Ward Valley An Examination of Seven Issues in Earth Sciences and Ecology (1995) / Chapter Skim
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5 GROUND-WATER PATHWAYS TO THE COLORADO RIVER
5 GROUND-WATER PATHWAYS TO THE COLORADO RIVER
Pages 133-150
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From page 133... ...
As the water table beneath Ward Valley is 300 m higher in elevation than the Colorado River, the Wilshire group considers it possible that ground water flows Tom Ward Valley to other ground-water basins that discharge directly into the Colorado River. On the basis of interpretations of surface geology, subsurface materials, and data from wells and springs, they generalized these routes into five possible pathways (figure 5.
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From page 134... ...
. ~ arker Figure 5.1 Postulated ground-water pathways from the Ward Valley ground-water basin to the Colorado River (Wilshire et al., 1994~.
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From page 135... ...
The only possible interference from bedrock is the divide between Rice Valley and the Colorado River. Because it has yet to be proven that a cone of depression in the water table encircles Danby Dry Lake, such a pathway is possible.
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From page 136... ...
. DHS argues that, given a very low probability that dissolved radionuclides in the aliuvlal aqulter under the disposal site will ever reach the Colorado River, and because such a release would lead to no discernable radiological impact on the Colorado River, there is no risk to the public or to the environment.
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From page 137... ...
It is their position that, although direct evidence is insufficient to demonstrate conclusively the presence, position, and elevation of a ground-water divide between Ward and Rice Valleys, multiple lines of indirect evidence support the interpretation of a shallow ground-water divide. For example' they noted that the Wilshire group's postulated alluvial aquifer connection between Ward and Rice Valleys is contradicted by differences in the chemical composition of the ground water in southern Ward Valley and Rice Valley.
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From page 138... ...
The configuration ofthe bedrock surface and whether or not bedrock highs beneath the alluvium rise above the present water table bear directly on the validity of some of the postulated pathways to the Colorado River. The tectonic setting of the proposed Ward Valley LLRW site has been described by Wilshire et al.
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From page 139... ...
A Hydrologic Evaluation of the Proposed Ground-Water Pathways The hydrogeologic database is inadequate to determine whether or not any component of the ground water flowing beneath the Ward Valley site eventually reaches the Colorado River. In order to evaluate potential pathways, it would be necessary to know: (a)
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From page 140... ...
The majority of the ground-water flow beneath the site appears to go to Danby Dry Lake, based on limited hydrologic and geologic data and topographic conditions. The extensive ef~orescent deposits indicating continuous, long-term evaporation Tom a shallow capillary fringe at Danby Dry Lake, the shallow level of the ground water (approximately I.5 m below the playa surface)
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From page 142... ...
The license application presumes that the surrounding and underlying rocks are of relatively low permeability and that ground-water flow divides are associated with the topographic divides, thus creating an enclosed ground-water basin as well as an enclosed surface-water basin. Flow in the carbonate rock province of the Great Basin, which includes much of Utah and Nevada and extends into California to a point about 80 km north of the Ward Valley site, is characterized by interbasin movement of ground water through the permeable lower carbonate aquifer (Winograd and Thordarson, 1975~.
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From page 143... ...
If no intervening water table highs-or low permeability hydraulic barriers exist, which would create a ground-water flow divide, ground water could flow towards the lower elevation of the Colorado River. Routes ~ and 2 (Rice Valley and Vidal Valley!
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From page 144... ...
Route 4 (Sacramento Wash to Piute Valley) : Another potential impediment to ground water flow Tom beneath the site eastward to the Colorado River along the postulated pathways discussed in this section is influence of potential recharge from Homer Wash.
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From page 145... ...
As indicated above, the gradient along the Ward Valley portion of routes 1 and 2 is estimated to be about 0.0037 m/m, based on water levels in the monitoring wells at the proposed site and the elevation of Danby Dry Lake. The overall change in hydraulic head to the Colorado River is about 360 m in 130 km for a gradient of 0.0028 m/m.
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From page 146... ...
Potential Impacts on the Colorado River Potential Radioactive Contamination by Ground Water Plutonium is one of the longer-lived components of low-level waste that can be examined. DHS estimates that the total plutonium inventory of all the waste received by the site over its 30-year operational history will be from "a Faction of a curie to 2 curies from decontamination waste, and a fraction of one curie to several curies from other sources" (Brandt, ~ 994b)
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From page 147... ...
It is also important to note that this hypothetical discharge of 0.33 Ci/yr Tom the site to the Colorado River would require a combination of circumstances that has an incredibly low probability of occumng. This calculation is presented, therefore, only to show that actual potential impacts, if any, would be much less than the result calculated here.
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From page 148... ...
Conclusion Concerning Contamination of the Colorado River Although the committee considers that there are conceivable, but unlikely, flow paths for some of the Ward Valley ground water to the Colorado River, we conclude that the potential impacts on the river water quality would be insignificant relative to present natural levels in the river and to accepted regulator health standards. Potential Radioactive Contamination by Airborne Dust Another potential scenario that has been postulated for impacting the Colorado River or the water in the Colorado River Aqueduct is by airborne transport of radioactive dust Tom Danby Dear Lake.
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From page 149... ...
to cause anv substantial portion of the long-lived isatone.s to become ~l~~.nneit~1 in ~ ~ ~ ~ -- rib -to ~ -rid r~ -- ~~~ ^-^ the Danby Dry Lake sediments Therefore, the committee concludes that the potential impact of airborne radionuclides on the water quality of the Colorado River or Colorado River Aqueduct is minuscule, even much less than the upper bounding calculation made previously for the direct ground-water pathway scenario to the river. SUMMARY OF CONCLUSIONS The committee concludes that: I
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From page 150... ...
1987. Maps showing distribution of dissolved solids and dominant chemical type in ground water, Basin and Range province, southern California.
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