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Subbasins -  Nashua River Main Stem
Geographic & Ecosystem Characteristics | Land Ownership & Land Use Patterns
Major Water Resource Issues | Recreation & Priority Habitat Areas
Resource Protection Goals & Recommended Actions

Land Area: 65.8 sq miles
Primary Municipalities: Bolton, Groton, Harvard, Lancaster, Pepperell, and Shirley MA; Hollis and Nashua, NH
Permanently Protected Land Area: 3,611 acres or 9.8%
Limited Protection Land Area (Chap. 61, etc.): 1,324 acres
River length: 36.86 miles
Feeder Streams: Bowers-Nonacoicus, Catacunemaug, Flints, James, Mulpus, Unketey Brooks; South, Still and North Nashua Rivers

% Imperviousness: 9.1%
Land Use: 64% forest, 13% residential, 7% ag/open
# of MA NHESP Priority Sites: 15
# of discharge permits: 3 NPDES major; 4 NPDES minor
Most threatened waterbodies: Pepperell Pond
Dams: 4 Ayer, Pepperell and 2 in Nashua
Location within the Nashua River Watershed Water Resources Habitat Analysis
Open Space Water Resources Natural Heritage
Limited Protection Water Resources Recreation

Geographic Overview and Ecosystem Characteristics: This north to south running, long and narrow subbasin 1 lies within portions of the following communities: Bolton, Groton, Harvard, Lancaster, Pepperell and Shirley, Massachusetts and Hollis and Nashua, New Hampshire. Located in the Southern New England Coastal Plains and Hills ecoregion of central Massachusetts, the Mainstem Nashua River flows into the Merrimack River in Nashua, New Hampshire. The Mainstem Nashua River officially begins in Lancaster at the confluence of its two major tributaries: the North and South Nashua Rivers. Routes 2, 2A, 110, 111, 113, 117, 119 and 225 cross through this subbasin. A notable ridgeline in this subbasin runs from Shipley Hill to Mt. Lebanon in Pepperell.

The Southern New England Coastal Plains and Hills ecoregion is an area with generally similar soils, vegetation, shape of the land, and especially, cool climate and bedrock geology (glacial tills and outwash deposits). The river maintains a good flow rate until it deepens and slows near its mouth. Streamflow, as in most of New England, has significant seasonal changes 2. It is interesting to note that this subbasin is unusual in having once been the site of a glacial lake (Lake Nashua) that flowed southward toward the Worcester area. At the end of the last Ice Age, its direction reversed, creating the Nashua River as we know it today. The Mainstem now flows northward from its impoundment at Wachusett Reservoir to the Merrimack River in Nashua, New Hampshire. In contrast, all of the river's major tributaries flow in a southeasterly direction, turning sharply as they join the less turbulent Mainstem: which makes it more susceptible to oxygen depletion from pollution. This vulnerability is compounded by four dams along its length.

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Land Ownership and Land Use3 Patterns: The land-use pattern is 64% forest (hardwood mixed with softwood) or wetland. Low-density residential settlement as well as concentrated settlements and strip development located near town centers and along major roads account for a total of 13% residential. Approximately 7% of total land area is agriculture and/or open space. Although these land-use estimates do not suggest a high risk for potentially contaminated runoff, the land-use along the Mainstem Nashua River in Ayer, MA and Nashua, NH — as well as the Fitchburg-Leominster area upstream along the North Nashua River — is primarily high-density residential, industrial, and commercial. Such land-use types have a much greater potential to negatively impact water quality due to urban runoff/storm sewers.

Indeed, a low percentage (9.1%) of total impervious surfaces4 — namely, paved areas such as streets, driveways, and parking lots — for this subbasin indicates that issues of compromised stormwater and other non-point sources of contaminants (for example: pesticides, fertilizers, oils, asphalt, pet wastes, salt, sediment, litter and other debris) are not an immediate pressing concern. Nonetheless, primary pollutants of concern in stormwater are: suspended solids, nutrients, metals, oil and grease, temperature and bacteria. The sources of bacteria in urban settings (i.e.: Ayer, Nashua) are typically human litter and animal waste left on driveways, lawns, commercial and residential streets, parking lots and rooftops. Furthermore, increasing urbanization leads to diminished groundwater recharge and to declining stream flow as well as stream channel widening and downcutting.

