Archaeological Analogues for Assessing the Long-Term Performance of a Mined Geologic ...

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Archaeological Analogues for Assessing
the Long-Term Performance of a
Mined Geologic Repository for
High-Level Radioactive Waste
By John S. Stuckless
U.S. GEOLOGICAL SURVEY
Open-File Report 00-181
Prepared in cooperation with the
NEVADA OPERATIONS OFFICE
U.S. DEPARTMENT OF ENERGY
(Interagency Agreement DE-AI08-97NV12033)
Denver, Colorado
2000
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director
The use of firm, trade, and brand names in this report is for identification purposes only and does
not constitute endorsement by the U.S. Geological Survey.
For additional information write to: Copies of this report can be purchased
from:
Chief, Earth Science Investigations Program
Yucca Mountain Project Branch U.S. Geological Survey
U.S. Geological Survey Information Services
Box 25046, Mail Stop 421 Box 25286
Denver Federal Center Federal Center
Denver, CO 80225-0046 Denver, CO 80225
CONTENTS
Abstract.................................................................................................................................................................................. 1
Introduction.................................................................................................................................................^ 1
Background.......................................................................................................................................................^ 2
Hydrologic Analogues in the Natural System....................................................................................................................... 2
Hydrologic Analogues in the Anthropogenic Systems.......................................................................................................... 12
Conclusions....................................................................................................................................................^ 25
References.............................................................................................................................................................................. 25
FIGURES
1. Map showing locations of prehistoric art work in France and Spain........................................................................ 3
2-4. Photographs of:
2. Painted rhinoceroses and horses from Chauvet cave showing evidence of water flow.................................... 5
3. Sculpted bison 14,000 years old from Tuc d'Audoubert.................................................................................. 7
4. Painted bison from the ceiling of Altamira....................................................................................................... 8
5. Map showing the location of known painted rock shelters in Africa........................................................................ 10
6-15. Photographs of:
6. Painting of the "hair dresser" from a rock shelter in the Sahara....................................................................... 11
7. Packrat midden from the Sheep Range, Nevada, dated at 10,000 B.P.............................................................. 13
8. Artifacts including nearly 6,000-year-old cloth, ivory, and brass from the Cave of the Warrior...................... 14
9. Pictures from the inside of the passage grave at Newgate, Ireland, showing the central chamber
and the corbeled ceiling..................................................................................................................................... 15
10. Painted wooden figurines from the tomb of Meketre, 1991 B.C....................................................................... 16
11. Ivory and ebony chairs from the tomb of Tutankhamen from about 1131 B.C................................................ 18
12. Paintings from the Ajanta temple in India......................................................................................................... 20
13. A room in the underground city of Kaymakli, Turkey...................................................................................... 21
14. Paintings from the Karanlik church at Goreme, Turkey.................................................................................... 23
15. Fracture in the blackened wall and ceiling of a kitchen in a monastery at Goreme, Turkey ............................ 24
CONVERSION FACTORS AND ABBREVIATIONS
Multiply ______ By _______ To obtain
centimeter (cm) 0.3937 inch
gram 0.03527 ounce, avoirdupois
kilometer (km) 0.6214 mile
liter (L) 0.2642 gallon
meter (m) 2.281 foot
millimeter (mm) 0.0394 inch
Temperature in degree Celsius (°C) can be converted to degree Fahrenheit (°F) as follows:
°F=1.8(°C) + 32
CONTENTS III
Archaeological Analogues for Assessing the
Long-Term Performance of a Mined Geologic
Repository for High-Level Radioactive Waste
By John S. Stuckless
Abstract nations today. There has been a general consensus that
a mined geologic repository will provide the best solu
A mined geologic repository must isolate
tion (National Academy of Sciences National
radioactive waste from the environment for a Research Council, 1957, 1978; Witherspoon, 1996).
minimum of 10,000 years; however, the interac However, demonstrating that the waste will not
tion of water with the waste may pose the greatest adversely affect later generations is one of the most
hazard to that objective. Mathematical models for difficult aspects of the disposal problem. Mathematical
Yucca Mountain in southern Nevada predict that, models have been developed that simulate the perfor
under conditions of low to moderate infiltration mance of a repository under a spectrum of anticipated
flux, most of the water passing through the unsat- future conditions (for example, U.S. Department of
Energy, 1998), but direct testing is not possible. The
urated zone at the level of a potential repository
dilemma is compounded by the great length of time
would be diverted around the storage tunnels
during which a repository must safely isolate waste
that would contain radioactive waste. Evidence
from the environment (10,000 years is specified by the
collected from natural analogues, including
Nuclear Regulatory Commission in their rule, U.S.
