Hydrogeochemical characterization and analysis for irrigation applicability of groundwater in the shallow coastal aquifers: a multivariate statistical approach.

Coastal groundwater is ubiquitously under threat due to a variety of natural and anthropogenic activities. Groundwater occurring along a stretch of the coastal tract (L = 15 km) of Thiruvananthapuram district, Kerala, India, was analyzed for hydrogeochemical characterization, identification of factors influencing water chemistry, suitability for drinking and irrigation purposes. A total of 48 water samples were collected over three sampling seasons (pre-monsoon – PRM, monsoon – MON and post-monsoon – POM) in 2012. The study area is sandwiched between two estuaries: the Akkulam–Veli estuary to the north and the Poonthura (Karamana River) estuary to the south, while a shore parallel man-made canal forms the eastern boundary on the landward side. The results of hydrogeochemical analysis showed that the parameters, such as electrical conductivity (EC), total dissolved solids (TDS) and total hardness (TH) are relatively higher in four locations towards the south due to proximity to the estuary/canal. Phosphate content exceeds the permissible limit for all samples in all sampling seasons. Water quality during POM is relatively good compared to other seasons. Hydrochemical facies of water samples suggests that groundwater samples belong to Ca-Cl type. Multivariate (R-mode) factor analysis identified a multitude of factors influencing groundwater chemistry. To assess the suitability of groundwater for irrigation use, different indices, viz., EC, percent sodium (%Na), sodium adsorption ratio (SAR), Kelley's ratio (KR), residual sodium carbonate (RSC), permeability index (PI), and magnesium hazard (MH) were computed. The study reveals that the quality of groundwater is of concern, warranting attention. It is fit for drinking purpose only after amelioratory measures, whereas, it is permissible for irrigational purposes. [ABSTRACT FROM AUTHOR]