Nichols Plan-NWMC Review Draft.pdf

United States Department Of Agriculture

Natural Resources Conservation Service

SUPPLEMENTAL

WATERSHED PLAN No. 7 &

ENVIRONMENTAL ASSESSMENT

For Rehabilitation of the

George H. Nichols Multipurpose Dam SuAsCo Watershed

Worcester County, Massachusetts

Prepared By:

U.S. Department of Agriculture

Natural Resources Conservation Service

TECHNICAL REVIEW PLAN-EA

July 2009 i

Technical Review Plan-EA Supplemental Watershed Plan No. 7 & Environmental Assessment for Rehabilitation of George H. Nichols Multipurpose Dam SuAsCo Watershed

Worcester County, Massachusetts

Prepared By U.S. Department of Agriculture

Natural Resources Conservation Service

In Cooperation With:

Massachusetts Department of Conservation and Recreation

AUTHORITY

The original watershed work plan was prepared, and works of improvement have been installed, under the authority of the Watershed Protection and Flood Prevention Act of 1954 (Public Law 83-566) as amended. The rehabilitation of the George H. Nichols Multipurpose Dam is authorized under Public Law 83-566 (as amended), and as further amended by Section 313 of Public Law 106-472.

ABSTRACT

The George H. Nichols Multipurpose Dam no longer provides the original protection planned for the watershed due to a greater than planned increase in development of the upstream drainage area. For current and future build-out development conditions the dam does not meet current Natural Resources Conservation Service design criteria for a high hazard dam. The local project sponsors have chosen to rehabilitate the dam to address the identified safety deficiencies. The purposes of the proposed rehabilitation of the George H. Nichols Dam are to maintain present level of flood control benefits and comply with current performance and safety standards. Rehabilitation of the site will require the following modifications to the structure: extending the current auxiliary spillway width from 100 feet to 350 feet and armoring the auxiliary spillway to provide scour protection. Project installation cost is estimated to be $2,900,500, of which $2,055,700 will be paid from Small Watershed Rehabilitation funds and $844,800 from local funds.

COMMENTS AND INQUIRIES

For further information, contact Carl Gustafson, State Conservation Engineer, USDA/NRCS, 451 West Street, Amherst, MA 01002-2953, 413-253-4362.

Submit comments by [NRCS insert date 45 days after submittal to IA review] to: Christine Clarke, State Conservationist, USDA/NRCS, 451 West Street, Amherst, MA 01002-2953 or christine.clarke@ma.usda.gov.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.)

Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

mailto:christine.clarke@ma.usda.gov� ii

Supplemental Watershed Plan No. 7 & Environmental Assessment for Rehabilitation of George H. Nichols Multipurpose Dam

Worcester County, Massachusetts

Contents:

LIST OF TABLES ......................................................................................................................... iii APPENDICES ............................................................................................................................... iii

SUMMARY OF WATERSHED PLAN

PURPOSE AND NEED FOR ACTION

INTRODUCTION

PURPOSE AND NEED FOR SUPPLEMENT

WATERSHED PROBLEMS AND OPPORTUNITIES

SCOPE OF THE ENVIRONMENTAL ASSESSMENT

AFFECTED ENVIRONMENT

EXISTING CONDITIONS

STATUS OF OPERATION AND MAINTENANCE

SEDIMENTATION

BREACH ANALYSIS AND HAZARD CLASSIFICATION

POTENTIAL MODES OF DAM FAILURE

CONSEQUENCES OF DAM FAILURE

ALTERNATIVES

FORMULATION PROCESS

ALTERNATIVES CONSIDERED BUT ELIMINATED FROM DETAILED STUDY

DESCRIPTION OF ALTERNATIVE PLANS

ENVIRONMENTAL CONSEQUENCES

DAM SAFETY

HUMAN HEALTH AND SAFETY

FLOOD DAMAGES

WATER QUALITY

WETLANDS

FISH AND WILDLIFE HABITAT

AIR QUALITY

RECREATION

CUMULATIVE IMPACTS

CONTROVERSY

RISK AND UNCERTAINTY

CONSULTATION AND PUBLIC PARTICIPATION

PROJECT SPONSORS

PLANNING TEAM

PUBLIC PARTICIPATION

AGENCY CONSULTATION

PROVISIONS OF THE PREFERRED ALTERNATIVE

PREFERRED ALTERNATIVE

RATIONALE FOR ALTERNATIVE PREFERENCE

iii

PERMITS, COMPLIANCE AND REQUIREMENTS PRIOR TO CONSTRUCTION

COST, INSTALLATION AND FINANCING

REFERENCES

LIST OF PREPARERS

INDEX

LIST OF TABLES

Table A – Identified Concerns Table B – Existing Structural Data – George H. Nichols Multipurpose Dam Table C – Important Farmland Soils Table D – Highly Erodible Land Table E – Water Quality and Stream Health, Assabet River Headwaters, October 25, 2008 Table F – Fish Species Observed at the Nichols Site Table G – Land Use in the Nichols Dam Drainage Area Table H – Land Use in the Nichols Dam Floodplain Table I – Summary of Socioeconomic Characteristics Table J – Hydrologic and Hydraulic Analyses Summary Table K – Summary and Comparison of Candidate Plans Table L – Comparison of Structural Data

APPENDICES

Appendix A. Economic and Structural Tables

Table 1 – Estimated Installation Cost ............................................................................. A-1 Table 2 – Estimated Cost Distribution, Structural and Nonstructural Measures ......................... A-2 Table 2a – Cost Allocation and Cost-Sharing Summary ............................................................ A-3 Table 3 – Structural Data – Dams with Planned Storage Capacity .............................................. A-4 Table 4 – Estimated Average Annual NED Costs ....................................................................... A-6 Table 5 – Estimated Average Annual Flood Damage Reduction Benefits .................................. A-6 Table 6 – Comparison of NED Benefits and Costs ..................................................................... A-7

