University of Nevada
Reno
tegrated Geochemical and Hydraulic Analyses
of Nevada Test Site Ground Water Systems
A thesis submitted in partial fulfillment of the
requirements for the degree of Master of Science in
Hydrogeology
by
Carol Jean Boughton HI
May 1986
Mines Library University of Nevada - Reno Reno, Nevada 89557-0044 MINES UBRARY
t h e s i s
The thesis of Carol Jean Boughton is approved:
University of Nevada
Reno
May 1986
IX
ACKNOWLEDGEMENTS
I would first like to thank Desert Research Institute
for its financial assistance provided under DOE Contract
#DE-AC08-81NV10162. This thesis could not have been at
tempted without this assistance.
My particular appreciation is extended to my advisor
and committee members: Dr. Paul Fenske, Dr. Roger Jacobson,
Dr. Steve Wheatcraft, and Dr. Jack Hess whose assistance and
encouragement were invaluable.
I also thank Bert Elliott, Kevin Sullivan, and Lee
Huckins for their field assistance. Without them, the 1 ‘♦c
carboys would never have made it to the lab.
Further thanks are extended to the personnel of the Las
Vegas EPA office, particularly Dan Wait and Frank Reed, who
helped in identification and location of pumping wells and who helped obtain samples which would have been difficult to obtain without their help.
Last, but certainly not least, I couldn't have done without the emotional support of my many friends who had more faith in me than I had in myself. I trust that faith was not misplaced. My daughter, Kim King, and my good
friend and office mate, Tom Panian, who were always there when I needed them. iii
ABSTRACT
Major ion, tritium, and stable isotope analyses and radio-carbon age dating have been utilized in conjunction with hydraulic data to further understanding of the ground water flow regimes at the Nevada Test Site. Tritium is found in regional aquifers having uncorrected radiocarbon ages from 22,700 to >39,920 years before present. Temporal geochemical fluctuations occur within deep aquifers pointing to rapid recharge mechanisms. Stable isotope samples from ground water lie below and parallel to the Craig meteoric water line, <$D = 8<$ 1 80+1 0 . 5 1 80 ratios ranae from -14.1 to
-12.4°/oo. Sp ratios range from -109 to -96°/oo.
Radiocarbon ages are corrected based upon S13C analyses of various media which ranqe from +4.1 to -24.2°/oo.
Evidence points to rapid 613c dilution within the soil zone toward -12.0°/oo, with no additional dilution in tuffa- ceous aquifers. Overall evidence points to complex mixing between the various saturated units located within the study area. IV
TABLE OF CONTENTS
Acknowledgements ii
Abstract iii
List of Figures vi
List of Tables vii
List of Appendices iix
1 . INTRODUCTION 1
2. ENVIRONMENTAL SETTING 5
2.1 Geographic Setting 5 2.1.1 Physiography 5 2.1.2 Climate 7 2.1.3 Flora 11
2.2 Geologic Setting 13 2.2.1 Stratigraphy 13 2.2.2 Structural Geology 14
2.3 Hydrologic Setting 15 2.3.1 Surface Water 15 2.3.2 Principal Aquifers and 15 Aquitards 2.3.3 Regional Ground Water Flow 19
3. THEORY OF HYDROCHEMICAL INVESTIGATIONS 26
3.1 Major Ion Chemistry 26 3.2 Radiocarbon Dating of Groundwater 29 3.3 Stable Isotope Chemistry 36 3.4 Tritium Dating of Groundwater 41
4. FIELD AND LABORATORY METHODS 45
4.1 Sampling Overview 45 4.2 Soil Gas Samples 46 4.3 Soil Samples 47 4.4 Caliche Samples 49 4.5 Core Samples 49 4.6 Discharge Area Sampling 52 4.6.1 Spring Sampling 52 4.6.2 Well Sampling 53 4.7 Laboratory Methods 56 V
5. RESULTS AND DISCUSSION 57
5.1 Water Table Map 57 5.2 Major Ion Chemistry 64 5.3 Radiocarbon Dating 71 5.3.1 Results of Soil and Rock Carbon Analyses 71 5.3.2 Caliche 613C Results 77 5.3.3 Soil Water and Soil Gas S13C Results 78 5.3.4 Radiocarbon Results 83 5.4 Tritium 87 5.5 Stable Isotope Chemistry 94
6. CONCLUSIONS 101
6.1 Overview 101 6.2 Proposals for Further Study 109
REFERENCES 112
APPENDICES 120 VI
LIST OF FIGURES
2.1 Setting of the Nevada Test Site Area within the Basin and RangePhysiographic Province 6
2.2 Climatic Distribution In and Near the Study Area 8
2.3 Mean Annual Precipitation 10
2.4 General Distribution of Major Aquifers and Aquitards in theSouthern GreatBasin 17
3.1 Expected Deviations from Craig MWL 42
5.1 NTS Water Table Map 58
5.2 Regional Perspective - NTS Water Table Map 62
5.3 Trilinear Diagram of NTS Samples 58
5.4 Relative <$13C Ratios of Samples from this Study 72
5.5 Tritium Versus Corrected Radiocarbon Ages 89
5.6 Oxygen Versus Hydrogen Isotopes from this Study 97
5.7 Oxygen Versus Hydrogen Isotopes from In and Near NTS 99
6.1 Comparison of Parameters Evaluated in this Study 102 vii
LIST OF TABLES
3.1 Natural Abundance of Carbon Species 29
3.2 Effect of Contamination by Modern Carbon on True Age 37
3.3 Environmental Isotopes of Hydrogen and Their Relative Abundance in Water of the Hydrologic Cycle 37
3.4 Characteristic Constants of H20 andD20 33
4.1 Physical Characteristics and Environmental Setting of Caliche Samples 50
5.1 Chemical Analyses of Selected Samplesfrom NTS 65
5.2 Percent Carbonate of Soil and Rocks 73
5.3 Radiocarbon Results 84
5.4 Tritium Results 88 ■ 11X
LIST OF APPENDICES
1. Stratigraphic and Hydrogeologic Units at Nevada Test Site and Vicinity 120
2. Locations of NTS Sampling Sites. 121
3. ^ R e s u l t s 122
4. Aquifer Characteristics - Desert Research Institute Sampling Sites 124
5. Summary of EPA Analyses 126
6. Tritium Analyses 128
7. Stable Isotope Data from in and near Study Area 131 1
CHAPTER 1
INTRODUCTION
Since 1951 approximately 500 underground nuclear tests have taken place on the Nevada Test Site (NTS). Records indicate that at least 95 of these tests took place below the water table. The remainder were conducted in the unsat urated zone (USDOE, 1983).
Those tests conducted in the saturated zone have caused localized radioactive contamination of the ground water and the possiblity of future contamination from the unsaturated zone exists. Because the saturated zone is a dynamic system, radionuclides may be transported with the ground water as it moves from the zone of contamination.
This provides the necessity for definition of the flow regime to determine whether the contaminated water may at some point in space and time leave the confines of the Neva da Test Site and enter the biosphere.
Theoretically a hydrologic test hole network could provide the definition required in the saturated zone.
However, there are major drawbacks to this type of program.
1) It would be prohibitively expensive. 2) If funds were available for drilling, packer tests, and geochemical and environmental isotope sampling studies such as that con ducted on Pahute Mesa (Blankennagel and Weir, 1972) would 2 greatly enhance the working knowledge of the Nevada Test
Site hydrologic regime. In that study, the drilling network provided an in-depth three dimensional understanding of the
flow system. However, all lithologies are not conducive to
such tests. Slaking, bridging, and caving can make it
impossible to isolate intervals of interest and conduct the desired hydrologic tests. 3) Finally, an extensive drilling program could in itself alter the hydrodynamics of the flow
system.
Since this so-called "Swiss cheese" approach was not practicable, other, more indirect and less expensive methods were needed to provide insight into the NTS hydrologic re gime. This study has implemented several such methods.
1. A water table map was developed using existing drill
hole, hydrologic test hole, and well data. This
tool is characteristically used for identifying
recharge and discharge areas, direction of flow, and
gradients within the flow system.
2. An environmental isotope sampling program was im
plemented utilizing existing wells as sampling
sites. Radiocarbon and tritium, a radioactive
isotope of hydrogen, produced in the upper atmos
phere by cosmic ray bombardment of 14N and 2H,
respectively, decay at known rates. This
characteristic allows these radioisotopes to be used
to estimate the age of ground water and the velocity 3 of various aquifers within the regional system.
Radiocarbon age dating is accomplished by measuring the activity of carbonate species dissolved in ground water and comparing it with modern activity.
Bicarbonate in ground water comes primarily from two separate sources:
a. carbon dioxide gas and soil carbonate from
the soil zone in the recharge areas and,
b. carbonate from the rocks encountered as
water passes through the aquifer.
Samples of soil zone C02, soil from recharge and discharge areas, and carbonate core samples and
^ein fillings were analyzed for 513c ratios to provide applicable correction factors for radio carbon age-dating. The presence of tritium usually indicates that recent waters, less than 50 years old, have entered the flow regime. Underground thermonuclear testing may also account for tritiated ground water.
Stable isotopes of oxygen and hydrogen were also sampled and analyzed. Use of these isotopes can be valuable in describing evaporation and conden sation processes which have taken place both prior to and after recharge occurs. These isotopes can help identify possible recharge areas and periods of recharge, fingerprinting waters from various source areas and identifying zones of mixing. 4
3. Major ion chemistry was included in the sampling
program since aqueous geochemistry can reveal
valuable information about the source area and the
lithologic environment which the water has passed
through.
For instance, predominantly calcium bicarbonate
waters indicate that the water has passed through a
carbonate aquifer. Sodium-potassium bicarbonate
waters may indicate a tuffaceous aquifer. Mixed
calcium, sodium-potassium bicarbonate waters may
indicate that the water has flowed from one aquifer
into another or that mixing between two aquifers has
taken place. Increased TDS may indicate a long
residence time within the flow system or that the
water has flowed through a highly soluble unit.
Geochemical and isotope data from prior studies by
Desert Research Institute and other agencies were
incorporated into this study as appropriate.
The various elements of this study were examined for
consistency. Where anomalies existed, hypotheses were of
fered to provide explanations for such inconsistency. The results of this study were compared with previous work and merged with that work in order to integrate the cumulative hydrogeologic research efforts which have been conducted on the NTS to date. This integrated approach was intended to maximize the interpretation of the complex flow system found in the study area. 5
CHAPTER 2
ENVIRONMENTAL SETTING
2.1 GEOGRAPHIC SETTING
The Nevada Test Site is located in southeastern Nevada,
90 miles northwest of Las Vegas, Nevada. The study area is
an area of approximately 1400 square miles in Nye County.
It is bounded by Nevada coordinates N960000 on the north,
N665000 on the south, E715000 on the east, and E525000 on
the west.
