2. Water in mines: pollution, discharge, control, and treatment

Water in mines, that is, "mine water," usually refers to the water contained in the mined-out open area or dug-out area generated as a result of mining of mineral. This excavated area is in open-pit form and contains surface water as well as groundwater. In the case of underground mine, the water encountered is principally groundwater. To address technical issues, it is always better to consider them as two entities, that is, surface water and groundwater (Figure 1), though difficult, to categorize in the case of surface mine.

The principal source of mine water is the "rainfall," and other possible sources could be enumerated as:

	- a. Nearby major water bodies in and around the mining area
	- b.Nearby mine workings, may be surface or underground

3. Incessant rainfall/heavy downpour

Mine water, a valuable commodity, is also a form of industrial wastewater (effluent) which can be a disaster in mining areas or a boon to ease the water scarcity problem locally. Both SW and GW are considered at all stages of the mining operation starting from planning to extraction to restoration stage. Different aspects

Figure 1. Problem and issues of water in mines.

of water covered include collection and handling of hydrological data, control of runoff, magnitude of water, diversion of water channels in mines, (if any), erosion and sediment control, dewatering, different water pollution forms as observed in mines, and water management. As said above that the interrelationship of water and mine is complex and far reaching, the solution should be practical to ensure the efficient running of mining operation while adequately protecting the environment.

## 2.1 Pollution

It has been observed that water pollution in mines is common and well described but their scientific importance is often ignored while managing the mine production. The reasons for this are enumerable. It is desirable that every mine's water, if present, is turned into a useful asset. In some situations water management at mine is neither environmentally friendly nor comparatively easier to manage, for example, acid mine/rock drainage (AMD/ARD), and its management is a costly affair compared to higher TDS water in a limestone quarry. Therefore, sincere attempts have to be made to ensure that AMD pollution and high TDS hard water are treated properly. Similarly, elemental concentration must be checked within permissible limit.

When water comes in contact with exposed mineral at the mine (either at pit or in underground), the potential for water contamination increases manifold. In order to reduce and minimize the water pollution requiring treatment, various control techniques are available. On case-to-case basis and looking at the type of mineral mined, the mine water pollution are dealt for different solutions, for example, heavy metal contamination into water, thereby raising pollution levels are quite frequent in the case of metallic mines.

Mine water control techniques and their selection strategies are cost based and site-specific. It should be carefully selected to prevent the release of contaminated water into the environment. From area to area, one or combination of more than one method may be applied for the pollution control. With high rates of precipitation in an area, significant emphasis must be placed on drainage and its combinations in varying topographies, whereas the mine environment in arid regions with little water availability must choose water recycling as the technique of mine water containment for pollution abatement. If pollution has to be controlled and contained in the mining areas alone, the mine water discharge must be routed effectively. This will make the water pollution management more cost-effective. Judicious utilization of water for the appropriate purpose and water conservation for the future need should be implemented into practice as per the law of land. In India, for prevention of pollution due to mine water, the principal act is Water (Prevention and Control of Pollution) Act, 1974 (amended in 1988 and 2003). This act, despite the prevention and control of water pollution, also guides for the maintaining or restoring of wholesomeness of water.

The topic of pollution is so vast and varied that its description in limited pages is beyond the scope of this chapter. Therefore, readers are advised to consult specific literature related with the problem.

#### 2.2 Discharge

Water discharge from a mine is often controlled by effective drainage around. In India, water discharged from mines are governed by general discharge standards/limits framed by the Ministry of Environment, Forest and Climate Change (MOEFCC) Govt. of India [7]. These effluent discharge standards of India containing about 33 pollutant parameters are framed under the Environment (Protection) Rule, 1986 (under Schedule VI).

### Mining of Minerals and Groundwater in India DOI: http://dx.doi.org/10.5772/intechopen.85309

Discharge of mine water into natural drainage system without any treatment is also an issue to be reckoned in mining geohydrology. In order to avoid the degradation of downstream water channels by excessive suspended sediments from mine, all runoff leaving the mining area should be routed through "sedimentation pond" where the suspended solid can be reduced to acceptable limits. Factors to be considered during design and construction of sedimentation pond include hydrology, its location in mine, construction material and its cost, maintenance/cleanout operations, and applicable legislative requirement [8].

In mining areas, either dendritic pattern or parallel drainage pattern is often present (Figure 2).

Intercepting and diverting surface water (rainwater, runoff water, stream water, snowmelt water, etc.) from entering the mine site are the first step to tackle water accumulation in a pit. Since surface mining causes land disturbance including the removal of vegetation, increased runoff, erosion, and sediment, every attempt should be made to control the mine water discharge. Proper relief and gradient together with adequate slope design are helpful in capturing drainage water which can control runoff and erosion of soil as well as sediments. Topography and watershed details of the project area are equally important from drainage and discharge angle. For the mine water discharge, the knowledge of flow direction together with reduced level (RL/MRL) detail helpsin planning. Smallseasonal nallahs/streams with first-,second-, and third-order drainage pattern are observed in the mining region. Drainage map of the studied mine area is generally drawn covering core zone or CZ (5 km radius) and buffer zone (BZ) of the mine lease (10 km radius). Together with drainage and the watershed area details, an assessment about the seepage from the pit, mine dumps and tailing dams, etc. in nearby area can be made. Such analysis provides the basis for delineating control measures of seepage flow and water management.

In mine-related studies, generally the term watershed [classified as first-, second-, third-, or higher order watershed or else they could also be delineated as micro (3000–5000 ha area), macro (>5000 ha area), or mini watershed (<3000 ha area)

Figure 2. Drainage patterns commonly encountered at mining sites.

according to their size] has been used for planning and management [9]. This term "watershed" is taken synonymously with catchment or drainage basin, an area of land which drains to a common outlet, and is said to be related with water only. But watershed and its management are not only related with water; it essentially relates to resource conservation which means proper land use, protecting land against all forms of deterioration, building and maintaining soil fertility, conserving water, proper management of water for drainage, sediment reduction, and increasing productivity from all land uses. According to the multilevel planning policy at national, state, district, and lower area levels, natural resource data management, which includes groundwater as well, is done on watershed basis considering each watershed as a constituent unit for planning. Thus, to facilitate area-specific microlevel planning for management of water resources (groundwater/surface water), it is convenient to apply "integrated strategy" on watershed basis. This integrated approach has close relation with watershed and management related therewith because it defines the optimum conservation of water with due regard to other resources. Watershed approach provides the mineral production which is resource-centered and environmentally friendly and helps in promoting sustainable development and pollution abatement.
