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National Estuary Program: A program established under the Clean Water Act 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.

National Municipal Plan:
A policy created in 1984 by EPA and the states in 1984 to bring all publicly owned treatment works (POTWs) into compliance with Clean Water Act requirements.

National Oil and Hazardous Substances Contingency Plan (NOHSCP/NCP):
The federal regulation that guides the determination of the sites to be corrected under both the Superfund program and the program to prevent or control spills into surface waters or elsewhere.

National Pollutant Discharge Elimination System (NPDES):
A provision of the Clean Water Act which prohibits the discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation.

National Priorities List (NPL): EPA's list of the most serious uncontrolled or abandoned hazardous waste sites identified for possible long-term remedial action under Superfund. The list is based primarily on the score a site receives from the Hazard Ranking System. EPA is required to update the NPL at least once a year. A site must be on the NPL to receive money from the Trust Fund for remedial action.

Natural Gas: Hydrocarbon gas found in the earth, composed of methane, ethane, butane, propane and other gasses.

Natural Gas Vehicle: Vehicles that are powered by compressed or liquefied natural gas.

Natural Gasoline: A mixture of liquids extracted from natural gas and suitable for blending with ordinary oil-derived gasoline.

Natural Monopoly: A situation where one firm can produce a given level of output at a lower total cost than can any combination of multiple firms. Natural monopolies occur in industries which exhibit decreasing average long-run costs due to size (economies of scale). According to economic theory, a public monopoly governed by regulation is justified when an industry exhibits natural monopoly characteristics.

Navigable Waters: Traditionally, waters sufficiently deep and wide for navigation by all, or specified vessels; such waters in the United States come under federal jurisdiction and are protected by certain provisions of the Clean Water Act.

NCSL(The National Conference of State Legislatures): A national advisory council which provides services to state legislatures "by bringing together information from all states to forge workable answers to complex policy questions."

Necrosis: Death of plant or animal cells or tissues. In plants, necrosis can discolor stems or leaves or kill a plant entirely.

Nematocide: A chemical agent which is destructive to nematodes.

Nephelometric:
Method of measuring turbidity in a water sample by passing light through the sample and measuring the amount of the light that is deflected.

Netting: A concept in which all emissions sources in the same area that owned or controlled by a single company are treated as one large source, thereby allowing flexibility in controlling individual sources in order to meet a single emissions standard.

Neutralization: Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.

Neutron: An uncharged particle found in the nucleus of every atom except that of hydrogen.

New Source Performance Standards (NSPS):
Uniform national EPA air emission and water effluent standards which limit the amount of pollution allowed from new sources or from modified existing sources.

New Source Review (NSR): A Clean Air Act requirement that State Implementation Plans must include a permit review that applies to the construction and operation of new and modified stationary sources in nonattainment areas to ensure attainment of national ambient air quality standards.

Newton:
A unit of force. The amount of force it takes to accelerate one kilogram at one meter per second per second.

NIMBY: "Not In My Back Yard." An expression of resident opposition to the siting of a solid waste facility based on the particular location proposed.

Nitrate: A compound containing nitrogen that can exist in the atmosphere or as a dissolved gas in water and which can have harmful effects on humans and animals. Nitrates in water can cause severe illness in infants and domestic animals. A plant nutrient and inorganic fertilizer, nitrate is found in septic systems, animal feed lots, agricultural fertilizers, manure, industrial waste waters, sanitary landfills, and garbage dumps.

Nitric Oxide (NO): A gas formed by combustion under high temperature and high pressure in an internal combustion engine; it is converted by sunlight and photochemical processes in ambient air to nitrogen oxide. NO is a precursor of ground-level ozone pollution or smog.

Nitrification: The process whereby ammonia in wastewater is oxidized to nitrite and then to nitrate by bacterial or chemical reactions.

Nitrilotriacetic Acid (NTA):
A compound now replacing phosphates in detergents.

Nitrite: 1. An intermediate in the process of nitrification. 2. Nitrous oxide salts used in food preservation.

Nitrogen Dioxide (NO2): The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.

Nitrogen Oxide (NOx):
The result of photochemical reactions of nitric oxide in ambient air; major component of photochemical smog. The product of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition.

Nitrogen Oxides (NOx):
Emissions that contribute to the formation of smog.

Nitrogenous Wastes:
Animal or vegetable residues that contain significant amounts of nitrogen.

Nitrophenols: Synthetic organo pesticides containing carbon, hydrogen, nitrogen, and oxygen.

No Till: Planting crops without prior seedbed preparation, into an existing cover crop, sod, or crop residues, and eliminating subsequent tillage operations.

Noble Metal: Chemically inactive metal such as gold; does not corrode easily.

Noise: Product-level or product-volume changes occurring during a test that is not related to a leak but may be mistaken for one.

