# EPA On-line Tools for Site Assessment Calculation

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## Parameterization of the Johnson & Ettinger Model

In the publication Identification of Critical Parameters for the Johnson and Ettinger (1991) Vapor Intrusion Model, (American Petroleum Institute Technical Bulletin Number 17, 2002), Paul Johnson writes the Johnson and Ettinger (1991) algorithm in terms of three dimensionless parameters:

where

Each of these parameters has a physical relevance, and by analyzing the value of these parameters for a given set of inputs, insight can be gained about vapor transport through the system.

A brief description of this process is given below and the user is directed to Paul Johnson's paper for more detailed information.

If B < 0.1 &#8594 Diffusion is the dominant mechanism across the foundation.

• If B < 0.1 and (AB/C)< 0.1 &#8594 Diffusion through soil is the overall rate-limiting process.
Critical inputs: (VB/AB), LT, DT eff, EB
Non-Critical inputs: (Qsoil/QB), Lcrack, Dcrack eff, &#951

• If B < 0.1 and (AB/C)>10(1+A) &#8594 Diffusion through foundation is the overall rate-limiting process.
Critical inputs: (VB/AB), Lcrack, Dcrack eff, EB, &#951
Non-Critical inputs: (Qsoil/QB), LT, DT eff

If B > 3 &#8594 Advection is the dominant mechanism across the foundation.

• If B > 3 and (A/C)< 0.1 &#8594 Diffusion through soil is the overall rate-limiting process.
Critical inputs: (VB/AB), LT, DT eff, EB
Non-Critical inputs: (Qsoil/QB), Lcrack, Dcrack eff, &#951

• If B > 3 and (A/C)>10 &#8594 Advection through foundation is the overall rate-limiting process.
Critical inputs: (Qsoil/QB)
Non-Critical inputs: (VB/AB), Lcrack, Dcrack eff, DT eff, &#951, LT, EB
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Contact Jim Weaver to ask a technical question on this material.