Environmental risk of mining - Environmental Deterioration and Contamination: Problems and their Management - page 115

was due to multiple failures involving a well integrity failure, followed by a loss of
hydrostatic control of the well, then the problem of controlling the flow from the
well with the blowout preventer, which allowed the release and subsequent ignition of
hydrocarbons (BP, 2013).
A novel combination of hydraulic fracturing (fracking) and directional drilling
is opening up new horizons in oil and gas production. This technology enables the
production of hydrocarbons from non-porous (shale) formations which were believed
to prohibit oil and gas from being extracted from them economically. In addition
to extremely high pressures used to fracture the layers, fracking uses a number of
aggressive chemicals to help remove oil and gas particles from the rock. All these
features (may) have environmental implications in as much as fracking liquid and the
chemicals contained in it may come into contact with drinking water resources and
contaminate them. Nevertheless, the huge economic potential attributed to fracking
due to its enormous effect of increasing oil and gas production suggests that it will
rapidly spread in the not so distant future.
2.2 Coal, ore and nonmetallic mineral mining and quarrying
Mining operations within the above three sectors can be classified into three levels:
extraction of the material, beneficiation (increasing the value of the material by physical
or chemical means) and manufacturing of finished products from the material.
2.2.1 Extraction
There are three basic extraction methods. They are explained below:
Surface mining is the primary method used for mining coal, phosphate rock, aggre-
gates, iron, copper, gold and silver. Techniques of surface mining include strip mining,
open-pit mining and mountaintop removal mining . Surface mining is a broad category
of mining in which soil and rock overlying the mineral deposit (the overburden) are
removed. It is the opposite of underground mining , in which the overlying rock is left
in place, and the mineral removed through shafts or tunnels. Strip mining consists of
stripping surface layers off to reveal ore/seams underneath. It is most commonly used
to mine coal and it is only practical when the ore body to be excavated is relatively near
the surface. Open-pit mining refers to a method of extracting rock or minerals from
the earth through their removal from an open pit or borrow pit. Although open-pit
mining is sometimes mistakenly referred to as strip mining, the two methods are dif-
ferent. Mountaintop removal mining is commonly associated with coal mining, which
involves taking the top of a mountain off to reach ore deposits at depth. Excess mining
waste or “overburden'' is dumped by large trucks into fills in nearby hollow or valley
fills. Dredging is a type of surface mining, with digging done from barges.
Underground (subsurface) mining involves sinking a shaft through the overbur-
den in order to reach the lode deposit. Horizontal passages are then cut through the
geologic material in order to access the ore or mineral. Underground mining can be
classified by the type of access shafts used, the extraction method or the technique used
to reach the mineral deposit. Drift mining is either the mining of an ore deposit by
underground methods, or the working of coal seams accessed by adits, slope mining
uses diagonally sloping access shafts and shaft mining employs vertical access shafts.
Mining in hard and soft rock formations require different techniques. Underground
hard rock mining refers to various underground mining techniques used to excavate