Abstract: Processes for treating hazardous wastes, such as impacted soils containing hexavalent chromium, to simultaneously both reduce Cr(VI) to Cr(III) and control leaching of chromium in soil or disposed waste. The processes includes a one-step reagent addition that results in treatment of the impacted materials in a single pass. The processes generally may include mixing the solid waste material containing hexavalent chromium to ensure a homogeneous mixture followed by treating the impacted material with a suitable treatment additive including sodium/calcium polysulfide. The processes result in a reduction of total concentration and leachable levels of chromium in the impacted material.