Symbol

Parameter

Units

Source

Tier 1 or Calculated Value

A_B

Surface area of enclosed space at or below grade

cm²

Equation J&E 12a or 12b, Appendix C, Table L

Residential = 1 x 10⁶

Industrial/Commercial = 4.0 x 10⁶

A_crack

Area of total cracks

cm²

Equation J&E 14, Appendix C, Table L

Calculated Value

AT_c

Averaging time for carcinogens

year

SSL, May 1996

70

AT_nc

Averaging time for noncarcinogens

year

AT_nc = ED

Residential = 30

Industrial/Commercial = 25

C_v^sat

Soil vapor saturation limit

mg/m³-air

Equation J&E 5, Appendix C, Table L

Chemical-Specific or Calculated Value

D_crack^eff

Effective diffusion coefficient through the cracks

cm²/s

Equation J&E 15, Appendix C, Table L

Calculated Value

D_i

Diffusivity in air

cm²/s

Appendix C, Table E

Chemical-Specific

D_i^eff

Effective diffusion coefficient for each soil layer

cm²/s

Equation J&E 11, Appendix C, Table L

Calculated Value

D_source

Distance from ground surface to top of contamination

cm

Field Measurement

Soil Gas Contamination = 152.4

Groundwater Contamination = 304.8  Site-Specific

D_T^eff

Total overall effective diffusion coefficient

cm²/s

Equation J&E 9a, Appendix C, Table L

Calculated Value

D_w

Diffusivity in water

cm²/s

Appendix C, Table E

Chemical-Specific

ED

Exposure duration

year

Residential:  SSL, May 1996

Industrial/Commercial: SSL 2002

Residential = 30 Industrial/Commercial = 25

EF

Exposure frequency

day/year

Residential:  SSL, May 1996

Industrial/Commercial:  SSL 2002

Residential = 350 Industrial/ Commercial = 250

ER

Air exchange rate

exchanges per hour

Illinois EPA

Residential = 0.53 Industrial/ Commercial = 0.93

f_oc

Fraction organic carbon content

g/g

SSL, May 1996, or Field Measurement

Appendix C, Table F

0.002 or Site-Specific

H_B

Height of building

cm

Illinois EPA

Slab-on-Grade Residential = 244 Industrial/ Commercial = 305 or Site-Specific in Tier 3 Basement Residential = 427 Industrial/ Commercial = 488 or Site-Specific in Tier 3

H'_TS

Dimensionless Henry's law constant at the system (soil) temperature 13˚C

unitless

Appendix C, Table E

Chemical-Specific

L_B

Length of building

cm

Illinois EPA

Residential = 1000 Industrial/Commercial = 2000 or Site-Specific in Tier 3

L_crack

Slab thickness

cm

USEPA, Users Guide, 2004

10

L_F

Distance from ground surface to bottom of slab

cm

USEPA, Users Guide, 2004

10 (slab on grade) 200 (basement)

L_i

Thickness of soil layer i

cm

Field Measurement for Capillary Fringe, USEPA, 2004

Site-Specific

For Capillary Fringe, 37.5 cm

L_T

Distance from bottom of slab to top of contamination

cm

Field Measurement or Equation J&E 10, Appendix C, Table L

142.4 or Site-Specific

MW

Molecular weight

g/mole

Illinois EPA

Chemical-Specific

n

Total number of layers of different types of soil vapors migrate through from source to building

(if source is groundwater, include a capillary fringe layer of 37.5 cm as one of the layers)

unitless

Field Measurement

Site-Specific

P

Vapor Pressure

atm

Appendix C, Table E

Chemical-Specific

Q_bldg

Building ventilation rate

cm³/s

Equation J&E 13, Appendix C, Table L

Slab-on-Grade

Residential = 3.59 x 10⁴

Industrial/ Commercial = 3.15 x 10⁵

or Site-Specific in Tier 3

Basement

Residential = 6.28 x 10⁴

Industrial/Commercial = 5.04 x 10⁵

or Site-Specific in Tier 3

Q_soil

Volumetric flow rate of soil gas into the enclosed space

cm³/s

USEPA, Users Guide for Evaluating Subsurface Vapor Intrusion into Buildings, 2004

If L_T is less than 5 feet (152 cm),

Q_soil equals 83.33.

