Hydraulic properties of soils subjected to aqueous solutions with diesel or ethanol-blended diesel

Diesel-ethanol blends (“diesohol”) are used or being considered as (automotive) fuel in many countries similar to gasoline-ethanol blends (“gasohol”). Because diesel and ethanol do not mix well, additional emulsifiers or solvents are needed to obtain stable blends. There is concern that the ethanol and additives in diesohol may adversely affect the subsurface quality upon (accidental) release to the subsurface environment because of increased solubility and decreased degradation of other organic compounds. This study deals with the impact on the soil hydraulic properties of an aqueous solution saturated with diesohol compared to that of an aqueous solution saturated with diesel or of plain water. Soil water retention data and the saturated hydraulic conductivity Ks were measured in triplicate for two common California soils, of the Vista and Los Osos series, and blasting sand. The retention parameter α (inversely related to air entry) was significantly higher for diesohol compared to plain water (p = 0.02878) and somewhat higher compared to diesel (p = 0.1211). With respect to plain water, the value for Ks was significantly higher in the presence of either diesel (p = 0.04198) or diesohol (p = 0.04648), which was attributed to changes in soil structure. The HYDRUS model was used to simulate water flow as the result of either a constant head or a constant flux condition at the upper boundary of the Vista and Los Osos soils. For the Vista soil, water retention was clearly affected by the presence of ethanol whereas Ks was similar for all three solutions. Higher water contents in the upper soil profile and lower water fluxes to the underground were simulated for the aqueous solution with diesohol compared to the other two solutions. Although there was some change in retention due to ethanol (diesohol) for the fine-textured Los Osos soil, the four-fold increase in Ks for diesel and diesohol compared to the plain solution was far more important for the flow regime and the presence of ethanol did not have a great impact for this soil.

Research Highlights
► Water retention decreased due to ethanol because of lower air-entry value.
► Saturated hydraulic conductivity increased four-fold due to diesel rather than ethanol.
► Simulations for coarse-textured Vista soil showed reduced water flow due to ethanol.
► For fine-textured Los Osos soil water flow increased due to diesel.