Introduction

Groundwater is becoming a major concern with respect to coal mining (Karroum et al. 2017; Kumari et al. 2014). Dhanbad, the coal capital of India, is famous for coal mining. Groundwater of Dhanbad town is very much affected due to nearby mining activity in Jharia coalfields. During mining, a large amount of groundwater is pumped out to make mining possible (Prasad et al. 2014; Selvakumar et al. 2017; Srinivas et al. 2017). This creates problem to groundwater with respect to its quality as well as quantity (Custodio et al. 2016; Saravanakumar and Kumar 2011). Mining affects the physical and chemical changes in the mine environment resulting in groundwater pollution (Pathak and Banerjee 1992; Singh 1988; Verma et al. 2017). Bukowski et al. (2006) have reported that underground mining operations can be associated with many environmental effects like vulnerability of groundwater to pollution and the effects of mining on useful aquifers. Banks et al. (1997) have reviewed the variety of hydro-chemical characteristics, environmental impacts, and treatment methods pertaining to groundwater discharging from mines. Seeing the importance of groundwater quality in mining area, the investigation has been carried out to understand the changes in groundwater quality of Dhanbad township within 3 years of time duration (May 2011–May 2014). Heavy metal pollution index (HPI) of the groundwater has also been evaluated according to described methodology (Prasad and Jaiprakas 1999; Prasad and Bose 2001; Prasad and Kumari 2008; Prasad and Mandal 2008; Prasad et al. 2011; Chabukdhara et al. 2017). On the basis of this, groundwater quality of Dhanbad township has been predicted.

Materials and method

Study area

Dhanbad, one of the biggest coal belts of India, is actively associated with mining activities for more than a century. The oldest geological formations of the Dhanbad district are composed of crystalline metamorphic rocks which belong to Dharwar system in Indian stratigraphy. In these formations, rock types of both sedimentary and igneous origin are found. Course gritty soil is predominant in Dhanbad coal basin (Gautam et al. 2015). This type of soil mixed with big fragment of rocks is formed from the weathering of pegmatite, quartz, and conglomeratic sandstones. About 200 coal mines of Jharia coal fields, which produce prime coking coal, are located around Dhanbad Township. The large-scale industries such as coal washing and coke making are located nearby. There is drinking water shortage in the township, especially in summer season. The population here is mainly depended on ground water sources. Taking all these into consideration, 20 groundwater sampling points have been selected, which covered almost entire township of Dhanbad (Fig. 1). Study of quality of selected groundwater samples had been carried out in the lean period of the years 2011 and 2014 to know the changes if any due to mining and allied activities.

Fig. 1
figure 1

Layout of Dhanbad township showing different groundwater sampling points

Full size image

Sampling and analysis

Out of 20, four samples have been taken from open well and 16 from hand pumps. The depth of open wells has been 25–30 feet and hand pumps 100–120 feet. Sampling has been done for the month of May (Summer) 2011 and May 2014 to get an idea of the change in concentrations of water quality parameters in 3 year time duration. Groundwater samples have been collected in 2.5 l plastic containers pre-rinsed with groundwater. Analysis of different water quality parameters such as pH, total hardness, Ca hardness, Mg hardness, sulphate, chloride, and TDS has been carried out according to the standard method (IS: 3025 2009). For analysis of heavy metals, samples have been digested, concentrated, and prepared for analysis by Atomic Absorption Spectrophotometer (AAS) Model: M Series Thermo Fisher (Arnold et al. 1992). The digestion and concentration of water sample were carried out by reducing the volume of 1000–50 ml by slow heating on a hot plate with the addition of few milliliters of concentrated nitric acid. Slow heating was done to avoid metal loss due to evaporation. Analysis of metals has been performed by calibrating the instrument with different dilutions of the standard solutions and analysis of Cu, Mn, Pb, Fe, Cd, Zn, and Cr was performed at 324.7, 279.5, 217.0, 248.3, 228.8, 213.9, and 357.9 nm, respectively. Three replicates were run for each sample and the instrument was recalibrated after analysis of ten samples. The detection limit of AAS was well within the range for all elements analyzed. Overall precision expressed as percent relative standard deviation was obtained for all the samples. Because the samples were concentrated during digestion, the result obtained was calculated to get the actual concentration value.

