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A study has been carried out in KT (Cretaceous-Tertiary) boundary along the contact zones of hard rock, limestone and sedimentary formations to discern the geochemical processes governing the groundwater chemistry. A total of sixty-three groundwater samples were collected from the handpumps covering the entire study area and measured for hydrochemical species. Principal component analysis of the hydrochemical data inferred three major processes governing the geochemistry of the groundwater of the region as leaching, ion exchange and weathering. It was also inferred that there are few samples depicting the mixtures of these processes (what are they mention it) and few samples not representing any of these processes with adequate statistical significance. Hence, in order to know the geochemical behaviour of the samples representing each process, their combinations along with the samples which are not- representative samples of these processes were inferred using various standards plots to get an insight into their geochemical characteristics and affinity. This also inferred the samples representing different processes have a significant signature of geochemical facies. The major ions and the stable isotopes of groundwater were used to understand these processes. The carbonate and sulphate saturation states of these samples were calculated by PHREEQC and compared with major variations with the identified three geochemical processes. The state of saturation of Halite, Anhydrite, Gypsum, Aragonite, Dolomite, Calcite, Talc and Chrysolite were determined in all the samples. Inverse modeling was carried out considering the non-representative samples as initial solution and the samples representing each factor as final solution to understand the phase mole transfer in each process. An attempt was also made in this study to compare the geochemical behaviour of groundwaters from different KT boundaries. The samples representing these processes were plotted on an integrated map representing lithology, lineaments, drainage and elevation to determine their interrelationships. The study groups the samples into anthropogenic or geogenic. The leaching process is controlled by lithology and landuse, ion exchange processes is influenced by lithology and drainage patterns whereas weathering processes were controlled by lithology, drainage and lineaments. Non representation of samples (NRS) were mainly controlled by drainage and lineaments of the region.

Uranium (U) in groundwater is hazardous to human health, especially if it is present in drinking water. The semiarid regions of southern India chiefly depend on groundwater for drinking purposes. In this regard, a comprehensive sampling strategy was adopted to collect groundwater representing different lithologies of the region. The samples were collected in two different seasons and analysed for major and minor ions along with total U in the groundwater. Two samples during pre monsoon (PRM) and seven samples during post monsoon (POM) had U > 30 μgL−1, which is above the World Health Organization's provisional guideline value. The high concentration of U (188 μgL−1) was observed in the alluvial formation though a few samples showed the release of U near the pink granite (39 μgL−1) and the concentration was low in the lateritic formation (10 μgL−1). The uranyl carbonato complexes UO2(CO3)22− and UO2(CO3)34− were associated with high pH which facilitated the transport of U into groundwater especially during POM. U3O8 is the major form observed in groundwater compared to either UO2 or UO3 in the both seasons. The uranium oxides were observed to be more prevalent at the neutral pH. Though U concentration increases with pH, it is mainly governed by the redox conditions. The principal component analysis (PCA) analysis also suggested redox conditions in groundwater to be the major process facilitating the U release mechanism regardless of the season. The POM season has an additional source of U in groundwater due to the application of nitrogenous fertilizers in the alluvium region. Furthermore, redox mobilization factor was predominantly observed near the coastal region and in the agricultural regions. The process of infiltration of the fertilizer-induced U was enhanced by the agricultural runoff into the surface water bodies in the region. Health risk assessment was also carried out by determining annual effective dose rate, cancer mortality risk, lifetime average daily dose and hazard quotient to assess the portability of groundwater in the study area. Artificial recharge technique and reducing the usage of chemical based fertilizers for irrigation are suggested as sustainable plans to safeguard the vulnerable water resource in this region.