1 Introduction

Sustainability of groundwater becomes a challenging environmental and social issue in the Indian scenario. Whereas, in the past, the management of groundwater resources was based predominantly on the concept of available renewable resources. Today it is necessary to protect groundwater to balance the obstacles and maintain groundwater sustainability to meet the human and environmental needs. Groundwater assessments involve multiple approaches based on the type of interpretation leading to management strategies. Understanding of qualitative and quantitative variation in the groundwater system because of existing and proposed hydrologic significance is a base for their proper management. Tainting of the groundwater by residential, industrial effluents and agrarian movement is a significant issue in developing nations. The conventional techniques (histograms, trilinear, semi-logarithmic) manage a set of factors accountable for groundwater quality (Matthees 1982; Hem et al. 1989; Vishnu et al. 2014), the constraining values (action limits) for tainted soil might be lower than natural concentrations (backgrounds) over wide regions (Salminen and Tarvainen 1997; Sakram et al. 2015).

Hydrochemical assessment of groundwater frameworks is generally found in accessibility of data pertaining to groundwater quality (Aghazadeh and Mogaddam 2010; Sakram et al. 2018; Sreedhar et al. 2018a), relies upon physical and substance dissolvable elements because of disintegration from rocks and manmade wastes bringing about a complex groundwater quality, it is unequivocally subject to bedrock, lithology and atmosphere. However, may likewise be affected in parts by contamination, especially from farming and mechanical sources. The most significant farming contaminations are abundant utilization of composts and pesticides; however, it is perceived that manure and pesticide applications are not as concentrated as in numerous western countries. Phosphate and potassium fertilizers are likewise utilized, however, versatility of these in the soil is considerably less than that of nitrate. Another effect of contamination is probably going to be a high concentration of total dissolved solids (TDS).

Overall, groundwater quality relies upon the extent of precipitation and water recharge, association between the rock and water, in a spread of time result with aquifer system (Appelo and Postma 2005; Vishnu et al. 2014; Narsimha and Sudarshan 2016). The significance of the quality of water in individuals has sporadically pulled in a lot of intrigue. In fast-growing nations like India, roughly 80% of all maladies are understood to be identified with the consumption of poor water quality and unhygienic surroundings (Olajire and Imeokparia 2001). The over-abstraction of subsurface water had numerous impacts on all water resources. Groundwater sources are exhausting continuously in several zones with an irregularity among recharge and discharge. This has come into an intense water deficiency with groundwater as the main option. Inadequacy and dependableness in groundwater in the region related to considerable change in groundwater chemistry and quantity.

Geophysical studies are important to portray sub-surface of the earth basically to outline water-bearing locations and help in locating groundwater zones of recharge and discharge. A wide scope of geophysical study systems includes electric, electromagnetic, gravity, magnetics, ground penetrating radar (GPR), and seismic strategies are accessible for examination of sub-surface topography. The decision of the geophysical technique depends on physical property differentiate and logistic support in the region. Electrical and seismic strategies are broadly utilized for groundwater applications. The simplicity of activity and practical utilization of electrical resistivity technique has turned out to be prominent for groundwater investigation particularly in India. The direct current (DC) electrical resistivity system has been broadly used to picture geoelectric structure of shallow subsurface earth (Zohdy et al. 1974; Parasnis 1986; Giao et al. 2003; Kumar et al. 2007; Dhakate et al. 2008, 2012). Electrical profiling (EP) method was used to study horizontal impacts of varieties in the sub-surface (Giao et al. 2003). A resistivity model got from the reversal of 1-D information brings about poor goals particularly for maximum depth limits and give point vertical data. Then again two-dimensional electrical resistivity tomography (2D-ERT) method has the point of interest over traditional resistivity and contemplated by numerous researchers (Batayneh 2001; Daily et al. 2004; Adepelumi et al. 2006; Kumar et al. 2010; Robert et al. 2011). One of the chief preferences of the multi-terminal resistivity tomography method bears an unmistakable perspective on geoelectrical changes inside regolith which promptly identify porosity and permeability in vertical profile through regolith in crystalline rocks (Owen et al. 2005). Low-recurrence electrical techniques for subsurface portrayal and checking in hydrogeology is clarified in ongoing study and exhibit subsurface portrayal and groundwater stream (Revil et al. 2012; Abdulaziz et al. 2012).

