## Calculator 17 - Effective Diffusion Calculator

### EFFECTIVE DIFFUSION CALCULATOR Back to Calculators

The effective diffusion coefficient takes into account the fact that diffusion can only take place through pore openings because mineral grains block many of the possible pathways.

 Cation Dd (10-6 cm2/s) Anion Dd (10-6 cm2/s) H+ 93.1 OH- 52.7 Na+ 13.3 F- 14.6 K+ 19.6 Cl- 20.3 Rb+ 20.6 Br- 20.1 Cs+ 20.7 HS- 17.3 Mg2+ 7.05 HCO3- 11.8 Ca2+ 7.93 CO32- 9.55 Sr2+ 7.94 SO42- 10.7 Ba2+ 8.48 Ra2+ 8.89 Mn2+ 6.88 Fe2+ 7.19 Cr3+ 5.94 Fe3+ 6.07

Using these values, the effective diffusion coefficient can then be calculated using one of the following equations/calculators:

Greenkorn(1983)

Dd'=µnDd

Where µ is an empirical value less than one, and n is porosity.

Dd   cm2/s

n

µ

Dd':   cm2/s

Greenkorn & Kissler(1972)

Dd'=(n/æ)Dd

Where æ is tortuosity, which will be discussed in the next newsletter.

Dd   cm2/s

n

æ

Dd':   cm2/s

Hellferich(1966)

The Hellferich equations give a range of values for the effective diffusion coefficient from:

Dd'=(n/2)Dd

to:

Dd'=(n/(2-n))2Dd

Dd   cm2/s

n

Dd': from to   cm2/s

References

Domenico P.A. and Schwartz, F.W. (1998). Physical and Chemical Hydrogeology. Published by John Wiley & Sons, Inc. New York, NY.

Fetter, C.W. (1994). Applied Hydrogeology; Third Edition.  Published by Prentice-Hall, Inc., Englewood Cliffs, NJ.

Freeze, R.A. and Cherry, J.A. (1979). Groundwater. Published by Prentice-Hall, Inc., Englewood Cliffs, NJ.