5. Quantitative estimation and qualitative analysis of groundwater

Mine water in the mining areas comes across two broad issues, namely, water quantity and water quality. In most of the mines and in different parts of the world, both quality and quantity of groundwater resources are required for management, for statutory compliance, and for planned extraction of minerals from the mine [19–23].

The groundwater resources have both static and dynamic dimension. But essentially it is a dynamic resource which is replenishable (annually or periodically) through precipitation. It is static in "saturated zone" and dynamic in the upper

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

unsaturated zone (upper part of the water table) where water-level fluctuation is recorded. Near accurate estimation of groundwater resources is possible by adopting a set of the steps and formula framed for the purpose. A brief about Indian methodology for groundwater estimation is given in this chapter below for reader's knowledge and understanding. This may be noted that from country to country, such estimation procedure or methodology may differ.

To estimate groundwater extraction in an open mining pit, two broader approaches are possible. First is "planned depletion approach" (sustainable yield method), and second is "safe yield approach." "Safe yield approach of assessment" is based on groundwater recharge that takes place in an area or region, and recharge is calculated using water balance method, discrete numerical modeling, or tracer technique. In the "sustainable yield method," assessment can be made using "discrete numerical modeling" only. In India, later one safe yield approach is adopted and found more appropriate for groundwater estimation. Based on this approach, groundwater estimation methodology (GEC)-1997 has been formulated by Central Groundwater Board (CGWB), Govt. of India, and the same is applied in Indian mining sector for groundwater assessment.

#### 5.1 Estimation of groundwater quantity (Q)

Groundwater Estimation Committee methodology, abbreviated as GEC '97 methodology, is an interactive methodology designed by the expert committee [24]. India has adopted it for estimation nationally, and since then mining water quantity is also estimated by this methodology. For groundwater estimation in India, methodologies for alluvium/soft-rocks and for hard-rock areas both have been formulated by the expert committee. This is significant to note that nearly 80% of the mine areas lie in hard-rock terrain.

India with its vast areal extent, long coastline, and large deltaic tracts forming a linear strip around peninsula is characterized by diversified geological, climatological, and topographic setup. Discontinuous aquifers of varying yield potentials occupy 2/3 area of the country, and as said above most of the mine area lies in hard-rock terrain. Thus, GEC '97 methodology and its norms for hard-rock areas [24] remain applicable for evaluation and assessment of groundwater. By understanding the behavior and characteristics of rocks, the water quantity as well quality in the mining area can be estimated. Steps and formulas of GEC '97 methodology and the calculation for open-pit mine (surface mine only) are shown below.

(A) Groundwater calculation

GW quantity available is that quantity which is likely to be experienced in the form of pit water either as punctured water table (groundwater) or in the form of seepage water from the footwall (FW)/hang wall (HW) sides of mine pit walls (see point C of this section below).

• Groundwater Quantity (W1)

(for mine lease area and maximum rainfall/maximum water-level fluctuation occurred for worst-case scenario)

Method 1: infiltration method

Maximum feasible groundwater quantity

˜ ° A m<sup>3</sup> <sup>¼</sup> lease area=pit area � rainfall <sup>ð</sup>max:Þ � RIF ðrefer Table 1 for rainfall infiltration factor ðRIFÞ valuesÞ Method 2: specific yield method

Maximum feasible groundwater quantity

˜ ° B m<sup>3</sup> <sup>¼</sup> lease area � max:fluctuation � specific yield

Average groundwater quantity within lease hold area in a year

˜ ° <sup>3</sup> <sup>C</sup> ¼ ð<sup>A</sup> <sup>þ</sup> <sup>B</sup>Þ=<sup>2</sup> in m <sup>=</sup>TCM=MCM

Considering, 365 days in a year, quantity in a day can be worked out

<sup>3</sup> Thus, available groundwater quantity in <sup>m</sup> <sup>=</sup>day <sup>¼</sup> W1=<sup>365</sup>

Note: Groundwater, as base flow, is present in the mine area during whole year, and seepage is governed by the geological and topographical features of the area. Thus, groundwater availability can be taken as 365 days in a year.

