Aquifers

~ Any underground layer of rock or sediment that holds water. ~ They can range in size from a small underground patch of permeable material to an area the size of several states. Aquifers

Ogallala Aquifer ~ Lies beneath the plains of the Midwest, stretching from South Dakota to Texas. ~ Millions of people obtain their drinking water from this underground storehouse. ~ Provides water for crops and livestock. Ogallala Aquifer

~ Groundwater is actually in motion, seeping through the layers of rock. ~ How fast it moves depends largely on how steeply the aquifers slopes and how permeable the rocks are. ~ Groundwater in some aquifers moves only a few centimeters a day. ~ At that rate, the water moves about 10 meters a year- less than the length of a typical classroom. ~ May travel hundreds of km and stay in an aquifer for thousands of years before coming to the surface again.

Groundwater to the surface In places where the water table meets the ground surface, groundwater seeps onto the surface. The groundwater may feed a stream or pond, or form a wetland. People can also bring groundwater to the surface.

WELLS ~ People can obtain groundwater from an aquifer by drilling a well below the water table. ~ Because the bottom of the well is in the saturated zone, the well contains water. ~ Long ago people dug wells by hand. They lined the sides of the well with brick or stone to keep the walls from collapsing. ~ To bring up water, they lowered and raised a bucket. ~ Today wells are dug with well- drilling equipment. ~ Pumps bring up the groundwater.

~ Pumping water out of an aquifer lowers the water level near the well. ~ If too much water is pumped out too fast, the well may run dry. ~ It will be necessary either to dig deeper to reach the lowered water table, or to wait for rainfall to wait for rainfall to refill the aquifer. ~ New water that enters the aquifer from the surface is called recharge.

ARTESIAN WELL: ~ Groundwater is trapped between two layers of impermeable rock or sediment. ~ The water is under great pressure from the weight of the water above it. ~ If the top layer of rock is punctured, the pressure sends water spurting up through the hole. ~ Water flows without pumping from a well dug in such an aquifer. tch?v=KMtEQqbi4CI Slide 9

SPRINGS: Places where groundwater bubbles or flows out of cracks in the rock are called springs. Most springs contain water at normal temperatures, but some springs, like those in Yellowstone, contain water that is warmed by the hot rocks deep below the surface. The heated water bubbles to the surface in hot springs