4. 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
5. 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
6. 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
7. 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
8.
9. 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
10. Principal sources and causes of pollution with
regard to their occurrence:-
a. Municipal sources and causes
b. Industrial sources and causes
c. Agricultural sources and causes
d. Miscellaneous sources and causes
11. 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
12. 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.
13. c) Solid wastes
Sources: Landfills
Results:
Leachate from landfills can pollute groundwater
Leachate include iron manganese, nitrate, trace
elements etc.
14. 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
15. 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
16. 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
17. 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
18. 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
19. 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
20. 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
21. 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
22. 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
23. 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.
24. 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
25. 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
26. 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
27. 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
28. 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
29. 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
31. 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.