3.13 Suppose engineers at an environmental testing firm received a project to compare mean percolation rates (mm/yr) for four different cover types used in landfills. Twelve different landfills located in areas comparable in terms of atmospheric temperatures are available for their experiment.

Four different cover types selected for this experiment are (1) conventional compacted clay,

(2) alternative monolithic, (3) conventional composite, and (4) alternative capillary barrier. Help these engineers design this experiment to compare the percolation rates.