Merrimack River Watershed Assessment Study: Descriptions of

Merrimack River

Watershed Assessment

Study

Description of Existing

Conditions

Prepared for:

Sponsor Communities:

Manchester, NH

Nashua, NH

Lowell, MA

GLSD, MA

Haverhill, MA

New England District

U.S. Army Corps of

Engineers

January 2003

The River Basin Community Coalition concept was conceived in June 1998 in response

to regulatory requirements to mitigate Combined Sewer Overflows (CSO) discharges.

Because the coalition communities faced an aggregate financial commitment of 0.5 to 1.0

billion dollars, the five founding technical managers and administrators from each

community believed that such an investment should be made wisely. They believed

that this wise investment should be founded on good science that holistically embraces

the needs of the watershed. Generally speaking the mission is to “spend smart” by

making wise science based investments in activities related to water quality

improvements that are not solely focused on CSO mitigation.

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Executive Summary

This report is submitted to fulfill the requirements of Task Order 1A of Contract

Number DACW33-02-D-0005: “Evaluation of Existing Conditions” for the Merrimack

River Watershed Assessment Study. This is the first Task Order for Phase I of the

comprehensive study, which has been jointly funded by the United States Army

Corps of Engineers (USACE) through the New England District and the five

sponsoring communities of Manchester and Nashua, New Hampshire; Haverhill and

Lowell, Massachusetts; and the Greater Lawrence Sanitary District, Massachusetts.

Phase I of this study is aimed at identifying relative planning level benefits (and costs)

of generalized investment strategies such that beneficial uses of the water can be

effectively improved through a shared-vision approach to watershed management.

Task Order 1A of the Study authorized the review of existing documentation on the

Merrimack River watershed, and a summation of the findings in this report.

Specifically, the Task Order requires “discussions of water quality, water quantity,

dams and impoundments, sediment quality, and biological resources and habitat

including phytoplankton, macroinvertebrates, fisheries (anadromous and resident

fish population), shellfish, and wetlands (freshwater and tidal).” Additionally, the

Task Order requires a review and discussion of designated water uses and

attainment, and a limited discussion of pollution sources within the watershed. The

discussions in this report focus on the mainstem of the Merrimack River, along with

its significant tributaries. The report does not include new findings, but rather serves

as a unifying summary of other documents that have been issued primarily within the

past ten years.

This “Description of Existing Conditions” report is intended to serve two purposes.

First, it is a medium to communicate the current state of the watershed to project

participants, sponsors, and interested stakeholders. Second, portions of the report

(especially the sections on designated use attainment and water quality) will serve as

a reference during subsequent evaluations and comparisons during Phase I of the

comprehensive study.

Watershed Overview

The Merrimack River is formed by the confluence of the Pemigewasset and

Winnipesaukee Rivers in Franklin, New Hampshire. The River flows southward for

approximately 78 miles in New Hampshire; it turns abruptly across the New

Hampshire- Massachusetts border and flows in a northeasterly direction for

approximately another 50 miles before discharging to the Atlantic Ocean at

Newburyport, Massachusetts. The final 22 miles of the River are tidally influenced

downstream of Haverhill, Massachusetts.

The Merrimack River watershed covers an area of approximately 5010 square miles in

the south-central portion of New Hampshire (76-percent of the drainage area) and the

northeastern portion of Massachusetts (24-percent of the drainage area), making it the

fourth largest watershed in New England.

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Physical Setting

The Merrimack River watershed encompasses a variety of terrain and climate

conditions, from the mountainous White Mountain region in northern New

Hampshire to the estuarine coastal basin of northeastern Massachusetts. Precipitation

in the watershed is fairly evenly distributed throughout the year. There are, however,

large inter-basin variations in the amount and type of precipitation (i.e. rain versus

snow) primarily as a result of the effects of terrain, elevation, latitude, and proximity

to the ocean (Flanagan et al. 1999). Temperatures in the basin generally vary widely

on an annual basis. Based on a review of climate data, July is typically found to be the

warmest month and January is generally the coldest.

A mix of deciduous and evergreen forest, covering approximately 77 percent of the

watershed area, dominates the land use in the basin. Urban areas, including

residential, industrial, commercial and commercial land uses, make up the second

largest land use category, covering approximately 10 percent of the total watershed

area.

The U.S. Geological Survey (USGS) currently operates two gaging stations on the

mainstem Merrimack River at (1) Merrimack River near Goffs Falls, below

Manchester, New Hampshire and (2) Merrimack River below Concord River at

Lowell, Massachusetts. Numerous other gaging stations currently exist on major

tributaries to the Merrimack River. A review of the monthly discharge statistics on

the mainstem reveals that the highest average and most variable flows generally occur

during the month of April; the lowest and least variable flows generally occur during

the late summer (August and September).

Numerous hydropower dams currently exist on the mainstem Merrimack River and

its major tributaries that significantly impact the daily, weekly, and monthly

streamflow conditions. During high flow conditions, the hydropower facilities

generally operate under “run of the river ” conditions, with substantial spillage.

During periods of low flow, the dams are required to pass a minimum flow, while

still operating to meet peak demands. This often results in short-term water level

fluctuations during summer months.

Water Quality

Historically, the water quality of the Merrimack River was severely degraded by

industrial and domestic wastes. In the 1960s, the River was listed as one of the

nation’s ten most polluted waterways, primarily as a result of raw sewage, paper and

textile mill wastes, and tannery sludge (USEPA 1987). However, the passage of the

Federal Clean Water Act in 1972 ushered in a period of rebirth for the River. An

infusion of large amounts of state and Federal funding for water resources

infrastructure investments, such as wastewater treatment plant (WWTP’s), helped to

revive the River into one that is currently a significant natural and economic resource

in the New England region.

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Despite the significant improvements, further work to improve water quality is

required. For example, a 1997 study conducted as part of the Merrimack River

Initiative (MRI) indicated that the four largest causes of non-support of designated

uses in the basin are pollution from (1) urban runoff, (2) natural sources, (3) municipal

point sources, and (4) combined sewer overflow (CSO) discharges. This study also

identified elevated bacteria levels as the primary cause of non-supporting use in the

basin, followed distantly by low dissolved oxygen concentrations and high nutrient

levels (Donovan and Diers 1997). Other issues of concern include low-flow conditions,

water supply, flooding, contamination of shellfishing beds, and fish and wildlife

habitat and contamination issues.

The primary water quality data collection agencies in the watershed have been state

and federal agencies, including the New Hampshire Department of Environmental

Services (NHDES), the Massachusetts Department of Environmental Protection

(MADEP), and the USGS. Recently, several volunteer monitoring programs have also

started collecting data within the watershed with the help of these state agencies and

the Merrimack River Watershed Council. The majority of the water quality data that

exists in the basin from MADEP was collected prior to 1990. NHDES also collected

water quality and biomonitoring data in the watershed throughout the 1990s. The

most recent comprehensive analysis of the River’s quality was performed under the

Merrimack River Initiative (MRI) during the 1990’s. This project was a collaborative

effort between the USEPA, NHDES, MADEP, and the New England Interstate Water

Pollution Control Commission. The MRI collected water quality samples throughout

the basin during one wet-weather and one dry-weather event; benthic

macroinvertebrate sampling was also performed.

