Technical Approach

Low permeability zones in the subsurface contain clay and previous research with landfill liners suggests that contact between nonchlorinated organic liquids can cause the clay structure to compress, creating macropores in the clay and resulting in an increase in hydraulic conductivity of up to five orders of magnitude. If such a process occurs with chlorinated DNAPLs in the subsurface, then diffusion into the low permeability regions may be enhanced, and advection, which is usually considered negligible, may also be important. Furthermore, waste DNAPLs contain surfactants. If these surfactants diffuse into the low permeability materials and sorb to the mineral surfaces, the materials may become organic-wet, resulting in active imbibition of the DNAPL.

This project will comprise both experimental and numerical modeling work. The experimental work will measure the changes in clay structure that occur due to contact with DNAPLs using X-ray diffraction and high resolution transmission electron microscopy. In addition, rates of diffusion and hydraulic conductivities will be measured in column experiments using pure DNAPLs, DNAPLs containing surfactants, and a waste DNAPL from a Department of Defense (DoD) site. A numerical model will be developed using a model from DoD’s Ground Water Modeling System and modifying it to incorporate the temporally and spatially varying processes observed in the experimental work. Simulations will then be performed to show the impact of altered clay structure on dissolved plume development and the selection of source remediation strategies.