GASOHOL (E24) EFFECTS ON THE FREE PHASE THICKNESS WITHIN MONITORING WELLS COMPARED TO PURE GASOLINE EFFECTS

Abstract

Free-phase gasoline remedial schemes are based on the gasoline’s thickness layer measured on monitoring wells. The relationship of the thickness within the well and in the aquifer depends on the elevation of the water table. Ethanol presents in gasoline affects the elevation of the capillary fringe. This paper presents the effects of E24 (76% gasoline, 24% ethanol by volume) compared to pure gasoline on the elevation of the capillary fringe and the correspondent thickness of free phase within the monitoring well and in the aquifer. Two plexiglass columns filled with glass beads were used to perform visualization experiments and to produce an appropriate relationship that can be applied to the field situations. The results indicated that the elevation of the capillary fringe was lower for E24 compared to gasoline, as expected from the ethanol cosolvent effects on the interfacial tension; E24 established a free phase layer faster than that of the gasoline; E24 spill would reach a microcosm edge faster compared to that of gasoline; the migration of E24 to the well was faster than that of the gasoline, indicating that a subsurface spill could be detected earlier by monitoring wells installed within the gas station limits; the relationship of the thickness of the free phase product within the well to thickness in the aquifer for E24 was 4 and for gasoline was 2.6. This indicates that a remedial scheme for E24 based on gasoline relationship would overestimate the volume of product to be extracted from the aquifer by 20%.