Q10 outflow from the sub-basin equals or
exceeds the estimated natural 7Q10. 7Q10 is the lowest consecutive
7 day streamflow that is likely to occur in a ten year period in
a particular river segment under current conditions.
And in the 2020 projection for a high stress level, the net average
August outflow from the sub-basin equals or exceeds the estimated
natural August average flow.
The calculated 7Q10 virgin flow (estimated undeveloped
or pre-development) is 0.622 MGD (million gallons/day) and the existing
7Q10 is (-2.519) MGD. In other words if the Monoosnoc had
never been developed 0.622 MGD should be passing through during
a seven day 10 year low. However, the real seven day
10 year low is (-2.519) MGD - meaning it would be drawing from the
aquifer for the discharge.
The calculated average August virgin flow 3.840 MGD and the existing
average August flow is 0.699 MGD a deficit of about 82%.
The calculated 2020 average August virgin flow remains the same
3.840 MGD and the 2020 average August flow is (-0.194) MGD
a deficit of over 100%
Fall Brook
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Fall Brook sub-basin is currently
under a medium level of stress. Looking ahead to the year 2020,
Fall Brook remains under a medium level of stress.
This means that the net 7Q10 outflow from the sub-basin equals or
exceeds the estimated natural 7Q10. 7Q10 is the lowest consecutive
7 day streamflow that is likely to occur in a ten year period in
a particular river segment.
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.393 MGD (million gallons/day) and the existing 7Q10 is (-0.277)
MGD. In other words if Fall Brook had never been developed
0.393 MGD should be passing through during a seven day 10
year low. However, the real seven day 10 year low is (-0.277)
MGD meaning it would be drawing from the aquifer for the
discharge.
The calculated average August virgin flow 2.426 MGD and the existing
average August flow is 1.756 MGD a deficit of about 28 %.
The calculated 2020 average August virgin flow remains the same
2.426 MGD and the 2020 average August flow is 1.573 MGD a
deficit of about 35%
Wekepeke Brook
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Wekepeke sub-basin is currently
under a medium level of stress. Looking ahead to the year 2020,
Wekepeke Brook remains under a medium level of stress.
This means that the net 7Q10 outflow from the sub-basin equals or
exceeds the estimated natural 7Q10. 7Q10 is the lowest consecutive
7 day streamflow that is likely to occur in a ten year period in
a particular river segment.
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.125 MGD (million gallons/day) and the existing 7Q10 is (- 0.712)
MGD. In other words - if the Wekepeke had never been developed 0.125
MGD should be passing through during a seven day 10 year
low. However, the real seven day 10 year low is (- 0.712)
MGD meaning it would be drawing from the aquifer for the
discharge.
The calculated average August virgin flow 5.254 MGD and the existing
average August flow is 4.416 MGD a deficit of about 15%.
The calculated 2020 average August virgin flow remains the same
5.254 MGD and the 2020 average August flow is 4.211 MGD a
deficit of about 20%
Mulpus Brook
Based on recent findings in an Hydrologic Analysis (inflow/outflow)
by Camp, Dresser, Mckee, under contract with EOEA for the Massachusetts
Watershed Initiative Nashua Team, the Mulpus Brook sub-basin is
currently under a medium level of stress. Looking ahead to 2020,
the Mulpus remains under a medium level of stress.
This means that the net 7Q10 outflow from the sub-basin equals or
exceeds the estimated natural 7Q10. 7Q10 is the lowest consecutive
7 day streamflow that is likely to occur in a ten year period in
a particular river segment.
The calculated 7Q10 virgin flow (estimated undeveloped or pre-development)
is 0.173 MGD (million gallons/day) and the existing 7Q10 is (-0.396)
MGD. In other words - if Mulpus Brook had never been developed 0.173
MGD should be passing through during a seven day 10 year
low. However, the real seven day 10 year low is (-0.396)
MGD - meaning it would be drawing from the aquifer for the discharge.
The calculated average August virgin flow 7.233 MGD and the existing
average August flow is 6.665 MGD a deficit of about 7.8%.
The calculated 2020 average August virgin flow remains the same
7.233 MGD and the 2020 average August flow is 6.646 MGD a
deficit of about 8.1%.
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Tables
Existing (2000) Stress Level
Predicted (2020) Stress Level
Maps:
August (2000) Water Balance
August (2020) Water Balance
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