2.1.1 Physiography
The study area is located in the southern Great Basin
section of the Basin and Range physiographic province (Fig
ure 2.1). This province is characterized by north trending
mountain ranges and topographically closed basins. The
mountains rise to 10,000 feet in the Sheep Range, a north
trending range which lies approximately 40 miles east of the
Nevada Test Site. Approximately 20 miles to the south lies
the Spring Mountain Range which trends northwest and rises
to an altitude of nearly 12,000 feet.
In the northwestern portion of the study area are Pa-
hute Mesa, Rainier Mesa, the Kawich Range, and the Belted
Range which all exceed 7000 feet in altitude.
These mountain ranges are flanked by bajadas which
terminate as dry playa lake beds in the topographically 200 kilometers
Figure 2.1 (Adopted from Stewart, 1980) Setting of the NTS Study Area within the Basin and Range Physiographic Province 7 closed basins. The low-lying areas of most interest to this study are Yucca Flat, Frenchman Flat, and Jackass Flats, all located on the Nevada Test Site, and Ash Meadows and the
Amargosa Desert located, respectively, south and southwest of the NTS. The elevations of Yucca, Frenchman, and Jackass
Flats vary from 3000 feet to 4000 feet. The altitude of the
Amargosa Desert and Ash Meadows averages between 2000 feet and 3000 feet above mean sea level.
2.1.2 Climate
The present-day climate of much of the study area is one of the most arid in the United States. However, temper ature and precipitation vary with latitude, longitude, and elevation. Figure 2.2 shows the climatic distribution rang ing from low-latitude desert in the discharge area to humid continental in the high mountain recharge areas (Houghton, et al. 1 975) .
Mean daily temperatures range from 20°F to 28°F in
January to 92°F to 100°F in July in the playas, with an all-time high for Nevada of 122°F having been recorded in the Amargosa Desert on June 23, 1954. In the mountains the temperature range is somewhat lower with January lows down to 12°F and July highs of up to 92°F (Houghton et al.,
1975). In addition there is a large daily temperature fluctuation. For instance, Houghton et al. (1975) reported 3
Figure 2.2 (Modified from Houghton et al., 1975) Climatic Distribution in and near Study Area 9
a daily range of 71°F in Las Vegas on July 13, 1972, the
maximum being 119°F and the minimum 48°F.
The average annual rainfall ranges from less than 4
inches per year in the Amargosa Desert up to greater than 28
inches in the recharge areas such as the Sheep Range (Wino-
grad and Thordarson, 1975). Figure 2.3 shows the distribu
tion of precipitation throughout the study area. Precipita
tion is seasonal, occurring mostly during summer and winter.
Summer precipitation typically comes from the southeast or
south and occurs as convective storms. These storms may produce intense precipitation over short periods of time.
The amount of precipitation in a given storm may vary drama tically from the area in which it is concentrated to an immediately adjacent area where there may be virtually no precipitation. For instance, one such event occurred on
August 23, 1982. Mercury, Nevada, received 1.02 inches of precipitation while Camp Desert Rock, approximately five miles to the southwest received only .32 inches (NOAA,
1982) .
Winter precipitation comes mostly in the form of snow in the higher elevations of the study area. The low-lying areas receive less than 10 inches of snowfall. The moun tains, which provide recharge to the regional aquifer, re ceive up to 80 inches of snowfall.
Houghton et al. (1975) reported that the average annual evaporation potential in the study area ranges from 58 to 72 0 1,0 2.0 3,0 4 0 Sp mi 0 1'0 2 0 3 0 4 0 5 0 km RANGE OF ANNUAL PRECIPITATION, IN INCHES.
le s s th an 8 - 1 6 1 6 - 2 4 8
Figure 2.3 (Modified from Winograd and Thordarson, 1975) Mean Annual Precipitation 11 inches per year. It is emphasized that those data represent only potential evaporation and that actual evaporation may vary from this estimate. Meyers (1962) has estimated po tential evaporation up to 82 inches per year. Houghton et al. (1975) reported actual evaporation from Lake Mead of about 80 inches per year compared with a computed potential evapotranspiration rate of 42 inches per year.
During the Pleistocene, particularly the past 70,000 years, several pluvial periods have occurred in the Great
Basin. Wells and Jorgensen (1964) used botanical evidence to show that a much more humid climate previously existed in the study area. These periods of increased precipitation accompanied stages of worldwide cooling in which the average temperature dropped by 10° to 15° F. During these periods there was heavy snowfall with little melting and evapora tion .
Minor glaciation occurred in Nevada during this period.
However, up to 20 percent of the Great Basin was under water
(Houghton et al., 1975).
2.1.3 Flora
Vegetation types may have a significant effect on the
The NTS lies on the transition between the Great Basin and Mohave deserts. As such, it contains flora typical of both regions. Beatley (1974, 1975) has conducted extensive vegetation studies on the NTS. A summary of the general plant types identified in that work follows. The flora on the NTS reflects temperature, altitude, precipitation, and soil variations. Atriplex associations appear in highly calcareous soils adjacent to playas on Yucca Flat and Frenchman Flat. Predominant species are shadscale (Atriplex confertifolia) and four-winged saltbush (Atriplex canescens). Lycium pallidum-Grayia and Lycium schockleyi associations occur adjacent to the playas where temperature, soil, and salinity conditions permit. Creosote bush (Larrea tridentata) dominates the al luvial fans of Jackass Flats, Frenchman Flat and upper al luvial fans on Yucca Flat. The lower to mid-alluvial fans on Yucca Flat support hopsage-desert thorn (Grayia spinosa- Lycium andersonii) associations. Between 4,000 and 5,000 feet blackbrush (Coleogyne ramosissima) replaces creosote on Jackass Flats and giant yucca or Joshua tree (Yucca brevifolia) is found on Yucca Flat. Sagebrush (Artemisia tridentata and Artemisia arbuscula ssp. nova) predominant at elevations above 5,000 feet. 13 Above 6,000 feet the sagebrush becomes mixed with or domin ated by the conifers pinyon pine (Pinus monophylla) and juniper (Juniperus osteosperma) (Beatley, 1974, 1975). 2.2 GEOLOGIC SETTING 2.2.1 Stratigraphy The study area lies within the miogeosynclinal belt of the Cordilleran geosyncline. During Precambrian and Paleo zoic eras as much as 40,000 feet of marine sediments were accumulated. Superposed upon these massive depositional units are complex orogenic and volcanic events. Hess and Mifflin (1978) have pointed out two assemblages which are of importance in a hydrogeologic study. They are: 1) Precam brian and lower Paleozoic carbonate and transitional assem blages consisting of limestone, dolomite, sandstone, quartz ite, siltstone, and shale. 2) Upper Paleozoic carbonate and siliceous detrital rocks which include limestone, siltstone, and conglomerate within the study area. Of further interest to this study are Cenozoic volcan- ics which serve as significant aquifers in the western por tion of the study area. Sinnock (1982) provides an in-depth review of the volcanic rocks in the NTS study area. A comprehensive correlation of eastern Nevada strati graphic units is provided by Hess and Mifflin (1978). Stewart (1980) provides the most comprehensive overview of 14 Nevada geology. Sinnock (1982) presents a comprehensive site-specific review of Nevada Test Site geology. 2.2.2 Structural Geology The study area lies in the structurally complex Great Basin. Complex thrusting and folding took place in Mesozoic time. Tertiary and Quaternary age tectonics produced block faulting, major strike-slip fault zones, and volcanic struc tures. Some geologists believe that the block faulting may be a surficial feature associated with Tertiary volcanism. In other locations it is thought that deep-lying shear zones may exist with only very subtle surface expression (Carr, 1974) . Structural features such as fracturing, folding, and faulting can serve as controls on a regional ground water flow system. Structural trends in the study area tend to be of north-south orientation. This is in agreement with a general north to south regional ground water flow path. Sinnock (1982) identified major thrust zones and strike-slip zones within the study area. Those which may have a major influence on the hydrogeology of the study area are the Mine Mountain thrust zone, the CP Tippinip thrust zone, the Spotted Range thrust zone. In addition to the larger regional trends, other features such as the deep structural trough under Yucca Flat (Carr, 1974), the Mine Mountain, Cane Spring, and Rock Valley fault zones (Sinnock, 15 1982), and the fault-controlled Ash Meadows spring line may play a significant role in the hydrogeology of the study area (Winograd and Pearson, 1976). 2.3 HYDROLOGIC SETTING 2.3.1 Surface Water There are no perennial streams located within the study area. There are several washes which may flow during flash flood conditions or heavy runoff conditions but which are otherwise dry. 2.3.2 Principal Aquifers and Aquitards Winograd and Thordarson (1975) have provided the most comprehensive review of the various stratigraphic and hydro- geologic units on the Nevada Test Site (Appendix 1). They report six major aquifers and five major aquitards in the vicinity of the study area. These are, in decreasing order of age: Precambrian through lower Cambrian lower aquitard, Cambrian through Devonian lower carbonate aquifer, Devonian through Mississippian upper clastic aquitard, Cretaceous to Permian aquitard, Tertiary tuff aquitard, Tertiary lava- flow aquitard, Tertiary bedded-tuff aquifer, Tertiary weld- ed-tuff aquifer , Tertiary lava-flow aquifer, and Tertiary and Quaternary valley-fill aquifer. Of the aquifers listed, the lower carbonate aquifer and the valley-fill aquifer have the widest areal extent within the study area. Mifflin 16 (1968) has delineated the carbonate rock province in Nevada. Figure 2.4 illustrates the general distribution of major aquifers and aquitards in and near the study area (Winograd and Doty, 1980) . The lower carbonate aquifer includes middle Cambrian through Devonian age carbonate rocks including the upper Carrara Formation through the Devil's Gate Limestone. This entire unit consists primarily of limestone and dolomite with minor beds of quartzite, shale, and siltstone. The total thickness of these strata would be up to 15,000 feet thick were it present in any one location. However, defor mation, uplift, and subsequent erosion have caused a variable thickness throughout the study area. These processes have further caused a non-uniform depth to formation and thickness of saturation (Winograd and Thordarson, 1975). Outcrop studies show low intercrystalline porosity. Vugs with as large as 0.4 inches in diameter have been ob served with no vuggy oorosity, except in some brecciated zones. The effective porosity is a function of jointing, fracturing, and brecciated zones. Both throughgoing and local joint sets have been identified (Winograd and Thordar son, 1975). Joint density is related to the rock type with the fine-grained carbonate rocks having the greatest joint density. Local joints have consistent trends for short distances. Throughgoing joint sets were found running para- opo.ooo in______ooo;ooBH______ooo'dodn os OS lim it l im it s o c x s s o c x s a r o STW a S WESTWARO c a r b o n a t e c a r b o n a t e SATURATED VOLCANIC SOCXS OVERLYING approximate s a t u r a t e d s a t u r a t e d approximate SATURATED VOLCANIC SOCXS LOWSFVCARBONATE AQUIPER s o c k s aro . MAY 1NCUJOE . MAY UIT ao ] ioumno d e p o s it s alluvium p o r m a t io n i clastic a o u is h b s Figure 2.4 (From Winograd and Doty, 1980) Doty, and Winograd (From 2.4 Figure General Distribution of the Major Aquifers Major the of Distribution General and Aquitards in the Southern Great Basin Great Southern the in Aquitards and a n a ATURATED ATURATED S l a c u s t r in e UPPER CLASTIC SATURATED VOLCANIC (SLE lower SILTS70NES) rss AMO OUARTEJ ctupp [PRECAMBRIAW AMO LOW S3[PRECAMBRIAW LOW CAMBRIAN AMO inns ip vsoouvrtv 18 llel to associated fault sets for up to several hundred feet. Outcrops show increased subaerial chemical and mechani cal weathering near the surface. Small secondary solution channels have been observed for short distances along bed ding and joint planes. Small isolated caves exist in the lower carbonate aquifer, but no field evidence has shown development of karst topography on the Nevada Test Site. Nearby, major solution features are found at Devil's Hole at Ash Meadows, about 23 miles southwest of Mercury, and Gypsum Cave, about 13 miles east northeast of Las Vegas. Winograd and Pearson (1976) hypothesize that a highly transmissive zone extends from the southeastern portion of the Nevada Test Site to the Ash Meadows area near Devil's Hole. Poten- tiometric, geochemical and isotopic evidence supports their hypothesis that this zone exists in the lower carbonate aquifer. In the absence of direct evidence such as from drill holes or outcrops showing solution features, the indirect evidence shown makes a strong case for the pos sibility of zones of high-transmissivity in the carbonates within the study area. It is not known whether water is transmitted along this zone through solution channels or a fault zone with subdued surface expression. 