Paleolithic to Neolithic paintings in caves and
Department of Energy, 1993, and in their proposed
rock shelters, biological remains preserved in
rule, U.S. Department of Energy, 1999), a time span
caves and rock shelters, and artifacts and paint
that is greater than all of recorded history. Natural
ings preserved in manmade underground open
analogues taken from the geologic record can be used
ings, strongly supports these models and shows to address the time aspect for predicting future perfor
that flow around openings in the unsaturated zone mance. An additional advantage of using analogues
is both a long-term feature and one that can be from the archaeologic record is that these analogues
observed in a variety of climates and for a variety are generally more comprehensible to the public than
of geologic media. Analogue information also are mathematical models (Winograd, 1986). In other
shows that fragile and easily destroyed items are words, the long-term performance of a natural
better preserved when open to circulating air than analogue can be qualitatively compared to the perfor
mance of a mined geologic repository predicted by a
when buried within the unsaturated zone, which
model such as Total System Performance Assessment
suggests that backfilling a mined geologic reposi
(U.S. Department of Energy, 1998).
tory in the unsaturated zone may not enhance its
performance. There are no analogues that are exactly like a
mined geologic repository. No one buried high-level
radioactive wastes thousands of years ago and in the
exact same geologic setting for which predictions are
INTRODUCTION
being made, but there is an abundance of examples for
The safe disposal of high-level radioactive waste various aspects of a repository. Perhaps the most
is one of the more serious problems facing developed important aspects are within the field of hydrology
Abstract
because water would be the principal transport Yucca Mountain differs from sites being consid
medium for nuclear waste from a potential repository ered by other countries for the disposal of high-level
to the accessible environment. Analogues available for radioactive waste (for example, Witherspoon, 1996) in
studying the long-term behavior of water in tunnels that the potential repository would be above the water
include caves and ancient underground workings that table in what is called the unsaturated zone. In this
have been open for centuries to tens of millennia. This zone, not all voids are filled with water. Wells in the
paper describes several of these examples and exam unsaturated zone cannot produce water, and therefore,
ines the factors that appear to account for the long- the movement of water in this zone has historically
term preservation of natural and archaeological mate received much less study than water in the saturated
rials present in these environments. zone. Direct observation of water movement in the
unsaturated zone is hampered by apparent slow rates
of movement and the need for long-term observation.
Thus, natural analogues for ground-water flow at
BACKGROUND
Yucca Mountain provide a means to examine long-
term flow in the unsaturated zone for both fracture and
Yucca Mountain in southern Nevada is currently
matrix flow.
being studied as a potential site for a mined geologic
repository for high-level radioactive waste. Several Recent work at Yucca Mountain (Wang and
geotechnical aspects of this site can be addressed with others, 1999) and theoretical studies (Birkholzer and
the use of natural analogues. Before doing so, a few others, 1999) have suggested that most water moving
technical terms and concepts should be described. through the unsaturated zone should move around
tunnels driven into the ash-flow tuffs. Mangin and
Age terms used in this report are approximately:
Andrieux (1984) also concluded from field observa
Paleolithic, before 10 thousand years ago; Mesolithic,
tions that much water preferentially flowed around
10 to 7 thousand years ago; Neolithic, 7 to 4.6 thou
caves. Of the water that seeped into caves, most flowed
sand years ago; and Chalcolithic, 4.6 to 2.7 thousand
down the walls or dripped from specific points in the
years ago.