Both Massachusetts and New Hampshire categorize waters according to their use

class. Each class is associated with a series of designated uses; the ability of a

waterbody to support these uses is assessed based on its ability to meet the applicable

water quality standards. In New Hampshire, designated use categories include

swimming (primary contact recreation), fish and shellfish consumption, drinking

water, and aquatic life support. In Massachusetts, these uses include fish

consumption, aquatic life support, drinking water, shellfishing, primary contact

recreation (swimming), and secondary contact recreation (boating).

In general, the most recent statewide surface water assessments published by

Massachusetts and New Hampshire in 2002 show that bacteria (E. Coli and fecal

coliform) is the largest cause of water quality violations in the Merrimack River

mainstem. This translates into a non-supporting use of primary and secondary

contact recreation in the majority of the River downstream of Manchester, New

Hampshire, as well as a closure of the shellfishing beds in the tidally influence portion

of the River. The New Hampshire assessment report lists CSO’s as the primary cause

of these violations; Massachusetts does not provide a similar listing. The

Massachusetts assessment report also lists metals, nutrients, and priority organics as

significant problems along the mainstem, resulting in a non-attainment of the aquatic

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life use. Additionally, the recent MRI study also discovered exceedances of water

quality standards for lead and zinc in the lower portion of the River during wet and

dry-weather conditions, affecting aquatic life in the river. The following table

provides a summary of the major causes of non-supporting use in the Merrimack

River mainstem based on the states’ 2002 assessment reports.

Causes of non-support in the Merrimack River mainstem

Listed Miles/ Area

Pollutant

NH MA Total

Non-supporting Use

Pathogens 19.82 mi

27.9 mi,

7.14 mi

47.72 mi,

7.14 mi

Primary and secondary

contact recreation (MA

and NH), shellfishing

(MA only)

Metals --- 20.8 mi 20.8 mi Not listed

Nutrients

--- 18.7 mi 18.7 mi Not listed

Priority Organics --- 15.9 mi,

6.97 mi

15.9 mi,

6.97 mi

Not Listed

pH 4.88 mi --- 4.88 mi Aquatic Life

Unionized Ammonia --- 4.37mi

4.37mi

Not Listed

Flow Alteration 0.59 mi --- 0.59 mi Aquatic Life

Area (in mi

) is provided for the tidally influenced portion of the basin in Massachusetts

Massachusetts does not specify which nutrients are a problem; however, phosphorus is

generally the limiting nutrient in freshwater and nitrogen is the limiting nutrient in marine

waters.

Source: MADEP 2002, NHDES 2002

Elevated bacteria levels were also identified as a major problem on many of the

tributaries to the Merrimack River, particularly in the Massachusetts portion of the

basin, translating into a non-supporting use for primary and secondary contract

recreation in the listed areas. Additionally, violations of the pH criteria for aquatic

life support were identified in a majority of the New Hampshire tributaries. The

Massachusetts assessment report listed metals, nutrients, and organic enrichment/

low dissolved oxygen as the other top causes of designated use non-attainment. The

MRI study also discovered elevated levels of lead during wet and dry-weather in the

Sudbury/Assabet/Concord (SuAsCo) and Nashua River watersheds, as well as

elevated copper concentrations in the SuAsCo watershed.

Resource Summary

The Merrimack River watershed is a high value resource area that supports a range of

biological, recreation, and other resources, such as hydropower and public drinking

water supplies. The watershed also supports a range of important habitats, as

follows:

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n Aquatic Habitat- These habitats include quickwaters in the northern portion of the

watershed, cold and warm water fisheries throughout the watershed, and an

estuarine environment in the River’s final reaches.

n Riparian Habitat- The diversity of river riparian habitat provides a valuable

resource for wildlife. One of the riparian habitats found along the mainstem River,

the pitch/scrub oak barrens, are considered globally rare and support the only

identified New England population of Karner blue butterfly, a federally-listed

endangered species.

n Freshwater Wetland Habitat- Freshwater wetlands play an integral role in the

ecology of the Merrimack River corridor. The combination of high nutrient levels

and primary productivity found in these habitats is ideal for the development of

organisms forming the base of the food chain.

n Tidal Wetland Habitat- The unique freshwater/saltwater habitat in the lower 22

miles of the mainstem River supports a wide range of aquatic species, including

extensive shellfishing beds (which are currently closed due to elevated bacteria

levels).

Biological resources in the watershed include shellfish populations in the tidally

influenced portions of the mainstem Merrimack River, various resident and

anadromous fish populations, and numerous threatened and endangered species. In

the past 20 years an extensive anadromous fish restoration program has been

implemented on the Merrimack River designed to bring back extirpated stocks of the

endangered Atlantic salmon, American shad, alewife, and blueback herring. The

largest threats to the fish populations currently include mercury and polychlorinated

biphenyl (PCB) contamination, hydromodification, thermal pollution, and flow

regulation resulting in insufficient in-stream flow requirements.

The Merrimack River watershed also supports a range of primary and secondary

contact recreation activities, including a Class II and III rapids and slalom kayaking

course in Manchester, New Hampshire, a public beach at the Lowell Heritage State

Park, and numerous marinas and private boat docks. In addition, hiking, camping,

cross-country skiing and picnicking are popular activities associated with the River

and adjacent back areas. The portion of the mainstem River from its origin at

Franklin, New Hampshire to the backwater impoundment at Hooksett Dam is under

Congressional study for designation to the Wild and Scenic River System.

In additional to the biological and recreational resources, the watershed supports a

variety of economic uses, including seven hydroelectric dams, which currently

operate on the mainstem Merrimack River and the Pemigewasset River. The

mainstem River also supports numerous public and industrial water users along its

length.

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Pollution Source Summary

Water quality in the Merrimack River mainstem is affected by both point and non-

point source pollution. Municipal wastewater treatment plants, CSO’s, stormdrain

discharges, and industrial dischargers are considered to be the largest cause of point

source pollution in the watershed. These sources contribute significantly to the non-

attainment of designated uses throughout the basin. Both CSO and stormdrain

pollution are generally a wet-weather problem, whereas municipal and industrial

dischargers are a continuous source.

The primary sources of non-point source pollution in the watershed include: urban

and non-urban stormwater runoff, atmospheric deposition, natural sources (such as

wildlife and waterfowl populations), pet waste, in situ contaminants, agricultural

runoff, septic systems, illicit connections, and groundwater plumes from sites

regulated under the Resource Conservation and Recovery Act (RCRA) and from

landfills. Unlike point source discharges, pollution from non-point sources is very

difficult to quantify and remediate. However, these sources may contribute

significantly to the non-attainment of designated uses in the Merrimack River

watershed.

