Deciphering the groundwater–saline water interaction in a complex coastal aquifer in South India using statistical and hydrochemical mixing models

Abstract

Hydrogeochemical investigations were carried out in a coastal aquifer along the East coast of Cuddalore district in Tamil Nadu, Southern India, to analyse the groundwater-seawater interactions. Multiple techniques including Hydrochemical Facies Evaluation Diagram (HFE-D), principle component analysis (PCA), ionic ratios, hydrochemical ionic changes models and salinity mixing index (SMI) models were applied to refine the results and exactly understand the salinization process. EC and Ionic constituents along with the Gibbs plot showed controls of evaporation and the rock-water interaction o hydrogeochemistry, which is later proved by the bivariate plots. Major ions listed under PC1 (Na, Mg, Cl and SO 4 ) and PC2 (Ca, HCO 3 , and CO 3 ) showing the influence of seawater and carbonate dissolution processes go together with cation exchange. Definitive results, shown by HFE-D plot than the piper plot, indicate that 58% of the samples either completely fall in the seawater zone or on the mixing line. Results of the ionic changes calculation indicate that 6 wells (50%) have a positive seawater fraction in the groundwater. Analogous results were observed for the SMI values ([1) in these wells, except in sample number 3. Encouragingly, after each method the results significantly rectified. Impact of seawater mixing with fresh groundwater is found in the entire starch (perpendicular to coast) of samples in the southern end of the aquifer, and samples located in very near to the coast in the central part. Good quality groundwater in the northern end indicate that the aquifer was unaffected by the seawater mixing.

Hydrogeochemical characteristics and evaluation of groundwater quality for domestic and irrigation purposes: a case study of the Heuningnes Catchment, Western Cape Province, South Africa

“…The dominance of rock-water interaction suggests that groundwater in the area had sufficient time to interact with the lithology material and in the course of this interaction, different ions were released into the water. Similar results were obtained in a study done by [21,26,31] using the Gibbs plot to differentiate between mechanisms controlling groundwater and surface water chemistry. The majority of samples suggested that the chemical weathering of rock-forming minerals is influencing the groundwater quality.…”

“…Using the Gibbs plot, conclusions concerning the influence of various dominant geochemical processes such as precipitation, rock-water interaction mechanism and evaporation in controlling the hydrochemistry of groundwater in the aquifer can be deduced [21]. Most samples in the study region were confined in the rock-dominant and evaporation dominant zone (Fig.…”

Investigation of groundwater salinity using geophysical and geochemical approaches: heuningnes catchment coastal aquifer. Western Cape Province, South Africa

“…The Gibbs diagram can be used to display the evolution of groundwater composition and can indicate the mechanism that governs the chemical composition of groundwater, its evaporation, rock-water interaction or precipitation (Kumar 2016). Gibbs plots for this study using (TDS vs. Na/(Na + Ca), and Cl/(Cl + HCO3) suggest that evaporation is the main process controlling chemistry of the shallow groundwater (Fig.…”

“…If the dissolutions of calcite, dolomite and gypsum are the foremost reactions in a system then the bivariate plot of Ca 2+ + Mg 2+ versus SO 4 2− + HCO 3 − will be close to the 1:1 line (Kanagaraj et al 2018;Kumar 2016). If the points shift more to the left due to an excess of SO 4 2− + HCO 3-this indicates ion-exchange as a result of silicate weathering.…”

“…12) suggesting that the samples are not from the same source of origin and seawater is not the influence of groundwater in the aquifer. Therefore, the fact that the majority of the samples were found to be above the theoretical mixing 1:1 line insinuates that cation-exchange processes modified the groundwater chemistry by replacing it with Ca 2+ /and Mg 2+ (Papazotos et al 2019;Kumar 2016).…”