Appendix B. Letters and Oral Comments Received on Draft Supplemental Watershed Plan and Environmental Assessment

Appendix C. Support Maps Figure 1 Vicinity Map Figure 2 Project Schematic Figure 3 Field-delineated Wetlands Figure 4 Floodplain Area Map 1 Figure 5 Floodplain Area Map 2 Figure 6 Floodplain Area Map 3 Figure 7 Floodplain Area Map 4 Figure 8 Floodplain Area Map 5 Figure 9 Floodplain Area Map 6 Figure 10 Current Land Use Figure 11 Build-out Land Use

Appendix D. Investigation and Analysis Report Appendix E. Consultation and Public Scoping Process

Supplemental Watershed Plan No. 7 & Environmental Assessment For Rehabilitation of the George H. Nichols Multipurpose Dam

Massachusetts

SUMMARY OF WATERSHED PLAN

Project Name: Rehabilitation of the George H. Nichols Multipurpose Dam1

Description of Recommended Plan: The weir width of the auxiliary spillway on the George H.

Nichols Multipurpose Dam would be increased from 100 feet to 350 feet by extending the spillway eastward onto the existing dam embankment. The auxiliary spillway crest would remain at its existing elevation. The increased capacity of the auxiliary spillway would prevent the dam from being overtopped by the freeboard storm under current land use and watershed build-out conditions. The auxiliary spillway would be armored with articulated concrete blocks to prevent spillway erosion. The principal spillway, the main dam crest and embankment, and the size and elevation of the permanent pool above the dam would not be affected by the project.

The evaluated life of the rehabilitation structure is 60 years.

Resource Information:

Size of SuAsCo watershed: 241,000 acres (377 square miles) Drainage area of the George H. Nichols Dam: 4,447 acres (6.94 square miles) Land Use in the George H. Nichols Dam drainage area:

, SuAsCo Watershed

County: Worcester State: Massachusetts

Sponsors: Massachusetts Department of Conservation and Recreation (DCR)

Worcester County Conservation District Middlesex Conservation District Massachusetts Division of Fisheries & Wildlife (DFW)

Acres % of drainage area Agricultural 603 14 Forest 1,993 45 Developed, residential 1,212 27 Developed, commercial/industrial 47 1 Other (wetlands, open land, water, etc.) 592 13

Land Ownership:

George H. Nichols Dam drainage area: Private 82 % State-Local 18 % Federal 0 % George H. Nichols Dam floodplain area: Private 78 % State-Local 18 % Federal 4 %

1 George H. Nichols Dam is identified in the original SuAsCo Watershed Plan (NRCS 1958). It is designated as dam A-1 in the original work plan, as MA301 in the NRCS list of PL-566 dams, as 3-14- 328-9 by the DCR Office of Dam Safety, and as MA01000 in the National Inventory of Dams database.

Number of farms (Worcester County): 1,547 Average farm size (Worcester County): 69 acres Prime and important farmland:

Drainage area (acres) Floodplain (acres)

Prime farmland 592 264 Farmland of statewide importance 494 434 Farmland of unique importance 209 797

Project Beneficiary Profile: The primary beneficiaries of the project are residential, industrial, and commercial property owners in the floodplain of the Assabet River; the towns of Northborough, Westborough, Berlin, Hudson, Stow, and Maynard; the City of Marlborough; and the Commonwealth of Massachusetts.

Characteristic Westborough Worcester Co. Massachusetts United States Per capita income Median annual household income

$35,063 $73,418

$22,983 $47,874

$25,952 $50,502

$21,587 $41,994

Median house value $149,784 $192,978 $120,467 Median age 37 36 36 35 Population Population age 65 and over

17,997 12%

750,963 13 %

6,349,097 13 %

281,421,906 12 %

Unemployment rate Poverty level Minority population

2.3% 3.0% 12%

2.8% 6.8% 10 %

3.0% 6.7% 15 %

3.7% 9.2% 25 %

Note: 2000 Census data.

The secondary purpose of the George H. Nichols Multipurpose Dam is recreation. The recreational use of the 380-acre permanent pool consists of boating, canoeing, kayaking, and fishing in the summer and ice skating, hockey, and ice fishing in the winter. The rehabilitation project would not affect these uses other than to maintain the integrity of the facility for their continued use.

Wetlands: Wetlands delineated at the George H. Nichols Dam site included Bordering Vegetated Wetlands (BVWs), Banks, Land Under Water Bodies, and Riverfront Area wetland types. Within 0.5 miles of the dam, approximately 182 acres of wetlands occur upstream and 14 acres of wetlands occur downstream, as interpreted and classified by the Massachusetts Department of Environmental Protection (DEP).

Floodplains: Land uses within the 3,222-acre floodplain downstream of the dam:

Acres % of floodplain area Agricultural 224 7 Forest 1,007 31 Developed, residential 314 10 Developed, commercial/industrial 297 9 Other (wetlands, open land, water, etc.) 1,380 43

Highly Erodible Land (acres):

George H. Nichols Dam drainage area: 414 acres George H. Nichols Dam floodplain: 108 acres

Fisheries and Wildlife: The impoundment behind the dam provides fish and wildlife habitat.

Eight species of fish are known to occur in the reservoir. The area is known as a migratory bird stopover area in spring and fall. Central Massachusetts’ only nesting pair of osprey has been observed at the site.

