NATIONAL WATER-QUALITY
ASSESSMENT PROGRAM New England Coastal Basins |
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WHAT IS THE NATIONAL WATER-QUALITY ASSESSMENT PROGRAM? During the past 25 years, industry and government made large financial investments that have resulted in better water quality across the Nation; however, many water-quality issues remain. To address the need for consistent and scientifically sound information for managing the Nation's water resources, the U.S. Geological Survey began a full-scale National Water-Quality Assessment (NAWQA) Program in 1991. This program is unique compared to other national water-quality assessment studies in that it integrates the monitoring of the quality of surface and ground waters with the study of aquatic ecosystems. The goals of the NAWQA Program are to (1) describe current water-quality conditions for a large part of the Nation's freshwater streams and aquifers (water-bearing sediments and rocks), (2) describe how water quality is changing over time, and (3) improve our understanding of the primary natural and human factors affecting water quality.
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Assessing the quality of water in every location of the Nation would not be practical; therefore, NAWQA Program studies are conducted within a set of areas called study units. These study units are composed of 59 important river and aquifer systems that represent the diverse geography, water resources, and land and water uses of the Nation. The New England Coastal Basins is one such study unit; it has been designed to (1) include many important New England rivers, (2) represent a mixture of urban and industrial areas, rapidly urbanizing areas, and large forested areas and, (3) include major sole-source aquifers such as the Cape Cod and Plymouth-Carver aquifers. Study activities in the New England Coastal Basins began in 1996. | |||
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STUDY UNIT DESCRIPTION The New England Coastal Basins study unit encompasses 23,000 square miles (mi2) in western and central Maine, eastern New Hampshire, eastern Massachusetts, most of Rhode Island, and a small part of eastern Connecticut. Important drainage basins include the Kennebec (5,890 mi2), Androscoggin (3,520 mi2), Saco (1,700 mi2), and Merrimack (5,010 mi2) River Basins in Maine, New Hampshire, and northern Massachusetts, and the Charles (321 mi2), Taunton (530 mi2), and Blackstone (335 mi2) River Basins in Massachusetts and Rhode Island. Mean annual streamflow in these rivers ranges from 302 cubic feet per second (ft3/s) in the Charles River at Waltham, Massachusetts to 9,080 ft3/s in the Kennebec River at North Sidney, Maine. Most of these rivers originate in mountainous forested areas and their headwaters are often fast-flowing, cobble and boulder bottom streams. Flow in these rivers is generally regulated by upstream lakes, reservoirs, flood-control dams, and (or) powerplants. The study unit also contains a large number of natural lakes, many of which are enlarged and controlled by dams. The largest are Moosehead Lake in Maine (117 mi2) and Lake Winnipesaukee in New Hampshire (69 mi2). Cape Cod has no major streams yet has more than 350 lakes and ponds. An estimated 7.8 million people lived in the study unit in 1990. The largest population centers are typically in the southern part of the study unit and include Boston, Worcester, Lowell, and New Bedford, Massachusetts; Providence, Rhode Island; Manchester, New Hampshire; and Portland, Maine. In 1990, land use was an estimated 75 percent forested; 11 percent residential, commercial, and industrial; 6 percent agricultural; 5 percent water bodies, and 3 percent other uses. Major industries include light manufacturing, pulp and paper production, silviculture, hydroelectric-power generation, tourism, and seasonal recreation. The New England Coastal Basins study unit contains a mixture of rugged mountains, narrow to broad valleys, and flat plains. The entire study unit is within the New England Physiographic Province with the exception of the southern coastal islands of Martha's Vineyard, Nantucket, and Block Island, which are in the Coastal Plain Province. Elevations in the study unit range from sea level along the coast to greater than 6,000 ft in the White Mountains of New Hampshire. Average annual precipitation ranges from 40 to 50 inches, with higher amounts in the mountainous regions; about one-half of this precipitation becomes surface runoff. Average annual air temperatures varies from about 43 degrees Fahrenheit (o F) in the north to about 50o F in the south. Two principal types of aquifers underlie the study unit: stratified-drift aquifers and fractured- bedrock aquifers. Stratified-drift aquifers are the most productive and are used intensively for public drinking-water supply; several are sole-source aquifers. These aquifers were formed during the retreat of the last glaciers more than 12,000 years ago, as meltwater streams deposited stratified drift composed of sand, gravel, silt, and clay in valleys and broad plains. Bedrock in the study unit ranges in age from Precambrian to Mesozoic and includes primarily fractured crystalline igneous and metamorphic rocks; small areas of Pennsylvanian age sedimentary rocks are found around Narragansett Bay and in southeastern Massachusetts. Wells drilled in the fractured crystalline and sedimentary rocks in the study unit generally yield less ground water than wells completed in the stratified drift, but the bedrock aquifer remains an important source of water for |
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some municipalities, industries, and many individual homes not connected to a municipal water-supply system. The rivers in the New England Coastal Basins study unit have influenced the development of the region's economy. During the past two centuries, the transportation of timber to mills and shipping ports and the generation of power to run the sawmills and industrial mills depended on the rivers and streams. These rivers and streams continue to be used extensively for drinking water, industry, power generation, fishing, swimming, and boating. In 1990, approximately 1,520 million gallons per day (Mgal/d) of water were withdrawn from the rivers and aquifers in the study unit. Both cold- and warm-water fish communities are found throughout the study unit. |
