In order to reduce the concentration of calcium in low-radioactivity-level process waste water and thereby make the water more suitable as a feed to a countercurrent foam column in which strontium and other radioactive nuclides can be removed, a modified limesoda precipitation process was developed. The process consists in adding sodium carbonate and sodium hydroxide to the water to a concentration of 0.005 M each (calculated before chemical reaction) and using a slowly stirred, suspended-bed sludge column to remove (by a filtering action) the resulting calcium carbonate and magnesium hydroxide. With this procedure, and with Fe3(a few parts per million) as a coagulant, the residual hardness of the water was reduced at 5 ppm (as CaCO3) or less. This tow value was achieved with sludge columns of diameter up to 9 in., at water flow rates up to 60 gal/ft2/hr, at sludge-height to column-diameter values of 4 to 0.5, and at stirring-paddle peripheral rates of 5 to 10 in./sec. With ORNL low-radioactivity-level process waste water as feed, the radionuclide decontamination factors across the sludge column were as follows: 10 to 15 for 90Sr, 30 to 40 for 144Ce, 10 to 50 for 60Co, 1.7 to 2.2 for 106Ru and 1.1 for 137Cs. The calcium concentration can be reduced to a point such that it will not significantly interfere with subsequent removal of strontium in a foam separation column. The degrees of softening and decontamination are significantly better than can be achieved in the ORNL limesoda plant. The process is being evaluated on a 15,000 gal/day basis.