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Major Water Resource Issues: The mainstem Nashua River is classified as a Class B* waterbody, and a warm water fishery. The Mainstem Nashua River shows high phosphorus levels and some high bacteria counts. Treated wastewater accounts for about 30% of the Nashua River's summertime flow, making the river vulnerable to malfunctions at treatment facilities and other wastewater dischargers. Combined sewer overflows (CSOs) — a type of point-source pollution — which carry both wastewater and stormwater originating in upstream urban areas of the larger Nashua River watershed, negatively impact the Mainstem Nashua River. Non-point source pollution — polluted runoff and sedimentation — is an increasingly serious issue in rapidly developing communities.

Major waterbodies in this subbasin include Pepperell Pond, which is classified as hypereutrophic, excessively turbid, and, containing low dissolved oxygen, excessive nutrients (otherwise known as "organic enrichment") and noxious non-native plants. As metals (Hg) have been detected, there is a fish consumption advisory. This stretch of the Mainstem River -from the confluence with the Squannacook River to Pepperell Dam — is being considered for inclusion on the MA DEP 303(d)* list of impaired waters.

According to the 1998 Nashua River Watershed Report Card:

  1. The Nashua River Mainstem from the confluence of the North Nashua River to the Ice House Dam in Shirley/ Ayer/Harvard is rated as non-supportive of biology, nutrients, toxicity, and sediment and was assessed as supportive for the primary and secondary contact uses (swimming and boating, respectively). This 10.6 mile reach encompasses the Oxbow National Wildlife Refuge.
  2. From the Ice House Dam to the intersection with the Squannacook River it is rated as non-supportive of biology, nutrients, toxicity, sediment, swimming and boating because of elevated fecal coliform bacteria levels and degraded aesthetic quality (objectionable turbidity and sewage odors) due to known municipal point sources. Downstream from this confluence to Pepperell Pond neither of the recreational uses was assessed.
  3. Throughout the 3.5 mile reach of the Pepperell Pond it is rated as non-supportive of biology, chemistry, nutrients, fish tissue, boating and swimming. From Pepperell Pond to the Nissitissit River it is rated as non-supportive of biology, nutrients and swimming; partially-supportive of boating due to dense macrophyte cover and excessive turbidity; and on alert status for hydrology.
  4. From the Nissitissit River to the New Hampshire line it is rated as non-supportive of swimming — because of elevated levels of fecal coliform bacteria possibly from illicit sewer connections — and partially supportive of biology and nutrients.

The two major municipal effluent National Pollutant Discharge and Elimination System (NPDES)* permits in the subbasin are for the Ayer WWTF and the MCI Shirley WWTF, while the Pepperell WWTF is considered to be a minor municipal permitee. Additional NPDES minor industrial discharge permitees are: Groton School, Indeck Pepperell Power Association, and Bemis Company, while Pepperell Paper Company is considered a major industrial permitee. Pepperell Paper Company is the one registered water withdrawals permitee. Finally, and not surprisingly, there are water quality issues in Nashua, NH — the most urbanized population center in this subbasin — where point sources of pollution are five Combined Sewer Overflows (CSO) releasing, of particular concern, floatables and bacteria.