19 2.3.3 Regional Ground Water Flow The most simplistic graphical model of regional ground water flow is that of flow lines delivering ground water from topographic highs, recharge areas, to topographic lows, discharge areas. In this model ground water divides occur coincidentally with surface water divides and the minima of the flow lines define the hinge line which separates areas of recharge from areas of discharge (Hubbert, 1940). Toth (1962, 1963) derived analytical solutions to develop an equipotential net to which flowlines could be added. This analytical technique was limited to homogeneous, isotropic systems with a gradual water-table configuration which could be defined by simple algebraic functions. Freeze and Witherspoon's (1967) numerical simulation of ground water flow removes the limitations of Toth's (1962) technique. They numerically simulated the effect of topog raphy and geology on regional groundwater flow patterns in an otherwise homogeneous, isotropic flow system. The idealized regional ground water flow patterns may be affected by inhomogeneties such as units of varying hydraulic conductivities, dipping beds, and localized recharge and discharge areas superimposed upon a region system. Given the topographic and geologic complexity of the study area, it is readily understood that the regional ground water flow is equally complex. 20 Structurally—closed basins, such as those encountered throughout the Basin and Range Province, are theoretically hydrologically-closed basins. In theory, recharge from the surrounding mountains drains into the playas where it is evaporated from the discharge area. However, as early as 1960, Hunt and Robinson (1960) advanced hydrogeochemical evidence in support of their hypothesis that water being discharged in the Death Valley Salt Pan had come, in part, from Mesquite Flat and Ash Meadows, topographically higher basins nearby. They further hypothesized that this inter basin groundwater flow was along faults in the thick Paleozoic carbonate formations. In 1962, Winograd supported this hypothesis with hydraulic evidence for interbasin flow through Paleozoic carbonate rocks. The water levels in Yucca, Frenchman, and Jackass Flats ranged from 2390 feet to ✓ 2440 feet, indicating the possiblity that they were hydrau lically connected. In addition, he proposed that, were there not a hydraulic connection, these basins would be full to playa level as are other nearby basins. Eakin et al. (1963), using hydrogeochemical, hydraulic, and water budget relationships expanded the study area and concluded that regional ground water flowed south, southwesterly between basins through Paleozoic carbonate rocks. The first statewide attempt to delineate ground water flow systems in Nevada was conducted by Mifflin (1968). Water chemistry, water temperature, variation in discharge, 21 tritium concentrations and radiocarbon determinations were used in his study. Two systems were delineated on the NTS. The first flowed from Pahute Mesa and discharged at the Amargosa Desert south of Beatty. The second and larger system was bounded by the Spring Mountains, the Pintwater Range, the Belted Range, and the Timber Mountain volcanic complex. This system has a complex flow pattern, dis charging to the Amargosa Desert near Ash Meadows. He con- permeable bedrock existed. An investigation by Winograd and Thordarson (1968), emphasized the importance of structural controls as possible conduits or barriers, depending on the stratigraphy and type of faulting involved. Further geologic mapping, partic ularly of clastic strata, was recommended to further the understanding of the effect such heterogeneities have on the flow system. Attempts to use radiocarbon dating and deuterium as tracers of the regional ground water flow met with limited success. Grove, et. al. (1969) concluded that ground water from Yucca Flat, Frenchman Flat, Jackass Flats, northwestern Spring Mountains, and a small amount from Indian Springs Valley all discharged at the Amargosa Desert based upon unadjusted radiocarbon ages which ranged from 1,400 to 28,000 years before present. 22 Winograd and Friedman (1972) used deuterium as a tracer of regional ground water flow. They concluded that 35 per cent of the discharge at Ash Meadows came from the White River groundwater basin, with the remainder coming from sources within the Ash Meadows flow system. They also con cluded that spring discharge in east-central Death Valley might come from Ash Meadows. This theory has not been substantiated by subsequent research. Winograd and Pearson (1976) used aqueous geochemistry and environmental isotopes to define a major zone of high permeability extending from Frenchman Flat to Crystal Pool in Ash Meadows. Rush's (1970) reconnaissance study redefined two major flow systems in the study area. The Ash Meadows system was extended westward from the Pahranagat and Spring Ranges to the Spring Mountains on the south, with the Belted and Groom Ranges forming the drainage divide at the northerly portion ' of Emigrant Valley. The drainage divide between the Ash Meadows flow system and the Pahute Mesa flow system extended from Jackass Flat in the south and followed the topographic divide of the Eleana and Belted Ranges. The Ash Meadows system was shown with a general south-southwesterly flow, discharging at Ash Meadows. The Pahute Mesa system also had a south-southwesterly flow component, but discharging into the Amargosa Desert west of Ash Meadows. Blankennagel and Weir's (1972) study of the hydro geology of Pahute Mesa supplemented Rush's (1970) interpre- 23 tation of the Pahute Mesa flow system. In addition it provided in- depth hydrological data, including vertical head profiles. These data show vertical components of flow, with recharge and discharge zones superimposed on the general regional trend. Naff et al. (1974) presented geochemical and geologic evidence which disputed earlier reports of under flow from the Pahrump Valley to Ash Meadows. They attributed the discharge at Ash Meadows to recharge of the carbonate aqui fer in the highlands to the east with flow through a contin uous block of carbonate to Yucca and Frenchman Flats where it was shunted via a potentiometric trough to Ash Meadows. Winograd and Thordarson (1975) studied interbasin, intrabasin, and perched flow systems of the south-central Great Basin. They concluded that perched ground water occurs principally within the tuff aquitard. Ground water movement through the tuff aquitard was thought to be controlled by interstitial permeability. Intrabasin flow from welded-tuff and valley-fill aqui fers passes slowly through the tuff aquitard into the under lying lower carbonate aquifer in several intermontane val leys within the study area. Downward leakage rates in Yucca v and Frenchman Flats were estimated to be less than 100 acre- feet per year (Winograd and Thordarson, 1975). Where major hydraulic barriers cut the lower carbonate aquifer, there is 24 movement from the lower carbonate aquifer upward into young er units. Interbasin movement was thought to occur through the lower carbonate aquifer which underlies much of the study area. Evidence of geologic structural controls was present ed in explanation of the south southwestward flow from Yucca and Frenchman Flats, through the Mercury Valley, and dis charging at Ash Meadows and for the proposed drainage divide which is coincident with the Mine Mountain thrust zone. Hess and Mifflin (1978) investigated the feasibility of water production in deep carbonate aquifers in Nevada. Among other recommendations, they proposed additional subsurface data acquisition from petroleum wildcat wells and a test drilling program to enhance the hydrogeologic knowledge of the deep carbonate system. Claassen (1983) concluded that overland flow of snow melt in or near present-day stream channels during late Wisconsin time provided ground water recharge to the west- central Amargosa Desert. He also hypothesized upward leak age from a semiconfined regional carbonate aquifer into the valley fill aquifer at Jackass Flats. Fenske and Carnahan (1975) developed a set of hydrolog ical maps for the Nevada Test Site. This set included a water table map, depth-to water map, and water table gradi ent map. These maps were simulated using subdued topogra phy. The series of programs, using known control points, 25 calculated a probable water level at each grid point inter section of the region mapped. The flow path projected by this map was one of recharge in the highlands, discharging in the Ash Meadows region. Interbasin movement was inferred from Emigrant Valley southwestward to the NTS. Overall flow was south south-westward. Waddell (1982) developed a two-dimensional, steady- state, finite-element model of the ground water flow system of the Nevada Test Site and vicinity. His model encompassed both the Ash Meadows and the Pahute Mesa ground water flow systems. With the exception of eastern Pahute Mesa, his results appeared to substantiate conclusions from Winograd and Thordarson's (1975) conceptual model. He recommended that a more detailed geophysical and geohydrologic data base should be acquired and that more detailed transport model ling would be necessary to determine rates of transport of radionuclides in specific areas of interest. Harrill et al. (1983) have proposed, among other objec tives, to develop mathematical models of "type areas" under the Great Basin RASA (Regional Aquifer-System Analysis) project. It was hoped that this approach would provide delineation and quantitative description of all Great Basin ground water flow systems, from recharge to discharge. 26 CHAPTER 3 THEORY OF HYDROCHEMICAL INVESTIGATIONS 3.1 MAJOR ION CHEMISTRY Aqueous geochemistry can be helpful in the interpreta tion of the diagenesis of groundwater as it passes from recharge area to discharge area. In his classic paper, Cnebotarev (1955) examined nearly ten thousand aqueous geo chemical samples from sources as variable as fresh water, salt water, geothermal, and deep artesian aquifers. He concluded that the normal cycle of metamorphism for natural waters proceeds in general: bicarbonate -*■ sulfate -*■ chloride. The comparative solubility of these ions, in Ca2+ solution, HCO~ (K = 10~8*3) , SO" (K = 10~4), and Cl" (K = 10°), confirms that this would be the expected geochemical sequence (Drever, 1982). Maxey and Mifflin (1966) observed this sequence in carbonate rocks of Nevada. 