Interpretive Glossary of Water-related Terms and Expressions - N

National Environmental Policy Act: NEPA. Federal law enacted to ensure the integration of natural and social sciences and environmental design in planning and decision-making for federal projects or projects on federal lands. CSU.

National Pollution Discharge Elimination System: NPDES. Description taken from a section of the Federal Clean Water Act. NPDES is the mechanism for applying effluent standards, water quality standards, and monitoring requirements. EPA is authorized to issue a permit to any applicant whose discharge meets federal requirements. Douglas Co.

National Pollution Discharge Elimination System (NPDES) Permit: A permit required under Section 401 of the Clean Water Act regulating discharge of pollutants into the nation’s waterways. CSU.

natural: Describes a product of nature. Not reclaimed, not reused. Innate, untreated, not manmade.

natural recharge: A renewal process. Replenishment of water to an aquifer through a recharge area by natural means such as from meteoric precipitation, lakes, rivers or streams. Part of the hydrologic cycle.

natural stream: Relative to ground water. A natural stream's waters refers to the migratory waters in aquifers. See stream.

native waters: Surface and underground waters naturally occurring in a watershed. CSU.

net sand thickness: The net accumulated thickness of sand of a specific quality found within the total thickness of a formation of mixed lithology.

new: Relative to water, natural, not reused, not reclaimed.

non-consumptive use: Water drawn for use that is not consumed, such as hydroelectric power generation, recreation, etc.

non-exempt use: Any recognized beneficial use of water that is administered under the priority system. CSU.

non-exempt well: Most non-exempt wells require an augmentation plan. Most wells on single-home residential properties are exempt and do not require an augmentation plan. Water systems on multi-home subdivisions often are non-exempt and require an augmentation plan. CSU.

non-native waters: Water imported or not originally connected hydrologically to a watershed or drainage basin physically or by statute; nontributary ground water and transmountain water are non-native. CSU.

nonrenewable water: A water source that is not and cannot be replenished through the hydrologic cycle or by any natural means. This water is usually considered to be finite.

nontributary ground water: Relative to the Denver Basin, it is ground water that when pumped will not, within 100 years, affect the flow of any natural stream by greater than one-tenth of one percent of the annual pumping volume. This is a nonrenewable water supply. Douglas Co. Also see aquifer.

nonpoint source pollution: Pollution coming from a wide, non-specific source such as runoff from cities, farms, forest land. CSU.

normal pore pressure: The normal pore pressure is the hydrostatic pressure exerted by a column of formation water (or any and all other geofluids contained in the overburden) from the depth of the water table to the depth of interest. Normal pore pressure exhibits a normal pore pressure gradient. Formation water is found at some level of saturation in all formations that have porosity. The formation water communicates vertically in all sedimentary formations over the span of geological time. This is what allows normal pore pressure to exist in all formations except where abnormal pore pressure is found. Most rocks considered to be impermeable over the human time span exhibit permeability over geologic time, and the formation waters and their pressures are communicable. The timeless communication of fluids and their pressures allows an uninterrupted pressure gradient to exist and to be recognized and be measured in sedimentary formations in wells at virtually all depths presently drilled.

When overpressure has been exhausted, normal pore pressure remains in the formation fluids. But, normal pressure contributes very little to the recovery process for any geofluid because the drainage mechanism or mechanism to drive fluid into the well bore has decreased significantly or has diminished to nothing. Under this condition, there is very little fluid of any kind to replace potentially producible fluid. That is why secondary recovery methods are employed. See recovery, drainage, normal pore pressure gradient and compare abnormal pore pressure.

normal pore pressure gradient: (1) The rate of change in the normal pore pressure per unit of depth. The normal pore pressure gradient for water is 0.433 (psi per foot) times the specific gravity (a ratio) of the water of interest.

(2) A petrophysical curve showing any porosity-related well- log-derived parameter versus formation depth, from which pressure can be inferred or calculated. Departures from the normal pore pressure gradient curve, suggesting higher porosities, usually indicate the presence of overpressure in the formation. Preservation of higher porosities under an increasing overburden causes shale to lose rigidity and become plastic shale. These departures, in turn, can be interpreted to determine the drilling mud density that will be required to completely balance the overpressured zone. Seizing of drill pipe and blowouts, particularly in oil and gas wells, can occur if the drilling mud in the borehole does not adequately counterbalance the formation pressure. See abnormal pore pressure.

not-nontributary ground water: For the Denver Basin, it is waters that, when pumped, will, within 100 years, affect the flow of a natural stream by greater than one-tenth of one percent of the annual pumping volume. Because the pumping of not-nontributary water will cause an impact to the surface stream system, an adjudicated plan for augmentation is required prior to the use of not-nontributary ground water from the Denver Basin aquifers. This is a nonrenewable water supply. Douglas Co.

NSSH: National Soil Survey Handbook of the Natural Resources Conservation Service, U.S. Department of Agriculture.


Compiled and Edited by Robert C. Ransom


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