The aim of the study is to survey degrees of water quality as for normal centralizations of elements in the region, to study the relationship between contaminated components and their spatial occurrence as well as to distinguish potential pollution zones. The subsequent target is to recognize groundwater potential utilizing geophysical procedures in the region.

2 Location of the study area

The study area lies in the south-western part of Telangana State, 100 km away from Hyderabad City, comprising of 23 villages falling in Nyalkal and Zaheerabad Mandals located between latitude 17°45′–17°50′N and longitude 77°30′–77°40′E falling in toposheet number 56 G/9 and 56 G/10. The topographic elevation of the study area ranges from 553 to 665 m above mean sea level (amsl) (figure 1).

Figure 1
figure 1

Key map of the study area showing drainage pattern and topographic elevation.

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3 Geology and hydrology of the study area

Geologically the region comprises of traps and laterites. These rocks are hard-massive to foliated (resembles the skin of elephant endured) and very much jointed. The soil in the region observed fine black alluvium and reddish to brown in shading. The soil is porous and permeability high with respect to downpour, which can cause extensive surface stream and disintegration. Traps occurring within the region of Nyalkal show vesicular and non-vesicular structures. The top-soil spread is a fine-created leftover soil of traps and laterites. The non-vesicular huge units are alluvium of fine-grained, thick and conservative. Certain spots show columnar and spheroidal structures and normally show fine-created joints within different regions. The vesicular kind of basalts is exceptionally altered which offered to ascend to laterite. In the region, around 9 flows of traps observed, initial seven flows not endured and show up as basaltic nature, though eighth and ninth flows totally endured and modified to laterite. Accordingly, laterite occurs as a top-cover over basalts as flatlands around 600–660 m (amsl). They have open spaces regularly loaded up with yellow-red clay material. A portion of lithomarge denotes separation between traps and laterite. The lithomarge appears silica in nature and displays dark colour to green shading with lathery touch and difficult to break and also called as ‘SapaMurram’ in local terminology.

Hydrogeological, aquifers of the region are covered by traps, laterites and alluvial deposits. The traps include a sequence of volcanic rock flows (nearly horizontal in nature) separated by intratrappean beds, wherever every flow contains 40–70% of large volcanic rock within lower zones and 30–60% vesicular basalt in upper zones (Madhnure 2001; Sakram et al. 2019). The weathered thickness was found between depths of 6 and 29 m, and joints and fractures depth reduce within granitic environment. Sediment deposits occur on the Godavari stream courses with 12–30 m thickness, comprising clay, silt and gravels and occasionally cobbles that bear productive aquifers (Madhnure 2001; Sakram et al. 2019). In the present study, geological mapping was done using IRS-1C, LISS-III image, using image processing software ERDAS for better exposition of hydrogeological features. GIS package ARC-GIS (ARC-Map) was used for mapping features. Basalts exhibit a greenish tone with a coarse texture and laterite show yellow tone (figure 2).

Figure 2
figure 2

Geology and LISS III satellite image of the study area.

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4 Materials and methods

4.1 Hydro-geochemical investigation

Fifty groundwater samples were gathered from bore wells of the study region in non-reused Polyethylene bottles (2 L). The temperature, electrical conductivity, and pH were resolved infield because of their unstable nature with separate meters. Total hardness (TH) as \( {\text{CaCO}}_{3}^{2 - } \) and calcium (Ca2+) were examined titrimetrically, utilizing standard EDTA. Magnesium (Mg2+) was figured, taking contrast among TH and Ca2+ values. Carbonate (\( {\text{CO}}_{3}^{2 - } \)) and bicarbonate (\( {\text{HCO}}_{3}^{2 - } \)) were evaluated by titrating with \( {\text{H}}_{2} {\text{SO}}_{4}^{ - } \) Sodium (Na+), and Potassium (K+) was estimated by a flame photometer (Model-Mediflame 127). Chloride (Cl−) was assessed by standard \( {\text{AgNO}}_{3}^{ - } \) titration. Sulphate (\( {\text{SO}}_{4}^{ - } \)) was estimated by spectrophotometer (Model-Spectronic 21). Nitrate (\( {\text{NO}}_{3}^{2 - } \)) and fluoride (F−) were measured utilizing ion particular cathodes (Model-Orion 4 star). Total dissolved solids (TDS) were determined from specific conductance (EC) utilizing empirical formula (Richards 1954). The statistical summary of analyzed groundwater samples for major ions and trace elements is given in tables 1 and 2.

