In this paper the risk of heavy metals discharged from the acidic sludge leachate into groundwater in a landfill located in Fajr industrial area )Garmsar( has been assessed using IWEM software. Acidic sludge as one of the industrial hazardous wastes is produced during purification of used oil with Mienken )acidic( method. The concentrations of heavy metals )Cd, Ni, Co, pb, Zn, Mn, Cu( in the acidic sludge were determined and the discharge of these metals into groundwater was assessed by IWEM )using Monte Carlo analysis and simulating the parameters of case study for risk assessment (. Then, the best linear for the protection of the groundwater in landfill was recommended; which in this case was the NO Linear option. The low potential of groundwater pollution in the region was because of the deep location of groundwater level, low depth of the sludge in the landfill, dry climate and low amount of rainfall in the area, and soil type of the location )silt-loam(.