"Objectives There were two objectives of the column study. The first was to determine an ""effective"" diffusion coefficient for the upward migration of gasoline vapors in the sand to be used for the venting experiment. The term effective diffusion coefficient is used in recognition that there are many different hydrocarbon vapors diffusing and each has a different diffusion coefficient. The effective diffusion coefficient was needed for quantitative analysis of the venting experiment which is being conducted in the large scale model spill facility. The second objective of the experiment was to perform a quantitative mass balance in a highly controlled laboratory experiment to determine why the total gasoline could not be accounted for in the first large scale model spill experiment conducted last year."