Understanding the hydrogeochemistry of groundwater quality in Wassa East area of Ghana: implications for health risk assessment

Résumé

Groundwater is the primary drinking water source for communities in Wassa East, Ghana, but faces increasing threats from intensive farming, illegal artisanal mining, and improper waste disposal. This study integrates hydrogeochemical characterisation (Piper, Chadha, Gaillardet, Gibbs diagrams), multivariate statistics (PCA, hierarchical clustering), an Integrated Weighted Water Quality Index (IWQI) combining entropy and CRITIC weighting, and a USEPA-based human health risk assessment (carcinogenic and non-carcinogenic) to evaluate groundwater quality from 139 boreholes across the district. Results show that groundwater chemistry is controlled primarily by silicate weathering, with Ca-Mg-HCO₃, Ca-Mg-Cl, and Na-HCO₃-Cl as the dominant water types. Most physicochemical parameters are within WHO permissible limits, but iron (48 samples, mean 0.53 mg/L) and chromium (8 samples) exceed thresholds in localized areas. The IWQI classifies most groundwater as “good” for drinking, with poorer quality in southern/central zones driven by geogenic iron and colour. However, health risk assessment reveals a more concerning pattern: 12 samples exceed the non-carcinogenic hazard quotient for cyanide (maximum HQ = 4.56), 5 for arsenic, and 8 for chromium. Carcinogenic risks for arsenic and chromium exceed the 1 × 10 −4 threshold in several samples. Microbial contamination is widespread (89 samples positive for total coliforms; 35 for E. coli ). Hazard Index mapping shows unacceptable cumulative non-carcinogenic risks (HI > 1) concentrated in northern and central communities where mining and agricultural land use intensity is highest. The study concludes that while Wassa East’s groundwater is generally suitable for drinking based on IWQI classification, significant localised health risks exist from cyanide (artisanal mining), chromium, arsenic, and microbial pathogens. Routine monitoring and targeted interventions in hotspot communities (Daboase, Odumase, New Subri Zongo) are recommended.

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