Geoscience Reference
In-Depth Information
239
Fig. 17.11
Pu concentrations in 100 K-Area wells of the Hanford Site. Transect following the
groundwater flow toward the Columbia River. Data include two collections (1997 and 1999) (Dai
et al.
2005
). Reprinted from Dai et al. (
2005
). Copyright (2005) with permission from Elsevier
uranium concentration in the groundwater has remained 1,300 times greater than
the EPA drinking water standard, indicating a pseudo-irreversible change in the
groundwater chemistry (Pedroni
2000
).
Natural organic compounds in groundwater such as humic substances facilitate
the transport of radionuclides from the land surface into groundwater. As an
example, Fig.
17.13
shows the distribution of two actinides, Pu and Am, dissolved
in saline groundwater in the presence or absence of fulvic or humic acids. It may
be observed that even the percentage of Pu and Am dissolved in the saline
groundwater increases in the presence of humic substances. Their distribution
varies as a result of different complexation mechanisms.
17.3.2 Heavy Metals
Heavy metals detected in groundwater under heavily urbanized areas are often of
anthropogenic origin. Concentrations of heavy metals in groundwater are influ-
enced by the amount of contaminant released to the soil-subsurface zone, by the
chemical nature of the groundwater, by the recharge rate, and by the properties of
the solid matrix. Heavy metal mobility through porous media may also be linked to
interactions
between
metals
and
colloids,
which
themselves
are
transported
through the subsurface.
