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

Land Area: 18.8 square miles
Primary Municipalities: Harvard, Ayer
Permanently Protected Land Area: 1,013 acres or 9.4%
Limited Protection Land Area (Chap. 61, etc.): 128 acres
Feeder Streams: Cold Spring Brook

% Imperviousness: approximately 12%
Land Use: 50% forest, 16% residential, 15% ag/open
# of MA NHESP* Priority Sites: 3
# of NPDES* discharge permits: 1 minor; 1 major
Most threatened waterbody: Bare Hill Pond
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 subbasin1 predominantly lies in the community of Harvard and Ayer, with small extensions into Bolton and Groton. Located in the Southern New England Coastal Plains and Hills ecoregion2 of central Massachusetts, Bowers Brook flows northerly into Grove Pond and is renamed Nonacoicus Brook downstream of this point. Flowing out of Plowshop Pond, Nonacoicus Brook is joined by Willow Brook, and soon thereafter empties into the Main Stem Nashua River immediately upstream of Walker Brook's confluence with the Nashua and downstream of the Devens Wastewater Treatment Facility. Routes 2, 110 and 111 pass through this subbasin and parallels Interstate 495 which is just a few miles to the east. Two rail lines within this subbasin intersect in Ayer. Streamflow, as in most of New England, has significant seasonal changes3 . The southern half of the eastern boundary of this subbasin is defined by a northeast-southwest running ridgeline.

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Land Ownership and Land Use4 Patterns: The land-use pattern is 50% 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 16% residential use. A relatively high percentage, 16%, of total land area is agriculture and/or open space. Indeed, 11.9% of total impervious surfaces5 — namely, paved areas such as streets, driveways, and parking lots — for this subbasin indicate that issues of compromised stormwater and other non-point sources of contaminants6 (for example: pesticides, fertilizers, oils, asphalt, pet wastes, salt, sediment, litter and other debris) are an increasing concern.

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Major Water Resource Issues: Bowers Brook is classified as a Class B* waterbody. Its headwaters are in an unnamed pond in Bolton just south of the Harvard town line, whence it flows north through ¾ mile-long Bowers Spring swamp into Bare Hill Pond. Bare Hill Pond, at 316 acres, is one of the larger waterbodies (other than Wachusett Reservoir) in the Nashua River watershed. Bare Hill Pond is on the 303b list*, due to elevated Phosphorus levels leading to nuisance aquatic plant, and the Fish Toxics/Edibility list, due to elevated mercury concentrations in its largemouth bass. As mandated by federal law, all 303b listed waterbodies must receive a Total Maximum Daily Load (TMDL) study and report: Bare Hill Pond was the first lake in the Commonwealth of Massachusetts to have one completed.

Also on the 303b list are: Flannagan Pond7, Grove Pond, Mirror Lake and Plow Shop Pond. And Grove Pond, Plowshop Pond and Mirror Lake have been identified as having elevated mercury in resident fish tissue as well8. Robbins Pond in Devens is in a eutrophic state and has noxious and invasive aquatic plants as does Plowshop Pond in Ayer. Flannagan Pond in Ayer has noxious plants as well.

Flowing through Harvard, Bowers Brook is joined by Cold Spring Brook just south of the Ayer town line by the Barnum Gate into Devens. Cold Spring Brook has its headwaters in a wetland north of Mirror Lake on Devens. The chain of hydrologically-connected and heavily-developed ponds in Ayer (Long, Sandy and Flanagan Ponds) drains into Bowers Brook at Grove Pond. Grove Pond abuts Plowshop Pond, which upon discharging, and passing under roads and railroad tracks, is called Nonacoicus Brook: a low gradient stream. Less than a mile downstream after flowing through woods and wetlands, Willow Brook — which has its headwaters in Robbins Pond (an eutrophic pond*) in Devens — joins Nonacoicus Brook which itself discharges into the Nashua River less than ½ mile further downstream. Both Bowers and Nonacoicus Brooks abut the former Fort Devens Military Reservation and other developed areas, from which they receive impacted runoff. The numerous ponds and impoundments (i.e.: Old Millpond in Harvard) in this subbasin affect water quality as well, contributing to low dissolved oxygen content in particular.

