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.

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