Alum shale was mined and processed (leaching with sulphuric acid for uranium recovery) atRanstad, Sweden, during 1965—69, and the shale residues were deposited on site. A barrier system fortreatment of leachates from the deposit was constructed in 1999: (1) Sedimentation pond (2) pre-treat-ment filter, and (3) final filter in sequence. Iron, Al and Mn were precipitated in section (2). Retention ofother elements (As, Cr, Co, Ni, Zn and U) is attributed to adsorption by precipitated iron and componentsin section (3). More than 90% of the Fe and As and 50% of the Cr, Cd, Zn and U were removed from theleachates.