Received 29 February 2016; accepted 21 May 2016; published 24 May 2016
The urban groundwater has emerged as one of the world’s most challenging issues  . The quality of available groundwater resources is being increasingly degraded by geogenic and anthropogenic activities   . Asian countries face serious water problems almost everywhere mainly due to explosive population growth, heavy seasonal rains, massive flooding, decreasing of water levels, mixing of waste water, etc.  . In India, groundwater is used intensively for drinking, irrigation and industrial purposes. Several land and water-based human activities are causing pollution of these precious resources. India is now the biggest user of groundwater for agriculture in the World  . The most dramatic change in the groundwater scenario in India is that the share of tube wells in irrigated areas is rising tremendously. By now, tube wells have become the largest single source of irrigation water in India. Hence, groundwater has a high incidence of water quality problems such as increase in concentration levels of chemical species i.e. fluoride, iron, salinity, nitrate, arsenic, etc., may be due to mineralization  -  . In the present work, the urban groundwater quality of the most industrialized city of the country, Raipur is presented. The variations and sources of contaminants and quality assessment of the groundwater are described.
2. Materials and Methods
2.1. Study Area
Raipur is the capital of the Chhattisgarh state of the country with vast industrial growth having population of >2.0 million habitants. The groundwater is widely used for domestic, agricultural and industrial purposes. Several sponge iron, steel, alloy and cement plants are running using coal as source of energy. The water quality of city is deteriorated tremendously due to over use of groundwater and input of the industrial and sewage wastes in it  .
2.2. Sample Collection
The sampling locations for the groundwater are presented in Figure 1. Fifty six groundwater samples from 28 locations of the city from the residential, urban and industrial area in two seasons (i.e. post and pre monsoon) of years, 2012 were collected by using the established methodology  . The water was collected into cleaned and rinsed 1 lit polyethylene flask. The physical parameters i.e. pH, electrical conductivity (EC), dissolved oxygen (DO) and reduction potential (RP) of the groundwater were measured at the spot. The samples were dispatched to the laboratory by subsequent frizzing at −4˚C.
The total dissolved solid (TDS) value of the filtered samples (through glass fiber filter) was determined by the evaporation method  . The total hardness (TH) and total alkalinity (TA) values of the groundwater samples were analyzed by titration methods  . The CHNSO-IRMS Analyzer, SV Instruments Analytica Pvt. Ltd. was used for analysis of the dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). The Dionex DX-1100 Ion chromatograph (Dionex Corporation, Sunnyvale, CA, USA) equipped with anion and cation separation columns and conductivity detector was used for analysis of the ions. The Metrohm-781 ion meter was employed for monitoring of F− content in the presence of the buffer in 1:1 volume ratio. The buffer was prepared by dissolving sodium citrate (300 g), 1, 2-cyclohexanediamine-N-tetraaceticacid (22 g) and NaCl (60 g) in a volume of 1 lit with the de-ionized water by subsequent adjustment of pH value to 5.2 ± 0.2.
The indices i.e. sodium hazard (SH), magnesium hazard (MH), sodium adsorption ratio (SAR), permeability index (PI), Kelly’s ratio (KR) and water quality index (WQI) were evaluated by using the following equations.
where, all ions are expressed in meq/L
Ten parameters i.e. pH, EC, DO, TH, TA, Mg2+, Ca2+, Cl−, and were selected for evaluation of the WQI by using the standard values recommended by BIS and WHO   . The weighed arithmetic method was used for calculation of the WQI of the groundwater with the help of following expression.
Figure 1. Representation of sampling points in Raipur city, CG, India.
qn = Quality rating of the nth water quality parameter
Vn = Estimated value of the nth parameter of a given water
Sn = Standard permissible value of the nth parameter
Vio = Ideal value of the nth parameter of pure water (i.e., 0 for all other parameters except pH and Dissolved oxygen (7.0 and 14.6 mg/L, respectively)
Wn = Unit weight for the nth parameter
K = Proportionality constant
The Aquachem water quality software was used for the preparation of Piper diagrams. Multivariate statistical analysis i.e. hierarchical cluster analysis (HCA) and factor analysis (FA) were used for apportion of contaminant sources  -  . The windows statistical software STATISTICA 7.1 was employed for the multivariate statistical calculations.
