Assessment of Groundwater Quality in and around Neyveli Lignite Mines using GIS and Water Quality Index, Cuddalore District, Tamil Nadu

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1 Volume 3, Issue 7 December RESEARCH ARTICLE ISSN: Assessment of Groundwater Quality in and around Neyveli Lignite Mines using GIS and Water Quality Index, Cuddalore District, Tamil Nadu N. Gunalan 1*, R. Kamaraj 2, M. Krishnan 3 and R.R. Krishnamurthy 4 1 Additional Chief Manager/Geology; 2,3 Chief Manager/Geology, Neyveli Lignite Corporation Ltd., Neyveli; 4 Assoc. Prof., Dept. of Applied geology, School of Earth Science, University of Madras, Chennai gunalan.n@nclindia.com*, kamaraj_r@nclindia.com, Krishnam.m@nlcindia.com, r.r.krishnamurthy@gmail.com; * Abstract The most important natural source of drinking water is from the groundwater. By assessing the groundwater potential and its quality, it can be optimally used for different purposes depending up on its availability. The study area falls between Manimuthar in the north and Colirron River in the south. The aquifer falling with in this zone is called as Neyveli sub-basin which is known for its confined aquifer. The Neyveli sub-basin extends for an area of around 3500 sq.kms. This aquifer is considered as most important water source for drinking and irrigation. Lignite is being mined at Neyveli for five decades by depressurizing the aquifer by pumping the groundwater for safe mining. In order to study the effect of pumping on the groundwater quality, an attempt has been made to determine the spatial distribution of the groundwater quality parameters in the study area based on integrated analysis of physico-chemical parameters, use of Geographic Information System (GIS) and Water Quality Index calculations. The physico-chemical parameters were compared with BIS Indian standards and World Health Organisation (WHO) recommended standard guideline values for drinking and public health to have an overview of the present groundwater quality. The overall assessment of the study area shows that all the parameters are within the permissible limit of the BIS ( ) values. Using GIS Arc Map 10.1, spatial distribution maps for ph, TDS, EC, Cl, HCO 3, SO 4, NO 3, Ca, Mg, Na and K were generated. Ordinary Inverse Distance Weighted (IDW) was used for generation the spatial distribution of the quality parameters. The spatial distribution of the water quality parameters are within the permissible limits except TDS which exceeds the permissible limit of 1000 mg/l in nine samples. Keywords: Groundwater quality, geographic information system, water quality index, physico-chemical parameters. Introduction Mining of lignite from the Neyveli Lignite field is faced with a complex hydrological problem due to the pressurized water in confined aquifers below the lignite seam. The confined aquifer below the lignite seam, which is about m thick in the Neyveli area, exerts an upward pressure at the base of lignite seam. If the excavation is continued without reducing the upward thrust of the confined aquifer will result in the bursting of lignite and flooding of the mine. The pumping of groundwater for safe mining of lignite above the confined aquifer and overexploitation of groundwater for domestic, industrial activities and anthropogenic pollution-induced factors may influence the groundwater quality. In order to understand the impact of lignite mining and pumping of groundwater for safe mining activity, a study has been proposed to assess the ground water quality in and around Neyveli mine area. The objective of the study is to understand the groundwater quality in and around the Neyveli mines, since the mining activities is continuing for more than 5 decades. The objectives of the study are: 1. To identify any changes in the groundwater quality around Neyveli mines due to continuous mining activities with groundwater pumping based on the pre-and post monsoon ground water quality from dug wells. 2. To analyze the spatial variation in the groundwater using Water Quality Index (WQI). This will reflect the composite influence of different water quality parameters which was assigned using weighted arithmetic index method. Finally, preparing thematic maps using GIS tool, representing the spatial variation in the groundwater quality. Materials and methods Sample collection: Samples from 24 dug wells spread over the study area were collected periodically during pre-monsoon (April-June 2013) and post-monsoon (October-December 2013) (Fig. 1). The samples were collected in plastic containers and were immediately handed over to NLC laboratories CARD (Centre for Applied Research and Development) for preserving the samples at its original condition. Sample analysis: The samples were analyzed at NLC laboratories CARD (Centre for Applied Research and Development) using IS3025 standard procedures.

