An evaluation was made of the efficiency of the thermal agitation produced by immersion heaters in the Radioactive Waste Disposal System Test Tanks. Neither the first nor the second performance of this test proved that the thermal agitator was capable of mixing the test-tank water. The first performance showed a slight decrease in sulfate concentration, whereas the second performance indicated that the concentration increased during the test period, and in both tests the sulfate content of the samples was more than double the desired 200 ppm. (auth)