Michigan Administrative Code
Department - Environmental Quality
Remediation and Redevelopment Division
Environmental Contamination Response Activity
CLEANUP CRITERIA REQUIREMENTS FOR RESPONSE ACTIVITY
Section R. 299.26 - Generic cleanup criteria for soil based on inhalation of hazardous substances in ambient air
Current through Vol. 25-4, March 15, 2025
Rule 26.
(1) Inhalation of hazardous substance emissions in ambient air from soil shall be considered a reasonable and relevant pathway for all facilities.
(2) Generic cleanup criteria for soil based on inhalation of volatile hazardous substance emission to ambient air shall be called volatile soil inhalation criteria (VSIC). Generic cleanup criteria for soil based on inhalation of particulate hazardous substance emission to ambient air shall be called particulate soil inhalation criteria (PSIC). The generic residential VSIC and PSIC are calculated as follows, except as provided in R 299.34(3):
EQUATIONS FOR CARCINOGENS:
| where, | ||
| VSIC | (Volatile soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| TR | (Target risk level) | = 10-5 |
| AT | (Averaging time) | = 25,550 days (70 years x 365 days/year) |
| IURF | (Inhalation unit risk factor) | = chemical-specific (ug/m3)-1 |
| EF | (Exposure frequency) | = 350 days/year |
| ED | (Exposure duration) | = 30 years |
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
and,
| where, | ||
| PSIC | (Particulate soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| TR | (Target risk level) | = 10-5 |
| AT | (Averaging time) | = 25,550 days (70 years x 365 days/year) |
| IURF | (Inhalation unit risk factor) | = chemical-specific (ug/m3)-1 |
| EF | (Exposure frequency) | = 350 days/year |
| ED | (Exposure duration) | = 30 years |
| PEF | (Particulate emission factor) | = chemical-specific, m3/kg |
EQUATIONS FOR NONCARCINOGENS:
| where, | ||
| VSIC | (Volatile soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| THQ | (Target hazard quotient) | = 1 |
| AT | (Averaging time) | = 10,950 days (30 years x 365 days/year) |
| EF | (Exposure frequency) | = 350 days/year |
| ED | (Exposure duration) | = 30 years |
| ITSL | (Initial threshold screening level) | = chemical-specific, ug/m3 |
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
and,
| where, | ||
| PSIC | (Particulate soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| THQ | (Target hazard quotient) | = 1 |
| AT | (Averaging time) | = 10,950 days (30 years x 365 days/year) |
| EF | (Exposure frequency) | = 350 days/year |
| ED | (Exposure duration) | = 30 years |
| ITSL | (Initial threshold screening level) | = chemical-specific, ug/m3 |
| PEF | (Particulate emission factor) | = chemical-specific, m3/kg |
(3) The soil to air volatilization factor (VF) relates the concentration of a contaminant in the soil to the concentration of volatilized contaminant in the ambient air. If the vertical extent of the contaminant source has not been characterized, then the VF shall be calculated based on the infinite equation presented in subdivision (a) of this subrule. If the vertical extent of the contaminant source has been adequately characterized throughout the facility, then the VF shall be calculated either by the finite source equation presented in subdivision (b) of this subrule or the mass balance equation presented in subdivision (c) of this subrule, whichever yields the highest VSIC.
| where, | ||
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
| Jave s | (Normalized average flux from soil) | = chemical-specific, g/m2-second |
| DA | (Apparent diffusivity) | = chemical-specific, cm2/second |
| Q/C | (Dispersion factor for 1/2 acre) | = 82.33, g/m2-second per kg/m3 |
| T | (Exposure time) | = seconds (ED x 3.1536E+7 seconds/yr) |
| [THETA]a | (Soil air-filled porosity) | = 0.28 Lair/Lsoil |
| N | (Total soil porosity) | = 0.43 Lpore/Lsoil |
| [THETA]w | (Soil water-filled porosity) | = 0.15 Lwater/Lsoil |
| [RHO]b | (Dry soil bulk density) | = 1.5 g/cm3 |
| Da | (Diffusivity in air) | = chemical-specific, cm2/second |
| Dw | (Diffusivity in water) | = chemical-specific, cm2/second |
| H' | (Dimensionless Henry's law constant, where H' = HLC x 41) | = chemical-specific, unitless |
| HLC | (Henry's law constant at 250 C) | = chemical-specific, atm-m3/mol |
| TAF | (Temperature adjustment factor) | = 0.5 |
| Kd | (Soil-water partition coefficient) | = chemical-specific, cm3/g |
| For organic compounds | = Koc (cm3/g) x foc (g/g) | |
| For inorganic compounds | = chemical-specific, cm3/g | |
| Koc | (Soil organic carbon partition coefficient) | = chemical-specific, cm3/g |
| foc | (Organic carbon content of soil) | = 0.006 g/g (0.6%) |
| where, | ||
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
| Q/C | (Dispersion factor for 1/2 acre) | = 82.33, g/m2-second per kg/m3 |
