3.4.3 Cases of UG Mining
Many valuable minerals including some metals like gold,
building stone, diamond, salt, potash etc are mined through UG mining, such mining
requires lesser amount of excavation to reach the deposit and may be some additional
excavation that forms some dump of gangue mineral or tailing. However land damage
created by these are less in comparison to those caused by OC mining; main land
damage by of UG mining is mainfest if there is subsidence.
In case of GW withdrawal it is apparent that safe yield cannot exceed the long-time
mean annual water supply to the basin. Withdrawals exceeding this supply must
come from storage within the aquifer. Such permanent depletion is often referred
as "GW mining" in analogy to mining of minerals, because as, a mineral once mined
cannot get re-generated, just similarly withdrawal of water if conducted up to
this extent, the open space created in the aquifer cannot be recharged again if
the aquifer compaction is manifested above as subsidence (as detailed in section
3.3.3). Large scale withdrawal of GW from Kolkata and Howrah cities had resulted
in sharp decline of piezometric level in the areas which is inviting hazards of
land subsidence. The estimated amount of subsidence ranges from 3.33 m per yr
to 13.78 m per yr. Though clearly visible evidences of land subsidence was not
recorded, it has been suggested that these might spell danger in the future owing
to continuous overpumping of the aquifer (Sikdar et.al.1996).
3.4.4 Cases of OC & UG mining combined
Decrease of green cover over mining areas is a known fact.
To report a few among the studies conducted in the line mention may be made of
Jharia coalfield (Ghosh, 1989), Raniganj coalfield (Chatterjee & Ghosh, 1994),
Singrauli coalfield (Sekhar, 1996), Makum coalfield (Dutta 1997). Each of these
studies have revealed that forest cover has depleted in these coal mining areas.
This is happening inspite of a country-wide attempt, including the coal mining
sector, to increase the forest cover of India.
An attempt to search out the causes behind this makes one to recall the views
of Sharma (1982) and Banerjee (1982). Sharma (op.cit) reported that India is loosing
on an average 600 million tonnes of topsoil per year. According to some estimates
made by the Ministry of Agriculture in March, 1980, out of India's total land
area, as much as 175 million ha are subject to environmental problems, the situation
is fast deteriorating, further over 150 million ha of land are subject to serious
water and wind erosion. Banerjee (op.cit) mentioned that in case of OC coal mining
the actual land-area damaged is 10 to 20 times the area directly used for mining.
To list the causes of this, he mentioned about siltation in streams and ponds,
disfiguring of water table, high velocity runoff and withering of vegetations
as the only few. It is very obvious that afforestation activity on these lands
can't give good survival or growth unless special care is made to make up the
damage and restore land quality.
To view towards damage to water resources in mining areas, it is an established
fact that mining damages surface and ground water resources. To report a few among
the studies conducted in the line, mention may be made about the studies of Ghosh
(1993) and Chatterjee & Ghosh (1993). Through such studies it was revealed (Ghosh
op.cit) that in Jharia coalfield the relative heights of ground water level at
different points were so different at close intervals that the water table appeared
to be too uneven to be possible in a sedimentary terrain (Ghosh op.cit.). Otherwise,
it can be told that no specific plane representing the water table could be searched
out in the area. Another study in Raniganj coalfield (Chatterjee & Ghosh,op.cit)
revealed that in the period between 1965 to 1985 the region was suffering a lowering
of water table on an average @ 2mm per yr. That the situation is deteriorating
even after that, is proved by the fact that some parts of Raniganj coalfield are
declared drought-prone areas, and suffer from severe water scarcity in every summer.
Further, according to Ruthermund et al (1980) the Jharia coalfield, 100 years
ago, was mainly a forest-cum-agricultural land, but now it will be difficult for
any one to search out any real forest in this field. This is because the afforestation
activity conducted here has not been effective, in all probability due to non-availability
of topsoil and water.
