Simulation of NAPL Source and Plume Transport Characteristics Following Release of Fuel Alcohols
The objective of this research is to improve the current understanding of the physical-chemical impacts of alcohols on the transport characteristics of dissolved plumes and on the distribution of non-aqueous phase liquid (NAPL) sources resulting from subsurface releases of alcohol blended fuels. Simulations of NAPLs containing various alcohols (methanol, ethanol, isopropanol and tert-butanol) of varying fuel content (15 to 85 vol.%) were conducted with a multiphase, multicomponent finite difference numerical model (UTCHEM). The alcohol content and type impacts the dissolved plume that is generated from these spills. The alcohol content and type also influences the NAPL source that is formed. Increases in fuel alcohol content resulted in dissolved plumes that were more buoyant and NAPL sources of lower saturation that extended over larger areas. For the higher alcohol content fuels, NAPL generation was controlled largely by equilibrium phase behavior. Viscosity effects were also significant at the higher fuel contents particularly for isopropanol and tert-butanol which resulted in retardation of dissolved plumes migrating to a downstream well. Fingering was also observed at the higher alcohol contents due primarily to buoyancy effects. This work has implications for how to respond to releases of fuels containing alcohols: especially for assessing the potential impact of spills and for determining where to monitor pore water contamination for alcohols and hydrocarbon contaminants as well as NAPL source contamination.