If L_T is 5 feet (152 cm) or greater, Q_soil equals zero.

An input value of zero requires an institutional control. See Section 742.505(b) and (c).

R

Ideal gas constant

atm-L/mol-K

USEPA, Users Guide, 2004

0.08206

RfC

Reference concentration

µg/m³

Illinois EPA:  http://www.epa.state.il.us/land/taco/toxicity-values.xls

Toxicological-Specific

RO_gw

Groundwater remediation objective

mg/L

Appendix B, Table E, or Equation J&E 6, Appendix C, Table L

Chemical-Specific or Calculated Value

RO_indoor-air

Indoor air remediation objective

mg/m³

Equations J&E 1 and 2, Appendix C, Table L

Calculated Value

RO_soilgas

Soil gas remediation objective

mg/m³

Equation J&E 4, Appendix C, Table L

Calculated Value

S

Solubility in water

mg/L

Appendix C, Table E

Chemical-Specific

T

Temperature

°K

USEPA, Users Guide, 2004

286 (converted from 13^oC)

THQ

Target hazard quotient for a chemical

unitless

SSL, May 1996

1

TR

Target risk or the increased chance of developing cancer over a lifetime due to exposure to a chemical

unitless

SSL, May 1996

Residential = 10^-6 at the point of human exposure

Industrial/Commercial = 10^-6 at the point of human exposure

URF

Unit risk factor

(µg/m³)^-1

Illinois EPA:  http://www.epa.state.il.us/land/taco/toxicity-values.xls

Toxicological- Specific

w

Floor-wall seam gap

cm

USEPA, Users Guide, 2004

0.1

W

Moisture content

g of water/g of soil

Field Measurement, Appendix C, Table F

Site-Specific

W_B

Width of building

cm

Illinois EPA

Residential = 1000

Industrial/ Commercial = 2000

or Site-Specific in Tier 3

α

Attenuation factor

unitless

Equations J&E 7 or 8, Appendix C, Table L

Site-Specific

θ_a

Air-filled soil porosity

cm³/cm³

SSL, May 1996 or

Equation J&E 18, Appendix C, Table L

0.28 or Calculated Value

θ_a,crack

Air-filled porosity for soil in cracks

cm³/cm³

SSL, May 1996 or

Equation J&E 18, Appendix C, Table L

0.13

θ_a,i

Air-filled porosity of soil layer i

cm³/cm³

SSL, May 1996 or

Equation J&E 18, Appendix C, Table L

0.13 or Calculated Value

For capillary fringe, θ_a,i = 0.1 θ_T,i

θ_T,crack

Total porosity for soil in cracks

cm³/cm³

SSL, May 1996 or

Equation J&E 16, Appendix C, Table L

0.43

θ_T,i

Total porosity of soil layer i

cm³/cm³

SSL, May 1996 or

Equation J&E 16, Appendix C, Table L

0.43 or Calculated Value

θ_w

Water-filled soil porosity

cm³/cm³

SSL, May 1996 or

Equation J&E 17, Appendix C, Table L

0.15 or Calculated Value

θ_w,crack

Water-filled porosity for soil in cracks

cm³/cm³

SSL, May 1996 or

Equation J&E 17, Appendix C, Table L

0.15

θ_w,i

Water-filled porosity of soil layer i

cm³/cm³

SSL, May 1996 or

Equation J&E 17, Appendix C, Table L

For capillary fringe, US EPA, Users Guide 2004

0.15 or Calculated Value

For capillary fringe = 0.375 or 0.9 q_T,i

θ_b

Dry soil bulk density

g/cm³

SSL, May 1996 or

Field Measurement, Appendix C, Table F

1.5 or Calculated Value

θ_s,i

Soil particle density

g/cm³

SSL, May 1996 or

Field Measurement, Appendix C, Table F

2.65 or Calculated Value

θ_w

Density of water

g/cm³

Illinois EPA

1