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Contents

Executive Summary

Section 1 – Introduction

1.1 Study Authority............................................................................................... 1-1

1.2 Study Purpose.................................................................................................. 1-1

1.3 Report Scope.................................................................................................... 1-2

1.4 Watershed Overview....................................................................................... 1-2

1.5 Study Scope...................................................................................................... 1-3

1.6 Study Area....................................................................................................... 1-4

Section 2 – Physical Setting

2.1 Study Area....................................................................................................... 2-1

2.2 Geology and Land Use.................................................................................... 2-3

2.2.1 Bedrock and Surficial Geology.......................................................... 2-3

2.2.2 Soil Composition................................................................................ 2-3

2.2.3 Groundwater Aquifers...................................................................... 2-8

2.2.4 Land Use............................................................................................ 2-8

2.3 Climate and Hydrology..................................................................................2-11

2.3.1 Climate..............................................................................................2-11

2.3.2 Hydrology.........................................................................................2-15

2.4 Social and Economic.......................................................................................2-21

Section 3 – Water Quality

3.1 Sampling Programs......................................................................................... 3-3

3.2 Designated Uses............................................................................................... 3-9

3.3 Water Quality in the Merrimack River Mainstream......................................3-15

3.3.1 2002 New Hampshire and Massachusetts 303(d) Lists....................3-15

3.3.2 Other Studies....................................................................................3-20

3.3.3 Summary...........................................................................................3-22

3.4 Water Quality in Significant Tributaries........................................................3-22

3.4.1 2002 New Hampshire and Massachusetts 303(d) Lists....................3-24

3.4.2 Summary...........................................................................................3-30

3.5 Sediment Quality............................................................................................3-31

3.5.1 Monitoring Programs.......................................................................3-31

3.5.2 State Reporting.................................................................................3-31

Section 4 – Resource Summary

4.1 Biological Resources........................................................................................ 4-1

4.1.1 Habitat............................................................................................... 4-1

4.1.2 Biological Lifeforms........................................................................... 4-4

Table of Contents

Merrimack River Watershed Assessment Study

Description of Existing Conditions

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4.1.3 Fisheries ............................................................................................4-10

4.2 Recreational Resources...................................................................................4-18

4.3 Other Resources..............................................................................................4-21

4.3.1 Hydropower.....................................................................................4-21

4.3.2 Existing USACE Projects ..................................................................4-22

4.3.3 Water Supply....................................................................................4-22

Section 5 - Pollution Source Summary

5.1 Point Source Pollution Summary.................................................................... 5-1

5.1.1 Municipal WWTP’s and Industrial Point Source Discharges ........... 5-2

5.1.2 Combined Sewer Overflows.............................................................. 5-3

5.1.3 Stormwater Discharges...................................................................... 5-4

5.2 Non-Point Source Pollution Summary............................................................ 5-5

Section 6 – Future Directions................................................................................................. 6-1

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Figures

Figure 2.1 - Basemap.................................................................................................... 2-2

Figure 2.2 – Bedrock Geology...................................................................................... 2-5

Figure 2.3 – Soil Surface Texture................................................................................. 2-6

Figure 2.4 – Hydrologic Soils Group........................................................................... 2-7

Figure 2.5 – Land Use Map.........................................................................................2-10

Figure 2.6 – Climate Stations......................................................................................2-14

Figure 2.7 – Active USGS Gaging Stations.................................................................2-16

Figure 2.8 – Boxplots of Monthly Streamflow Data for Select Gaging Stations.........2-17

Figure 2.9 – Weekly Streamflow Record at USGS Gaging Station- Lowell, MA .......2-21

Figure 2.10 – U.S. Census Population Block Data ......................................................2-23

Figure 4.1 - Anadromous Fish Returns – Essex Dam Fish Lift in

Lawrence, Massachusetts.......................................................................4-14

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Tables

Table 2.1 – Summary of Major Tributaries.................................................................. 2-1

Table 2.2 – Land Use Summary................................................................................... 2-9

Table 2.3 – Active Climate Stations in the Merrimack River Watershed...................2-11

Table 2.4 – Summary of Monthly Precipitation and Temperature Statistics

For Select Stations.....................................................................................2-13

Table 2.5 – Summary of Active Streamflow Gaging Stations in the Merrimack

River Watershed.......................................................................................2-15

Table 2.6 – Summary of 7Q10 and Mean August Flow for Active Gaging

Stations on the Merrimack and Pemigewasset Rivers.............................2-20

Table 2.7 – 2000 U.S. Census Population Data for Urban Centers in the

Merrimack River Watershed....................................................................2-22

Table 3.1 – Summary of Water Quality Sampling Program........................................ 3-1

Table 3.2 – Causes of Non-support in the Merrimack River Mainstem...................... 3-3

Table 3.3 – Designated Water Class in the Merrimack River Watershed...................3-11

Table 3.4a – New Hampshire Guidelines for Use Classification................................3-12

Table 3.4b –Massachusetts Guidelines for Use Classification....................................3-14

Table 3.5 – 2002 CALM Listed Merrimack River Mainstem Segments in

New Hampshire for “Waters that do not require a TMDL”....................3-18

Table 3.6 – 2002 Category 5 Listed Waters in the Massachusetts Portion of the

Merrimack River Mainstem.....................................................................3-20

Table 3.7 – Status of Designated Use Support in Major Tributaries ..........................3-23

Table 3.8 – CALM Listed Tributary Segments in New Hampshire for Waters

That do not Require a TMDL...................................................................3-25

Table 3.9 – Listed Tributary Segments in the Massachusetts Portion of the

Merrimack River Watershed in Category 4c and 5..................................3-27

Table 4.1 – Summary of Shellfish Species.................................................................... 4-6

Table 4.2 – State Listed Mammals ............................................................................... 4-7

Table 4.3 – Federally and State Listed Birds................................................................ 4-8

Table 4.4 – State Listed Amphibians and Reptiles ...................................................... 4-9

Table 4.5 – List of Fish Identified in the Merrimack River, Sorted by Family ...........4-10

Table 4.6 – Cold-Water and Warm-Water Designated Fisheries in Massachusetts...4-15

Table 4.7 – Recreational Facilities Along the Lower Merrimack River......................4-18

Table 4.8 – Water Users Along the Merrimack River Mainstem

Downstream of Manchester, New Hampshire........................................4-23

Table 5.1 – Water Discharges to the Merrimack River Mainstem

Downstream of Manchester, New Hampshire......................................... 5-3

Table 5.2 – CSO Discharges to the Merrimack River Mainstem................................. 5-4

Table 5.3 – Potential Non-point Source Pollution Sources and Impacts..................... 5-5

Preface

The cities of Manchester and Nashua, New Hampshire, Lowell and Haverhill,

Massachusetts, and the Greater Lawrence Sanitary District (GLSD), Massachusetts are

currently working separately to develop and implement long-term Combined Sewer

Overflow (CSO) control plans in compliance with the Federal Clean Water Act. The

collective cost of these potential CSO improvements could reach upwards of $1 billion

over the next 20 years. Given this sizable investment, the communities are concerned

that decisions regarding potential CSO abatement measures are being made without

adequate understanding of the existing conditions in the Merrimack River, the

pollution sources to the River, and the potential benefits of the proposed CSO

improvements.

In order to develop a comprehensive assessment of the current Merrimack River

mainstem and watershed conditions, the five sponsors, in conjunction with the U.S.

Army Corps of Engineers - New England Division (USACE) are jointly funding the

Merrimack River Watershed Assessment Study. The community coalition has

provided 50 percent of the cost share for the first $2,000,000 phase of the Study. The

Federal government, through the USACE, is providing the remaining financial

support, in addition to technical assistance for the Study. Involvement of the USACE

is authorized under Section 729 of the Water Resources Development Act (WRDA) of

1986 entitled “Study of Water Resources Needs of River Basins and Regions,” as

amended by Section 202 of WRDA 2000.

