09 - PREVENTING POLLUTION OF SOURCES

is the introduction of harmful materials into the environment.

POLLUTION

These harmful materials are called

POLLUTANTS

EXAMPLES OF POLLUTANTS

• VOLCANIC ASH

• TRASH

• INDUSTRIAL RUNOFF

Although urban areas are usually more polluted than the countryside, pollution can spread to remote places where no people live. For example, pesticides and other chemicals have been found in the Antarctic ice sheet. In the middle of the northern Pacific Ocean, a huge collection of microscopic plastic particles forms what is known as the Great Pacific Garbage Patch.

POLLUTION as a Global Problem

the release of substances into subsurface groundwater or into lakes, streams, rivers, estuaries, and oceans to the point where the substances interfere with beneficial use of the water or with the natural functioning of ecosystems.

WATER POLLUTION

a pipe or channel (e.g. discharge from an industrial facility or a city sewerage system)

POINT SOURCE

easier to control than dispersed sources, because the contaminated water has been collected and conveyed to one single point where it can be treated.

POINT SOURCE

a very broad unconfined area from which a variety of pollutants enter the water body (e.g. runoff from an agricultural area)

DISPERSED SOURCE

• difficult to control

• continue to cause a large fraction of water pollution problems

DISPERSED SOURCE

WHAT ARE THE COMMON WATER POLLUTANTS

• DOMESTIC SEWAGE

• SOLID WASTE

• TOXIC WASTE

• SEDIMENT

• HEAT

• PETROLEUM

Several possible ways by which pollution and contamination of water sources can happen:

• INDUSTRIAL / COMMERCIAL POLLUTION

• MUNICIPAL AND RURAL POLLUTION

• PRIVATE POLLUTION SOURCES

• Many rivers in the country are already unsuitable for use in potable water schemes due to this pollution.

• Groundwater sources were once considered safe from contamination due to overlying layers of earth, but now many wells which are not properly protected have been found to be contaminated by surface water pollutants.

INDUSTRIAL / COMMERCIAL POLLUTION

POLLUTION SOURCE - POSSIBLE CONTAMINANTS

• Open well casing allowing animal or human waste to pollute the casing/shallow well directly

• Lack of sealing around the casing (annular space) allowing unfiltered surface water to drain directly into the filter setting

• Oil or chemical spillage seeping down (1 liter of oil can make 20 m3 of water undrinkable)

• Over-fertilization of fields

PRIVATE POLLUTION SOURCES

• The annular space between the borehole and casing provides an open pathway for contamination from the surface or from poor quality aquifers intersected by the bore hole before this reaches the desired aquifer.

• The annular space must be filled up with grout to protect the aquifer.

• The grout consists of cement and water plus bentonite to reduce shrinkage.

• A reinforced concrete well slab at the well top is also important to protect the well.

FORMATION SEALING OF DRILLED WELLS

• The top of the casing must extend approximately 0.3 m above the surface of the ground/floor and be watertight with a tight sanitary well seal where the pump connection enters the well.

• The seal must close all openings for riser mains, cables and monitoring equipment.

• Any vent pipe should be screened to prevent entry of insects, snakes and the like.

• The ground level around the well top must be sloping away in all directions from the well to prevent entry of surface runoff.

SANITARY SEALING OF DRILLED WELLS

• The dug diameter of the well is only a little larger than the concrete culvert and the lower annular space is usually filled up by cave-ins.

• The annular space around the culvert should first be filled by grout up to the water level or at least up to at 2 meters from the surface.

• The balance of the annular space can be filled up with clay up to the concrete slab.

FORMATION SEALING OF DUG WELLS

• Spring water suitable for drinking is normally located on a hill or mountainside. The spring water is collected by placing perforated drains in the aquifer.

• After installing these pipes, the aquifer should be enclosed in clay so that polluting surface water will not infiltrate.

• In constructing the spring box, all surfaces in connection with clay should be sealed with cement grout.

FORMATION SEALING OF SPRINGS

If the water source is safely protected against surface contamination but is still supplying polluted water, there are 2 possible major causes of pollution:

1. The groundwater is infiltrated by contaminated ground water.

2. The water source is contaminated by a septic tank or leachate water from a dumpsite.

When large quantities of rock containing sulphide minerals are excavated from an open pit or opened up in an underground mine, it reacts with water and oxygen to create sulphuric acid.

ACID MINE DRAINAGE

When the water reaches a certain level of acidity, a naturally occurring type of bacteria called _________________ may kick in, accelerating the oxidation and acidification processes, leaching even more trace metals from the wastes.

ACIDITHIOBACILLUS FERROOXIDANS

• The acid will leach from the rock as long as its source rock is exposed to air and water and until the sulphides are leached out – a process that can last hundreds, even thousands of years.

• Acid is carried from the mine site by rainwater or surface drainage and deposited into nearby streams, rivers, lakes and groundwater.

• AMD severely degrades water quality, and can kill aquatic life and make water virtually unusable.

ACID MINE DRAINAGE

• Heavy metal pollution is caused when such metals as arsenic, cobalt, copper, cadmium, lead, silver and zinc contained in excavated rock or exposed in an underground mine come in contact with water.

• Metals are leached out and carried downstream as water washes over the rock surface.

• Although metals can become mobile in neutral pH conditions, leaching is particularly accelerated in the low pH conditions such as are created by Acid Mine Drainage.

HEAVY METAL CONTAMINATION & LEACHING

• This kind of pollution occurs when chemical agents (such as cyanide or sulphuric acid used by mining companies to separate the target mineral from the ore) spill, leak, or leach from the mine site into nearby water bodies.

• These chemicals can be highly toxic to humans and wildlife.

PROCESSING CHEMICALS POLLUTION

• Mineral development disturbs soil and rock in the course of constructing and maintaining roads open pits, and waste impoundments.

• In the absence of adequate prevention and control strategies, erosion of the exposed earth may carry substantial amounts of sediment into streams, rivers and lakes.

• Excessive sediment can clog riverbeds and smother watershed vegetation, wildlife habitat and aquatic organisms.

EROSION AND SEDIMENTATION