3. Results & Discussion
3.1. Geological Characteristics of Tube Wells
The geological characteristics of the tube wells are presented in Table 1. The depth of tube wells was ranged from 30 - 150 m with mean value (p = 0.05) of 90 ± 13 m. The age of tube wells was found in the range of 1.0 - 46 Yr with mean value (p = 0.05) of 10 ± 5 Yr. Generally, younger tube was found to be contaminated with higher content of ions i.e. Na+, K+, Mg2+, Ca2+, Cl−, , and, may be due to poor scavenging fluxes. The T value of the groundwater was ranged from 20.1 - 22.9˚C with mean value (p = 0.05) of 21.6 ± 0.3˚C. The slight increase with respect to increasing depth of tube well from 30 - 150 m was observed, may be due to geothermal energy.
Table 1. Geological characteristics of tube wells.
C = Commercial, I = Industrial, R = Residential.
3.2. Physico-Chemical Characteristics of Groundwater
The physical characteristics of the groundwater of 28 locations are shown in Table 2. The groundwater was colorless when drawn out from the tube well but after some time (≈12 hr) become turbid due to precipitation of the bicarbonates as carbonates. The pH value of the water was ranged from 6.3 - 8.2 with mean value (p = 0.05) of 6.8 ± 0.2. The lowest pH value, 6.3 of the water was observed in the sewage dumping and industrial areas: Kachana and Siltara, due to presence of excessive levels of anions (i.e. Cl−, and). In 92% locations, the pH values of the water were marked in the range of desirable range i.e. 6.5 - 9.2  . The DO and RP values were ranged from 3.7 - 7.2 mg/L and 114 - 144 mV with mean value (p = 0.05) of 4.6 ± 0.5 mg/L and 126 ± 0.03 mV. The DO value of the water observed was above the recommended value of 4.0 mg/L   . The RP value of the groundwater was found at least 5-folds lower than the recommended value of 650 mV. Extremely high EC values of the water was marked, ranging from 1419 - 6300 μS/cm with mean value (p = 0.05) of 2629 ± 508 μS/cm. The EC value was found to be correlated well (r = 0.92) with the sum of total ionic concentration ions (i.e. Cl−, , and Na+). The highest EC value of water was marked at the location i.e. Kachana, may be due to input of the sewage waste.
Similarly, extremely high TDS, TH and TA values of the water were observed, ranging from 6338 - 14,568, 241 - 1432 and 209 - 878 mg/L with mean value (p = 0.05) of 10,731 ± 603, 519 ± 130 and 319 ± 74 mg/L,
Table 2. Mean value (n = 2) of physical characteristics of groundwater in post monsoon period, January, 2012.
respectively. The highest TDS value of the water was seen at the location: Gudhiyari may be due to huge commercial and transportation activities. However, the highest TA and TH values were recorded at location i.e. Kachana, may be due to input of the sewage waste.
The chemical characteristics of the groundwater are summarized in Table 3. The concentration of DIC and DOC was ranged from 1300 - 7400 and 4500 - 7900 mg/L with mean value (p = 0.05) of 4400 ± 1300 and 6500 ± 900 mg/L, respectively. Similarly, the highest DIC and DOC values were marked in the water at location i.e. Gudhiyari. The DOC value of the water was several folds higher than the recommended value of 2 mg/L, may be observed due to percolation of the industrial and municipal waste into the groundwater aquifer. The higher DIC value of the groundwater of this region was marked, may be due to oxidation of the DOC with the microbes.
