Section 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.

(3) For a regulated substance identified in § 250.301(b) (relating to scope) as a mutagen, except for vinyl chloride, 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 the TF for volatiles:

(4) For vinyl chloride, 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 the TF for volatiles:

(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
RfCi	Inhal. Reference Concentration (mg/m3)	Chemical-specific	N/A	Chemical-specific
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
ET	Exposure Time (hr/day)	24	24	8
EF	Exposure Frequency5 (d/yr)	250	250	180
ED	Exposure Duration (yr)	30	N/A	25
CF	Conversion Factor	1,000 µg/mg	1,000 µg/mg	1,000 µg/mg
TR	Target Risk	N/A	1 x 10-5	1 x 10-5
IUR	Inhalation Unit Risk (µg/m3)-1	N/A	Chemical-specific	Chemical-specific
(Footnotes on next page)
ATc	Averaging Time for carcinogens (yr)	N/A	70	70
AED	Combined Age-Dependent Adjustment Factor and Exposure Duration (yr)6	N/A	76	N/A

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). ⁵Assumes 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. ⁶The Combined Age-Dependent Adjustment Factor and Exposure Duration (AED) is calculated using the equation AED = ADAF_‹2 x ED_‹2 + ADAF_2-16 x ED_2-16 + ADAF_›16 x ED_›16, where ADAF_‹2 = 10, ED_‹2 = 2 yr, ADAF_2-16 = 3, ED_2-16 = 14 yr, ADAF_›16 = 1, ED_›16 = 14 yr.

(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 f_oc of 0.005, which falls between f_oc’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 equations:

(1) For regulated substances not identified as a mutagen in § 250.301(b):

The provisions of this § 250.307 amended January 7, 2011, effective January 8, 2011, 41 Pa.B. 230; corrected March 19, 2011, effective March 5, 2011, 41 Pa.B. 1458; corrected May 16, 2014, effective March 5, 2011, 44 Pa.B. 2975. Immediately preceding text appears at serial pages (356274) to (356284).