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Johnson and Ettinger Attenuation Factor

The attenuation factor, &#945, is a proportionality constant relating indoor air concentrations to soil or groundwater concentrations:

Cindoor air = &#945SG x Csoil gas or Cindoor air = &#945GW x Cgroundwater x H

This attenuation of vapor phase concentrations from the subsurface to indoor air can be computed by the simplified Johnson and Ettinger (1991) relationship:

A larger &#945 indicates less attenuation and a smaller value indicates more attenuation. For example, at an &#945 = 0.001 a subsurface concentration of 1000 [&#956g/m3] will attenuate to an indoor air concentration of 1 [&#956g/m3]. At an &#945 = 0.1, the same subsurface concentration of 1000 [&#956g/m3] will only attenuate to an indoor air concentration of 100 [&#956g/m3]. Note that different attenuation factors will be produced for soil gas and groundwater contamination sources (because of different DT eff values as explained below).

Building Terms:

Subsurface Terms:

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