groundwater contamination
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GROUNDWATER CONTAMINATION
GROUP MEMBERS
NAMITHA M.R. 2011-02-028NIDHIN J.K. 2011-02-029SAHLA N. 2011-02-030
POLLUTION vs.
CONTAMINATION
Pollution signifies any degradation of natural ground water quality while contamination is reserved for pollution that constitutes a hazard to human health
POLLUTION OF GROUND WATER
Defined as the artificially induced degradation of natural groundwater quality
Pollution can impair the use of
water and can create hazards to public health through toxicity or the spread of disease
In contrast with surface water pollution, subsurface pollution is difficult to detect and control, and may persists for decades.
Efforts are increasing to prevent, reduce and eliminate water pollution
Pollution in relation to water use
The possible pollutants in groundwater are virtually limitless
The sources and causes of ground water pollution are closely associated with human use of water
Ground water contamination scenarios :-
a. Point sources : Storage tanks, landfills, pipeline releases etc.
b. Nonpoint sources: Agricultural activities
Contamination originates from the disposal of groundwater following its use for a wide variety of purposes
SOURCES AND CAUSES OF POLLUTION
All sources and causes of pollution can be classified as to their geometry
a. Point sources : Originates from a single location
b. Line sources : Predominantly linear arrangement
c. Diffuse sources : Occupies an extensive area
Principal sources and causes of pollution with regard to their occurrence:-
a. Municipal sources and causesb. Industrial sources and causesc. Agricultural sources and causesd. Miscellaneous sources and causes
1. Municipal sources and causes
a) Sewer leakage Sources: Poor workmanship,
defective sewer pipe, breakage by tree roots, ruptures from heavy loads, earthquakes, loss of foundation support etc.
Results: Introduce high concentrations of BOD,COD, nitrate, organic chemicals, bacteria and heavy metals into groundwater
b) Liquid wastes Sources: Domestic wastes,
Disposal wells industries, storm, runoff etc.
Results: Introduce bacteria, viruses, trace elements and heavy metals, inorganic and organic chemicals etc.
c) Solid wastes Sources: Landfills
Results: Leachate from landfills can pollute
groundwater Leachate include iron manganese,
nitrate, trace elements etc.
2. Industrial sources and causes
a) Liquid wastes Sources: Industrial waste water
discharged into pits, ponds, lagoons etc.
Results: Introduction of hazardous and toxic industrial wastes into the groundwater
b) Tank and pipeline leakage Sources: Gasoline stations, fuel oil
tanks, petroleum and petroleum products from industrial pipelines and tanks
Results: Immiscible liquids like oil and petroleum, liquid radioactive wastes etc. reaches the water table and pollutes the groundwater
c) Mining activities Sources:- Coal, phosphate and uranium
mines Stone, sand and gravel quarries
Results: Low pH, increase in iron, aluminium and sulphate content in the soil
d) Oil-field brines Sources:- Substantial discharges of
wastewater in the form of brine Constituents of brine include
sodium, calcium, ammonia, boron, chloride, trace metals and high total dissolved solids
Results: Groundwater become saline
3. Agricultural sources and causes
a) Irrigation Return Flows Sources: Irrigation return flow drains
to surface channels or joins the underlying water
Results:- Increases salinity of groundwater Increases the amount of
bicarbonate, sulphate, chlorides, nitrates etc. in the groundwater
b) Animal wastes Sources: Wastes from slaughter
houses
Results:- The natural assimilative capacity of
the soil become overtaxed Salts, organic loads and bacteria are
transported into the soil Nitrate-nitrogen is the most
important persistent pollutant that may reach the water table
c) Fertilizers and Soil Amendments Sources: Leachate of phosphate and
potassium fertilizers Leachate of soil amendments like
lime, gypsum and sulphur
Results: Increases salinity of soil
d) Pesticides, insecticides and herbicides
Sources: Leachate of pesticides, insecticides and herbicides used in agricultural fields
Results: Causes serious consequences in relation to the portability of water
4. Miscellaneous sources and causes
a) Urbanisation Groundwater pollution can occur
both in rural as well as urban areas and is affected by differences in chemical composition, biological and chemical reactions, density and distance from discharge areas
b) Spills and Surface Discharges Causal activities includes leaks from
pipes and valves, uncontrolled waste disposal, intermittent dumping of fluids on ground, flushing hazardous and flammable liquids into water etc.
Washing aircraft with solvents and spills of fuel at airports can form a layer of hydrocarbons floating on the water table.
c) Stockpiles Solid materials are frequently
stockpiled near industrial plants, construction
site etc.
Precipitation falling on unsheltered stockpiles causes leaching of heavy metals, salts and other pollutants into the groundwater
d) Septic tanks and Cesspools Septic tank: A watertight basin
intended to decompose the domestic sewage and to
discharge this into the biologically active zone
of the soil mantle through a subsurface percolation system
Cesspools: large buried chamber with porous walls designed to receive and percolate raw sewage
e) Roadway de-icing Results from the application of de-
icing salts to streets and highways in winter
Sodium chloride and calcium chloride are generally used
Salt reaches the groundwater in solution after spreading on roadways and also from stockpiles
g) Interchange through wells Because wells form highly
permeable vertical connections between aquifers, they can serve as avenues for groundwater pollution where inadequate attention is given to the proper construction, sealing or abandonment of wells
f) Saline water intrusion Salt water may invade freshwater
aquifers to create point or diffuse pollution sources
Polluted surface water bodies that contribute to groundwater recharge become sources of groundwater pollution
g) Surface water
Attenuation of pollution Pollutants in groundwater tend to
be removed or reduced in concentration with time and with distance travelled
The rate of pollution attenuation depends on the type of pollutant and on the local hydro geologic situation
Mechanisms involved include:-
Filtration
Sorption
Chemical processes
Microbiological decomposition
Dilution
conclusion The principal sources and causes of
groundwater pollution can be categorized- municipal, industrial, agricultural and miscellaneous
With the growing recognition of the importance of underground water resources, efforts are increasing to prevent, reduce and eliminate groundwater pollution.
THANK YOU
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