2Underground WaterUnderground water comes from precipitation that soaks into the ground.The water underground trickles down between particles of soil and through cracks and spaces in layers of rock – pore spaces
3PermeableDifferent types of rock and soil have different-sized spaces, or pores, between their particles.Materials that allow water to pass through easily are called permeable.
4When water soaks down into the ground, it passes through permeable materials. Eventually it reaches an impermeable layer.There, it stops trickling down and begins to fill the spaces in the permeable layer above it.
8A news report from 2011 states An underground river has now been discovered beneath the mighty Amazon River, flowing miles below the surface.Scientists detected this river after they analyzed data from 241 oil wells that were drilled in the 1970s and 1980s.The river was unofficially named the Hamza by scientists at Brazil's National Observatory in honor of their colleague, geophysicist Valiya Hamza.
18Ogallala Aquifer The aquifer was first tapped for irrigation in 1911. Large-scale use for irrigation began in the 1930s and continued through the 1950s, due to the availability of electric power to rural farming communities and the development of cheap
21Saturated thickness of the Ogallala Aquifer in 1997 after several decades of intensive withdrawals: The breadth and depth of the aquifer generally decrease from north to south
22Groundwater withdrawal rates (fresh water, all sources) in 2000.
23Image of fields in Kansas watered by the Ogallala aquifer using center pivot irrigation systems
24Water TableThe permeable layer that becomes filled with water is called the saturated zone.The level of the top of the water in the saturated zone is called the water table.The layer of rocks and soil above the water table is called the unsaturated zone (permeable zone)
29AquiferAn aquifer is an underground layer of rock or sediment where water has collected.The water in an aquifer seeps through the permeable rock layers where it is stored.
30People can obtain groundwater from an aquifer by drilling a well below the water table. If a hole is drilled in the impermeable layer above it, the water flows out of the aquifer without being pumped.