# Permeability



## pj9999 (May 24, 2012)

Can someone please advise a non-engineer on the correct way to talk about permeability with engineers. ie how do you say: 1 x 10-7 secs/cm or 5 x 10-10 secs/cm. Is it "one by ten seven", "five by ten ten"?


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## RIP - VTEnviro (May 24, 2012)

Are you referring to a perc rate?

Percolation is typically referred to to in units of time/distance.

I've usually seen infiltration rates reported in distance/time.

As for how to say it, I would say 'one times ten to the negative seven centimeters per second.'


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## envirotex (May 24, 2012)

If you are using the units "length/time" ([LT -1], then that's hydraulic conductivity (usually denoted with a capital "K") and lots of people use the term (although not correctly) permeability interchangeably with that term. Assuming you mean hydraulic conductivity above, I would say ten to the minus seven cm per sec or 5 times ten to the minus 10 cm per sec.

Permeability actually has units of [L2] and is usually denoted with a lowercase "k". Sometimes engineers (especially engineers rather than geoscientists) use the unit "darcy" to describe permeability magnitude. 1 darcy




10−12m2. The darcy is the unit of choice for the oil patch...

BTW, materials with those values for hydraulic conductivity would typically be described as "impermeable" or "impervious" depending on the origin and direction of flow. Confused? You're not alone; inconsistent nomenclature is one of the biggest problems in the technical literature when describing flow through porous media.


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## pj9999 (May 24, 2012)

Thank you for the replies.

The subject I want to discuss with the engineers is the permeability of liners for contaminated land. I understand these numbers I quoted are the coefficient of hydraulic conductivity.

As an example of the documents I have been looking at please see here:

http://lining.cetco....d=12&amp;TabId=1476

I understand that the standard for a contaminated ground water cut-off is a maximum coefficient of 1 x 10-7 cm/sec.


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