Solid waste disposal in landfills or open dumps may cause significant impacts on groundwater, which is the main source of water in Jordan. This paper aims to investigate the impact of Humra landfill on groundwater quality. Forty-eight samples of groundwater and 4 samples of leachate were collected and analyzed for pH, TDS, EC, TN, NH4, NO3, Cl, PO4, BOD, COD, and heavy metals during different seasons. The results revealed that the leachate has high concentrations of pollutants with average values of 27230, 1340, 1891, 940, 1428, and 3477 mg/l for TDS, Cl, NH4, NO3, BOD, and COD; respectively. High correlations between BOD with COD, pH with TDS, and TDS with NH4 were found. Analyses of groundwater quality showed that about 52%, 50%, 50%, 50%, 14.5%, and 23% of samples exceeded drinking water standards of Cl, TDS, NH4, Fe, Cu, and Mn; respectively. 75%, 75%, 60%, 50%, 37%, and 21% of the samples exceeded NO3, Ni, Cd, Cr, and Pb standard limits. The concentration of TN, BOD, and COD in groundwater decreased as the distance from the landfill site increased, while the other parameters showed insignificant trends. The calculated Leachate Pollution Index (LPI) was 22.48 indicating a potential impact of landfill on groundwater and could cause a health risk that needs urgent action. Based on the obtained results, it can be concluded that the landfill site has an impact on groundwater quality, which needs an immediate plan to avoid uncontrolled impacts. It is recommended to install landfill lining with a leachate collection system. Surface hydrology should be directed to reduce the impact of surface runoff on leachate transport.