Geology Unit 6

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Author:
truleo
ID:
207089
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Geology Unit 6
Updated:
2013-03-17 00:30:03
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groundwater geology
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Groundwater, geology
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  1. About what percentage of Earth's water is available as fresh water?
    2-3%
  2. About what percentage of US drinking water comes from groundwater?
    Groundwater supplies almost 50% (1/2) US drinking water (and to virtually all people living in rural areas)
  3. How do most rivers and lakes maintain their water level?
    By groundwater
  4. What is groundwater infiltration?
    The process of surface water entering into the ground or soil or rocks.
  5. Give the general definition of groundwater.
    water below the Earth's surface that has infiltrated from surface sources.
  6. What is potable water?
    Water infiltrated from surface sources. It is suitable for human use and genrally found at relatively shallow depths (generally above 1000 feet depth).
  7. How is connate water different from "potable water"? (Discuss connate water information)
    Water trapped in the pores of a rock during formation of the rock, can be described as fossil water, generally not potable (example-water found in oil and gas wells).
  8. In which geologic environment do we usually find juvenile ground water?
    Water brought to surface or added to underground supplies from magma and is never potable.
  9. In regards to rocks and soils, compare pore space with porosity.
    Porosity and pore space determine the quantity of water that can be stored in rocks and sediments. Variety of porosity depends upon the rock type.
  10. What type of porostiy is associated with clastics and clastic rocks?
    Intergranular porosity
  11. How can processes of compaction and cementation alter intergranular porosity?
    Compaction  pushes grains together will reduce porostiy. Cementation reduces porosity by minerals precipitated  from groundwater in the pore spaces of the sediment or rocks.
  12. Explain the process of precipitation (associated with cementation).
    Cementation by the process of precipitation can totally close pore spaces, or bond the sediments together as a rock (no longer a sediment).
  13. Give an example of the process of dissolution
    When acid rains dissolve calcite (limestone and marble) which is carried away as a mineral solution by the groundwater.
  14. What type of rock must be present for solution cavities (like caves) to develop? (Hint: not sandstone)
    Openings remaining after the acid dissolution of limestone. Basically this is the removal of materials (calcite) by acid water.
  15. What is the difference between permeability and porosity?
    Porosity is the total volume of rock or sediment in pore space. Permeability is ability and capacity of rock or sediment to transmit water.
  16. Compare the water yield of high permeability vs. low permebility
    High permeability is where the water moves easily through rocks and sediments. Low permeability is when water moves slow through rocks and sediments.
  17. What does no permeability imply?
    Water does not flow through certain rocks and sediments. Example: sediments with abundant clay that has filled the pore spaces.
  18. Describe the volume of groundwater associated with very large underground rivers and lakes.
    The deeper the well, the purer the water.
  19. Describe how water dowsers find places to drill for groundwater.
    By forked sticks or bent wires.
  20. Are there large areas of land on Earth that have no ground water?
    No, water is found at some depth everywhere beneath the Earth's surface.
  21. At what depth is most useable groundwater found?
    Most useable groundwater is limited to about 1000 feet below the surface.
  22. What is the difference between zone of aeration and a saturated zone?
    For zone of aearation, the pore space is filled with air and minor amounts of water, so it is not truly saturated. With zone of saturation, the pore spaces are filled with water.
  23. What is the difference between a water table and a saturated zone?
    With the water table, it is on an actual plane or surface. The zone of saturation lies below the water table.
  24. What is the effect of an aquiclude (aquitard or confining layer) on groundwater?
    It can act as a "bottom dam".
  25. What is another name for an unconfined aquifer?
    Water table aquifer.
  26. How does a perched aquifer differ from an unconfined aquifer?
    The upper surface of a local zone of saturatiion that lies above the regional water table on a small impermeable layer. Overtime, the groundwater will flow over the edge of the impermeable layer and no water will remain here. This should be considered aas a temporary aquifer.
  27. What basically is an artesian aquifer?
    A pressurized aquifer.
  28. How (geologically) does an artesian aquifer build up water pressure?
    The aquifer is between aquitards and aquitards form both confining top and bottom layers and confines the water to the aquifer. Thus the water becomes pressurized like within a pipe.
  29. Describe the water well level differences (in the pipe) between the following: unconfined aquifer well vs. an artesian flowing well (See drawings of study guides).
