# EPA On-line Tools for Site Assessment Calculation

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#### Retardation Factor

In the report the retardation factor for benzene was set to 10. We will work through the following list of questions to evaluate this number.

• What other parameter values were used in determining this value?
• Is this a reasonable value?
• Under what circumstances would we have a retardation factor of 10?

We'll use the OnSite retardation factor calculator and the parameter values from the site report to answer these questions.

The calculation of the retardation factor uses the:

• porosity
• bulk density
• organic carbon partition coefficient, Koc
• fraction of organic carbon, foc

The values used in the report were

• porosity = 0.35
• bulk density = 2.65 g/cm3
• organic carbon partition coefficient, Koc for benzene = unreported
• fraction of organic carbon, foc = unreported

#### Porosity and Bulk Density

The porosity and bulk density are related quantities. The bulk density refers to a density of the packed grains (including the grains and the void space).

 Since there is not a separate calculator for bulk density, use the retardatation factor calculator to determine the bulk density for a porosity of 0.35.

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