Dynamics of DNAPL penetration into fractured porous media
- Disposal Safety Inc., Washington, DC (United States)
- Colorado School of Mines, Golden, CO (United States). Div. of Engineering
Dense nonaqueous phase liquids (DNAPLs) that pool above stratigraphic contacts as a result of capillary forces can migrate downward through fractures in the underlying fine-grained layer. Although the DNAPL in the fracture is excluded from the surrounding porous matrix by capillary forces, the DNAPL constituent will dissolve and migrate by diffusion into the matrix. As a front of moderately soluble DNAPL advances into a fracture, the flux of dissolved material into the matrix increases until it becomes comparable to the rate of flow into the fracture, reducing the pressure in the DNAPL phase and slowing its advance. If the DNAPL front encounters a constriction with sufficiently large entry pressure, its advance will halt temporarily. But as the concentration gradients driving diffusion into the matrix decrease, there will be less DNAPL lost by diffusion and the DNAPL pressure at the constriction will increase until it exceeds the entry pressure, causing the downward advance of the front to suddenly resume. Because the time scales of diffusion are much slower than those of density flow, this analysis suggests that under certain circumstances a DNAPL can suddenly resume its downward advance after a long period of apparent immobility. In one plausible example, a dichloromethane front passes through 5 m of fractured clay in 16 days, is immobile for more than four years, and then suddenly moves again. Where this phenomenon is possible, removal of DNAPL to protect underlying aquifers becomes more important as a remediation goal.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 323780
- Journal Information:
- Ground Water, Journal Name: Ground Water Journal Issue: 1 Vol. 37; ISSN GRWAAP; ISSN 0017-467X
- Country of Publication:
- United States
- Language:
- English
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