R 299.24 Generic cleanup criteria for soil based on indoor inhalation of hazardous substance vapors volatilized from soil.

Rule 24. (1) Indoor inhalation of hazardous substance vapors volatilizing to indoor air from soil shall be considered a reasonable and relevant exposure pathway only for hazardous substances that have a Henry’s law constant greater than or equal to 0.00001 atm-m3/mole. (2) Except as provided in subrule (1) of this rule, if any of the following conditions exist, the generic criteria developed pursuant to this rule shall not apply and a site-specific evaluation of indoor inhalation risks shall be conducted: (a) There is a structure present or planned to be constructed at the facility which does not have a concrete block or poured concrete floor and walls. (b) There is a sump present that is not completely isolated from the surrounding soil by its materials of construction. (3) Soil cleanup criteria based on indoor inhalation of volatile emissions from hazardous substances in soil shall be called soil volatilization indoor air inhalation criteria (“SVIIC”). The SVIIC is determined by the following series of calculations, except as provided in R 299.34(3): EQUATION FOR CARCINOGENIC EFFECTS: building CR ED EF IURF AIR X AT TR SVIIC      where, SVIIC (Soil volatilization indoor air inhalation criterion) = chemical-specific, ug/kg TR (Target risk level) = 10-5 AT (Averaging time) = 25,550 days (70 years x 365 days/year) AIR (Adjusted inhalation rate) = 1 (residential) = 2 (nonresidential) IURF (Inhalation unit risk factor) = chemical-specific, (ug/m3)-1 EF (Exposure frequency) = 350 days/year (residential) = 245 days/year (nonresidential) ED (Exposure duration) = 30 years (residential) = 21 years (nonresidential) CRbuilding (Ratio of indoor air concentration to soil concentration) = chemical-specific, (ug/m3)/(ug/kg) EQUATION FOR NONCARCINOGENIC EFFECTS:   building CR ED EF ITSL 1 AT THQ SVIIC      where, SVIIC (Soil volatilization indoor air inhalation criterion) = chemical-specific, ug/kg THQ (Target hazard quotient) = 1 AT (Averaging time) = 10,950 days (residential) = 7,665 days (nonresidential) EF (Exposure frequency) = 350 days/year (residential) = 245 days/year (nonresidential) ED (Exposure duration) = 30 years (residential) = 21 years (nonresidential) ITSL (Initial threshold screening level) = chemical-specific, ug/m3 CRbuilding (Ratio of indoor air concentration to soil concentration) = chemical-specific, (ug/m3)/(ug/kg) The contaminant vapor concentration in the building indoor air is written as:    soil source building CR CR where, CRbuilding (Ratio of indoor air concentration to soil concentration) = chemical-specific, (ug/m3)/(ug/kg)  (Attenuation coefficient) = chemical-specific, Unitless soil source CR (Ratio of soil vapor concentration to soil/source concentration) = chemical-specific, (ug/m3)/(ug/kg) The vapor-phase contaminant concentration at the source for soil is written as:    a b d w 3 3 6 3 b s soil source TAF ' H k m cm 10 g kg 10 C TAF ' H CR                 where, soil source CR (Ratio of soil vapor concentration to soil/source concentration) = chemical-specific, (ug/m3)/(ug/kg) H’ (Dimensionless Henry’s law constant, where H’ = HLC x 41) = chemical-specific, unitless HLC (Henry’s law constant at 25 degrees Celsius) = chemical-specific, (atm-m3/mol) TAF (Temperature adjustment factor) = 0.5, unitless s C (Uniform concentration in soil) = 1 ug/kg b  (Dry soil bulk density) = 1.5 g/cm3 w  (Soil water-filled porosity) = 0.3 cm3/cm3 d k (Soil-water partition coefficient) = chemical-specific, cm3/g (equivalent to L/kg) For organic compounds = Koc (cm3/g) x foc (g/g) For inorganic compounds = chemical-specific, cm3/g oc K (Soil organic carbon partition coefficient) = chemical-specific, cm3/g oc f (Fraction of organic carbon content of soil) = 0.002 g/g (0.2%) a  (Soil air-filled porosity) = 0.13 cm3/cm3 The intrusion rate of hazardous substance vapors into buildings is predicted using an analytical solution which couples both diffusive and convective transport of vapors emanating from subsurface soil into enclosed spaces. An attenuation coefficient () is calculated that is expressed as the ratio of building indoor air concentration to the vapor- phase concentration at the source. Values of  are calculated assuming infinite source conditions. For infinite source conditions  is written as follows:                                                                                   1 A D L Q exp L Q A D L Q A D A D L Q exp A D L Q exp L Q A D crack crack crack soil T soil b T building b crack crack crack soil crack crack crack soil T building b eff v eff v eff v where,  (Attenuation coefficient) = unitless eff v D (Effective diffusion coefficient through vadose zone) = chemical-specific, cm2/s Dcrack (Effective diffusion coefficient through crack) = cm2/s, (Dcrack = eff v D , see equation for eff v D below) Ab (Area of enclosed space below grade) = 1.96E+6 cm2 (residential) = 3.83E+6 cm2 (nonresidential) Qbuilding (Building ventilation rate) = 1.51E+5 cm3/s (residential) = 5.04E+5 cm3/s (nonresidential) Lcrack (Building foundation thickness) = 15 cm LT (Source-building separation distance) = 15 cm (All land use categories) Qsoil (Volumetric flow rate of soil vapor into the building) = 0.81 cm3/s (residential) = 2.10 cm3/s (nonresidential) Acrack (Total area of cracks below grade) = 196 cm2 (residential) = 383 cm2 (nonresidential) exp(p) (The base of the natural logarithm raised to power p) = ep The effective diffusion coefficient calculation for the vadose zone ( eff v D ) is written as:               2 33 . 3 w w 2 33 . 3 a a eff v n TAF ' H D n D D where, eff v D (Effective diffusion coefficient through vadose zone) = chemical-specific, cm2/s Da (Diffusivity in air) = chemical-specific, cm2/s a (Soil air-filled porosity) = 0.13 cm3/cm3 n (Total soil porosity) = 0.43 cm3/cm3 Dw (Diffusivity in water) = chemical-specific, cm2/s H’ (Dimensionless Henry’s law constant, where H’ = HLC x 41) = chemical-specific, unitless HLC (Henry’s law constant = chemical-specific, (atm-m3/mol) w (Soil water-filled porosity) = 0.3 cm3/cm3 (4) Facility-specific measurements of the following parameters may be substituted individually for the generic assumptions and still allow the facility to satisfy the categorical criteria in section 20120a(1)(a) to (e) of the act: (a) Dry soil bulk density. (b) Fraction of organic carbon in soil. (c) Soil vapor permeability. (d) Temperature adjustment factor for Henry’s law constant. Facility-specific measurements shall be based on representative characterization. Documentation of all facility specific values shall be provided in the response activity plan or no further action report. (5) The department may approve methods to demonstrate compliance with criteria for this exposure pathway if those methods are more representative of in-situ conditions at the facility. Methods acceptable to the department may include, but are not limited to, evaluation of representative soil gas concentrations.