Wettability of NAPL-Contaminated Sands

Abstract

The potential for changes in the wettability of a subsurface system following exposure of sands to a variety of non–aqueous-phase liquids (NAPLs) was assessed. Many of the NAPLs were collected from field sites with on-going NAPL recovery systems. Three methods were used to evaluate the wetting conditions: contact angle measurements, a qualitative bottle test, and capillary pressure-saturation curves. The results clearly show that a wide range of wetting conditions can be expected following spills of complex NAPL mixtures to the subsurface. NAPLs comprised of higher molecular weight constituents—such as creosote—or with added surfactants—such as gasoline—had a greater impact on the system wettability than the lower molecular weight NAPLs. Neat solvents did not have a significant impact on the wettability of quartz surfaces. Many of the petroleum products tested resulted in the formation of weakly water-wet surfaces. Under these conditions, the potential recovery of NAPL from the subsurface would be maximized. Much lower recoveries would be expected for the NAPL-wetting creosote and coal tar contaminants, however.