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Recreation and Priority Habitat Areas: There is a considerable amount of permanently protected open space in this subbasin. Partially this is a result of decades of conservation efforts on the part of the Nashua River Watershed Association and the municipal greenway committees, which have focused on riparian corridor protection. The largest individual open space holdings in Massachusetts are: Oxbow National Wildlife Refuge (NWR), J. Harry Rich State Forest, Rich Tree Farm, Throne Hill, Bolton Flats Wildlife Management Area (WMA), Ayer Game Farm, Groton Town Forest, and Groton Place in addition to many conservation commission and other assorted local land trust parcels. Fruitlands Museum and Groton School are large holdings with only limited protection. Much of this subbasin is classified as either distinctive or noteworthy in the Massachusetts Landscape Inventory (1983), given its orchards and farmland rolling scenery. In New Hampshire the largest individual open space holdings include: Mine Falls Park in Nashua, Town of Hollis Conservation Lands, Spaulding Farm Open Space, and assorted conservation easement and large subdivision open space set-asides.

This subbasin's fifteen state-designated MA Natural Heritage and Endangered Species Project (NHESP) Priority Habitat areas include all of the Rare Wetlands Wildlife sites listed in the footnote below5 plus: a site within the J. Harry Rich State Forest; two nearby sites on the South Post-Devens6; two nearly adjacent sites to the east of Moore Airfield in Ayer; and, along the east bank of the Nashua River on Devens just north of Route 2 Jackson Road exit.

Two medium priority habitat protection focus area identified in the Priority Sites for Wildlife Habitat Protection in Pepperell, Massachusetts (MAS, 2001) are the Nissitissit Hills and at Bancroft Brook east of Shipley Hill in Pepperell. Three high priority habitat protection focus areas are:

  1. the Nashua River area from the east of the Nissitissit Hills to Four Corners in East Pepperell;
  2. the Nashua River Oxbows opposite the J. Harry Rich State Forest to the east of Route 111 and north of Route 119; and,
  3. the Throne7 in West Groton and Pepperell, which is special for the extent of undeveloped upland, and the number of vernal pools it harbors on its upper slopes.

Nashua River-Mulpus Brook is the one habitat protection corridor identified in the Nashua River Habitat Assessment Report (MAS, 2000). There are four habitat protection focus areas identified in the Report.

  1. Nashua River-Mulpus Brook.
  2. Hound Meadow Hill-Hawk Swamp: the lightly developed northwestern corner of Dunstable important for its 2.5 miles of undeveloped riverbank along the Nashua River.
  3. Squannacook Hill: featuring the confluence of the Squannacook and Nashua Rivers, this focus area is important for its floodplain forest habitat, extensive wetlands with adjacent uplands, as a riparian corridor buffer, and as a stepping stone for wildlife movement north from the Oxbow NWR.
  4. J. Harry Rich State Forest: the Nashua River as it passes through this focus area has been identified by Nashua River Watershed Association aquatic experts as important habitat for birds, fish, and turtles8.

Devens South Post is identified in the Nashua River Habitat Assessment Report (MAS, 2000) as the one core habitat area in this subbasin. This large focus area is a wildlife habitat anchor in the east-central section of the watershed. Located in Lancaster, Harvard, and Bolton, the protected and largely trail-less Oxbow NWR and Bolton Flats WMA, and restricted-public-access Devens South Post9 create what could be the largest, least human-impacted habitat in the watershed.

More than half of this subbasin (in the Massachusetts portion) is considered to be a Natural Heritage and Endangered Species Project (MA NHESP) BioMap10 core area including such areas as: the Throne; Devens: the North, South and Middle Posts; Morse, Walker and Reedy Meadow Brooks riparian corridors, etc.

A very small portion of the Central Nashua River Valley Area of Critical Environmental Concern11 (ACEC) — currently the only ACEC in the Nashua River watershed — falls within the northern section of this subbasin in the Five Corners neighborhood of South Lancaster. The entire northern half of this subbasin (within Massachusetts) falls within the proposed Petapawag Area of Critical Environmental Concern (ACEC) nomination.

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Resource Protection Goals and Recommended Actions:

GOAL: Protect wildlife habitat and migration corridors in the subbasin.