27 Of the chemical elements found in the earth's crust, Chebotarev (1955) identified Na+, K+, Ca2+, Mg2+, H+, HCO3, CO 3 , Cl , and SO2 as "...those ions which are constantly present in water,..., and the occurrence of which determines the physical properties and geochemical type of water." Sodium, calcium, and magnesium have low ionic potential (ratio of ionic radius to ionic charge) and, as such, should remain in ionic solution. However, these cations have the following relative exchange property as they pass through montmorillonite clays: Na+ < H+ < K+ < Mg2+ < Ca2+ thus replacing Na+ with Ca2+, Mg2+, and K+ in ground water (Ronov, 1945, as cited in Chebotarev 1955). The composition of a particular water will be a result of several factors: 1. Ground water reflects the geologic formations through which it has flowed, subject not only to rock types, but cementation and other diagenetic alterations of sedimentary rocks. 2. Water of a given salinity concentration will have a greater solvent action at high velocities than will slowly moving water of a similar salinity. 3. The salinity concentration is lower as the quantity of water passing through the system increases. 28 Structural controls may provide stagnant under ground pools or fracture flow systems which may affect the quanitity and velocity of flow. 5. The overall salinity concentration will increase as water passes through the system and the ionic constituents of that salinity will change. While all chlorine and most of the sodium in an aqueous system tend to stay in solution, carbonates will precipitate out. 6. Temperature may be one of the most significant parameters determining the equilibrium concentra tions of the various ionic constituents (Garrels and Christ, 1965) . Trilinear diagrams, as outlined by Piper (1944), are used for graphic presentation in this study. Major ions, Mg2+, Ca2+, Na2+, K+, C0§“, HCO^, So£~, and Cl”, are plotted percent epm. The cations are plotted in the lower left triangular field and the anions are plotted in the lower right. The intersection of the rays from the lower triangles are plotted on the diamond-shaped central field showing overall chemistry of the water. These plots help make an immediate identification of water types. In addition, possible mixtures of waters may be identified. If plots of two analyses define a straight line on which a third analysis lies, the plot of the third analysis may represent a mixture of some proportion. Further extrapola 29 tions of this procedure may be used to determine multi component mixtures. Since the data points show only relative percent epmf caution must be used in interpretation where samples may have the same relative percent epm, but entirely different total ionic concentration. Several graphical methods have been used to differentiate waters of low concentrations from high concentrations. 3.2 RADIOCARBON DATING OF GROUNDWATER Three carbon isotopes exist. The natural abundance of the various carbon species is shown in Table 3.1 (Fritz and Fontes, 1980). TABLE 3.1 NATURAL ABUNDANCE OF CARBON SPECIES Isotope % Abundance Carbon - 12 98.89 Carbon - 13 1.11 Carbon - 14 ~ TO" 10 Carbon-14 is the only radioactive carbon isotope. It is formed in the upper atmosphere when nitrogen is bombarded by cosmic rays: 1 ^N + n 14C + p The radioactive carbon is oxidized to 14C02 and is rapidly mixed with the inactive atmospheric CO2 reservoir. 30 This makes the radiocarbon available to the hydrosphere and biosphere. This radioactive product then decays according to: 1 14N + e The rate of decay follows the law of radioactive decay where: A = measured radioactivity; A0 = standard activity "13.56dpm/gC; * = decay constant = ln2/t1/2; t1/2 for 14C of groundwater = 5730(±40)years; T = apparent age in years. International convention defines standard activity as 0.95 times the specific activity of NBS oxalic acid, AQX in 1950 (A0 = 0.95xAQX = 0.95x14.27dpm/gC = 13.56 dpm/gC). Deviations of the measured activity from standard activity are given as: <5lt+C = (a-A0 )/Aq x 10 3 or A = ( <511+C Aq )/1 000 + AQ 31 The measured activity is usually reported as percent of standard activity (aQ) or percent modern carbon (pmc). a1 4(pmc) = A/AQ x 100 From this, the apparent age of the ground water can be determined by Ta = - 8270 ln(A/A ) (Mook, 1980). Modern instrumentation allows calculation of apparent radiocarbon ages up to 70,000 years before present (Brown- low, 1974). However, isotope fractionation occurs as carbon travels from one reservoir to another. This must be accounted for in determining a "true" or corrected age. The stable carbon isotope ratio 13C/12C or 13R is used as an indicator of the magnitude of this fractionation effect. Kinetic and equilibrium fractionation theory predict that 1 enrichment is twice that of 13C enrichment: (Ac/A) -1 = 2(13Rc/13R -1) (Mook, 1980), where subscript c refers to corrected values and all other terms are as previously defined. When A and R are divided by the respective AQ and R 13PBD standard values, this leads to the relationship 14 14 ac ~ am /p where: C*13c 5 1 3C ) P sample rock (T^Cplants S ^ C rock ) (Ingerson and Pearson, 1964). The conventional assumption for the value of 5l3crock is that value is 0 °/oo, therefore P = S13C sample7 , /<513c plants, Again, by convention, 513Cplants has been assumed to be -25 °/oo (Payne, 1972). When analyses provide a14 and 513Csamplef one can then calculate a corrected age, using Tc = - 8270 ln(a/aQ ) 513Cpiants :'-s a comPosite of several sources with in the soil zone of the recharge area. Root respiration, plant debris, atmospheric C02, and carbonate minerals are 33 commonly considered the primary contributors of carbon from the soil zone. The expected <5 C value from the biogenic sources var ies with the photosynthetic process of the plant type: ° C4 type: Hatch-Slack photosynthesis, 613c = -13 °/oo; • C3 type: Calvin photosynthesis, 513C = -27 °/oo; • Succulents: CAM photosynthesis, <$13C = C4 when stressed, 613C = C3 when unstressed, Average • Atmospheric: No biogenic source, <513C = -6.3 °/oo (from Lerman, 1972; Troughton, 1972; and Allaway et al., 1974) . Until oxidation of the plant debris takes place, this source may be disregarded since the carbon must be in a soluble form to be of interest in hydrologic studies (Inger- son and Pearson, 1964). Atmospheric PCq 2 is 10“3,5 atm (Garrels and Christ, 1965). Since Pcq2 in the soil zone ranges from 10 to 1000 times atmospheric C02, it is assumed that atmos pheric CO2 is a negligible contributor to the CO2 in the soil zone (Ingerson and Pearson, 1964). Some atmospheric CO2 may enter the soil profile in solution with rainwater (Payne, 1972). 34 Traditional theory has been that the largest contri bution to soil C02 comes from production of C02 by plant respiration and decay (Payne, 1972). When water comes in contact with this soil gas, the pH is lowered as carbonic acid is formed: H20 + C02 + ~ H2C03 - HCO'i + H+ As carbonic acid continues through the system, coming in contact with calcite, that mineral is dissolved: H2C03 + CaCO3 + - 2 HC03 + Ca++ (Brownlow, 1979). Available carbon dioxide is the limiting reactant in this reaction, with more calcite dissolution taking place as available C02 is increased. Edmunds and Walton (1980) have proposed that inorganic carbon dissolution may be a greater contributor to 613C enrichment in the soil zone than biogen ic production. In addition, recent studies by Bohm and Jacobson (1984) and Wallick (1976) have demonstrated that dissolution-evaporation effects in semi-arid soils have a significant effect on the carbon dioxide content in the soil zone. Given the variables involved in radiocarbon correction, a more precise correction can be provided if direct measure 35 ments of <51 3c of soil CO 2 gas, representative of ^13(-plants ;*'n recharge area, <$13C of carbonate in the soil zone, and 513C of rocks, through which the ground water has passed, can be made. Two other recent, man-caused phenonmena affect AQ. The first is the so-called "Suess" effect or industrial dilution effect (Rankama, 1963). This effect relates to man's increased consumption of fossil fuel during the past century. Authors have reported estimates of this dilution effect from <1 percent to 10 percent (Suess, 1953; Suess, 1955; Craig, 1957; all as cited by Rankama, 1963; Mook, 1980). Since atmospheric testing of nuclear devices began in 1954, the "Suess" effect has been overshadowed by the atom-bomb effect. The nuclear weapons tests were primarily conducted in the northern hemisphere, where the tropospheric 11+C content has increased to 200 percent of normal back ground level (Mook, 1980). In addition, underground nuclear testing can also increase the radiocarbon activity in con taminated groundwater. This may give misleading results in radiocarbon dating. Using the relationship: 613C = 51 3C , ( A )• + 513C rock ^ A+B where: A = moles of limestone derived carbonate; 36 B - moles of soil gas derived carbonate; and A+B = total moles of limestone plus soil gas derived carbonate (Ingerson and Pearson, 1964), it can be readily seen that, if even a minor amount of mixing between aquifers containing modern water with water containing only radioactively dead water were to occur, large errors in age-dates could result. Kim et al. (1969) have developed a table which clearly illustrates the effect of such contamination (Table 3.2). 3.3 STABLE ISOTOPE CHEMISTRY Stable isotopes can help identify type, origin, age, and mixing ratios of water. Environmental isotopes of hydrogen and oxygen serve as the best possible tracers because they are constituents of the water molecule (Freeze and Cherry, 1979). Altogether there are eighteen possible combinations of isotopes in the water molecule. Of these, the most common form is 1H215°* The average abundance of hydrogen and oxygen isotopes prior to the advent of thermonuclear testing is given in Table 3.3. Of the six isotopes shown, only tritium is radioactive, having a half-life of 12.3 years. This isotope is discussed in the next section. If the stable isotope content does not change within the aquifer, it reflects the origin or source of the water. Location, period and processes of recharge define the ori ginal isotopic signature. The history of the water is reflected as it moves along the flow path with mixing, 37 TABLE 3.2 EFFECT OF CONTAMINATION OF MODERN CARBON ON TRUE AGE2 (from Kim et al., 1969) Apparent Age Derived as Result of 1% 5% 10% True Age Contamination Contamination Contamination 600 540 160 modern 1 ,000 910 545 160 5,000 4,870 4,230 3,630 10,000 9,730 8,7 10 7,620 25,000 23,400 19,000 15,500 40,000 32,800 23,200 18,400 60,000 36,600 24,000 18,400 Activity of modern carbon is considered the same as 95 percent of the radioactivity of NBS oxalic acid. 2A detailed graph showing other ages and degrees of contam- ination was given by Olsson (1968). TABLE 3.3 ENVIRONMENTAL ISOTOPES ' OF HYDROGEN AND OXYGEN AND THEIR RELATIVE ABUNDANCE IN WATER OF THE HYDROLOGIC CYCLE (Modified from Fritz and Fontes, 1980). Relative Abundance Isotope (%) Type *H proteum 99.984 Stable 2H deuterium 0.015 Stable 1 — 1 on 1 3H tritium 0 o Radioactive half-life 12.3 years 160 oxygen 99.76 Stable 170 oxygen 0.037 Stable 180 oxygen 0.1 Stable 33 salinization, concentration, and discharge processes deter mining the ultimate isotopic composition of the water. Stable isotope ratios are controlled by the number of con densation stages in the precipitation and by subsequent evaporation caused by changes in ambient temperature and pressure conditions. The extranuclear structure of an element determines its chemical behavior. The nucleus determines its physical characteristics. In the lighter elements mass differences cause more pronounced physico-chemical differences, which can cause isotope fractionation. See Table 3.4 for a com parison of some physio-chemical properties of H20 and D20. TABLE 3.4 CHARACTERISTIC CONSTANTS OF H 20 AND D 20 (from Hoefs, 1973) . Constants H20 D20 Melting point (760 torr, in °F) 32.0 34.1 Boiling point (760 torr, in °F) 212.0 214.6 Vapor pressure (at 212°F, in torr) 760.00 721.60 Quantum theory explains the isotopic physio-chemical difference. The total energy of a molecule is the sum of the electronic, translational, rotational, and vibrational energies. Isotopes of the same element have approximately equal electronic, translational, and rotational energies. Therefore, isotope effects are caused by differences in molecular vibrations. The potential energy of a diatomic molecule is related to interatomic distance. 