Groundwater quality around Tummalapalle area, Cuddapah District, Andhra Pradesh, India

Water is an indispensable natural resource on earth. Safe drinking water is the primary need of every human and also their basic fundamental right (Nagaraju et al. 2015, 2016c; Li et al. 2015). Fresh water has become a scarce commodity due to over exploitation and pollution of water. Groundwater is the most important source of water supply for drinking, agriculture, irrigation and industrial purposes (Gupta and Sunita 2009; Bhattacharya et al. 2012; Li et al. 2013a, 2014a; Nagaraju et al. 2013, 2014a, 2016a, b; Wu and Sun 2016). There is a growing awareness of the environmental legacy of mining activities that have been undertaken with little concern for the environment (Mahesh et al. 2001; Brindha et al. 2010; Tripathi et al. 2011). Mine water can vary greatly in the concentration of contaminants present, and some mine water discharges can be a potential water resource, where the local water demands for industrial, irrigation and even drinking and domestic uses can be fulfilled by effective utilization (Cidu et al. 2007; Manish Kumar et al. 2007; Suresh et al. 2007; Li et al. 2013b; Nagaraju et al. 2006, 2014b, 2015; Wu et al. 2014).

Metal pollution by mining and associated industrial activities is somewhat mitigated today by strict implementation of clean technology and environmental measures. The drastic increase in population, urbanization and modern land-use applications and demands for water supply has limited the globally essential groundwater resources in terms of both its quality and quantity. Further, the quality is a function of the physical, chemical and biological parameters, and can be subjective, since it depends on a specific intended use (Ravikumar and Somashekar 2013). Tummalapalle is a famous uranium mining area in India, and the mining activities generally cause groundwater pollution. Therefore, the purpose of this paper is to summarize groundwater quality in and around Tummalapalle uranium mining area and focus its impact on water quality for irrigation and drinking purpose.

In this area, the climate is tropical with seasonal rainfall. This area has rather a hot summer with temperature as high as 42 °C and minimum temperature being 15 °C. This region is known for its wide variation in contour, heavy vegetation, low rainfall and significant variation in meteorological parameters. The average annual rainfall of the Cuddapah District is about 710 mm and it ranges from nil rainfall in January to 137 mm in October and this is the wettest month of the year. The mean seasonal rainfall distribution is 402.4 mm in south-west monsoon (June–September) and in north-east monsoon (October–December) this is about 239.1 mm. The percentage distribution of rainfall is about 56.7% in south-west monsoon and 33.7% in north-east monsoon (Central Ground Water Board 2013).

Groundwater occurs under water table conditions in the weathered zones of Papaghni and Chitravati group of rocks. The water present in the dug wells is mainly due to the numerous joints, fractures and fissures present in these rock types. The quartzites and the basal part of the massive limestone are good aquifers, and the permanent water table in these is generally shallow. Water is alkaline in nature and suits both for irrigation and drinking purposes (Geological Survey of India 2001). It is found that the groundwater in the Tummalapalle village is saline due to unhygienic conditions, since water found away from the village in surrounding area is generally sweet. The depth of water level is observed between 10 and 20 m in Vemula mandal (Central Ground Water Board 2007, 2013).

Geochemical properties and principles that govern the behaviour of dissolved chemical constituents in groundwater are referred to as hydrogeochemistry. The dissolved constituents occur as ions, molecules or solid particles. The chemical composition of groundwater is related to the solid product of rock weathering and changes with respect to time and space. Hence, the variation in the concentration levels of the different hydrogeochemical constituents determines its usefulness for domestic, industrial and agricultural purposes. The minimum, maximum, average, SD and SE values of the hydrochemical data of the study area are shown in Table 1 along with the calculated parameters of the hydrogeochemical data.

The high concentration of sodium in irrigation water may negatively affect the soil structure and decrease the soil hydraulic conductivity in fine-textured soil. The degree to which sodium will be absorbed by a soil is a function of the amount of sodium to divalent cations (Ca²⁺ and Mg²⁺) and is regularly stated by the sodium adsorption ratio (SAR) (Bouwer and Idelovitch 1987). This parameter is basically used for assessment of alkalinity hazard in irrigation water and it is ranging from 0.33 to 4.59 (Table 1). The result showed that the concern due to sodium hazard of the water became more emphatic because in all water samples adj.SAR is higher than SAR (Suarez 1981; Lesch and Suarez 2009).

This can be calculated with the following formula (Ayers and Westcot 1985):

Based on Ayers and Tanji (1981) classification, majority of samples have adj.SAR values are showing <3 and are safe for irrigation. The minimum value of adj.SAR is 0.33 and maximum value is 4.59 and average is about 1.79.

Potential salinity is defined as the chloride concentration plus half of the sulphate concentration. Doneen (1954) explained that the suitability of water for irrigation is not dependent on soluble salts. It is true that the low solubility salts may precipitate in the soil and accumulate with each successive irrigation, whereas the concentration of highly soluble salts increases the soil salinity (Doneen 1962). The potential salinity of the water samples ranges from 0.72 to 6.13 (Table 1).

It is another parameter used to classify groundwater for irrigation purposes (Siddiqui et al. 2005). The RSC in groundwater is mainly due to the higher concentration of bicarbonate ions, which precipitates Ca²⁺ and Mg²⁺ ions as their carbonates and elevates Na⁺ ions, which increases the sodium carbonate in the groundwater (Srinivas et al. 2014). In addition to the total dissolved solids, the relative abundance of sodium with respect to alkaline earths and boron and the quantity of bicarbonate and carbonate in excess of alkaline earths also influence irrigation water quality. This excess is denoted by residual sodium carbonate and determined as suggested by Richards (1954). The water with high RSC has high pH and land irrigated by such waters becomes infertile owing to deposition of sodium carbonate as indicated by the black colour of the soil (Eaton 1950). In waters having high concentration of bicarbonate, there is tendency for calcium and magnesium to precipitate as the water in the soil becomes more concentrated. As a result, the relative proportion of sodium in the water is increased in the form of sodium carbonate.