  • Land protection efforts along the west bank of the Nashua River across from J. Harry Rich State Forest and a connector between Bolton Flats WMA and Oxbow NWR.
  • Pursue continued and long-term appropriate management of the Ayer Game Farm, Groton Town Forest and Devens South Post in ways that are conducive to maintaining wildlife habitat.
  • Sponsor local events to raise public understanding about native wildlife and the impacts of development patterns on ecosystem and habitat integrity.
  • Work with local conservation commissions to gain their backing of natural resource and habitat inventories.

GOAL: Protect high-priority open space, vistas, and community character in the subbasin.

  • Encourage the use of MA Executive Order 418* funding for Open Space and Resource Protection Plans for each Massachusetts community in this subbasin.
  • Conduct public education sessions to promote local passage of Community Preservation Act*.
  • Support efforts of the Squannassit Regional Reserve Initiative* (facilitated by the NRWA) and the Squannassit ACEC nomination which encompasses much of this subbasin.
  • Work toward ideal of at least 25-50% protected open space in each municipality. Determine which Chapter 61, 61A and 61B properties to pursue Right of First Refusal* options on if the opportunity arises.
  • Work with municipal officials to develop subdivision standards that require proponents to devote at least 50% of land (not including already undevelopable wet or steep land) for open space conservation and encourage mixed-use development and cluster zoning by-right bylaws.

GOAL: Increase recreational opportunities throughout the subbasin.

  • Survey water chestnut invasive plant infestation and control spread of noxious aquatics at Pepperell Pond.
  • Educate the public and municipal departments (especially Public Works Depts) on efforts relating to invasive species identification and removal.

GOAL: Improve water quality in the subbasin.

  • Considered Pepperell Pond for inclusion on the MA DEP 303(d)* list of impaired waters.
  • Identify sources of fecal coliforms and other contaminants. Identify all water withdrawals.
  • Track proceedings of Ayer's wastewater management plan and Groton School upgrading of their effluent discharge system as mandated by DEP enforcement orders.
  • Determine locations of combined sewer overflows (CSOs) in Nashua. Continue to track progress of CSO abatement activities. Conduct additional dry and wet weather fecal coliform bacteria monitoring in most impacted segments of Mainstem Nashua River to identify potential sources of pathogens and other contaminants.
  • Encourage Best Management Practices (BMPs) at area trailer parks and golf courses.
  • Identify and rectify problems with factory floor drains that may still discharge pollutants to waterways (versus to discharging to tight tanks or sewer systems).
  • Evaluate current status of stormwater runoff controls (i.e., permits, pollution prevention plans, BMPs) in particular, at Pepperell Paper Company and Indeck Pepperell Power Company. Inventory, monitor and improve stormwater drainage structures.
  • Assist Groton with its Clean Water Act-mandated MS-4 Phase II Stormwater* requirements.
  • Implement recommended BMPs from TMDL-urban runoff.
  • Identify any other WMA withdrawals in the subwatershed of this segment of the Nashua River. Evaluate any potential impacts of WMA withdrawals on streamflow/habitat.
  • Continue to monitor nutrient concentrations in most impacted segments of the Mainstem Nashua River and evaluate the Nashua River Basin major municipal NPDES facilities (i.e.: WWTFs) compliance with their effluent total phosphorous (TP)* limits. These municipal permits will include total phosphorus limits of 1.0 mg/L to reduce nutrient inputs to the Nashua River/ Pepperell Pond.
  • Conduct SMART12 monitoring, and instream and chronic toxicity testing.
  • Identify underground storage tanks (USTs) and work to have them removed.

GOAL: Reduce potential negative effects of some development in this subbasin.

  • Require that substandard septic systems of homes on Pepperell's Yale St. ("The Ivy's") neighborhood are brought into compliance (through inspections at point of sale).
  • Help local volunteer board members responsible for development and land-use rulemaking and enforcement get technical assistance and information regarding techniques to control/guide land use and development balanced with adequate resource protection (e.g., Citizens Planner Training Collaborative13 workshop offerings).
  • Increase or establish staff hours for municipal conservation agents to more effectively monitor construction sites runoff and assist with the preparation of bylaws such as erosion-sedimentation controls.