Table 1 Statistical summary of groundwater sample for major ions and comparison with WHO (2004) standards.
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Table 2 Statistical summary of groundwater sample for trace elements and comparison with WHO (2011) standards.
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4.2 Geophysical investigation

Geophysical information incredibly helps in finding the groundwater potential in any hydrogeological arrangement. The property and thickness of overburden acquired from geophysical overview at the area can yield a groundwater potential model of higher reliability quality and exactness. However, variations in electrical resistivity of different segments litho units in a geologic arrangement rely upon numerous components including type of rocks and soils, penetrability, degree of satiety and nature of the saturating fluid and digenetic cementation factors. Wenner technique was utilized to recognize groundwater potential points, where four electrodes are set in a line, and a realized flow is gone through two extreme electrodes, the potential contrast estimated between two inward terminals gives a proportion of the resistivity of the ground. The estimation of resistivity ‘ρ’ is estimated by the formula:

$$ \rho = \left( {V/I} \right) \times 2\pi a\, \,\,\,\left( {{\text{in}}\;{\rm{\Omega}} {\text{m}}} \right), $$

where V is voltage (potential) measured in millivolts between two inner electrodes, and I is current measured in milliamperes passed into ground, a is the distance between consecutive electrodes and 2π is constant. Since V/I = R, resistance (in Ωm), the formula may be expressed as:

$$ \rho = 2\pi aR\,\,\,\,\left( {{\text{in}}\;{\rm{\Omega}} {\text{m}}} \right). $$

The interpreted layered earth model is deciphered utilizing IPI2 WIN programming, to decrease interpretation error as far as possible (Barker 1989). Geo-electric segments were found from deciphered information. Every geoelectric layer relates to the inferred lithological property. The subsurface order fluctuates starting with a single geoelectric layer then onto the next. The electrical resistivities differentiate over lithological divisions to depict geoelectric cross-sections (Schwarz 1988).

Total 103 Vertical Electrical Soundings (VES) using Wenner configuration were carried out using DDR-III Resistivity Meter (IGIS make) with maximum current electrode dispersing (AB/2) have the greatest spread of 180 m (figure 3). Initial curve matching techniques were adopted for getting initial layer parameters (Orellana and Mooney 1966). Further, interpretation was done using IP2WIN software. The final interpreted layer parameters are given in table 3. Based on interpreted VES results, the resistivity ranges of different sub-surface layers were calculated and given in table 4.

Figure 3
figure 3

Profiles along with the vertical electrical soundings conducted in the study area.

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Table 3 Interpreted results of VES carried out in the study area (ρ is resistivity in Ωm, h is layer thickness in m).
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Table 4 Resistivity ranges of different sub-surface formation.
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5 Results