2 Volume 3, Issue 7 December Fig.1. Sample location map. Table 1. Methods for determination of water quality parameters. Parameters Methods ph Digital ph Meter (Global ) Conductivity Digital conductivity meter (Global ) Calcium Volumetric titration Magnesium Volumetric titration Chlorine Volumetric titration sulphates Volumetric titration Alkalinity Volumetric titration Iron and Aluminium Gravimetric method TDS Gravimetric method Dissolved oxygen DO meter Fluoride High performance iron Chromatography Nitrate High performance iron Chromatography Copper Inductively coupled plasma atomic emission spectroscopy Manganese Inductively coupled plasma atomic emission spectroscopy Zinc Inductively coupled plasma atomic emission spectroscopy Potassium Flame photometer 128 µc systronics Sodium Flame photometer 128 µc systronics The details of the specific methods of estimation of physico-chemical parameters of groundwater samples are given in Table 1. The results were evaluated and compared with the water quality guidelines of WHO as well as Bureau of Indian Standards (BIS). GIS analysis: Survey of India (SOI) Toposheets of 1: 50,000 scale, Arc Map 10.1 GIS software were used for preparing the location map and was digitized in UTM coordinate system by using the Arc Map. GPS was used for the map location of each sampling dug wells. Finally the results of each parameter were analyzed and added to the point feature as attributes and the File Geo database was created. The Geo database was used for generating surfaces to represent the spatial distribution of the chemical parameters of the groundwater. In the present study, Inverse Distance weighted (IDW) method was used for generating the surfaces. Inverse distance weighted (IDW) interpolation determines cell values using a linearly weighted combination of a set of sample points. Weight is a function of inverse distance. This method assumes that the variable being mapped decreases in influence with distance from its sampled location. i.e., the value of an attribute z at some non-sampled point is the distance weighted average of data points occurring within a neighborhood or surrounding the non-sampled point. Estimation of WQI: Water quality index (WQI) will reflect the composite influence of different water quality parameters which was assessed using the weighted arithmetic index method. The quality parameters such as ph, TDS, Ca, Mg, Na, K, Cl, SO 4, HCO 3 and NO 3 were used for the above study. Bureau of Indian standards (BIS, 1991) and World Health Organization (WHO, 1993) stands have been considered for calculating the index. Ten parameters has been assigned weight according to the relative importance in the overall quality of water for drinking purpose and the relative weight (W i ) is computed (Table 2) using a weighted arithmetic index method as given below (Brown et al., 1970; Tiwari and Mishra, 1985). wi W i = (1) Where, W i is the relative weight, wi is the weight of each parameter and n is the number of samples. A quality rating scale (Q i ) for each parameter is assigned by dividing its concentration in each water samples by its respective stranded according to the guidelines of BIS (2004) and then multiplied by 100. Q i = (C i /S i ) X 100 (2) Where Q i is the quality rating, C i is the concentration of each chemical parameter in each of the water sample in mg/l and S i is the BIS drinking water standard for each chemical parameter in mg/l according to the guidelines of BIS (2004). SI is first determined for each chemical parameter, which is then used to determine the WQI as per the equation given below: SI = W i Q i (3) Where SI is the sub-index of the parameter and Q i is the rating based on the concentration of i th parameter. The overall water quality index was calculated by adding together each sub-index values of each groundwater sample. The classification of water quality based on the WQI is given in Table 3.

3 Volume 3, Issue 7 December Table 2. BIS standards, weight and relative weight for each parameter. Chemical Parameters BIS Standard Weight (wi) Relative weight (Wi) ph TDS (mg/l) Cl - (mg/l) SO 4 (mg/l) NO 3 (mg/l) HCO 3 (mg/l) Na + (mg/l) Ca 2+ (mg/l) Mg 2+ (mg/l) K + (mg/l) wi=29 Wi = 1.00 Fig. 2a. Concentration of ph and b. Electrical conductivity in the study area. Table 3. Classification of water quality based on WQI values. WQI range Type of water <50 Excellent water Good water Poor water Very poor water >300 Unfit for drinking Results and discussion In order to determine the suitability of the groundwater, the quality parameters i.e., physical and chemical parameters of the groundwater are to be understand in detail. Hence, the following water quality parameters were selected for generating the thematic maps using Arc GIS namely ph, TDS, EC,,Ca 2+, Mg 2+, Na +, K +, Cl -, SO 4 2-, HCO 3 -. ph is one of the most important operational water quality parameter with optimum range between 6.5 to 8.5. The maximum permissible limit is 8.5 and may be extended up to 9.2 in the absence of alternate water source. The values of ph in the groundwater samples collected from the study area varies from 6.7 to 8.35 (Fig. 2a) during the pre-monsoon and post-monsoon period. The ph values of all the samples are within the desirable limit of BIS ( ). The Electrical Conductivity (EC) of water at 25 C varies widely from 158 to 2240 µs/cm during post-monsoon and maximum of 1292 µs/cm during the pre-monsoon season with a mean value of 750 µs/cm (Table 1). Considering the maximum prescribed limit of EC in drinking water, 98% of the samples value lies with good drinking water (Fig. 2b). The TDS values in the study area ranges from 114 to 1352 mg/l. Nine samples exceeds the desirable limit of BIS standard (500 mg/l) but are within the permissible limit of BIS standard except one sample D-10 (1000 mg/l) (Fig. 2c). The TDs values increases in the east-west direction of the study area. The total hardness of the sample D-10 is higher during pre-monsoon and post-monsoon period, which leads to higher value of TDS. Total Hardness (TH) in water is caused primarily by Ca and Mg cations. The principal chemical sources for Ca and Mg ions are the compounds of calcium and magnesium bicarbonate, carbonate and sulphates. Groundwater exceeding the limit of 300 mg/l is considered as very hard. In the study area, all the samples are within the BIS Indian standard desirable limit (300 mg/l) except in one sample D-10 (Fig. 2d). The abundance of the major anions in the Neyveli aquifer 2- - is in the following order: SO 4 > HCO 3 > Cl - > NO - 3. The aquifer is characterized by more or less equal 2- - concentration of SO 4 and HCO 3 with slightly higher sulphate ion and ranges from 13 mg/l to maximum of 345 mg/l with an average value of 118 mg/l. a b

