Hydrogeochemical analysis of Groundwater in Thanjavur district, Tamil Nadu; Influences of Geological settings and land use pattern

The influence of land use patterns and geological settings on the hydrogeochemistry of the Thanjavur district in Southern India is assessed. Thirty-four samples were analyzed for groundwater quality in pre-monsoon and post-monsoon seasons. The water quality Index (WQI) values derived based on these values show that, over 80% of the samples were categorized as either as excellent or good quality for drinking. A spatial variation map of WQI is generated and compared with geological and land-use maps. The major hydrogeochemical processes acting are silicate weathering - evaporation deposition (post-monsoon) and carbonate dissolution (pre-monsoon). The results agree with the mineralogy of geological formations such as sandstone with clay and fluvial depositions. The main land-use pattern in the district is agricultural, built areas and industrial regions. The most common contaminant in agricultural lands is nitrate pollution from fertilizers. However, nitrate in the groundwater did not exceed the WHO standard of 50 mg/L. High salinity in many samples may be due to water logging as well as salt usage in the textile and chemical industries, which is correlated with the landuse as well as WQI Map. Overall, geology and land use have significant influence on groundwater quality of the region.