Vapor Intrusion Assessment Calculator

Evaluate the vapor intrusion pathway using Johnson-Ettinger model attenuation factors and EPA screening levels.

Sub-slab soil gas (µg/m³)

Groundwater concentration (µg/L)

Henry's law constant (dimensionless)

Building footprint (m²)

Mixing height (m)

Crack fraction of slab

Air exchange rate (ACH)

Indoor air screening level (µg/m³)

Tab to move between fields

J&E attenuation factor

Total indoor air (µg/m³)

0.22

Risk ratio (J&E model)

0.71

Soil gas from GW (µg/m³)11,400

Indoor air from sub-slab (µg/m³)0

Indoor air from GW (µg/m³)0.22

Exceeds screening (0/1)0

Risk ratio (EPA generic)1,112.9

How to Use This Calculator

Enter sub-slab soil gas concentration (µg/m³) from vapor probes or building surveys.
Set groundwater concentration (µg/L) and Henry's Law constant for your contaminant.
Enter building footprint (m²) and mixing height (m) for indoor air dilution modeling.
Review calculated indoor air concentrations from both sub-slab and groundwater pathways.
Compare results to indoor air screening levels to determine if mitigation is required.

What each input means

Sub-slab soil gas (µg/m³): Measured or modeled contaminant concentration in soil gas beneath the building slab.
Groundwater concentration (µg/L): Dissolved contaminant concentration in the shallow aquifer.
Henry's law constant (dimensionless): Dimensionless Henry's law constant. Benzene = 0.228, TCE = 0.403, PCE = 0.723.
Building footprint (m²): Ground floor slab area of the building.
Mixing height (m): Height of the indoor air mixing zone (typically ceiling height of lowest occupied floor).
Crack fraction of slab: Fraction of slab area occupied by cracks/penetrations. EPA default 0.0005-0.001.
Air exchange rate (ACH): Building air changes per hour. Residential 0.3-0.5, commercial 1-5.
Indoor air screening level (µg/m³): Target indoor air concentration. Benzene 0.31, TCE 0.48 µg/m³ at 1e-6 risk.

J&E attenuation factor: Calculated Johnson-Ettinger attenuation factor (sub-slab to indoor).
Soil gas from GW (µg/m³): Estimated soil gas concentration from groundwater via Henry's law.
Indoor air from sub-slab (µg/m³): Indoor air contribution from measured sub-slab soil gas.
Indoor air from GW (µg/m³): Indoor air contribution from groundwater pathway.
Total indoor air (µg/m³): Combined predicted indoor air concentration from all pathways.
Risk ratio (J&E model): Indoor concentration / screening level. Values >1 indicate potential concern.
Exceeds screening (0/1): 1 = predicted indoor air exceeds screening level, further action needed.
Risk ratio (EPA generic): Risk ratio using EPA generic attenuation factor of 0.03 for comparison.

Identify Input Parameters
4 parameters
Sub-slab soil gas (µg/m³) = 100, Groundwater concentration (µg/L) = 50, Henry's law constant (dimensionless) = 0.228, Building footprint (m²) = 200 = 8 input(s) provided
Calculate J&E attenuation factor
J&E attenuation factor = ventilationRate > 0 ?
0.00002 = 0.00002
Calculate Total indoor air
Total indoor air = indoorFromSubSlab + indoorFromGW
0.221 = 0.221
Calculate Risk ratio
Risk ratio = totalIndoorConc / screeningLevel
0.71 = 0.71
Calculate Soil gas from GW
Soil gas from GW = gwConc * henryConstant * 1000
11400 = 11400
Calculate Indoor air from sub-slab
Indoor air from sub-slab = subSlabConc * alphaSoilGas
0.002 = 0.002