Hydrogeochemical and spatial assessment of landfill-associated groundwater contamination in a tropical megacity

Abstract

Municipal landfills in rapidly urbanizing tropical cities represent major sources of groundwater contamination, yet integrated hydrogeochemical and spatial risk assessments in developing countries remain limited. This study eval - uates groundwater contamination and associated human health risks around the Tamangapa landfill in Makassar, Indonesia, using an integrated framework combining hydrochemical analysis, multivariate statistics, geospatial modeling, and risk assessment. Groundwater samples from 36 monitoring wells were analyzed for physicochemi - cal parameters and heavy metals, particularly hexavalent chromium [Cr(VI)] and iron (Fe). Spatial interpolation using inverse distance weighting (IDW) and principal component analysis (PCA) were applied to identify contam - ination patterns and dominant controlling factors. The results revealed that Fe concentrations exceeded drinking water standards in 80.8% of wells, while Cr(VI) exceeded permissible limits in 40% of sampling points. Contami - nation hotspots were concentrated north of the landfill, consistent with regional groundwater flow direction. Ex - ploratory PCA analysis identified three principal covariance structures associated with groundwater contamination variability, interpreted as potential landfill-related hydrochemical influence, hydrogeochemical control conditions, and secondary anthropogenic associations. Exponential decay modeling showed that Fe contamination extended up to 4 km from the landfill, exceeding the conventional 1 km regulatory buffer and indicating higher contaminant mobility under tropical hydrogeological conditions. Human health risk assessment indicated that children living within the 1 km exposure zone faced significant non-carcinogenic risk (HI > 1), while carcinogenic risk from Cr(VI) exceeded acceptable thresholds in several locations. The findings indicate that tropical landfill systems may generate broader groundwater contamination plumes than those commonly reported in temperate regions, al - though the spatial extent identified in this study should be interpreted within the limitations of the sampling density and seasonal coverage. The findings suggest that groundwater contamination surrounding tropical landfill systems may extend beyond commonly applied regulatory monitoring distances under certain hydrogeological conditions. This study provides an integrated preliminary scientific basis for improving landfill monitoring