Groundwater pollution: Difference between revisions
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=== Fecal pollution === |
=== Fecal pollution === |
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[[Pathogens]] contained in human or animal [[feces]] can lead to groundwater pollution when they are given the opportunity to reach the groundwater, making it unsafe for drinking. Of the four [[pathogen]] types that are present in feces ([[bacteria]], [[viruses]], [[protozoa]] and [[helminth|helminths]] or helminth eggs), the first three can be commonly found in polluted groundwater, whereas the relatively large helminth eggs are usually filtered out by the soil matrix. |
[[Pathogens]] contained in human or animal [[feces]] can lead to groundwater pollution when they are given the opportunity to reach the groundwater, making it unsafe for drinking. Of the four [[pathogen]] types that are present in feces ([[bacteria]], [[viruses]], [[protozoa]] and [[helminth|helminths]] or helminth eggs), the first three can be commonly found in polluted groundwater, whereas the relatively large helminth eggs are usually filtered out by the soil matrix. |
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=== Volatile organic compounds (VOC) === |
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VOCs (volatile organic compounds) are a dangerous contaminant of groundwater. They are generally introduced to the environment through careless industrial practices. Many of these compounds were not known to be harmful until the late 1960s and it was some time before regular testing of groundwater identified these substances in drinking water sources. |
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== Causes due to human activity == |
== Causes due to human activity == |
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Revision as of 21:22, 21 March 2015
Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and work their way down into groundwater, which creates a contaminant plume within an aquifer. Movement of water and dispersion within the aquifer spreads the pollutant over a wider area, its advancing boundary often called a plume edge, which can then intersect with groundwater wells or daylight into surface water such asseeps and springs, making the water supplies unsafe for humans and wildlife. The movement of the plume, called a plume front, may be analyzed through a hydrological transport model or groundwater model. Analysis of groundwater contamination may focus on soil characteristics and site geology, hydrogeology, hydrology, and the nature of the contaminants.
Pollution can occur from landfills, naturally occurring arsenic, on-site sanitation systems or other point sources, such as petrol stations or leaking sewers. Using contaminated ground water causes hazards to public health through poisoning or the spread of disease.
Different mechanism 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.
Mechanisms
The stratigraphy of the area plays an important role in the transport of pollutants. An area can have layers of sandy soil, fractured bedrock, clay, or hardpan. Areas of karst topography on limestone bedrock are sometimes vulnerable to surface pollution from groundwater. Earthquake faults can also be entry routes for downward contaminant entry. Water table conditions are of great importance for drinking water supplies, agricultural irrigation, waste disposal (including nuclear waste), wildlife habitat, and otherecological issues.[1]
Interactions with surface water
Although interrelated, surface water and groundwater have often been studied and managed as separate resources.[2] Surface water seeps through the soil and becomes groundwater. Conversely, groundwater can also feed surface water sources. Sources of surface water pollution are generally grouped into two categories based on their origin.
Interactions between groundwater and surface water are complex. Consequently, groundwater pollution, sometimes referred to as groundwater contamination, is not as easily classified as surface water pollution.[2] By its very nature, groundwater aquifers are susceptible to contamination from sources that may not directly affect surface water bodies, and the distinction of point vs. non-point source may be irrelevant. A spill or ongoing release of chemical or radionuclide contaminants into soil (located away from a surface water body) may not create point or non-point source pollution but can contaminate the aquifer below, creating a toxic plume.
Pollutant types
Contaminants found in groundwater cover a broad range of physical, inorganic chemical, organic chemical, bacteriological, and radioactive parameters.
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. The pollution occurs because aquifer sediments contain organic matter that generates anaerobic conditions in the aquifer. These conditions result in the microbial dissolution of iron oxides in the sediment and, thus, the release of the arsenic, normally strongly bound to iron oxides, into the water. As a consequence, arsenic-rich groundwater is often iron-rich, although secondary processes often obscure the association of dissolved arsenic and dissolved iron.[citation needed]
Fecal pollution
Pathogens contained in human or animal feces can lead to groundwater pollution when they are given the opportunity to reach the groundwater, making it unsafe for drinking. Of the four pathogen types that are present in feces (bacteria, viruses, protozoa and helminths or helminth eggs), the first three can be commonly found in polluted groundwater, whereas the relatively large helminth eggs are usually filtered out by the soil matrix.