A large high-yield aquifer underlies a portion of this subbasin running in a north-south direction from the Willow and Nonacoicus Brooks intersection north of Grove-Plowshop Ponds in Devens and Ayer to Mirror Lake in Devens. As this aquifer is pumped by both Ayer and Devens there is concern about pre-existing metals in Grove Pond (due to indirect withdrawal of this surface water through induced infiltration into the valley aquifer wells9). This area is a wellhead protection area and therefore receives greater protection from present and future sources of pollution. An even larger medium-yield aquifer surrounds the entirely of the high-yield aquifer above and extends further: from just to the east of Sandy Pond in Ayer to the Willow Brook-Shepley Hill area on Devens. Other connecting arms of this very large medium- and high-yield aquifer system — that underlies the Squanncook and Mainstem Nashua Rivers — extend to the north, south and west of this subbasin's boundary. Polluted runoff and sedimentation is an increasingly serious issue in rapidly developing communities.

There are three NPDES* permits in this subbasin: the Ayer Municipal Wastewater Treatment Facility is the one major permitee with effluent discharging to the Nashua River; CPF Inc. is a minor permitee; and Old Town Village Apartments is a minor industrial permitee that discharges to Day Brook, a tributary to Flanagan Pond. There are many identified areas of concern (AOCs) from a contamination standpoint on Devens, which include: Shepley Hill Landfill (AOCs 4,5, 8), West Rail/Industrial zone (AOCs 32 and 43A), South Post Impact Area, Army Enclave Property (AOC 43 G & J), site of Parker Charter School (AOC 69W), Moore Airfield (AOC 50), Barnum Road Area (AOC 57) and Consolidation Landfill (AOC 9 and SA 13). There is on-going long-term monitoring plans for groundwater — also known as ground-water institutional controls — for which the US Army is responsible for each of the above sites.

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Recreation and Priority Habitat Areas: The Department of Environmental Protection's (DEM) 1983 Scenic Inventory Protect identified two sections in this subbasin as contributing "distinctive" scenic character to the entire region. Others have also identified this area as having special agricultural character, which ought to be protected10. Mirror Lake in Devens is a highly-used recreational destination and public swimming area. Grove Pond and associated Pirone Park are locally popular recreation sites in Ayer. Bare Hill Pond is heavily-developed around its shoreline and heavily-used by abutting property-owners and by Harvard residents who have sole access to the town beach (which abuts Bromfield High School) during beach use dates. The 12 mile-long Ayer to Dunstable Rail Trail, owned and managed by the Department of Environmental Management (DEM), is just being constructed as a combined bicycling, walking, and bridle trail. Its southern terminus/trailhead is in Ayer center exactly at the terminus of a 14-mile potential Ayer to Townsend Rail Trail.

Nearly all of Bowers Brook from Pine Hill in Harvard north to Grove Pond and including some of its tributaries is considered to be a Natural Heritage and Endangered Species Project (MA NHESP) BioMap core area11 as is all of the Snake Hill-Long Pond area. There are three state-designated MA NHESP Rare Wetlands Wildlife Habitat areas in this subbasin, which are designated Priority Habitat areas as well. These are: 1) a wetland through which Bowers Brook flows just east of the Route 2 interchange at Route 110/111 and west of Poor Farm Road; 2) along Cold Spring Brook by Barnum Road to the east of Robbins Pond; and, 3) along all of Nonacoicus Brook to the north of West Main St. including the mouth of Willow Brook. A fourthMA NHESP Priority Habitat area is located between Shepley Hill and Plowshop Pond north of the railroad tracks.

