020-1 Wyo. Code R. §§ 1-40 - Soil Human Health Risk Assessment

(a) Introduction. A risk assessment for potential human health impacts is required for storage tank remediation actions to evaluate the risk component from a release and to develop quantitative soil cleanup concentrations directly related to the environmental risk. The human health risk assessment model is based on existing EPA methodologies and exposure constant values. The routes of potential exposure to be considered are soil ingestion and inhalation of substances released from regulated storage tank systems. A remedial action plan shall be submitted to the department for approval. The remedial action plan shall be approved by the department after it has been determined that the plan will adequately protect human health, safety, and the environment. In making this determination, the department shall consider the following factors, as appropriate:

(i) The physical and chemical characteristics of the released substance, including its toxicity, persistence, and potential for migration;

(ii) The hydrogeologic characteristics of the site and the surrounding area;

(iii) The proximity, quality, and current and future uses of nearby surface water and groundwater;

(iv) The potential effects of residual contamination on nearby surface water and groundwater;

(v) An exposure assessment; and

(vi) Any additional factors relevant to assessing risks to human health and the environment.

(b) Risk Assessment Calculation Model. Using soil property data collected during site investigation, site-specific soil risk assessment calculations shall be completed using equations in this Section. This model estimates chronic exposure(s) on a site-specific basis by combining an average exposure point concentration with reasonably conservative values for human intake and exposure duration. Thus, all site-specific soil parameters used to calculate risk assessment remedial concentrations at each site should reflect average or typical site conditions. In addition to site-specific soil conditions and chemical compounds, default values have been established for other equation input parameters.

(i) Combined Oral Ingestion and Inhalation Exposures to Carcinogenic Contaminants in Residential Soil:

Equation 3:

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(ii) Combined Oral Ingestion and Inhalation Exposures to Non-carcinogenic Contaminants in Residual Soil:

Equation 4:

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where: Equation 5:

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where: Equation 6:

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where:

Cs =	Soil contaminant cleanup concentration, mg/kg.
RISK =	Cancer risk for soil cleanup actions, 1 x 10-6.
ATc =	Averaging time, carcinogens, 25,550 d.
EF =	Exposure frequency, residential, 350 d.
IFS adj=	Ingestion factor, soil, 114 (mg-yr)/(kg-d).
CPFo =	Cancer potency factor, oral, chemical specific, (mg/kg-d)-1.
CPFi =	Cancer potency factor, inhalation, chemical specific, (mg/kg-d)-1.
INHFadj =	Inhalation factor, air, 11 (m3-yr)/(kg-d).
VFs =	Volatilization factor, soil, m3/kg.
HQ =	Hazard quotient, 1
BWc =	Body weight, child, 15 kg.
EDc =	Exposure duration, child, 6 yrs.
IRS =	Soil ingestion rate, child, 200 mg/d.
IRAc =	Soil inhalation rate, child, 10 m3/d.
RfD o=	Reference dose, oral, mg/kg-d.
RfDi =	Reference dose, inhalation, mg/kg-d.
Q/C =	Inverse of the mean concentration at the center of a 0.5 acre square source in Wyoming, 100.13 (g/m2-s per kg/m3).
DA	Apparent diffusivity, cm2/s.
Di =	Chemical diffusivity in air, cm2/s, chemical specific.
Dw =	Chemical diffusivity in water, cm2/s, chemical specific.
T	Exposure interval, s, 9.5E08.
[RHO]b	Soil density, g/cm3, 1.5 or actual value.
[RHO]s	Soil particle density, g/cm3, 2.65.
[THETA]a	Air filled soil porosity, Lair/Lsoil, 0.28 or, n - [THETA]w
[THETA]w	Water filled soil porosity, Lwater/Lsoil, 0.15.
n	Total soil porosity, Lpore /Lsoil , 0.43 or, 1 - [RHO]b/[RHO]s).
H' =	Dimensionless Henry's Law Constant, H(41), chemical specific.
Kd =	Soil-water partition coefficient cm3/g, Kocfoc, chemical specific.
Koc =	Soil organic carbon-water partition coefficient, cm3/g, chemical specific.
foc =	Fraction organic carbon in soil, g/g, 0.001 or site specific value.

Values for oral toxicological reference doses (RfD_o) and/or oral cancer potency factors (CPF_o) are obtained from current data in the U.S. Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS), the EPA Health Effects Assessment Summary Tables (HEAST), or the EPA Region IX Preliminary Remediation Goals Data Base. If an oral reference dose or cancer potency factor is not listed in the above database sources, the administrator will determine an acceptable soil cleanup concentration using the latest available toxicological information from other appropriate sources.

Notes

020-1 Wyo. Code R. §§ 1-40

Adopted, Eff. 6/29/2018.