    For unconfined  water well the groundwater level within a pipe, within the unconfined aquifer, is at the same level  as the water table. Artesian flowing well is groundwater confined in an aquifer and under pressure great enough to cause the water to rise up high enough in the well pipe to flow out on the surface (no pumping. See sketch)
  30. What type of rocks and sediments makes the best aquifers?
    • Snd within sand dunes and river sands.
    • Sandstone, gravel and conglomerates.
    • Cavernous limestone (lots of openings here).
    • Highly fractured rocks.
  31. What type of rocks and sediments makes the best aquitards?
    • Clay and silt/mudstone and shale (clay can seal up openings and pores)
    • Strongly cemented sediments and rocks (pore filled with cementing minerals)
    • Most igneous and metmorphic have few or no pores
  32. What water property prevents us from achieving 100% water extraction?
    Water Surface Tension where intermolecular force that binds a film of water to a grain surface.
  33. What is the host rock for the Edwards Aquifer near San Antonio and Austin?
    Limestone.
  34. What is the potential problem with the High Plains (Ogallala) Aquifer of the Texas panhandle?
    The High Plains (Ogallala) Aquifer (Texas Panhandle)  of sand and gravel is rapidly running out of water because most of its recharge zone is covered by clays.
  35. Describe the quality of water from the local aquifers that include  present and ancient barrier islands and the local Pleistocene fluvial system.
    Present and ancient barrier islands that extend from Flour Bluff to Rockport have good permeability but poor quality water.
  36. Describe the water qualities of the Goliad formation near Sinton
    Has good permeability, good quality water, is mostly but privately owned.
  37. Discuss the qualities of local clays for filtering surface water as it enters a local aquifer, especially in regards to dissolved iron content.
    Surface clay and clay in aquifers cannot trap dissolved iron and salt molecules. Most of our local aquifers have an abundance of dissolved salts and dissolved iron.
  38. What is "hard water" and what effect does this have on hot water heaters and pipes?
    This scale can fill up (iron) hot water pipes and can fill hot water heaters with coatings of calcite.
  39. What are some of the major contaminants of local area aquifers?
    Some of these local aquifers contain such metals as dissolved uranium and selenium.
  40. Know the difference between leaching and leachate.
    • Leaching is dissolving and removing the soluble constituents of a rock or soil or trash or anything (process).
    • Leachate is a water solution or pollution produced by leaching that can enter and aquifer (product).
  41. Draw and describe a "cone of depression".
    A conical deperression of the water table surrounding a well after heavy pumping. 
  42. Be able to defend yourself from lawsuits by explaining the TX "rule of capture", in regards to your pumping of large quantities of groundwater. What would you tell the accuser?
    The "rule of capture" applies (different rules if you are in an election-mandated water district). The land owner can capture or pump all the water possible from a water well on his property, without regards to the effect of the water table on neighboring property.
  43. Describe the "vertical positioning" of oil, gas, and water in a petroleum reservoir.
    From top to bottom in the trap. expect to find the following "layers": gas on top, then oil then water at the bottom.
  44. What is the cause of major ground subsidence around Houston?
    Withdrawing groundwater too rapidly can cause major ground subsidence such as at the Houston-Galveston area. You should pump out water only as fast as the water is entering the aquifer.
  45. How can acid be created with rainfall?
    Rain water combines with carbon dioxide in the air to form carbonic acid. Acid round water also comes from decaying plants, pollution and leaking gas wells.
  46. How are caves created and how long does it take to create large caves?
    A naturally formed subterranean open area. The open chambers or series of chambers are produced in limestone by solution activity. Large caves take millions of years to form.
  47. What is the host rock for most caves? GUARANTEED EXAM QUESTION
    Limestone
  48. Distinguish between stalacitites and stalagmites.
    Stalacitites are on the roof of caves. Stalagmites are on the floor of caves.
  49. How do sinkholes develop?
    A depression formed by the collapse of a cavern roof.
  50. Describe required rainfall amounts needed for Karst topography.
    Abundant rainfall is required for strong karst development.
  51. Describe a geyser.
    A thermal spring that intermittently erupts steam and boiling water. Locally there must be hot fractured rocks, and a nearby heat source such as a "recent" volcano or intrusion.

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