The water that sits beneath the ground is classified as groundwater. This water can either be contained between soil and sediment or in aquifers. Aquifers are large bodies of water contained below the ground. Groundwater extraction is the process of extracting water from the rocks and sediment under the ground. There are many instances where groundwater needs to be extracted for testing purposes, drinking or growing crops. Groundwater is essential for many industries. In this article we take a closer look at groundwater and groundwater extraction.

How much do we depend on groundwater?

Often people are surprised about the level of dependency we have as a population on groundwater as a source of water. In the U.S., groundwater supplies over 50% of the drinking water. In rural areas this increases, up to 100% of the drinking water is groundwater in rural areas. Other industries that use groundwater include crop growth and irrigation and many industrial processes where a constant supply of water is needed. Groundwater is used by lakes, rivers, and wetlands to recharge their water supplies. Without groundwater many industries and crops would struggle to survive and as a human population we would have a worldwide drought. Groundwater is essential to the survival of the modern human race.

Groundwater sampling

Before groundwater extraction is installed in an area it is a good idea to take samples of the groundwater to check if it is suitable for purpose. The aquifers may not have the right balance of chemicals, it may be unsuitable for drinking or it could be contaminated. Groundwater sampling can analyse the water in the aquifers before extraction takes place, this makes sure the water is of an acceptable quality.

Groundwater sampling is also required as part of the monitoring process for landfill sites, underground gas tanks, and other instances where the water could become polluted. It is essential that the groundwater is regularly tested to make sure no pollutants are entering the water.

Groundwater can be polluted by a number of different substances, this includes landfills, septic tanks, leaky gas tanks, and the overuse of pesticides or fertilizers. When an aquifer becomes polluted by substances it cannot be used for crops or drinking water. In this instance another area must be used to extract water.

There are several methods that can be used to extract groundwater for sampling. The main and most common method is low-flow purging and sampling. This method of extraction uses a well which is slowly pumped until the water stabilises. This method only needs to extract a small amount of water for the sample to be representative of the whole aquifer. If a well isn't present above the body of water then a bore hole can be drilled in order to access the aquifer. A bore hole is created using a drilling rig or direct-push rig, it creates a long narrow hole in the ground for groundwater extraction.

Groundwater extraction

Groundwater is usually extracted through a well which is created in the ground and fills up with water. The well needs to be deep enough to penetrate the unsaturated zone into the saturated zone or aquifer. A pipe and a pump are then used to extract the water out of the ground and into a tank where it can be stored to be used at a later date. Groundwater extraction is a simple process that only needs a few pieces of equipment. It is however important to monitor groundwater levels during extraction. Over extraction of an aquifer can leave it dry, it can take many years to fill up again and become usable.

Water table

One consideration when extracting groundwater and using it for crops, drinking water or other purposes is the level of the water table. The water table can vary in locations, depending on the level of water in the saturated zone, and the amount of recent rainfall or snow in that area. Hotter weather and periods of drought can push the water table lower into the ground. Shallow wells may dry up if the water table moves below the level of the well. In these instances the well needs to be dug deeper into the ground in order to access the groundwater below.

Resources:

• Landfill Gas Monitoring - ArcGIS StoryMaps

• Methane Gas Monitors - Business Connection Zone

• Leachate Collection System - Diaspora