• Groundwater development/groundwater utilization for mine area

Groundwater development can be assessed and estimated by the established procedure of GEC '97. An assessment about the stage of groundwater development is helpful in knowing the overall groundwater scenario of the study area.

The stage of groundwater development in a given sub-unit is defined as the current annual gross groundwater draft for all uses (C) in that sub-unit expressed as a percentage of the net annual groundwater availability (B) in that sub-unit (GEC '97). Thus, if stage of groundwater development is "A," this can be calculated as follows:

˜ ° <sup>A</sup> <sup>¼</sup> gross availability=net availability � <sup>100</sup> ¼ ðC=BÞ � 100%

Similarly, for a mine area GW utilization = output/input (in percentage) = total discharge through mine/net groundwater availability


The sub-unit for the purpose of assessment can be a lease area of mine or a command/non-command area. Having known the GW development/utilization in the mining area, the same can be compared with the standard regional norms. Based on this, the very purpose of evaluation and assessment of groundwater analysis can be categorized as "safe" or "critical."

According to the availability, the current stage of development, and water table fluctuation trend, its allocation for various uses in future, that includes domestic and industrial uses, can be made.

• Groundwater recharge or total annual replenishable recharge (TARR) (unit—m<sup>3</sup> /TCM/MCM)

This is the maximum feasible recharge per annum (Rc or Rc'), and usually referred as total annual replenishable recharge (TARR) is calculated by two methods as per the formula given below.

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

Method 1: rainfall infiltration method

Rc <sup>¼</sup> catchment area � rainfall <sup>ð</sup>averageÞ � rainfall infiltration factor <sup>∗</sup> <sup>3</sup> or Rc in million <sup>m</sup> <sup>ð</sup>MCM<sup>Þ</sup>

Method 2: specific yield method

Rc' ¼ catchment area � water table fluctuation ðaverageÞ x specific yield <sup>3</sup> or Rc' in million <sup>m</sup> <sup>ð</sup>MCM<sup>Þ</sup>

Note:

i. Here \* = rainfall infiltration factor (RIF) = values as per GEC '97 (Table 1).

ii. For TARR calculation catchment area or alternatively the active mining area can be taken.

iii. Normalization of rainfall recharge: the water table fluctuation in an aquifer corresponds to the rainfall of the year of observation. The rainfall recharge estimated should be corrected to the long-term normal rainfall for the area. For calculating the annual recharge during monsoon, the formula indicated below is adopted as per GEC '97 methodology.


#### (B) For hard-rock terrain of India


Table 1.

Rainfall infiltration factor (RIF) as per GEC '97 and terrain conditions.

˜ ° Monsoon recharge <sup>¼</sup> area km<sup>2</sup> � water � level fluctuation <sup>ð</sup>mÞ � specific yield:

Groundwater recharge may also take place through other point/line sources namely tanks, ponds and river/nala. Thus, recharge through different sources includes:


This can be estimated for the catchment area and command/non-command area as the case may be using GEC '97 methodology. Its descriptive details can be referred from [25]. With increasing focus on sustainable development of groundwater resources, augmentation of water conservation structures, with the aim of increasing groundwater recharge, can be implemented in the field. The water conservation structures include percolation tank, check dam, nalla-bund, etc. Recharge through such planned/proposed recharge structure can then be calculated by knowing average water spread area, seepage factor, and water containment days.

• Draft calculation/estimation (unit—m3 /TCM/MCM per year)

"Draft" means consumption. In mining case study, which is an industrial setup, three types of drafts are considered prominent in estimation/calculation, namely, "domestic draft," "draft through mine discharge," that is, pumped out water quantity from pit, and "industrial water draft" for mineral processing (consumption). To estimate domestic draft, total population of the study area and sources of groundwater abstraction must be known. For such calculation all villages and human settlements in the core zone (CZ) and buffer zone (BZ) area are considered which covers 10 km radius area around the pit center. Thus, domestic draft/year (considering groundwater as the only sources).