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* See glossary.

1 For this Plan, subbasins were delineated and analyzed using USGS defined boundaries which sometimes are truncated at the gaging station and may not appear to be consistent with topographically determined drainage areas.

2 Corresponding to seasonal stream flow changes are notable spikes in bacteria levels during summer and fall. Seasonal cycles of high bacteria concentrations may be attributed to decreased dilution during summer months, when tributary flows are lowest. (Wachusett Reservoir Watershed Protection Plan Update 1998, pp. 2-29)

3 "Land Use" description at

4 According to the Center for Watershed Protection's Rapid Watershed Assessment Handbook protocol, an area with less than 10% (8 - 12%) impervious surfaces is considered "partially threatened"; less than 8% is considered "sensitive" or what one would say is a relatively pristine environment;" 12 - 20% is considered "threatened"; and more than 20% is considered "non-supporting" or urbanized. The figures cited in the narrative are based on NRW Estimated Impervious Cover by Sub-basin based on '85/'92 Land Use: MDC '98 Methods Estimate by Bruce Bayne and Jo Anne Carr of the EOEA Nashua River Watershed Team.

5 The nine MA NHESP Rare Wetlands Wildlife sites are: 1) by Shipley Hill in Pepperell; 2) from the east of the Nissitissit Hills to Four Corners in East Pepperell; 3) northwest of Benjamin Hill in Shirley; 4) along the Nashua River for three-quarters of a mile north of the mouth of Trout Brook; 5) the Nashua River area from the east of the Nissitissit Hills to Four Corners in East Pepperell; 6) Bancroft Brook east of Shipley Hill in Pepperell; 7) Reedy Meadow in Groton; 8) opposite the Harry Rich State Forest to the east of Route 111 and north of Route 119; and 9) the very large area that encompasses much of the Oxbow WMA and Devens South Post.

6 Nineteen listed species have been identified in these two MA NHESP Priority Habitat areas.

7 The Throne itself has been identified as a land conservation priority by the Nashua River Watershed Association and the Town of Groton. The Throne is a central part of the set of focus areas that provide functional habitat in the northeastern corner of the watershed. It is an important link between the Squannacook River corridor and the J. Harry Rich State Forest and Squannacook Hill focus areas.

8 The slow, meandering nature of the river here, with many oxbows and backwaters offers a rich combination of warm, sluggish water, a few marshy areas, and wide, sandy lowlands that provide shelter, feeding, and breeding habitat for a variety of wildlife.

9 Even with military training in the South Post, the lack of buildings, low traffic, and periodic nature of human presence on the property mean that animals move relatively unmolested across this landscape. Tracks of bobcat, black bear, and moose have been recorded within this focus area. Bobcat are particularly sensitive to human disturbance and their presence in an area is a very strong indicator of high quality habitat. The "drop zone," a large grassland maintained through mowing and occasionally used for parachute training, and the "impact zone" used for mortar training are two very important, uncommon habitat types. Pitch pine woodlands and adjacent openings host one of the largest whip-poor-will populations in the state, and the frequently burned scrubby cover of the impact zone is habitat for brown thrashers, another species in statewide decline. These are the largest, highest quality grassland habitat and pitch pine woodland habitat in the watershed. Uncommon plant communities include Pitch Pine/Scrub Oak Barrens around impact zone, an alluvial red maple swamp, small river floodplains, and bogs. (Nashua River Habitat Assessment Report, MAS, 2000)

10 BioMap url:

11 ACEC url:

12 SMART (Strategic Monitoring for River Basin Teams) is a collection of low cost and no-cost methods for building the capacity of EOEA Watershed Teams for water quality monitoring. Project objectives include: develop a comprehensive monitoring plan for the Nashua River watershed; better integrate monitoring data into the EOEA Watershed Initiative; and augment DEP's DWM monitoring efforts through better use of DEP staff.

13 Citizens Planner Training Collaborative (CPTC)

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