4 Volume 3, Issue 7 December Fig. 2c. Spatial distribution of TDS and d. TH conc. Fig. 2e. Spatial distribution of SO 4 and f. HCO 3 ion conc. c e The concentration of bicarbonate alkalinity ranges from 30 to 400 mg/l with an average value of 110 mg/l. The spatial distributions of the sulphate ion and bicarbonate ion concentrations are given in the Fig. 2e and f. The next dominant anion is chloride and its concentration ranged from 21 to 320 mg/l with mean value of mg/l during post-monsoon and 66.5 mg/l during the pre-monsoon period. About 90% of the samples are having the values less than the desirable limit of 250 mg/l and remaining 10% of the samples having the value less than the permissible value of 1000 mg/l (2 samples D-9 and D-10). Nitrates are the end product of conversion of nitrogenous material. This process occurs in polluted water. d The concentration of nitrate in the study area varies from 2.36 to 37.6 mg/l with an average value of 36.5 mg/l which is well below the permissible limit of 75.0 mg/l which indicates that the Neyveli basin water is not polluted (Table 4 and 5). The abundance of major cations trend in the Neyveli aquifer is Na + > Ca 2+ > Mg 2+ > K +. Sodium is the dominant cation in the Neyveli basin and the concentration ranges from 9.7 to 284 mg/l with mean value of during post-monsoon and during the pre-monsoon period. According to the BIS Indian standards, the desirable limit is 200 mg/l. The concentration of Na is below the desirable during the pre-monsoon period and 4 samples exceed the desirable limit but the concentration is within the permissible limit (Fig. 2g). f

5 Volume 3, Issue 7 December Table 4. Physico-chemical parameters of groundwater sample (Post-monsoon). Sample ID ph EC TH TDS Ca Mg Na K Cl SO 4 HCO 3 F NO 3 Cu Mn Zn Fe D D D BDL 0.00 BDL 0.18 D BDL 0.10 D D BDL D BDL BDL BDL 0.25 D D D BDL 0.01 BDL 0.30 D D D D BDL 0.42 D D D D BDL D D BDL 0.03 BDL 0.34 D D D BDL 0.26 D BDL 0.06 Min Max Mean SD Conc. of Ca-Fe: mg/l; Conc. of EC: (µs/cm). Table 5. Physico-chemical parameters of groundwater sample (Pre-monsoon). Sample ID ph EC TH TDS Ca Mg Na K Cl SO 4 HCO 3 F NO 3 Cu Mn Zn Fe D Nil D D BDL 0.3 D D D Nil D D D D D Nil D D BDL BDL D D D BDL D D D D D D BDL D D Min Max Mean SD Conc. of Ca-Fe: mg/l; Conc. of EC: (µs/cm). The second dominant cation is Ca and the concentration ranges from 11.8 to mg/l during post-monsoon and 11.2 to 84.0 mg/l during the pre-monsoon period (Table 4 and 5). The average values of calcium during pre and post-monsoon period are 43.5 and 40.9 mg/l respectively. Two samples are below the permissible limit (200 mg/l) and the remaining samples are having the value below the desirable limit of 75 mg/l (Fig. 2h). Magnesium ion concentration ranges from 3.3 to mg/l during post-monsoon and 2.9 to 31.1 mg/l during pre-monsoon period with average mean value of mg/l and mg/l respectively (Fig.2i). One sample is below the permissible limit of 100 mg/l during pre-monsoon and all other samples have the value within the desirable limit of 30 mg/l (Table 6).