ceiling such as asperities along fractures. The caves
Yucca Mountain is composed of a variety of
examined by Mangin and Andrieux (1984) are in lime
volcanic products, the most common being ash-flow
stone, which is hydrologically similar to welded tuff in
tuffs. These rocks originate as extremely hot ash that is
that water moves through both rock types principally
blown out of a large volcano with subsequent outward
by flow along fractures. If most water moving through
flow sustained by expanding gases. The gases create a
the unsaturated zone does not drip into underground
very low internal friction for the ash such that flow can
openings, there should be abundant evidence in the
occur down shallow slopes until enough gas has
geologic and archaeologic records that could provide
escaped for the flow to come to rest. At that time, most
excellent long-term analogues to a potential mined
of the ash is in the form of minute fragments of glass,
geologic repository for radioactive waste.
and, where that glass is hot enough, the pressure of
overlying ash causes the fragments to deform and to
weld together until nearly all voids and air bubbles are
gone. The resulting rock is called a welded tuff. Where HYDROLOGIC ANALOGUES IN THE
there is insufficient heat or pressure to weld the ash, NATURAL SYSTEM
the resulting rock is called a nonwelded tuff. Such a
rock may contain as much as 40 percent voids or pore Abundant qualitative information is available
spaces. Welded tuffs are extremely hard and brittle, about the preservation of materials both in natural and
and they fracture readily in response to geologic manmade openings in the unsaturated zone. The
stresses. The differences between the two types of tuff following examples are rarely defined in the literature
cause them to affect the flow of ground water in cited as being from the unsaturated zone, but the fact
different ways: water moves through welded tuff that they are not flooded or being actively dewatered
mainly along fractures (fracture flow) and through demonstrates that they are within that hydrologic zone.
nonwelded tuff mainly through connected pore spaces The examples chosen do not constitute an exhaustive
(matrix flow). listing but rather are representative and are largely
Archaeological Analogues for Assessing the Long-Term Performance of a Mined Geologic Repository for High-Level
Radioactive Waste
from sources that are readily available to nonspecial- Perhaps the best known of the older examples of
ists in the scientific disciplines. preservation within the unsaturated zone are the Pale
olithic cave paintings of southern Europe (fig. 1). The
Caves provide an excellent analogue to a mined
oldest authenticated of these is the recently discovered
geologic repository for the flow of water in the unsat-
Chauvet. The cave is located in a subhumid region
urated zone. Water flow around caves and tunnels
where reported annual precipitation totals within the
depends in part on the size of the opening (Philip and
region range from 58 to 78 cm (centimeters). The cave
others, 1989; Philip, 1998). Water is more likely to be
diverted around small openings than around large contains paintings of animals that are extinct, such as
ones, and most caves cited in this study have as large mammoths, and other species that no longer live in
or larger cross-sectional area than that proposed for a Europe, such as rhinoceroses (Chauvet and others,
mined geologic repository. In addition, both environ 1996). The paintings in the French caves were largely
ments are humid. For example, the humidity at made with oxides of iron and minor amounts of
Chauvet (southern France) is measured at 99 percent manganese and small amounts of clay and silica
(Baiter, 1999). (Leroi-Gourhan, 1984; Ruspoli, 1986). Charcoal was
Cave with art mentioned in text
MEDITERRANEAN SEA
Figure 1. Locations of prehistoric art work in France and Spain.
HYDROLOGIC ANALOGUES IN THE NATURAL SYSTEM 3
commonly used for black. None of these materials currently 37 m below sea level and thus must have
would be expected to survive long in the presence of been occupied prior to the current interglacial period
abundant water. (that began approximately 10,000 years ago). The cave
The charcoal in Chauvet (fig. 1) has been dated is also the first discovered to have two greatly different
by the 14C method as 32,410 to 32,340 B.P. (before sets of ages (27,000 and 18,500 B.P.) for its paintings.
