[en] Both passive and active radon mitigations were installed in four houses with slab-on-grade or combined crawlspace/slab-on-grade basements. Passive mitigation reduced indoor radon by 40 to 80%. Combined passive and active mitigation was necessary for reducing radon levels to below 150 Bq m^-3. Active mitigation employed sub vapor-barrier and/or subslab depressurization. The number of subslab mitigation pits needed at each house was determined by diagnostic measurements of permeability and pressure-field extension. Performances of the mitigation systems at three houses were stable over one year. Increasing permeability in the hard-packed clay beneath the slab of one house may result in decreased effectiveness of the subslab depressurization. 2 refs., 2 figs., 1 tab