¼ Population=no of persons ðtotalÞ � water consumption per head ˜ ° liter=person=day � days in <sup>a</sup> year

(B) Surface water calculation

In general, surface water (SW) quantity, that is, W2, is calculated on per day basis because surface water quantity differs from season to season. This quantity is dependent on rainfall/precipitation (during wet season of monsoon). For estimation purpose, maximum rainfall occurred (i.e., worst-case scenario) or average rainfall for 10 years or more can be considered. Separate estimation should be done/shown for peak rainfall period indicating number of days and either the lease area or catchment area as the case may be is considered for calculation.

Surface water quantity (W2)

Surface water quantity=day ¼ W2 ¼ fX–ðY1 þ Y2Þg=no:of rainy days

```
where X = [(M1 + M2) � rainfall]/2
```
Mining of Minerals and Groundwater in India DOI: http://dx.doi.org/10.5772/intechopen.85309

> where M1 = lease area/catchment area; M2 = water filled area; Y1 = evaporation losses (30% of the rainfall); Y2 = infiltration losses (10% of the rainfall).

> Y1 + Y2 are the "water losses," which are taken into account for the estimation/calculation. Nearly 40% of the rainfall goes as waste in the form of "total runoff" for the hard-rock areas.

In India, where monsoonal climatic condition exists, the maximum surface water quantity in a mining pit will be available for a period of 92 days (3 months approximately) in a year, that is, during monsoon and post-monsoon period of July to September end only. In summer season, quantity of water present in pit as well as in lease area will be minimum and always less than the quantity during monsoon period (Table 2).

(C) Seepage water calculation

Normally, seepage water in mine pits occurs as a result of interconnection of pit wall with water body located either in vicinity or at a distance. Capillary action with aquifer also leads to the seepage on pit walls even at upper elevation. If less seepage is observed, the same can be ignored, and seepage water quantity can be taken as "nil." For more seepages, the calculations are based on the general principle of water outflow from the seeped surface area in a recorded time. It is simply added to the SW and GW quantity to obtain total water quantity. Thus, seepage water quantity (Qseepw) of mine pit is equal to flow rate in a given time of that surface area from where seepage is occurring.

#### (D) Water balance

When GW, SW, and seepage water quantity is known, the water balance of the assessment area is calculated as follows:


Important notes:

1. Since, surface water quantity varies widely over the time period of one complete year, total yearly calculation should not be indicated/shown.

2.Groundwater and surface water quantity and availability shown above are applicable for Indian mines/geomining condition and elsewhere the situation may change according to the pattern and period of precipitation.

3.Groundwater availability (W1) and surface water quantity (W2) in m<sup>3</sup> /day should be shown separately indicating the area and period considered. Summation of groundwater quantity and surface water quantity of the study area should not be done because groundwater and surface water quantity and availability fluctuate throughout the year.

#### Table 2. Quantity-wise surface water availability over different periods in a year

Water balance ¼input – output ¼ net GW availability – discharge through mine ¼ þð Þ or ð Þ � can be expressed in TCM or MCM=year

