This paper presents the results on the heavy metals concentrations in leachates and on the quality of groundwater resources as impacted by leachates leaking from Iringa municipal solid waste dumpsite. The results on physicochemical properties such as pH, electrical conductivity (EC), and total dissolved solids (TDS) that were analyzed by using an electronic multiparameter analyser in both leachates and groundwater samples are also presented. Heavy metals (Fe, Pb, Cd, Cr, Cu, Ni, Mn, and Zn) were quantified using Atomic Absorption Spectrophotometer (AAS). Relatively higher electrical conductivity which ranged from 14090 ± 62.34 to 26700 ± 104.10 µS/cm and total dissolved solids (76930 ± 41.39–13360 ± 59.40 mg/L) than FAO irrigation water standard were recorded in all leachates. All leachates were identified to be alkaline in nature with pH ranging from 7.40 ± 0.02 to 9.10 ± 0.01; this signified older age of the Iringa municipal dumpsite which is at its methanogenic phase. Heavy metals analysis indicated no potential threat of Cd as its concentrations in all leachates were below the detection limit (< 0.01 mg/L). Meanwhile, the concentrations of Fe, Pb, Cr, Cu, Ni, Mn, and, Zn in all leachate samples were either above TBS guideline limits for wastewater reuse, or FAO standards for irrigation water. In all groundwater samples, total dissolved solids (446 ± 55.30–776 ± 52.34 mg/L) and pH (7.15 ± 0.02–7.6 ± 0.03) were within WHO acceptable range (pH = 6.5–8.5) for drinking water. Electrical conductivity (869 ± 89.64 to 1570 ± 105.50 µS/cm values) in three groundwater samples was above the WHO's desirable limit for drinking water. Whereas in some groundwater samples, the concentrations of Fe, Pb, Mn, and Zn exceeded WHO guideline limits for drinking water quality, implying that the water is unsuitable for human consumption without treatment. The results of Principal Components Analysis (PCA) in groundwater samples indicated that both geologic and anthropogenic processes could be the possible source of heavy metals pollution in the groundwater. However, the presence of heavy metals can be used as tracers of groundwater contamination in the study area. Moreover, water quality indices (WQI) for all groundwater samples ranged from 169.07 to 220.72 translating from poor quality (≤ 100 WQI ≤ 199.99) to very poor quality ((≤ 200 WQI ≤ 299.99). Therefore, the present study calls for the proper management of solid waste in the Iringa municipality to reduce further pollution of groundwater reservoirs through leachate percolation.
