A Preliminary Investigation of Surface and Groundwater Quality Along the Upper Part of the Ankobra River, Impacted by Illegal Mining Activities

The Ankobra River Basin has a long history of gold mining activities and the recent intensification of Galamsey (illegal small-scale gold mining) activities has worsened the quality of water resources, especially in the upper part, which was less prone to water quality issues in the past. This study, therefore, is a preliminary assessment of the current spatial and seasonal variations of the water quality, the heavy metal pollution index (HPI), and the factors controlling the sources of variation in the water chemistry in the upper part of the Ankobra Basin impacted by illegal mining activities. Sampling was carried out in December 2017, for the dry season, and August 2018, for the wet season. The groundwater (GW) range of measured values for all parameters passed the 2011 WHO guideline for drinking water permissible limits except for pH, TDS, Fe, Mn, As, and Al, which failed for a sample or a particular season. Likewise, for surface water (SW), the range of measured values for all parameters fell within the WHO acceptable guideline limit except for pH, turbidity, TSS, Fe, Mn, Hg, Cd, Cr, As, and Al in at least a sample or during a particular season. The GW was generally more acidic than the SW. The surface water turbidity ranged from 20 to 29,550 NTU and 22 to 29,550 NTU for the dry and wet seasons. The turbidity was relatively higher in the downstream communities. The SW is unacceptable as a drinking water source as its HPI value (124.78) is above the permissible critical value of 100. The processes contributing to the variation in the surface and groundwater hydrochemistry include the natural evolution of minerals of the geological complex from silicates, carbonates, and sulphides; leaching of trace metals from mine tailings; the oxidation of pyrite; and geogenic contamination caused by elevated Fe and Mn. The release of trace metals, particularly arsenic, and the turbidity of SW have increased due to Galamsey activities even though the general hydrochemistry of the surface–groundwater has not altered.