39 The molecule is restricted to discrete energy levels, the lowest being 1/2 hv above the lowest point on the energy curve, where: h = Planck's constant; and v - molecular vibration of the atoms with respect to one another. Since atoms with larger masses have lower vibrational fre quencies, the heavier isotope has a lower zero-point energy than the lighter isotope. During a chemical reaction the lighter isotope is more reactive (Hoefs, 1973). Kinetics, therefore, accounts for isotopic fractiona tion effects observed in nature: 1. The H20 vapor phase becomes progressively lighter, that is, more depleted in the heavier D and 180 isotopes. 2. The isotopic composition becomes lighter with in creased altitude. 3. The isotopic composition becomes lighter as the amount of precipitation increases. 4. As the distance to the source of vapor increases, the isotopic composition becomes lighter. Continental precipitation is depleted in 180 and D as compared with marine and coastal precipitation. 5. Precipitation from cooler climatic conditions, e.g., paleoclimatic precipitation, is depleted with respect to heavy isotopes. 40 6. There are seasonal and short-term variations. Win ter precipitation is depleted in 180 and D as compared with summer rains. Variations in stable isotopes are reported as the iso topic ratios D/H and 180/160, or in delta units, Sd and <$180. A 6 unit is qiven in °/oo by: 5 °/oo = (R-R . - ,)/R . , , x 1000 standard standard where: R = isotopic ratios D/H or 180/150 of the sample; and Rgtandard = SMOW (Standard Mean Ocean Water) which approximates the average isotopic composi tion of the oceans. A mass spectrometer is used to measure the isotopic ratios. The precision of measurement is approximately ±0.2 °/oo for <51 80 and ± 2.0 °/oo for <$D depending on the instrument used. Since 6d values are approximately eight times larger than 6180 values, the levels of precision are approximately comparable (Payne, 1972). Craig (1961) developed the widely accepted global mete oric water line (MWL) using a linear regressional relation ship between SD and 61 80: <$D = 8 <5180 + 10 °/oo 41 The intercept of the Craig MWL, + 10 °/oo <$D, is typical for oceanic precipitation (Figure 3.1). Inland seas typically have higher intercepts. Evaporation from bodies of water is a linear function with a slope usually ranging from 2 to 5. Geothermal alteration lies on a straight line showing deviation in <$180, but no change in <$D (Fritz and Fontes, 1980). Regional variations from Craig's MWL have been shown. For instance, data from eight North American continental stations show 6d = 7.95<518o + 6.03 °/oo, while data from fifteen tropical island stations show <5d = 6.17 51 8o + 3.97 °/oo (Gat, 1980). This meteoric water line not only has a lower slope, but also has a lower intercept. 3.4 TRITIUM DATING OF GROUND WATER Tritium, 3H, is a radioactive isotope of hydrogen. It has a t1/2 of ~12.3 years and is produced in the upper at mosphere by cosmic ray bombardment of nitrogen. This natural reaction produces a steady-state back ground concentration of 5-20TU in precipitation (Payne, 1972). With the advent of open-air thermonuclear tests between 1952 and 1963, background tritium levels were increased by 2 to 3 orders of magnitude (Gat, 1980). This background concentration varies within the strato spheric and tropospheric reservoirs by latitude and season. Figure 3.1 (From Fritz and Fontes, 1980) Expected Deviations from Craig MWL 43 Mid and high latitudes have high tritium activities with respect to low latitudes. Closely tied to the latitudinal relationship is the fact that continental rains are enriched with respect to marine rains. Since there is considerably more land mass in the northern latitudes than the southern, one would expect such a relationship. See Stable Isotope section for further explanation of fractionation mechanisms. Seasonal variations occur with maximum tritium activity in spring and a minimum in the winter. .Seasonal fluctuations have been the subject of other studies (Szecsody, 1982; Freeze and Cherry, 1979). Since tritium decays at a predictable rate, once the water enters the hydrogeologic regime, it serves as a conservative tracer with the tritium activity decreasing at a predictable rate according to the decay formula: where: A = Activity at time t; AQ = initial activity; T = 1/2 life = 12.3 years; and t = time elapsed since water entered system. In order to determine the time elapsed since the triti- ated water entered the system, or the age of the water, the following equation is used: 44 -T t ln2 As previously discussed, post-atmospheric thermonuclear testing so dramatically affected background tritium levels as to make exact post-1952 dating impossible. What can be concluded is that a concentration of less than 5 TU virtual ly assures that the water was recharged prior to 1952 or that it has been so diluted through mixing with dead water as to obscure detectable traces of tritium. If levels above 10 TU are measured, there is virtual assurance that the water is modern water or bomb-tritium water. Post-1952 concentration curves have been developed for specific areas (Szecsody, 1982). Piston flow with no mixing and no disper sion must be assumed in order to utilize these curves. This study deals with large-scale regional aquifers in which mixing is expected and assumed. Unless mixing ratios are clearly defined through other geochemical or hydraulic means, it would be impossible to have a known AQ, original activity. Therefore, t, age, could not be calculated with any meaningful accuracy. For this reason no attempt was made to adapt such concentration curves. In this study water samples containing detectable tritium will be consi dered "modern". 45 CHAPTER 4 FIELD AND LABORATORY METHODS 4.1 SAMPLING OVERVIEW The sampling program was undertaken after an extensive literature review which was intended to determine the scope of geochemical and isotopic sampling which had been con ducted prior to this study. The sampling program was then designed for maximum areal coverage with a minimum duplica tion of previous work. Sites were resampled when previous procedures or results appeared to be questionable or when there appeared to have been temporal changes at a particular site. Previous work consisted primarily of major ion geochem istry from wells and springs in and near the study area. In addition, radiocarbon and tritium age dating had been done at a number of sites. Sporadic and incomplete 6180 and <5d suites had been sampled. Samples were taken from recharge areas, discharge areas, and intervening flow paths in order to optimize the integrated sampling scheme. Soil, soil gas, soil water, well water, tunnel water, tunnel rock, caliche, and drill core samples were taken from throughout the study area (Appendix 2). Two criteria were used in site selection. 1. The site was to be representative of a particular aspect of the groundwater flow path. 46 2. Access to the site or sample was necessary. A review of the locations of sample sites, sampling methods, and tests conducted follows. 4.2 SOIL GAS SAMPLES Soil gas in recharge areas was sampled for 513C analy sis. The soil conditions were unsaturated at each site. At sites PT-3, RT-1, and RML-deep L, samples were taken from previously emplaced suction lysimeters. Two to three test tubes were connected in series to the suction lysimeter. The tubes contained a highly alkaline, carbonate free (pH 12) SrCl2 solution which had been especially prepared to elim inate all trace C02 from the solution (Pearson, 1970). As suction was applied, the soil gas was drawn through the connective tubing into each test tube where it was diffused through a stone aerator and into the SrCl2 solution. The C02 in the soil gas was precipitated as SrC02. The remaining gas was passed through the subsequent test tubes in order to precipitate all remaining C02 and avoid possible fractionation. Pumping continued until approximately 10 mg of precipitate had been collected. The tubes were then sealed with parafilm and taped with black electrical tape to avoid atmospheric contamination. The samples were stored at room temperature until 513c analysis was conducted. At sites ST-1 and TT-2, a soil gas sampler similar to that described by Henne (1982) was driven into the ground to a depth of approximately one and one-half feet. A portable 47 vacuum pump was attached to the test tube series and soil gas was drawn through as described above. The pump was run at a rate of approximately 2 1/min for 20 minutes to max imize the soil gas sampled and yet avoid pulling atmospheric C02 through the soil and into the sample. Sample containers were then sealed and stored as described above. 4.3 SOIL SAMPLES Soil samples taken from seven sites throughout the study area were analyzed for C02 and 513c content. All samples were double bagged in heavy plastic sample bags. Sample FF was taken on the Frenchman Flat Playa near the Rad-Safe 5E-15 sign at an elevation of approximately 3100 feet above MSL. This sample consisted of a light tan, fine-grained, playa deposit. Sample YF consisted of the surface layer, approximately 0-1 inch, near the ponds on Yucca Flat at approximately 3900 feet elevation above MSL. This sample was also a light tan, fine-grained playa deposit. Sample RMT-2 was taken from 2-4 inches below the soil surface at the RT-2 site, approximate elevation 6220 feet above MSL and consisted of a dark, fine, sandy clay. Samples RMT-Tel and RML Deep L were taken from the top two inches of the soil profile at the RMT-Tel site, approxi mate elevation 6200 feet above MSL. This location had a 6-8 inch snow cover at the time of sampling, January 4, 1983. 48 The snow was cleared from the site, and samples were dug from the frozen soil. The soil was saturated and contained large ice crystals within the samples. The dried soil sam ple was a dark sandy clay. Samples CJCAL—4 and CJCAL-8 were sampled on September 27, 1983. CJCAL-4 was obtained from a depression on the north side of Rainier Mesa Road about four miles from its intersection with Pahute Mesa Road at approximately 7000 feet above MSL. The soil profile at this location consisted of about 3/8 inch of fine, dark silt to clay material over lying a dark clay-rich sand. The total soil depth was ap proximately four inches to bedrock. The sample, which was taken from the 1-4 inch interval, had a high soil moisture content, apparently from heavy thundershowers which had passed through the area two days prior, on September 25, 1983. Soil sample CJCAL-8 was taken from a site approximately 2.75 miles north east of the intersection of Pahute Mesa Road and Buckboard Mesa Road in Area 20, at approximately 6900 feet above MSL. The sample, a dark, fine-grained clay- rich sand, came from the 0-1 foot interval at approximately 50 feet south of the Pahute Mesa Road. The soil profile appeared uniform to a depth of one foot. Total depth to bedrock is unknown but greater than one foot. 49 4.4 CALICHE SAMPLES Eight caliche samples, representing varying environ ments within the study area were collected for <5 ^ ^c analy sis. Samples were labeled, recorded and double-bagged in plastic bags for transport to the laboratory. Table 4.1 provides information about the physical characteristics and the environmental setting of these samples. All samples exhibited layering which varied in color, hardness, and texture. Colors varied from white to medium brown. Hardness ranged from 1 to 3 on Mohs Scale of Hardness (Hurlburt, 1971), with some samples being soft, moist, and friable, while others could be scraped with a penknife only with difficulty. Texture varied from smooth to rough and pitted. 