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NAPLS: Nonaqueous phase
liquids; i.e., chemical solvents such as trichloroethylene (TCE) or carbon tetrachloride
– often toxic. Many of the most problematic NAPLs are DNAPLs – dense nonaqueous
phase liquids.
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Natural
flow: The rate
of water movement past a specified point on a natural stream. The flow comes
from a drainage area in which there has been no stream diversion caused by storage,
import, export, return flow, or change in consumptive use caused by man-controlled
modifications to land use. Natural flow rarely occurs in a developed country.
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Natural
resource: Any
form of matter or energy obtained from the environment that meets human needs.
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Navigable
waters: Traditionally,
waters sufficiently deep and wide for navigation by all, or specific sizes of,
vessels.
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Navigational
water use: Water
utilized as a means of commercial (and sometimes recreational) transportation.
Includes water used to lift a vessel in a lock, or maintain a navigable channel
level. Navigational water use is considered a nonconsumptive instream use of
water and is generally not measured.
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Net water
use: Water withdrawals
plus or minus water transfers. In most counties, the net water use and water
withdrawals are equal. However, in counties involved in water transfers (imports
and exports), the net water use represents the actual amount of water used regardless
of the amount of water withdrawn.
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Neutralization: The addition
of substances to neutralize water, so that it is neither acid, nor basic. Neutralization
does not specifically mean a pH of 7.0, it just means the equivalent point of
an acid-base reaction.
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Neutron
probe: Type of
probe used to monitor soil moisture conditions to help determine when water
should by applied.
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Neutrons: Uncharged building
blocks of an atom that play a part in radio-activity. They can be found in the
nucleus.
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NIPDWR: National interim
primary drinking water regulations.
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Nitrification: A biological
process, during which nitrifying bacteria convert toxic ammonia to less harmful
nitrate. It is commonly used to remove nitrogen substances from wastewater,
but in lakes and ponds it occurs naturally.
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Nitrogen: A plant nutrient
that can cause an overabundance of bacteria and algae when high amounts are
present, leading to a depletion of oxygen and fish kills. Several forms occur
in water, including ammonia, nitrate, nitrite or elemental nitrogen. High levels
of nitrogen in water are usually caused by agricultural runoff or improperly
operating wastewater treatment plants. Also see phosphorous.
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Non-Community
water system:
A public water system which
provides piped water for human consumption to at least 15 service connections
or which serves at least 25 individuals at least 60 days out of the year but
which is not a community water system. The difference between a community water
system and a non-community water system is that the former serves inhabitants
whereas the latter serves transients or non-residents who other wise do not
inhabit the building served by the system.
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Nonconsumptive
use: Using water
in a way that does not reduce the supply. Examples include hunting, fishing,
boating, water-skiing, swimming, and some power production. Compare consumptive
use.
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Noncontact
recreation: Recreational
pursuits not involving a significant risk of water ingestion, including fishing,
commercial and recreational boating, and limited body contact incidental to
shoreline activity. Compare contact recreation.
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Non-point
source: Source
of pollution in which wastes are not released at one specific, identifiable
point but from a number of points that are spread out and difficult to identify
and control. Compare point source.
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Nonporous: Something which
does not allow water to pass through it. Compare porous.
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Non-potable: Not suitable
for drinking. Compare potable.
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Non-renewable
resources: Natural
resources that can be used up completely or else used up to such a degree that
it is economically impractical to obtain any more of them; e.g., coal, crude
oil, and metal ores.
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Nonthreshold
pollutant: Substance
or condition harmful to a particular organism at any level or concentration.
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Non-Transient
Non-Community water system:
A public water system that
is not a community water system and that regularly serves at least 25 of the
same persons over a 6 month period.
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NPDES permit: Permit issued
under the National Pollutant Discharge Elimination System for companies discharging
pollutants directly into the waters of the United States.
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NTU: Nephlometric
turbidity units.
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Nucleus: The center of
an atom, that contains protons and neutrons and carries a positive charge.
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Nuisance
Contaminant:
Constituents in water, which are not normally harmful to health but may cause
offensive taste, odor, color, corrosion, foaming, or staining.
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Nutrient: As a pollutant,
any element or compound, such as phosphorus or nitrogen, that fuels abnormally
high organic growth in aquatic ecosystems (e.g., eutrophication of a lake).
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Nutrient
Pollution: Contamination
of water resources by excessive inputs of nutrients. In surface waters, excess
algal production is a major concern.
