WETTABILITY OF NAPL-CONTAMINATED SANDS

The potential for changes in the wettability of a subsurface system fo llowing exposure of sands to a variety of non-aqueous-phase liquids (N APLs) was assessed. Many of the NAPLs were collected from field sites with on-going NAPL recovery systems. Three methods were used to evalua te the wetting conditions: contact angle measurements, a qualitative b ottle test, and capillary pressure-saturation curves. The results clea rly show that a wide range of wetting conditions can be expected follo wing spills of complex NAPL mixtures to the subsurface. NAPLs comprise d of higher molecular weight constituents-such as creosote-or with add ed surfactants-such as gasoline-had a greater impact on the system wet tability 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 w ater-wet surfaces. Under these conditions, the potential recovery of N APL from the subsurface would be maximized. Much lower recoveries woul d be expected for the NAPL-wetting creosote and coal tar contaminants, however.