Any addition of undesirable substances to groundwater caused by human activities is considered to be contamination.
Groundwater contamination also called Groundwater pollution occurs when pollutants are released to the ground and make their way down into groundwater.
It can also occur naturally due to the presence of a minor and unwanted constituent, contaminant or impurity in the groundwater.
Different mechanisms have influence on the transport of pollutants, e.g. diffusion, adsorption, precipitation, decay, in the groundwater.
The interaction of groundwater contamination with surface waters is analyzed by use of hydrology transport models.
On-site septic systems.
Leaky sewer lines.
Leaks or spills of industrial chemicals at manufacturing facilities.
Sludge disposal areas at petroleum refineries
Underground injection wells (industrial waste).
Chemicals used at wood preservation facilities.
Leaky tanks or pipelines containing petroleum products.
Fly ash from coal-fired power plants.
Non-point (distributed) sources:
Fertilizers on agricultural land.
Pesticides on agricultural land and forests.
Contaminants in rain, snow, and dry atmospheric fallout.
Volatile organic compounds: They are generally introduced to the environment through careless industrial practices.
Pathogens: Pathogens contained in feces can lead to groundwater pollution when they are given the opportunity to reach the groundwater, making it unsafe for drinking.
(Diseases: cholera, diarrhoea).
Nitrate: Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause blue baby syndrome (acquired methemoglobinemia).
Others: Organic pollutants can also be found in groundwater, such as insecticides and herbicides. Inorganic pollutans might include ammonia, nitrate, phosphate, heavy metals or radionuclides.
Fluoride: In areas that have naturally occurring high levels of fluoride in groundwater which is used for drinking water, both dental and skeletal fluorosis can be prevalent and severe.
Arsenic: In the Ganges Plain of northern India and Bangladesh severe contamination of groundwater by naturally occurring arsenic affects 25% of water wells in the shallower of two regional aquifers.
Groundwater pollutants can enter the body directly through water supplies or by eating foods prepared with contaminated groundwater or grown in fields using contaminated sources.
It may also affect humans when they are in direct contact with polluted waters.
Health effects from groundwater pollution depend on the specific pollutants in the water.
Pollution from groundwater often causes diarrhoea and stomach irritation, which can lead to more severe health effects.
Accumulation of heavy metals and some organic pollutants can lead to cancer, reproductive abnormalities and other more severe health effects.
Locating on-site sanitation systems: On-site sanitation systems can be designed in such a way that groundwater pollution from these sanitation systems is prevented from occurring.
The following criteria have been proposed for safe siting (i.e. deciding on the location) of on-site sanitation systems:
a) Horizontal distance between the drinking water source and the sanitation system.
b) Guideline values for horizontal separation distances between on-site sanitation systems and water sources vary widely (e.g. 15 to 100 m horizontal distance between pit latrine and groundwater wells).
c) Vertical distance between drinking water well and sanitation system.
d) Aquifer type.
e) Groundwater flow direction.
f) Impermeable layers.