In the framework of a German-Romanian scientific cooperation, expts. were performed to evaluate feasible and cheap techniques for the safe storage of mine waste to prevent acid rock drainage (ARD). A large 4-chamber percolator (4CP) was installed in a waste heap at Ilba Mine, Romania, to test the effect of biocides and alk. layers on the bacteria causing acid rock drainage (ARD). The 4CP consisted of 4 chambers each contg. 65 m3 of sulfidic waste material. The 4CP enabled the transfer of lab. results to a tech. scale. The detergent Na dodecylsulfate (SDS) was proved to be active against the leaching bacteria. Organotrophic microorganisms were not affected by the SDS application. The alk. layers caused an increase of pH, however, a decrease of cell nos. was measured only in adjacent ore layers, but not in the whole ore body. A rapid evaluation of the effects of these countermeasures on ARD formation became possible by microcalorimetric activity measurements for bioleaching.