present) with errors of approximately ±600 years. These dates correspond to approximate sea-level
Because this method determines the age of the char decreases of 131 m and 121 m relative to present-day
coal, including carbon removed from the atmosphere levels (Fairbanks. 1989). The size of the painted area
while the plant was alive, there has been some contro (approximately 15 m by 30 m) of the cave is again
versy about the possibility that the paintings were larger than the opening proposed for a mined geologic
created recently using old charcoal. To address this repository at Yucca Mountain. As at Chauvet, several
possibility, Chauvet and others (1996) also collected of the Cosquer paintings have a thin layer of calcite
soot deposited on the ceiling of the cave by the oil precipitated over them. Unlike Chauvet, paintings in
lamps used for illumination by prehistoric humans. the Cosquer cave have been destroyed up to the high-
The samples of soot yielded ages of 26,980 (two tide mark, and none exist along the sloping entrance,
samples) and 26,120 B.P. with errors of approximately which is currently under water. A map and cross
±400 years. (The fact that even soot can be preserved section, as well as a few paintings, can be examined on
on the roof of a cave for nearly 30,000 years is testa the web site for the French Ministry of Culture
ment to the protection afforded by openings within the (http://www.culture.fr/, accessed 02/29/00).
unsaturated zone.) The dated soot, together with the Lascaux (fig. 1), with some 600 paintings, is
pictures of animals no longer indigenous to the area, perhaps the best known of the prehistoric caves in
demonstrates the antiquity of the artwork. France. It was discovered September 12, 1940, and
Chauvet cave also provides evidence of water became a tourist attraction in 1949. The art work can
flow down the walls of the caves. Some of the paint be seen in a book by Ruspoli (1986), which has the
ings show deterioration where water has flowed across most complete photographic record of the cave, or in
them (fig. 2). Water also has been observed directly in the October 1988 issue of National Geographic
contact with paintings. Breisch (1987) reported that (Rigaud, 1988). In addition, there are several web sites
during wet years in some caves, water oozes out of the with pictures and other information that can be
wall and coats the paints with a film of water. In these accessed by searching the name "Lascaux." Like
instances, there does not appear to have been sufficient Chauvet and Cosquer, the openings in the Lascaux
flow to remove the paintings, but evaporation of this cave are larger than that proposed for the potential
water could have deposited thin (4-mm-thick) layers repository at Yucca Mountain. The Great Hall of the
of calcite (CaCO3) over some paintings, as has been Bulls is approximately 8 m by 20 m (Leroi-Gourhan,
observed at Chauvet (Baiter, 1999) and elsewhere. 1984). No quantitative dates for the paintings of
The cave of Chauvet is more than 100 m long, Lascaux were found in the current literature search,
and the painted areas are generally more than 5 m but the style of the paintings suggests an age of 13,000
wide and several meters high. Thus, the opening is to 17,000 B.P.
generally larger than that proposed for a potential Lascaux cave provides an alternate line of
mined geologic repository at Yucca Mountain, which evidence that enough water would destroy the paint
is proposed to be about 5 m in diameter. ings. A block has fallen out of one of the paintings on
There are more than 100 caves in France with the ceiling and landed on the moist floor of the cave.
prehistoric art work. At least two others merit some The block was found on the floor of the cave, and it fits
description. The cave of Cosquer (Clottes and Courtin, geometrically in the hole in the painting, but all the
1996) appears to be unique in that the entrance is paint dissolved while the block was on the floor of the
cave (Breisch, 1987).
In 1960, a deterioration of the art work was
^y convention, years before present is measured noted, and the Lascaux cave was closed for 3 years.
as before 1950 and implies that a correction has been The deterioration was due to patches of green algae,
made for the non-uniform rate of production of 14C in which was introduced by the hundreds of tourists
the atmosphere as a function of time. visiting the site and exacerbated by changes in atmo-
Archaeological Analogues for Assessing the Long-Term Performance of a Mined Geologic Repository for High-Level
Radioactive Waste
HYDROLOGIC ANALOGUES IN THE NATURAL SYSTEM
spheric conditions in the cave and by artificial lighting. and found an average total seepage of 7,000 mm/mo
It is estimated that each visitor expires 40 liters of (millimeters per month), which Solana (University of
carbon dioxide per hour and introduces 40 grams of Santander, Spain, written commun., 2000) estimates
water per hour (Breisch, 1987). The carbon dioxide represented about 80 percent of the total seepage.
