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Environmental impact assessment and environmental management plan
When we talk about environmental impact , Refractory industries cannot be ignored as in 2007, when Dr. Hrushikesh Panda was at the helm of Forest & Environment Department, Tata Refractories Limited (TRL) at Belpahar and Indo Flogate Refractories Ltd (IRL) at Rourkela was accused of pollution. Orissa Pollution Control Board (OPCB) issued closure notice and the Chief Minister announced the closure of TRL and IRL in the floor of the House.(www.orissalinks.com,2007)
Salem in Tamil Nadu, South India, is the hub of basic refractory industry in the country(ex. Tata refractories Ltd(TRL)). Magnesite, the chief raw material for basic refractories as well as calcined Magnesia, is being mined from three large and several small mines located in Salem. The ultramafic complex of Salem spreads over an area of 30 km and is known as the Chalk Hills region. It is the repository of both refractory and non-refractory grades of magnesite.
The deposits occupy numerous N-S trending small and moderately high hillocks (ranging in height from 5m to 70m from the mean ground surface). In addition to magnesite, dunite, one of the host rocks of mineralisation, is also being mined. Dunite which contains about 45% MgO, is mainly used as a flux in steel manufacturing. It is used as a refractory in brick form and in bulk form.
Method of mining
Complete mechanization of mining operations is not implemented in any of the mines because of the vein type mineralization. At present, a combination of both manual and mechanized mining methods is in use and hence can be aptly called as ‘semi-mechanized’ method.
In semi-mechanized mining the mineralised zone is blasted by 83 mm diameter slurry explosives, charged in 115 mm diameter blast holes that are drilled using wagon drills. Bulldozers spread the blasted muck and magnesite lumps are collected manually. The leftover waste, comprising soil, dunite and peridotite of different grades of weathering are loaded into 35 MT capacity dump trucks using hydraulic excavators or wheel loaders. The waste is dumped at places ear-marked for spoil dumps on non-mineralized land. Fresh dunite, whenever encountered, is removed and stacked separately (Manoj, 2001). Hence, men working crow-bars and sledge hammers are a common site in these mines, where Heavy Earth Moving Machines (HMM) like wagon drills, dozers, dumpers and hydraulic excavators are deployed. The absence of distinct overburden and mineral beds coupled with hard formations necessitates the employment of men and deployment of machines, simultaneously
Environmental impacts of mining
Modern opencast mining involves a high degree of mechanisation of the operations. Deep hole drilling, blasting of formations and sizing by crushing of the mineral are essential activities in most large open cast mines. Heavy Earth Moving Machines (HEMM) are the essential features of all large open mines. Operation of HEMM, crushers and blasting causes environmental degradation from dust, noise and ground vibration.
Dust pollution
Mining environment is often encountered with major environmental pollution from dust. Drilling, blasting, haulage of HEMM, loading of ore/overburden by shovels, crushing and screening of ore and noxious fumes generated by explosives during blasting etc. lead to excessive production and accumulation of dust in the atmosphere. Excessive dust in the working environment can lead to pneumoconiosis, a general occupational lung disease, which depends on the quantity, quality and size distribution of air-borne dust, period of exposure and the susceptibility of the individual subjected to exposure. Specific names such as silicosis, asbestosis, and black lung disease have been used to indicate pulmonary diseases caused by dusts mainly composed of silica, asbestos, and coal respectively Dust can impede with the functioning of machines too. Engine life of machines, working in excessively dusty conditions, tends to be reduced. Efficiency of machines is also affected. Sensitive electronic parts of electronic equipment, especially the optical, sonic and heat sensors attached to automatic Fire Detection and Extinguishing Systems become less sensitive or malfunctional.
Agricultural crops cultivated near mining sites also are affected by dust deposited on the leaves. Crops like cotton and chilly are found to be affected by dust as the process of photosynthesis is interfered by partially obstructing the sunrays required for the process. This leads to a fall in the crop yield of about 20%. Spoil dumps, devoid of vegetation allows blowing hot winds to lift dust from the exposed surface of land (Krishnakumar & Manoj 1998).
Noise pollution
Noise emitted by machines in a mine during drilling, blasting, crushing and loading ranges from 64 dBA to 115 dBA-decibel A. The adverse effects are auditory and non- auditory on the health of the mineworker, the operating system of the mine and the physical objects.
