How do aquifers work?

Since a significant portion of the U.S. drinking water is pumped from aquifers, it is important to understand what an aquifer is and how it works. Aquifers are underground basins that hold water. Aquifers are full of sediment such as silt, or larger material such as gravel and rocks. The water in aquifers is what fills the spaces between tiny silt particles or larger gravel pores. Aquifers are similar to bowls of cereal: the aquifer itself is like a giant bowl, that is full of “stuff” (rocks or sediment instead of cereal), with water filling the space between each piece of the sediment.
Aquifers are usually good options for water supplies because in natural systems, the water must first pass through hundreds—sometimes thousands—of feet of dirt and sediment before it enters the aquifer and is usable. Water often cannot be pumped out of the ground until it reaches the aquifers because it is not concentrated enough. In other words, there is not enough water per unit of sediment to efficiently pump it out. However, the water can easily be pumped out once it reaches an aquifer because it saturates the sediment.
The largest aquifer in the continental United States is the Ogalalla Aquifer. It reaches from South Dakota all the way south to Texas. The Ogalalla Aquifer held approximately 3,250 million acre-feet of water in 1980. As a result of over-drafting (pumping out more water than re-enters), the Ogalalla Aquifer has been steadily draining. Consequently, it becomes more energy-intensive to pump out water as the levels drop, and can create other problems such as sinkholes. In some places, the water level in the Ogalalla Aquifer has dropped more than 100 feet. The annual drop in water level from 1980 to 1999 was 3.2 feet. Without implementing water conservation measures, only time will tell how long our natural water sources will last.
Brian O’Neill
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