Volatile organic compounds (VOC)
VOCs (volatile organic compounds) are a dangerous contaminant of groundwater. They are generally introduced to the environment through careless industrial practices. Many of these compounds were not known to be harmful until the late 1960s and it was some time before regular testing of groundwater identified these substances in drinking water sources.
Causes due to human activity
Landfill leachate
Leachate from sanitary landfills can lead to groundwater pollution.
Love Canal was one of the most widely known examples of groundwater pollution. In 1978, residents of the Love Canal neighborhood in upstate New York noticed high rates of cancer and an alarming number of birth defects. This was eventually traced to organic solvents and dioxins from an industrial landfill that the neighborhood had been built over and around, which had then infiltrated into the water supply and evaporated in basements to further contaminate the air. Eight hundred families were reimbursed for their homes and moved, after extensive legal battles and media coverage.
On-site sanitation systems
Groundwater pollution with pathogens and nitrate can also occur from the liquids infiltrating into the ground from on-site sanitation systems such as pit latrines and septic tanks, depending on the population density and the hydrogeological conditions. As liquid leaches from the pit it first passes the unsaturated soil zone (which is not completely filled with water), then it enters the groundwater and is transported with the flow, all too often towards a nearby supply well which pumps groundwater. During this passage, pathogens can die off or be adsorbed significantly, mostly depending on the travel time between the pit and the well. Most, but not all pathogens die within 50 days of travel through the subsurface. The degree of pathogen removal strongly varies with soil type, aquifer type, distance and other environmental factors.[3] A well-researched example of this is the strongly karstified system in areas of Lusaka, Zambia where groundwater pollution from pit latrines is a major public health threat.[4]
Others
Groundwater pollution can also occur from leaking sewers which has been observed for example in Germany.[5]
Furthere sources are over application of fertilizer or pesticides, spills from industrial operations and infiltration from urban runoff.
Prevention
Treatment
Groundwater pollution is much more difficult to abate than surface pollution because groundwater can move great distances through unseen aquifers. Non-porous aquifers such as clays partially purify water of bacteria by simple filtration (adsorption and absorption), dilution, and, in some cases, chemical reactions and biological activity; however, in some cases, the pollutants merely transform to soil contaminants. Groundwater that moves through open fractures and caverns is not filtered and can be transported as easily as surface water. In fact, this can be aggravated by the human tendency to use natural sinkholes as dumps in areas of karst topography.
Pollutants and contaminants can be removed from ground water by applying various techniques thereby making it safe for use. Ground water treatment (or remediation) techniques span biological, chemical, and physical treatment technologies. Most ground water treatment techniques utilize a combination of technologies. Some of the biological treatment techniques include bioaugmentation, bioventing, biosparging, bioslurping, and phytoremediation. Some chemical treatment techniques include ozone and oxygen gas injection, chemical precipitation, membrane separation, ion exchange, carbon absorption, aqueous chemical oxidation, and surfactant enhanced recovery. Some chemical techniques may be implemented using nanomaterials. Physical treatment techniques include, but are not limited to, pump and treat, air sparging, and dual phase extraction.
Legislation
Environmental protection of groundwater in the U.S.
In November 2006, the Environmental Protection Agency published the Ground Water Rule in the United States Federal Register. The EPA was worried that the ground water system would be vulnerable to contamination from fecal matter. The point of the rule was to keep microbial pathogens out of public water sources.[6] The 2006 Ground Water Rule was an amendment of the 1996 Safe Drinking Water Act.
References
- ^ Groundwater Sampling; http://www.groundwatersampling.org/
- ^ a b United States Geological Survey (USGS), Denver, CO (1998). "Ground Water and Surface Water: A Single Resource." Circular 1139.
- ^ Graham, J.P., Polizzotto, M.L. "Pit Latrines and Their Impacts on Groundwater Quality: A Systematic Review". Environ Health Perspect. 121: 521–530.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Nick, A. (2011). Methodology and results of the vulnerability map for Lusaka and surroundings using the PI-method - a documentation and manual - Technical note no. 6. Department of Water Affairs (DWA), Zambia & Federal Institute for Geosciences and Natural Resources (BGR), Germany
- ^ John H. Tellam, Michael O. Rivett, Rauf G. Israfilov, Liam G. Herringshaw (2006). Urban Groundwater Management and Sustainability. Springer Link, NATO Science Series Volume 74 2006. p. 490. ISBN 978-1-4020-5175-3.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Ground Water Rule (GWR) | Ground Water Rule | US EPA. Water.epa.gov. Retrieved on 2011-06-09.
External links
