National Academies Press: OpenBook

Ground Water at Yucca Mountain: How High Can It Rise? (1992)

Chapter: Might Increased Rainfall Cause Flooding of the Proposed Repository?

« Previous: Water Levels in the Vicinity of the Proposed Repository in the ast 100,000 Years
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

3

Might Increased Rainfall Cause Flooding of the Proposed Repository?

INTRODUCTION

Although available geological and geochemical evidence does not support the contention that the water table has risen to the proposed repository level in the past 100 ka (see Chapter 2 of this report), the possibility that it may do so in the future must be assessed, because the most likely mode for release of significant radioactivity to the outside environment is ground-water transport. It is, therefore, of utmost importance to understand the ground-water system and the various mechanisms that may cause the ground water to rise to the repository level over the next 10 ka. This assessment requires the use of mathematical models, based on known physical principles, that can simulate what might happen in the future given certain known or assumed conditions, and expert judgement to determine the input and to evaluate the results. The uncertainty in the results of these simulations depends in part on the current understanding of processes and rates that can affect the mechanisms.

One mechanism that might cause a rise in water level is increased recharge to the ground-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. The computed rise in the water table strongly depends on (1) the assumed increase in precipitation, (2) the relationship of precipitation to recharge, and (3) the specifics of the particular mathematical (ground-water) model used

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

in the computations for the Yucca Mountain area. These issues are addressed in this chapter.

HYDROGEOLOGICAL SETTING

Yucca Mountain lies within the Alkali Flat/Furnace Creek subdivision of the Death Valley ground-water system (see Figure 3.1). The regional ground-water system also includes the Ash Meadows and Oasis Valley subbasins. The ground-water flow within all three subbasins is generally in a north-south direction. The principal aquifers in the Alkali Flat/Furnace Creek subdivision are in Cenozoic tuff and alluvium formations. Although a regional Paleozoic carbonate aquifer underlies a large part of southern Nevada and is thought to underlie the alluvium/tuff aquifers, only one borehole (UE-25p#1), southeast of Yucca Mountain, was drilled deep enough to encounter the carbonates (see Figure 3.2 for borehole locations). Its presence under Yucca Mountain, therefore, is still problematic.

Discharge, or outflow of groundwater, 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). Discharge rates in the Franklin Lake Playa are poorly known. It is also possible that part of the ground water bypasses the Franklin Lake Playa and discharges at lower elevations elsewhere. No estimates of such a discharge rate at lower elevations are available. Czarnecki (1985) assumes that the major modern recharge areas, which supply the ground water for the Furnace Creek/ Alkali Flat subsystem, are the Pahute Mesa area to the north of Yucca Mountain and the Fortymile Wash area (Figure 3.3) east of Yucca Mountain. The amount of present-day recharge in other recharge areas (Jackass Flats, Crater Flat, and the Amargosa Desert (Figure 3.3)) is negligible compared to the recharge from the higher elevations of Pahute Mesa and Fortymile Wash. Carbon isotope age data imply that the water present in the deeper parts of the Alkali Flat/ Furnace Creek subbasin was recharged about 10-15 ka (Dudley, 1990a). This recharge presumably occurred under conditions that were cooler and possibly wetter during the last 5 ka of Wisconsin glaciation than those prevailing now. These ground-water age data raise the interesting possibility that the Alkali Flat/Furnace Creek subbasin is still draining, and is presumably not in a steady state (see also Czarnecki, 1990). Sufficient data on ground water age in the subbasin are not yet available to describe the evolution of the ground-water system over the past 10-20 ka.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.1 Regional ground-water systems and heat flow in the south-central Great Basin. (From Dudley, 1990a.)

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.2 Preliminary composite potentiometric-surface (water table elevations) map of the saturated zone. Yucca Mountain. (From Dudley, 1990b.)

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.3 Location of subregional area modeled by Czarnecki and Waddell (1984).

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

The ground-water system in the Alkali Flat/Furnace Creek subdivision has been modeled by Czarnecki and Waddell (1984). These authors used a two-dimensional (areal) finite element model to simulate the steady-state ground-water flow occurring principally in the tuffs. The model was calibrated using available measurements of the elevation of ground-water levels. 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 ~730-750 meters above mean sea level (m AMSL), measured in wells G-1 and H-1, to ∼1030 m AMSL (in well G-2) over a maximum distance of approximately 2.5 km (Figure 3.2). The actual gradient may be steeper, but there are too few data at present to define it adequately. Understanding the nature and source of this steep hydraulic gradient is of fundamental importance in evaluating the long-term safety of the site for high level radioactive waste storage. In fact, it is the rapid decline of the water table level north of Yucca Mountain that allows for the “unsaturated” condition 300 m below the surface that was considered so important in the selection of the repository depth. The position of the gradient does not appear to correlate with presently known stratigraphic or structural features in the upper kilometer of the mountain (C. Fridrich, written communication, 1991).

Currently, the reasons for this large lateral increase in hydraulic head are a matter of speculation. Three conceptual models have been considered by scientists associated with the project to explain the occurrence of the steep potentiometric gradient: (1) a hydrologic dam or barrier—a narrow vertical zone (1.5 km wide) of greatly decreased transmissivity; (2) a hydrologic drain—a highly transmissive vertical zone diverting most flow from the high water table region into the lower carbonate aquifer; and (3) a low transmissivity zone north of Yucca Mountain caused by tectonically controlled stress fields. Clearly, the fundamental differences between the models involve the geometry and characteristics of the causative feature. Both the dam and the drain models require a local, east-west-trending near-vertical zone coinciding in location with the steep gradient. In the dam model this vertical zone has very low transmissivity and acts as a barrier; in contrast, the drain model requires the vertical zone to have significant vertical permeability. The third model evokes high compressive horizontal stresses north of the gradient to cause the low transmissivity. Each of these models has some supporting

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

data and none can be eliminated with the currently available data (C. Fridrich, pers. comm.). The model of Czarnecki and Wadell (1984) treats only the dam hypothesis. The results of this model are discussed briefly further on in this chapter.

