2003 CPEO Military List Archive

From: petestrauss1@attbi.com
Date: 27 Feb 2003 21:18:21 -0000
Reply: cpeo-military
Subject: Re: [CPEO-MEF] indoor air sampling

Let me try to give you answers to your questions.  You've asked several,
although I'm not sure you were intending to.

1.  Does anyone know how soil gas vapor concentrations relate to TCE levels
at bedrock or simply the source below for the vapors?  There is a
correlation, but it is site specific depending on rate of groundwater flow,
thickness of water-bearing zone , geo-chemical conditions, and geological
parameters in the unsaturated zone (a dense layer made of clay in the
unsaturated zone is more likely to impede soil vapor than a layer of sand).

2. If  the measurement at the wellhead is 120 ppb are the soil gas vapors
greater or less than they would be if the measurement at the wellhead is  25
ppb?  Generally yes, so long as site specific factors are identical.

3. What effect does time have on the soil gas vapor as it rises even if its
source is being diluted down below?  Again, this is a question that can only
be answered through site-specific analysis. In most cases, however, I would
expect that dilution of soil gas will continue through the soil matrix.
Changes in chemical composition may occur as vapors move from an anaerobic
environment to an aerobic environment.

Peter Strauss

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