The concentration of F−, Cl−, , , Na+, K+, Mg2+ and Ca2+ in the post monsoon period was ranged from 0.4 - 1.6, 88 - 446, 46 - 991, 45 - 173, 31 - 130, 4 - 56, 16 - 84 and 56 - 256 mg/L with mean value (p = 0.05) of 1.0 ± 0.2, 224 ± 45, 206 ± 101, 105 ± 20, 60 ± 13, 18 ± 5, 28 ± 7 and 92 ± 22 mg/L, respectively. The highest concentration of all ions (except F− and Na+) was seen at location i.e. Kachana, may be due to input of the sewage waste. At two locations i.e. Gogaon and Khamtarai, the concentration of F− was found to be above the permissible limit of 1.5 mg/L   .
Table 3. Mean value (n = 2) of chemical characteristics of groundwater during post monsoon period, January, 2012, mg/L.
Chloride in ground water may originate from various sources including: the dissolution of halite. The recommended tolerance limit for Cl− reported is 250 mg/L   . The Cl− concentration beyond permissible limit was observed in the water of 50% tube wells. The ionic ratio of [Cl−]/[Na+] in the water was ranged from 0.9 - 6.8 with a mean value (p = 0.05) of 2.7 ± 0.5 with exceeding of [Cl−] to [Na+] in water of the 96% tube wells, may be due to dissolution of halite minerals. The high Na+ concentration (beyond 20 mg/L) in the water may cause health hazards i.e. high blood pressure, heart disease, kidney problem, etc. In the water of all tube wells, the [Na+] was found above the limit of 20 mg/L. The ionic ratio of [Na+]/[K+] in the water was ranged from 2 - 17 with a mean value (p = 0.05) of 7 ± 1 similar to natural water.
High concentration of (150 mg/L) in groundwater of 18% tube wells was marked, ranging from 254 - 2330 mg/L with mean value (p = 0.05) of 1059 ± 392 mg/L. The water of all tube wells was contaminated with above the permissible limit of 45 mg/L   . Groundwater of 31% and 62% tube wells of the studied area was found to be contaminated with Mg2+ and Ca2+ beyond permissible limit of 30 and 75 mg/L, respectively.
The domination of the DOC, DIC and Cl− in the water was observed. The chemical species i.e. carbons and ions in the water was found to occur in following decreasing order: DOC > DIC > Cl− > > > Ca2+ > Na+ > Mg2+ > K+.
3.3. Seasonal Variation
The variation of ion concentration during post (January, 2012) and pre monsoon (May, 2012) periods is presented in Figure 2. The T value of the groundwater (n = 28) was increased during the pre monsoon period (i.e. May, 2012) in the range of 26.0 - 28.0˚C with mean value (p = 0.05) of 27.3 ± 0.2˚C. The value of pH, EC, TDS, TH, TA, DOC, DIC, F−, , Na+, Mg2+ and Ca2+ of the water was found to be increased in the pre-monsoon
Figure 2. Parameters of groundwater during post and pre monsoon period (i.e. January, 2012 and May, 2012).
period, may be due to increase in the water temperature, ≈4˚C and shrinking of the water Table up to ≈30 m. However, the concentration of ions i.e. and K+ was found to decrease, may be due to decrease of the anthropogenic activities.
In the present study, HCA was used to classify the sample sites into hydrochemical groups in the post monsoon period. The Ward’s linkage method was used by using Euclidean distance for similarity measurement in the classification scheme. The result obtained by HCA detected the similar groups, yielding a dendrogram into three statistically significant clusters such as Group-I, -II and -III in the post monsoon period (Figure 3). The Group-I presented groundwater sample of location: Kachana which showed the highest values of parameters i.e. EC, TA, TH, and major cations (i.e. K+, Mg2+ and Ca2+) become as an outlier. The Group-II and Group-III were characterized by moderate and high pollution load of the chemicals in the groundwater, respectively.
