§ 250.307. Inhalation numeric values.
(a) For a regulated substance which is a systemic toxi- cant, the following applies:
(1) For a volatile compound, the numeric value for inhalation from soil shall be calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the following equation using TF for volatiles:
(2) For a regulated substance attached to particulates, the numeric value for inhalation from soil was calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the equation in paragraph (1) using TF for particulates.
(b) For a regulated substance which is a carcinogen, the following apply:
(1) For a volatile compound, the numeric value for inhalation from soil was calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the following equation using TF for volatiles:
(2) For a regulated substance attached to particulates, the numeric value for inhalation from soil was calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the equation in paragraph (1) using TF for particulates.
(c) For a regulated substance which is both a systemic toxicant and a carcinogen, the inhalation numeric value is the lower of the two numbers as calculated by the equations in subsections (a) and (b).
(d) The default exposure assumptions used to calculate the inhalation numeric values for soil are as follows:
| Residential | Nonresidential | |||
| Term | Systemic1 | Carcinogens2 | (Onsite Worker) | |
| THQ | Target Hazard Quotient | 1 | N/A | 1 |
| RfDi | Inhal. Reference Dose (mg/kg-day) | Chemical-specific | N/A | Chemical-specific |
| BW | Body Weight (kg) | 70 | N/A | 70 |
| ATnc | Averaging Time for systemic toxicants (yr) | 30 | N/A | 25 |
| TF | Transport Factor (mg/kg)/(mg/m3) Volatilization3 Particulate4 | Chemical-specific 1 x 1010 | Chemical-specific 1 x 1010 | Chemical-specific 1 x 1010 |
| Abs | Absorption (unitless)5 | 1 | 1 | 1 |
| ET | Exposure Time (hr/day) | 24 | 24 | 8 |
| EF | Exposure Frequency6 (d/yr) | 250 | 250 | 180 |
| ED | Exposure Duration (yr) | 30 | N/A | 25 |
| IR | Inhalation Rate (m3/hr) | 0.83 | N/A | 1.25 |
| TR | Target Risk | N/A | 1 x 10-5 | 1 x 10-5 |
| CSFi | Inhalation Cancer Slope Factor (mg/kg-day)-1 | N/A | Chemical-specific | Chemical-specific |
| (Footnotes on next page) | ||||
| ATc | Averaging Time for carcinogens (yr) | N/A | 70 | 70 |
| Ifadj | Inhalation Factor7 (m3-yr/kg-hr) | N/A | 0.5 | 0.4 |
Notes: Modified from USEPA Region III Risk-based Concentration Table, dated October 20, 1995.
N/A = Not Applicable
1Residential exposure to systemic toxicants is based on adult exposure, consistent with USEPA (1991).
2Residential exposure to carcinogens is based on combined child and adult exposure.
3Volatilization transport factor is calculated using TF = (ER x DF)-1, where DF = 12 (mg/m3)/(m2-sec). See soil depth-specific algorithm for the calculation of ER.
4Particulate transfer factor was calculated using TF = (ER x DF)-1, where ER = 8.25 x 10-12 (mg/m2-sec)/(mg/kg) and DF = 12(mg/m3)/(mg/m2-sec).
5In cases where the inhalation RfD or CSF is based on absorbed dose, this factor can be applied in the exposure algorithm. The default value is 1.
6Assumes approximately 100 days/yr with the ground being frozen. Exposure to surficial soils when the ground is frozen is considered de minimis. The nonresidential exposure frequency is defined as 5/7 x 250 days/yr.
7The inhalation factor for the residential scenario is calculated using the equation IFadj = EDc x IRc/BWc + EDa x IRa/Bwa, where EDc = 6 yr, IRc = 0.5 m3/hr, BWc = 15kg, EDa = 24 yr, IRa = 0.83 m3/hr, and BWa = 70 kg. The inhalation factor for the nonresidential scenario is calculated using the equation IFadj = ED x IR/BW, where ED = 25 yr, IR = 1.25 m3/hr and BW = 70 kg.
