Wyoming Administrative Code › Agency 020 - Environmental Quality, Dept. of › Sub-Agency 0011 - Water Quality › Chapter 17 - STORAGE TANKS › Part J - ENVIRONMENTAL RESTORATION STANDARDS FOR LEAKING STORAGE TANK REMEDIATION ACTIONS › Section 17-40 - Soil Human Health Risk Assessment Calculations

Current through July 13, 2024
(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 are soil ingestion and
				  inhalation from volatile organic hydrocarbons and total petroleum
				  hydrocarbons.
(b)
Risk
				  Assessment Calculation Model
. With the soil properties data collected
				  during the subsurface investigation and/or extended remedial design
				  investigation phases, site specific soil risk assessment calculations shall be
				  made 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:
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(ii)
				  Combined Oral Ingestion and Inhalation Exposures to Non-carcinogenic
				  Contaminants in Residual Soil:
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where:
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and;
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and;
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.
IFSadj = 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.
IRSc = Soil ingestion rate, child,
					 200 mg/d.
IRAc = Soil inhalation rate, child,
					 10 m3/d.
RfDo = 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, Koc
					 foc , 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
					 (RfDo) and/or oral cancer potency factors
					 (CPFo) 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 data base sources, the
					 administrator will determine an acceptable soil cleanup concentration using the
					 latest available toxicological information from other appropriate
					 sources.