Effects of vibration
Vibration is a reciprocating motion, which reverses itself twice every cycle. Vibration due to mining operations can be from three sources viz. tools and equipment in a mechanised mine, blasting of rock formations and movement of HEMM. Generally the vertical component of vibration is more severe. Below the 2 Hz.frequency, the human body responds as a single mass. Between 4 Hz. and 8 Hz. Considerable amplification of vibration is achieved and results in increased discomfort to the operators of hand held drills, dozer, shovel, tractor and dumper. Vehicle driven vibration can be detrimental to spinal health and cause digestive disorders to operators of the above equipments. Drivers’ steering ability, foot pressure constancy, reaction time, and vision are affected by continuous exposure to vibration. High frequency (above 20 Hz.) can cause head resonance. Frequency between 60 Hz. and 90 Hz. causes eyeball resonance. Intense, high frequency vibration of the hands (4 Hz. to 250 Hz.) may lead to nervous and circulatory damage known as ‘Reynauld’s Disease’.
One of the undesirable effects of rock blasting is ground vibration, which may result in structural damage. Ground vibrations are due to transmission of energy from explosive charge in waveform. These waves, called seismic or elastic waves depend on the elasticity of rocks. Some of the opencast workings are located near surface structures like residential buildings, schools, commercial buildings, hutments with large population etc. During rock blasting in a mine only about 20 % to 30 % of the energy released is utilized for rock fragmentation. The remaining energy is transmitted outwardly and can cause damage to surrounding surface structures (Arumugam & Makesh 1998) While structures may not show any damage at a peak particle velocity (ppv) of 10-50 mm/sec human response may show reduced comfort at 2mm/sec. Human response to blast vibration and air over pressure is a concern that received little attention while sufficient details are available on the human response and annoyance due to air craft noise, road traffic or industrial noise. Mostly the annoyance has been referred to as motivated by political and social reasons on the basis of immediate response to the blasts (Raina et al 2002).
Deforestation and loss of surface soil
Cleaning the surface of vegetation precedes any opencast mining operation. Felling of trees leads to changes in the weather pattern besides threatening the life of fauna living in it. It can lead to local increase in the diurnal temperatures in addition to losing aesthetic beauty. The humus rich surface soil is to be scraped off before planning a box-cut and drilling blast holes. The invaluable topsoil is sometimes transported to the spoil dumps and is lost forever due to burial under the consequently produced mining spoils which are largely infertile (Krishnakumar & Manoj 1998).
Environmental management plan
The systematic analysis of various pollution parameters has indicated that the environmental impacts of dust, noise and ground vibration are above the desirable limits and can adversely affect the mine workers in the long run. Consequent on these findings, the management adopted and implemented several corrective measures to minimise the impact. As a precaution to check dust pollution, systematic sampling and analysis of air inside the mine was initiated and emission of dust was minimised. The exposure of workers to breathable dust were limited to such extend that the limits are not harmful to their health. Dust levels during drilling were reduced by introducing wet drilling and providing dust extractors to wagon drills. Dust respirators were supplied to drillers and HEMM operators where the air-borne breathable dust could not be brought below 3 mg/M Haul roads and loading points were sprinkled with water and slopes of the spoil dumps were planted with tree saplings to prevent dust Control of noise in mines can be achieved by reducing the sound at source or by interrupting the path of noise. The best approach would be to control noise at the source. There are several general practices on controlling noise. They are designing of the machine, its proper installation, periodic maintenance, lubrication etc. Damping impact noise and noise insulation by sound absorbing materials and properly covering the machine with enclosure/ bonnet etc helps to control noise at source. Interrupting the path of noise comprises erection of acoustic barriers to prevent its propagation. Noise can be prevented from reaching surrounding places by creation of green belts around the mine complex. In addition to the noise reducing techniques the worker can be protected from noise by controlling the time of exposure of a worker to the noise and by providing earplugs and earmuffs to the men working under hazardous noise levels. For frequencies greater than 20Hz, the threshold limit of ground vibration (no damage level) for safety of structures has been found to be 50 mm/sec. (ppv- peak particle velocity). In case of frequency less than 20Hz the amplification of the maximum permissible limit of ground vibration or ‘safe value’ for the structures is 12.5 mm/sec. Major factors that control ground vibration are the type and quantity of explosive charge used, distance from the charge/blast site to the point of observation, geological parameters of the formation, physicomechanical characteristics of the rock that transmits the vibration and blast geometry including depth, inclination, spacing and burden of rocks (Arumugam & Makesh 1998). Use of safe maximum charge per delay, hole to hole delay, adoption of non electric (‘nonel’) initiation system, adoption of deck-charging, use of sequential blasting machine, effective muffling of the holes etc. were a few of the measures undertaken to minimise the ground vibration.