[en] The methods considered were those which use the Radon Progeny Integrating Sampling Unit (RPISU) technique, grab sampling, radon exhalation rate, alpha track registration, time-integrated radon measurements, continuous measurements, gamma exposure rates, and radium measurements. The methods were evaluated to determine whether they satisfied two critieria, namely, that the method provide reasonable assurance of compliance with the standards for cleanup as set by the Environmental Protection Agency and codified in federal regulations; and that the method minimize the cost of verifying that the standards had been met. The RPISU method and the alpha track method, as used by the Colorado Department of Health, were found to satisfy these criteria and are therefore recommended for use in remedial action programs. Methods that use grab sampling of radon and radon daughters gamma exposure rates, radium measurements, and continuous measurements were found to be unacceptable. Data obtained for grab sampling of radon and radon daughters had unacceptable coefficients of variation (close to 80%). Grab sampling appeared to be most useful for highly ventilated structures or for structures where immediate assessments are required. The estimation of the radon daughter concentration by the indoor gamma exposure rate or the radium content of construction material was found to be influenced by too many variables to be reliable. The time-integrated radon measurement technique using alpha track or Passive Environmental Radon Monitor (PERM) devices showed promise for being an excellent approach for estimating average radon daughter concentrations. However, more data are necessary before a definitive judgment can be rendered on this approach. The radon exhalation rate method for estimating average radon daughter concentration also could not be fully evaluated because of insufficient data