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Section 1

Introduction

The cities of Manchester and Nashua, New Hampshire the City of Lowell,

Massachusetts, the Greater Lawrence Sanitary District (GLSD), Massachusetts, and

the City of Haverhill, Massachusetts are currently working separately to develop and

implement long-term Combined Sewer Overflow (CSO) control plans in compliance

with the Federal Clean Water Act. The collective cost of these potential CSO

improvements may reach upwards of one billion dollars over the next 20 years. Given

this sizable investment, the communities are concerned that decisions regarding the

potential mitigation measures are being made without adequate understanding of the

existing conditions in the Merrimack River, the pollution sources to the River, and the

potential benefits of the proposed CSO improvements. The cities are looking to

conduct a comprehensive assessment of the current River and watershed conditions,

the results of which can then be used to guide decisions regarding CSO mitigation

measures.

1.1 Study Authority

The Federal government, through the United States Army Corps of Engineers

(USACE), is providing 50 percent of the cost share for the Merrimack River Watershed

Assessment Study (hereafter referred to as the “Study”), as well as technical

assistance. Involvement of the USACE is authorized under Section 729 of the Water

Resources Development Act (WRDA) of 1986 entitled “Study of Water Resources

Needs of River Basins and Regions” as amended by Section 202 of WRDA 2000. This

report was prepared in response to specific language contained in Section 437 of

WRDA 2000 that directed the USACE to conduct a comprehensive study of the water

resource needs of the Merrimack River basin in Massachusetts (MA) and New

Hampshire (NH).

Directed funds for this effort were provided to the USACE by Congress in the fiscal

year 2001 and 2002 Energy and Water Development Appropriation. The City of

Lowell, Massachusetts, serving as the local sponsor of this project, entered into a

Memorandum of Understanding with the four other communities in the watershed

(Haverhill and GLSD, Massachusetts; Manchester and Nashua, New Hampshire) to

provide the remaining financial support for the Study.

1.2 Study Purpose

The purpose of this Study is to develop a comprehensive Watershed Management

Plan (WMP) for the Merrimack River watershed. The WMP will be used to guide

investments in the environmental resources and infrastructure of the basin and will be

aimed at achieving conditions that support beneficial uses and ecosystem health, with

a particular emphasis on water quality. The WMP will encompass the diverse

interests and goals of the various partners and stakeholders throughout the

Merrimack River watershed, which include local, state, and Federal governments,

industry, and concerned citizen groups. Stakeholders will be consulted throughout

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the planning process to help ensure that the final plan is balanced and

comprehensive.

The assessment will include a water resources and ecosystem restoration

investigation of the Merrimack River and will be used to answer the following

questions:

n What are the existing and potential future feasible beneficial uses of the River?

n What are the pollutant sources that may impact these uses?

n What is the relative contribution of pollutants from various sources?

n What project(s) will provide the most significant return on investment?

n Which projects have the highest priority?

1.3 Report Scope

The purpose of this “Description of Existing Conditions” report is to provide a

comprehensive description of the current conditions in the watershed based on

available resources. The report is not intended to serve as an evaluation of these

existing conditions with respect to accuracy and adequacy of existing data, but rather

as unifying summary of the relevant documents that have been issued primarily in

the past ten years. Topics addressed in this report include the Merrimack River’s

physical setting; biological, recreational, and other resources; water quality of the

mainstem and its significant tributaries; and potential contributors to point and non-

point source pollution in the watershed. This report will serve as a reference for

comparison during subsequent tasks of this Study.

1.4 Watershed Overview

The Merrimack River is formed by the confluence of the Pemigewasset and

Winnipesaukee Rivers in Franklin, New Hampshire. The River flows southward for

approximately 78 miles in New Hampshire; it turns abruptly across the New

Hampshire-Massachusetts border and flows in a northeasterly direction for

approximately another 50 miles in Massachusetts before discharging to the Atlantic

Ocean at Newburyport. The mainstem Merrimack River flows past the five major

urban centers of Manchester and Nashua, New Hampshire and Lowell, Lawrence,

and Haverhill, Massachusetts. The final 22 miles of the River are tidally influenced

below Haverhill.

The Merrimack River watershed covers an area of approximately 5,010 square miles

in the south-central portions of New Hampshire (76 percent of the drainage area) and

the northeastern portions of Massachusetts (24 percent of the drainage area), making

it the fourth largest watershed in New England. Geographically, the basin

encompasses a variety of terrain, from the relatively steep conditions of the White

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Introduction

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Mountain region in northern New Hampshire to the estuarine coastal basin of

northeastern Massachusetts.

Historically, the water quality of the Merrimack River was severely degraded by

industrial and domestic wastes. In the 1960s, the River was listed as one of the

nation’s ten most polluted waterways, primarily as a result of raw sewage, paper and

textile mill wastes, and tannery sludge (U.S. Environmental Protection Agency

(USEPA) 1987). However, the passage of the Federal Clean Water Act in 1972 ushered

in a period of rebirth for the River. An infusion of large amounts of state and Federal

funding for spending on water resources infrastructure investments, such as

wastewater treatment plant (WWTP’s), helped to revive the River into one that is

currently a significant natural and economic resource in the New England region.

Despite the significant improvements, further work to improve water quality is

required. A 1997 study by the Merrimack River Initiative (MRI) reported that in the

entire Merrimack River watershed, 268.2 river miles fully support, 67.5 river miles

partially support, and 193 river miles do not support their designated uses (Donovan

and Diers 1997). The reported 530 river miles represent only the assessed portion of

the basin, as per the 305(b) Reports issued by Massachusetts and New Hampshire.

Although this is only a small percentage of the 4,000 total river miles in the entire

watershed, it includes most portions of the River where there are concerns over the

ability of the river segment to support designated uses. The term “fully-supports” is

used to describe segments where water quality is sufficient to fully support the

designated uses; “partially supporting” describes segments where one or more

designated uses is partially supported and the other uses are fully supported; “non-

supporting” describes segments where one or more uses are not supported.

The 1997 MRI study indicates that the four largest causes of non-support of

designated uses in the basin are pollution from (1) urban runoff, (2) natural sources,

(3) municipal point sources, and (4) CSO discharges. This study also identified

elevated bacteria levels as the primary cause of non-supporting use in the basin,

followed distantly by low dissolved oxygen concentrations and high nutrient levels

(Donovan and Diers 1997). Other issues of concern include low-flow conditions, water

supply, flooding, contamination of shellfishing beds, and fish and wildlife habitat and

contamination issues.

1.5 Study Scope

Given the size of the Merrimack River watershed and the range of issues identified for

potential analysis, a phased implementation plan has been developed for this Study.

Phase I efforts will focus on the following topics:

n Assessment of existing conditions in the watershed

n Identification of potential and future uses of the River

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n Identification and quantification of pollutant sources

n Development of screening level models

n Collection of water quality and streamflow data (wet- and dry-weather)

n Development of water quality models

n Evaluation of various CSO and non-CSO abatement projects and other water

management options

n Inventory of potential ecosystem restoration projects in the watershed

The data collection aspect of the project will be aimed at determining the causes of

water quality degradation in the Merrimack River, particularly the impacts of CSO’s,

point, and non-point sources.