Threatened and Endangered Species: No federally listed or state-protected species are known to occur in the area.

Cultural Resources: No historic properties that are listed on or eligible for listing on the National Register of Historic Places are present in the project’s Area of Potential Effect.

Construction will occur within the area of previous disturbance for the dam. [Note to NWMC:

we will have SHPO and THPO opinions prior to finalizing the plan and will reword this steno accordingly.]

Problem Identification: The George H. Nichols Dam does not meet current dam design and safety criteria. Hydrologic and hydraulic modeling of the freeboard storm predicts that the dam would be overtopped by 2.7 and 2.9 feet for current land use and build-out conditions, respectively. Overtopping of the dam could lead to embankment erosion and dam failure. The models also predict that maximum permissible velocities for the auxiliary spillway would be exceeded, and erosion of the spillway slope could then occur. Dam failure from one or both of these causes would result in flood damages to approximately 370 residences, 84 industrial or commercial properties, 113 roads, 2 schools, 1 fire department, and 1 dam, plus utilities in the floodplain. Dam failure would also potentially cause the loss of life of residents, workers, or motorists.

Alternative Plans Considered:

Alternative 1 – Future Without Project (No Action Alternative) The dam owner, DCR, has stated that it will rehabilitate the George H. Nichols Multipurpose Dam to meet current federal dam safety standards if federal funding assistance is not provided. DCR may choose to use rehabilitation methods other than those identified in this plan or develop its own plan to bring the dam into compliance with federal standards.

Alternative 2 – Rehabilitation (National Economic Development (NED) Alternative) In this alternative, the George H. Nichols Dam would be rehabilitated by widening the auxiliary spillway from 100 feet to 350 feet and armoring the spillway. Federal funding assistance would be provided to the project sponsors by the Natural Resources Conservation Service (NRCS).

Project Purpose: Flood prevention. Rehabilitation of the George H. Nichols Multipurpose Dam is necessary to meet current state and federal safety and performance standards. The rehabilitation project would not affect the dam’s secondary purpose of recreation.

Principal Project Measure: Rehabilitation of the George H. Nichols Dam involves two primary actions:

• Widening the auxiliary spillway from 100 feet to 350 feet.

• Armoring the spillway with articulated concrete blocks.

Project Cost:

PL 83-566 funds Other funds Total Structural measures Flood prevention Recreation

$2,055,700

$0

$844,800

$2,900,500

Project Benefits: Economic benefits of the project are derived from ensuring the continued flood prevention purpose of the George H. Nichols Dam by meeting current performance and safety standards. Benefits are based on continuing flood protection to the downstream area, which has an annual benefit of $310,000. Rehabilitation would also minimize the risk of loss of life to residents and motorists traveling on downstream roadways within the breach flood area.

Project benefits would continue to be derived through recreational opportunities and incidental benefits would continue to be derived through maintenance of fish and wildlife habitat, water supply for irrigation, groundwater recharge, and base flow for downstream wastewater assimilation. Net average annual equivalent benefits between the Future with Federal Project (Rehabilitation Alternative) and the Future without Federal Project (No Action Alternative) = $0.

Environmental Values Changed or Lost:

Resource Impact Air quality Short-term impact from construction equipment emissions Floodplains No effect; no new structures in floodplain; existing floodplain hydrology maintained Wetlands No permanent impact to wetlands; potential temporary impact to wetlands adjacent to construction area (less than 1 acre) – wetlands to be avoided if possible and restored with native vegetation if affected by construction

Fisheries and fish habitat No long-term effect, existing fisheries maintained; temporary disturbance near construction area

Wildlife and wildlife habitat

Potential for loss of up to 0.8 acres of wildlife habitat;

temporary disruption near construction area (less than 1 acre) – disturbed areas would be re-planted with native vegetation;

noise during construction may cause wildlife to relocate temporarily

Threatened and endangered species

No effect

Land use No effect Cultural resources No effect

Resource Impact Recreation No long-term affect; temporary disruptions near construction area – noise and limited access to walking paths and bank fishing areas

Prime farmland No effect

Major Conclusions: Rehabilitation of George H. Nichols Multipurpose Dam is necessary to minimize the risk of loss of life and property damage within the potential breach area and to allow the continuance of flood prevention benefits.

Areas of Controversy: There are no known areas of controversy.

Issues to be Resolved: None.

Permits: The site-specific need for permits and mitigation, if required, will be determined during final design. The owner (DCR) will be responsible for obtaining the necessary local, state, and federal permits, including (1) National Pollutant Discharge Elimination System (NPDES) general permit for construction, (2) U.S. Army Corps of Engineers (USACE) permit under Section 404 of the Clean Water Act of 1972, (3) Chapter 253 Permit to Construct or Alter a Dam, (4) Chapter 91 Waterways License, (5) Order of Conditions through the Massachusetts Wetlands Protection Act, and (6) Section 401 Water Quality Certification.

PURPOSE AND NEED FOR ACTION

INTRODUCTION

The George H. Nichols Multipurpose Dam (referred to hereafter as the Nichols Dam or the dam) is one of ten floodwater retarding dams built between 1962 and 1987 in the watershed of the Sudbury, Assabet, and Concord Rivers (known as the SuAsCo watershed). Nine of those dams, including the Nichols Dam, were authorized to provide flood protection benefits in a 48-square-mile subwatershed by NRCS’s 1958 Watershed Work Plan for Watershed Protection and Flood Prevention, SuAsCo Watershed, Middlesex and Worcester Counties, Massachusetts and five supplemental plans. The Nichols Dam, which was completed in 1970 in the Town of Westborough, Worcester County, Massachusetts (Figure 1, Appendix C), impounds the Assabet River. The dam is a multipurpose dam that provides flood control and maintains a 380-acre pool for recreation.