4.5 CORE SAMPLES Samples of drilling core from the U.S.G.S. Core Library in Mercury, Nevada were selected on the following basis. 1 . Cores from various limestone and dolomite aquifers were sampled. 2. Several tuffaceous core intervals were examined in an attempt to locate calcite vein fillings which could be analyzed. No calcite vein fillings were found in the tuffaceous core samples examined. 3. Availability of samples was limited by whether drill cores had been recovered from a given hole and whether those cores were stored in a readily TABLE 4.1 PHYSICAL CHARACTERISTICS AND ENVIRONMENTAL SETTING OF CALICHE SAMPLES Sample # Location Description Hardness l 3C(°/oo) CJCAL1-2 C P Hogback Pinkish white, moderately hard, -7.7 middle layer contains vol canic layer. Formed as fracture-filling subsurfi- cially. Road construction had brought it to the surface CJCAL2-2 Cane Spring Wash Dark reddish tan, soft, -6.5 moist and friable. With road cut exposure on allu vial fan CJCAL3-1 Rainier Mesa Weathered, nodular outer 7.5 layer, tan-colored, soft, moist, and friable. Formed as fracture-filling subsur- ficially and brought to sur face by road construction CJCAL5-1 Rainier Mesa Off-white, nodular, outer 7.9 layer, less than 0.1cm thick. Vein filling ap proximately 7 ft from top of outcrop. Cliff face recently exposed due to mechanical weathering CJCAL5-2 Rainier Mesa Buff-colored, soft, friable 5.8 inner layer of same sample as CJCAL5-1 U1 o TABLE 4.1 (continued) Sample # Location Description Hardness 6 1 3C ( °/oo ) 1 kO 1 CJCAL6-1 Rainier Mesa Off-white, nodular, outer 3 • layer, less than 0.1cm thick. Exposed surface same cliff area as CJCAL5-1 and -2 CJCAL7-2 Pahute Mesa Buff-colored, fine tex 3 -5.6 tured, inner layer from surface exposed on boulder in wash CJCAL9-2 Head of Silent Buff-colored, soft, fria 1 -7.1 Canyon ble, moist inner layer from cliff exposure at head of canyon Ul 52 accessible warehouse. Appendix 3 provides a list of those cores analyzed for 613c along with the results of those analyses. Samples were labeled, recorded and double-bagged in plastic bags for transport to the laboratory. 4.6 DISCHARGE AREA SAMPLING 4.6.1 Spring Sampling There are at least eleven known springs within the boundaries of the Nevada Test Site. In addition, more than forty springs are. found in the Desert National Wildlife Range, east of the Nevada Test Site. Previous investiga tions have provided hydraulic, geochemical, and environment al isotopic evidence which indicates that, with the excep tion of Corn Creek Springs, these springs are probably not part of the regional groundwater flow, but come from perched water tables (Kisler, 1982; Jacobson, 1984). Since this study deals with the regional groundwater flow, spring sampling was considered incidental. More than twenty-seven large springs exist in Ash Mead ows, the proposed discharge area. Several previous investi gations have been conducted in this area, providing compre hensive hydraulic, geochemical, environmental isotopic stud ies of the springs in Ash Meadows (Grove et al., 1969; Dudley and Larson, 1976; Winograd and Friedman, 1972; Wino- grad and Pearson, 1976; Claassen, 1983). Duplicate sampling was considered unnecessary for the purposes of this study. 53 Data from these studies were incorporated in appropriate sections of this report. 4.6.2 Well Sampling In addition to the criteria outlined in the Sampling Overview, there were two additional criteria for selection of sampling sites from the many wells in the study area. 1 . Samples from the various known aquifers were desired. 2. The well not only had to be accessible, it had to have a pump available due to the large volume of water needed for radiocarbon samples. Water well sampling sites chosen for this study include five of the six aquifers shown in Table 2.1. The producing intervals for two of the wells sampled are from units iden tified as aquitards. The aquifers sampled are valley-fill aquifer, welded-tuff aquifer, bedded-tuff aquifer, upper carbonate aquifer, and lower carbonate aquifer. The well log for Well 8 shows two producing intervals. The major zone is in the Tertiary Indian Trail Formation, Split Ridge member, which is a vitrophyric ash flow tuff and lava flow. A minor producing zone was in Tertiary welded tuff and ash-flow tuff. Interstitial permeability was neg ligible, indicating poor hydraulic connection except through fractures. The well log for Well Ue15d shows zones of production in the lower clastic aquitard, specifically the Lower Cam 54 brian Wood Canyon Formation which consists of fractured quartzite, quartzite siltstone, and dolomite. Again the effective permeability is fracture-controlled. Appendix 4 provides a complete listing of aquifer characteristics for all wells sampled. Specific sampling procedures are out lined below. All well samples were captured directly from spigots at well heads. Wells were pumped until temperature and specific conductance equilibrated before sampling was started. Thirteen wells and two tunnel seeps were sampled for major ion analyses and stable isotope analyses. Major ion samples were collected in one gallon plastic cubi- tainers. Air was evacuated by overtopping the cubitainers. Teflon-lined caps were used to seal the samples, which were packed in ice immediately. No preservatives were used in the samples. The samples were refrigerated until analyses were conducted. Field measurements of pH, temperature, and specific conductance were taken at the time of sampling. Stable isotope samples were taken from the same well loca tions as those sampled for major ion chemistry. The samples were collected in three dram glass vials. The vials were overfilled and capped with Teflon-lined caps to avoid atmos pheric contamination. They were then sealed with parafilm and taped with black electrical tape. The samples were stored at room temperature until they were analyzed. Water well samples for 5 and radiocarbon analyses were collected in fifty liter polyvinyl carboys. The amount of sample collected was determined by use of the following 55 procedure (I.A.E.A., 1971). The concentration in ppm of the total carbonate and bicarbonate in the water was determined from previous geochemical analyses or, in some instances, use of the Hach field titration method. Then the following formula was applied: V(liters) of H 20 required = 10,000/ppm "C" x 150% where: ppm"C" = ppm total carbonate plus bicarbonate. The 150 percent factor was used to insure that an ex cess of sample was collected in order to provide more than the two grams of carbon that was required by Teledyne Iso topes for radiocarbon analyses. The samples were collected in most instances by immers ing a hose into the bottom of the carboy in order to avoid atmospheric mixing. Water was run directly from the spigot into the carboys at Well 2, Well Ue15d, Well C-1, and Well 4. No preservatives were used on the samples. The samples were then transported to precipitation facilities within 24 hours. Ten tritium samples were taken from the same sampling sites as those sampled for radiocarbon. The samples were collected in one liter glass bottles with Teflon-lined caps. No preservatives were added. After the samples were col lected, the caps were taped with black electrical tape to minimize atmospheric contamination. The samples were stored at room temperature until the analyses were run. 56 4.7 LABORATORY METHODS Tritium and major ion analyses were conducted by Desert Research Institute, Water Resources Center Laboratory facility, in Reno, Nevada according to U.S. EPA approved procedures. This laboratory is approved by the State of Nevada, Department of Conservation and Natural Resources, Division of Environmental Protection, as a water pollution control laboratory. Anion-cation balances are usually within ± 3% epm. Acceptable laboratory error is < 5%. Deuterium, oxygen-18, and carbon-13 analyses were con ducted by Desert Research Institute Isotope Laboratory in Las Vegas, Nevada, using a mass spectrometer. Reported analytical error is approximately ± 1% for deuterium, ± 0.3% for oxygen-18 and ± 0.5% for carbon-13. Radiocarbon analyses were conducted by Teledyne Iso topes Radiocarbon Laboratory in Westwood, New Jersey. Analytical error is less than 1%. 57 CHAPTER 5 RESULTS AND DISCUSSION 5.1 WATER-TABLE MAP A water-table contour map was developed to study the regional ground water flow pattern on and near the NTS (Figure 5.1). The data for this map were primarily obtained from USGS data (Thordarson and Robinson, 1971) and Lawrence Livermore National Laboratory's inventory (Howard, 1979). Supplemental data points were added as data became available. Data for all holes containing saturated units within the study area were reviewed. Where available information indicated that the water was perched or if the water level was anomalously high compared with surrounding water levels, the data were omitted from the data base. Anomalously low data points were similarly scrutinized for drawdown and were eliminated if there was evidence that there had been draw down without full recovery. Whenever possible, drilling records and reports were reviewed to verify the validity of water levels. The water levels on this contour map may be either hydraulic heads or elevation heads, depending on whether the measurement was made in a confined or unconfined aquifer. In this sense, the water-table map is thought to be repre sentative of the elevation to which the water would rise by 58 .4800 4800 4600 4400 4200 2400 LEGEND 4000 - Mater level contours in feet above MSL Study Area Boundary Figure 5.1 NTS Water Table Map 59 hydrostatic pressure or more precisely might be called a called a potentiometric surface map. In addition, the heads may be composite, representing more than one aquifer. Since this map includes head data from tuffaceous, carbonate, and alluvial aquifers, the contours are represen tative of regional patterns. Neither delineation between aquifers nor definition of localized systems was attempted in this study. However, interpretation of localized patterns may ultimately be of importance to have a clearer understanding of the complex regional system which exists on the NTS. For instance, the pressure head within a given hole may vary with depth. Normally the head increases with depth. This was observed in Well Ue16d where the head in the Eleana Formation was approximately 300 feet higher than that in the overlying Tippipah Limestone (Dinwiddie and Weir, 1979). However, the reverse may be true. This was demon strated in Blankennagel and Weir's (1973) geohydrologic study of Pahute Mesa. During that study, vertical head distribution was profiled as test wells and test holes were drilled. The data, viewed in three dimensions, show both distinct localized recharge and discharge zones within the Pahute Mesa regional recharge area. The SACM (Cybernet, 1980) contouring program was chosen to contour the water table map. The program uses a weighted least squares fit to determine the contour shapes. 