This report presents the results of a program to develop backfilling techniques to mitigate undesirable effects of hydraulic borehole uranium mining. To prevent ground subsidence and to allow mining of adjacent uraniferous sandstone, large underground cavities, formed during the borehole mining process, can be backfilled. Three techniques that were tested in the laboratory and the field with sand and with sand and 1 wt-pct cement mixtures were bulk dumping of slurry into the boreholes from ground level, slurry injection under water, and slurry injection above the cavity water level. The project was accomplished by equipment preparation and transport, mining operation to generate a full-sized cavity, backfilling operations, and assessment through core samples and subsidence checks. Both slurry techniques filled the cavity satisfactorily; however, underwater injection is the recommended backfilling technique because the borehole water level does not need to be pumped down during backfilling. The borehole was filled by bulk dumping of slurry.