Results and discussion

The results of physico-chemical analysis of 20 groundwater samples of Dhanbad Township, in lean period (summer) are given in Table 1. From Table 1, it has been observed that the highest pH value of 7.68 and the lowest of 5.82 in the year 2011, whereas the highest pH of 7.15 and the lowest of 5.95 in the year 2014 have been obtained. The pH value has not shown any remarkable change during the 3 years of period. In the year 2011, highest total hardness, Ca hardness, Mg hardness, chloride, sulphate, and total dissolved solids have been found 684, 456, 59.3, 260, 379, and 1184 mg/l, respectively. Whereas in the year 2014, these values have been found 860, 504, 86.51, 356, 547, and 1402 mg/l, respectively (Fig. 2). The increased concentrations of the above parameters in 2014 clearly indicate that it may be due to increased mineral content in groundwater in the lean period of 2014 as recharge of aquifers is lesser in 2014 than in 2011. In six groundwater samples in 2011 and 2014, the total hardness value exceeded the desirable limit of 300 mg/l as per drinking water specification (IS: 10500). Increased concentration of sulphate in 2011 and 2014 has been observed in groundwater sampling point 20 (379 mg/l) and 5 (547.36 mg/l), respectively. In rest all groundwater samples, sulphate has been found less than 200 mg/l (desirable limit of drinking water specification, IS: 10500). Chloride concentration in one sampling point 11 (260 mg/l) in 2011 and four sampling point 4, 8, 13, and 17 (356, 256, 312, and 300 mg/l) in 2014 are higher than the desirable limit (250 mg/l) of Indian drinking water specification. This observation favours decrease in recharge of aquifers and increased mineral content in groundwater in 2014. Eight groundwater samples in 2011 and ten in 2014 have exceeded the desirable limit of 500 mg/l with respect to TDS value (Table 1). During the investigation period, the highest TDS of 1184 mg/l in 2011 and 1401 mg/l in 2014 has been obtained which indicate high dissolved mineral content in groundwater of Dhanbad Township.

Table 1 Analysis of different parameters of groundwater in lean period of years 2011 and 2014 (in mg/l except pH)
Full size table
Fig. 2
figure 2

Variation in concentration of different water quality parameters in groundwater of Dhanbad township, a pH, b Ca hardness, c total hardness, d Mg hardness, e sulphate, f chloride, and g TDS

Full size image

The evaluation of concentration of seven heavy metals such as Cu, Mn, Fe, Pb, Cd, Zn, and Cr in the years 2011 and 2014 in groundwater of Dhanbad town is listed in Table 2. The highest concentration of Cu, Mn, Fe, Pb, Cd, Zn, and Cr in groundwater in the years 2011 and 2014 has been found 0.033, 1.246, 2.451, 0.049, 0.004, 0.469, 0.006 and 0.008, 0.495, 0.511, 0.009, BDL, 0.195, 0.045, respectively (Fig. 3). From the results, it has been observed that concentrations of Cu, Pb, Cd, Zn, and Cr were well below the permissible limit of Indian drinking water specification (IS: 10500). The concentration of Mn and Fe has been found more than the permissible limit at many places in both the years, but the concentrations have shown a declination trend from 2011 to 2014. In 2011, at seven sampling site (2, 6, 7, 9, 11, 18, and 19), Mn concentration has been more than the permissible limit of 0.1 mg/l, but in 2014, six sampling sites (4, 6, 7, 11, 12, and 16) have concentration above the permissible limit. Similarly, in 2011 at 11 sampling points (4, 5, 6, 7, 8, 9, 15, 16, 17, 18, and 19), Fe concentration has been more than the permissible limit of 0.3 mg/l, and in 2014, only one sampling site 8 has shown higher concentration of Fe (0.511 mg/l). The decrease in metal concentration in 2014 as compared to 2011 indicates that less leaching of these metals from ground strata to groundwater has been taken place.

