# 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 → Diffusion is the dominant mechanism across the foundation.**

- If B < 0.1 and (AB/C)< 0.1 → Diffusion through soil is the overall rate-limiting process.

Critical inputs: (V_{B}/A_{B}), L_{T}, D_{T}^{eff}, E_{B}

Non-Critical inputs: (Q_{soil}/Q_{B}), L_{crack}, D_{crack}^{eff}, η

- If B < 0.1 and (AB/C)>10(1+A) → Diffusion through foundation is the overall rate-limiting process.

Critical inputs: (V_{B}/A_{B}), L_{crack}, D_{crack}^{eff}, E_{B}, η

Non-Critical inputs: (Q_{soil}/Q_{B}), L_{T}, D_{T}^{eff}

**
If B > 3 → Advection is the dominant mechanism across the foundation.**

- If B > 3 and (A/C)< 0.1 → Diffusion through soil is the overall rate-limiting process.

Critical inputs: (V_{B}/A_{B}), L_{T}, D_{T}^{eff}, E_{B}

Non-Critical inputs: (Q_{soil}/Q_{B}), L_{crack}, D_{crack}^{eff}, η

- If B > 3 and (A/C)>10 → Advection through foundation is the overall rate-limiting process.

Critical inputs: (Q_{soil}/Q_{B})

Non-Critical inputs: (V_{B}/A_{B}), L_{crack}, D_{crack}^{eff}, D_{T}^{eff}, η, L_{T}, E_{B}

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