Groundwater is water that is present below the ground surface which is usually located in rock or aquifers. This water forms a large portion of the drinking supply, but it is also used by farmers to water and irrigate crops and by companies to manufacture certain materials. In some instances, this water can become contaminated, which may be due to a landfill site leak or an oil spill. When this occurs, it is vital to remove or reduce the pollutants in the water as soon as possible, using a process known as groundwater remediation.

What is groundwater remediation?

Groundwater remediation is the method of treating polluted groundwater by either removing the contamination entirely or converting it into safe products. Find out more about groundwater remediation and why it is carried out in our guide.

How is groundwater remediated?

Groundwater can be remediated either in-situ (in place) or ex-situ (off-site). In-situ refers to the process of cleaning it where it is, instead of removing it and cleaning it elsewhere. Ex-situ on the other hand is where the water is removed from where it is and either treated or disposed of off-site. The most appropriate solution will depend on the contaminants in question, the area impacted and how much water has been polluted.

Ex-situ methods of groundwater remediation

There are two key ways that groundwater may be remediated off-site: extraction and disposal and pump and treat.

Extraction and disposal

This is one of the easiest and most cost-effective options available, however, it does present a number of challenges. Namely, figuring out how to access the water, extract it and then where to dispose of it safely. In terms of access, this may be carried out by digging boreholes or using sumps. Extraction methods will depend on whether the water needs to only be removed once or if ongoing extraction via a pumping system is required. Finally, disposal will likely involve sending the groundwater off-site to a registered waste processing centre or third-party waste management specialist.

Pump and treat

Pump and treat is an extremely common method of groundwater remediation and a great choice when the contamination needs to be reduced before moving it to an off-site location. Additionally, it is particularly useful for oil sites for spill clean-up as water can be separated from oil and then the oil can be reused.

During this method, the groundwater gets pumped through a specialist water treatment system and then it is either returned to the ground or placed into the drainage system. There is a range of pump and treat systems available, from basic carbon filters to more expensive reverse osmosis systems, the most suitable option will depend on the pollutants in question, available budget and how much water needs to be treated.

Once in place, water treatment systems will need to be run 24/7 for weeks or even months, but the good news is that they require very little maintenance and supervision.

In-situ methods of groundwater remediation

When there are smaller amounts of contamination, in-situ treatment methods may be suitable, some of the most common methods are as follows:

Chemical oxidation

Chemical oxidation, also known as chemox is often used to reduce contamination in the water and surrounding soil. Prior to use, soil testing will need to be carried out to determine the best product which will be either a specialist synthetic or man-made treatment product.

Biological options

Biological groundwater remediation options use organic matter, micro-organisms, or plants to clean the water and break down chemicals and compounds. This may be done via bioaugmentation, bioventing or biosparging.

Air sparging

This method is the most popular for groundwater that has been contaminated with fuel, oil or hydrocarbons. It involves pumping air through the water which forces the contaminants out and into the air. At the same time, it introduces oxygen into the water which speeds up the action of bacteria and helps to break down the contaminants even further. Sometimes air sparging is used in line with other methods or it can be carried out in isolation if contamination levels are low.

Soil vapor extraction

Soil vapor extraction is where odors from contaminated groundwater or soil are removed, this is particularly useful for fuel spills. The process involves vacuuming smells out of the ground, the extracted vapor then passes through layers of carbon filter and then once it is safe, is sent out via exhaust into the air. When used alone it is not very effective, but it is useful for removing odors when used with other methods.

Want to find out more about other environmental remediation methods? Learn about environmental gas monitoring next.