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• 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.
• Point sources:
– Municipal landfills.
– 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).
– Livestock wastes.
– 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.