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90TH PERCENTILE—(Water Quality) Term used in conjunction with water sampling standards as required under the Safe Drinking Water Act (SDWA) and amendments thereto. The 90th percentile value is calculated by first placing all sample results in order from the lowest concentration to the highest concentration (i.e., concentration of specific contaminants). Next, assign each sample result a number, starting with the number 1 for the lowest (concentration) result up to the highest concentration being given the number equal to the total number of samples collected from a particular water supply system. Then multiply the total number of samples collected by 0.9. The sample result with the number corresponding to this calculated value is the 90th percentile.

NADIR—Refers to a low or the lowest point, as the lowest point of a lake or other body of water attained of a certain period of time (period of record).

NANOPLANKTON—Very minute plankton not readily retained in ordinary plankton nets.

NANSEN BOTTLE—An ocean-water sampling bottle with spring-loaded valves at both ends that are closed at an appropriate depth by a messenger device sent down the wire connecting the bottle to the surface.

NAPPE, also Nap—(1) A sheet or curtain of water flowing over a dam or weir or similar structure. (2) (Geology) A large sheetlike body of rock that has been moved far from its original position.

NARGHILE—A water pipe that originated in the Near East.

NARROW—(1) A body of water with little width that connects two larger bodies of water. (2) A part of a river or an ocean current that is not wide. Often used in the plural, i.e., narrows.

NATANT—Floating or swimming win water.

NATIONAL AUDUBON SOCIETY—An American environmental interest group founded in 1905 that emphasizes natural resource and wildlife conservation and protection. Named in honor of John James Audubon (1785-1851), who was one of the first American conservationists and who gained recognition for his paintings of birds.

NATIONAL ECONOMIC DEVELOPMENT—One of the two main objectives of planning for water and related land resources by governmental agencies whose activities involve planning and development of water resources. Such activities are reflected in the increase in the nation's productive output, an output which is partly reflected in a national product and income accounting framework to measure the continuing flow of goods and services into direct consumption or investment.

NATIONAL ENERGY POLICY ACT (EPAct)—See (National) Energy Policy Act (EPAct).

NATIONAL ENVIRONMENTAL POLICY ACT (NEPA)—A 1970 Act of Congress that requires all federal agencies to incorporate environmental considerations into their decision-making processes. The act requires an Environmental Impact Statement (EIS) for any "major federal action significantly affecting the quality of the human environment."

NATIONAL ESTUARY PROGRAM—(Water Quality) A nationwide program established under the Clean Water Act (CWA) Amendments of 1987 to develop and implement conservation and management plans for protecting estuaries and restoring and maintaining their chemical, physical, and biological integrity, as well as controlling point and nonpoint pollution sources. The program encompasses a watershed management approach to the identification and protection of nationally significant estuaries that are threatened by pollution, development, or overuse and to promote long-term planning and management processes that improve or protect water quality. If selected, the Environmental Protection Agency (EPA) will provide 75 percent of the funding for a three to five-year research and management effort to identify the various environmental problems in the "estuarine zone" and to develop a comprehensive conservation management plan.

NATIONAL FLOOD INSURANCE PROGRAM (NFIP)— A federal program enabling property owners in participating communities to purchase insurance protection against losses from flooding. This insurance is designed to provide an alternative to disaster assistance to meet the escalating costs of repairing damage to buildings and their contents caused by floods. Participation in the NFIP is based on an agreement between local communities and the federal government that if a community will implement and enforce measures to reduce future flood risks to new construction in Special Flood Hazard Areas (SFHA), then the federal government will make flood insurance available to protect against flood losses that do occur. The NFIP was established by Congress through the passage of the National Flood Insurance Act of 1968. Features of the program were modified and extended with the 1973 passage of the Flood Disaster Protection Act, and other legislative measures. The NFIP is administered by the Federal Insurance Administration (FIA), which is a component part of the Federal Emergency Management Agency (FEMA).

NATIONAL FOREST—A federal reservation, generally forest, range, or wildland, which is administered by the Forest Service, U.S. Department of Agriculture, under a program of multiple use and sustained yield for timer production, range, wildlife, watershed, and outdoor recreation purposes.

NATIONAL GEODETIC VERTICAL DATUM (NGVD)—As corrected in 1929, a vertical control measure used as a reference for establishing varying elevations.

NATIONAL MONUMENT—An area owned by the federal government and administered by the National Park Service, U.S. Department of the Interior, for the purpose of preserving and making available to the public a resource of archaeological, scientific, or aesthetic interest.

NATIONAL MUNICIPAL PLAN—A policy created in 1984 by the U.S. Environmental Protection Agency (EPA) and the states to bring all Publicly Owned Treatment Works (POTWs) into compliance with Clean Water Act (CWA) requirements.

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA)—An agency of the U.S. Department of Commerce, the National Oceanic and Atmospheric Administration was formed in 1970, but its origins may actually be traced as far back as 1807 when President Thomas Jefferson ordered a survey of the new nation's coastline. Today, NOAA has translated the United States' geographic, atmospheric, oceanic, and meteorological informational needs into an organization concentrating in the following principal areas:

[1] Research and Analysis—NOAA researchers and scientists in the areas of oceanography, meteorology, biology, and physics explore the sea and air for new clues aimed at understanding or reversing environmental damage such as ozone depletion, the greenhouse effect, and possible global warming;
[2] Satellite Imaging and Mapping—NOAA's satellites provide essential information for accurate weather forecasts, monitor winter snowpack conditions across the country, and gauge the health of coastal estuaries;
[3] Data Compilation and Dissemination—The results of NOAA's data collection, satellite mapping, and research and analysis affords vast stores of information in NOAA's global data centers available for climate, oceanographic and geophysical reports vital to the public and industry;
[4] Forecasting and Weather Warning—Through the National Weather Service (NWS), NOAA provides extensive information and warnings when severe weather threatens life and property.

The National Oceanic and Atmospheric Administration consists of a number of separate agencies to