Ground Water at Yucca Mountain How High Can It Rise? (1992) / Chapter Skim
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Might Increased Rainfall Cause Flooding of the Proposed Repository?
Might Increased Rainfall Cause Flooding of the Proposed Repository?
Pages 62-92
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From page 62... ...
One mechanism that might cause a rise in water level is increased recharge to the grouncl-water system as a result of an increase in precipitation. The ability of scientists to predict the response of the water table to possible increased recharge in the future must rely to a large extent on mathematical modeling.
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From page 63... ...
problematic. Discharge, or outflow of grounclwater, from the Alkali Flat/Furnace Creek subbasin occurs by springs near Furnace Creek Ranch in Death Valley, and by evapotranspiration, a surface process of removing water by plant activity and surface evaporation, at Franklin Lake Playa (Figure 3.3~.
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From page 64... ...
: 0 <42; ~ 42-63; ~ 63-84; 84-105; 0 >105. Abbreviations: AV, Amargosa Valley; BR, Belted Range; OF, Crater Flat; CH, Calico Hills; FOR, Furnace Creek Ranch; FF, Frenchman Flat; OF, Gold Flat; GR, Groom Range; IS, Indian Springs; M, Mercury; TM, Timber Mountain; YF, Yucca Flat; YM, Yucca Mountain.
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From page 65... ...
\ .......... ~-25~ ~ UE-~$3 72~9.5} ~$1: ~J-t3 728~3 A' o 1 2 MILES 65 l -36°52' 30' —36°= —36° 47' 30" KILOMETERS Figure 3.2 Preliminary composite potentiometric-surface (water table elevations)
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From page 66... ...
66 36°30' GROI1TJD WATER AT YUCCA MOUTON 37 o 1 1 6°30' 80un~rv of / nM8E~1 alp/ ~ modeled areas |' it. \ ~oC.,~ /~: two< E,~ Hi, 9 o \ " 1 ,~'./i - ~ At'< Seek Ranch ~ AS \ ~ primary ~ Vest - ' repository ' 'A | area I ~ J^a.ASS `~¢~\~\ Death Valley Junction Ad> \ Ye" bent;: E.~GI.E \ N~ MOUNTAIN ~ S 70 15 20 IS 30 c1LOMETERS 0 5 10 IS ARES Figure 3.3 Location of subregional area modeled by Czarnecki and Waddell (1 984)
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From page 67... ...
The transmissivities, or parameters describing how readily rocks will transmit ground water, and the amount of recharge in the Fortymile Wash area were adjusted until the model-calculated values of ground-water head were close to measured values. Only a few hundred meters north of Yucca Mountain, the water table level rises northward from~73~750 meters above mean sea level (m AMSL)
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From page 68... ...
a line sink east of Furnace Creek Ranch and (2) an areal discharge out of Alkali Flat.
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From page 69... ...
HYDROLOGY AND PALEOCLIMATIC HISTORY 37o 36°30' 69 1 1 6°30' l l 6 o Beatty O l .
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From page 70... ...
used a very small transmissivity in zone 11 (see Figure 3.4) to simulate the large hydraulic gradient north of Yucca Mountain.
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From page 71... ...
UR SHOWING ALTITUDE OF SIMUI^T~ ~g~ut~tC 1t~ .~ 80 mean 0 1 ~ . l O S 10 15 20 ZS 30 KILO - BEERS T ~ I I O S 10 IS - ICES Figure 3.5 Simulated hydraulic heads.
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From page 72... ...
These are issues of special interest because the answers to these questions affect projections concerning the magnitude of the impact of pluvial climates on the water table. Chronological Framework Regulations mandate that calculation of the potential for release of radionuclides from the proposed Yucca Mountain repository be per
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From page 73... ...
The last glacial age, the Wisconsin, ended about 10 ka, an age agreed upon by international convention (Olausson, 1982) which is based on carbon isotope dating of organic matter found in glacial debus.
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From page 74... ...
Black rectangle in southwestern Nevada is the Yucca Mountain area. Note that not all these lakes experienced maximum filling at the same time, and some may antedate the Wisconsin glacial age.
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From page 75... ...
The Paleozoic carbonate aquifer of the Las Vegas Valley is a confined system, sandwiched between impermeable layers. Increased recharge in the highlands of the Spring and Sheep Ranges should increase the hydrologic gradient, which is the pressure difference between recharge and discharge areas, resulting in a rapid increase in outflow through springs at the end of that gradient.