A MODEL OF GROUND-WATER FLOW AT YUCCA MOUNTAIN

The area of the steady-state ground-water model of Czarnecki and Waddell (1984) covered the region extending from Timber Mountain in the north to Alkali Flat and Franklin Lake Playa in the south (see Figure 3.3). Recharge from the Pahute Mesa area was simulated by prescribing a constant pressure boundary. Some minor fluxes were also applied to account for recharge from Jackass Flats and the Amargosa Desert, based on the earlier modeling work of Waddell (1982). However, all these fluxes amount to less than 2.5 percent of the total recharge or discharge. The recharge along Fortymile Canyon (zone 8, Figure 3.4) was obtained from the parameter estimation procedure. For the calculations the recharge in the Fortymile Wash area, estimated at 2.214 × 104 cubic meters per day (m3/d), was assumed to account for 40.3 percent of the total recharge. Most of the rest of the recharge (about 57.3 percent) was modeled to enter the subbasin through the constant head boundary along the northernmost end of the modeled region. Discharge from the subbasin was represented as: (1) a line sink east of Furnace Creek Ranch and (2) an areal discharge out of Alkali Flat. The discharge from the Alkali Flat area is 2.214 × 104 m3/d. It equals 64.8 percent of the total discharge from the subbasin. The remainder of the discharge was assumed to take place in the Furnace Creek Ranch area. All other boundaries were assumed to be no-flow boundaries.

Czarnecki and Waddell (1984) divided the subbasin into 13 regions (Figure 3.4); transmissivities were assumed to be uniform in each of these regions. As part of a parametric estimation procedure, the recharge in the Fortymile Wash area and the transmissivities for zones 1 through 9 were varied until a satisfactory match was obtained between the computed and measured hydraulic heads. Final transmissivity values computed by Czarnecki and Waddell are given in Table 3.1. Considering the uncertainties in head measurements, the agreement between computed and measured head values is good. Model residuals for simulated versus measured heads range from −28.6 to 21.4 meters; most are less than ±7 meters. The simulated hydraulic heads are shown in Figure 3.5.

Despite the impressive match between the measured and computed heads, the model results must be used with caution. The computed

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.4 Model zone numbers, parameter groupings, and model boundary fluxes employed by Czarnecki and Waddell (1984).

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Table 3.1 Values of model transmissivities and standard errors. (excerpted from Czarnecki and Waddell, 1984).

[T, transmissivity, in meters squared per day; number following letter T in model variable column is zone number; dashes indicate that value was held constant]

Model Variable

Parameter Number

Value

Standard Error

Coefficient of Variation

 

T1, T2

1

1.336 × 103

31.92

0.024

Alluvium

T3, T4a

2

1.282 × 102

2.421

0.019

Volcanic Rocks

T4b

2

1.197 × 102

2.260

0.019

Carbonate Rocks

T5

1

1.169 × 104

2.792 × 102

0.024

Carbonate Rocks

T6, T7, T8

1

3.340 × 103

79.79

0.024

Tuff

T9

3

95.90

0.2711

0.003

Tuff

T10

78.62

Tuff

T11

3.888

Tuff

T12

8.64 × 10−3

Lakebeds

transmissivities in zones 5, 6, 7, and 8 are extremely high. The available permeability measurements do not provide support for these high values (see Appendix B for details of the measured permeabilities of the area). An extremely small transmissivity value was assumed for zone 11 to simulate the large hydraulic gradient north of the Yucca Mountain. As indicated above, the cause of this large hydraulic gradient is not understood. The uncertainty in the amount of total discharge from and recharge to the subbasin produces a corresponding uncertainty in the computed transmissivity values. The data currently available on discharge/recharge and transmissivity distribution in the subbasin provide inadequate constraints for the model.

Czarnecki and Waddell (1984) used a very small transmissivity in zone 11 (see Figure 3.4) to simulate the large hydraulic gradient north of Yucca Mountain. The trend of this barrier (zone 11) is east-west, normal to the known faults in the area. Recently, Czarnecki modeled a sudden removal of this postulated permeability barrier. Such a removal of the barrier could occur due to faulting associated with an earthquake. This “dam break” causes a maximum rise of about 40 meters in the computed water-level at the repository site (J. Czarnecki, pers. comm., 1992).

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.5 Simulated hydraulic heads. (From Czarnecki and Waddell, 1984.)

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Czarnecki (1985) presented a slightly modified form of the subbasin model. The constant head boundary condition along the northernmost boundary was replaced by a constant flux boundary. The prescribed flux was the same as that computed by Czarnecki and Waddell (1984). The prescribed flow conditions along the Furnace Creek and Alkali Flat were changed to constant head conditions. Hydraulic head values in these areas were estimated from values of land surface altitudes. This model also produced satisfactory agreement with observed heads.

To the extent that the mathematical model reflects reality, it can be used to predict how ground-water levels may change in response to changes in precipitation. Before considering speculative modeling of this type, however, it is instructive to consider the paleoclimatic, paleoecological, and paleohydrological data that offer guidance on the likely magnitude of precipitation changes over the next 10,000 years.

EVIDENCE FOR PAST VARIABILITY IN RAINFALL

Evidence of former, wetter climatic conditions is widespread throughout the semi-arid southwestern United States. Among the most striking examples are the wave-cut terraces on the margins of closed valleys, evidence that these basins once supported vast lakes. In the late nineteenth century Gilbert (1890) was among the first to correlate high stands (or levels) of these lakes, and the “pluvial” (or wet) climates that they indicated, with glacial ages. The correlation between pluvial climatic episodes and glacial ages (or stades) has provided a basic time scale for major climatic fluctuations in North American deserts. Although the correlation does not hold true in other of the world 's great deserts (the last pluvial climatic episode in North Africa, for example, is broadly correlated with the beginning of the present interglacial 10 ka (Ritchie et al., 1985; Spaulding, 1991a), it applies well in the western U.S. Other important issues relating to climate change in the southwestern desert regions include what constitutes a pluvial climatic regime in this region, and how much of an impact pluvial climatic episodes have in terms of increased recharge to the aquifer. 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-

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

formed to assess a 10 ka period. Predicting the behavior of the water table over that period of time requires estimating the changes in climate that are likely to occur, especially the amount of precipitation. However, projecting future climatic fluctuations depends in part on the knowledge of climate changes during the late Quaternary (the last 130 ka). The historic meteorological record is, of course, too brief to encompass the major changes that take place in such a time span, as are tree-ring reconstructions of past climates.