The scope of the Phase II assessments will be determined based on the results of the

Phase I findings and will be contingent upon the availability of funding from local

and Federal sources. It is anticipated, however, that the Phase II efforts will focus on

in-stream flow issues, additional water quality monitoring for non-standard

parameters, and supplemental analysis of potential abatement alternatives and

ecosystem restoration projects.

1.6 Study Area

For the purposes of this report, existing conditions in the entire Merrimack River

watershed, as defined in Section 1.4, are discussed wherever possible. Future tasks to

be performed under Phase I will be limited in geographic range to the portion of the

mainstem River south of Hooksett Falls Dam in Hooksett, New Hampshire. Water

quality sampling and flow monitoring efforts will be concentrated in this area, as well

as at the mouth of 11 major tributaries that join the mainstem south of Hooksett, New

Hampshire. Water quality and flow models will be developed for this lower portion

of the mainstem.

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Section 2

Physical Setting

This section of the report summarizes the physical setting of the Merrimack River

watershed, including the basin delineation, the geology and land use, the climate and

hydrology, and the social and economic composition of the basin.

2.1 Watershed Area

The Merrimack River watershed is comprised of numerous subwatersheds of varying

size. Table 2.1 presents a summary of the watershed area, river length to the

Merrimack River confluence, and distance upstream of the Newburyport Light for

major tributaries to the Merrimack River mainstem. A map of the watershed and

major subbasins is provided in Figure 2.1; the five sponsor communities of

Manchester and Nashua, New Hampshire and Lowell, GLSD (Andover, North

Andover, Lawrence, and Methuen, Massachusetts; and Salem, New Hampshire), and

Haverhill, Massachusetts are also highlighted on the figure.

Table 2.1: Summary of Major Tributaries

Location of

Headwaters

Tributary

Drainage

Area

(mi

)

Length

(mi)

Distance above

Newburyport

Light (River miles)

Pemigewasset River 1021 64 116 New

Hampshire Winnipesaukee River 486 23 116

Contoocook River 766 66 101

Soucook River 91 28 86

Suncook River 260 39 83

Piscataquog River 220 24 71

Cohas Brook 68 7 68

Souhegan River 219 34 62

Beaver Brook 91 12 40

Spicket River 75 15 28

Powwow River 49 NA

Merrimack River mainstem 577 --

Massachusetts

Nashua River 530 34 55

Salmon River 32 NA NA

Stony Brook 46 NA NA

Shawsheen River 74 24 27

Assabet/Sudbury/Concord

Rivers

400 16

Sources: Merrimack River Watershed Council (http://www.merrimack.org)

NA= Not available,

Concord River only

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2.2 Geology and Land Use

The Merrimack River watershed is located in the New England Physiographic

Province, and traverses each of the three major sections -- the White Mountains, the

New England Uplands, and the Seaboard Lowlands (Flanagan, et al. 1999). The

majority of the basin falls within the New England Uplands region, which is

characterized by rolling hills and local relief ranges from a few hundred feet to 1,000

feet in more mountainous regions. The watershed elevation ranges from a high of

5,249 feet on Mount Lafayette in the White Mountain region to mean sea level along

the northeastern Massachusetts coast (Seaboard Lowlands).

2.2.1 Bedrock and Surficial Geology

Bedrock in the Merrimack River watershed (Figure 2.2) is generally of similar age and

genesis. Intrusive igneous rocks, primarily Granitoid Plutonic Rocks, dominate the

northeastern portion of the basin. Large deposits of metamorphic mixed and sulfide-

bearing granofels cover the north-central and northwestern portion of the basin. A

strip of metamorphic grade rocks, including mixed schist and gneiss deposits, cuts

across the Massachusetts-New Hampshire border in a northeasterly direction. The

southeast corner of the basin is dominated by sulfide-bearing schistose granofels and

granitoids, and volcanics.

The Merrimack River basin is generally covered by a sheet of glacial till, with areas of

large fine- and large-grained glacial-lake deposits along the River mainstem and

major tributaries (Flanagan, et al. 1999). The till cover is composed of variable,

unstratified, silty, gravelly, sand and clays. The cover is generally thin on the hilltops

and in the deep valleys, with exposed bedrock typically visible in the hilly upland

regions (USACE 1977). The immediate coastal portion of the basin is characterized by

areas of fine-grained marine deposits (Flanagan, et al. 1999). Large glacial melt-water

lakes formed throughout the basin during glacial retreat. Figure 2.3 presents a

summary of the soil surface texture in the watershed.

2.2.2 Soil Composition

The soil composition of the basin is largely a result of the physiography and varying

glacial deposits. The Natural Resources Conservation Service (NRCS), formerly the

Soil Conservation Service (SCS), developed a national soils classification system

known as the Hydrologic Soils Group. A hydrologic group is defined as a group of

soils having similar runoff potential under similar precipitation and land use cover

conditions. The NRCS divided soils into four classes: A, B, C, and D, with the

following definitions:

Group A (Low runoff potential): The soils have a high infiltration rate even when they

wetted. They chiefly consist of deep, well drained to excessively drained sand or

gravels. They have a high rate of water transmission.

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Group B: The soils have a moderate infiltration rate when thoroughly wetted. They

are generally moderately-deep to deep, moderately well-drained to well-drained soils

that have moderately fine to moderately coarse textures. They have a moderate rate

of transmission.

Group C: The soils have a slow infiltration rate when thoroughly wetted. They

generally have a layer that impedes downward movement of water or have

moderately fine texture. They have a slow rate of water transmission.

Group D (High runoff potential): The soils have a very slow infiltration rate when

thoroughly wetted. They chiefly consist of clay soils that have a high swelling

potential, soils that have a permanent high water table, soils that have a claypan or

clay layer near the surface, and shallow soils over nearly impervious material. They

have a very slow rate of water transmission.

Following the soil hydrologic group classifications the majority of soils in the

watershed may be broadly classified as soil group C, interspersed with large deposits

of soil group B. Soil group C is typically found in upland areas where glacial till is

most commonly found at the surface (Flanagan, et al. 1999). This group is used to

describe soils with slow infiltration rates and moderate to high runoff potential. Soil

group B is typically found in areas of stratified-drift deposits and is characterized by

moderate infiltration rates. Along the immediate coast, soils are classified as soils

hydrologic group D, which is used to describe clayey soils with very slow infiltration

rates and minimal depth to groundwater. The generalized hydrologic soils mapping

for the basin is provided in Figure 2.4.

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2.2.3 Groundwater Aquifers

There are three primary types of aquifers in the Merrimack River watershed:

stratified-drift, till, and bedrock. Highly productive stratified-drift aquifers dominate

the Massachusetts portion of the basin. They are also found in the valleys of New

Hampshire along the mainstem and significant tributaries. These aquifers consist

mainly of layered sand and gravel deposits formed by the retreating glaciers. They

serve as the main source of drinking water for many communities that rely on

groundwater supplies and also supply the majority of streamflow during dry seasons

(i.e., late summer and early fall) and during droughts. Annual groundwater recharge

to stratified-drift aquifers is approximately half of the annual precipitation. This

translates to 20 to 24 inches per year in glaciated portions of eastern Massachusetts

and in east-central and southeastern New Hampshire, and 14 inches per year in

south-central New Hampshire (Flanagan, et al. 1999).