Since 1970, urban development upstream of the dam has increased the quantity of stormwater runoff, and predicted hydrologic conditions during design storm events now exceed current design standards for freeboard and earthen spillway design under both current land use and watershed build-out conditions. As a result, DCR applied to NRCS in 2005 for funding assistance for rehabilitation of the dam to comply with current standards and ensure continued flood damage protection downstream of the dam.

PURPOSE AND NEED FOR SUPPLEMENT

The George H. Nichols Multipurpose Dam was built under the Watershed Protection and Flood Prevention Act of 1954 (Public Law (PL) 83-566) for the purposes of flood prevention and recreation. The dam was constructed in 1970 in a rural setting. Since then, urban development upstream of the dam has increased the quantity of storm water runoff, and the 2004 Nichols Dam Assessment Report (USDA-NRCS 2004) determined:

For current and build-out conditions the existing dam is overtopped by 2.2 and 2.4 feet respectively during the routing of the freeboard storm. The dam does not provide the original protection planned for the watershed.

As a result, DCR applied to NRCS in 2005 for funding assistance for rehabilitation of the dam to comply with current standards and ensure continued flood damage protection downstream of the dam. The purpose of the proposed dam rehabilitation project is to continue to prevent flood damages by complying with current performance and safety standards. . Failure of the dam would cause serious damage to homes and commercial facilities downstream of the dam and potentially result in loss of life. Rehabilitation of the dam is needed to protect downstream properties, public utilities, highways, and a railroad and to reduce the risk of loss of life.

Rehabilitation of the dam would extend the service life by 60 years and ensure the continued safe service of the dam throughout its original 100-year evaluation period.

This Supplemental Watershed Plan and Environmental Assessment was prepared to evaluate the rehabilitation of the Nichols Dam. The dam was built in accordance with the 1958 SuAsCo Watershed Plan, the 1964 Supplement No. 1, and the 1968 Supplement No. 3. An amendment to PL 83-566, the Watershed Rehabilitation Amendments of 2000 (PL 106-472), Section 313, authorizes funding and technical assistance to upgrade dams under the U.S. Department of Agriculture (USDA) Watershed Program. The rehabilitation upgrade of the Nichols Dam is authorized under this amendment. This supplemental plan documents the planning process by which the NRCS provided technical assistance to the local sponsors, technical advisors, and the public in addressing resource issues and concerns within the Assabet River watershed downstream of the Nichols Dam. DCR cooperated in the preparation of the plan by leading the public meeting, reviewing technical studies (hydrology and hydraulic modeling, preliminary engineering), and reviewing the draft plan-EA.

WATERSHED PROBLEMS AND OPPORTUNITIES

Modeling results indicate that the auxiliary spillway does not meet all necessary design criteria for current land use and ultimate watershed build-out conditions. During a freeboard storm, pool elevation would overtop the dam by 2.7 feet under current conditions and 2.9 feet under build-out conditions, potentially leading to failure of the dam. Flow through the auxiliary spillway would exceed NRCS maximum permissible velocities, which would erode the dam slope and potentially lead to failure of the dam.

The Nichols Dam provides approximately $310,000 in average annual flood damage reduction benefits for the Assabet watershed. The beneficiaries of the structure are the Commonwealth of Massachusetts and the localities of Westborough, Northborough, Marlborough, Berlin, Hudson, Stow, and Maynard.

Primary concerns are the safety of the dam and the potential problems that failure of the dam would cause. Associated downstream hazards include residential, commercial and industrial developments, public utilities including the Westborough Wastewater Treatment Plant, main highways and local roads, and railroads. The Emergency Action Plan (EAP) for the Nichols Dam estimates that an uncontrolled breach of the dam would cause flood damages to approximately 370 residences, 84 industrial or commercial properties, 113 roads, 2 schools, and 1 fire department, plus utilities in the floodplain (GZA GeoEnvironmental 2008). The Washington Street Dam in the Town of Hudson would be overtopped and fail because it does not have the hydraulic capacity to pass the flood wave. Catastrophic failure of the Nichols Dam would also potentially cause the loss of life of residents, workers, or motorists.

Opportunities that would be realized through the implementation of this watershed rehabilitation plan are:

• Compliance with current dam safety criteria,

• Protection of human health and safety,

• Protection of infrastructure and transportation systems,

• Maintenance of flood control benefits,

• Prevention of increased flooding in the floodplain

• Protection and maintenance of recreation benefits, and

• Protection and maintenance of fish and wildlife habitat.

SCOPE OF THE ENVIRONMENTAL ASSESSMENT

A scoping process was used to define project needs, determine important issues and formulate alternatives. Scoping included a public meeting; written requests for input from state, local, and federal agencies; and coordination meetings with appropriate agencies. A steering committee of NRCS, DCR, and technical experts was also formed to assist in the formulation and evaluation of alternatives.

Stakeholder agencies that were contacted concerning the proposed project are:

• Worcester County Conservation District

• Massachusetts DCR

• Massachusetts DFW

• Massachusetts Department of Fish & Game, Riverways Program

• Massachusetts DEP

• Town of Westborough (Board of Selectmen, Conservation Commission, Planning Board, Engineering Department)

• Organization of the Assabet River

• Massachusetts Executive Office of Energy and Environmental Affairs

• Massachusetts Executive Office of Energy and Environmental Affairs, Environmental

Policy Act Office

• US Environmental Protection Agency (EPA) Region 1, Regulatory Section

• USACE, Regulatory Division

• Massachusetts Office of Dam Safety

• Westborough Community Land Trust

Table A presents the results of the scoping process.

