Effect of excavation on water resource
Deeper OC excavation on land or UG digging causes damage
to aquifer and the WT to sink locally, often drastically, resulting in the drying
up of wells and springs of the neighbourhood; at least the perennial ones may
be altered to seasonal. In case of contour strip mining, subsequent land slides
may expose passages of UG water, thus depriving the springs which were being supplied
from the source. Some such situation has deprived the Sahasradhara seepage of
Mussoorie hills, altering land quality of the region.
Overburden (or solid waste) dumping
Amount of OB (or gangue) generated depends upon the mode
of occurrence of the deposit. The huge mass of material which lies above the mineral
deposit needs excavation during OC mining. These are left over the land in the
form of OB or spoil (SP) dumps. These occupy large amount of land, which loses
its original use and gradually gets its qualities degraded. If uncared, these
create greater damage to the surrounding lands by several processes :
a. The dumped materials gradually roll down to the surrounding land, disturb the
men, materials and LUs there by hurting these by big pieces of OB/SP, covers a
major part of the land and degrades its quality, by its physical presence as well
as by its chemical composition.
b. The OB/SP may contain materials soluble in slightly acidic water (as in acid
rains). These may get spread over the surrounding land and poured in the receiving
water bodies. This may result water pollution and more land degradation in turn
producing acidic, alkaline or saline land by direct wash-off-running or due to
using the polluted water for irrigation.
c. As the dump is generally loose, fine particles from it become highly prone
to blowing by wind. These get spread over the surrounding plants and disturb their
growth, specially sprouting of fresh leaves.
d. The dump is generally loose, highly prone to rain-washing, weathering and erosion.
Fine particles generated out of these get spread over the surrounding land and
water bodies. Thus the water bodies get their turbidity increased, increased siltation,
decreased water storage capacity, gradual drying, following to land degradation
as detailed in Fig. 3.1 & 3.2. The land which receives eroded and washed fines,
gets covered by these, which also damage the land's infiltration potentiality
and greenery growing potentiality.
Pumping out of mine water
Any excavation may damage aquifer in the region and invite
huge volume of water in the excavation site. This necessitates pumping out of
mine water and several consequences on land as detailed below.
* Pumping out of huge volume of water from certain points may create local lowering(s)
of water table (WT) in the form of cone(s) of depression (Fig. 3.4). This may
ultimately result regional lowering of WT and aggravate the process of land degradation
through a process detailed in Fig. 3.2. The matter of lowering of WT has been
detailed in section 3.4.4.
* This pumped out water, if poured on land, provides a chance of additional evaporation
and disturbs the natural hydrologic cycle and hence invites lowering of WT and
hence land degradation.
* The pumped out water if poured on water bodies flowing off the region, the water
flows away and goes out of the region causing depletion of water resources, hence
regional lowering of WT and hence land degradation.
* The pumped out water may contain any soluble mineral brought from the rocks
at its original residence at depth (Hammer & Mackichan, 1981). This when poured
over a land or a water body or used for irrigation, the receiving body gets polluted.
Haulage, storage & transportation
Excavation is followed by haulage, storage and transpiration
of excavated materials. All these activities spread dust and thus create air pollution,
water pollution, damage to greenery in the surroundings and hence land degradation
due to spreading of the fine rock and mineral particles.
Treatment and use
These are done through various processes depending upon
chemical character of the ore. Most of such treatments produce some byproducts
which, if not used-up, form a huge dump of waste creating land degradation just
as the OB dumps. Seriousness of the matter may be reaslised from the following
facts :
* As per Valdiya (1987, pp.149) by A.D. 2000 India will be mining annually 7 Mt
of copper ores. The yearly production of tailings will amount to 36,50,000 m3
or nearly 40 million m3 in 20 years. The problem of disposal of the tailings would
be equally acute.
*Many valuable minerals e.g. gold, diamond etc. are mined from even two miles
depth. Tailings separated from the ores excavated with these are dumped in unsighty
piles. Also dust and water coming out of these are sources of land degradation..
* Ore of Aluminium is bauxite, which contains iron and occurs in association with
ferruginous bauxite. The bauxite needs treatment to get aluminium. It has been
observed that, on an average, treatment of 1 ton of bauxite releases as byproduct
about 0.5 ton of red mud (Sharma, 1982). It has been estimated by some environmental
geologists that, by 2000 AD India will produce 10 million m3 of red mud. Which
on spreading can disturb physical and chemical quality of huge amount of land,
(the actual amount of land disturbed will however depend upon topography).
* At Kudremukh mines in Western ghats region more than 13 million ton of dominantly
siliceous tailings are produced per year (Valdiya, op.cit.).
* At lead-zinc mines the spoils produced are highly toxic, particularly if the
metal content is more than 1,000 ppm. ã If water gets polluted, it is able enough
to create degradation of land on which it is applied. Cases of river pollution
due to mining and ancillary activities are common. Mention may be made of Bailadila
iron ore mines site at Kirandih in Bastar districts MP. More than 12 million ton
of ore fines had accumulated here in a time span of ten years, 1977 to 1987 (Valdiya,
op.cit.). The rains washed the wastes down stream turning the river near about
red .
* The Tiri stream, which drains the lead mines at Zawar in Rajasthan, was noted
to be polluted for 15 km downstream. As a result of lead and zinc pollution, not
only the aquatic fauna was adversely affected, even the timber plants and other
vegetation had registered perceptible decline. A similar situation was discernible
around Jhammarkotra phosphorite mines near Udaipur and in the Khetri copper mines
in Rajasthan (Valdiya, 1987).
* The magnesia dust at Jhirauli and Chandak mines generated by calcination plants
had caused disappearance of a few species of shrubs like Beriberis (Pant, 1982.
* Mining, handling and dealing of radioactive minerals bear chances of spreading
of radioactive emanations on all matters in the surroundings. This may disturb
greenery and land characteristics of the region inviting land degradation.
* In central Florida large scale phosphate mines exist. The rocks from the mines
are processed to produce phosphoric acid. Further phosphogypsum is produced as
a by-product of processing phosphate rock to produce fertilizer chemicals. For
each ton of phosphate rock processed approximately 0.5 tons of phosphogypsm is
produced. The standard method of disposal of this phosphogypsm is to form stacks
on land.
The best management of such wastes is to use-up those for
any purpose suitable to its physical and chemical character. An example of management
of such waste can be obtained from a very old case detailed next.
* In early mining of iron-ore from the Adirondack mountains, it was noted that
the ore was associated with ilmenite (TiO2). The rock that contained a high concentration
of ilmenite was being discarded to form huge tailings piles, until after world
war II when new uses of titanium in paints were discovered, so that the old tailings
were reworked for ilmenite and partially used up. (Coates 1981, pp. 20)
Some other uses may be as road material, filling material (as detailed in chapter
5, for aquifer regeneration), or in ripraps or gabion cages (Valdiya, op.cit.)
for erosion control on slopes, or even for landscaping for beautification of a
land depending upon the physical and chemical characters of the waste.