observation well: See monitoring well.
open hole: The drilled hole before casing is set in place, or that part of the hole that is not cased.
original right: The first right awarded to a ditch or storage structure. Douglas Co.
organic materials: Unconsolidated sediments or deposits in which carbon is an essential, substantial component. Ultimately, these deposits can become peat, coal, kerogen.
outcrop: Of an aquifer. That part of the aquifer at the surface of the ground that is exposed to the atmosphere, lakes, rivers, and streams. The outcrop either escaped burial or was uncovered at the ground surface. This part of the aquifer has been exposed to extreme weathering by wind, rain, freezing, leaching and sun and all other attacks that weathering can bring to bear over a period of thousands if not millions of years. The characteristics and properties of the outcrop, or near surface aquifer, might have characteristics and properties quite different from the buried aquifer. All weathering of the outcrop increases those factors that increase the permeability of surface samples.
over appropriated: An over-appropriated stream is one in which the availability of water is less than the total of the adjudicated water rights on the stream. Douglas Co.
overburden: (1) A general term referring to the accumulated total of earth and rock and the fluids that they contain overlying a stratum or depth of interest.
(2) Relative to weight or load in the natural process of compacting earthen materials and rock, it is referred to as geostatic load. Expressed in units of psi. See compaction (2).
overdraft: With respect to an aquifer, a withdrawal of water in excess of the natural system's ability to renew that water. The overdraft is equal to the amount of water withdrawn minus the amount of recharge to the aquifer. Douglas Co.
overpressure: (1) A fluid state or condition within a formation where the pressure of the formation fluid is greater than normal pore pressure. See abnormal pore pressure, normal pore pressure, and normal pressure gradient.
(2) The amount of pressure that exceeds normal pressure.
Compiled and Edited by Robert C. Ransom
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