3 rd Guided Notes about Groundwater Section 10.3.
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3rd Guided Notes about GroundwaterSection 10.3
In most cases, groundwater emerges wherever the water table intersects the Earths surface. Such intersections commonly occur in areas that have sloping surface topography.
Groundwater tends to discharge at Earths surface where an aquifer and an aquiclude come in contact. These natural discharges of groundwater are called springs.
In regions of near-horizontal sedimentary rocks, springs often emerge on the sides of valleys at the same elevation, at the bases of aquifers.
Springs may also emerge at the edges of perched water tables, which are zones of saturation that overly an aquiclude, which separates it from the main water table.
The temperature of groundwater is generally the average annual temperature of the region in which it is located.
Compared to air temperatures, groundwater is colder in the summer and warmer in the winter.
7. Hot springs have temperatures higher than that of the human body. Most of these are located in the Western United States, in areas where the subsurface is still quite hot from recent igneous activity. Underground water is hot because temperatures in Earths crust increase with depth by 25C for every kilometer.
Geysers are explosive hot springs that erupt at regular intervals.
Wells are holes dug or drilled deep into the ground to reach groundwater. A well must tap into an aquifer. The simplest wells are those that are dug or drilled below the water table, into the zone of saturation.
Overpumping of the well lowers the water level in it and produces a cone of depression in the water table. The difference between the original water table level and the level in a pumped well is called the drawdown.
Recharge is water from precipitation and runoff that is added back to the zone of saturation.
12. Water table aquifers are unconfined and unprotected, and thus, easily polluted. More reliable and less easily polluted water supplies can be found in deeper aquifers, called confined aquifers, which are generally sandwiched between aquicludes. The aquicludes form barriers that prevent pollutants from reaching such aquifers.
Because the area of recharge is usually at a higher elevation than the rest of the aquifer, a confined aquifer contains water under pressure. The aquifer is called an artesian aquifer.
14. When the rate of recharge is high enough, the pressurized water in a well drilled into a confined aquifer may spurt above the land surface in the form of a fountain called an artesian well.
Agriculture= 41%Electric Power Plants= 38% Domestic Use= 10% Industry= 11%
Ground subsidence, the sinking of land, is a problem caused by the excessive withdrawl of groundwater.
17. The most common sources of groundwater pollution are sewage, industrial waste, landfills, and agricultural chemicals. These pollutants enter the ground above the water table, but they are eventually flushed downward by infiltrating precipitation and become mixed with the groundwater. Most sewage enter the groundwater from faulty septic tanks.
Salt pollution is a threat to groundwater supplies in many coastal areas. The overpumping of wells can cause the underlying salt water to rise into wells and contaminate the freshwater aquifer.