60 The SACM program produces a numerical approximation of a surface defined by a set of points with varying Z values, in the case, head data. A uniform grid system is developed based upon the average distance between data points and the distribution of the data. The average distance between points was determined using the formula Average distance = (X x Y) ^ N where X = Xmax - Xmin Y = Ymax - Ymin, and N = number of data points. Since the data were unevenly spaced, the grid spacing used was 1/5 of the average distance as determined above. The data are then read and the value of the surface at each point within the arid system is computed. An eight—sector search around each data point is conducted. A weighted least sauares fit of a surface passing through uhe point being evaluated is calculated based upon the nearest data point found in each of the eight sectors. Each data point is weighted by its distance from the evaluated point, with those being more nearly egual to the center point having greater weight. 61 Once values have been found for all intersections of grid squares containing data points, the remaining grid intersections are evaluated by conducting a column by column search from evaluated grid intersections into uncalculated grid intersections. First approximations, to the uncalculated grid intersections are calculated by determining the slope of adjacent grid intersections. An eight-sector search around the intersection is conducted and a weighted least sauares fit is performed as described above. A weighted average is performed between the projected value and the least squares fit value. When all grid points have been calculated, the grid file is then used as the basis for other tasks such as the contour package used to develop the water table map in this study. The water-table map developed shows an overall regional trend from north and east to southwest. This corresponds with previous interpretations showing regional recharge in the higher elevations of the Sheep Range, and Pahute Mesa with regional discharae at Ash Meadows and Death Valley. Superimposed upon this regional trend is recharge in the vicinities of Rainier Mesa and Pahute Mesa and flow south west from Emigrant Valley toward Frenchman Flat (Figure 5.2). A steep gradient, as shown by closely spaced contours, lies between Rainier Mesa and Yucca Flat. This steep gradient may be associated with the Mine Mountain 62 Figure 5.2 Regional Perspective - NTS Water Table Map 63 thrust zone (Sinnock, 1982) and appears to parallel the drainage divide between the Ash Meadows and Pahute Mesa groundwater basins identified by Winoqrad and Thordarson ( 1975). However, this hydraulic interpretation does not illustrate a drainage divide, but shows the divide at the Pahute Mesa recharge area with components of flow both toward the southeast and the southwest. A potentiometric trough appears in a north- south trend in the vicinity of Yucca Flat. This coincides with previous reports of possible discharge from the Tertiary volcanic aquifer to the underlying Paleozoic limestone aquifer in the vicinity of Yucca Fault (Winograd and Thordarson, 1975). The flow from Pahute Mesa toward the south-southwest, indicates possible discharge through Crater Flat to the Amargosa Desert northwest of Ash Meadows. The flow in the central portion of the study area shows a gradual gradient from Rainier Mesa in the north, southward toward Jackass Flats where it joins the component flowing toward the south west and discharge at Ash Meadows. This water table map further confirms the potential for interbasin flow from Gold Flat, Kawich Valley, and Groom Lake to the north of the study area and Emigrant Valley to the north and east. Steep gradients to the north and west of Yucca Flat correspond to the lower clastic aquitard of the Groom Range and the upper clastic aquitard of the Eleana Range. 64 An apparent trough occurs in the southwestern corner of the study area near Fortymile Canyon which lies between Yucca Mountain to the west and Jackass Flat to the east. This trough may be nothing more than an aberration within the SACM. program due to the relative paucity of data in the Shoshone Mountain area versus the extensive number of data points available on Yucca Mountain. It may appear due to drawdown in Wells J-12 and J-13 to the south of Fortymile Canyon. A final possibility is that this trough may reflect a fault trace similar to that in Yucca Flat where there is thought to be- downward leakage from the Tertiary volcanics to the underlying Paleozoic carbonate aquifer. Caution should be exercised in the strict interpreta tion of this flow model due to the paucity of data, particu larly in the areas of Timber Mountain, to the west of the study area and Shoshone Mountain south toward Jackass Flats. As control points become available, the flow pattern may vary, although the overall regional trend would not be expected to change. 5.2 MAJOR ION CHEMISTRY Major ion analyses were conducted on water from throughout the study area in order to characterize the geo chemistry of the flow regimes. Results of the major ion sampling are summarized in Table 5.1. The geochemical analyses show three major types of water. Sodium bicar TABLE 5, CHEMICAL ANALYSES OF SELECTED SAMPLES FROM NTS HCO3 SamplIng Date of Spec. Log Location Col lection Ca2+ Mg2+ Na+ K+ Cl" SO2** ■tco2" SI02 Cond. T pH pco2 613C l“c 3H 60 618o »4 3 mg/l u •c °/oo yrs. B.P. | tu I °/oo I °/oo _J------Wel 1 NTS 86(D) Arm/ #1 6/21/82 44.80 21.90 33.20 4.86 14.50 50.40 258 20 532 31.8 7.84 -2.1 NA NA NA - 99 -13.1 NTS87(D) Well 5C 6/21/82 2.19 0.56 128.00 6.20 8.80 25.40 297 54 566 25.5 8.71 -3.2 NA NA NA NA NA NTS88(D) Well J — 13 6/21/82 13.00 1.83 41.30 4.87 6.80 18.80 121 63 276 31.2 7.88 -2.3 - 7.8 10,150 <2 - 96 - 12.7 NTS89(D) Wel 1 C 6/22/82 72.70 28.70 118.00 13.60 32.90 70.00 585 31 1050 36.7 7.65 -1.0 NA NA NA -106 -13.3 NT S90(D) Well A 6/22/82 22.30 6.82 48.30 9.25 6.40 20.00 209 78 395 26.9 7.79 -2.5 - 8.9 23,832 <2 -107 -13.0 NTS9KD) Well 2 6/22/82 33.70 14.00 27.40 6.77 7.00 23.60 215 52 401 34.8 8.00 -1.9 - 11.2 19,038 <2 -102 -13.2 NTS92(D) Wel 1 8 6/22/82 7.91 1.15 30.30 3.29 7.60 15.80 78.1 48 190 26.8 7.72 - 2.5 - 11.3 11,396 <2 -101 -12.9 TABLE 5.1 CHEMICAL ANALYSES OF SELECTED SABLES FROM NTS (Continued) HCO- Samp 1Ing Date of Spec. Log Location Collection Ca2+ Mg2+ Na + K+ Cl* SO2- +C02- SIO, Cond. T pH PC02 a13C i-c 3H ao a18o H 3 1 mg/l M •c °/oo yrs. B.P. TU °/oo °/oo NTS93(D) U19c 6/22/82 1.02 0.03 34.20 0.36 2.40 6.30 78, 46 154 38.5 8.05 -3.4 -11.6 21,757 <2 -109 -14.1 NTS95(D) UE16d 6/29/82 75.70 22.90 36.80 6.77 10.60 58.80 370 31 679 24.5 7.65 -2.1 - 8.7 22,224 <2 - 96 -12.4 NTS99(D) Watertown 3 7/29/82 21.40 4.23 55.70 6.70 11.00 38.20 179 78 392 23.0 8.09 - 7.1 13, 144 <2 NA NA CJC-1 C-1 9/27/83 75.40 29.70 127.00 14.00 33.60 65.50 587 30 1082 36.4 6.58 -0.8 - 3.8 >39,920 10.2 -102 -12.8 CJ-15d* Ue15d 9/27/83 56.00 15.70 71.50 15.50 14.80 39.80 378 41 682 30.0 6.89 -1.3 - 4.1 22,728 15.6 - 99 -14.1 -14.2 CJ-4, 4 9/27/83 23.00 7.75 50.20 4.99 11.90 41.60 161 60 420 27.5 7.53 -2.3 -10.9 13,390 <5 - 94 -12.6 NA ■ Not Analyzed 67 bonate waters are present in the tuffaceous aauifers. Calcium bicarbonate water predominates in Paleozoic car bonate aquifers. Mixed waters occur in some tuffaceous aquifers and in three wells which produce from tuffaceous alluvium. Fiaure 5.3 illustrates the types sampled during the course of this study. The dominant anion in all cases is bicarbonate. It should be noted Well 5C and Well U19c plot identically on the diagrams, the total ionic concentration of the water in Well 5C is approximately 3.5 times greater than that of Well U19c. This indicates that the water in Well 5C has been in contact with a similar hydrogeologic environment as the water in Well U19c , but, perhaps, for a longer period of time. It is of further interest that, while U19c produces from tuffaceous units, 5C produces from Tertiary and Quaternary tuffaceous alluvium. Relative percentages of major ions of well water from Well U19c and Well 5C are nearly identical. These samples typify sodium-potassium bicarbonate waters found in tuffaceous aquifers throughout the NTS. White et al. (1980) analyzed water contained in fractures and in interstices of the volcanics of Ranier Mesa. The geochemical character istics of the water from Well U19c and Well 5C are typical of the sodium-potassium bicarbonate- end member identified in water from the fractures of Rainier Mesa. The interstitial water had considerably higher concentrations of chloride and 69 sulfate than that of the fractures or from Wells U19c and Well 5C. Schoff and Moore (1964) characterized sodium-potassium bicarbonate waters as occurring in both tuffaceous aquifers as well as alluvial aquifers containing tuffaceous detritus. That study indicated that the water from the volcanics of the Rainier Mesa tunnels was low in TDS and that deep wells tapping tuffaceous aquifers retained low TDS. The authors concluded that the low TDS inferred that the water had not traveled far from the recharge area. However, Henne (1982) found that migration through the fractured, friable Paintbrush Tuff of Rainier Mesa was rapid and that the major ion chemistry changed little from the soil zone in the recharge area through the tuffaceous fractures into the area 12 tunnels. He estimated that the travel time from the mesa top recharge area into the Area 12 tunnels was from 6 weeks to 3 months. Clebsch (1961) estimated that waters from Rainier Mesa tunnel fractures ranqed in age from 0.8 to 8 years. This offers an alterna tive explanation for the relatively low TDS. Dilute waters may be transported rapidly through fractures, thus mini mizing the time the water is in contact with the aquifer. None of the analyses conducted for this study indicated diagenetic maturity which would be expected in waters which have evolved through differine environments. For instance, the highest chloride content is approximately 12% of total 70 anions. The sulfate content is less than 20% of the total anionic content. This water may reflect the influence of interstitial water from the tuffaceous aquifer as discussed by White et al (1980). However, several wells, Wells C, C-1, Ue15d, A, 4, and 2 all lie between the calcium and sodium-potassium end members. This may indicate a blendinq of waters from the carbonate and tuffaceous aquifers, but does not reflect the anionic diaqenises which is apparent at Ash Meadows, a proposed discharge area. The waters from Devil's Hole, Rogers Spring, Longstreet Spring, and Crystal Pool all reflect a chloride-sulfate content of greater than 30 per cent of anions which is approximately a 10 percent shift from the carbonate wells, C, C-1, and Ue15d found in the eastern portions of the study area. This tends to support Schoff and Moore's (1964) contention that the water in the discharge area indicated a lonqer path and more complicated chemical history than found in other waters from the study area. Specific conductance ranged from 1082 umhos in Well C-1 to 154 Umhos in Well U19c. Water in Well J-13, located near the discharge area has a specific conductance of 276 umhos. This may reinforce Schoff and Moore s ( 1964) hypothesis that recharge to tuffaceous aquifers is mostly from local precipitation within each basin and that groundwater move- raent in the volcsnics is downward to the carbonate aquifers. 5.3 RADIOCARBON DATING In this study, several carbonate sources were analyzed for their 513C content: soil, rock, caliche, soil gas, soil water, and well water. The purpose of analyzing these various sources was to determine appropriate corrections to be applied to radiocarbon age dating. Discussion of the results from this study follows. A complete listing of the <$13C results is contained in Appendix 3. Comparative <513c results also appear in Figure 5.4. 