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 debris. The Early and Late Wisconsin were periods of maximum expansion of northern hemisphere ice sheets and maximum depression of global temperatures. The two major episodes of global climate change encompassed by the carbon isotope time scale (roughly the last 50 ka) are the Middle/Late Wisconsin transition at 23 ka, and the Late Wisconsin/Holocene transition at 10 ka. The first transition involved a change to colder environments, while the second involved a shift to a warmer and effectively drier climate accompanying worldwide deglaciation. The full glacial, or Wisconsin-maximum, witnessed the maximum extent of continental glaciers at ca. 18 ka (Spaulding, 1985; Benson and Thompson, 1987). It should be noted that at their furthest extent in North America, the ice sheets, which spread out across the continent from Labrador and Keewatin in the Canadian Shield, rarely reached south of the northern tier states. However, the continent south of the ice, including southern Nevada, experienced a colder and, in some cases, wetter (pluvial) climate.

Geographic and Paleohydrologic Framework 1

The Yucca Mountain region lies astride the climatic and vegetation transition between the warm-temperate Mojave Desert to the south and the cold-temperate Great Basin Desert to the north (Cronquist et al., 1972; Beatley, 1975). Sparse creosote bush 2 desertscrub characteristically occupies the warm valleys of the Mojave, while relatively productive sagebrush and sagebrush-bunchgrass vegetation typifies many cooler valleys to the north. This environmental transition

1  

See Appendix C for detailed discussion of paleoclimate and evidence, which is more briefly summarized in this chapter.

2  

See Appendix C Supplement for descriptions and explanations of plant species used as indicators of moisture and temperature in paleoclimate studies.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

from warm conditions in the south to relatively cold conditions in the north has apparently persisted through the late Quaternary.

In their study of pluvial lakes, that is, those present during former, wetter climatic intervals in Nevada (Figure 3.6), Mifflin and Wheat (1979) noted that south of 38°N latitude very few closed basins possess wave-cut terraces, it is unlikely that they supported pluvial lakes.

Figure 3.6 Pluvial lakes (shaded closed areas) of Quaternary age in the Great Basin. 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. (After Morrison, 1965; modifications from Mifflin and Wheat, 1979.)

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

The only known exception is a small basin on the northwest end of the Sheep Range, ca. 100 km east of Yucca Mountain. The widespread paleohydrologic evidence for a drier ice-age climatic regime in the vicinity of Yucca Mountain contrasts with the central and northern Great Basin record of wetter climatic conditions. Other lines of evidence that indicate that the last pluvial climatic regime in the Yucca Mountain region was actually relatively arid are presented in the following discussion.

The data from two sites within the southern Great Basin are relevant to understanding the chronology of paleohydrologic changes: Searles Lake in southeastern California (Smith, 1979; Smith and Street-Perrott, 1983) and the springs of Las Vegas Valley in southern Nevada (Figure 3.7) (Haynes, 1967; Quade, 1986; Quade and Pratt, 1989). Artesian springs are end-points of a hydrologic system that differs from that of a pluvial lake. High stands of a pluvial lake largely reflect surface water runoff (Enzel et al., 1989), while spring discharge, or outflow, is affected by the amount of water entering the water table, known as aquifer recharge, chiefly from snowmelt in the high mountains. Both systems, however, should be sensitive to significant pluvial episodes. 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. A persistent increase in rainfall should also result in increased lake levels. Thus, there is a reason for the apparent correlation of major “pluvial” episodes evident in a comparison of the record of lake-level fluctuations from Searles Lake with Las Vegas Valley spring records (Figure 3.7). It should be noted that Benson et al. (1990) have published an alternative chronology of Searles Lake to that shown in Figure 3.7. Unfortunately, they offer no guidance regarding which chronology is more reliable. In the absence of defensible arguments to the contrary, we rely on the chronology originally proposed by G. I. Smith (Smith and Street-Perrot, 1983; Benson et al., 1990).

The Paleoecological Record

Ancient packrat (Neotoma spp.) middens, or den deposits, provide much of the data discussed here. Descriptions of these deposits and the methods used in their analysis are offered by Betancourt et al. (1990). These middens, composed primarily of mummified plant fragments and fecal pellets encased in a matrix of crystallized packrat urine, are common in the hills of the region. The fossilized plants

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Figure 3.7 Comparison of paleohydrologic chronologies from the southern Great Basin (Smith and Street-Perrott, 1983; Quade, 1986) with the temporal distribution of packrat midden samples from the Yucca Mountain vicinity.

from a midden are assumed by most workers to have come from no more than a 30 to 50 m radius around the den, 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. The known climatic affinities of these plant species are then used to infer climatic

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

conditions. The time of such conditions is established by carbon isotope dating of organic material selected from the midden sample.

The paleoecological record derived from fossil pollen and plants found in carbon isotope-dated packrat middens provides direct evidence of environmental conditions during the last glacial age. Before the development of a comprehensive packrat midden record, the most detailed paleoecological evidence for the region was provided by fossil pollen studies from Tule Springs in the Las Vegas Valley. Wisconsin-age sediments there yielded abundant pine pollen, and were used to reconstruct glacial-age vegetation zonation in which pinyon-juniper woodland and pondersa pine-white fir forest extended down into the valleys some 1000 m below their current lower elevational limits (Mehringer, 1967). This reconstruction was in accord with the paleoclimatic models that were most widely accepted at that time (e.g., Leopold, 1955; Antevs, 1948): a mild and wet pluvial climatic regime with average annual precipitation perhaps double today's meager amount and a decline in average annual temperature of less than 5°C (∆Ta< 5°C).

More recent studies of fossil packrat middens provide more precise information on environmental change in the Yucca Mountain region. Comparison of the temporal distribution of midden samples from the vicinity of Yucca Mountain with the available paleohydrologic record (Figure 3.7) suggests that periods of increased recharge over the last ca. 22 ka can be well characterized due to a more thorough sample coverage during these times. These midden sites span ca. 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.

