THWRC Awarded Proposal 515UHH0047H

Project Number:       515UHH0047H

Title:                           Long-term Groundwater Impacts of Unsaturated Zone Releases of Fuels

                                    Containing Alcohols

Lead PI:                     William Rixey

Awarded Amount:    $20,000


The objective of this research is the assessment of the long-term impact of fuels containing alcohols on groundwater quality.  The use of ethanol in gasoline continues to expand and along with that expansion there also continues to be concern about the long-term impact of alcohol on groundwater contamination following releases to the subsurface.  In this study, the longer-term fate and transport characteristics of both ethanol and hydrocarbons (benzene, toluene, xylenes, etc.) associated with these fuels will be quantified.

Previous research has focused on the shorter-term impacts of ethanol releases.  Experimental visualization studies in laboratory-scale aquifers have been used to characterize the migration of ethanol into pore water as well as the formation of NAPL (non-aqueous phase liquid) from a release.  However, the longer-term release characteristics have not been assessed. It is anticipated that only a fraction of ethanol released into the capillary fringe within the unsaturated zone enters the saturated zone.  Due to its lower density and high water solubility, ethanol tends to remain in the pore water within the unsaturated zone.  This reduces the pore water impacts of the ethanol to the saturated zone.  Some recent field studies have also indicated that ethanol becomes trapped in the capillary fringe and remains for a long period of time.  In addition the NAPLs formed from spills of ethanol fuels have characteristics that may reduce the longer-term rate of release of hydrocarbons from the source to the saturated zone.

This work will quantify the amount of ethanol released into the subsurface and will also study the longer-term release characteristics of the hydrocarbons from the NAPL sources that are formed following the release of the alcohol containing fuels.  Experiments will be conducted in two-dimensional physical model aquifers that simulate the release of fuel into the subsurface.  Fuels of low ethanol content (15%) and high ethanol content (85%) will be studied.  The goal is to understand the fate of ethanol resulting from the release and determine: 1) how much of the ethanol is retained in the capillary fringe and within the pore water of the unsaturated zone 2) how much is volatilized, and 3) how much is released to the saturated zone.  In addition to the fate of ethanol, the longer-term release characteristics of hydrocarbons from these NAPL sources will be quantified.

This study focuses on the key physical-chemical effects associated with ethanol fuel releases and complements other studies assessing the impact of microbial processes.  This proposal is for a two-year study.  In Year 1, 2-D physical model aquifer experiments will be conducted for ethanol.  In Year 2, additional 2-D experiments will be continued for ethanol fuels and the results will be quantitatively analyzed with transport models that include unsaturated zone transport and NAPL source dissolution processes.  Budgets for Year 1 and Year 2 of $25k/yr have been provided.  In addition to ethanol, the results from this work will also be relevant to other alcohols that are being considered as alternative fuels.