Leachate-Induced Groundwater Contamination Near the Pugu Kinyamwezi Dumpsite, Dar es Salaam, Tanzania: Hadrochemical Facies and Pollution Risks

This study assessed the impact of leachate induced groundwater contamination near the Pugu Kinyamwezi dumpsite and associated pollution risks - the region's largest dumpsite by landmass and waste volume. Groundwater samples were collected from ten stations around the dumpsite, including one control station, with physicochemical parameters analyzed at Ardhi University’s Environmental Engineering Laboratory. Key parameters analyzed included pH, electrical conductivity (EC), total dissolved solids (TDS), major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺), anions (NO₃⁻, Cl⁻, SO₄²⁻, HCO₃⁻), and selected heavy metals (Fe, Mn, Zn, Pb, Cu). Aquachem modeling was used to assess water types and hydrochemical evolution. The results revealed that most groundwater samples met East African Standards (EAS 12:2018) and WHO drinking water standards. However, three stations (S5, S6, and S8) showed elevated levels of magnesium (up to 896.61 mg/L), nitrate (100.32 mg/L), and electrical conductivity (up to 2245 µS/cm), indicating contamination linked to landfill leachate. pH levels at several stations were below acceptable limits (<6.5), suggesting acidic conditions unfavorable for potable use. Elevated chloride of up to 421.37 mg/L and sulfate concentrations were also detected. Scatter plots confirmed a strong correlation between sodium and chloride, suggesting a common pollution source and Magnesium dominance over calcium in several stations were observed, indicating chemical alteration due to leachate intrusion. These findings highlight the urgent need for improved waste management, continuous groundwater quality monitoring and policy enforcement to mitigate further contamination. Strategic planning, landfill design improvements, and implementation of sustainable environmental practices are critical for safeguarding public health and the aquifer system.