Groundwater Contamination

Groundwater Contamination

Introduction: • 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. Sources: • 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. Pollutant types: • 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. Naturally occurring: • 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. Exposure Pathways: • 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: • 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. Prevention: • 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.