Movement of Nonaqueous Liquids in Groundwater

Abstract

Evidence from field sites indicates that when nonaqueous liquids, such as organic solvents and gasoline, are released into the subsurface environment they tend to remain as a separate liquid phase in the form of discrete ganglia and lenses. The presence of the separate phase is often not recognized because water samples may not necessarily be saturated by the contaminants. Therefore, soil sample analysis is essential in defining the extent of the separate phase contamination. The movement of the ganglia of the separate phase can be described using two relatively simple relationships derived from the consideration of capillary phenomena: the Bond Number for gravity driven motion, and the Capillary Number for groundwater flow driven displacement. An analysis of field situations using these relationships shows that lighter than water liquids can be trapped below the water table and that groundwater pumping is unlikely to mobilize the trapped ganglia and lenses.