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2011-04-13 15:09:44
ASBOG Study Guide Chap Eight

ASBOG Study Guide Chapter 8 - Hydrogeology
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  1. Area of Influence
    The area within which the potentiometric surface is lowered by withdrawal or raised by injection, of water through a well
  2. Aquifer
    A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs
  3. Capillary Fringe
    The lowest par of the zone of aeration, immediately above the water table, where water is under pressure that is less than atmospheric pressure
  4. Cone of Depression
    A depression in the potentiometric surface of ground water that has the shape of an inverted cone and develops around a well from which water is being withdrawn. It defines the area of influence of a well
  5. Confined Aquifer
    An aquifer overlain by a confining layer of low permeability
  6. Darcy
    A unit of intrinsic permeability = 9.87x10-9cm2
  7. Darcy's Law
    The basic equation describing ground water flow: Q=KiA
  8. Discharge Area
    An area where subsurface water is dischanged to land, bodies of water or the atmosphere
  9. Drawdown
    The amount the water level in a well is lowered due to withdrawal of water
  10. Effective Porosity (ne)
    The percentage of the total volume of a soil or rock that consists of interconnected pore space. The term is sometimes used analogously to specifi yield.
  11. Field Capacity
    The quantity of water held by the soil or rock against the pull of gravity. Field capacity is dependent on the length of time the soil or rock has been undergoing gravity drainage, while specific retention is not
  12. Flow Net
    Two-dimensional representation of flow lines and equipotentials
  13. Head
    A measure of the potential energy of a fluid at any given point with respec to a given datum. In practice, it is the elevation to which water rises at a given point as a result of reservoir pressure
  14. Hydraulic Conductivity (K)
    The capacity of a porous medium to transmit water. The rate at which fluid can move through a permeable medium depends on properties of the fluid (viscosity and specific weight) and properties of the medium (intrinsic permeablity)
  15. Hydraulic Gradient (i)
    Rate of change in the total head per unity of distance of flow in a given direction
  16. Intrinsic Permeablity (ki)
    A property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient. Dependent on pore size and measured in Darcys
  17. Juvenile Water
    Water that is derived directly from magma and is though to have come to the Earth's surface for the first time
  18. Meinzer
    A unit of hydraulic conductivity in gpd/ft2. Rate of flow in gallons per day through a cross section of 1 ft2 under a unity of hydraulic gradient at 60oF
  19. Packer Test
    An aquifer test in which two inflatable seals (or packers) are set in an open borehole to prevent movement of ground water in the test section while the permeability of the isolated rock is determined
  20. Perched Ground Water
    Unconfied ground water separated from an underlying body of ground water by an unsaturated zone
  21. Percolation (Perc) Test
    A test made by digging a hole, filling it with water, and meausring the rate of decline of the water level. This is test is used to determine the soil suitability for sewage disposal systems
  22. Permeability
    The property of a porous rock or soil for transmitting a fluid. It measures the relative ease of flow under unequal pressure
  23. Porosity (n)
    The precentage of the bulk volume of a rock or soil that is occupied by void space
  24. Potentiometric Surface
    A surface that represents the total head of ground water and is defined by the level to which water will rise in a well
  25. Pumping Test
    A test made by pumping a well for a period of time and observing the change in hydraulic head in the aquifer
  26. Recharge Area
    An area where water infiltrates downward into the saturated zone
  27. Runoff (R)
    That part of preciptitation appearing in surface streams
  28. Slug Test
    An aquifer test made either by pouring a small charge of water into a well or by removing a slug of water from the well. The removal of water from the well is also called a bail-down test
  29. Specific Retention (Sr)
    Ratio of the volume of water a soil or rock can retain against gravity drainage to the total vouume of the soil or rock, usually stated as a percentage
  30. Specific Storage (Ss)
    Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head. Units are ft-1
  31. Specific Yield (Sy)
    Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total voume of soil or rock, stated as a percentage
  32. Storativity or Storage Coefficient (S)
    Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer of the aquifer per unit change in head. In an unconfined aquifer, storage = specific yield
  33. Transmissivity (T)
    The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T=Kb, where b = saturated thickness of the aquifer. Dimensions are gpd/ft or ft2/day
  34. Unconfined Aquifer
    An aquifer having a water table
  35. Underflow (U)
    Ground water that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions
  36. Vados Zone or Zone of Aeration
    A subsurface zone containing water under pressure that is less tha atmospheric pressure. A synonym of vadose zone is unsaturated zone
  37. Water Table
    The surface within unconfined ground water at which the hydraulic pressure is equal to atmospheric pressure
  38. Watershed
    The region drained by a stream or body of water, or a drainage divide
  39. Well efficiency
    The ratio in percent of theoretical drawdown to actual drawdown measured in a well