Groundwater is water beneath the surface of the earth, that has seeped down through soil layers above, through spaces in soil and fissures in stone, collecting in aquifers below the ground. This water naturally returns to the surface of the soil through springs and wetlands, and is replenished with rainfall.
For centuries, the active filtration of these layers of soil and stone were sufficient to purify the groundwater, making the water that emerged from springs clean and fresh. However, many human activities pollute the soil. These pollutants either seep down themselves into the aquifer or contaminate rain water as it penetrates the soil and are carried down into the groundwater. This can render the spring water unsafe for humans or animals to drink.
Difference Between Contamination and “Pollution
Groundwater contamination is generally used to refer to water that is unsafe to drink due to natural causes. Fluoride, arsenic, and nitrate are harmful natural compounds that can seep into groundwater. Contamination can also be caused by animal feces that may contain pathogens that filter into the water.
Groundwater pollution is generally used to refer to water that is unsafe to drink due to human activity. Fertilizers and pesticides, industrial leaks, sewage, and similar human activities all have a harmful effect on groundwater.
Causes of Groundwater Pollution
There are hundreds of potential causes and sources of groundwater pollution, large and small. Groundwater can get polluted through many of the daily activities that we may take for granted, such as:
In junkyards and auto repair shops, it's common for oil to be spilled or to leak gradually into the ground. In salting and de-icing, large quantities of salt or chemicals are sprayed onto roads and runways, where they leak into the ground as ice melts. Dry cleaning, photography, furniture refinishing, and medical care often involve specific solvents, chemicals, and compounds that can cause pollution when they aren't properly disposed of.
While all these factors contribute incrementally to groundwater pollution, the biggest contributors to large-scale groundwater pollution are:
Sewage and septic leaks. In places where sewage or septic facilities are inadequate or in poor repair, pathogens from human waste can seep into and pollute groundwater. Whether modern sewage treatment or septic systems develop a leak or discharge poorly-filtered materials into surface water, or whether less developed areas use pit latrines located near wells for drinking water, groundwater can get polluted by human waste and cause a variety of health issues, including skin lesions and dermatitis as well as intestinal problems.
Fertilizers and pesticides. Modern agricultural practices often include sweeping use of fertilizers and pesticides on acres of land at a time. Only a fraction of the nitrogen in fertilizers is used by the plants, leaving high levels of nitrate in the soil, potentially seeping down into the groundwater.
Often animal manure also contains residues of pharmaceuticals used in veterinary drugs, which can then enter groundwater. While many commercial pesticides have reduced risk of entering groundwater, the insecticide monocrotophos is persistent, soluble, and does not bind with minerals in soils, meaning that it can reach groundwater and potentially drinking water.
The effects of pesticides on groundwater are not well known due to the high cost of conducting analysis.
Commercial and industrial leaks. Mining and metal processing have both been shown to pollute groundwater, including increasing concentrations of arsenic. In addition, we store gasoline, oil, and chemicals in large underground tanks.
There are an estimated 10 million of these tanks in the United States, and they risk groundwater pollution in two ways: because they are underground, a leak may be undetected for longer than if the storage tanks were aboveground and visible. And because they are underground, potential leaks are closer to the water table, reducing the natural filtration of the aquifer.
Hydraulic fracturing. Hydraulic fracturing is the process of injecting high-pressure fluid to create cracks in deep rock formations. While there is debate about the degree to which fracking pollutes groundwater, with some studies finding elevated levels of methane, ethane, and propane gasses, as well as increased concentrations of helium and other noble gasses near fracking sites, the United States Environmental Protection Agency has not found evidence of a widespread, systemic impact on the quality of groundwater due to fracking.
Of potentially greater concern are the repeated spills of enormous volumes of fracking fluids at fracking sites, with major spills causing massive species deaths and home evacuations. Fracking fluid is generally made of water, solid materials, polymers, surfectants, friction reducers, biocides, and often radioactive tracer isotopes.
Controversially, hydraulic fracking fluid was specifically excluded from the 2005 American Clean Water Act, a decision believed to be due to lobbying from special interest groups.
What Can We Do About Groundwater Pollution?
While everyone can do their part to dispose properly of their household waste and chemicals, plant native plants, and conserve water, the truth is, the causes of groundwater pollution aren't due to the efforts and activities of most private individuals. If you want to prevent groundwater pollution, you have to get involved: