In addition to the general data requirements discussed in Subsection 2.2.2, it may
be necessary to know other subsurface information to remediate
radionuclides in ground water, surface water, and leachate. Treatability
studies are usually necessary to ensure that the contaminated
ground water can be treated effectively at the design flow. A subsurface
geologic characterization would be particularly important to
characterize the effects of adsorption and other processes of
attenuation. Ground water models are also often needed to
predict flow characteristics, changes in contaminant mixes and
concentrations, and times to reach action levels.
Precipitation, filtration, and ion exchange are widely used
treatment technologies for radionuclides in ground water and are
discussed in the following paragraphs.
The combination of precipitation/flocculation
and sedimentation is a well-established technology for
radionuclides removal from ground water. This technology pumps
ground water through extraction wells and then treats it to
precipitate radionuclides and heavy metals. Typical removal of
radionuclides employs precipitation with hydroxides, carbonates,
or sulfides. Hydroxide precipitation with lime or sodium
hydroxide is the most common choice. Generally, the precipitating
agent is added to water in a rapid-mixing tank along with
flocculating agents such as alum, lime, and/or various iron
salts. This mixture then flows to a flocculation chamber that
agglomerates particles, which are then separated from the liquid
phase in a sedimentation chamber. Other physical processes, such
as filtration, may follow.
solid particles by running a fluid stream through a porous
medium. The driving force is either gravity or a pressure
differential across the filtration medium. Pressure
differentiated filtration techniques include separation by
centrifugal force, vacuum, or positive pressure. The chemicals
are not destroyed; they are merely concentrated, making
reclamation possible. Parallel installation of double filters is
recommended so ground water extraction or injection pumps do not
have to stop operating when filters backwashed.
Ion exchange is a
process whereby the toxic ions are removed from the aqueous phase
in an exchange with relatively innocuous ions (e.g., NaCl) held
by the ion exchange material. Modern ion exchange resins consist
of synthetic organic materials containing ionic functional groups
to which exchangeable ions are attached. These synthetic resins
are structurally stable and exhibit a high exchange capacity.
They can be tailored to show selectivity towards specific ions.
The exchange reaction is reversible and concentration dependent;
the exchange resins are regenerable for reuse. The regeneration
step leads to a 2 to10% wastestream that must be treated