33rdrd Guided Notes Guided Notes about Groundwaterabout Groundwater

Section 10.3Section 10.3

1.1. In most cases, groundwater In most cases, groundwater emerges wherever emerges wherever the water the water table intersects the Earth’s table intersects the Earth’s surfacesurface. Such intersections . Such intersections commonly occur in areas commonly occur in areas that that have sloping surface have sloping surface topographytopography..

2.2. Groundwater tends to discharge Groundwater tends to discharge at Earth’s surface where at Earth’s surface where an an aquifer and an aquiclude come aquifer and an aquiclude come in contactin contact. These natural . These natural discharges of groundwater are discharges of groundwater are called called springssprings..

3.3. In regions of near-horizontal In regions of near-horizontal sedimentary rocks, sedimentary rocks, springs springs often emerge on the sides of often emerge on the sides of valleys at the same elevationvalleys at the same elevation, , at the bases of aquifers.at the bases of aquifers.

4.4. Springs may also emerge at the Springs may also emerge at the edges of edges of perched water tablesperched water tables, , which are which are zones of saturation zones of saturation that overly an aquiclude, which that overly an aquiclude, which separates it from the main separates it from the main water table.water table.

5.5. The temperature of The temperature of groundwater is generally groundwater is generally the the average annual temperature of average annual temperature of the region in which it is locatedthe region in which it is located..

6.6. Compared to air temperatures, Compared to air temperatures, groundwater is colder in the groundwater is colder in the summer and warmer in the summer and warmer in the winterwinter..

7. Hot springs have 7. Hot springs have temperatures temperatures higher than that of the human bodyhigher than that of the human body. . Most of these are located in the Most of these are located in the Western United States, in areas where Western United States, in areas where the subsurface is still quite hot from the subsurface is still quite hot from recent igneous activityrecent igneous activity. Underground . Underground water is hot because water is hot because temperatures in temperatures in Earth’s crust increase with depth by Earth’s crust increase with depth by 2525ºC for every kilometerºC for every kilometer..

8.8. Geysers are Geysers are explosive hot explosive hot springs that erupt at regular springs that erupt at regular intervalsintervals..

9.9. Wells are Wells are holes dug or drilled holes dug or drilled deep into the ground to reach deep into the ground to reach groundwatergroundwater. A well must tap . A well must tap into into an aquiferan aquifer. The simplest . The simplest wells are those that are dug or wells are those that are dug or drilled below the drilled below the water table, water table, into the zone of saturationinto the zone of saturation..

10.10.Overpumping of the well Overpumping of the well lowers lowers the water level in itthe water level in it and and produces produces a cone of depression a cone of depression in the water tablein the water table. The . The difference between the original difference between the original water table level and the level water table level and the level in a pumped well is called in a pumped well is called the the drawdowndrawdown..

11.11.Recharge is Recharge is water from water from precipitation and runoff that is precipitation and runoff that is added back to the zone of added back to the zone of saturation.saturation.

12. Water table aquifers are 12. Water table aquifers are unconfinedunconfined and and unprotectedunprotected, and thus, easily , and thus, easily polluted. More reliable and less easily polluted. More reliable and less easily polluted water supplies can be found in polluted water supplies can be found in deeper aquifersdeeper aquifers, called , called confined confined aquifersaquifers, which are , which are generally generally sandwiched between aquicludessandwiched between aquicludes. The . The aquicludes form aquicludes form barriers that prevent barriers that prevent pollutants from reaching such aquiferspollutants from reaching such aquifers..

13.13.Because the area of recharge is Because the area of recharge is usually usually at a higher elevation at a higher elevation than the rest of the aquiferthan the rest of the aquifer, a , a confined aquifer contains confined aquifer contains water water under pressureunder pressure. The aquifer is . The aquifer is called an called an artesian aquiferartesian aquifer..

14. 14. When the rate of recharge is When the rate of recharge is high enough, high enough, the pressurized the pressurized water in a well drilled into a water in a well drilled into a confined aquifer may spurt confined aquifer may spurt above the land surfaceabove the land surface in the in the form of a fountain called an form of a fountain called an artesian wellartesian well..

15.15.Agriculture= 41%Agriculture= 41%

Electric Power Plants= 38%Electric Power Plants= 38%

Domestic Use= 10%Domestic Use= 10%

Industry= 11%Industry= 11%

16.16.Ground subsidence, the Ground subsidence, the sinking sinking of landof land, is a problem caused by , is a problem caused by the the excessive withdrawl of excessive withdrawl of groundwatergroundwater..

17. The most common sources of 17. The most common sources of groundwater pollution are groundwater pollution are sewage, sewage, industrial waste, landfills, and industrial waste, landfills, and agricultural chemicalsagricultural chemicals. These pollutants . These pollutants enter the ground above the water table, enter the ground above the water table, but they are but they are eventually flushed eventually flushed downward by infiltrating precipitationdownward by infiltrating precipitation and become mixed with the and become mixed with the groundwater. Most sewage enter the groundwater. Most sewage enter the groundwater from groundwater from faulty septic tanksfaulty septic tanks..

18.18.Salt pollution is a threat to Salt pollution is a threat to groundwater supplies in groundwater supplies in many many coastal areascoastal areas. The . The overpumping of wells can cause overpumping of wells can cause the underlying salt water to the underlying salt water to rise rise into wells and contaminate the into wells and contaminate the freshwater aquiferfreshwater aquifer..