The existing paleoecological record can be examined for evidence of (1) full-glacial climatic conditions, and (2) plants that require wet ground to exist (phreatophytes) regardless of when they occurred. The data relating to the full-glacial period yield insight into climate during the time when conditions were most different from those of the present. The data relating to wet-ground plants yield evidence for the extent and timing of outflowing ground water where none now exists. Contrary to earlier interpretations, the more extensive fossil record demonstrates a relatively dry glacial-age climate, and the paleobiotic evidence shows the limited former extent of perennial surface water. The evidence for these more recent interpretations is discussed in more detail in Appendix C.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

During the last glacial age, juniper woodland extended to the valley bottoms, while the driest sites supported steppe shrubs such as shadscale and sagebrush. Nowhere in the Wisconsin fossil record is there evidence for the warm-desert shrubs that typify the current Mojave Desert. Above ca. 1600 m on tuffaceous substrate, and above 1800 m on calcareous rocks, there existed subalpine conifer woodland dominated by limber pine. No macrofossil evidence has been found for ponderosa pine-white fir forest during the last glacial age (Spaulding, 1985, 1990; Spaulding et al., 1983). Such forest vegetation would indicate wetter, milder conditions than those which appear to have prevailed. Rather, the widespread presence of cold-desert and dry-woodland plants indicates drier, colder conditions during the last glacial maximum. The absence of evidence for perennial water in the uplands during this time is consistent with these interpretations. Although there are extensive Wisconsin-age spring deposits in the valley bottoms of southern Nevada (Quade, 1986; Quade and Pratt, 1989), such geological evidence is generally absent from the highlands and wet-ground species appear only rarely in the southern Great Basin midden record.

To date there are but two sites that provide unequivocal records of wet-ground habitat in uplands where none now exists. Both occur in currently dry canyons that nevertheless have extensive drainage areas. Abundant seeds of the net-leaf hackberry bush (Celtis reticulata) from Dead Man Canyon-2 in the Sheep Range, dated by carbon isotopes at 9.6 ka, indicate the presence of perennial water at 2075 m elevation at that time. The tree is now extinct in the range (Spaulding, 1981). The second site is in Fortymile Canyon (FMC), the major drainage east of Yucca Mountain. The FMC-7 midden site lies at ca. 1250 m elevation and is a small rock shelter ca. 60 m above the canyon floor. Samples from the top and bottom strata of the FMC-7 midden yielded dates of 47.2 ± 3 ka and older than 52 ka respectively. They contained the remains of willow (Salix sp.), knotweed (Polygonum lapathifolium-type), and wild rose (Rosa woodsii), phreatophytes, or plants that require perennial water.

Elevation of the water table below this site is currently 1150 m AMSL. This would imply that at ca. 50 ka the water table was 100 m higher than now. However, except for the fossil flora, no evidence for ancient springs in the area has been recognized to date. 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 FMC-7 midden, with glacial age samples dating to 21.8, 18.5, 16.4, 15.9, and 12.9 ka. Lack of wet-

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

ground species in even the full-glacial age samples (ca. 18 ka) is consistent with other evidence for a relative dry, cold climate (see next section).

PALEOCLIMATIC RECONSTRUCTIONS

Important contrasts between Middle Wisconsin, Late Wisconsin and early Holocene fossil records are that (1) 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. These suggest that effective moisture and temperature may have been lower during the Late Wisconsin, and particularly during the full glacial when the coldest temperatures prevailed. This makes sense on meteorological grounds; low temperatures can lead to decreased precipitation, because the ability of the atmosphere to evaporate and transport water is strongly affected by air temperature.

Full-Glacial Climates

Paleoecological data indicating a substantial reduction in winter temperature (−∆Tw) in the Yucca Mountain region during the Late Wisconsin have been discussed by Spaulding (1985). The absence of warm-desert plants from even the lowest altitude and most arid sites is consistent with a −∆Tw of at least 6°C. The prevalence of steppe shrubs and drought-adapted conifers suggests similarities between the full-glacial fossil records from this area and the modern vegetation and climate of the northern Great Basin.

Most paleoclimatic reconstructions call for lowering full-glacial summer temperatures (−∆Ts) in excess of −∆Tw (Spaulding et al., 1983). Values of −∆Ts derived from the lower elevations at which key plant types have been found in the Yucca Mountain region range from 6.4° to 9°C. The decline in average annual temperature (−∆Ta) in the area during the Late Wisconsin is estimated to have been ca. 7°C (Spaulding, 1985). These reconstructions accord well with the distribution of relict features indicating permanently frozen ground on Great Basin mountain ranges (Dohrenwend, 1984).

Moisture-loving mountain trees such as ponderosa pine and white fir were expected in the fossil record when the model of a mild, moist glacial-age climate was thought to apply (see, e.g., Mehringer, 1967). Subsequent research showed that these plant species were actually rare (white fir) or apparently absent (ponderosa pine) from the fossil record of the southern Great Basin (Spaulding, 1990). An estimated

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

increase in average annual precipitation (Pa) of 40 percent is all that is required to account for the paleobiotic record in this region (Spaulding, 1985), rather than the 100 percent increase inferred from less extensive data sets. With the fossil record dominated by drought-and cold-tolerant species it is difficult to see how the increase could have been greater.

General analogs and model simulations of the full-glacial climate in this part of the Southwest suggest even less summer precipitation than today's meager amounts (at present <25 percent of the annual total in southern Nevada, which is approximately 158 mm (6 inches) per year (DOE, 1988). Thus, a substantial increase in winter precipitation is necessary to account for the apparent increase in full glacial Pa. This strong winter-seasonality of precipitation is analogous to present conditions in the central and northern Great Basin. Appendix C discusses the changes in atmospheric circulation that could have forced increased winter precipitation.

The Terminal Wisconsin-Early Holocene

The southern Great Basin paleohydrologic record indicates that there was a general decline in effective moisture between ca. 17 ka and 13 ka (Figure 3.7). This is consistent with model simulations of late-glacial climate change, which indicate the northward retraction of the westerly jet stream between 18 ka and 12 ka, largely due to the retreat of the North American ice sheets (COHMAP, 1988). The result in the Yucca Mountain area should have been a decline in the frequency and intensity of winter precipitation events. The later (14-13 ka) high stand of pluvial Lake Lahontan to the north (Benson and Thompson, 1987) may have been caused by increased precipitation associated with the repositioning of the prevailing westerlies at this more northerly latitude.

Despite evidence for the northward retreat of the westerly jet stream, effective moisture continued to exceed that of the present until the close of the early Holocene in southern Nevada (Spaulding, 1985; Van Devender et al., 1987). The Searles Lake and the Las Vegas Valley records even suggest episodes of increased effective moisture between ca. 12 and 9 ka (Figure 3.7). At most sites there was near-complete turnover in plant community composition between 13 ka and 11 ka. This involved the reduction or elimination of steppe shrubs and low-elevation conifer populations. Increases in summer seasonality of precipitation and warmer winter temperatures may account for these changes. Increased summer precipitation is indicated by the frequency of grasses and succulents (agave, yucca, cacti) in low-elevation

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Table 3.2 Packrat midden records of hydrophilic species from the Nevada Test Site and vicinity.