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From page 76... ...
with the temporal distribution of packrat midden samples from the Yucca Mountain vicinity STRATIGRAPH I C UNITS AND SOILS ENV I ROYAL ERPR~T I ON N = 1 48 , 20 Is NUMBER 10 OF SAMPLES Low s from a midden are assumed by most workers to have come from no more than a 30 to 50 m radius around the Len, which is believed to encompass nearly all packrat foraging activities. Although normally dominated by the remains of one or two plant species, the fossil assemblages also contain a diverse array of other plants.
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From page 77... ...
These midden sites span cat 2000 m of relief, from low elevations in the Amargosa Desert and Las Vegas Valley to high elevations in the Sheep Range. Fossil records from such an extensive range of elevations can be used to illustrate some principal features of the Late Quaternary environments of the region, and to demonstrate that the area was drier during the Late Quaternary than the earlier models widely accepted in the 1950's and 1960,s assumed for that period of time.
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From page 78... ...
Moreover, other packrat middens, within 0.5 km of this site, and at elevations slightly below and above show no evidence of wet-ground plant species. These midden sites are at elevations of 1230 m, 1240 m, 1280 m, and 1310 m, and are younger than the F~IC-7 midden, with glacial age samples dating to 21.S, 18.5, 16.4, 15.9, and 12.9 ka.
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From page 79... ...
wet-ground plant species appear to have been more abundant during the Middle Wisconsin and early Holocene, and (2) steppe shrubs appear to have been dominant during the Late Wisconsin.
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From page 80... ...
The Searles Lake and the Las Vegas Valley records even suggest episodes of increased effective moisture between cat 12 and 9 ka (Figure 3.71. At most sites there was nearcomplete turnover in plant community composition between 13 ka and 11 ka.
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From page 82... ...
MODEL CALCULATIONS OF POTENTIAL RISE IN THE GROUNDWATER TABLE DUE TO INCREASED PRECIPITATION Czarnecki (1985) applied the two~imensional model for groundwater flow at Yucca Mountain to estimate the magnitude of water Petrel changes that might occur in response to a change to a plunal climate.
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From page 83... ...
The computed rise in the water table beneath the proposed repository area, based on the assumed 100 percent increase in precipitation is about 130 m (Figure 3.~. Interestingly, a modeled increase in precipitation acting in concert with the "clam break" of the steep hydraulic gradient does not cause a larger rise In computed groundwater level than that caused by climate change alone.
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From page 84... ...
. ma_ 5 to t5 AWES l Figure 3.8 Differences in simulated hydraulic head between baseline simulation representing present-day conditions and the simulation involving a postulated 100 percent increase in precipitation.
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From page 85... ...
The panel concludes that identifying the cause of the steep hydrologic gradient north of Yucca Mountain, where the potentiometric surface descends sharply about 300 m southward, is the top priority in predichng future behavior of the Yucca Mountain flow system in general, and the water table in the vicinity of the proposed repository, in particular. There is virtually no evidence in the glacial-age fossil record for an increase in average annual precipitation exceeding 40 percent of modern amounts.
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From page 86... ...
The one known record of local wet-ground vegetation in Fortymile Canyon, which is dated to the Middle Wisconsin, is consistent with modeled responses of ground-water to increased recharge north of the steep hydraulic gradient north of Yucca Mountain (Czarnecki, 19851. This record deserves further consideration' in part because it lies cat 60 m above the present floor of For~nile Canyon, and 100 m above the present water table.
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From page 87... ...
If these studies confirm that the last recharge episode actually dates to 10-15 ka, then important inferences may be drawn regarding the coupling of climatic change and recharge events, for instance, that the full glacial was not wet enough to recharge the hydrologic system in the Yucca Mountain region. Furthermore the ground water history can be deduced from the isotopic content of the water.
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From page 88... ...
· One of the major sources of uncertainty in the present understanding of the hydrologic regime is the recharge in the Fortymile Canyon area, and the rate of evapotranspiration in the Franklin Lake Playa area. The panel therefore recommends that efforts be made to characterize more fully the recharge and discharge rates for the ground-water system in the vicinity of Yucca Mountain.
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From page 89... ...
It is essential to consider methods to reduce uncertainty in estimates of ground water recharge under different climatic conditions. In particular, the panel recommends undertaking an assessment of the reliability of empirical methods and newly developing considerations in estimating recharge under present arid, as well as much wetter and cooler, conditions to evaluate the potential effects of climate change on the water table.
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From page 90... ...
1990. Fossil packrat middens: The last 40,000 years of biotic change in the American southwest.
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From page 91... ...
1989. Late Wisconsin groundwater discharge environments of the southwestern Indian Springs Valley, southern Nevada.
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From page 92... ...
1986. The last pluvial climatic episodes in the deserts of southwestern North America.
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