Glacial till aquifers are most commonly found in the New Hampshire portion of the

basin. These aquifers are characterized by low-permeability and thus, are limited in

their use for drinking water supplies. Recharge to till aquifers is approximately nine

inches per year (Flanagan, et al. 1999). Fractured bedrock aquifers serve as the

drinking water supply for numerous rural households, as well as for several

communities and commercial and industrial users. Coarse-grain rocks, such as granite

and basalt typically have higher yields than finer-grained rocks, such as schist and

gneiss. Recharge to these aquifers is primarily controlled by land surface relief and the

portion of bedrock above groundwater sinks, such as lakes. Recharge to crystalline

bedrock aquifers is approximately three to five inches per year (Flanagan, et al. 1999).

2.2.4 Land Use

Historically, the Merrimack River played a large role in the development of the

region’s economy and land use patterns. The onset of the industrial revolution in the

mid-1800s pulled many families from traditional subsistence farming towards more

promising work in urban settings. Many of the larger towns adjacent to the

Merrimack mainstem, including the five sponsor communities, began as factory or

mill towns due to the need for hydropower to power the emerging industries. This

economic shift resulted in the reclamation of previously predominantly agricultural

lands by forest and woodland. Today, the basin is dominated by a mix of deciduous

and evergreen forest cover (over 75 percent of the watershed area). Urban areas,

including residential, industrial, and commercial land uses, make up the second

largest land use category, covering approximately 10 percent of the watershed area.

Table 2.2 and Figure 2.5 present a more detailed breakdown of land use in the

Merrimack River watershed.

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Table 2.2: Land Use Summary

Land Use Category Area (mi

) Percent of Total Area (%)

Forest 3892 77

Wetland 56 1.1

Water 214 4.3

Residential 350 7.0

Commercial & Industrial 119 2.4

Transportation 36 0.7

Urban 47 0.9

Agricultural 294 5.9

Unknown 23 0.4

Beaches/Other Sandy Areas/Exposed Rock 1.2 0.02

Source: US EPA (http://www.epa.gov/ostwater/basins)

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2.3 Climate and Hydrology

2.3.1 Climate

Climatic conditions within the Merrimack River watershed vary significantly from its

headwaters in the White Mountain National Forest, to the mouth of the River along

the Atlantic Ocean. The basin is located partially with the Northern and Coastal

Climatic divisions along its far northern and southeastern boarders; the majority of

the watershed falls within the Central Climatic division (Flanagan et al. 1999).

Weather systems throughout the basin are primarily the result of prevailing westerly

winds and the confluence of many continental weather patterns in North America.

The climate of the Northern division is primarily influenced by high elevation and

latitude. The Central division is generally more moderate than the Northern section

due to its lower elevation and latitude; this division experiences some climate

modification due to maritime influences. The climate of the Coastal division is

influenced primarily by its low elevation and proximity to the Atlantic Ocean

(Flanagan et al. 1999).

Table 2.3 and Figure 2.6 present a summary of the active climate stations in the basin;

these stations are operated as part of the National Weather Service’s Cooperative

Station Network.

Table 2.3: Active Climate Stations in the Merrimack River Watershed

State Climate Station Location COOP ID Start of Record

NH Alexandria 270045 September 1995

Bow Garvins Falls 270834 June 1948

Bradford 270913 April 1998

Bristol 270998 June 1948

Concord Municipal Airport 271683 October 1933

Deering 271950 April 1976

Franklin Falls Dam 273182 June 1948

Franklin Junction 273172 June 1948

Grafton 273530 June 1955

Greenville 273658 June 1988

Hopkinton Lake 274218 June 1963

Laconia 54736 January 1965

Lincoln 274732 June 1948

Macdowell Dam, Peterborough 275013 June 1950

Manchester 275072 June 1948

Manchester Airport 14710 February 1937

Massabesic Lake 275211 June 1948

Meredith 275350 December 1993

Milford 275412 June 1948

Nashua 275712 June 1948

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State Climate Station Location COOP ID Start of Record

NH Nashua Boire Field 54754 May 1953

(cont’d)

New Hampton 275813 April 1998

Plymouth 276945 July 1984

Salisbury 277833 September 1995

South Lyndeboro 278081 June 1948

Warren 278885 June 1948

Weare 278972 July 1969

Wentworth 279091 June 1948

MA Ashburnham 190190 July 1985

Bedford 190535 May 1957

Bedford Hanscom Field 14702 September 1942

Groveland 193276 June 1992

Haverhill 193505 October 1899

Lawrence 194105 June 1948

Lawrence Municipal Airport 94723 May 1946

Lowell 194313 June 1948

Natick 195175 December 1968

Newburyport 195285 June 1948

Source: http://www.ncdc.noaa.gov

Precipitation in the watershed is fairly evenly distributed throughout the year. There

are, however, large inter-basin variations in amount and type of precipitation (i.e.,

rain versus snow) primarily as a result of the effects of terrain, elevation, latitude, and

proximity to the ocean (Flanagan et al. 1999). Locations in the far northern portions of

the basin may receive upwards of 60 inches per year of precipitation, while the

majority of the low-lying portions receive approximately 42 inches per year. A

summary of the normal monthly precipitation and snowfall is presented in Table 2.4

for select climate stations in the watershed.

Temperatures in the watershed generally vary widely on an annual basis.

Temperature data taken from several weather observatories throughout the basin

found that July was typically the warmest month and January was the coldest

(Flanagan et al. 1999). Additionally, winter temperatures were found to vary more

widely than did summer temperature across the basin. A summary of the normal

minimum, maximum, and average daily temperatures for each month is presented in

Table 2.4 for the COOP stations in Concord, New Hampshire and Bedford,

Massachusetts.

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Table 2.4: Summary of Average Monthly Precipitation and Temperature

Statistics for Select Stations

Concord, NH

Bedford, MA

Month

Max.

Temp

Min.

Temp

Ave.

Temp

Ave.

Precip

Ave.

Snow

Max.

Temp

Min.

Temp

Ave.

Temp

Ave.

Precip

Ave.

Snow

Jan 31.1 10.5 20.8 2.86 16.8 34.8 15.5 25.1 3.85 14.4

Feb 33.6 12.4 23.0 2.47 14.4 37.3 17.3 27.3 3.45 13.5

March 42.7 22.7 32.7 3.19 11.2 46.0 26.3 36.1 4.12 11.1

April 56.0 32.3 44.2 3.13 2.8 58.1 35.4 46.8 3.87 2.2

May 68.7 42.3 55.5 3.12 0.1 69.5 45.5 57.5 3.56 0.2

June 77.5 52.0 64.7 3.32 0.0 77.8 54.7 66.2 3.57 0.0

July 82.2 57.1 69.7 3.38 0.0 82.7 60.0 71.4 3.48 0.0

Aug 80.0 55.1 67.6 3.04 0.0 80.9 58.6 69.8 3.31 0.0

Sept 72.0 47.0 59.5 3.27 0.0 73.0 50.2 61.6 3.66 0.0

Oct 61.0 36.0 48.5 2.94 0.1 62.5 39.2 50.9 3.67 0.1

Nov 47.5 28.1 37.8 3.68 3.9 50.9 31.4 41.1 4.34 2.4

Dec 34.9 16.1 25.5 3.07 12.7 39.0 20.9 29.9 4.17 11.0

Temperatures in degrees F; precipitation and snowfall in inches

Based on period of record from 1921- 2001

Based on period of record from 1957-2001

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2.3.2 Hydrology

The U.S. Geological Survey (USGS) currently operates three flow gaging stations on

the Merrimack River mainstem (including the Pemigewasset River) and 16 stations on

its tributaries. Numerous additional historical records of varying length are available

throughout the basin. Daily streamflow data and daily, monthly, and annual

streamflow statistics are available for download from the USGS-NWIS website at

http://water.usgs.gov/nwis. Table 2.5 and Figure 2.7 presents a summary of the

active gaging stations in the watershed, the start year, and mean annual discharge.