5.1 Hydro-geochemistry

The statistical summary of analyzed parameters of 50 groundwater samples for major ion and trace elements is shown in tables 1 and 2. pH ranges from 6.67 to 8.9; EC ranges from 87 to 900 µS/cm with average of 255.05 µS/cm at 25°C; TDS 56–576 mg/l with average of 163.23 mg/l; Ca2+ ranges from 6 to 59 mg/l; Mg2+ ranges from 1 to 45 mg/l; Na+ ranges from 0.13 to 263 mg/l with average of 0.91 mg/l and K+ ranges from 4 to 64 mg/l with average of 8.04 mg/l; TH 20–265 mg/l; \( {\text{HCO}}_{3}^{ - } \) 109.8–732 mg/l; Cl− 46–461 mg/l; \( {\text{SO}}_{4}^{ - 2} \) 1–132 mg/l; \( {\text{NO}}_{3}^{ - } \) 5–32 mg/l; F− 0.13–2.63 mg/l with averages of 278.44, 136.57, 16.43, 14.15, 0.82 mg/l, respectively. The loads of major ions are in order of Ca2+ > Mg2+> Na+> K+ and \( {\text{HCO}}_{3}^{2 - } \) > Cl−> \( {\text{NO}}_{3}^{2} \) > \( {\text{SO}}_{4}^{ - } \) > F− (table 1). The trace elements showed Al ranging from 30.16 to 386.98 µg/L, 34% of samples exceeding permissible limits (WHO 2011). Ni ranges from 5.72 to 258.97, 52% samples exceeding permissible limits. Pb ranges from 5.11 to 50.22, 52% samples exceeding permissible limits, and Zn ranges from 18.74 to 427.05, 64% of samples exceeding permissible limits, remaining are within the permissible limits (WHO 2011). The spatial distribution maps of major ions and trace elements are shown in figures 4 and 5.

Figure 4
figure 4

Distribution map of pH, TDS, \( {\text{CO}}_{3}^{2 - } \), \( {\text{HCO}}_{3}^{2 - } \), F−, EC, Cl−, TH and \( {\text{NO}}_{3}^{2} \) in the study area.

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Figure 5
figure 5

Distribution map of trace elements of groundwater in the study area.

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The hydrochemical fundamental elements of groundwater can be comprehended by plotting cations mobile phase and anions mobile phase (Piper 1944) (figure 6). Facies are prominent parts of various types having a hereditarily related framework. The plot demonstrates that a greater part of groundwater samples fall in the area of Na+–Cl− category by Ca2+–Na+–Cl− and Ca2+–Cl− types. From the plot, it is seen that alkalinity (Na+ and K+) surpasses the basic globe (Ca2+ and Mg2+) and solid acids surpass frail acids. By and large, groundwater chemistry is commanded via soluble base and acids.

Figure 6
figure 6

Trilinear diagram (after Piper 1944) in the study area.

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The major part of samples is well within possible permissible limits with few exceptions pH, EC, TDS, TH, Na+, K+, Ca2+, Mg2+, \( {\text{CO}}_{3}^{2 - } \), Cl−, \( {\text{SO}}_{4}^{ - } \), \( {\text{NO}}_{3}^{2} \), and F−. TDS in all samples are within limits with the exception in sample from Mungi Village. Spatial distribution of TDS, differentiated based on excellent (> 300 mg/l), poor (< 900 mg/l) shows popular of region abstaining lower TDS suitable for drinking purposes. High TDS in water may create terrible taste (Spellman and Drinan 2000). The pH of groundwater differed from 6.64 to 8.9. Ninety-eight percent of groundwater samples are found within the permissible limit. Chloride concentration differed from 46 to 461 mg/l, 84% of samples are within permissible limit, exception in Mungi (461 mg/l), Metalkunta (312 mg/l), Nyalkal service station (316 mg/l), Krishnapur (202 mg/l). Elevated chloride in water gives delectable taste to water because of the enduring of rocks, infiltration from the anthropogenic source. Water hardness is caused principally by the presence of cations and anions in water (Sadashivaiah et al. 2008). Calcium and Magnesium are within the permitted limit. Total hardness discusses to effect with soap and scale formation, the capacity of water to promptly increase in the boiling point of water form lather with soap. Nitrate in the region are within the permissible limits of WHO, the suitability of groundwater for cultivation system relies on its mineral constituents.