The factor analysis (FA) derived a subset of uncorrelated variables called factors that explained the variance observed in the original dataset. In FA, all the variables were standardized at the z-scale (mean and variance set to zero and one, respectively) to minimize the effects of different units and variance of variables  . The FA was performed for the set of 28 sample locations with 20 variables in order to establish the association between the chemical and physical variables of the groundwater. Factor extraction was carried out by using principal components based on Kaiser Criterion  . Factors with eigenvalues higher than 1 were retained and presented in Table 4. Six factors explaining 84.62% of the total variance were retained after normalized varimax rotation. Factor-1 accounted for 44.18% of the total variance, revealed strong associations (high positive loadings) with TDS, EC, TH, Ca2+, Mg2+, Cl−, , and TA. This factor was characterized by complex processes derived from anthropogenic sources. Factor-2 explained 11.81% of the total variance, had strong positive loadings on pH and Na+. Factor-2 could represent weathering of Na-bearing minerals. Factor-3 accounted for 9.69% of the total variance, had a negative loading on RP, which confirmed that RP in the groundwater did not contribute significantly to the hydrochemistry. Factor-4 accounted for 8.67% of the total variance, had a negative loading on F−. This factor did not contribute significantly to the variation of the groundwater hydrochemistry. In the same order, Factor-5 which accounted for 5.26% of the total variance, had a negative loading on depth and did not contributed significantly to the groundwater hydrochemistry. At last, factor-6 accounted for 5.01% of the
Figure 3. Dendrogram of groundwater samples in the post monsoon period, January 2012.
Table 4. Factor analysis of variables of groundwater during post monsoon period, January, 2012.
Significant loadings > 0.7 (in italic and bold) at p < 0.05.
total variance, had a positive and negative loading on DOC and age which did not contribute statistically.
The results of FA in the pre monsoon period are shown in Table 5. Three factors explaining 79.37% of the total variance were extracted. Factor-1 accounted for 56.67% of the total variance, described complex processes such as mineralization and dissolution of evaporate in the water. Factor-2 represented 13.44% of the total variance, had positive and negative loading on and pH, which did not contribute statistically to the hydrochemistry. Factor-2 was related to anthropogenic activities (i.e. runoff and waste water). Factor-3 was accounted for 9.26% of the total variance, had a positive and negative loading on T (˚C) and F−. Factor-3 characterized the importance of temperature on the dissolution of evaporate.
3.5. Water Quality Assessment
As per Piper diagram, the groundwater in the post monsoon season was mostly classified into two types: Ca-Cl- SO4-NO3-HCO3 and Ca-SO4-NO3-HCO3 of water. The most dominating type of water was Ca-Cl-SO4-NO3- HCO3. In the pre monsoon season, only Ca-SO4-NO3-HCO3 water was observed. The WQI of the water in the post and pre monsoon period was ranged from 218 - 846 and 321 - 889 with mean value (p = 0.05) of 361 ± 45 and 504 ± 56, respectively. The value of TDS, TH, TA, F−, , Cl−, , Mg2+ and Ca2+ in the pre monsoon period was found above the recommended values of 500, 200, 120, 1.5, 45, 200, 150, 30 and 75 mg/L, respectively   . These data showed that the groundwater of Raipur city was found to be unsuitable for the drinking purposes.
The values of SAR, KR, SH, MH and PI values of the groundwater in the post monsoon period were ranged from 1.3% - 6.2%, 0.3% - 2.0%, 26% - 70%, 28% - 38% and 47% - 87% with mean value (p = 0.05) of 3.0 ± 0.5, 0.9 ± 0.2, 48 %± 4%, 33% ± 1% and 71% ± 4%, respectively. Generally, the MH, SAR, KR and PI value of <50,
Table 5. Factor analysis of variables of groundwater during pre monsoon period, May, 2012.
Significant loadings > 0.7 (in italic and bold) at p < 0.05.
<10, <1 and <25 were considered good for the irrigation purposes   -  . The SH value in the water of all tube wells was found in the range of 26% - 70%, indicating permissible water quality for the irrigation purpose  .
The water of Raipur city is found to be very hard with high EC and TA values. The domination of Ca-Cl-SO4- NO3-HCO3 type water was observed, may be due to huge industrial and urban activities. The quality of water was found to be deteriorated due to excessive mineralization of species i.e. DOC, DIC, Cl−, , , , Na+, K+, Mg2+ and Ca2+, and not found to be suitable for drinking purposes.
We are thankful to the UGC, New Delhi for awarding the RG scholarship to one of the author, NSD for doing this work.
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