Area & Site

N. lat.

W. long.

Elev. (m)

Sample

Species

Source

14-C date (ka)

Amargosa Desert

Skeleton Hills-1

36° 32′

116° 20′

910

Sk-1B(2)

Celtis reticulata seed

long distance

9.2 ± 0.14

Skeleton Hills-2

36° 38′

116° 17′

940

SK-2(2)

muskrat tooth

long distance

8.17 ± 0.1

Sheep Range

Willow Wash-4

36° 28′

115° 15′

1585

WW-4B

Populus sp. twig

local (?)

9.82 ± 0.11

Flaherty Shelter

36° 30′

115° 14′

1650

Unit 3/125cm

Celtis reticulata seed

long distance

*

Deadman-2

36° 37′

115° 16′

2075

Dm-2

Celtis reticulata seeds

local

9.56 ± 0.18

North Yucca Mountain

Fortymile Canyon-7

36° 57′

116° 22′

1250

FMC-7(1)

Salix sp., Rosa woodsii local Polygonum lapathifolium-type

local

47.2 ± 3.0

 

36° 57′

116° 22′

1250

FMC-7(3)

several phreatophytes

local

>52

Sandy Valley

Sandy Valley-2

35° 53′

115° 42′

935

SaV-2(3)3

Celtis reticulata seed

long distance

9.4 ± 0.09

* Sample from bioturbated cave sediment, 75 cm below a radiocarbon date of 6.95 ± 0.32 ka (A-1297).

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

fossil records between ca. 12 ka and 8 ka (Spaulding, 1990). However, because conditions were changing rapidly, it is premature to offer specific climatic reconstructions for the terminal Wisconsin and early Holocene. Early Holocene records of wet-ground plant species (Table 3.2) do suggest that recharge was still sufficient to support expanded springs and water courses, despite the development of increasingly arid-climate vegetation on upland slopes. The contrasting lack of wet-ground plants from full-glacial middens is suggestive, but may be simply due to sample distribution (Figure 3.7).

Climates of the Last 8,000 Years

Essentially modern vegetation and climatic conditions were established in the Southwest between 7.8 ka and 7 ka. Within the last seven millennia it appears unlikely that ∆Ta exceeded 1.5°C or that Pa varied more than 20 percent from current long-term averages. However, there were marked variations within these limits. Much of the first half of the middle Holocene (from ca. 7.5 ka to 5.5 ka) appears to have been effectively more arid than the present (Hall, 1985; Spaulding, 1991). And much of the late Holocene (after 3.5 ka) appears to have been characterized by levels of effective moisture equal to or slightly exceeding those of the present (Cole and Webb, 1985; Spaulding, 1990).

MODEL CALCULATIONS OF POTENTIAL RISE IN THE GROUND-WATER TABLE DUE TO INCREASED PRECIPITATION

Czarnecki (1985) applied the two-dimensional model for ground-water flow at Yucca Mountain to estimate the magnitude of water level changes that might occur in response to a change to a pluvial climate. He used the empirical approach of Eakin et al. (1951) (see Czarnecki (1985) for a detailed discussion) to estimate the increase in ground-water recharge that would occur under an assumed 100 percent increase in modern-day precipitation. He calculated that the consequent increase in recharge would exceed current amounts by more than an order of magnitude (13.7 times greater than at present, rounded upward to 15 times present recharge). It is important to note in this context that the 100 percent value for an increase in precipitation is a speculative figure proposed by Spaulding et al. (1984) to account for poorly constrained evidence of “monsoonal pluvial” climatic conditions between 12 ka and 8 ka (Spaulding and Graumlich, 1986; Spaulding 1991a). Detailed analyses, as discussed earlier in

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

this report, indicate that a ca. 40 percent increase above current average annual precipitation, coupled with a decline in average annual temperature of more than 6°C, accounts for conditions during the last glacial maximum. Despite the present uncertainties about the climatic conditions obtaining during the terminal Wisconsin and early Holocene, it is very likely that the 100 percent increase in precipitation assumed by Czarnecki is overly conservative.

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 3.8). Interestingly, a modeled increase in precipitation acting in concert with the “dam break” of the steep hydraulic gradient does not cause a larger rise in computed ground-water level than that caused by climate change alone. The predicted rise in ground-water level is extremely sensitive to the recharge in the Fortymile Wash area. To the extent that the modern recharge (and its 15-fold increase due to a 100 percent increase in precipitation) in the Fortymile Wash area is poorly constrained, the computed rise in water level must be regarded as speculative. The magnitude of the calculated rise in water level would place the water level some 70 m below the proposed MGDS and suggests that further investigation of this scenario is required. The modeled effect of a 15-fold increase in recharge is a substantial increase in spring discharge north of the steep hydraulic gradient immediately north of the Yucca Mountain (Czarnecki, 1985). This area of spring discharge includes the middle reaches of Fortymile Canyon, where as previously mentioned, there is one Middle-Wisconsin (>47 ka) record of wet-ground plant species at the Fortymile Canyon-7 site. It is significant that no such records have been recovered from middens in the same area that date to the last glacial maximum. This supports the inference that, during the Late Wisconsin, precipitation and recharge amounts were well below the maximum values incorporated into Czarnecki's model (Czarnecki, 1985, 1990).

Estimates of ground-water recharge must be viewed with caution. Ground-water recharge, which is the movement of surface water to the water table through the unsaturated zone, cannot be measured directly. Recharge rates are controlled by the amount of rainfall, by plant and soil factors that govern evapotranspiration, and by geologic characteristics that determine the rate of movement of water to the water table. In semi-arid and arid regions, according to a National Research Council (NRC) ground-water study on recharge, evapotranspiration is nearly equal to precipitation, so that little or no water is available for recharge to the ground-water system except after very large rainfall events, which are infrequent in such climates (NRC,

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

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. (From Czarnecki, 1985.)

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

1990). While there are several methods for estimating recharge, the NRC study cautions that different methods result in different estimates even for the same locale and time period, and concludes that recharge estimation is difficult and characterized by large uncertainties. Moreover, it suggests that reliable estimates of recharge in dry climates may be beyond present-day technology (NRC, 1990). For this reason, hydrologic models that describe water table responses to changing climatic conditions using simplified recharge assumptions must be used with caution because of the large uncertainty associated with those assumptions.

