Assessment of groundwater vulnerability to impacts of underground mining:

Abstract

Underground mining posed significant risks to groundwater systems, particularly in geologically complex regions. This study assessed the vulnerability of groundwater resources to the impacts of underground mining at Greenstone Resources Ltd., located in Tiira Town Council, Busia District, Uganda. The research aimed to (i) identify and categorize the geological and hydrological features of underground mining tunnels and their surrounding groundwater systems, (ii) develop a numerical model to determine groundwater flow behavior, and (iii) simulate the extent of directional changes in groundwater flow due to tunneling. A combination of field data, borehole logs, and spatial analysis using GIS and MODFLOW 6 was employed. The study area exhibited a shallow water table (12–20 m), with dominant geological features including shear zones, quartz veins, and weathered regolith influencing water movement. A three-layered aquifer system was defined and modeled, incorporating weathered regolith, weathered rock, and fractured rock, each with distinct hydraulic properties. Simulation results revealed flow redirection, particularly around highly fractured and faulted regions. The modeling confirmed that mining activities disrupted natural groundwater gradients, intensified hydraulic head loss, and increased vulnerability in adjacent aquifer units. The study underscored the importance of hydrogeological characterization and numerical modeling in assessing and mitigating groundwater risks in mining-impacted areas. The findings provided critical input for groundwater management, policy development, and the design of environmentally responsible mining practices, contributing to the achievement of Sustainable Development Goals 6 (Clean Water and Sanitation) and 12 (Responsible Consumption and Production).