Snake Hill-Long Pond is the one habitat protection focus area identified in the Nashua River Habitat Assessment Report (MAS, 2000), encompassing the northernmost portion down to Ayer center. Straddling the Ayer-Groton border, this area contains a diverse combination of uplands adjacent to extensive wetlands. Powerline and gas rights-of-way provide movement corridors and the network of swamps and marshy areas are likely important undisturbed breeding habitat for multiple species. The network also provides dispersal routes between the large ponds in the area — Flannagan and Sandy Ponds to the southwest, Spectacle Pond to the southeast, and Knops Pond and Lost Lake to the northeast. As very little of the area is protected land, habitat conservation priorities should focus here and especially unprotected lands adjacent to Long Pond. Snake Hill-Long Pond area is also the southeastern most section within the proposed Petapawaug Area of Critical Environmental Concern (ACEC)12 nomination. Likewise, the Nonacoicus Brook-Grove and Plowshop Ponds section of Ayer is the southwestern most section within the proposed Squannassit ACEC nomination.

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Resource Protection Goals and Recommended Actions

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

  • 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*.
  • 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 invasive plant infestation and conduct spot treatment to control spread of noxious plants at Flannagan Pond, Grove Pond, Long Pond , Mirror Lake, Plowshop Pond and Robbins Pond.
  • Implement restoration plan for Bare Hill Pond as detailed in Diagnostic/Feasibility Study (1987) and TMDL Final Report (2000) including non-point source (NPS) watershed field survey; lake association to organize and establish septic inspection program and annual septic pumping for all lakeside homeowners; as part of erosion control ordinance help Town Department of Public Works (DPW) to reduce erosion from town roadways and runoff sources; Town Conservation Commission to ensure minimized erosion from construction; establish vegetated buffer around lake; establish phosphorus use program and encourage use of non-phosphorus lawn fertilizer; and, phased implementation of a berm/uptake system to reduce nutrient loading.
  • Educate the public and municipal departments (especially DPWs) on efforts relating to invasive species identification and removal.
  • Investigate the feasibility of establishing an Ayer to Townsend Rail Trail along the abandoned B & M Greenville line which begins in Ayer center.
  • Support implementation efforts of the Devens Open Space and Recreation Plan, the Devens Regional Trails Initiative, and the Squannassit Regional Trails Initiative.
  • Support confirmation of upcoming Squannassit and Petapawag Areas of Critical Environmental Concern (ACEC) nominations.

GOAL: Improve water quality in the subbasin.

  • Help develop and disseminate Best Management Practices (BMPs) for small-scale, hobby type agricultural operations.
  • Identify any Water Management Act (WMA) withdrawals in this subbasin.
  • Identify underground storage tanks (USTs) and work to have them removed.

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

  • 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 of 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.

4 "Land Use" description at

5 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.

6 Primary pollutants of concern in stormwater are suspended solids, nutrients, metals, oil and grease, temperature and bacteria. The sources of bacteria in urban settings are typically human litter and animal waste left on driveways, lawns, commercial and residential streets, parking lots and rooftops.

7 Flannagan Pond needed 303d "impaired waters" list confirmation as of 1998.

8 MA DEP 1999 Fish Toxics Monitoring Public Request and Year 2 Watershed Surveys.

9 Low concentrations of volatile organic carbons (VOC), including trichloroethylene, have been detected at Grove Pond. The Town of Ayer's Grove Pond wells #1 and #2 each draw approximately 1 million gallons of public drinking water per day. The Grove Pond wells share the same aquifer with a Grove Pond wellfield on the Devens property (another 1.1 mgd safe yield). Potential contamination of these wells comes from VOCs detected in Grove Pond, the former Shepley and Cold Spring Brook landfills in Devens, the Massachusetts National Guard motor pool area, former Hartnett Tannery, and the B&M Railroad tracks and yard. At present, the Town of Ayer has no Aquifer Protection District By-Law in place, but is under development.

10 According to the Trustees of Reservations 1999 report: Conserving our Commonwealth: A Vision for the Massachusetts Landscape.

11 BioMap url:

12 ACEC url:

13 Citizen Planner Training Collaborative (CPTC) url:

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