5. Technicality of Implementation of LUMP
5.0 Introduction
Implementation of LUMP requires land reclamation as per
LUMP. This requires suitable reclamation techniques. Further, implementability
of the LUMP obviously depends upon its technical feasibility. Hence a provision
has been kept in the suggested LUPg system for assessing technical feasibility
of developing any suggested scenario through a specific reclamation activity.
In this reference it appears justified to detail some reclamation technologies
to be used to mitigate the environmental impacts of mining on land and LU together
with technical feasibility of these reclamation technologies.
Land reclamation in mining areas concerns mainly reclamation of quarries, solid
waste dumps and subsided areas. The reclamation method to be followed depends
upon the depth (& real extent) of the quarry, geology of the quarry site and
the volume of OB/spoil available. Thus the matter has been discussed next following
the different possible conditions.
5.1 Shallow pit without topsoil/solid waste
There may be shallow pits without any (or much) of top
soil or OB or SP as in case of clay quarries or other shallow deposits. The
best way to reclaim these is to backfill with suitable soil or soil substitutes,
greenmulch, compost etc. and renewed for agriculture. Some abandoned pits resulting
from exploitation of float ores in the neighbourhood of Mansar mine of MOIL
have been refilled by OB and reclaimed by spreading topsoil stored earlier (Anon,
2000, pp.10).
5.2 Deep quarry without solid waste
In case the quarry is deep without OB or any other form
of solid waste or SP or has not been back filled due to some cause or other,
the most economic way to reclaim the quarry is to form a lake. These generally
form perennial water bodies, as in most cases such OC mines behade aquifers.
These hence form a perennial water source for the region around and helps compensating
water scarcity due to mining, (if any such is caused). These can be dressed
to generate fishery, swimming pool or any recreational facility to form an economic
resource even (Nelson et al. 1982). In Indian condition quarries from limestone,
manganese, dolomite iron ore etc. are best suitable for such reclamation.
However, all quarries cannot be turned into lakes because that will cause huge
number of water bodies disturbing the balance in the land-water-ecosystem in
mining areas and will keep OB/SP-dumps unused, to be reclaimed separately. Hence,
side by side, there should be an attempt to restore the original topography
as far as possible, the final suggestion should however follow from LUMP.
5.3 Deep quarry with solid waste
If it follows from LUPg that a big quarry is to be reclaimed
by backfilling, it is better to decide it at the premining stage itself; and
the workplan should be chalked out to decide whether the quarry is to be backfilled
by OB generated at the neighbourhood or by any other solid waste (SP). In such
backfilling care should be taken on two points:
* Filling should be made as compact as possible, using dumper or heavy earth
moving machinery (HEMM) after each 2.5 to 3.5 meter, and finer compaction should
be made by rollers, otherwise the openspace below the land generated by backfilling
may disturb its usability. Even some layers of finer solid waste (if locally
available) may be put in intermediate positions.
* The newly developed land should match with surrounding topography, keeping
in mind that such filling materials generally do not have soil or soil nutrient.
These are to be covered by 25cm to 40cm of fertile soil or soil substitutes
e.g. green mulch, organic compost etc. and then can be used for plantation of
local hardy species. After long period of plantation the land will get compacted
and come back to original condition.
* Such backfilling will help using-up huge volume of OB and SP material also.
If it happens that the excavation takes out the total thickness of aquifer together
with its base, simple backfilling cannot regenerate the impermeable base of
the lost aquifer and the aquifer is lost for ever (Fig. 3.3). While the land
generated by such backfilling is attempted for biological reclamation, i.e.
to generate a sustainable greenery, common activity is to blanket the total
land by topsoil (transported from somewhere else) or make pits of optimum size
on the land and fill these with similar good soil, then greeneries are put on
it.
Such activity grows greenery on the land with low survival rate because the
abandoned quarry filled with OB material retains very high porosity and permeability
(even if mechanically compacted), so that the topsoil put on it whenever receives
any amount of water, the total soil together with water goes down rapidly upto
the base of the backfilled quarry, far beyond the reach of the saplings planted
on the land. This results virtually to loss of topsoil. The saplings cannot
get natural water from underground as the aquifer has already been excavated
out.
Further, whatever greenery grows on such land, it grows at the cost of greenery
growing potentiality of some other piece of land from which the topsoil was
taken. The problem can be alleviated by regenerating some aquifer at optimum
depth and searching out some substitute of topsoil. The procedure for these
and hence the system to be followed for backfilling of such abandoned quarries
has been detailed in Fig. 5.1 and in the flow chart Fig. 5.2 (Ghosh 2000c).
Information on rainfall becomes specially required if the quarry is not in sedimentary
terrain or if the information on pre-mining water table/ aquifer can not be
made available. With reference to the flow of activities required for the purpose
(Fig. 5.2) to decide the position of the impermeable barrier to be formed, one
has to know the depth (dm) and thickness Tm of the aquifer to be re-generated
(or generated freshly).
The best means to decide this is by knowing the geology of the area. To plan
any mining project it needs drilling in the region as a pre-requisite to confirm
the deposit. Such bore-hole logs (or drill-cores if available) may be analysed
thoroughly to know the depth and thickness of the aquifer lost or to be lost
by excavation. The impermeable layer should be made at a calculated depth such
that the lower boundary of the porous and permeable layer (made by the filling
material) be in continuity of the base of the previous aquifer.
If due to some cause (stated above) or other, such information is not available,
an alternative procedure of calculating the depth and thickness of aquifer to
be constructed may be as detailed next: