Impacts of Beach Placer Mineral Mining in the Shallow Coastal Aquifers of Southern Tamil Nadu Coast, India

Abstract

Groundwater in the coastal area is relatively vulnerable to the contamination by seawater intrusion, which makes it unsuitable for drinking or irrigation. This study was carried out along the coastal aquifer of southern Tamil Nadu, India. To access the impact of mining, the coast was divided into three sites, namely (i) non-placer sand area, (ii) active mining area and (iii) inland dune area. The non-placer sand area is assumed to be undisturbed and is considered as reference site. The inland dunes sand area is the area with no active mining but within the impact of the mining activity. Hydrogeochemical and groundwater table characteristics of shallow coastal aquifer system in the mining and non-mining area were investigated to identify the salinization process. The Na/Cl ratio, correlation matrix and ionic relationship between major ions showed a marked increase in salinization in the active mining area and nearby wells. The reverse ion exchange and seawater intrusion control the groundwater chemistry along the active mining aquifers. The spatial visualization of electrical conductivity, salinity, chloride and groundwater quality index map (GWQI) that reflects active mining areas are exhibiting poor water quality and are comparatively low in non-placer mining areas. Gibb’s diagram representing evaporation is the dominant process more than the rock water interaction and precipitation. The groundwater level fluctuation in both inland dune and non-placer sand area aquifers blocks a little variation due to lack of rainfall, irrespective of volumes of water recharge and over pumping of groundwater for irrigational purposes. In the active mining region, the groundwater level shows high fluctuation of ±3 to ±5 m below the ground level. Depth profile study indicates the highly depleted groundwater level in the active mining region that has induced higher EC value and salinity. The process might, therefore, be related to the saltwater encroachments. Tidal induces changes in water level in the Karamaniyar river estuary and near the active mining wells around 1.03 m and the Vembar river estuary water level increased in the wells around 0.68 m.