Influence of mining activities on groundwater hydrochemistry and heavy metal migration using a self-organizing map (SOM)

Abstract

Tongling is a typical metal ore concentration area in the Yangtze Metallogenic Region. Years of mining activities have resulted in serious regional groundwater problems. Therefore, it is of great significance to systematically study the impact of mining activities on the local groundwater. In this paper, a self-organizing map (SOM) calculation and stable isotopes were used to illustrate groundwater hydrochemistry and heavy metal migration, especially concerning Fe, based on the test results of 92 groundwater samples from the study area. Due to mining activities and acid mine drainage (AMD), SO4–Ca-type groundwater with high total dissolved solids (TDS) and low pH values was mainly distributed in the mining areas. In the runoff area, carbonate neutralization and runoff rates were accelerated, while the groundwater TDS gradually decreased and the pH increased. Due to the influence of evaporation and surface water recharging, the major component and heavy metal contents of groundwater increased in the discharge area. With changes in the redox conditions and the influence of variable-valency metals, such as Fe and Mn, heavy metals are easily coprecipitated from groundwater or absorbed by secondary minerals, such as ferrihydrite and birnessite. Therefore, the contents of heavy metals in the groundwater of the study area were relatively low. The main controlling factors determining the groundwater hydrochemical characteristics and heavy metal precipitation are mining activities, redox conditions and rock-water interactions. This study may be helpful for the sustainable development and protection of groundwater resources in the study area and other mining zones in the Yangtze Metallogenic Region.