The severity of groundwater pollution is of particular significance on account of the following:

· Its vulnerability to pollution ;
· The associated complexity in pollution source identification ;
· Limited feasible options for treatment of groundwater, all of which are cost prohibitive ;
· Complicated process in fixing geophysical boundaries ;
· Difficulty in prediction of movement ;
· Insufficient dilution ;
· Slow movement ;
· Lack of any natural cleansing capability ;

Moreover, in most of cases where Groundwater is observed polluted, the area is densely populated and as commonly seen, there is no immediate fresh water substitute available at such locations.

A variety of adverse impacts due to Groundwater contamination is possible - including effects on public health, the environment, agricultural productivity (e.g. due to increased salinity in irrigation water) and on the out put of industries requiring high quality water.

Until recently one of the major reasons for the critical status of Groundwater pollution is a common myth that groundwater is pristine i.e. potential contaminant percolating through the subsurface would adhere to the soil or be degraded by natural process and therefore would not enter or greatly affect Groundwater quality. Thus the Groundwater had been regarded as a safe and convenient depository for the waste and non-waste by-products, generated by the society. However, with the passage of time and increasing number of serious incidences, there is a growing concern of Groundwater pollution. Its impact can be appreciated by categorizing the type of contaminants usually observed in Groundwater.

Fig. 6 : Sources of Groundwater Pollution

 

a. Biological contaminants
Pathogenic biological organisms that have been found in groundwater include
· Bacteria
·Viruses (e.g. Entero-viruses and hepatitis)
· Parasites (e.g. Protozoa, worms and
   fungi)

The potential for bacterial contamination of groundwater depends on both the survival rate of the species and characteristics of the sub-surface eg. moisture content, pH and temperature. Bacterial contamination most commonly result from the introduction of human (or animal) fecal material usually when septic tanks or cess pools leak or over flow. The common disease associated with biological contaminants present in groundwater can be one or more of the following :

b. Inorganic Contaminants

The concentration of most bulk and trace inorganic contaminants found in groundwater varies by area and in many instances, over time . Some of the common inorganic constituents of groundwater and their impact are described in table-3.

c. Organic Contaminants

The organic substances that pose the greatest threat to the quality of groundwater are those that are relatively soluble, non-volatile and refractory. The main mechanism that influences most of these compounds from readily migrating water from land surface into aquifer system is 'adsorption in soil water zone'.

Apart from naturally occurring humic and fulvic acids, there are many complex organic compounds which result from anthropogenic activities and with-stand bacterial decomposition.

The most common pathway for organic compounds to reach groundwater is through excessive use of pesticides and herbicides and indiscriminate burial of their containers.
Some of the commonly observed organic compounds in groundwater are aldrine, lindane, methoxychlor, toxaphene , DDT, trichloroethylene, carbon tetrachloride, tetrachloro ethylene etc. Almost all the above compounds are known to promote/cause carcinogenicity and their severity depends upon the extent and scale of exposure.

d. Radionuclides

These result as waste from nuclear plants, nuclear weapon testing or use of radioisotopes in scientific laboratories medicine and industry.

The most commonly found radionuclides in groundwater is Radium-226. It results from specific geological conditions and hence classed as naturally occurring. The abundance of radioactive gas Radium-222 formed by the decay of Radium-226 can also be present in groundwater but has no appreciably adverse impact. However, it has been reported that continuous consumption of water containing Radium-226 at 5 pci/liter may cause between 1 to 3 cancer cases per year per million exposed persons.