The migration and entrapment of DNAPLs in physically and chemically heterogeneous porous media. Annual progress report, September 15, 1996--August 25, 1997

'The overall objective of this research is to investigate the influence of coupled physical and chemical heterogeneity on the migration and entrapment of DNAPLs in the saturated zone. This research includes laboratory and numerical investigations for a matrix of fluid and solid properties encompassing a range of wettability characteristics. Specific objectives include: (1) quantification of medium wettability and interfacial tensions; (2) determination of hydraulic property relations; (3) two-dimensional infiltration experiments; (4) modification of a continuum based multiphase flow simulator to account for physical heterogeneity, saturation independent and saturation dependent wettability, and concentration dependent wettability and interfacial tension; and (5) utilization of this model to explore the potential influence of coupled physical and chemical heterogeneities on the migration of DNAPLs and the development of innovative remediation schemes. Research conducted during this period was directed primarily towards the accomplishment of goals (1), (2), (4) and (5); specific details are given below. Goal (3) builds upon results from the other objectives and will, therefore, be started in the coming year.

The migration and entrapment of DNAPLs in physically and chemically heterogeneous porous media. 1998 annual progress report

'The migration and entrapment of dense nonaqueous phase liquids (DNAPLs) at hazardous waste sites is typically believed to be controlled by physical heterogeneities. This belief is based upon the assumption that permeability and capillary properties are determined by soil texture. These transport properties however, also depend on porous media wettability characteristics, which may vary spatially in a formation due to variations in aqueous phase chemistry, contaminant aging, and/or variations in mineralogy and organic matter distributions. The overall objective of this research is to investigate the influence of such coupled physical and chemical heterogeneities on the migration and entrapment of DNAPLs in the saturated zone. This research includes laboratory and numerical investigations for a matrix of organic contaminants and solid media encompassing a range of wettability characteristics. Specific objectives include: (1) quantification of system wettability and interfacial tensions; (2) determination of transport property relations; (3) two-dimensional infiltration experiments; (4) modification of a continuum based multiphase flow simulator to account for physical heterogeneity, saturation independent and saturation dependent wettability, and concentration dependent wettability and interfacial tension; and (5) utilization of this model to explore the potential influence of coupled physical and chemical heterogeneities on the migration of DNAPLs and the development of innovative remediation schemes. The accomplishment of the above research objectives will facilitate the characterization and remediation of contaminated field sites. This section summarizes research conducted towards the accomplishment of goals (1), (2), (4), and (5) during the first 1.5 years of this 3-year project. Goal (3) builds upon results from the other objectives and will be initiated in the coming year.

Characterization of grain-size distribution, thermal conductivity, and gas diffusivity in variably saturated binary sand mixtures

Characterization of differently textured porous materials, as well as different volumetric porous media mixtures, in relation to mass and heat transport is vital for many engineering and research applications. Functional relations describing physical (e.g., grain-size distribution, total porosity), thermal, and gas diffusion properties of porous media and mixtures are necessary to optimize the design of porous systems that involve heat and gas transport processes. However, only a limited number of studies provide characterization of soil physical, thermal, and gas diffusion properties and the functional relationships of these properties under varying soil water contents, especially for soil mixtures, complicating optimization efforts. To better understand how mixing controls the physical, thermal, and gas diffusion properties of porous media, a set of laboratory experiments was performed using five volumetric mixtures of coarse-and fine-grained sand particles. For each mixture, the grain-size distribution (GSD), thermal conductivity, and gas diffusivity were obtained and parameterized using existing and suggested parametric models. Results show that the extended, two-region Rosin–Rammler particle-size distribution model proposed in this study could successfully describe the bimodal behavior of the GSD of binary mixtures. Further, the modified Côté and Konrad thermal conductivity model adequately described the thermal conductivity–water saturation relations observed in different mixtures. The proposed simple soil-gas diffusivity descriptive model parameterized the upper limit, average, and lower limit behavior in gas diffusivity–air content relations in apparently texture-invariant gas diffusivity data. Results further show a close analogy between gas diffusivity and thermal conductivity and their variation with saturation across different binary mixtures. Overall, the results of the study provide useful numerical insight into the physical, thermal, and gas transport characteristics of binary mixtures, with wide implications for future engineering and research applications that involve multicomponent porous systems