Table A – Identified Concerns

Economic, social, environmental, and cultural concerns

Degree of Concern

Degree of Significance to Decision Making Remarks

Dam safety High High Primary concern of sponsors and

NRCS

Human health and safety High High Primary concern of sponsors and

NRCS

Flood damages High High Primary concern of sponsors and

NRCS

Table A – Identified Concerns

Economic, social, environmental, and cultural concerns

Degree of Concern

Degree of Significance to Decision Making Remarks

Recreation High Moderate Second purpose of dam; concern locally that recreation benefits be maintained; temporary, minor impact

Fish and wildlife habitat Moderate Moderate Evaluated for all NRCS projects;

fish and wildlife habitat important for recreational purpose of the dam;

possible minor loss of field and wood habitat (less than 1 acre).

Wetlands Moderate Moderate Analysis of effects required by Clean Water Act and Executive Order 11990; minimal, temporary impact; no permanent impact.

Water quality Moderate Low Evaluated for all NRCS projects;

minimal, temporary impact.

Threatened and endangered species

Moderate Low Analysis of effects required by the Endangered Species Act; no federally protected species or state-listed species present.

Cultural resources Moderate Low Analysis of effects required by National Historic Preservation Act;

no historic sites present in Area of Potential Effect

Prime farm lands Moderate Low Evaluated for all NRCS projects;

none affected by the project.

Highly erodible cropland Moderate Low Evaluated for all NRCS projects;

none affected by the project.

Aesthetics Low Low Minimal, temporary impact Air quality Low Low Minimal, temporary impact Sedimentation and erosion Low Low Minimal, temporary impact Water quantity Low Low No impact

AFFECTED ENVIRONMENT

The area potentially affected by rehabilitation of the Nichols Dam is the dam structure itself, the area adjacent to the dam that could be affected by construction, and the flood protection area downstream of the dam. The following discussions of existing conditions focus on these areas, plus the general project vicinity—the Town of Westborough—where appropriate.

EXISTING CONDITIONS

Original Project

The Nichols Dam was one of eight floodwater-retarding structures proposed in the 1958 SuAsCo Watershed Plan under the authority of PL 83-566. The dam was constructed in 1970 with federal assistance provided by the U.S. Department of Agriculture, Soil Conservation Service (now the NRCS). Subsequently five supplements to the original plan were prepared and approved between 1964 and 1996. Through these supplements, two of the original dams were deleted from the plan and three others were added, and as a result nine floodwater retarding structures were planned and constructed between 1962 and 1974 for watershed protection and flood prevention. As originally authorized in the 1958 Plan, Nichols Dam had the single purpose of flood prevention. In 1964, Supplement No. 1 added recreation as a purpose and increased pool storage for low-flow augmentation to support fishing along the Assabet River downstream of the dam. Massachusetts was responsible for operating the outlet gate for low-flow augmentation. Supplement No. 3, in 1968, added additional storage for floodwater retention and for recreation to support fishing, hunting, development of wildlife habitat, and other water-associated recreational uses at the dam and pool site. Concurrently with this 2009 supplement for the Nichols Dam, NRCS is preparing Supplement No. 6 for rehabilitation of the Hop Brook Floodwater Retarding Dam.

The Middlesex Conservation District and the Northeastern Worcester County Conservation District were the original local sponsoring organizations for the SuAsCo Watershed Plan. The three conservation districts in Worcester County have combined into one district, known as the Worcester County Conservation District. Through the supplemental planning process and reorganization of state agencies, by 1996 the local sponsoring organizations also included the DFW and the Massachusetts Department of Environmental Management (DEM). Further state reorganizations since 1996 have resulted in renaming DEM as DCR. DCR is the local sponsoring organization for this supplement because it is the owner of the dam and has requested funding assistance for rehabilitation of the dam from NRCS.

Since the construction of the dam, use of the impoundment has increased, and it now provides several other ancillary benefits to the community:

• Water supply for irrigation of the town golf course through pumping from the impoundment;

• Support through groundwater recharge of public drinking water wells and residential wells located along the upstream reaches of the impoundment; and

• Maintenance of base flows in the Assabet River to provide water for combination with the effluent from the Westborough Wastewater Treatment Plant located downstream.

Description of Existing Dam

The Nichols Dam was originally designed and constructed as a federal Class C dam, a hazard classification given to dams whose failure “may cause loss of life or serious damage to homes, industrial and commercial buildings, important public utilities, main highways, or railroads.”

The floodwater retarding structure consists of three major elements: the earthen embankment, the principal spillway, and the auxiliary spillway. The embankment has a total structural height of approximately 20 feet, a hydraulic height of approximately 13.5 feet, and an overall length of approximately 1,550 feet, inclusive of the auxiliary spillway. Figure 2 in Appendix C presents an aerial photo of the Nichols Dam.

The dam is located on the northeastern side of the impoundment area. The upstream side of the dam is an earthen slope. The upper portion slopes at 3 horizontal (H):1 vertical (V) from the crest to an approximately 5.5-foot wide berm. Below the berm, the slope is a more gradual 4H:1V. The top of the dam is 12 feet wide, grass covered, and extends from the east abutment to the auxiliary spillway for a total length of approximately 1,440 feet (exclusive of the auxiliary spillway) at a settled elevation of 318.5 feet (National Geodetic Vertical Datum). The downstream side of the dam is a grass-covered 3H:1V slope.

The structure consists of compacted earth fill on poorly graded, gravelly sands and silty sands, overlying compact silt that sits on the bedrock. The upper few feet of bedrock are moderately fractured. An earthen core of silt is present in the center of the embankment with a top width of 12 feet at elevation 313.0 and slopes of 1H:2V. A cutoff trench extends along the dam centerline extending into the underlying natural layers of silt and bedrock.