The most significant criteria for making a decision about water quality is the concentration of total salt estimated by the conductivity of electricity (EC) and sodium/alkali hazard normally communicated as absorption of sodium ratio (SAR) and percent sodium (%Na+). Richard (1954) characterized groundwater based on electrical conductivity, 100% of the samples belong to excellent water class under range 10. SAR evaluate the extent of Na+, Ca2+ and Mg2+ ions in the sample and its utility for cultivation purpose. At the point when sodium value is high, because of Ca2+ and Mg2+ in clay particles decreases the soil permeability (Srinivasamoorthy et al. 2009). Subsequently, sodium concentration plays a significant role in assessing groundwater quality for the irrigation water system. The SAR values for groundwater samples vary from 0.18 to 0.70 meq/l, suggested that groundwater in the region could be excellent for water irrigation system (Richards 1954).

It is seen that among the groundwater samples of the region, about 72% fall under C1S1 class representing low salinity-low sodium waters, 26% fall under C2S1 class showing medium salinity and low sodium waters and 2% of the samples fall under C3S1 class representing high salinity and low sodium water. Electric conductivity influences total salt concentration and soil salinity and consequently influencing the yield of the crop and its resistance consequently.

5.2 Geophysical interpretation

Hydro-geologically, the aquifer of the region is confined to traps, laterite and alluvium. The Deccan traps involve a sequence of basaltic magma flows (about flat in nature) isolated by red, dark or green bole as intratrappean beds, where each flow includes 40–70% of huge basalt in the lower zones and 30–60% vesicular basalt in the upper zones (Madhnure 2001; Sakram et al. 2013; Sreedhar et al. 2018b). In rock joints, cracks and fissures, due to enduring and faulting, create secondary porosity for aquifers. The endured thickness was found between depths of 6 and 29 m and joints and fractures diminish with depth in the granitic region. Alluvium dump occurs along the Godavari River track with 12–30 m thickness, containing clay, silt and gravels and irregularly cobbles that bear good aquifers (Madhnure 2001; Sakram et al. 2013, 2019).

A total of five cross-sections A–A′, B–B′, C–C′, D–D′ and E–E′ comprising of 103 Vertical Electrical Soundings (VES) was drawn for deciphering the sub-surface information and heterogeneities in the hard rock terrain (figure 3). The objective of the quantitative interpretation of resistivity data deciphered a range of three–four geo-electric succession: topsoil, laterite, sandy clay and weathered/fractured/vesicular basalt/massive basalt/weathered/fractured fresh bedrock (table 3). The electrical resistivity ranges across various lithological units are presented in table 4. The topsoil has resistivity values range from 26.61–930 Ωm, lateritic horizon (453–738 Ωm), clayey/sandy clay layer (4.71–94.2 Ωm), this prospect is target for hand wells and dug wells. Resistivity values of weathered/fractured rock layer range from 60.5 to 928 Ωm and weathered/vesicular/massive basalt ranges from 8.05 to 0.676 Ωm.

A–A′ geophysical pseudo section was drawn using VES nos. V1, V2, V3, V4 and V5 showing 20–200 Ωm resistivity up to 20 m indicating that the subsurface have weathered and fractured formation. After this depth, the pseudo section shows a resistivity range of 300–1000 Ωm indicating hard massive jointed basalt formation up to a depth of 100 m except at VES no. 3 (figure 7). The pseudo section B–B′ represented by VES nos. V11, V12, V13, V14 and V15 depicting very thick weathered/fractured formation with resistivity of 42–133 Ωm up to a depth of 80 m in the center part of the pseudo section, while hard rock with resistivity >500 Ωm was observed at VES No. V11 (figure 8). The pseudo section C–C′ represents VES nos. V16, V17, V18, V19 and V20 representing resistivity of >200 Ωm up to 40 m and 15 on the left and right side, whereas in the center part shows the resistivity >500 Ωm with the basement as hard rock (figure 9). D–D′ pseudo section was drawn by using VES nos. V21, V22, V23, V24 and V25 showing a low resistivity of 79–200 Ωm in centre part up to a depth of 50 m indicating a highly weathered/fracture formation which is good for groundwater prospecting. Top of the pseudo section shows high resistivity of >500 Ωm indicating a boulder formation, while the left portion of the section shows a resistivity >300 Ωm indicating a jointed basaltic formation (figure 10). Similarly, E–E′ pseudo section was drawn by using VES No. V6, V7, V8, V9, and V10. A thick zone of low resistivity of 100–167 Ωm seen in the middle of the pseudo section up to 40 m indicating weathered formation, below this a semi-weathered/fractured zone of resistivity 215–278 Ωm was seen followed by hard rock formation with high resistivity (figure 11).

