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Groundwater is underground water found in the pore spaces and cracks of soil, sand, and rock. The source of all groundwater is precipitation, either through direct percolation into the earth's surface, or through replenishment from local surface water including lakes, ponds, wetlands or rivers. Sometimes groundwater also flows into surface water through a process called baseflow. The process of groundwater replenishment is termed recharge.

Groundwater is stored in and moves at varying speeds through aquifers. An aquifer is a water-bearing geologic formation that can store and yield usable amounts of water, and consist of permeable layers of soil, sand, gravel or fractured rock such as granite or limestone. They are classified according to type, areal extent, thickness, yield, and direction of groundwater movement. There are two ...

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