While these caveats are true, the method suggested by Eakin et al. (1951, P. 14-16)—often referred to as the Maxey/Eakin Method—has been widely utilized in Nevada for more than 40 years. The method is purely empirical but has been shown to provide reasonable estimates of recharge. However, the use of this method to predict recharge under climatic conditions that are quite different from the present is speculative.

Thus, to the extent that an increase in the number of discharge points (indirectly measurable with the fossil record) indicates an increase in recharge, the sparse fossil record of wet-ground species allows a qualitative observation that recharge increase during the last glacial maximum was moderate (Table 3.2).

Czarnecki's model of increased recharge predicts discharge in the central Amargosa Desert west of Ash Meadows in an area that is currently dry. Sediments in this area indicate the existence of a past discharge area (J. Czarnecki, written comm., 1992).

CONCLUSIONS

Much more information is needed on discharge, recharge and transmissivity to characterize the ground-water flow system. 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 predicting 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. The nature of full-glacial plant species assemblages can be attributed to a relatively cold and dry climatic regime with increased average annual precipitation approximately 40 percent above that of the present, coupled with mean annual temperatures approxi-

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

mately 7°C below those of the present. The only local record of perennial water where none exists now, other than the Fortymile Canyon-7 site, comes from Dead Man Canyon in the Sheep Range. The general dearth of fossils of wet-ground plant species in the Late Quaternary fossil record and their absence during the full glacial, suggest that an arid to semi-arid climate and low recharge conditions have prevailed over the last ca. 50,000 years. The panel concludes that pluvial climates in this region were much drier than that which would be inferred from the standard application of the word “pluvial.” Therefore, models of climate variability that call for 100 percent increase in precipitation are probably overly conservative. More refinements in the data and techniques for estimating recharge, together with the use of model scenarios that reflect more closely established paleoclimatic conditions, are necessary to obtain realistic models of the response of the water table to increases in precipitation.

Nevertheless, according to the only model to date, an increase in precipitation due to a climate change has the potential to cause a rise of the water table on the order of 100 m. Until more complete hydrologic data of the area are obtained to constrain the model assumptions, the panel must regard climate change as a possible means of raising the water table significantly in the Yucca Mountain area.

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, 1985). This record deserves further consideration, in part because it lies ca. 60 m above the present floor of Fortymile Canyon, and 100 m above the present water table. It points to the need for additional investigations of paleohydrologic conditions in the vicinity. However, it does not necessarily constitute evidence for a radical change in the elevation of the water table in the vicinity of the Yucca Mountain, south of the break in elevation of the potentiometric surface. As previously mentioned younger, full-glacial middens from the same area, within 0.5 km of that site, provide no evidence of wet-ground vegetation at elevations somewhat below and above the site at which the wet-ground evidence was found.

RECOMMENDATIONS

Because of the importance of understanding the steep hydrologic gradient, the panel recommends that a series of wells be drilled in the region of the gradient north of Yucca Mountain. These wells should be drilled both within and outside the gradient, and should

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

be deep enough to penetrate the pre-Tertiary carbonates underlying the tuffs. Hydraulic head and permeability measurements from both pumping and interference tests in these holes should lead to at least a qualitative improvement in understanding the hydrological regime in this important area, as well as the cause of the steep gradient.

These wells would also provide data on the elastic properties of the Paleozoic rocks underlying the site, data that are much needed to understand the potential for rises in the water table due to seismic activity (see Chapter 5 of this report). The wells should be designed in close coordination with those responsible for geochemical studies (including isotopic, studies) because, as outlined in Chapter 2, an understanding of hydrogeological processes at Yucca Mountain will depend heavily on inferences based on geochemical signals.

There is a need for a better characterization of the long-term variability of the hydrologic regime in the Yucca Mountain area. Additional chronological data are needed from isotopic analyses of ground waters, as well as of spring deposits and dry lake sediments. The panel recommends that samples of water present at various depths in the Alkali Flat/Franklin Lake subbasin be dated and further analyzed for the isotopic concentrations. 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.

The results of mathematical modeling are also strongly conditioned by available hydraulic data (Appendix B). The panel has several specific recommendations on the collection and interpretation of hydraulic data, which should lead to improvements in the ability to estimate potential changes in water level, are listed below.

  • Existing well data (drilling, stratigraphy, repeat temperature surveys, pumping tests) should be re-examined to determine if the major permeable horizons are associated with specific formations and/or formation interfaces.

  • Permeability studies of the “slug test” variety in some Yucca Mountain area wells produced an anomalous fall-off response in the graphic representation of fluid behavior. This has been interpreted to indicate the state of the minimum horizontal stress in the crust (Szymanski, 1989). The panel recommends that the anomalous response in the slug tests be reanalyzed to determine the cause of the observed behavior. (See Appendix B for a fuller discussion).

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
  • The panel considers it worthwhile to attempt to remeasure hydraulic potential in isolated sections of existing boreholes. A knowledge of the three-dimensional hydraulic head distribution is essential for developing a detailed three-dimensional model of fluid flow in the Yucca Mountain area.

  • 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.

  • Independent determination of permeability is necessary to constrain and guide computer modeling studies. Since much of the permeability is believed to be fracture controlled, laboratory measurements of permeability on small rock samples may not be representative of flow conditions in situ. Well tests in this case are invaluable. The panel recommends, therefore, a carefully designed set of pressure interference tests between wells to delineate the permeability structure in the Yucca Mountain area.

The hydrologic models of the Yucca Mountain area have been restricted to the Tertiary tuff aquifer, which may be an oversimplification of the ground-water system. The panel recommends that a multi-layered model be constructed which includes both the shallow Tertiary aquifer and the Paleozoic carbonate rocks with currently available data. The data should also be used in a sensitivity analysis to test the coupling between the tuff aquifer and the Paleozoic carbonates. Current hydrologic information from the single hole penetrating the carbonate aquifer in the Yucca Mountain area is insufficient to characterize such a model. Additional drill hole data and tests in the carbonate aquifer are critically needed. Such a model should also be useful in assessing the “drain” concept as an explanation for the steep hydraulic gradient north of Yucca Mountain. Moreover, the panel recommends that geochemical data, as well as hydraulic data, be used to assess the validity of the modeling. The panel strongly urges that the use of geochemical interpretations become an integral part of the hydrogeological modeling at Yucca Mountain.