Figure 7
figure 7

Geophysical pseudo cross-section A–A′.

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Figure 8
figure 8

Geophysical pseudo cross-section B–B′.

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Figure 9
figure 9

Geophysical pseudo cross-section C–C′.

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Figure 10
figure 10

Geophysical pseudo cross-section D–D′.

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Figure 11
figure 11

Geophysical pseudo cross-section E–E′.

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Stacked isopach map of overburden and basement resistivity maps revealed thick overburden, and fractured basement in few areas. High resistivity values (930, 676, 547 and 284.4 Ωm) topsoil in VES points 17, 18, 10 and 23 due to embedding of boulders at VES points and bedrock zone resistivity range (60.5–135901 Ωm). An iso-resistivity map of region demonstrates generally low resistivity towards endured or fissured rock layer and zones through moderate in height resistivity towards deciphered fresh bedrock (Olorunfemi and Olorunniwo 1985) though zones with either thick overburden or endured/fractured basement are outlined having medium yield while regions with slight overburden and high bedrock resistivity (fresh basement) as low groundwater potential zones. So as to guarantee the greatest and enduring yield, boreholes are best referred to regions where the regolith could be maximally drilled (Lenkey et al. 2005). The hydrological properties of traps are complex. Dependable groundwater bodies are often confined to near-surface weathered and jointed zones. Partly weathered traps form good aquifers, while in highly weathered form they become black cotton soil, which is impervious. In the case of massive basalts, groundwater occurs in joints and crevices. Vesicular basalts act as good aquifers when vesicles are interconnected and are not filled with secondary minerals like calcite and zeolite quartz. The basic controlling point in the region, observed from geophysical survey and litho-log at the time of drilling indicates good weathered zone with proper depth and ash bed/intratrappean/tuff beds were encountered, there was good yield in wells and failure cases have only massive basalt or clay formation. The iso-resistivity map of overburden, indicate high and low zones overburden thicknesses relate basement ridge and basement valley separately. The stacked iso-resistivity map utilized to create a groundwater source map of the region (figure 12).

Figure 12
figure 12

Iso-resistivity maps showing top soil, weathered and fractured thickness for further groundwater prospects in the study area.

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6 Conclusion

Integrated studies using hydrochemical and geophysical investigation were conducted in parts of Medak District, Telangana. The water quality analysis results of major ions and trace elements show good water quality except for few samples exceeding the permissible limit. However, the parameters like TDS, TH, K+, \( {\text{CO}}_{3}^{ - } \), and Cl− exceeds the concentration of permissible limits of 2%, 8%, 2%, 76% and 16% of the total samples. While, trace elements concentration exceeds the permissible limit in Al, Pb, Zn and Cr. The elevated concentration was due to anthropogenic source in the study area. Piper plot reveals that the groundwater was Ca2+–Na+–Cl− and Ca2+–Cl− types. Majority of the sample falls under C1S1 class and few sample falls under C2S1 category representing low to medium salinity. Geophysical investigation reveals that the area was consisting of three–four geo-electric subsurface formations consisting of soil/alluvium, laterite, fractured/jointed basalts and massive bedrock. The groundwater prospects are more in the area having thick overburden and jointed and fractured hard rock. Vesicular basalts also act as good aquifers when vesicles are well interconnected. The iso-resistivity map of overburden, indicate high and low zones, overburden thicknesses relate basement ridge and basement valley separately and can be utilized to create groundwater source map of the region. North-western and eastern part of the study area was moderately covered by thick overburden overlie on endured or fractured bedrock distinguished have most potential possibilities and outlined for good groundwater yield. This study helps to identify the best feasible points for groundwater exploration, which in turn helps the society to abstract potential wells in the study area. Furthermore, the less groundwater potential zones identified will be made more potential by adapting groundwater recharge system. This also benefits in improving the water quality.