This article is concerned with investigating the role of a fracture system and groundwater flow in dispersing contaminants from in situ coal gasification sites. It was found that the dispersivities must be calculated with a knowledge of the natural groundwater flow to obtain the correct values. In practice the magnitude and direction of groundwater flow are fixed by geologic conditions. However it demonstrates that field experiments to obtain the dispersivities must be conducted in such a manner as to largely duplicate the direction of naturally occurring groundwater flow to obtain correct values.