Table 3-1 Inorganic Contaminants of Particular Concern at DOE Sites

Element

Mediuma

Priorityb

Site

Tc

GW

High

Portsmouth

Cr(VI)

GW

Medium-High

Hanford

 

Soil

Medium

Hanford, Sandia National Laboratories, White Sands

U

GW

Medium-High

Fernald, Oak Ridge, Rocky Flats

 

Soil

Medium

Rocky Flats, Fernald, Oak Ridge

137Cs

Soil

Medium-High

Hanford, Savannah River Site

90Sr

GW

Medium-High

Hanford

 

Soil

Medium

Hanford

Pu

Soil

Medium

Mound, Rocky Flats, Nevada Test Site

Ra

Soil

Medium

Uranium mill tailings sites

3H

GW

Medium-Low

Savannah River Site, Hanford, Brookhaven

Hg

GW

Low

Oak Ridge

 

Soil

Low

Oak Ridge

Th

Soil

Low

Uranium mill tailings sites

a GW groundwater

b Priority based on prevalence in DOE complex, mobility, and toxicity (according to a survey by the SCFA).

compounds biodegrade, reducing the potential for human and ecological exposure over the long term. Metals, on the other hand, are infinitely persistent. Radionuclides undergo natural radioactive decay that, for some compounds (such as tritium), may significantly reduce risks over relatively short time periods. However, for other radionuclides (including various isotopes of Tc, U, Pu, and Th), half-lives are very long, meaning that risks posed by the presence of these compounds will persist for a very long time. As shown in Table 3-2, half-lives for radionuclides vary quite significantly depending on the isotopes present.

The potential for humans or sensitive ecosystems to be exposed to metals and long-lived radioactive materials is strongly affected by a number of factors that must be considered in assessing these contaminants. Some metals and radioactive contaminants have more than one oxidation state, which differ in mobility and toxicity (see Box 3-1). Like organic compounds, metals and radioactive contaminants can partition into organic matter present in soils. They also can be sorbed by other soil components, including cation exchange sites and metal oxides, and they can precipitate. Because of the mul-



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