(e) For the inhalation numeric values in subsections (a) and (b), the TF was calculated by the following equation:
TF = (ER x DF)-1
The Dispersion Factor (DF) value of 12 (mg/m3)/(mg/m2/sec) is taken from the default value in the EPA Draft Soil Screening Guidance (U. S. EPA, 1994. Technical Background Document for Soil Screening Guidance. Review Draft. Office of Emergency and Remedial Response. EPA-540/R-94/106) and the Emission Rate (ER) is calculated by the following equations (from Jury et al. 1990. Water Resources Research, Vol. 26. No. 1. pp. 13-20):
| Parameter | Definition | Unit | Recommended Value(1) | |
| ER | Chemical vapor emission rate from surface soil or subsurface soil | mg/m2-sec per mg/kg | Chemical-specific | |
| Co | Chemical concentration in soil, Co = CS[rho ]b | g/m3 | 1.8 | |
| CS | Chemical concentration in soil | mg/kg (ppm) | 1 | |
| DE | Effective diffusion coefficient | m2/sec | Chemical-specific | |
| Dai | Air diffusivity for chemical i | m2/sec | Chemical-specific | |
| DLi | Water diffusivity for chemical i | m2/sec | Chemical-specific | |
| t | Time | sec | N/A | |
| T | Emission averaging time | sec | Equal to exposure duration | |
| [thgr ] | Total soil porosity, [thgr ] = [thgr ]a + [thgr ]m | cm3/cm3 | 0.32(2) | |
| [thgr ]a | Air-filled soil porosity | cm3/cm3 | 0.12(2) | |
| [thgr ]m | Moisture-filled soil porosity, [thgr ]m = w[rho ]b | cm3/cm3 | 0.20(2) | |
| w | Moisture content for soil | g water/g soil | 0.11 | |
| [rho ]b | Dry bulk density of soil, [rho ]b = (1-[thgr ]) [rho ] | g/cm3 | 1.8(2) | |
| (Footnotes on next page)
| ||||
| [rho ] | Soil particle density | g/cm3 | 2.65 | |
| Kd | Partition coefficient, Kd = Kocfoc | cm3/g | Chemical-specific | |
| H | Henry’s Law constant | dimensionless | Chemical-specific | |
| DG | Effective gas-phase diffusion coefficient | m2/sec | Chemical-specific | |
| DL | effective liquid-phase diffusion coefficient | m2/sec | Chemical-specific | |
| L | Depth of the contaminated surface soil | m | 0.6(3) | |
| l | Depth of the clean soil cover | m | 0.6(3) | |
| W | Thickness of the contaminated subsurface soil | m | 4.0(3) | |
| KOC | Organic carbon partition coefficient for chemical i | cm3/g | Chemical-specific | |
| fOC | Fraction of organic carbon in soil | dimensionless | 0.005(4) | |
(1)All default values from USEPA (1994) Draft Soil Screening Guidance, EPA-540/R-94/106, except as noted.
(2)Consistent with Standards Subcommittee recommendation.
(3)Based on Act 2 SAB-agreed depths.
(4)The Risk Assessment Subcommittee selected a foc of 0.005, which falls between foc’s of 0.006 for surface soil and 0.002 for subsurface soil.
(f) For a regulated substance which is a systemic toxicant and is a volatile compound, the numeric value for the inhalation of volatiles from groundwater was calculated by using the appropriate residential or nonresidential exposure assumptions from subsection (h) according to the following equation:
(g) For a regulated substance which is a carcinogen and is a volatile compound, the numeric value for the inhalation of volatiles from groundwater shall be calculated by using the appropriate residential or nonresidential exposure assumptions from subsection (h) according to the following equation:
(h) The default exposure assumptions used to calculate the inhalation numeric values for the inhalation of volatiles from groundwater are as follows:
| Residential | Nonresidential | |||
| Term | Systemic1 | Carcinogens2 | (Onsite Worker) | |
| THQ | Target Hazard Quotient | 1 | N/A | 1 |
| RfDi | Inhal. Reference Dose (mg/kg-day) | Chemical-specific | N/A | Chemical-specific |
| BW | Body Weight (kg) | 70 | N/A | 70 |
| ATnc | Averaging Time for systemic toxicants (yr) | 30 | N/A | 25 |
| Abs | Absorption (unitless)3 | 1 | 1 | 1 |
| ET | Exposure Time (hr/day) | 24 | 24 | 8 |
| EF | Exposure Frequency6 (d/yr) | 350 | 350 | 250 |
| ED | Exposure Duration (yr) | 30 | N/A | 25 |
| IR | Inhalation Rate (m3/hr) | 0.625 | N/A | 1.25 |
| TF | Transfer Factor (L/m3)4 | 0.5 | 0.5 | 0.5 |
| TR | Target Risk | N/A | 1 x 10-5 | 1 x 10-5 |
| CSFi | Inhalation Cancer Slope Factor (mg/kg-day)-1 | N/A | Chemical-specific | Chemical-specific |
| ATc | Averaging Time for carcinogens (yr) | N/A | 70 | 70 |
| Ifadj | Inhalation Factor5 (m3-yr/kg-hr) | N/A | 0.4 | 0.4 |
(Footnotes on next page)
Notes: Modified from USEPA Region III Risk-based Concentration Table, dated October 20, 1995.
N/A = Not Applicable
1Residential exposure to systemic toxicants is based on adult exposure, consistent with USEPA (1991).
2Residential exposure to carcinogens is based on combined child and adult exposure.
3In cases where the inhalation RfD or CSF is based on absorbed dose, this factor can be applied in the exposure algorithm.
4Default Transfer Factor is as presented in USEPA’s RAGS, Part B.
5The inhalation factor for the residential scenario is calculated using the equation IFadj = EDc x IRc/BWc + EDa x IRa/Bwa, where EDc = 6 yr, IRc = 0.5 m3/hr, BWc = 15 kg, EDa = 24 yr, IRa = 0.625 m3/hr, and BWa = 70 kg. The inhalation factor for the nonresidential scenario is calculated using the equation IFadj = ED x IR/BW, where ED = 25 yr, IR = 1.25 m3/hr and BW = 70 kg.
This section cited in 25 Pa. Code § 250.304 (relating to MSCs for groundwater); and 25 Pa. Code § 250.305 (relating to MSCs for soil).
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