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)

D_d'=µnD_d

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

D_d:    cm²/s

n: 

µ: 

D_d':   cm²/s

 

Greenkorn & Kissler(1972)

D_d'=(n/æ)D_d

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

D_d:    cm²/s

n: 

æ: 

D_d':   cm²/s

 

Hellferich(1966)

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

D_d'=(n/2)D_d

to:

D_d'=(n/(2-n))²D_d

D_d:    cm²/s

n: 

D_d': 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.