Interpretive Glossary of Water-related Terms and Expressions - G

gas: A fluid with low density that can completely fill any container. It is compressible, and its volume depends on its pressure and the size of its container.

gas in solution: Under pressure, gases often are dissolved in liquids such as water and crude oil, thus reducing both their density and specific gravity. When the pressure is reduced the gases can come out of solution. Under some conditions, the released gas can maintain the pressure within the formation.

geofluid: Any fluid, liquid or gas, that occurs naturally in earthen formations, beds, or strata.

geology: The science related to the study of the earth, its history, lithology, depositional and structural history, and development revealed in the rocks, minerals, and fossils.

geophysical well log: Petrophysical well log. A well log that provides a permanent record of the environment of the borehole. See petrophysical log and well log.

geostatic: Pertains to the weight of the overburden and its contents. Includes rock and all geofluids, both liquids and gases.

geostatic load: At any specific depth of interest, it is the combined weight of the overburden, including its fluid content, that any underlying formation, bed, or stratum is subjected to. Expressed in psi. See also overburden and compaction (2).

geostatic pressure: A compactive stress. The pressure on any formation, bed, or stratum resulting from the geostatic load at a specific depth of interest.

giardia: See cryptosporidium and giardia.

gradient: There are many gradients. (1) Relative to water wells and aquifers the gradient usually refers to pressure gradients, hydraulic or hydrostatic. Observe pressure gradient, see hydraulic and hydraulic pressure.

(2) Sometimes used to refer to the slope or inclination of the ground surface with the horizontal.

gravel: Generally, from pebble size to coarse and fine grains of mixed mineral nature.

gravel pack: In a water well. The quantity or mass of fine gravel that sometimes is packed in the annular space between the slots or perforations in the casing and the wall of the formation to help prevent sand production or the free flow of sand from an unconsolidated sand bed during the production of water.

gravity, gravitation: The universal attraction between the centers of material bodies. Newton’s Law of gravitation: Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the two bodies and inversely proportional to the square of the distance between their centers. Every particle of matter attracts every other particle of matter, no matter how far apart their centers, or how much other matter is found in the space that separates them. Mass is the amount of matter in a body. The mass of a body is its weight measured at a specific point on the earth’s surface where the distance to the center of the earth is a fixed constant, and the same constant for all bodies measured relative to earth. The gravitational force of a body relative to the earth is the weight of the body at its existing location on the surface of the earth. The gravitational force for that body is not constant because of the distance factor to the center of the earth, but mass is considered constant. Example: Man on the surface of the moon where the two masses, that of man and that of the moon, are two constants, but the gravitational force (weight of man)on the moon is considerably smaller than on earth because of the smaller net attractional force of the moon.

gravity drainage: See drainage (1).

groundwater, ground water: There is no consistency in literature relative to the words groundwater or ground water. Probably groundwater is better as an adjective, and ground water is better for a noun. This is water that occupies the interstices of porous and permeable aquifers. Relative to water wells it refers to water, found in and produced from aquifers, that can be put to beneficial use.

groundwater basin: A basin system that contains one or more aquifers, has defined boundaries, and is mappable. The Denver Basin is such an example. See basin.

Ground Water Commission: A twelve member body created by the legislature, nine of which are appointed by the Governor to carry out and enforce the state statutes, rules, regulations, decisions, orders, and policies of the Commission dealing with designated ground water. CSU.

groundwater divide: A ridge in the water table or other potentiometric surface from which ground water moves away in both directions normal to the ridgeline. GWAC.

ground water management district: Any district organized for the purpose of consulting with the Ground Water Commission on all designated ground water matters within a particular district. CSU.

groundwater mining: Pumping ground water from a basin or aquifer at a rate that exceeds safe yield, thereby extracting ground water that had accumulated over a long period of time. See overdraft. GWAC.

groundwater reservoir: Observe aquifer and reservoir. To help understand aquifers, see drainage, drive mechanism, pressure gradient, and movable water. Also see pass-through aquifer.

groundwater storage: See injection of potable water.

grout: A term sometimes used in water-well language to describe the cement, or the cementing process, used during well completion.

growing season: That portion of the year, usually May through October, during which the plants are consuming water and nutrients. Douglas Co.

gun, gun perforating: Generally refers to the carrier for the shaped charges, and the holes through the casing and into the formation, made by shaped charges. Bullets can be used, but have been superceded by more effective, designed shaped charges.

GWAC: Ground Water Atlas of Colorado.

gypsum: A common name for the naturally occurring hydrated calcium sulfate. The naturally occurring monoclinic crystalline form of hydrated calcium sulfate (CaSO4 (H2O)2 ). Anhydrite is calcium sulfate (CaSO4) existing in the orthorhombic crystalline form. The hydrated gypsum crystal cannot become a crystal of anhydrite (orthorhombic form) in a single dehydration step. Gypsum first must become dissociated in solution before the ions can recrystallize as anhydrite. Compare anhydrite.


Compiled and Edited by Robert C. Ransom


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