Table 2 Analysis of heavy metals concentration (ppm) in ground water (in mg/l)
Full size table
Fig. 3
figure 3

Variation in concentration of different heavy metals in groundwater of Dhanbad Township, a Fe, b Mn, c Cu, d Zn, e Pb, f Cr, and g Cd

Full size image

The Heavy Metal Pollution Index (HPI) model (Eqs. 1 and 2) proposed given by (Mohan et al. 1996) has been used for knowing the total quality of groundwater with respect to heavy metals in the years 2011 and 2014:

$${\text{HPI}} = \frac{{\sum\nolimits_{i = 1}^{n} {W_{i} Q_{i} } }}{{\sum\nolimits_{i = 1}^{n} {W_{i} } }},$$
(1)

where Q i is the sub-index of the ith parameter. W i is the unit weightage of the ith parameter and n is the number of parameters considered.

The sub-index (Q i ) of the parameter is calculated by

$$Qi = \mathop \sum \limits_{i = 1}^{n} \frac{{\left\{ {M_{i} \left( - \right)I_{i} } \right\}}}{{\left( {S_{i} - I_{i} } \right)}} \; \times \;100,$$
(2)

where M i is the monitored value of heavy metal of the ith parameter, I i is the ideal value of the ith parameter, and S i is the standard value of the ith parameter. The sign (−) indicates the numerical difference of the two values, ignoring the algebraic sign.

Since the unit weightage (W i ) of Fe and Mn is very less in HPI calculation of groundwater, these metals contribute very less on HPI value. Heavy metals such as Pb, Cd, and Cr have no relaxation in drinking water standard and they have high unit weightage (W i ) value in HPI calculation. Hence, even their very low concentration present in water makes it of poor quality and gives high values in HPI evaluation. The HPI calculation of groundwater quality of Dhanbad Township in the years 2011 and 2014 in the lean period is given in Tables 3 and 4. The value of HPI calculation in the year 2011 is 4.7640 and its value decreased to 1.4735 in the year 2014 supports the fact that less leaching of these metals from ground strata to groundwater is taking place. Overall, the groundwater of Dhanbad town with respect to heavy metal contamination is not a serious issue and groundwater contamination of the township is not taking place due to severe coal mining activity near the township, though the concentration of few water quality parameters such as total hardness, Ca hardness, Mg hardness, chloride, sulphate, and total dissolved solids has increased in 2014 as compared to 2011, which may be due to increased mineral content in groundwater in lean period and decrease in recharge rate of aquifers in 2014. From overall study, it has been seen that different water quality parameters in the year 2014 have not shown any significant change with respect to the year 2011 and there is no significant degradation in the quality of groundwater. In the incoming years, quality of groundwater of Dhanbad Township will not show any drastic change in its quality unless and until any anthropogenic activity will affect it.

Table 3 HPI calculation for groundwater of Dhanbad Town in 2011
Full size table
Table 4 HPI calculation for groundwater of Dhanbad Town in 2014
Full size table

Conclusion

The concentration of various water quality parameters such as total hardness, Ca hardness, Mg hardness, chloride, sulphate, and total dissolved solids has been increased in 2014 as compared to 2011 which might be due to increase in mineral content in the lean period and decrease in the recharge of aquifers in 2014. The value of HPI calculation in the year 2011 was 4.7640 and its value decreased to 1.4735 in the year 2014 supports the fact that less leaching of heavy metals from ground strata to groundwater had taken place. Overall, the contamination of groundwater of Dhanbad town was not a serious issue and groundwater contamination of the township was not taking place due to severe coal mining activity near the township. Different water quality parameters in the year 2014 did not show any significant change with respect to the year 2011 and there was no significant degradation in the quality of groundwater. On the basis of the study, it was predicted that in the coming years, quality of ground water will not show any drastic change in its quality unless and until any anthropogenic activity will affect it.