The principal spillway for the structure is located approximately 600 feet from the east abutment and consists of a reinforced concrete riser that leads to a 48-inch diameter reinforced concrete outlet pipe. During normal operating conditions, flow through the riser occurs through four rectangular orifices. Two orifices on each side of the riser are 6 feet wide by 9 inches high with invert elevations of 310.0 feet. During elevated impoundment conditions, additional discharge capacity is provided by 7-foot long weirs at 311.5 feet that are located along the sides of the risers above the orifices. Along the upstream side of the riser, a slide gate provides pond drain capacity through a 24-inch diameter, 16-gage, non-perforated, corrugated metal pipe which extends from the riser approximately 24 feet upstream to a reinforced concrete intake structure.

The spillway discharges through a reinforced concrete impact basin to a natural stream channel with riprap-lined earthen banks.

The auxiliary spillway, which was designed to convey flows from storms greater than the 100-year flood event, is located at the western end of the embankment and is cut into the western abutment, which defines the western side of the spillway. The auxiliary spillway is a grass-lined channel with a crest elevation approximately 5.5 feet below the top of the dam. The crest of the auxiliary spillway is a 100-foot wide (perpendicular to flow) and 30-foot long (parallel to flow) level section with a 2 percent slope in the upstream approach and a downstream slope of 3.5 percent. The upstream entrance to the auxiliary spillway is located approximately 200 feet from the crest of the spillway within the normal impoundment. Downstream of the crest, the western and northern abutments of the spillway are defined by a cut slope¸ and the eastern and southern sides are confined by an earthen training dike between the downstream slope of the dam and the spillway. The auxiliary channel discharges to the outlet channel approximately 850 feet downstream from the spillway crest. A catch basin with a drain system, which was added subsequent to original dam construction, is located along the downstream north side of the auxiliary spillway.

A rectangular foundation drain is present along the downstream side of the embankment with a width of approximately 5 feet and a varying height. Seepage water collected by this drain is conveyed by a 10-inch diameter, 16-gage, perforated corrugated metal pipe to outlets through the sidewalls of the principal spillway impact basin.

An 8-inch diameter underdrain is located below the auxiliary spillway and discharges to the primary spillway channel. Subsequent to the original construction of the dam, drainage tiles were added during the placement of additional fill within the area of the auxiliary spillway.

These tiles discharge to the original drainage system.

A series of relief wells, observation tubes, and piezometers were installed during subsequent work in 1970 to provide hydraulic flow relief and to monitor groundwater levels in the foundation area just downstream of the dam.

Existing Structural Data

Table B provides a summary of the existing structural data for the George H. Nichols Multipurpose Dam.

Table B – Existing Structural Data – George H. Nichols Multipurpose Dam Year completed 1970 Drainage area 6.94 square miles (4,447 acres)1/ Stream Assabet River Purposes Flood prevention, recreation Dam type Earthen embankment Dam height 20 feet Dam crest length 1,440 feet Dam crest elevation (minimum) 318.5 feet Storage:

Total, maximum pool 3,400 acre-feet Total, auxiliary spillway crest 2,900 acre-feet Total, permanent pool 1,624 acre-feet Sediment 44 acre-feet Flood 1,276 acre-feet Recreation 1,580 acre-feet

Principal spillway:

Type Reinforced concrete Lower-stage crest elevation 310.0 feet Upper-stage crest elevation 311.5 feet Conduit size 48 inches

Table B – Existing Structural Data – George H. Nichols Multipurpose Dam Auxiliary Spillway:

Type Grass-lined channel Width 100 feet Crest elevation 313.0 feet

1/6.94 square miles is the revised contributing area based on NRCS 2004 assessment.

Original design was 7.17 square miles.

Physical Features and Environmental Factors

Project Location: The Nichols Dam is located in the western section of the Town of Westborough in Worcester County, Massachusetts. The Assabet River begins as a small stream from the headwaters located at the Nichols impoundment in Westborough. From the Nichols dam, the Assabet flows through suburban residential neighborhoods to wetlands near Route 9.

The Westborough Wastewater Treatment Plant discharges into the river just before the river flows under Route 9 (OAR 2009a). The Assabet River flows north for approximately 30 miles from the Nichols Dam to its confluence with the Sudbury River in Concord, Massachusetts. The Assabet and Sudbury Rivers form the Concord River which flows north 15.5 miles to its confluence with the Merrimack River in Lowell, Massachusetts. The SuAsCo Watershed encompasses a large network of tributaries that drain approximately 377 square miles in Middlesex and Worcester counties.

Climate: The average annual precipitation for Worcester County is 49.2 inches, and the average seasonal snowfall is 59.7 inches. In winter, the average temperature is 26.2 degrees Fahrenheit (ºF), and the average daily minimum is 18.4 ºF. In summer, the average temperature is 67.7 ºF, and the average daily maximum temperature is 76.9 ºF. The average (50 percent) freeze-free period of 172 days extends from April 27 through October 16 (NRCS 2008a).

Geology and Soils: The dam is generally located at the boundary between the Marlboro foundation (Ozm) of Mafic Rocks and Avalon Granite (Zsg). The boundary between the two formations crosses below the dam between the primary spillway and the auxiliary spillway. The dam is generally underlain by two distinct soil types derived from glacial depositions; a deposit of sand and gravel and a till. The sand and gravel deposit is generally upstream of the dam and towards the west of the primary spillway. A similar deposit is also located along the eastern side of the normally impounded area. Bedrock at the dam is a variety of gradations between gneisses and schists.

