Depleting Aquifers: Will They Refill?
We often hear about aquifers and how wells are drawing water out of them. Are we draining them or do they refill? Aquifers come in different types and have various ways of distributing water.
First things first, an aquifer is not an underground lake or river. There is not a huge chasm under your feet holding water that you could float a boat on. It is actually made of permeable rocks, sandstone and other porous materials. Water is easily able to move around in this drenched storage area.
There are two basic types of aquifers; confined and unconfined. A confined aquifer happens when water in porous layers is trapped by layers that are relatively impermeable, like granite or dense clay. Confined layers tend to be under pressure and typically are saturated through out. Unconfined layers are where ground water is located. This is water right under the soil, the top of this is considered the water table.
The amount of water stored in an aquifer can vary from season to season. Depending on its permeability, aquifers can gain water at a rate of 50 feet per year to 50 inches per century. They have both recharge and discharge zones. A recharge zone usually occurs at a high elevation where rain, snowmelt, lake or river water seeps into the ground to replenish the aquifer. A discharge zone can happen anywhere. Natural springs, wetlands and streams can all be areas where the aquifer is losing water.
Many people with wells are accessing an unconfined aquifer layer for drinking water. This can be an issue when there is a drought. If little or no water is entering the ground, the water table can drop and pumps will then go dry. Problems can also occur when industrial, agricultural and other chemicals leach down through the soil and enter the water. Arsenic, which occurs naturally in rocks and soil, is one of many contaminates that can be found in drinking water. Once water in the aquifer becomes polluted, it can be very difficult to fix.
Take a look at this map (click here to enlarge) of aquifers. Which one is closet to where you live? Numerous towns and some cities utilize aquifers as their water supply and are rapidly depleting them. A few areas now are part of an aquifer storage and recovery program where they inject drinkable water back for later use. Aquifers are found all over the US and since people, animals and plants need water to live, it is important that we take care of them.