changes the stability of calcite (the principal mineral They also measured the average rainfall and reported
in the wall rock of the caves and a potential coating of an average of approximately 95 mm/mo. The average
the paintings). Such chemical changes should not evapotranspiration was calculated as approximately
occur in a mined geologic repository, and so the 55 mm/mo, which results in an average net infiltration
observed deterioration would not be part of the of about 40 mm/mo. The area of the painted cave
analogy between caves and a potential underground studied was reported as 150 m2 (square meters), which
repository. would result in a monthly volume of infiltration water
In addition to paintings on the walls and ceilings of more than 6,000 liters. The material overlying the
of caves, the prehistoric art of France includes a set study area was reported as approximately 7 m of inter-
of three clay sculptures that were found on the floor of bedded limestone and mudstone; figure 4 shows that
Le Tuc d'Audoubert (Ariege region). A photograph of the rock is obviously fractured. Nonetheless, less than
these can be seen in National Geographic (Putman, 1 percent of the infiltrating water seeped into the cave.
1988). Figure 3 shows one of the bison with the only The study of Palomera cave in Burgos, Spain
visible damage being cracks. The clay floor of the (fig. 1), is used as a final example of preservation in a
nearby Niaux cave still preserves the footprints of a Paleolithic cave in southern Europe. The painted
prehistoric artist (White, 1986). section of the cave is 60 m by 25 m and is 30 m in
All of the cited examples from France are in a height. Four 14C dates for charcoal range from
subhumid climatic zone with rainfall in excess of 10,950 ±100 to 11,540 ±100 B.P. (Corchon and others,
50 cm per year. In contrast, rainfall at Yucca Mountain 1996). The cave has had a stream flowing in it at times,
is approximately 15 cm per year. These climatic which has left organic debris plastered to heights of
conditions have not been constant at either location several meters on the walls. Flooding postdates the
during the period 15,000 to 30,000 years ago. In both paintings and has apparently destroyed the paintings to
regions the climate was significantly cooler (by 5° to the height of the flooding.
10°C) during the glacial period, and rainfall at Yucca Reports of Paleolithic art preserved in caves are
Mountain may have been twice that of today (Forester common only in southern Europe, but examples of late
and others, 1999). Paleolithic, and more commonly, Neolithic art are
There are dozens of painted caves in Spain known throughout the world. Podesta (1996) reports
(fig. 1). One of the first to be discovered and one of the 14C dates for charcoal from two sites in Argentina that
best studied is Altamira (Saura, 1998). The cave was range from 9,200 to 10,600 B.P. Similar and perhaps
discovered in 1875 by Marcelino Sanz de Sautuola. It older ages are suspected in Brazil, but most of the
is located in the province of Santander about 156 m early art seems to date from 4,000 to 7,000 years ago
above sea level and 120 m above the Saja River, which (Prous, 1996). Prins and Woodhouse (1996) report one
is 2 km away. The cave is 270 m long and varies in cave painting from South Africa dated at 26,000 B.P.,
width from 2 m to 20 m. The ceiling is 2 to 12m high, which is probably the Apollo cave (fig. 3) mentioned
and averages approximately 9 m below land surface by Coulson (1999). Very little cave art is known in
(Saura, 1998). There are abundant fractures visible China, but a few examples exist that may date back to
in the bedrock, but few drip water, and the paintings 5,000 B.P. (Fu, 1996). A few other sites throughout the
that cross the fractures do not appear to be damaged world are summarized by Saura (1998) and Bahn
(fig. 4). Also found were shoulder blades of deer (1996).
engraved with heads of doe. Carbon-14 dating of Although many examples of Paleolithic art are
charcoal from one of the painted bulls yielded an age preserved in western Europe, there persists a question
of 14,000 ±400 B.P. (Valladas and others, 1992). of whether of not an equal or perhaps even larger
Villar and others (1985) studied the hydrology number have been completely destroyed. Null
of Altamira. They measured the volume of water evidence cannot be evaluated easily, but two lines of
flowing from 9 of 14 "significant drips" for 22 months evidence suggest that Paleolithic paintings have not
6 Archaeological Analogues for Assessing the Long-Term Performance of a Mined Geologic Repository for High-Level
Radioactive Waste
Figure 3. Sculpted bison 14,000 years old from Tuc d'Audoubert (from Putman, 1988).
HYDROLOGIC ANALOGUES IN THE NATURAL SYSTEM 7