Management of Commercially Generated Radioactive Waste - U.S. ...

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natural gas storage, freshwater storage, and disposal of other wastes of lower or shorter-
lived toxicity. In addition, as noted earlier, exploration for natural resources and subse-
quent mining in a large area around the disposal facility would be subject to control. The
extent of exclusion and limited activity buffer zones would depend on the characteristics of
the disposal formation, and in particular, its hydrologic and geochemical conditions. Fi-
nally, evidence exists that injection of wastes into certain formations could potentially
lead to seismic activity and earthquakes.
Potential Events
Natural Events. The long-term leaching and transportation of radionuclides in the
ground-water system to the biosphere would be a fundamental pathway in the well injection
concept, as it is with all geologic concepts. Assessment of the environmental impact would
require predictive modeling of the rock mechanics, hydrology, and geochemistry of the dis-
posal and containment formations, together with an adequate data base to characterize the
biosphere. The disposal area would be selected to minimize the risks from seismic and vol-
canic activities and their effect on the hydrologic regime. Seismic events could induce tec-
tonic effects within the disposal area, causing permeability and flow changes. Volcanic
activity could result in catastrophic breach of the containment formation, or could generate
unacceptable, thermally induced flow patterns. The risk of meteorite impact would be similar
to that for a mined geologic repository; however, with deep-well liquid disposal, the waste
would be in a more mobile form. The impact of gross changes, such as climate variations or
polar ice melting, would, in general, depend on their effect on the hydrologic regime.
Increased erosion (because of glaciation, for example) could reduce the cover of the disposal
formation.
An impact of potentially major significance is the increased chance of an earthquake that
could result from injecting waste material into rock formations. A relationship between deep
well liquid injection and increased seismicity has been suggested (Evans 1966) in connection
with earthquakes at Denver and injection at the Rocky Mountain Arsenal well. Other studies
(Hollister and Weimer 1968, Dieterich et al. 1972) have shown that deep well injections in
the Rocky Mountain Arsenal Range have been instrumental in producing seismic events. Obvi-
ously, such concerns are significant and would have to be seriously evaluated for specific
sites. Knowledge of the in situ stress state for both concepts would be needed before pro-
ceeding with the well injection option because of the chance of earthquakes developing. The
depth of shale grout injection would be limited by the requirement that vertical stresses be
less than horizontal stresses.
Manmade Events. Exclusion and controlled-use buffer zones would be set up around an
injection facility. Nevertheless, the risks associated with drilling into a waste-liquid or
grout disposal formation would have to be considered. Changes in the surface and subsurface
hydrologic regime of the area, because of reservoir construction, deep excavation and con-
struction, and resource exploitation outside the buffer zone, would require analysis.