Table 2.5: Summary of Active Streamflow Gaging Stations in the Merrimack

River Watershed

Station

Station Name

Start

Mean

Annual Q

(cfs)

Mainstem

01076500 Pemigewasset River at Plymouth, NH 1903 1370

01092000 Merrimack River near Goff Falls, below

Manchester, NH

1936 5339

01100000 Merrimack River below Concord River at

Lowell, MA

1923 7707

Tributaries

01074520 East Branch Pemigewasset River at Lincoln,

1993 337

01081000 Winnipesaukee River at Tilton, NH 1937 710

01080500 Lake Winnipesaukee Outlet at Lakeport,

1933 540

01078000 Smith River near Bristol, NH 1918 145

01089100 Soucook River at Pembrooke Road near

Concord, NH

1988 125

01093800 Stony Brook tributary near Temple, NH 1963 7.3

010965852

Beaver Brook at North Pelham, NH 1986 75

01100505 Spicket River at Island Pond Rd. at North

Salem, NH

2000

01094400 North Nashua River at Fitchburg, MA 1972 122

01094500 North Nashua River near Leominster, MA 1935 201

01096500 Nashua River at East Pepperell, MA 1935 584

01097000 Assabet River at Maynard, MA 1941 190

01098530 Sudbury River at Saxonville, MA 1979 195

01099500 Concord River below R. Meadow Brook at

Lowell, MA

1936 649

01100568 Shawsheen River at Hanscom Field near

Bedford, MA

1995 5.1

01100600 Shawsheen River near Wilmington, MA 1963 59

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Boxplots of the monthly streamflow data for the period of record are provided in

Figure 2.8 for the three stations on the Merrimack River mainstem (including the

Pemigewasset River). Each box on the graph describes the range and location of the

streamflow data for the respective month. At all three stations, the highest average

flows occur during the month of April; this is also month with greatest variability in

flow conditions. The lowest and least variable flows occur during late summer

(August and September).

Figure 2.8: Boxplots of monthly streamflow data for select gaging stations

The bottom of the box coincides with the lower quartile of the data and the top with

the upper quartile of the data; a line through the box marks the median of the data.

The vertical lines on each side of the box run from the quartiles to the smallest and

largest numbers that fall within 1.5 times the inter-quartile range (IQR). The IQR is

the difference between the upper and lower quartiles of the distribution. The lower

quartile is defined as that number such that at least 25-percent of the data fall at or

below it and at least 75-percent of the data falls at or above it. Similarly, the upper

quartile is the number such that at least 75-percent of the data fall at or below it and at

least 25-percent falls at or above it. Outliers beyond the IQR are marked by a point on

the graph.

121110987654321

10000

5000

Discharge (cfs)

Pemigewasset River at Plymouth, NH (01076500)

Month

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121110987654321

25000

20000

15000

10000

5000

Discharge (cfs)

Merrimack River below Manchester, NH (01092000)

Month

121110987654321

50000

40000

30000

20000

10000

Discharge (cfs)

Merrimack River at Lowell, MA (01100000)

Month

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Low-flow Conditions:

Low-flow conditions on the Merrimack River are a priority concern for the protection

of wildlife habitat and water quality, as well as for the ability of the River to meet its

water demands from municipal and industrial users. Typically, low-flows are

expressed in terms of the magnitude, duration, and frequency of the condition. For

regulatory purposes in Massachusetts, “the lowest flow condition at and above which

[water quality] criteria must be met is the lowest mean flow for seven consecutive days to be

expected once every ten years” (314 CMR 4.00). This is commonly referred to as the 7Q10

and is used as a guide for worst-case water quality assessments. The median or mean

August flow is also a frequently used statistic in Massachusetts for water

management and planning purposes.

In 1988, New Hampshire enacted the Rivers Management and Protection Act (RSA

483) in response to concerns over the balancing of water use priorities in the state.

The Act gives the New Hampshire Department of Environmental Protection

(NHDES) the authority and responsibility to maintain flow in support of “instream

public uses” in river segments that have been designated by the state for special

protection under the Act. Instream public uses include navigation, recreation, fishing,

conservation, maintenance, and enhancement of aquatic life, fish, and wildlife habitat,

protection of water quality and public health, pollution abatement, aesthetic beauty,

and hydropower protection. In November 2001, NHDES completed draft Instream

Flow Rules (ISFR); these rules were originally intended to apply to 14 designated

rivers in the state. However, in August 2002 the ISFR were revised to apply only to

two of the 14 rivers as a pilot program- the Lamprey River in the coastal watershed

and the Souhegan River in the Merrimack River watershed. If the pilot rules are

successfully implemented, they will be revised to be applied to the other 12 rivers. As

part of this pilot program, an instream flow water management plan will be

developed for each of the rivers. Additionally, NHDES will develop a report on the

impacts on water users, wildlife, recreation, and other interests along the rivers, and

recommendations for proposed legislation

(www.des.state.nh.us/rivers/instream/legfacts.htm).

A 1994 study performed by the Cadmus Group, commissioned by the MRI, evaluated

the low-flow hydrology of the Merrimack River watershed. The following table (Table

2.6) presents a summary of the 7Q10 statistics developed for those stations currently

operating on the mainstem Merrimack and Pemigewasset Rivers. Statistics were

calculated using the Log Pearson III extreme value distribution. This table also

presents the mean August flow, based on monthly statistics published by the USGS

(http://waterdata.usgs.gov/nwis).

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Table 2.6: Summary of 7Q10 and Mean August Flow for Active Gaging

Stations on the Merrimack and Pemigewasset Rivers

Station ID

Station Name 7Q10 (cfs)

Period of Record

Used in

Calculation

Mean August

Flow (cfs)

01076500 Pemigewasset River at

Plymouth, NH

117 1904-1992 504

01092000 Merrimack River near Goff

Falls, below Manchester, MA

653 1937-1992 1958

01100000 Merrimack River below

Concord River at Lowell, MA

950 1923-1992 2802

Hydropower Impacts:

Numerous hydropower dams currently existing on the mainstem Merrimack River

and its tributaries have significant impacts on the daily, weekly, and monthly

streamflow conditions in the River. Figure 2-9 shows the streamflow measured at the

USGS gaging station on the Merrimack River downstream of Lowell, Massachusetts

(01100000) during a one-week period from December 5 to December 12, 2002. This

station is located downstream of the Pawtucket Dam in Lowell, Massachusetts. The

effect of the hydropower operations is particularly evident on December 9, 2002 when

a drop of over 5,000 cubic feet per second (cfs) is observed in the streamflow

measured at this site, from a daily high of over 7,000 cfs to a daily low of less than

2,000 cfs.

