The influence of Surface Roughness on Air-Water Interfacial Areas of Porous Media

B.A. Thesis, 2007, Chemistry/Environmental Studies, Middlebury College

Abstract: The air-water interface (AWI) is a critical parameter that influences the retention and transport of volatile contaminants through porous media, including soils. The areal extent of the AWI, Aia, has been shown to vary with media texture and water saturation (Sw), with larger Aia values generally corresponding to increased adsorption capacity and retention of contaminants. The objective of this work is to characterize the Aia/Sw relationship using gas-phase interfacial tracer tests for two media: Vinton (fine sand with small amounts of silt and clay) and Granusil 7030 (fine sand). The media were chosen to represent two sands with similar particle sizes, but different surface roughness as represented by N2/BET surface areas of 3.33 and 0.56 m2/g, respectively. Media with greater surface roughness are hypothesized to yield larger interfacial areas, leading to increased retardation of contaminant transport. Aia was measured using decane vapor as the interfacial tracer for porous media at water saturations ranging from approximately 2.5% to 20%. Once Aia was measured for a particular system, its value was used to predict the gas-phase retardation of a contaminant, trichloroethylene (TCE) vapor, an industrial organic solvent and carcinogen, traveling through the same soil system. The predicted retardation for TCE was then compared to its observed retardation through the soil column. Results show that overall, Aia generally decreased with increasing Sw, in agreement with the literature. For all Sw studied, measured Aia values were greater for Vinton than for Granusil 7030 as a result of the greater surface roughness for Vinton. Predicted retardation factors for TCE matched the general Sw trend of the observed data, however, predictions were consistently greater than observed values. This difference is attributed to uncertainty in the interfacial adsorption coefficient for decane.

Publications:
- Senior Thesis: Surface Roughness and Air-Water Interfacial Areas.
- Costanza-Robinson, M.; Harrold, K.; Lieb-Lappen, R. 2008. X-ray Microtomography Determination of Air-Water Interfacial Area-Water Saturation Relationships in Sandy Porous Media. Environmental Science and Technology, 42(8): 2949-2956

Advisor: Molly Costanza-Robinson