Assessment of the transportation of abandoned mine water contaminants to the surrounding aquifers: a case of Mlolongo open-pit lake, Kenya

This study investigated water quality and modelled potential transportation of contaminants from the abandoned mine to the surrounding aquifers, providing a comprehensive assessment of the impacts of post-mining activities on groundwater. The objectives included determining key water quality parameters and modelling contaminants’ spatial distribution and migration to understand their impact on the surrounding aquifers. The sampled water from the Mlolongo abandoned mine was tested in a laboratory to monitor the level of selected contaminants. The measured contaminants that exceeded the WHO recommended threshold limits were then modelled using the MODFLOW and MT3DMS codes to predict spatial distribution and transportation of the contaminants to the surrounding aquifers. Among the measured chemical water quality parameters, calcium (Ca2+), potassium(K+), aluminium (Al3+), sulphates (SO42−), chlorides (Cl−), nitrite (NO2−) and nitrate (NO3−) were within the WHO threshold recommended limits. However, sodium (Na+), ammonium (NH4+), manganese (Mn2+), fluoride (F−), carbonates (CO32−), iron (Fe3+), and phosphates (PO43−) exceed the WHO recommended threshold limits. The key findings from predictive modelling indicate that the spatial distribution and travel distance of contaminants increase with time, posing a higher risk to shallow aquifers within approximately a 5.1 km radius. The findings highlight that the aquifers close to the Mlolongo open-pit Lake are more vulnerable to pollution by contaminants. Therefore, continuous monitoring is required to assess water quality in the abandoned mining and the surrounding aquifers.