| C0 | (Uniform contaminant concentration at t=0) | = 1.5 E-6 g/cm3 |
| [RHO]b | (Dry soil bulk density) | = 1.5 g/cm3 |
| Jave s | (Normalized average flux from soil) | = chemical-specific, g/m2-second |
| Js | (Instantaneous flux from soil at time t) | = chemical-specific, g/m2-second |
| DA | (Apparent diffusivity - see equation above) | = chemical-specific, cm2/second |
| T | (Time) | = seconds |
| ds | (Thickness of source) | = site-specific, meters |
| exp(p) | (The base of the natural logarithm raised to power (p)) | = ep |
| where, | ||
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
| Q/C | (Dispersion factor for 1/2 acre) | = 82.33, g/m2-second per kg/m3 |
| AT | (Exposure period) | = scenario-specific, years |
| [RHO]b | (Dry soil bulk density) | = 1.5 mg/m3 |
| ds | (Average source depth) | = site-specific, meters |
(4) The particulate emission factor shall be calculated as follows:
| where, | ||
| PEF | (Particulate emission factor) | = chemical-specific, m3/kg |
| Q/C | (Dispersion factor for 1/2 acre) | = 82.33, g/m2-second per kg/m3 |
| Ew | (Emission due to wind) | = g/m2 per second |
| Ev | (Emission due to vehicle traffic) | = g/m2 per second |
| V | (Vegetative cover) | = 0.5 (50%), unitless |
(5) VSIC and PSIC for nonresidential facilities shall be calculated as follows, except as provided in R 299.34(3):
EQUATIONS FOR CARCINOGENS:
| where, | ||
| VSIC | (Volatile soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| TR | (Target risk level) | = 10-5 |
| AT | (Averaging time) | = 25,550 days (70 years x 365 days/year) |
| AIR | (Adjusted inhalation rate) | = (20 m3/day)/(10 m3/day) |
| IURF | (Inhalation unit risk factor) | = chemical-specific (ug/m3)-1 |
| EF | (Exposure frequency) | = 245 days/year |
| ED | (Exposure duration) | = 21 years |
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
and,
| where, | ||
| PSIC | (Particulate soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| TR | (Target risk level) | = 10-5 |
| AT | (Averaging time) | = 25,550 days (70 years x 365 days/year) |
| AIR | (Adjusted inhalation rate) | = (20 m3/day)/(10 m3/day) |
| IURF | (Inhalation unit risk factor) | = chemical-specific (ug/m3)-1 |
| EF | (Exposure frequency) | = 245 days/year |
| ED | (Exposure duration) | = 21 years |
| PEF | (Particulate emission factor) | = chemical-specific, m3/kg |
EQUATIONS FOR NONCARCINOGENS:
| where, | ||
| VSIC | (Volatile soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| THQ | (Target hazard quotient) | = 1 |
| AT | (Averaging time) | = 7,665 days (21 years x 365 days/year) |
| EF | (Exposure frequency) | = 245 days/year |
| ED | (Exposure duration) | = 21 years |
| ITSL | (Initial threshold screening level) | = chemical-specific, ug/m3 |
| VF | (Volatilization factor) | = chemical-specific, m3/kg |
and,
| where, | ||
| PSIC | (Particulate soil inhalation criterion) | = chemical-specific, ug/kg or ppb |
| THQ | (Target hazard quotient) | = 1 |
| AT | (Averaging time) | = 7,665 days (21 years x 365 days/year) |
| EF | (Exposure frequency) | = 245 days/year |
| ED | (Exposure duration) | = 21 years |
| ITSL | (Initial threshold screening level) | = chemical-specific, ug/m3 |
| PEF | (Particulate emission factor) | = chemical-specific, m3/kg |
(6) The generic SIC are calculated for a source area size of 1/2 acre. The generic SIC shall be adjusted for other source area sizes by multiplying the generic SIC by the modifiers given in the following table. Where the actual source area size falls between the sizes given in this subrule, generic SIC shall be multiplied by the modifier for the next largest source size.
| Modifiers | ||
| Source Size (ft2 or acres) | Q/C (g/m2-s per kg/m3) | Modifier |
| 400 ft2 | 261.26 | 3.17 |
| 1000 ft2 | 180.76 | 2.2 |
| 2000 ft2 | 144.91 | 1.76 |
| 1/4 acre | 94.56 | 1.15 |
| ½ acre | 82.33 | 1 |
| 1 acre | 71.74 | 0.87 |
| 2 acres | 63.51 | 0.77 |
| 5 acres | 54.62 | 0.66 |
| 10 acres | 49.13 | 0.6 |
| 32 acres | 41.55 | 0.5 |
| 100 acres | 35.66 | 0.43 |
(7) Facility-specific measurements of the following parameters may be substituted for the generic assumptions and still allow the facility to satisfy the categorical criteria in section 20120a(1)(a) to (e) of the act:
Facility-specific measurements shall be based on representative characterization. Documentation of all facility-specific values shall be provided in the response activity plan, no further action report, or other response activity documentation.
(8) A person who is implementing response activity may demonstrate compliance with the generic criteria developed under this rule through the collection and analysis of ambient air samples within the facility boundaries, if the hazardous substance concentration in surficial soil is representative of facility conditions.