The panel recommends that, as sufficient data become available, more definite three-dimensional modeling studies be carried out for both the transient and steady states. A transient three-dimensional model can provide new insights into the evolution of the ground-water system over the past 10-20 ka. Such modeling of the transient

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

state is routinely used in geothermal reservoir engineering to model the natural state.

As discussed earlier in this Chapter, an understanding of the relationship between recharge and precipitation is still evolving. 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.

The panel recommends that the assumptions and results of Czarnecki 's (1991) model of increased rainfall and recharge be critically reviewed considering paleoclimate reconstructions, the potential for increased precipitation, and methods of calculating recharge in arid regions. To reduce the present uncertainty level, it will be necessary to obtain additional hydrologic, paleoecologic, and recharge data to provide constraints on future modeling efforts.

To resolve the apparent contradiction between what appears to be increased discharge (as a consequence of increased high-elevation recharge at Fortymile Wash) and evidence in the Yucca Mountain area for increased aridity in existing fossil records, the panel recommends a continued search for evidence of perennially moist conditions in currently dry water courses in the area, and for high-elevation (>2000 m) fossil records contemporaneous with a possible latest Wisconsin-early Holocene pluvial episode. The panel also recommends establishment of a data base relating species' ranges to measured climatic parameters, and its application to the macrofossil record. This would provide a great deal of new information on climatic stability of the Yucca Mountain vicinity, and would allow more sophisticated climatic interpretations of the fossil data. The known climatic affinities of plant species within a given fossil assemblage could be used for quantitative derivation of paleoclimatic parameters, if standardized data existed.

REFERENCES

Antevs, E. 1948. The Great Basin, with emphasis on glacial and postglacial times. University of Utah Bulletin 38: 1-24.

Beatly, J.C. 1975. Climates and vegetation pattern across the Mojave/Great Basin Desert transition of southern Nevada American Midland Naturalist 93: 53-70.

Beatly, J.C. 1976. Vascular plants of the Nevada Test Site, and central-southern Nevada National Technical Information Service Rpt. TID-26881.

Benson, L. V., and R. S. Thompson. 1987. The physical record of lakes in the Great

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Basin In North America and Adjacent Oceans During the Last Deglaciation. W. F. Ruddiman and H. E. Wright, Jr., eds. The Geology of North America, Vol. K3. Geological Society of America, Boulder, pp. 241-260.

Benson, L. V., D. R. Currey, R. I. Dorn, K. R. Lajoie, C. G. Oviatt, S. W. Robinson, G. I. Smith, and S. Stine. 1990. Chronology of expansion and contraction of four Great Basin lake systems during the past 35,000 years. Palaeogeography, Palaeoclimatology, Palaeoecology 78: 241-286.

Berger, A. L., J. Imbrie, J. Hays, G. Kukla, and B. Saltzman, eds. 1984. Milankovitch and climate: Understanding the response to astronomical forcing. Dordrecht, D. Reidel. Germany.

Betancourt, J. L., T. R. Van Devender and P. S. Martin, eds. 1990. Fossil packrat middens: The last 40,000 years of biotic change in the American southwest. Univ. Arizona Press, Tucson.

COHMAP Project Members. 1988. Climatic changes of the last 18,000 years. Observations and model simulations. Science 241: 1043-1052.

Cole, K. L., and R. H. Webb. 1985. Late Holocene vegetation changes in Greenwater Valley, Mojave Desert, California. Quaternary Research 23: 227-235.

Cronquist, A. H., N. H. Holmgren, and J. L. Reveal. 1972. Intermountain flora. Vascular Plants of the Intermountain West, U.S.A. Vol. 1 Hafner, NY.

Czarnecki, J. B. 1985. Simulated Effects of Increased Recharge on the Ground-Water Flow System of Yucca Mountain and Vicinity, Nevada-California Water-Resources Investigations Report 84-4344. U.S. Geological Survey, Denver, Colorado.

Czarnecki, J. B. 1990. Geohydrology and Evapotranspiration at Franklin Lake Playa, Inyo County, California. Open-File Report 90-356. U.S. Geological Survey, Denver, Colorado.

Czarnecki, J. B., and R. K. Waddell. 1984. Finite-Element Simulation of Ground-Water Flow in the Vicinity of Yucca Mountain, Nevada-California. Water-Resources Investigations Report 84-4349. U.S. Geological Survey, Denver, Colorado.

Dohrenwend, J. C. 1984. Nivation landforms in the western Great Basin and their paleoclimatic significance Quaternary Research 22: 275-288.

Dudley, W. M. 1990a. Multidisciplinary hydrologic investigations at Yucca Mountain, Nevada Proceedings of the International High-Level Radioactive Waste Management Conference, Las Vegas, Nevada April. pp. 1-9.

Dudley, W. M. 1990b. Gradients and stability of the hydraulic regime in the Yucca Mountain area Presented at a meeting of the National Academy of Sciences Panel on Coupled Hydrologic/Tectonic/Hydrothermal Systems at Yucca Mountain, Menlo Park, California. May

Eakin, T. E., G. B. Maxey, T. W. Robinson, J. C. Fredericks, and O. J. Loeltz. 1951. Contributions to the hydrology of eastern Nevada: Nevada State Engineer 's Office Research Bulletin 12. 171 pp.

Enzel, Y., D. R. Cayan, R. Y. Anderson, and S. G. Wells. 1989. Atmospheric circulation during Holocene lake stands in the Mojave Desert: Evidence of regional climate change Nature 341: 44-48.

Galloway, R. W. 1983. Full-glacial southwestern United States: mild and wet or cold and dry? Quaternary Research 19: 236-248.

Galloway, D., and S. Rojstaczer. 1988. Analysis of the frequency response of water levels in wells to earth tides and atmospheric loading. In Proceedings of the Fourth Canadian/American Conference on Hydrology National Water Well Association, Dublin, Ohio, pp. 100-113.

Gilbert, G.K. 1890. Lake Bonneville. U.S. Geological Survey Monograph No. 1.

Grant, M. A., I. G. Donaldson, and P. F. Bixley. 1982. Geothermal Reservoir Engineering, Academic Press. New York.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Hall, S. A. 1985. Quaternary pollen analysis and vegetational history of the Southwest In Pollen Records of Late Quaternary North American Sediments. V. M. Bryant, Jr. and R. G. Holloway, eds. American Association of Stratigraphic Palynologists Foundation, Dallas, TX, pp. 95-124.