An analysis of the mining and reclamation activities in coalfields revels that,
as coal occurs in close association with sandstone and shale, which occasionally
contains aquifer, whenever the aquifer occurs above the coal seam it gets excavated
out together with the OB. When coal exploitation starts, water from the remaining
parts of the aquifer flows continuously into the excavation site and requires
continuous pumping out to facilitate mining. This creates firstly a cone of depression
in the water table (WT) and gradually a regional lowering of WT. These effects
have been identified in Ghosh (1993) and Chatterjee & Ghosh (1993).
These quarries while attempted to reclaim, is generally filled-up by materials
from OB dumps, which are large pieces of sandstone and shale with high percentage
of interspaces. These backfilled quarries when attempted to green, topsoil and
water are applied on these. A major part of these topsoil and water goes down
rapidly, through the interspaces of the filling material, to the base of the quarry,
far beyond the reach of the roots of newly planted saplings on the land.
The excavated out aquifer is lost for ever because the impermeable layer below
the aquifer, that was holding the water in the aquifer in undisturbed condition,
is never regenerated (Fig. 3.3). The cumulative effect of all these have been
studied in Jharia coalfield as has been reflected in its land-use change through
a period between 1925 to 1993 (Ghosh 2000a).
It is a time to think twice whether such loss of topsoil and water to deep underground
and hence loss of land quality are really assessed in the EIAs conducted. Whatever
hydrogeological modeling, or water-budget analysis or even hydrogeological studies
are conducted sometimes to supplement EIA, these never record such loss of aquifer.
Even if the realization ever comes into the assessors' mind, any EMP does not
take up any activity plan to regenerate the excavated out aquifer. Hence, there
remains very remote chance that afforestation on such lands will be a successful
programme.
The afforestation job is generally given to forest department. Mining companies
spend for the purpose @ of about Rs 3.00 Lakhs/ha for getting the land green with
saplings upto certain height, upto certain survival rate, upto certain number
of years. After their responsibility is over, it is considered that the plants
will survive on their own. The fact is, for such plantation topsoil is taken from
somewhere else, thus it grows greenery at one place at the cost of greenery growing
potentiality at some other place from where the topsoil is taken. Further, after
the forest department withdraws the responsibility, the plants start withering
because of not getting sufficient topsoil and water at the root zone. A major
part of topsoil that was used for plantation has, by this time, gone down to the
base of the backfilled quarry. Thus topsoil is lost once by getting mixed with
subsoil and OB during excavation and again by going down to quarry base through
open spaces of the filling material. It is not unknown to any environmentalist
or an ecologist how worthy this topsoil is, what a long time is required for its
generation through natural process, and hence how serious is its cost and how
intangible is the loss.
A detailed study on LU of JCF through a time span from 1925 to 1996 has been provided
in the previous monograph of this series (Ghosh 1999a). The total finding is that
the LUP in the field in going on suffering serious changes. Damage was maximum
by the mining under private sector. Some benevolent approach was there after nationalisation
of the coal mining industry in India. It shows some indication of increase in
the amount of green cover in 1980s. However, implementation of Land Use Management
Plans (LUMPs) could not be made notably effective due to some cause or other (detailed
in chapter 4 and 5 of this monograph). Further, nothing could be commented on
the matter firmly because of several facts. The most notable one was
* non availability of systematic data and
* not following any definite LUPg procedure.
LU data had been generated wherever and whenever required; and LU classes have
been decided differently in different cases based upon the requirement e.g. in
some cases it is reported that fire protection was done over this-much amount
of land, or this-much amount of land was greened. No systematic dependable data
is available to know really how much land could sustain that green cover upto
what extent of time generating what percent of green cover. Some similar comments
have been made by scientists working on LU over the globe, as has been detailed
in chapter 2. Hence demand of the situation in MAs is
* to decide some definite LULC classes, under which data will be collected from
MAs
* to collect and report data on some regular intervals so that it can be used
for the purpose of monitoring.