According to the NRCS soil survey for Worcester County, several major soil types are located within the area surrounding the dam (Taylor and Hotz 1985). Mapped soils at the site are primarily Udorthents, smoothed. These areas consist of man-made landforms over firm loamy basal till. Other soils adjacent to the dam include Scarboro, Walpole, Sudbury, Ningret, Agawam, Paxton, and Merrimac fine sandy loams; Hinckley sandy loam; Swansea muck; and Whitman loam.

The original design geology as interpreted from the boring logs provided on the as-built drawings indicated a variety of soil materials along the alignment of the dam and dikes. These materials varied from poorly graded silty sands and silt to poorly graded sands and gravel over bedrock. Although there was observed variation across the site, all foundation soils appeared to represent a granular type material with variable amounts of gravels and silts, which is typical of the glacial environment that is prominent in the area, or weathered rock and bedrock near the abutments (H&S Environmental 2009).

Topography: The SuAsCo watershed lies within an area of previous glaciation, and many glacial features are present. In addition, the watershed is characterized by the prevalence of swamps, ponds, and lakes. The drainage pattern is dendritic with many tributary streams.

Within the SuAsCo watershed, the Assabet River has a steeper gradient than the lower Sudbury and upper Concord Rivers and as a result has a more rapid runoff of floodwaters (NRCS 1958).

Prime Farmland: Prime farmland is protected by the Farmland Protection Policy Act in order to “minimize the extent to which federal programs contribute to the unnecessary and irreversible conversion of farmland to non-agricultural uses” (NRCS 2008b). Soils that are designated as prime farmland and are present in the Nichols Dam drainage area are the Agawam, Paxton, Merrimac, and Hinckley series sandy loams. Table C presents the acreages of soils designated as prime farmland, farmland of statewide importance, or farmland of unique importance in the Nichols Dam drainage area and the downstream floodplain.

Table C – Important Farmland Soils Soil Designation Drainage Area (acres) Floodplain (acres) Prime Farmland 592 264 Farmland of statewide importance 494 434 Farmland of unique importance 209 797

Source: Massachusetts Geographic Information System (MassGIS 2008a)

Highly Erodible Land: As summarized in Table D, approximately 9 percent of the Nichols Dam drainage area and less than 5 percent of the downstream floodplain are highly erodible lands.

Table D – Highly Erodible Land Drainage Area Floodplain Acres Percent Acres Percent Highly erodible land 414 9 108 3 Potentially highly erodible land 924 21 405 13 Not highly erodible land 3,109 70 2,709 84 Source: MassGIS (2008a)

Water Quality: The Assabet River is designated by the state as a Class B Warm Water Fishery, which is defined as waters designated “as a habitat for fish, other aquatic life, and wildlife, and for primary and secondary contact recreation” (DWM 2005). The Organization for the Assabet River (OAR) conducts monthly water quality monitoring of the Assabet River at Route 9 in Westborough (above the first wastewater treatment plant). Recently available water quality data for the Assabet River headwaters are presented in Table E (OAR 2009b). Three municipal drinking water wells are located in the Headwaters Conservation Area adjacent to the southwestern shoreline of the reservoir (Town of Westborough 2003).

Table E – Water Quality and Stream Health, Assabet River Headwaters, October 25, 2008

Parameter Result Parameter Result Total nitrogen 0.24 mg/L pH 7.1 Total phosphorus 0.018 mg/L Water temperature 10.4 ºC Total suspended solids 3 mg/L Streamflow 4.0 cfs Dissolved oxygen 10.1 mg/L Habitat availability (0-20) 17 Note: mg/L = milligrams/liter; cfs = cubic feet per second; ºC = degrees Celsius (centigrade) Source: OAR (2009b)

In summer 2001 surveys of the pool above Nichols Dam, DWM found high pH and high dissolved oxygen concentrations in surface waters and low dissolved oxygen concentrations at depths greater than 8 feet, conditions indicative of nutrient enrichment (DWM 2005). Total phosphorus concentrations in the pool were not high, but there was evidence of phosphorus release from anoxic sediments.

The release from Nichols Dam forms the headwaters of the Assabet River. Under drought conditions, the river for about 1.2 miles downstream of the dam is dry (DWM 2005). DWM (2005) summarized water quality in the Assabet River:

Historically, wastewater discharges and water withdrawals for public supply have deleteriously affected the Assabet River. A nutrient TMDL for the Assabet River was completed in 2004... Implementation of the TMDL requires removal of total phosphorus to 0.1 mg/L in the effluent of the major municipal wastewater treatment plants and evaluation of the feasibility of sediment remediation to reduce phosphorus flux from the sediments.

Wetlands: Assabet Swamp begins at the impoundment of the dam and extends southwest from Arch Street forming the headwaters of the Assabet River (Town of Westborough 2003). Vernal pool habitat is located along a trail from the Headwaters Conservation Area to the boat ramp (Westborough Community Land Trust 2006).

Wetlands on both sides of the dam where project construction could be located were field-delineated in February 2009 (Figure 3, Appendix C). State-regulated wetland resources identified at the site, as defined in the Massachusetts Wetlands Protection Act Regulations 310 CMR 10.00 (Regulations), include Bordering Vegetated Wetlands (BVW), Banks, Land Under Water Bodies (LUWB), and Riverfront Area, as described below. These wetland resources are associated with, or adjacent to, the impoundment and principal spillway.

