Hydrogeologic Controls on Groundwater Quality in the West Mamprusi Area, Northern Ghana

In the Northern Region of Ghana where groundwater is scarce and borehole success rates are low, there are still large gaps in groundwater quality research. Generally, groundwater is a safer source of drinking water than surface water, but it can contain naturally occurring elements, such as fluoride and arsenic, that pose health risks. A better understanding of hydrogeologic controls on groundwater quality helps to target water treatment efforts and provide better drinking water. This study focuses on the West Mamprusi area of Northern Ghana, where geology varies from coarse- to fine-grained sedimentary rocks to basement complexes consisting of metavolcanics and granitoids. Forty-seven groundwater samples were analyzed for major ions and trace elements, and 25 samples were analyzed for carbon isotopes. Graphical and statistical analyses, including Piper and Stiff diagrams, are used to categorize the water chemistry, resulting in a variety of groundwater types: sodium-dominated facies within the sedimentary rocks, calcium-dominated facies within all geologic units, and Na-Ca-SO4 groundwater among the high total dissolved solids (TDS) outliers. Cluster analysis showed that samples from the same lithology do not necessarily have the same groundwater chemistry; the TDS of the samples were more distinctive than the geologic unit, though high-TDS samples were most likely in shale and siltstone. Principal component analysis (PCA) and correlations were used to understand important water-rock interactions within the aquifer, determining that the dissolution of halite and gypsum is the major control on the highest TDS groundwater. Geochemical modeling with NETPATH did not corroborate groundwater flow paths determined from static water levels in many cases, suggesting that shallow aquifers reflect localized groundwater flow. The localized problems with contaminants such as high fluoride, arsenic, barium, and TDS also point toward a complex shallow groundwater system. Water quality data, including element concentrations, were integrated into geographic information systems (GIS), focusing on potentially harmful elements. The analysis leads to a better characterization and understanding of the geochemistry of groundwater resources in the West Mamprusi area