Interpretive Glossary of Water-related Terms and Expressions - M

magma: Molten rock below the surface of the ground.

major dissolved constituents: In water. The greatest proportion of dissolved constituents in water are calcium, magnesium, calcium bicarbonate, chloride, sulfate, and silica, although nitrate can be a major constituent. GWAC.

marine deposit: Sediments (predominantly sands, silts and clays) of marine origin, laid down in the waters of an ocean. NSSH. Also includes carbonates.

marl: A generic term loosely applied to a variety of materials, most of which occur as an earthy, unconsolidated deposit consisting chiefly of an intimate mixture of clay and calcium carbonate formed commonly by the chemical action of algae mats and organic detritus, specifically an earthy material containing predominantly clay and calcium carbonate mud; formed primarily under freshwater lacustrine conditions, but varieties associated with more saline environments and higher carbonate contents also occur. NSSH.

mass: See gravity.

matrix: (1) The solid matter of rock, the framework, that surrounds the pores.

(2) The finer, natural material that surrounds imbedded fossils, stones, pebbles, crystals or other features of the rock.

maximum contaminant level: (MCL) Maximum level of a contaminant allowed in water by Federal law, based on health effects and currently available treatment methods. GWAC.

metamorphic rock: See rock (3).

meteoric precipitation, meteoric water: Water derived from the atmosphere. Rain, snow.

methane: Methane is a natural hydrocarbon gas that is flammable and explosive in certain concentrations. It is produced either by bacteria or by geologic processes involving heat and pressure. COGCC. See biogenic methane and thermogenic methane, also flaming water.

microannulus: A defect in the quality of the cement bond caused when the casing is subjected to excessive pressure and the cement sheath surrounding the casing is forced to expand along with expansion of the casing. When the excess pressure inside the casing is relieved the casing contracts leaving a microannulus or defect in the cement bond to the casing. This defect can degrade into a channel. See cement bond, channel, and channeling.

mineral: A naturally occurring chemical element or compound having distinguishing crystalline structure.

minimum streamflow requirement: Water right decreed to the Colorado Water Conservation Board requiring that a set amount of water be maintained in a water course for the purpose of reasonably maintaining the environment. CSU.

manmade process: Any process devised by man and performed by mechanical or chemical means, in contrast to any process performed by nature.

mobile water: In aquifers, in contrast with irreducible water, mobile water represents only the water that is static, but can respond to stimulation and has the freedom to move. Sometimes referred to as free water. It is part of water in place until sufficient force is applied to move it. Compare irreducible water and movable water. See in place and depleted.

mobility: The ease with which any specific fluid can be moved through a porous medium for any specific pressure gradient. In aquifers, it is a measurement of the ease with which ground water can be moved in an aquifer. The expression is k / μ where k is the absolute permeability to water in the aquifer, and is effective permeability where water exists in the presence of another fluid; and μ is the viscosity of water. Mobility and hydraulic conductivity are the same. See Darcy’s equation under hydraulic conductivity where mobility is developed.

monitoring well: Observation well. A non-producing well that is used primarily for taking periodic static water-level depth measurements and for taking water samples for comparisons and for water quality control. Observation wells are not only used for monitoring conditions in an aquifer, but also are used for monitoring changes in the levels of contamination and pollution over time. See artesian water, biochemical oxygen demand, water analysis, pH and potentiometric surface.

The static water-level depth is the depth that artesian water rises in the well bore. The pressure of the artesian head is not necessarily the same as the water pressure in the aquifer. See artesian water, biochemical oxygen demand, water analysis, pH and potentiometric surface.

montmorillonite: smectitite montmorillonite. A calcium, sodium, magnesium, iron, aluminum silicate. Exhibits an intermediate radioactivity level for the clays. A water sensitive, swelling clay. Density 2.41 g/cm3. Diagenetic or authigenic montmorillonite is typified by its web-like morphology. Authigenic montmorillonite, same morphology as diagenetic montmorillonite, has a noncrystalline cellular, honeycomb structure that adheres from pore wall to pore wall that causes visible pore bridging and pore throat plugging.

moraine: In glacial geology. A mound, ridge, or other topographically distinct accumulation of unsorted, unstratified glacial drift, predominantly till, deposited primarily by the direct action of glacier ice, in a variety of land forms. NSSH.

movable water: In aquifers, it represents only the water that has the freedom to move, but is dynamic and has been made to move under the force of a drive mechanism. It is water in a state of motion, or water that has been produced. For this water to be movable, it must be subjected to sufficient force to shear the junction between mobile and irreducible waters and to overcome both the resistance to flow and back pressure. See in place. Compare depleted.

mud: See drilling mud.

mud cake: The precipitate of mud solids that are filtered from the drilling mud by the drilled face of a porous and permeable formation. The presence of mud cake protects the drilled formation face and, depending on the water loss quality of the mud, inhibits further invasion of filtrate into the formation. In the laboratory, it is filter cake.

mud density: The density of drilling mud usually expressed in pounds per gallon or pounds per cubic foot. The density of the drilling mud should be designed to counterbalance the hydraulic pressure within the formation.

mud filtrate: The effluent from a drilling mud that penetrates the aquifer or other permeable formation after leaving a precipitate of mud solids on the face of the drilled formation. See also mud cake.

mud pit: A containment created to capture the drilling mud that returns to the surface during the well drilling operation. The mud then is available for conditioning and is cycled into the drill pipe and used again and again.

mud weight: A misnomer. See mud density.

municipal water system: The network of pipes, pumps, and storage and treatment facilities designed to deliver potable water to homes, schools, businesses, and other users in a city or town and to remove and to treat waste materials. CSU.


Compiled and Edited by Robert C. Ransom


Terms Beginning With:

Glossary Download

Please click on the bold text to follow related terms and expressions. Use your browser's "back" button to return to your previous page.



























Interpretive Groundwater Glossary
InterpretiveGroundwaterGlossary.com Interpretive Groundwater Glossary