A geologic setting shall exhibit an appropriate combination of the conditions specified in paragraph (b) of this section so that, together with the engineered barriers system, the favorable conditions present are sufficient to provide reasonable assurance that the performance objectives relating to isolation of the waste will be met.

If any of the potentially adverse conditions specified in paragraph (c) of this section is present, it may compromise the ability of the geologic repository to meet the performance objectives relating to isolation of the waste. In order to show that a potentially adverse condition does not so compromise the performance of the geologic repository the following must be demonstrated:

The potentially adverse human activity or natural condition has been adequately investigated, including the extent to which the condition may be present and still be undetected taking into account the degree of resolution achieved by the investigations; and

The effect of the potentially adverse human activity or natural condition on the site has been adequately evaluated using analyses which are sensitive to the potentially adverse human activity or natural condition and assumptions which are not likely to underestimate its effect; and

The potentially adverse human activity or natural condition is shown by analysis pursuant to paragraph (a)(2)(ii) of this section not to affect significantly the ability of the geologic repository to meet the performance objectives relating to isolation of the waste, or

The effect of the potentially adverse human activity or natural condition is compensated by the presence of a combination of the favorable characteristics so that the performance objectives relating to isolation of the waste are met, or

The potentially adverse human activity or natural condition can be remedied.

Favorable conditions. (1) The nature and rates of tectonic, hydrogeologic, geochemical, and geomorphic processes (or any of such processes) operating within the geologic setting during the Quaternary Period, when projected, would not affect or would favorably affect the ability of the geologic repository to isolate the waste.

For disposal in the saturated zone, hydrogeologic conditions that provide:

A host rock with low horizontal and vertical permeability;

Downward or dominantly horizontal hydraulic gradient in the host rock and immediately surrounding hydrogeologic units; and

Low vertical permeability and low hydraulic gradient between the host rock and the surrounding hydrogeologic units.

Geochemical conditions that:

Promote precipitation or sorption of radionuclides;

Inhibit the formation of particulates, colloids, and inorganic and organic complexes that increase the mobility of radionuclides; or

Inhibit the transport of radionuclides by particulates, colloids, and complexes.

Mineral assemblages that, when subjected to anticipated thermal loading, will remain unaltered or alter to mineral assemblages having equal or increased capacity to inhibit radionuclide migration.

Conditions that permit the emplacement of waste at a minimum depth of 300 meters from the ground surface. (The ground surface shall be deemed to be the elevation of the lowest point on the surface above the disturbed zone.)

A low population density within the geologic setting and a postclosure controlled area that is remote from population centers.

Pre-waste-emplacement groundwater travel time along the fastest path of likely radionuclide travel from the disturbed zone to the accessible environment that substantially exceeds 1,000 years.

For disposal in the unsaturated zone, hydrogeologic conditions that provide—

Low moisture flux in the host rock and in the overlying and underlying hydrogeologic units;

A water table sufficiently below the underground facility such that fully saturated voids contiguous with the water table do not encounter the underground facility;

A laterally extensive low-permeability hydrogeologic unit above the host rock that would inhibit the downward movement of water or divert downward moving water to a location beyond the limits of the underground facility;

A host rock that provides for free drainage; or

A climatic regime in which the average annual historic precipitation is a small percentage of the average annual potential evapotranspiration.

Potentially adverse conditions. The following conditions are potentially adverse conditions if they are characteristic of the postclosure controlled area or may affect isolation within the controlled area.

Potential for flooding of the underground facility, whether resulting from the occupancy and modification of floodplains or from the failure of existing or planned man-made surface water impoundments.

Potential for foreseeable human activity to adversely affect the groundwater flow system, such as groundwater withdrawal, extensive irrigation, subsurface injection of fluids, underground pumped storage, military activity or construction of large scale surface water impoundments.

Potential for natural phenomena such as landslides, subsidence, or volcanic activity of such a magnitude that large-scale surface water impoundments could be created that could change the regional groundwater flow system and thereby adversely affect the performance of the geologic repository.

Structural deformation, such as uplift, subsidence, folding, or faulting that may adversely affect the regional groundwater flow system.

Potential for changes in hydrologic conditions that would affect the migration of radionuclides to the accessible environment, such as changes in hydraulic gradient, average interstitial velocity, storage coefficient, hydraulic conductivity, natural recharge, potentiometric levels, and discharge points.

Potential for changes in hydrologic conditions resulting from reasonably foreseeable climatic changes.

Groundwater conditions in the host rock, including chemical composition, high ionic strength or ranges of Eh-pH, that could increase the solubility or chemical reactivity of the engineered barrier system.

Geochemical processes that would reduce sorption of radionuclides, result in degradation of the rock strength, or adversely affect the performance of the engineered barrier system.

Groundwater conditions in the host rock that are not reducing.

Evidence of dissolutioning such as breccia pipes, dissolution cavities, or brine pockets.

Structural deformation such as uplift, subsidence, folding, and faulting during the Quaternary Period.

Earthquakes which have occurred historically that if they were to be repeated could affect the site significantly.

Indications, based on correlations of earthquakes with tectonic processes and features, that either the frequency of occurrence or magnitude of earthquakes may increase.

More frequent occurrence of earthquakes or earthquakes of higher magnitude than is typical of the area in which the geologic setting is located.

Evidence of igneous activity since the start of the Quaternary Period.

Evidence of extreme erosion during the Quaternary Period.

The presence of naturally occurring materials, whether identified or undiscovered, within the site, in such form that:

Economic extraction is currently feasible or potentially feasible during the foreseeable future; or

Such materials have greater gross value or net value than the average for other areas of similar size that are representative of and located within the geologic setting.

Evidence of subsurface mining for resources within the site.

Evidence of drilling for any purpose within the site.

Rock or groundwater conditions that would require complex engineering measures in the design and construction of the underground facility or in the sealing of boreholes and shafts.

Geomechanical properties that do not permit design of underground opening that will remain stable through permanent closure.

Potential for the water table to rise sufficiently so as to cause saturation of an underground facility located in the unsaturated zone.

Potential for existing or future perched water bodies that may saturate portions of the underground facility or provide a faster flow path from an underground facility located in the unsaturated zone to the accessible environment.

Potential for the movement of radionuclides in a gaseous state through air-filled pore spaces of an unsaturated geologic medium to the accessible environment.