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 September 21, 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.
where:
and;
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.
