Experimental and Numerical Investigation of the Effect of Diesel or Ethanol-Blended Diesel on Hydraulic Properties of Unsaturated Soils

Abstract

Reformulated fuels such as diesel-ethanol blends (“diesohol”) are currently used or being considered in many countries to reduce atmospheric emissions and to reduce the dependence on foreign oil. Additional emulsifiers are usually added to enhance the stability of the mixture. A common concern is that the ethanol and additives, upon (accidental) release of diesohol in the subsurface, may adversely affect the water quality because of increased solubility and decreased degradation of other organic compounds. In this study we investigated the hydraulic properties of unsaturated soils containing an aqueous solution saturated with either diesohol or diesel or containing just plain water. The soil water retention data and the saturated hydraulic conductivity Ks for two common California soils, of the Vista and Los Osos series, were measured. The experimental data showed that the retention parameter α was significantly higher for diesohol compared to plain water and somewhat higher compared to diesel for both soils. With respect to plain water, the value for Ks was slightly lower in the presence of diesohol for the Vista soil, while it was significantly higher in the presence of either diesel or diesohol for the Los Osos soil. This effect cannot be explained by the presence of ethanol because the higher viscosity would result in a commensurate decrease of the saturated hydraulic conductivity. The higher Ks is attributed to changes in soil structure caused by the ethanol. Water flow in the vadose zone was simulated using the HYDRUS 1-D model. The model was applied to simulate a ponding scenario for the Vista and Los Osos soils. Ethanol greatly affected the water retention for the Vista soil, whereas Ks was similar for all three solutions. For the fine-textured Los Osos soil the increase in Ks for diesel and diesohol compared to the plain solution was far more important for the flow regime than the change in retention due to ethanol (diesohol).