Geology Reference
In-Depth Information
The quality of groundwater in deep-seated crystalline rocks is not only of
geochemical interest but is also of importance for the disposal of radioactive
waste and tapping of geothermal power.
CONTAMINANT TRANSPORT AND WASTE DISPOSAL
Hydrogeological studies in fractured rocks are also required to find suitable
sites for the disposal of hazardous waste material and site selection of land-
fills etc. The transport of hazardous dissolved contaminants, especially radio
nuclides and other hazardous waste, in the subsurface, especially in complex
environments through highly deformed and fractured rocks is quite
complicated. Under such situations the contaminants undergo rapid transport
through fractures and the movement of solutes into the high-porosity low-
permeability matrix by chemical diffusion. Sorption by very large surface
area of the matrix will retard the transport of reactive contaminants.
Dense non-aqueous phase liquids (DNAPLs) are also an important class
of groundwater contaminant. DNAPLs, released on ground surface underlain
by fractured rocks, migrate under the influence of gravitational and viscous
forces while capillary forces retard their forward movement.
Local industries, such as tanneries in South India using Cr (iv) and textile
industries using large salt concentration for dyeing, cause point source
contamination. Use of fertilizers and human and animal excreta are the main
cause of nitrate contamination especially in shallow groundwaters. However,
at greater depths, nitrate is reduced by denitrifying bacteria.
Special care is required for the disposal of high level radioactive waste
(HLW) produced from nuclear reactors for power production, weapons
manufacturing and research. Crystalline rocks including salt, shale and clay
beds, being impervious, are regarded to be suitable host rocks for HLW
disposal in repositories at depths of more than few hundred metres.
Most of the waste from nuclear power plants and nuclear weapons consists
of radioactive isotopes, which are long-lived and, therefore, require several
thousands of years of isolation from the environment. Therefore, the safety
requirements of such repositories pose considerable technical, social and
political challenges. The movement of dissolved radio nuclides in groundwater
through fractures is a matter of great concern. It has to be demonstrated that
the disposal of HLW will not have any adverse effect on the environment
and human health so that such programmes are acceptable to the public. This
has led to the establishment of Underground Research Laboratories (URLs)
for detailed hydrogeological and geotechnical studies in different parts of the
world viz., USA, Canada, Europe, Japan and Korea.
In USA, a repository for the disposal of HLW is proposed at the Yucca
Mountain in Nevada in the unsaturated (vadose) zone within basaltic tuffs
at a depth of about 350 m below the ground surface and 225 m above the
water table. The area is located in a desert environment having an annual
