Aquifers come in many shapes, sizes, and locations. They are an important source of our drinking water and hold the groundwater that we pump out of private and public wells. The general definition of an aquifer is an underground body of rock, sand, soil, or sediment below the water table that is able to store water.
There are two general types of aquifers: confined and unconfined. Unconfined aquifers lie below a permeable layer and are impacted by atmospheric pressure. Water can move in and out vertically of these aquifers. Unconfined aquifers are referred to often as “water table aquifers” because their upper surface is generally at the water table. Unconfined aquifers are usually closer to the Earth’s surface, and as such are impacted by drought conditions sooner than confined aquifers.
Confined aquifers have an impermeable layer (such as clay) above and below them so that water is not able to flow freely vertically. Because they are under pressure, when a well is drilled in a confined aquifer, the water level in the well rises above that of the aquifer. Sometimes the well water level will even reach the land surface and be referred to as a “flowing artesian well”. Confined aquifers are generally deeper and may have water stored in them for a much longer time than unconfined.
Recharge, contamination, and groundwater protection
When we pump water out of aquifers, we have to understand the underlying geology to understand the aquifer recharge. Recharge refers to water being ‘put back’ into the aquifer as part of the water cycle. Unconfined aquifers are recharged quicker due to water seepage from soil, rainwater, or neighboring surface bodies of water. Since they are closer to the ground, unconfined aquifers are also more subject environmental conditions such as drought and contamination.
Confined aquifers cannot be recharged directly by rainwater but in general are recharged at areas where they are in contact with a permeable surface that allows water in.
All aquifers naturally filter groundwater by forcing it to pass through small pores and between sediments, which helps to remove substances from the water. However this natural filtration process may not be enough to remove all of the contaminants – we need to be extra vigilant in our pollution protection efforts in areas where we have drinking water wells (drinking water protection areas).
It’s much easier to prevent drinking water contamination then to clean it up, especially as we go into deeper aquifers. Whether you are an individual or a business, be mindful of your chemical usage. Keep substances in their appropriate containers and follow all directions and best practices to prevent spills. This groundwater in our aquifers is our drinking water – let’s protect it!
