R 299.14 Generic cleanup criteria for groundwater based on hazardous substance vapors emanating from groundwater to indoor air.

Rule 14. (1) Inhalation of hazardous substance vapors volatilizing from groundwater to indoor air shall be considered a reasonable and relevant exposure pathway for hazardous substances in groundwater 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) The highest water table elevation of a contaminated saturated zone at the facility, considering seasonal variation, is within 3 meters of the ground surface. (c) There is a sump present that is not completely isolated from the surrounding soil by its materials of construction, or there is other direct entry of contaminated groundwater into the basement. (3) Groundwater cleanup criteria based on inhalation of hazardous substance vapors volatilizing from groundwater to indoor air shall be called groundwater volatilization indoor air inhalation criteria (“GVIIC”). The GVIIC 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 x AIR AT TR GVIIC      where, GVIIC (Groundwater volatilization indoor air inhalation criteria) = chemical-specific, ug/L TR (Target risk level) = 10-5 AT (Averaging time) = 25,550 days (70 x 365) 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 groundwater concentration) = chemical-specific, (ug/m3)/(ug/L) EQUATION FOR NONCARCINOGENIC EFFECTS:   building CR ED EF ITSL 1 AT THQ GVIIC      where, GVIIC (Groundwater volatilization indoor air inhalation criteria) = chemical-specific, ug/L 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 groundwater concentration) = chemical-specific, (ug/m3)/(ug/L) The ratio of the indoor air concentration to the groundwater concentration is calculated as:    gw source building CR CR where, CRbuilding (Ratio of indoor air concentration to groundwater concentration) = chemical-specific, (ug/m3)/(ug/L)  (Attenuation coefficient) = chemical-specific, unitless gw source CR (Ratio of soil vapor concentration to groundwater/source concentration) = chemical-specific, (ug/m3)/(ug/L) The soil vapor-phase concentration generated from a hazardous substance in groundwater is assumed to be in equilibrium with the aqueous phase concentration (Cw) of that substance as related by the dimensionless Henry’s law constant (H’) such that: 3 3 w gw source /m 10 C TAF x H CR L '    where, gw source CR (Ratio of soil vapor concentration to groundwater/source concentration) = chemical-specific, (ug/m3)/(ug/L) 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 Cw (Uniform unit groundwater concentration) = 1 ug/L 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 groundwater 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 T eff T eff T where,  (Attenuation coefficient) = unitless eff T D (Total effective diffusion coefficient) = 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) = 115 cm (residential) = 300 cm (nonresidential) 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 To characterize contaminant diffusion from groundwater into buildings a total effective diffusion coefficient ( eff T D ) is calculated to account for both liquid phase diffusion of the contaminant through the capillary fringe, ( eff cf D ) , and vapor phase diffusion through the vadose zone, ( eff v D ). The calculation is as follows:      eff cf cf eff v crack v T eff T D h D L h L D    where, eff T D (Total effective diffusion coefficient) = chemical-specific, cm2/s LT (Source-building separation distance) = 115 cm (residential) = 300 cm (nonresidential) hv (Thickness of vadose zone below enclosed space floor) = 75 cm (residential) = 260 cm (nonresidential) Lcrack (Building foundation thickness) = 15 cm eff v D (Effective diffusion coefficient through vadose zone) = chemical-specific, cm2/s hcf (Thickness of capillary fringe) = 25 cm eff cf D (Effective diffusion coefficient through capillary fringe) = chemical-specific, cm2/s 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) TAF (Temperature adjustment factor) = 0.5 w (Soil water-filled porosity) = 0.3 cm3/cm3 The effective diffusion coefficient calculation for the capillary fringe ( eff cf D ) is written as:             2 3.33 cf w, w 2 3.33 cf a, a eff cf n θ TAF H' D n θ D D where, eff cf D (Effective diffusion coefficient through capillary fringe) = chemical-specific, cm2/s Da (Diffusivity in air) = chemical-specific, cm2/s a,cf (Soil air-filled porosity in capillary fringe) = 0.078 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) TAF (Temperature adjustment factor) = 0.5 w,cf (Soil water-filled porosity in capillary fringe) = 0.352 cm3/cm3 N (Total soil porosity) = 0.43 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 generic categorical criteria under 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. (e) Source-building foundation separation distance. (f) Vertical thickness of capillary fringe. 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. (5) The department may approve methods to demonstrate compliance with criteria for the 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, use of representative soil gas concentrations.