user's guide and background technical document for the nevada ...

concentrations is expected at a site (e.g., sites with shallow water tables, fractured media, karst
topography, or source size greater than 30 acres).
The LBCL values (for DAF = 1 and 20) calculated using Equation E, along with the sources of
the various parameter values, are listed in Appendix D Table D-1.
Further NDEP guidance on leaching from soil to groundwater is provided in the following
documents:
http://ndep.nv.gov/bmi/docs/cover_let-%20leach_guidance.pdf
http://ndep.nv.gov/bmi/docs/100116%20leaching_guidance.pdf
5.0 BCLS FOR RADIONUCLIDES
Radionuclide health effects are based on the deposition of energy in body tissues resulting from
radioactive decay. Soil BCLs were calculated for direct exposure pathways related to an
individual exposed to site soils, and also for protection of groundwater from leaching of soil
radionuclides over time. For each radionuclide, soil BCLs related to direct exposure (ingestion,
inhalation, and external irradiation) are back-calculated from a target risk level of one-in-amillion
(1×10 -6 ) incremental lifetime cancer risk. BCLs for the migration-to-groundwater
pathway are back-calculated from the following groundwater activity limits (in order of
preference): non-zero maximum contaminant level goals (MCLGs), maximum contaminant
levels (MCLs), or risk-based limits based on a cancer risk of 1×10 -6 .
Radionuclide BCLs are calculated for a limited number of radionuclides for which soil samples
are routinely analyzed at the BMI Complex and Common Areas. These radionuclides include
isotopic uranium (uranium-234, uranium-235, uranium-238), isotopic radium (radium-226 and
radium-228), and isotopic thorium (thorium-228, thorium-230, and thorium-232). The BCLs for
these eight radionuclides and the basis of their derivation are presented in Appendix E.
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