Non-Aqueous Phase Liquid (NAPL): Contaminants that remain undiluted as the original bulk liquid in the subsurface, e.g. spilled oil.

Non-Compliance Coal: Any coal that emits greater than 3.0 pounds of sulfur dioxide per million BTU when burned. Also known as high-sulfur coal.

Non-Contact Cooling Water: Water used for cooling which does not come into direct contact with any raw material, product, by-product, or waste.

Non-Conventional Pollutant:
Any pollutant not statutorily listed or which is poorly understood by the scientific community.

Non-Degradation: An environmental policy which disallows any lowering of naturally occurring quality regardless of pre-established health standards.

Non-Depletable Energy Sources: Energy which is not obtained from depletable energy sources.

Non-discharging Treatment Plant: A treatment plant that does not discharge treated wastewater into any stream or river. Most are pond systems that dispose of the total flow they receive by means of evaporation or percolation to groundwater, or facilities that dispose of their effluent by recycling or reuse (e.g. spray irrigation or groundwater discharge).

Non-Ferrous Metals: Nonmagnetic metals such as aluminum, lead, and copper. Products made all or in part from such metals include containers, packaging, appliances, furniture, electronic equipment, and aluminum foil.

Non-Firm Energy:
Electricity that is not required to be delivered or to be taken under the terms of an electric purchase contract.

Non-Friable Asbestos-Containing Materials:
Any material containing more than one percent asbestos (as determined by Polarized Light Microscopy) that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.

Non-Hazardous Industrial Waste:
All non-inert and non-hazardous waste generated by companies, manufacturers, retail outlets, self-employed tradesmen and service providers. It includes scrap iron and other metals, paper and cardboard, glass, textiles, wood, and plastics.

Non-ionizing Electromagnetic Radiation:
1. Radiation that does not change the structure of atoms but does heat tissue and may cause harmful biological effects. 2. Microwaves, radio waves, and low-frequency electromagnetic fields from high-voltage transmission lines.

Non-Methane Hydrocarbon (NMHC): The sum of all hydrocarbon air pollutants except methane; significant precursors to ozone formation.

Non-Methane Organic Gases (NMOG):
The sum of all organic air pollutants. Excluding methane; they account for aldehydes, ketones, alcohols, and other pollutants that are not hydrocarbons but are precursors of ozone.

Non-Point Sources:
Diffuse pollution sources (i.e. without a single point of origin or not introduced into a receiving stream from a specific outlet). The pollutants are generally carried off the land by storm water. Common non-point sources are agriculture, forestry, urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.

Non-potable:
Water that is unsafe or unpalatable to drink because it contains pollutants, contaminants, minerals, or infective agents.

Non-Renewable Energy: Sources of energy that cannot be replaced in a reasonable period of time. Fossil fuels (coal, petroleum, natural gas) are examples of non-renewable energy sources.

Non-Road Emissions
: Pollutants emitted by combustion engines on farm and construction equipment, gasoline-powered lawn and garden equipment, and power boats and outboard motors.

NOx:
Oxides of nitrogen that are a chief component of air pollution that can be produced by the burning of fossil fuels. Also called nitrogen oxides.

NOx:
Nitrogen oxides (NO (nitrogen oxide) and NO2 (nitrogen dioxide) act as indirect greenhouse gasses by producing the tropospheric greenhouse gas 'ozone' during their breakdown in the atmosphere.

Nuclear Energy: Power obtained by splitting heavy atoms (fission) or joining light atoms (fusion). A nuclear energy plant uses a controlled atomic chain reaction to produce heat. The heat is used to make steam run conventional turbine generators.

Nuclear Reactors and Support Facilities:
Uranium mills, commercial power reactors, fuel reprocessing plants, and uranium enrichment facilities.

Nuclear Regulatory Commission (NRC):
An independent federal agency that ensures that strict standards of public health and safety, environmental quality, and national security are adhered to by individuals and organizations possessing and using radioactive materials. The NRC is the agency that is mandated with licensing and regulating nuclear power plants in the United States. It was formally established in 1975 after its predecessor, the Atomic Energy Commission, was abolished.

Nuclear Winter: Prediction by some scientists that smoke and debris rising from massive fires of a nuclear war could block sunlight for weeks or months, cooling the earth's surface and producing climate changes that could, for example, negatively affect the world agricultural and weather patterns.

Nuclide: An atom characterized by the number of protons, neutrons, and energy in the nucleus.

Nug: A non-utility generator. A generation facility owned and operated by an entity who is not defined as a utility in that jurisdictional area.

Nutrient: Any substance assimilated by living things that promote growth. The term is generally applied to nitrogen and phosphorus in wastewater but is also applied to other essential and trace elements.

Nutrient Pollution:
Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern.