4.2 Hydrochemical facies
Areal distribution and Hydrochemical evolution can be understood by plotting graphs of groundwater main dissolved components.
4.2.1 Piper plot
Piper 1944 had proposed one tri-linear plotting method which is the most widely utilized method for studying geochemical facies of groundwater. This plot allows clustering of data points to show samples which have same constitutions (Sankaran et al. 2015). The diamond plot is at the center and it is merged by two tri-linear plots that are on the two sides of the diamond. On the basis of supremacy in ion concentration dissimilar quadrants of diamond show the dissimilar kind of water as shown in Fig. 2a. Figure 2a shows the depiction of the results obtained from Unai and Saputara on the piper diagram. From figure it can be seen that U2, U3, and S2 fall in Sodium Chloride water region while U1, S1, and S3 come under Calcium Sulphate supremacy water region. Figure 2b represents the piper diagram of WCGP Maharashtra, India. In WCGP, Koknere, Unhavre-Farare, Akloli, Mandangad, Pali, Sativili, and Padusapada fall in Sodium Chloride water region while Tural 1, Tural 2, Rajwadi, Anjaneri-Math, Dasgaon, and Ganeshpuri fall in Calcium Sulphate water region.
4.2.2Extended Durov plot
The geochemical process which alters the groundwater quality can be disclosed by Durov (1948) plot (Lloyd and Heathcoat, 1985). In extended Durov plot, pH and TDS plots are included to the downside and right side of the diagram. In Durov diagram there are two tri-linear plots of cations and anions. The Hydrochemical process such as dissolution or precipitation and type of water like NaCl or CaCO3 will be identify by point of intersection of lines from tri-linear plots of the similar water sample in the binary plot. In Unai and Saputara, Higher concentration of Ca and HCO3− + CO32− and lower concentration of NaCl was observed in U1, S1, and S3 in comparison of U2, U3, and S2as shown in Fig. 3a. Higher concentration of Ca and HCO3− was observed in Koknere and Rajpur-Unhale compare to other regions in WCGP. In Unhavre-Farare NaCl concentration is quite high which is represented in Fig. 3b. Piper and Extended Durov plots are showing similar conditions of cations and anions in both regions but there are many other features which can affect the geochemistry of groundwater hence several other plots and graphs should be combined to find the conclusion.
4.2.3 Schoeller plot
The semi-logarithmic illustration of the concentrations of major ionic constituents present in the water is known as a Schoeller diagram (Schoeller, 1961). The anions and cations present in the water samples have taken on the X-axis and their concentrations have been plotted on Y-axis for all the samples. Different ions present in various samples can be compared with the help of this plot. From Fig. 4a it can be seen that U2 and U3 are having great similarity and U1 is different from other two. S1, S2, and S3 are having almost similar pattern. In all the samples supremacy of Na + K cations and Cl anions is there. Figure 4b represents the major ion concentration present in the water sample from WCGP. In Koknere, dominance of Na + Ca cation and Cl anion were observed.
4.2.4 Stiff Diagram
The chemical analyses of geothermal water can be done by graphical representation which is defined as a stiff diagram. Hydrogeologists and geochemists are widely use stiff diagram to depict the main ion composition of a water sample. In this diagram one vertical zero axis and four similar horizontal axis are plotted. These four horizontal axis expanding on either side of a vertical axis which generates a polygonal shape (Stiff 1951). The ion concentrations have taken in meq/l. In the stiff diagram, left side of the zero axis cations have plotted and right side of the zero axis anions have plotted. Comparison of ion concentrations present in water samples from the different regions can be done by plotting stiff diagram. Stiff diagram for South Part of Gujarat and West Coast Geothermal Province is as shown ion Fig. 5.
4.2.5 Gibbs plot
With the help of Gibbs diagram water chemistry and its chemical formation from the consequent aquifers such as evaporation rate, precipitated chemistry, and rock form chemistry can be understood (Ronald J 1970). In order to understand nature of geothermal water chemistry from different regions of Gujarat and Maharashtra, Gibbs difference Cl−/(Cl− + HCO3−) i.e. anions and Gibbs variance Na+/(Na+ + Ca2+) i.e. cations of water samples have been plotted discretely against respective values of TDS in mg/l. From TDS Vs Na+/(Na+ + Ca2+) (Fig. 6a) it can be observed that U2 and U3 have shown evaporation dominance and U1, S1, S2, and S3 have shown rock dominance in geothermal water composition. TDS Vs Cl−/(Cl− + HCO3−) is similar to the TDS Vs Na+/(Na+ + Ca2+). In the case of WCGP, TDS Vs Na+/(Na+ + Ca2+) (Fig. 6b) has indicated that Koknere, Pali, Akloli, Padusapada, Unhavre-Farare, Mandangad, Dasgaon, Ganeshpuri, Sativili, and Anjaneri-Math have shown evaporation dominance and Tural 1, Tural 2, Rajwadi, Aravali, and Rajpur-Unhale have shown rock dominance in geothermal water composition. TDS Vs Cl−/(Cl− + HCO3−) is almost similar to the TDS Vs Na+/(Na+ + Ca2+) except Dasgaon. In this plot Dasgaon has shown rock dominance. In the case of alluvial plains, the groundwater chemistry is majorly dominated by rock-water interference occurrence (Alam 2014). From Fig. 6a and Fig. 6 bit can be observed that none of the water samples have precipitation dominance. Precipitation dominance indicates that samples have taken during monsoon. Geothermal water of Unai and Saputara is having TDS concentration near 1000 mg/l thus it can be use for societal purposes while water from WCGP is having high concentration of TDS > 1000 mg/l which is not suitable for any purposes. After desalination of this water it can be used for various purposes like drinking, irrigation, domestic, and industrial.
4.2.6 Ternary plot
The proportion of major ions presented in geothermal spring water is represented by Ternary diagram (Giggenbach, 1991). Two different Ternary diagrams of cations and anions have plotted with a view to differentiate fluids from various sources. Ternary diagram for cation is combining Na-K with K-Mg. In Unai and Saputara, all locations are having water with lower concentration of Mg. All the points fall on the Na-K line since there is very less concentration of Mg is present as shown in Fig. 7a. Similarly, in WCGP concentration of Mg is very less and Na and K concentrations are comparatively very high as depicted in Fig. 7b. Therefore, all the points are fall on the Na-K line. Figure 7c represents the major anion concentration present in the water sample from Unai and Saputara. This type of ternary plot is used to categorize the forms of geothermal water of a field under study. There are four types of geothermal water: Mature water, volcanic water, steam heated water, and peripheral water which can be discriminated from the ternary diagram.U1, U2, U3, S1, S2, and S3come under Cl rich domain of geothermal water and which shows that it is mature water. All the points are fall on the Cl-SO4 line because HCO3 concentration is comparatively low. In geothermal water of U2 andU3 supremacy of SO4 over HCO3 as compared to U1 indicates that geothermal water may have been blended with marginal steam heated water or it may be due to interaction of water with sulfur bearing environment during water-rock interaction. High chloride content of water is suggesting influence of seawater intermixing with thermal fluids. Distribution of anion concentration in geothermal water of WCGP is as shown in Fig. 7d.Due to the high Cl concentration, most of the thermal spring waters plot near the chloride apex. Spring waters of Dasgaon, Anjneri-Math, and Aravali are having high SO4/Cl ratios and hence it is somewhat shifted towards the SO4 field indicates dissolution of sulfur bearing minerals. Thermal springs (1, 6, 8,9,3,and 4 from Table 2) on the northern part of the study area drop on the Cl-SO4 line which has shown high concentration of Cl due to seawater mixing. Thermal springs (10, 14, 13, and 11 from Table 2) pointing towards two different saline sources. In WCGP, all locations come under Cl rich domain of geothermal water and which shows that it is mature water except Rajpur-Unhale (15 from Table 2). It falls on the Cl-HCO3 line and it is peripheral water as shown in the Fig. 7d.
4.2.7 Wilcox diagram
Groundwater suitability for irrigation purposes can be analyzed very effectively with the help of Wilcox diagram (Wilcox, 1955). Percentage of sodium (%Na) Vs. Conductivity graph has been plotted for geothermal water samples from Unai and Saputara as shown in Fig. 8c. Geothermal water from Unai 1 has fallen under the range of good to permissible and Saputara 1, 2, & 3 have fallen under the range of permissible to doubtful. Unai 2 and Unai 3 have fallen on the border of permissible to doubtful and doubtful to unsuitable as shown in Fig. 8c.Therefore, geothermal water of Unai 1 is suitable for drinking and irrigation purposes. Water from Saputara 1, 2, & 3 and Unai 2 & 3 are not suitable for drinking but it can be used for irrigation, domestic, and industrial purposes. No samples from South part of Gujarat have fallen under unsuitable that means geothermal water of this region is suitable for various purposes. As shown in Fig. 8d Rajapur-Unhale has fallen within the range of excellent to good means it can be directly used for drinking and irrigation purposes. Tural 1, Tural 2, Rajwadi, and Dasgaon have fallen under the range of permissible to doubtful and Aravali, Anjaneri-Math, Ganeshpuri, Sativili, Padusapada, and Mandangad have come under the range of Doubtful to unsuitable which indicates that it is not suitable for drinking purposes but it can be used for irrigation. Unhavre-Farare, Akloli, and Pali have fallen within the range of unsuitable (Fig. 8d) and thus water from these regions require pre-treatment before using it for drinking and irrigation.
In the Wilcox log plot, Sodium Adsorption Ratio (SAR) has plotted on the Y-axis and Conductivity has plotted on the X-axis. The Conductivity has represented in a log scale. This plot is also helpful in testing suitability of water for irrigation. From Fig. 8ait can be seen that S1, S2, S3, and S4 are sodium hazard classes and C1, C2, C3, and C4 are salinity hazard classes. Unai 1 has fallen within the range of S1-C3 (Fig. 8a); it shows that it can be used for drinking and irrigation purposes. All other locations i.e. Unai 2 & 3 and Saputara 1, 2, & 3 have fallen within the range of S2-C3 and it indicates that it is suitable for irrigation, domestic, and industrial purposes but not suitable for drinking purposes. In the case of WCGP, geothermal water of Rajapur-Unhale has fallen within the range of S1-C2 and which shows that it is suitable for drinking and for agricultural purposes as shown in Fig. 8b. Anjaneri-Math, Dasgaon, Rajwadi, Tural 1, and Tural 2 have fallen under the range of S2-C3 means it can be used for all other purposes except drinking. Aravali has come under the range of S3-C3 which is showing that it cannot be used for drinking purposes. Ganeshpuri, Padusapada, Sativili, Akloli, and Pali have fallen under the range of S2-C4 (Fig. 8b), which indicates that geothermal water of these regions require pre-treatment before using it for various purposes. Unhavre-Farare has come within the range of S3-C4 (Fig. 8b) which is also very high hence it requires pre-treatment before its use for drinking and irrigation.
4.2.8 Spatial distribution plot
Spatial distribution curves for various locations in South part of Gujarat and West Coast Geothermal Province are as shown in Figs. 9 and 10, respectively.