Saltwater
encroachment associated with over drafting of aquifers or natural leaching
from natural occurring deposits are natural sources of groundwater pollution.
Most
concern over groundwater contamination has centered on pollution associated
with human activities.
Human
groundwater contamination can be related to waste disposal (private sewage
disposal systems, land disposal of solid waste, municipal wastewater,
wastewater impoundments, land spreading of sludge, brine disposal from the
petroleum industry, mine wastes, deep-well disposal of liquid wastes, animal feedlot
wastes, radioactive wastes) or not directly related to waste disposal
(accidents, certain agricultural activities, mining, highway deicing, acid
rain, improper well construction and maintenance, road salt).
The
following table shows a list of the potential groundwater contamination
sources:
Large quantities of organic compounds are manufactured and used by industries, agriculture and municipalities. These man-made organic compounds are of most concern. The organic compounds occur in nature and may come from natural sources as well as from human activities.
In
many locations groundwater has been contaminated by chemicals for many
decades, though this form of pollution was not recognized as serious
environmental problem until the 1980s.
A brief description of the contamination
sources follows.
Natural: groundwater contains some
impurities, even if it is unaffected by human activities. The types and
concentrations of natural impurities depend on the nature of the geological
material through which the groundwater moves and the quality of the recharge
water.
Groundwater
moving through sedimentary rocks and soils may pick up a wide range of
compounds such as magnesium, calcium, and chlorides.
Some
aquifers have high natural concentration of dissolved constituents such as arsenic, boron, and selenium. The effect of these natural sources
of contamination on groundwater quality depends on the type of contaminant
and its concentrations.
Agricultural: Pesticides, fertilizers,
herbicides and animal waste are agricultural sources of groundwater
contamination. The agricultural contamination sources are varied and
numerous: spillage of fertilizers and pesticides during handling, runoff from
the loading and washing of pesticide sprayers or other application equipment,
using chemicals uphill from or within a few hundred feet of a well.
Agricultural
land that lacks sufficient drainage is considered by many farmers to be lost
income land. So they may install drain tiles or drainage wells to make the
land more productive. The drainage well then serves as a direct conduit to groundwater
for agricultural wastes which are washed down with the runoff.
Storage
of agricultural chemicals near conduits to groundwater, such as open and
abandoned wells, sink holes, or surface depressions where ponded water is
likely to accumulate.
Contamination
may also occur when chemicals are stored in uncovered areas, unprotected from
wind and rain, or are stored in locations where the groundwater flows from
the direction of the chemical storage to the well.
Industrial: Manufacturing and service
industries have high demands for cooling water, processing water and water
for cleaning purposes. Groundwater pollution occurs when used water is
returned to the hydrological cycle.
Modern
economic activity requires transportation and storage of material used in
manufacturing, processing, and construction. Along the way, some of this
material can be lost through spillage, leakage, or improper handling.
The
disposal of wastes associated with the above activities contributes to
another source of groundwater contamination. Some businesses, usually without
access to sewer systems, rely on shallow underground disposal. They use
cesspools or dry holes, or send the wastewater into septic tanks.
Any
of these forms of disposal can lead to contamination of underground sources
of drinking water. Dry holes and cesspools introduce wastes directly into the
ground. Septic systems cannot treat industrial wastes.
Wastewater
disposal practices of certain types of businesses, such as automobile service
stations, dry cleaners, electrical component or machine manufacturers, photo
processors, and metal platters or fabricators are of particular concern
because the waste they generate is likely to contain toxic chemicals.
Other
industrial sources of contamination include cleaning off holding tanks or
spraying equipment on the open ground, disposing of waste in septic systems
or dry wells, and storing hazardous materials in uncovered areas or in areas
that do not have pads with drains or catchment basins.
Underground
and above ground storage tanks holding petroleum products, acids, solvents
and chemicals can develop leaks from corrosion, defects, improper
installation, or mechanical failure of the pipes and fittings.
Mining
of fuel and non-fuel minerals can create many opportunities for groundwater
contamination. The problems stem from the mining process itself, disposal of
wastes, and processing of the ores and the wastes it creates.
Residential:
Residential wastewater systems can be a source of many categories of
contaminants, including bacteria, viruses, nitrates from human waste, and
organic compounds.
Injection
wells used for domestic wastewater disposal (septic systems, cesspools,
drainage wells for storm water runoff, groundwater recharge wells) are of
particular concern to groundwater quality if located close to drinking water
wells.
Improperly
storing or disposing of household chemicals such as paints, synthetic
detergents, solvents, oils, medicines, disinfectants, pool chemicals,
pesticides, batteries, gasoline and diesel fuel can lead to groundwater
contamination.
When
stored in garages or basements with floor drains, spills and flooding may
introduce such contaminants into the groundwater. When thrown in the
household trash, the products will eventually be carried into the groundwater
because community landfills are not equipped to handle hazardous materials.
Similarly,
wastes dumped or buried in the ground can contaminate the soil and leach into
the groundwater.
source: lenntech.com
|
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Sunday, July 17, 2016
GROUNDWATER POLLUTION - Wastes dumped or buried in the ground can contaminate the soil and leach into the groundwater. Any forms of disposal can lead to contamination of underground sources of drinking water.
Sources of groundwater
pollution
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