6 Volume 3, Issue 7 December Fig. 2g. Spatial distribution of Na and h. Ca ion conc. Fig. 2i. Spatial distribution of Mg and j. K ion conc. g i h j

7 Volume 3, Issue 7 December Table 6. Details of samples falling within the desirable and permissible limits. BIS Parameter ( ) Post-monsoon Pre-monsoon Post-Monsoon Pre-monsoon DL PL Min Max Mean Min Max Mean < DL <PL >PL < DL <PL >PL ph EC TH TDS Ca Mg Na K Cl SO HCO F NO Cu Mn Zn DL-Desirable limit, PL Permissible limit, Conc. of Ca-Fe: mg/l; Conc. of EC: (µs/cm). Fig. 3a. WQI map of Pre-monsoon and b. Post-monsoon. a b

8 Volume 3, Issue 7 December Table 7. Water quality classification based on the WQI. Post-monsoon Pre-monsoon Sample ID WQI Classification Sample ID WQI Classification D Good Water D Good Water D Good Water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Good Water D Good Water D Poor water D Good Water D Excellent water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Good Water D Excellent water D Good Water D Excellent water D Good Water D Excellent water D Good Water The concentration of potassium ion in the study area ranges from 0.58 to 3.8 mg/l during the post-monsoon and 0.56 to 54.6 mg/l during pre-monsoon period. The mean value during pre-monsoon and post-monsoon are 2.2 and mg/l respectively. It is found that all the samples during the post-monsoon were less than the desirable limit whereas during the pre-monsoon period 4 samples have concentration above the desirable limit (Fig. 2j). In general, all the parameters were within the permissible limit of BIS Indian standards (Table 6). The concentration of other elements namely Cu, Fe, Zn and F are within desirable limit during both pre-monsoon and post-monsoon period. Details of samples falling within the desirable and permissible limits are given in Table 6. The calculated WQI for the individual samples are given in Table 7. The spatial distributions of the water quality based on the calculated WQI were plotted using GIS (Fig. 3a and b). It is inferred from the thematic maps that the entire study area falls under two categories i.e., excellent water (WQI<50) and good water (50-100) during the pre-monsoon and during the post-monsoon, a small area near Vridhachalam (sample location-d-10) shows poor water quality. The reason for the poor quality of the water is due to contamination by the daily use of well water near the well itself for domestic use by the house owner. Conclusion The spatial distribution of the ground water quality such as ph, TDS, TH, EC, Ca, Mg, Na, K, Cl, SO 4, HCO 3 and NO 3 were studied using GIS. It is inferred from the study that majority of water quality parameters are within the desirable limit of BIS ( ). Some of the samples have shown higher values than the desirable limits but the values are less than the permissible limit of BIS standards. ph values are within the desirable limit. Total hardness is also within the desirable limit during both pre and post-monsoon seasons. Whereas, the TDS values of 9 samples exceeds the desirable limit of 500 mg/l during both the seasons. Only one sample exceeds the permissible limit of 1000 mg/l. EC values are within the permissible limits in the entire study area. The concentrations of Ca were within the desirable limits except two samples but the within the permissible limit. The concentrations of potassium for all the samples are below the desirable limits during post-monsoon whereas 5 samples exceed the desirable limit during pre-monsoon but not exceeding the permissible limit of BIS. The spatial distribution of the sulphate concentration in two samples exceeds the desirable limit but within the permissible limits during both pre and post-monsoon seasons. The other quality parameters like F, Zn, Cu and Fe are within the desirable limits as per BIS standards. The water quality index is a very useful tool to understand the status of the groundwater as well as helps in decision making in future. The overall view of the WQI of the present study shows normal values indicating good water quality. North of study area covering Nadiyapattru, Vadalur and Kullanchavadi falls under excellent water quality whereas in the southern part, the water falls under good quality.

9 Volume 3, Issue 7 December Only one sample during post-monsoon period showed poor water quality i.e., >100. The reason for the poor water quality is due to mixing of waste water into the well by the domestic users. This study indicates that the use of GIS and WQI method can provide useful information for water quality assessment. Acknowledgements Authors extend their sincere thanks to Neyveli Lignite Corporation (NLC) for approving the paper for publication and Centre for Applied Research and Development (CARD) for analyzing the groundwater water samples at their laboratory. Authors also thank the executives of the Regional Geology division for extending their support in preparing the paper. References 1. Brown, R.M., MeCeiland, N.J., Deinimger, R.A. and Tozer, R.G A water quality index. Do we dare? Water Sewage Works. 117: Bureau of Indian Standards (BIS) , Indian standard drinking water specification, First revision, pp Tiwari, N. and Mishra, M.A A preliminary assignment of groundwater quality index of major Indian rivers. Ind. J. Environ. Prod. 5: World Health Organization (WHO) Guidelines for drinking water quality, 2 nd edn., 1: 188.