In this chapter, it is shown that the interpretation of even fundamental tests for permeability such as the high pressure test described in Chapter 4 is not as simple as it would appear. It was observed that, depending on the strength of the sample, the permeability either increased or decreased during the testing process. Also the results were affected by sample size. This makes the measurements difficult to interpret due to experimental effects of sample size and changes of flow with time. However, the results did not change significantly with pressure, and results obtained for tests with water were not significantly different when synthetic leachate was tested.