Haynes, Jr., C.V. 1967. Quaternary geology of the Tule Springs area, Clark County, Nevada In Pleistocene Studies in Southern Nevada. H. M. Wormington and D. Ellis, eds. Nevada State Museum Anthropological Papers 13: 15-104.

Kutzbach, J. E., and F. A. Street-Perrott. 1985. Milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr BP Nature 317: 130-134.

Leopold, L. B. 1951. Pleistocene climate in New Mexico. American Journal of Science 249: 152-168.

Mehringer, Jr., P. J. 1967. Pollen analysis of the Tule Springs site, Nevada. In Pleistocene Studies in Southern Nevada. H. M. Wormington and D. Ellis, eds. Nevada State Museum Anthropological Papers 13: 129-200.

Mifflin, M. D., and M. M. Wheat. 1979. Pluvial Lakes and Estimated Pluvial Climates of Nevada. Nevada Bureau of Mines and Geology Bulletin 94.

National Research Council (NRC). 1990. Surface Coal Mining Effects on Ground Water Recharge. Water Sciences and Technology Board, National Academy of Sciences Washington, D.C.

Olausson, E., ed. 1982. The Pleistocene/Holocene boundary in southwestern Sweden. Sveriges Geologiska Undersoking, Serie C, Nr. 74. Stockholm.

Peng, T.-H., J. G. Goddard, and W. S. Broeker. 1978. A direct comparison of 14C and 230Th ages at Searles Lake, California Quaternary Research 9: 319-329.

Quade, J. 1986. Late Quaternary environmental changes in the Upper Las Vegas Valley, Nevada. Quaternary Research 26: 340-357.

Quade, J., and W. L. Pratt. 1989. Late Wisconsin groundwater discharge environments of the southwestern Indian Springs Valley, southern Nevada Quaternary Research 31: 351-370.

Ritchie, J. C., C. H. Eyles, and C. V. Haynes. 1985. Sediment and pollen evidence for an early to mid-Holocene humid period in the eastern Sahara. Nature 314: 352-355.

Smith, G. I. 1979. Subsurface stratigraphy and geochemistry of Late Quaternary evaporites, Searles Lake, California. U. S. Geological Survey Professional Paper 1043.

Smith, G. I., and F. A. Street-Perrott. 1983. Pluvial lakes of the western United States. In The Late Pleistocene. S.C. Porter, ed. University of Minnesota Press, Minneapolis, pp. 190-214.

Spaulding, W. G. 1981. The late Quaternary vegetation of a southern Nevada mountain range Ph.D. thesis, University of Arizona, Tucson.

Spaulding, W. G. 1985. Vegetation and climates of the last 45,000 years in the vicinity of the Nevada Test Site, south-central Nevada U. S. Geological Survey Professional Paper 1329.

Spaulding, W. G. 1990. Vegetational and climatic development of the Mojave Desert: The last glacial maximum to the present In Packrat middens: The Last 40,000 Years of Biotic Change J. L. Betancourt et al., eds. University of Arizona Press, Tucson, pp. 166-199.

Spaulding, W. G. 1991a. Pluvial climatic episodes in North America and North Africa: types and correlation with global climate. Palaeogeography, Palaeoclimatology, Palaeoecology 84: 217-227.

Spaulding, W. G. 1991b. A middle Holocene vegetation record from the Mojave Desert and its paleoclimatic significance Quaternary Research 35: 427-437.

Spaulding, W. G., E. B. Leopold, and T. R. Van Devender. 1983. Late Wisconsin paleoecology of the American Southwest. In The Late Pleistocene. S.C. Porter, ed. University of Minnesota Press, Minneapolis, pp. 259-293.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×

Spaulding, W. G., S. W. Robinson, and F. L. Paillet. 1984. Preliminary assessment of climatic change during Late Wisconsin time, southern Great Basin and vicinity, Arizona, California, and Nevada U. S. Geological Survey Water-Resources Investigations Rpt. 84-4328

Spaulding, W. G., and L.J. Graumlich. 1986. The last pluvial climatic episodes in the deserts of southwestern North America. Nature 320: 441-444.

Szymanski, J. S. 1989. Conceptual Considerations of the Yucca Mountain Ground-water System with Special Emphasis on the Adequacy of This System to Accommodate a High-Level Nuclear Waste Repository Unpublished DOE report.

Van Devender, T. R., J. L. Betancourt, and R. S. Thompson. 1987. Vegetation history of the deserts of southwestern North America: The nature and timing of the Late Wisconsin-Holocene transition In North America and adjacent oceans during the last deglaciation W. F. Ruddiman and H. E. Wright, Jr., eds. Geological Society of America, Boulder, pp. 323-352.

Waddell, R. K. 1982. Two-Dimensional, Steady-State Model of Ground-Water Flow, Nevada Test Site and Vicinity, Nevada-California Water Resources Investigations Report 82-4085. U.S. Geological Survey, Denver, Colorado.

Winograd, I. J., and W. Thordarson. 1975. Hydrogeologic and hydrochemical framework, south-central Great Basin, with special reference to the Nevada Test Site U. S. Geological Survey Professional Paper 712-C.

Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 62
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 63
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 64
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 65
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 66
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 67
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 68
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 69
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 70
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 71
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 72
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 73
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 74
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 75
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 76
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 77
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 78
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 79
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 80
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 81
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 82
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 83
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 84
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 85
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 86
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 87
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 88
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 89
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 90
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 91
Suggested Citation:"Might Increased Rainfall Cause Flooding of the Proposed Repository?." National Research Council. 1992. Ground Water at Yucca Mountain: How High Can It Rise?. Washington, DC: The National Academies Press. doi: 10.17226/2013.
×
Page 92
Next: Can an Igneous Intrusion Raise the Water Table to the Proposed Repository Level? »
Ground Water at Yucca Mountain: How High Can It Rise? Get This Book
×
Buy Paperback | $50.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

The site of a proposed repository for high-level radioactive waste from the nation's nuclear power plants is not at risk of ground water infiltration, concludes this important book. Yucca Mountain, located about 100 miles northwest of Las Vegas, has been proposed as the site for permanent underground disposal of high-level radioactive waste from the nation's civilian nuclear power plants.

To resolve concerns raised by a Department of Energy (DOE) staff scientist concerning the potential for ground water to rise 1,000 feet to the level proposed for the repository, DOE requested this study to evaluate independently the past history and future potential of large upward excursions of the ground water beneath Yucca Mountain.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!