[en] Protective barriers are being considered for use at the Hanford Site to enhance the isolation of radioactive wastes from water, plant, and animal intrusion. This study is part of an ongoing effort to assess the effectiveness of protective barriers for isolation of wastes from water. Part I of this study was the original modeling assessment by Pacific Northwest Laboratory of various protective barrier designs (e.g., soil type, vegetation). In Part 11 of this study, additional barrier designs were reviewed and several barrier modeling assumptions were tested. A test plan was then produced that detailed the requirement for hydrologic modeling of protective barriers. Part III of this study summarized the status of work in FY 1990 dealing with two-dimensional flow beneath the barrier and with validation testing using lysimeter data. This report (Part IV) addresses the application of a calibrated model to a much longer data set, the application of the calibrated model to a lysimeter that received a different treatment, and the effect of hysteresis on the behavior of water in the protective barrier