THE DIFFUSIVE TORTUOSITY OF FINE-GRAINED UNLITHIFIED SEDIMENTS

Use of Fick's First Law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and envi ronmental chemistry of fine-grained unlithified sediments. In such por ous media, the diffusion coefficient in this law must be reduced by th e square of the tortuosity to account for the longer diffusive paths. Experimental methods to estimate tortuosity are specialized or time co nsuming, and not routinely done. An analysis of available data shows t hat tortuosity, theta, is accurately correlated to readily measured po rosity values, phi, through the simple relation: theta(2) = 1 - ln(phi (2)).