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LEQ: How does water move through underground layers of soil and rock? Key Terms: pores, permeable, impermeable, saturated zone, unsaturated zone, water table, aquifer, artesian well Where does groundwater come from? Begins as precipitation. Water from precipitation that doesn’t evaporate, or runoff soaks into the ground. Affected by the permeability of the land cover. Permeability is determined size of the pores in the land cover. The smaller the pores the more impermeable the land cover. The larger the pores the more permeable the land cover. Water is pulled into the ground by gravity. Some of the water is absorbed by roots and used by plants. The remainder trickles down between particles of soil and through cracks and spaces in rock layers. Underground Water Layers Water will continue to travel downward between the pores or cracks in the soil or rock. When the water reaches an impermeable layer it becomes trapped. Water then begins to fill the pores and cracks in the soil or rock above the impermeable layer. The soil or rock above the impermeable layer becomes saturated and is known as the saturated zone. The top of the saturated zone is called the water table. Soil and rock layers above the water table still have water flowing through and are not saturated. This layer above the water table is called the unsaturated zone. To help you visualize this concept, see the image on the next slide. The Water Table Generally follows the shape or contour of the underground impermeable rock layer. Depth can vary greatly even over a small area of land. Heavy rain or lots of melting snow raises the level of the water table. Level drops during extended periods of dry weather. Can meet the ground surface and seep onto the surface as a spring or into: Rivers or streams Ponds Wetlands Aquifers An aquifer is any underground layer of rock or soil that holds water. The saturated zone between the impermeable layer and the water table. Range in size. Water flows or moves through the aquifer. The movement and speed of the water in the aquifer depends on: How steep the aquifer slopes. How permeable the rocks and soil are. Water can travel hundreds of kilometers and stay in an aquifer for thousands of years before coming to the surface again. Bringing Groundwater to the Surface People can remove groundwater from an aquifer by drilling a well. For the well to be filled with water, it must be drilled below the water table and into the aquifer. Can become dry if to much water is removed to fast. New water from precipitation that soaks in from the surface can recharge the aquifer. Artesian wells. A well in which water rises because of pressure within the aquifer Aquifer is trapped between two layers of impermeable rock or sediment. Water is under great pressure due to the weight of the water above. Water will flow out of an artesian well drilled into this aquifer without pumping. To help you visualize this concept, see the image on the next slide. Investigating Groundwater Enter the subterranean world of Groundwater One More Time ! The Groundwater Story