Many people rely on groundwater as a source of drinking water, while others use it to irrigate their farms. For those who rely on groundwater, it’s important that their water be free of contaminates and pollution.
A pollutant of ground water is any substance, that, when it reaches an aquifer makes the water unclean, or unsuitable for its intended use. Sometimes that substance is a manufactured chemical, but, just as often it is a microbial contamination. Contamination can also be caused by the minerals and metallic deposits in rocks and soils.
For many years it was believed that the soil and sediment layers deposited above an aquifer acted as a natural filter that was able to keep many pollutants on the surface from infiltrating down to the ground water, however it has been found that soil layers don’t actually protect aquifers adequately. Despite this a significant amount of contamination was already present in both soil and groundwater, and, unfortunately, once an aquifer has been contaminated it can become unusable for decades. It is impossible for this to be cleaned up quickly – and – inexpensively.
Types of groundwater contamination
Ground water that has been polluted by humans falls into two categories – point source pollution and nonpoint source pollution.
Pesticides and fertilisers applied to crops can eventually reach underlying aquifers, particularly if it is shallow and hasn’t been protected by materials such as clay. Drinking water wells that have been located close to farms are sometimes contaminated by agricultural chemicals.
Point-source pollution refers to contamination that has originated from a single tank, disposal site or facility. Accidental spills, industrial waste disposal sites, dumps, landfills, or leaking petrol storage tanks are all examples of point sources.
Non-point pollution includes chemicals that are used in agriculture – herbicides, pesticides and fertilisers are all examples because they are spread out across wide areas. Run off from urban areas is also another example of a nonpoint source of pollution. Because non-point source substances are used over large areas, they can have a bigger impact on the quality of water in an aquifer than do point source pollutants.
Cleaning up contaminated ground water
Ground water becomes polluted when rain that has soaked into the ground comes into contact with buried waste, or other sources of contamination, it picks up these chemicals and carries them down into the groundwater. Sometimes the volume of the spill or leak is large enough that the chemicals can reach the groundwater without the help of rainwater.
Ground water tends to move very slowly and with little turbulence, dilution or mixing, therefore, once a contaminant has reached the groundwater, they tend to form a concentrated *plume* that flows along with the groundwater. Despite this slow movement of a pollutant through an aquifer, groundwater contamination often goes undetected for years.
There are normally several steps taken to clean up a site once it has been contaminated. Initially, an investigation is launched to determine the nature of and extent of the contamination, the risks are then evaluated – if the risks are high, the various ways the site can be cleaned up are looked at via a feasibility study.
Methods of clean up
The various ways to respond to a site contamination –
- Containing the contaminants to prevent them from migrating to another source
- Removing the contaminants from the aquifer
- Treating the groundwater at its point of use
- Abandoning the aquifer and finding an alternate source of water
There are several ways to contain groundwater contamination
- Physically – by using an underground barrier of cement, clay or steel
- Hydraulically – by pumping wells to keep contaminants from moving past the wells
- Chemically – by using a relative substance to either detoxify or immobilise the contaminant
The most common way to remove contaminants from an aquifer is to capture the pollution in groundwater extraction wells. Once it has been removed from the aquifer, the contaminated water is treated above ground and the resulting clean water is then pumped back into the ground, or into a river. This can take a long time but can be a successful way to remove most of the contamination from an aquifer.
Another way is known as air sparging. Small-diameter wells are used to pump air into the aquifer and as the air moves through it evaporates the chemicals. The contaminated air that rises to the top of the aquifer is then collected using extraction wells.
The content is provided by Interfil. Interfil is a supplier of Filter Media and Oil Centrifuges in Sydney. They also provide Industrial liquid waste management and waste water treatment system.