appendix o exposure scenarios and unit dose factors ... - Hanford Site

HNF-5636 Rev. 0
HNF-SD-WM-TI-707 Revision 1
concentration was not based on the waste concentration, but rather on the average soil
concentration after spreading. In effect, the 0.64 m³ of exhumed waste is diluted to a total
volume of 15 m³. These assumptions lead to the inhalation of 0.12 mg soil containing 0.0051 mg
of waste, as shown in the calculations below.
3 3
Soil Inhaled (Grout PA) = (1 h)(1.2 m /h)(0.1 mg/m )
= 0.12 mg soil inhaled
3 3
Waste Inhaled (Grout PA) = (0.12 mg soil)(0.64 m )/(15 m )
= 0.0051 mg waste inhaled
If the well-driller's dust is undiluted waste, the worker would inhale 0.12 mg of waste.
However, the actual inhalation time is probably greater than one hour. Since the waste layer is
about 10% of the total well volume, and the well takes 40 h to drill, the time of exposure to the
waste is (40 h)(0.10)=4 h. This would mean the worker inhales 4.8 mg of soil containing
0.48 mg of waste, as shown in the calculations below.
3 3
Soil Inhaled (ILAW PA) = (40 h)(1.2 m /h)(0.1 mg/m )
= 4.8 mg soil inhaled
3 3
Waste Inhaled (ILAW PA) = (4.8 mg soil)(0.14 m )/(1.4 m )
= 0.48 mg waste inhaled
For estimating inhalation exposure in the post-drilling residential scenario, the individual
spends the entire year living in the contaminated area. The Grouted Waste performance
assessment (WHC-SD-WM-EE-004) used an average inhalation rate of 8520 m³ per year and an
average air concentration of 0.1 mg/m³. The annual amount of soil inhaled was 852 mg. The
200 West Area Burial Ground performance assessment (WHC-EP-0645) used more detailed
inhalation assumptions based on PNNL-6312. The inhalation dose was based on an annual
inhalation of 445 milligrams.
Inhalation dose for the ILAW PA will be based on a refinement of the model used for the
200 West Area Burial Ground. It is also very similar to the method discussed in NUREG/CR-
5512.
The air concentrations shown in Table 17 are used to estimate the equivalent time of
exposure to an average air concentration of 0.1 mg/m³. The actual air concentrations used in the
table are discussed at length in NUREG/CR-5512, Section 6.3.1. The values chosen represent
conservative bounds on likely concentrations for the activities indicated. The exposure times are
also based on the NUREG/CR-5512, although the document is not as explicit as to the
assumptions behind the time periods used. It appears that NUREG/CR-5512 includes a vacation
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