Colorado State Matrix Diffusion Video

This three-minute video produced by Lee Ann Doner and Dr. Tom Sale of Colorado State University shows the effect of matrix diffusion in groundwater systems. The video is silent with no narration. A green dye in flowing groundwater is introduced into a ~0.6 meter by ~1 meter sand tank containing four different bentonite clay lenses for 23 days. Then the dye injection is stopped, but the dye persists in the tank for over 130 days. The key point is that contaminants can diffuse into low-permeability zones rapidly from transmissive zones, but back diffuse out of the low permeability zones very slowly, much slower than diffusion into the low permeability zones. (Note the timing is in units of days, with 1:26 being 60 days + 26 days = 86 days.) The tank experiment extends for 2:17 (137 days), and then the breakthrough curves are show.

Posted by request of Dr. Tom Sale of Colorado State University.