Case records: To know the field scenario, four open-pit mines of India are studied, and they are (i) Partipura limestone mine, Banswada district, Rajasthan [26]; (ii) Rajhara iron ore mine, Balod district, Chhattisgarh [27]; (iii) Malanjkhand copper ore mine, Balaghat district, Madhya Pradesh [28]; and (iv) Lanjiberna limestone and dolomite mine, Sundergarh district, Odisha [29, 30]. In all these mines, different minerals are excavated, and varying geo-mining conditions exist. At Partipura limestone mine, mining conditions are that of a normal open-pit mine, whereas twin mining, that is, surface mining and underground mining, both exist in close vicinity at Malanjkhand copper ore mine and Rajhara mechanized mine of Chhattisgarh state, the excavated iron ore is very hard, and ore reserves are getting exhausted, that is, mine has reached at its last stage of life. "Lanjiberna mine" of Odisha is a typical surface mine in which three pairs of pits (i.e., total six dug-out areas) are excavated for obtaining limestone and dolomite, which is filled with water. All these working pits have different depths (Table 3), and water table is intercepted as a result of mining. At all these mines, comprehensive geohydrological studies had been carried out, and groundwater quantity using GEC '97 is assessed (Table 3). It is observed that all the four mines are having hard-rock formations with unconfined aquifers (GW occurs under water table condition). Average rainfall and maximum rainfall (for the worst-case scenario) in all these mines differ widely, and average water-level fluctuations (WLF) are less than 10 m below ground level. In different seasons the water quantities fluctuate widely for which number of reasons and factors are responsible. When water quantity Q is checked (verification by ground truth), it was found correct by the concerned statutory agencies with �10–20% variations from actual. Based on this, necessary permission for continuance of mining operation was granted for these mines.

## 5.1.1 How to estimate Q for an underground mine (Qu/g)

Having discussed the groundwater quantity for an open-pit mine, an obvious question arises. Whether groundwater calculation for underground mine (Qu/g) is also estimated in the same way? Its answer is no. The approach for estimating groundwater quantity with respect to an underground mine is sharply different. Q for an u/g mine is full of uncertainties and based on the actual field conditions encountered. Such field conditions are many, either created or naturally encountered, for example, extent of underground mine development affects the creation of void's underground, this in turn has a close connection with groundwater movement in encountered aquifers.

Secondly, depth of underground workings from surface has linkages with groundwater recharge occurring in that particular area, which in turn is related with local rainfall. Obviously, rock types, its porosity, and hydrological characteristics have key role in groundwater movement. Similarly, geological features such as faults, folds, unconformities, lineaments, etc. reflect their own dominance in groundwater quantity as well as movement. Thus, both rock type (different formations) and geology, for either open-pit mine or an underground mine, have tremendous importance. Its detailed study and engineering judgment can help one to estimate the groundwater quantity approximately, if not exactly. Thus, approach for estimating Qu/g must incorporate study of borehole litho-logs of the mine/area and other related parameters, namely, rainfall, recharge, aquifer and its characteristics, extent of underground mine development, and working depth. Based on

Annual GW quantity at 70 m pit depth = 0. 1616 Annual GW quantity at 250 m pit depth = 1.713 MCM MCM

(iii) Malanjkhand copper ore mine [28] (iv) Lanjiberna limestone mine [29, 30]

Annual GW quantity at 240 m pit depth = 4.735 Annual GW quantity for pit depth from 39 m MCM to 56 m = 0.268 MCM to 1.4 MCM [pit depths: pit 1 Note: MCM = Million cubic mèter; and pit 3 = 41 m; pit 2 and pit 6 = 56 m and pit 4 GW = Groundwater and pit 5 = 39 m]

#### Table 3.

Estimated GW quantity for different case studies using GEC '97

groundwater movement principles (Darcy's law), runoff and recharge relationship of surface water and general estimation formulas as applied in GEC '97 methodology Qu/g for quantitative can be estimated. Further, this may be noted that the "underground mine water quantity" is proportionally related with the actual excavation area exposed in underground workings (size and area of panel/stope) as well as surface area above the extraction/depillaring panel.

Here, it is important to reaffirm that in the paragraph above, author has clearly showed how the groundwater quantity can be calculated and how it is related with several factors. This water quantity calculation is helpful at the planning stage and operational stage of the project for "dewatering planning and related aspects." One can also know the water availability and how to use it whether within mine pit or outside. Similar excavations being operated below ground, for example, caverns, tunnels, etc., are the other beneficiaries for such knowledge. Since the estimated quantity(ies) are based on aquifer parameters and scientifically proven, it is true and near actual. Its immense benefits can be encashed, in terms of cost savings and cost overrun of project(s).