During high flow conditions, the hydropower facilities generally operate as “run of

the river” facilities, with substantial spillage. During periods of low flow, the dams

are required to pass a minimum flow, while still operating to meet peak demands.

This often results in short-term water level fluctuations during summer months.

Additional information on the dams located in the watershed and their hydropower

operations is provided in Section 4.3.

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Figure 2.9: Weekly Streamflow Record at USGS Gaging Station- Lowell, MA

2.4 Social and Economic

The 2000 U.S. Census survey indicates that the overall population of the Merrimack

River watershed is approximately 2.04 million. This represents an increase of

approximately 14 percent from the 1.76 million people living in the basin as of the

1990 U.S. Census survey (Flanagan et al. 1999).

Population density tends to increase from north to south in the Merrimack River

watershed, ranging from fewer than 100 people per square mile in the northeastern

and northwestern portions of New Hampshire to greater than 800 people per square

mile in Manchester and Nashua, New Hampshire, and in northeastern Massachusetts.

The expanding interstate highway system has precipitated the migration of people

from more traditional Boston “metropolitan” areas to expanding suburban

communities of northeastern Massachusetts and southern New Hampshire. Figure

2.10 presents a summary of the 2000 U.S. Census block data for the Merrimack River

watershed.

Major urban centers along the mainstem Merrimack River include the cities of

Concord, Manchester, and Nashua, New Hampshire, as well as Lowell, Lawrence,

and Haverhill, Massachusetts. Concord, New Hampshire is the state capital. A

summary of the 2000 U.S. Census population data for these communities is provided

in Table 2.7.

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Table 2.7: 2000 U.S. Census Population Data for Urban Centers in the

Merrimack River Watershed

City 2000 Population

Concord, NH 40,687

Manchester, NH 107,006

Nashua, NH 86,605

Lowell, MA 105,167

Lawrence, MA 72,043

Haverhill, MA 58,969

Source: 2000 U.S. Census (http://www.census.gov/)

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Section 3

Water Quality

This section of the Existing Conditions report presents a summary of the current and

historic water quality sampling programs conducted in the basin, as well as a

summary of the current water and sediment quality. This description of existing

conditions is based on a review of available resources for data collected in

approximately the last ten years. Existing data discussed in this section will be used

for reference and comparison purposes in subsequent tasks performed under Phase I

of the Merrimack River Watershed Assessment Study. It will not be utilized at the

same level as water quality data collected under Phase I of this Study.

The primary water quality data collection agencies in the watershed have been the

New Hampshire Department of Environmental Services (NHDES), the Massachusetts

Department of Environmental Protection (MADEP), and the U.S. Geological Survey

(USGS). Recently, several volunteer monitoring programs have also started collecting

data within the watershed with the help of these state agencies and the Merrimack

River Watershed Council.

The majority of the water quality data that exists in the basin from MADEP was

collected prior to 1990. In 1999, the MADEP initiated a Microbial Indicator Study of

the Merrimack River, as well as aquatic benthic macroinvertebrate biomonitoring on

major tributaries. NHDES also collected water quality and biomonitoring data in the

watershed throughout the 1990s. The most recent comprehensive analysis of the

River’s quality was performed under the Merrimack River Initiative (MRI) during the

1990’s. This project was a collaborative effort between the USEPA, NHDES, MADEP,

and the New England Interstate Water Pollution Control Commission. The MRI

collected water quality samples throughout the basin during one wet-weather and

one dry-weather event; benthic macroinvertebrate sampling was also performed. A

summary of water quality sampling program is provided in Table 3-1; additional

detail on each program is provided in subsequent sections.

Table 3.1: Summary of Water Quality Sampling Programs

Agency Program

Monitoring

Period

Impaired waters monitoring program 1993- 1996 New Hampshire

Department of

Environmental Services

Rotating watershed monitoring

program

1989- 1993;

1997 to present

National Water Quality Surveillance

System (NWQSS)

1989 to present

Primary Monitoring Network (PMN) 1989 to present

Biomonitoring Program 1995 to present

Massachusetts

Department of

Environmental Protection

“Massachusetts Watershed Initiative”

rotating watershed management

program

1993 to present

Microbial Indicator Study 1999

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Massachusetts Division of

Marine Fisheries

Shellfish bed sampling On-going

USGS National Water Quality Assessment

Program (NAWQA)

On-going

Merrimack River

Initiative (MRI)

Dry and wet-weather monitoring,

biomonitoring

1994 and 1995

Water and Wastewater

Treatment Facilities

Various locations in the watershed On-going

Soucook River Watershed Project 1999 to present

Upper Merrimack River Local

Advisory Committee

1996 to present

Volunteer Monitoring

Programs

Piscataquog Watershed Association 1991 and 1992

Nashua River Watershed Association 1993 to present

Merrimack River Watershed Council 1999- 2001

Both Massachusetts and New Hampshire categorize waters according to their use

class. Each class is associated with a series of designated uses; the ability of a

waterbody to support these uses is assessed based on its ability to meet the applicable

water quality standards. In New Hampshire, designated use categories include

swimming (primary contact recreation), fish and shellfish consumption, drinking

water, and aquatic life support. In Massachusetts, these uses include fish

consumption, aquatic life support, drinking water, shellfishing, primary contact

recreation (swimming), and secondary contact recreation (boating). In both states, the

recreation and shellfish standards are based on human health concerns. E. coli and

fecal coliform bacteria are used in New Hampshire and Massachusetts, respectively,

as indicators of the possible presence of pathogens in surface waters and the risk of

disease, based on epidemiological evidence of gastrointestinal disorders from the

ingestion of contaminated waters. Contact with contaminated waters can also lead to

ear or skin infections, and inhalation of contaminated water can cause respiratory

diseases (http://www.epa.gov/OST/beaches/local/sum2.html#intro).

In general, the most recent statewide surface water assessments published by

Massachusetts and New Hampshire in 2002 show that bacteria (E. coli and fecal

coliform) is the largest cause of water quality violations in the Merrimack River

mainstem. This translates into a non-supporting use of primary and secondary

contact recreation in the majority of the River downstream of Manchester, New

Hampshire. The New Hampshire assessment report lists combined sewer overflows

as the primary cause of these violations; Massachusetts does not provide a similar

listing. The Massachusetts assessment report also lists metals, nutrients, and priority

organics as significant problems along the mainstem, resulting in a non-attainment of

the aquatic life use. Additionally, the recent MRI study also discovered exceedances

of water quality standards for lead and zinc in the lower portion of the River during

wet and dry-weather conditions, affecting aquatic life in the river. Table 3-2 provides

a summary of the major causes of non-supporting use in the Merrimack River

Section 3

Water Quality

A 3-3

6149.001.001.1AEEC

9/27/02

mainstem based on the state’s 2002 assessment reports. Further information is

provided in Section 3.5.

Table 3.2: Causes of Non-support in the Merrimack River Mainstem

Listed Miles/ Area

Pollutant

NH MA Total

Non-supporting Use

Pathogens 19.82 mi

27.9 mi,

7.14 mi

47.72 mi,

7.14 mi

Primary and secondary

contact recreation,

shellfishing (MA only)