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Vol. 8  No. 4


**NEW** HYDRUS v1.02

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Retardation Coefficient Calculator

The process of retardation has been discussed in a previous newsletter, and will be briefly outlined again here.  For more detail, see the previous Retardation newsletter

Retardation is a general term that describes the many processes that contribute to remove a solute in groundwater.  Most solutes will travel slower than the groundwater, and so are considered to be 'retarded', hence the term a retardation factor.

In this newsletter we present a calculator that can be used to determine the retardation coefficient of a solute.  Many of the terms that go into the equation for retardation must be calculated or determined from field studies or literature review, and where necessary references to pre-existing calculators or information on this website will be provided.  Future newsletter may also present calculators to assist in the calculation of the retardation factor.

The retardation factor is defined as:

  R = [1 + (pb/θ)(Kd)]


pb = dry bulk density of the soil (M/L3)

θ = volumetric moisture content of the soil (porosity if saturated media) (dimensionless)

Kd = distribution coefficient for the solute with the soil (L3/M)

The following is an example calculation for the retardation coefficient.

Given: Kd = 3 mL/g (newsletter Vol. 8 No. 5 will cover details about the distribution coefficient)

         pb = 1.75 g/cm3

            θ = 0.20


R = [1 + (pb/θ)(Kd)]

R = [1 + {((1.75 g/cm3)/0.20)(3 mL/g)(1cm3/1mL)}]

R = [1 + 26.25]

R = 27.25

Retardation Coefficient Calculator

**Keep the units consistent**

pb   See dry bulk density calculator below

θ:  Click here to use the porosity calculator

Kd This parameter will be discussed in the next newsletter

Retardation Coefficient:   


Dry Bulk Density Calculator

Dry mass of soil particles:   

Volume of Sample: 

Dry Bulk Density:   



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

Schwartz, F.W. and Zhang, H. (2003). Fundamentals of Groundwater. Published by John Wiley & Sons, Inc. New York, NY.

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HYDRUS v1.02

Hydrus is a Windows based modeling environment for analysis of water flow and solute transport in variably saturated porous media.  It is a finite element model for simulating two- and three-dimensional movement of water, heat and multiple solutes in variably saturated media.  Version 1.02 has just been released, and the following is a list of some of the new features:

  • HYDRUS installation program has been optimized for Windows Vista

  • Colors for graphical display of Materials, Sub-regions and Anisotropy can now be customized

  • New option for importing domain geometry from a text file; there is a new key word that allows for the import of thickness variables with multiple sub-layers with variable thickness

For more info click here:  HYDRUS
To download demo click here: Download Demo

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