Section 742.717  J&E Soil Gas Equations for the Indoor Inhalation Exposure Route

a)         This Section sets forth the equations and parameters to be used to develop Tier 2 soil gas remediation objectives for the indoor inhalation exposure route using the modified J&E model.

b)         Equations J&E1 and J&E2 calculate, for carcinogens and noncarcinogens, respectively, an acceptable concentration of the contaminant of concern in indoor air that adequately protects humans who inhale this air.  Equation J&E3 converts indoor air concentrations from parts per million volume to milligrams per cubic meter.

c)         Equation J&E4 calculates an acceptable concentration of the contaminant of concern in the soil gas at the source of contamination.  This calculation is made using:

1)         an attenuation factor developed in accordance with Equations J&E7 through 18; and

2)         the acceptable concentration of the contaminant of concern in indoor air calculated in accordance with Equation J&E1 (for carcinogens) or J&E2 (for noncarcinogens).

d)         The attenuation factor (Equation J&E7 or J&E8) accounts for the following processes:

1)         Migration of contaminants from the source upwards through the vadose zone;

2)         Migration of contaminants through the earthen filled cracks in the building's full concrete slab-on-grade or full concrete basement floor and walls; and

3)         Mixing of the contaminants with air inside the building.

e)         Equation J&E7 must be used when the mode of contaminant transport is both diffusion and advection.  In this scenario, the Q_soil value equals 83.33 cm³/sec as described in Section 742.505.

f)         Equation J&E8 may be used only when the mode of contaminant transport is diffusion only.  In this scenario, the Q_soil value equals 0.0 cm³/sec as described in Section 742.505.  As an alternative to using Equation J&E8 pursuant to this subsection, it is permissible to use Equation J&E7, in which case the Q_soil value equals 83.33 cm³/sec as described in Section 742.505.

g)         Equations J&E9a through J&E18 calculate input parameters for either Equation J&E7 or J&E8 (the equations used to calculate an attenuation factor). These equations assume there are "n" different soil layers between the source of the contamination and the floor of the building. Equations J&E11, 16, 17 and 18 shall be used to calculate the needed parameters for each of the n layers (the general soil layer is referred to as soil layer "i" and i = 1,2,…n). Equations J&E16, 17, and 18 shall also be used to calculate needed parameters for the soil in the cracks of the building's full concrete slab-on-grade or full concrete basement floor and walls (it is through these cracks that contaminated soil gas is assumed to flow from the subsurface into the building).  As reflected in Equation J&E14, the only crack assumed to be present is the floor-wall seam gap.  To calculate the surface area of the enclosed space at or below grade, Equation J&E12a shall be used for a building with a full concrete slab-on-grade and Equation J&E12b shall be used for a building with a full concrete basement floor and walls.

h)         The default representative subsurface temperature for Henry's Law Constant is 13°C.  This value shall be used, as appropriate, in all calculations needed to represent the system by which contaminants migrate through the subsurface.

i)          The calculated soil gas remediation objective shall be compared with the soil vapor saturation limit (C_v^sat, Equation J&E5) for each volatile chemical. The calculated C_v^sat shall use the default representative subsurface temperature specified in subsection (h). If the calculated soil gas remediation objective is greater than C_v^sat, then C_v^sat is used as the soil gas remediation objective.

j)          The calculated soil gas remediation objective shall be compared to concentrations of soil gas collected at a depth at least 3 feet below ground surface and above the saturated zone. If a valid sample cannot be collected, a soil gas sampling plan shall be approved by the Agency under Tier 3.

(Source:  Added at 37 Ill. Reg. 7506, effective May 15, 2013)