The boundary of the BVW is generally situated at the toe of slope associated with the fill area for the dam and associated spillways. The only resource area that intersects the dam is the primary spillway as it passes underneath the dam through a concrete culvert. There are two categories of BVWs at the site and both meet the definition of a Freshwater Wetland according to the Regulations and, therefore, a 100-foot Buffer Zone is applied. The first is the wooded area located to the southeast of the dam adjacent to a boat ramp. This wooded area is dominated by red maple (Acer rubrum) trees. A small stream flows through this BVW and enters the impoundment to the southeast of the boat ramp. The other category of BVW on the site is fringing emergent wetlands adjacent to the impoundment and principal spillway. These emergent wetlands are dominated by broadleaf and narrowleaf cattail (Typha latifolia and T.

angustifolia, respectively), and numerous sedge and rush species. These BVWs generally occur where surface water from the impoundment or primary spillway overflow onto the land surface for significant portions of the year.

Bank wetland resources at the site include the Banks along the impoundment upstream of the dam and Banks along the principal spillway downstream of the dam. These banks are vegetated and are comprised of mineral soil material. Woody Bank vegetation includes red maple trees and sweet pepperbush (Clethra alnifolia), winter berry (Ilex verticillata), and arrowwood (Viburnum dentatum) shrubs. Emergent vegetation includes sensitive fern (Onoclea sensibilis), cinnamon fern (Osmunda cinnamomea), and sphagnum moss (Sphagnum sp.).

Land Under Water Bodies includes land under the impoundment and land under the principal spillway. This LUWB is generally comprised of mineral soil material.

A Riverfront Area is defined as the area of land between a river’s mean annual high water line and a parallel line measured 200 feet horizontally from said high water line. The primary spillway (Assabet River) is defined as a River as it is a perennial body of water that empties into another River. The boundary of the Riverfront Area associated with the spillway extends landward 200 feet from the mean annual high water line.

Fish and Wildlife Resources: The reservoir is maintained by DFW as migratory shorebird habitat, and dead standing trees in the reservoir provide nest sites for a great blue heron (Ardea herodias) rookery. The Assabet Headwaters Reservation provides habitat to the only nesting pair of ospreys (Pandion haliaetus) in central Massachusetts (Town of Westborough 2003; OAR 2009a). Waterfowl use the Nichols pond during migration. The Westborough Community Land Trust provides bird walks at the reservoir during spring and fall passerine migration (Westborough Community Land Trust 2009).

A 1974 natural resources inventory of the Town of Westborough found white-tailed deer (Odocoileus virginianus), eastern cottontail rabbit (Sylvilagus floridanus), gray and red squirrels (Sciurus carolinensis, S. vulgaris), raccoon (Procyon lotor), opossum (Didelphis virginianus), skunk (Mephitis mephitis), and many species of birds, reptiles, amphibians, and small mammals (Town of Westborough 2003).

The permanent impoundment formed by the Nichols Dam supports eight species of fish and is a popular fishing site. DFW considers the impoundment “one of the most productive largemouth bass waters in the state” (Town of Westborough 2003). Table F presents the species of fish known to occur in the reservoir.

Table F – Fish Species Observed at the Nichols Site Common Name Scientific Name Black crappie Pomoxis nigromaculatus Brown bullhead Ameiurus nebulosus Golden shiner Notemigonus crysoleucas Largemouth bass Micropterus salmoides Pumpkinseed Lepomis gibbosus White sucker Catostomus commersoni White catfish Ameiurus catus Yellow perch Perca flavescens

Threatened and Endangered Species: There are no federally listed or proposed, threatened or endangered species or critical habitat in the project area (FWS 2009). A search of the Massachusetts Natural Heritage and Endangered Species Program (NHESP) database using MassGIS showed that there are no rare, threatened, or endangered species or unique natural communities present within the project area (NHESP 2009).

Floodplain: The floodplain in Westborough downstream of Nichols Dam is shown in Figures 4- 9, Appendix C. Downstream of Northborough, Nichols Dam becomes a smaller influence on the floodplain of the Assabet River, which is controlled by multiple other dams in the watershed.

The floodplain would not be affected by the rehabilitation of the dam.

Air Quality: Westborough falls within the Boston-Lawrence-Worcester area as defined by EPA, which is a nonattainment area for 8-hour ozone. The area is in attainment for all other criteria pollutants (EPA 2009).

Recreation: The 380-acre permanent pool is used for fishing, boating, canoeing, and kayaking in the summer and ice skating, ice fishing, and hockey in the winter. Trails around the dam provide opportunities for hiking.

Cultural and Historic Resources: The Area of Potential Effect (APE) for the project is the access road into the site and the project construction area. The entire APE was previously disturbed for construction of the dam. Other than the dam itself there are no structures within the APE. No historic properties that are listed or eligible for listing on the National Register of Historic Places are present within the project’s APE (NPS 2008). [Note to NWMC: we will have SHPO and THPO opinions prior to finalizing the plan and will reword this steno accordingly.]

Land Use: In the 1958 watershed plan, the SuAsCo watershed is described as 10 percent developed and 90 percent cropland, grassland, forest, and open water. In the 50 years since, the area has developed as a residential area for Boston and Worcester commuters. At the time of the dam’s design, land use in the dam’s drainage area consisted of approximately 58 percent forest, 24 percent agriculture, and 5 percent urban. Current land use in the Nichols Dam drainage area (based on 1999 data in Massachusetts Geographic Information System (MassGIS)) is summarized in Table G; 27 percent of the area is residential, mostly low to medium density.

Land in the drainage area is predominantly privately owned (82 percent), with the rest being state- or local government-owned. The land immediately surrounding the pond is managed as an annex to Quinsigamond State Park (Town of Westborough 2003). The annex is approximately 469 acres and connects the Westborough Country Club with the Headwaters Conservation Area.

Table G also summarizes land use under ultimate…