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Map of the New England Coastal Basins Study Unit |
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ASSESSING WATER QUALITY IN THE NEW ENGLAND COASTAL BASINS STUDY UNIT The NAWQA Program is designed to assess the status of and trends in the quality of the Nation's ground- and surface-water resources and to link the status and trends with an understanding of the natural and human factors that affect the quality of water. The design of the Program balances the unique assessment requirements of individual study units with a nationally consistent design and data collection structure that incorporates a multiscale, interdisciplinary approach. Surface- and ground-water studies are done at local (a few square miles to hundreds of square miles) and regional (thousands of square miles) scales to understand the water-quality conditions and issues within a study unit. An Occurrence and Distribution Assessment is the largest and most important component of the first intensive study phase in each study unit. The goal of the Occurrence and Distribution Assessment is to characterize, in a nationally consistent manner, the broad-scale geographic and seasonal distributions of water-quality conditions in relation to major contaminant sources and background conditions. The following discussion describes the typical surface- and ground-water monitoring components of the Occurrence and Distribution Assessment. The New England Coastal Basins NAWQA study will have a similar design. SURFACE WATER The national study design for surface waters focuses on water-quality conditions in streams using three interrelated components--water-column studies, bed-sediment and fish-tissue studies, and ecological studies. Water-column studies monitor physical and chemical characteristics, which include suspended sediment, major ions, nutrients, organic carbon, and dissolved pesticides, and their relation to hydrologic conditions, sources, and transport. Most surface water is monitored at sites termed either basic-fixed sites or intensive-fixed sites, according to the frequency of the sampling. The sampling sites are selected to determine the quality of water in relation to important environmental settings in the study unit. Most NAWQA study units have 8-10 basic-fixed and 2-3 intensive-fixed sites. Basic-fixed sites are sampled monthly and at high-flows for 2 years of the 3-year high-intensity phase. The intensive-fixed sites are monitored more frequently (as often as weekly during key time periods) for at least 1 year, to characterize short-term variations of water quality. Basic-fixed or intensive-fixed sites can be either indicator or integrator sites. Indicator sites represent relatively homogeneous, small basins (less than 100 square miles) associated with specific environmental settings, such as a particular land use that substantially affects water quality in the study unit. Integrator sites are established at downstream points in large (thousands of square miles) relatively heterogeneous drainage basins with complex combinations of land-use settings. Indicator sites are typically located in the drainage basins of integrator sites. Water samples are also collected as part of synoptic (short-term) investigations of specific water-quality conditions or issues during a specific hydrologic period (for example during low streamflow) to provide greater spatial coverage and allow investigators to assess whether the basic-fixed or intensive-fixed sites are representative of streams throughout the study unit. Bed-sediment and fish-tissue studies assess trace elements and hydrophobic organic contaminants at 15-30 sites to determine their occurrence and distribution in the study unit. Ecological studies evaluate the relations among physical, chemical, and biological characteristics of streams. Aquatic biological communities at the basic- and intensive-fixed sites are surveyed during the 3 years of the high-intensity-sampling phase. These surveys are done along a delineated stream reach and include a habitat assessment of the site and annual surveys of the fish, algal, and benthic invertebrate communities. Additionally, ecological sampling may be integrated with surface water synoptic studies to provide greater spatial coverage and to assess whether the biological communities at basic- and intensive-fixed sites are representative of streams throughout the study unit. GROUND WATER The national study design for ground water focuses on water-quality conditions in major aquifers, with emphasis on recently recharged ground water associated with present and recent human activities, by using study-unit surveys, land-use studies, and flowpath studies. Ground-water samples are analyzed for major ions, nutrients, pesticides, volatile organic compounds, and trace elements. Study-unit surveys are used to assess the water quality of the major aquifer systems of each study unit. About 20-30 existing wells are randomly selected to be sampled in each of 2-3 aquifer subunits. Land-use studies focus on recently recharged shallow aquifer systems so that the influences of land-use practices and natural conditions can be assessed. Typically, about 20-30 new observation wells are randomly located within each land use and aquifer type. Results from the 2-4 land-use studies typically performed can be compared with results from the general study-unit survey to determine the effect of particular land uses on ground-water quality. Flow-path studies use transects and groups of clustered, multilevel observation wells to examine specific relations among land-use practices; ground-water flow; and contaminant occurrence, transport, and interactions between ground and surface water. |
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USGS Fact Sheet FS-060-97 | |||||
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