Page 167 - Soil Degradation, Conservation and Remediation

156 6 Soil Pollution

were old and unlined. The groundwater in the perimeter of the site contains volatile
organic compounds (VOCs) (i.e., benzene, toluene, and chlorinated hydrocarbons)
and heavy metals (i.e., arsenic, barium, cadmium, chromium, mercury, and nickel).

Leachate collected from the landfill contains VOCs and heavy metals. Potential
pathways of exposure to these contaminants included drinking contaminated
groundwater and surface water, as well as accidental ingestion of contaminated soil

and sediments. Modern landfills are lined with inert linings, but this does not exclude
the danger. These materials get damaged in the long run.

6.2.1.7 Open Dumping of Municipal Wastes

In most of the cities of South Asia, open dumping is the most preferred method

for the final disposal of solid waste. Even though government and municipalities are

already working to develop the sanitary landfill sites in few urban areas, open dump-
ing still remains the cheapest and most effective solution to get rid of the mounting
garbage. These open dumpsites in the course of time become haven for scavengers
(birds, animals, and human). Open dumping is the simplest and inexpensive method
on trash disposal, but at the same time, it the easiest way of polluting air, water,
and soil. Wastes are directly disposed of in water bodies or land. These wastes are
usually mixed wastes which contain several organic, biodegradable, and persistent
organic pollutants and heavy metals.
The chief disadvantages of open dumping are:
• Open dumping spreads foul odor.

• Open dumping provides the area for germs, viruses, fungi, bacteria, and vermin
to breed, so it becomes the source of many diseases.

• Open dumping can contaminate the groundwater with inorganic and organic
pollutants.
• Open dumping can contaminate the soil by leaking organic and heavy metal

pollutants.
• Open dumping is prone to cause slide down.

• Open dumping wastes occupy an unnecessarily large area.
6.2.2 Sewage Sludge

Sewage sludge is usually a liquid mixture, composed both of solids and of dissolved
organic and inorganic materials. The water is separated from the solid part by a number
of treatments before it is environmentally safe for discharge into streams or lakes.

The solid residue left is often discharged on open dumps, landfills, incinerators, or
composted for agricultural use.
Most wastewater treatment processes produce sludge. Conventional sewage
treatment plants typically generate a primary sludge in the primary sedimentation
stage of treatment and a secondary, biological sludge in final sedimentation after the