Lloyd and Heathcoat (1985) have classified irrigation water based on RSC as (1) suitable (<1.25) (2) marginal (1.25–2.5) and (3) not suitable (>2.5). In the present study, from Table 1, it can be interpreted that the groundwaters in the study area shows RSC values of ranging from −3.92 to 1.03 meq/l. Based on RSC values, all 40 samples have values less than 1.25 and are safe for irrigation.

From Table 1, it can be suggested that the Kelly’s ratio varies from 0.04 to 0.50, demonstrating that all water samples are suitable for irrigation.

Correlation analysis and bivariate diagrams are helpful in understanding the processes of groundwater chemical evolution (Wu et al. 2014; Tiwari and Singh 2014). In this study, bivariate diagrams were generated based on Pearson correlation analysis to get a better understanding of the groundwater chemical evolution processes, and the results are shown in Fig. 8.

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The correlation and trend line analyses between the groundwater constituents are exhibited in Fig. 8. The existence of a very strong correlation exist between HCO₃ ⁻ and Ca²⁺ + Mg²⁺ (r = 0.92); between HCO₃ ⁻ + SO₄ ²⁻ and Ca²⁺ + Mg²⁺ (r = 0.95); total cations and Ca²⁺ and Mg²⁺ (r = 0.96). There is a strong relation between HCO₃ ⁻ and Ca (0.69); Cl⁻ + SO₄ ²⁻ vs Na⁺+ K⁺ (r = 0.65); Cl⁻ + SO₄ ²⁻ vs Ca + Mg (r = 0.63).

The plot of Ca²⁺ + Mg²⁺ vs HCO₃ ⁻ shows a abundance of Ca²⁺ + Mg²⁺ relative to HCO₃ ⁻, and Fig. 8b shows that the abundance of (Ca + Mg) in most of the groundwater samples probably can be attributed to carbonate weathering. The climate also plays a vital role in the arid and semi arid areas. The plots between total cations and Ca + Mg as well as Na + K are 0.96 and 0.40, respectively (Fig. 8d, e).

The chemical composition of groundwater is the imprints of the rock–water interaction and chemical processes. Generally, the presence of rock–water interaction was identified using TDS vs Na/(Na + Ca) and TDS vs Cl/(Cl + HCO₃) scatter diagrams as reported by Gibbs (1970) (Fig. 9). These diagrams are widely employed to assess the functional sources of dissolved chemical constituents, such as precipitation, rock, and evaporation dominance. In these diagrams, samples falling in the centre of the curve are derived from rock–water interaction. Figure 9 presents Gibbs plots of Group (A) and (B) groundwater quality data of Tummalapalle area.

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This observation showed the involvement of silicate weathering in the geochemical processes, which contribute mainly sodium, calcium and potassium ions to the groundwater (Stallard and Edmond 1983; Sarin et al. 1989).

The groundwater in Tummalapalle area is alkaline in nature. In majority of the groundwater samples, concentrations of alkaline earths (Ca²⁺ + Mg²⁺) exceed alkali cations (Na⁺ + K⁺) and HCO₃ ⁻ dominate over (SO₄ ²⁻ + Cl⁻). Ca–Mg–HCO₃ is the dominant hydrogeochemical facies. The statistical analyses were used for determining the groundwater quality variations. Water chemistry of the study area strongly reflects the dominance of weathering of rock-forming minerals. The Gibbs diagram revealed that the hydrochemistry of groundwater falls in the rock weathering region and is due to dissolution with rock-forming minerals. Pearson correlation analysis reveals that natural processes such as mineral dissolution/precipitation and cation exchange are dominant factors influencing the groundwater chemistry. The high contribution of (Ca²⁺ + Mg²⁺) to the total cations suggest that the chemical composition of the water is largely controlled by bicarbonate weathering with limited contribution from silicate weathering. The Piper diagram has revealed that all the samples are characterized as carbonate hardness (secondary alkalinity) exceeds 50% and are due to the dolomitic rocks which are responsible for release of chemical elements into the groundwaters of the study area.

In this study, the assessment of groundwater for irrigational uses has been evaluated on the basis of various parameters. Sodium adsorption ratio (SAR) values are to be less than 10; and adj. SAR also less than 3; Residual sodium carbonate (RSC) values on the whole are less than 1.25 meq/l; Permeability index (PI) are also in acceptable range for irrigation. All these parameters indicating the water samples of the study are good for irrigation. According to the as per USSL diagram all water samples are falling under very high specific conductance and low sodium [C3S1] and are suitable for irrigation. The Wilcox classification has shown 65% of groundwater under “good to permissible” zone. Thus, the overall groundwater quality in the basin is fresh and suitable for irrigation use. The plots of dissolved solids (TDS) and total hardness (TH) suggest that about 12.5% of the samples are suitable for human consumption because they are fresh water with acceptable degrees of hardness. Suitable water treatment process such as water softening, ion exchange, and demineralization should be applied to reduce the concentration of contaminants. The various indices derived in the study indicate that the most of groundwater of the study area is suitable for agriculture irrigation use. The long-term use of such groundwater for irrigation will induce sodium hazard to soils. It will have negative impacts on the yields of crops and properties of soils. However, mixing of low and high salinity water is recommended before irrigation to reduce the salinity hazard in local areas.