5.3.1 Results of Soil and Rock Carbon Analyses Seven soil samples and four rock samples were analyzed for carbonate content by U.S.D.A. Salinity Laboratory in Riverside, California. The analyses were conducted primarily to determine which samples contained a high enough carbonate content to conduct radiocarbon dilution within the flow system. Soil samples contained between 0.24 percent and 10.5 percent carbonate. Playa samples were enriched in carbon ate, 9.0 percent and 10.5 percent, compared with samples from recharqe areas, 0.24 percent, 0.4 percent, 1.9 percent, and 7.00 percent (Table 5.2). o U Soil Caliche Caliche _ Pz Limestone Pz o M • • , • # Gas • Soil • • Water Soil ■ ■ i i a o / • • Water Well 13c(%0) • • • 6 • • • • • • • • • • • • • • • • • • • • i Figure Figure 5.4 Relative 613C Ratios of Samples Study from this • • • 410 TABLE 5.2 PERCENT CARBONATE OF SOIL AND ROCKS Sample NTS co3— 6 1 3C Number Number Sampling Location (%) (°/oo) S-1 NTS Rx5 Tuffaceous tunnel rocks 0 to <0.1 NA S-2 FF Playa soil 9,0 -0.4 S-3 YL Playa soil 10.5 -1 .0 -1 .3 S-4 NTS Rx2 Tuffaceous tunnel rocks 0 to <0.1 NA S-5 NTS Rx4 Tuffaceous tunnel rocks 0 to <0.1 NA S-6 NTS Rx1 Tuffaceous tunnel rocks 0 to <0.1 NA S - 1 RMT Tel Mesa topsoil 1.9 NA S-8 RMT deep Mesa topsoil 0.4 NA S-9 RMT 2 Hillslope soil 0.4 NA S-1 0 CJCAL-4 Mesa topsoil 0.24 NA S-1 1 CJCAL-8 Mesa topsoil 7.00 -3.8 NA = Not analyzed / <513C analyses were conducted on three soil samples. The (Ingerson and Pearson, 1964). This could indicate that the carbonate in the playa deposit is mainly derived from decom posed marine carbonate sedimentary rock. However, this heavy 513C value may reflect the presence of a dissolution-evaporation-reprecipitation cycle on the playa in which heavier isotopes are preferentially reprecip itated into the playa material as lighter isotopes fraction ate into the soil gas. CJCAL8, from Pahute Mesa, has a <513c value of -3.8 °/oo, slightly lighter than those results shown above, but still within that expected from marine limestone deposits (Brownlow, 1979). Several hypotheses may be offered for this deviation. It is possible that a large contributor to the mesa soil profile is eolian deposits transported from the lower-lying playas. Evidence in support of this hypothesis follows. Carbonate content of CJCAL8 was 7.00 percent. Playa samples FF and YL contained 9.0 percent and 10.5 percent carbonate, respectively. The bedrock in the sampling area, Pahute Mesa, is tuffaceous. Craig (1953) reported 613C values varying from -19. to -25.4 °/oo for igneous rocks. Noble et al. (1968) reported measurable CO2 percentages ranging from <.01 to 1 percent for various rock 75 units of the Silent Canyon volcanic center, which includes Pahute Mesa, the sampling point. Weathered tuffaceous material in combination with calcite-rich playa material could account for both the decrease in the carbonate content and the lighter 513C value observed. Wallick (1976) obtained a <513C soil carbonate average ratio of -3.4 ± 1.3 °/oo in the semi-arid Tuscon Basin. He concluded that the contribution of recent plant C02 to soil carbonate in an open system leads to lighter, more negative S13C ratios, than would be expected in marine carbonates. Simple dissolution-reprecipitation processes are re ported to produce more negative 513c values (Mook, 1980). In addition, Bohm and Jacobson (1984) demonstrate that the relatively high C02 pressures in arid soils may come from concentration by dissolution of eolion dust deposits and subsequent rapid evaporation within the soil zone. In laboratory experiments, C02 pressures were increased from 10“3 •15 to 10-2-65 atm within one 28 hour period. Since 61 3C from C02 soil gas in the study area ranged from -18.7 to -24.2 °/oo (Appendix 3), these processes may have con tributed to the lighter <$13C ratio in the soil gas of the recharge area. The dissolution-reprecipitation evaporative process in the unsaturated zone may also account for the presence of elevated C02 soil gas pressures in arid climates. For instance Henne (1982) measured C02 soil gas 76 on the top of Ranier Mesa which periodically ranged from 10 to 30 times higher than the atmospheric average of 330 ppm (Brownlow, 1979). Henne (1982) detected a temporal trend which he attributed to seasonal fluctuation in respiratory activity of vegetation. This hypothesis does not completely explain elevated levels of C02 in soil gas during periods of vegeta tive dormancy. Jacobson (1983) obtained similarity elevated CO2 soil gas measurements throughout the NTS. The C02 values ranged from 100 ppm to 3000 ppm with an average of 900 ppm, approx imately 3 times higher than the expected atmospheric C02 concentration. 613C values from carbonate rock core samples ranged from +4.1 to -2.5 °/oo. The averaae for the core samples was -0.5 °/oo. Previous authors have reported marine car bonate values rangina from. +2. to -2. °/oo (Mook, 1980), +2.4 to -3.3 °/oo (Craig, 1953), and > +4.5 to <-3.5 °/oo (Baertschi, 1951). All samples fall well within the expected range for marine carbonate sedimentary rock. The mean would tend to support the use of 0 °/oo as an averaqe value for the (613CXimestone} correction factor for adjusting uncorrected radiocarbon dates. 77 5.3.2 Caliche <$1 3C Results Caliche samples were analyzed for Results of <513c analyses appear in Appendix 3. 613C values for caliche samples range from -4.6 °/oo to -7.9 °/oo, with a mean of -6.6 °/oo. There is no apparent correlation between the values and their source area. CJCAL5-1 and CJCAL6-1 both came from the Rainier Mesa recharge area and had <513C values of -7.9 °/oo and -4.6 °/oo respectively, representing the extreme values found in the sampling. CJCAL2-2, from Cane Spring Wash, had a <$13C value of -6.5 °/oo, very near to the mean value of the samples. Table 4.1 describes the physical characteristics of the caliche samples. Caliche samples classified as "hard" appear to be slightly enriched with respect to & 13C. If this is a real enrichment, it is thought to be a product of dissolution and reprecioitation through the weathering pro cess as described above. One possibility is that, as the calcite dissolves and reprecipitates, the lighter isotopes are preferentially leached into the water and the heavier isotopes are reprecipitated into the soil zone. The data do show that the caliche samples are lighter than either dead marine carbonate rock or the playa deposits 78 sampled in the study area. This is probably due to precip itation from calcite rich waters which contained lighter isotopes into depositional environments which were subject to minor subsequent fractionation. Another hypothesis is offered by Riqhtmire ( 1967). In that study 513CpDB caliche values ranged from -3.11 °/oo to -5.66 °/oo with an average of -4.17 °/oo. Rightmire ( 1967) examined the relationship between <513C values and corrected radiocarbon ages for caliche in Hudspeth County, Texas. He observed a trend toward lighter carbon with increasing age. He concluded that the observed range in 613c values was related to pedological-climatic changes toward increasing aridity over the past 25,000 years. Although the overall trend appears to exist, no explanation is offered for outliers with 61 3C values lighter than -5.50 °/oo as recently as 8500 years before present. If meaningful conclusions are to be drawn about any correlation between either source area or hardness and <5 C of caliche samples, further mechanistic study, using a sta tistically significant number of samples is needed. 5.3.3 Soil Water and Gas Soil gas is suspected to be a primary source of carbonate dilution as water passes through the recharge area. Five soil gas samples and one soil water sample were 79 analyzed for 513C from suspected recharge zones within the study area. The 513C value for the one soil water sample was -18.0 °/oo (Appendix 3). This sample came from a recharge area. Its <513c value was slightly heavier than the. Appendix 3 provides a complete listing of soil gas 613c ratios obtained in this study. These results ranged from -24.2 to -18.7 °/oo with a mean value of -20.5 °/oo. All samples were taken from potential recharge areas. The soil gas correction factor (513Cplants) commonly used for adjusting uncorrected radiocarbon age dates is -25 °/oo. This correction factor is based on 613 c soil gas measurements from temperate climates (Mook, 1980). Recent studies in semi-arid environments have tended to support the use of heavier S13C ratios. Mook (1 980) sugqests that -15 °/oo is an appropriate correction factor in semi-arid areas. Average S13C(C02+) values reported by Rightmire (1967) were -16.7 °/oo and by Wallick (1976) were -12.9 °/oo, both considerably heavier than the 513C ratios found in this study. Comparisons of the studies follow. Rightmire's (1967) C02+ sampling procedure may have introduced atmospheric ($13C = _6.3 °/oo) contamination in 8.0 at least two steps. First, it is apparent that the ammonium hydroxide-strontium chloride solution was not scrubbed to eliminate any possible CC^t in solution as recommended by Pearson (1970). Secondly, there was an opportunity for atmospheric contamination when the solution and precipitate was poured from the bubblers into polyethylene bottles. The ammonium hydroxide-strontium chloride solution used in this study was specially prepared to eliminate all dissolved C02 + from solution prior to sampling. Samples from this study remained sealed in containers until they were analyzed. However, the difference between Rightmire's ( 1 970 ) 5 1 3C results and the S13C results of this study cannot be explained by simple atmospheric contamination since more than 25% dilution by atmospheric C02t ( would be necessary in order to account for the difference in 613c ratios observed between Rightmire results and the results in this study. An even larger difference exists between Wallick's <513C results and the results in this study. Theories are offered to account for the differences in observed 513C ratios in the three studies compared here. 1. The observed differences are accounted for by the differing vegetation in the recharge areas. The prevalent vegetation in the recharge areas on the NTS is pinyon pine and juniper. These plants exhibit C-3 photo synthesis (Sharkey, 1985). The 81 influence of the plant derived CO2 is confirmed by the relatively light 613C soil gas in the recharge area, 613C = -18.7 °/oo to -24.2 °/oo. 2. 513c ratios for C02 soil gas is primarily from dissolution and evaporation processes within the soil zone. As previously stated, Bohm and Jacobson (1984), Henne (1982), and Jacobson (1983) have found seasonally elevated levels of C02 soil gas within the study area which may be attributed to dissolu tion, evaporation and reprecipitation processes within the soil zone. If the predominant source of soil carbonate was marine limestone, one would expect the <513C C02 soil gas to be considerably heavier than that observed in this study. 3. The third possibility is that the observed 613C ratios of soil gas are a combination of both marine carbonate from the soil and from the plants in the recharge area. As stated above, the <513c soil gas ratios found in the recharge area ranged from -18.7 °/oo to -24.2 °/oo. However, the average was -20.5 °/oo which indicates dilution of C-3 photosynthesis derived soil gas (<513C=>-27 /oo) with a marine carbonate source (<513C“0 °/oo) . Rightmire's (1967) samples 1 and 2 were collected from sand dunes which were anchored by greasewood. Sample 3 came from loess sand where no 82 vegetation was observed. Samples 4 and 5 came from sediments in the bottom of arroyos where the vegeta tion was greasewood, mesquite, and grass. The evaporation rate was at least a magnitude greater than the average precipitation. Rightmire's study area is not a typical recharge area in a semi-arid environment and certainly not typical of those found on NTS. Therefore, one would not necessarily expect similar <513C results. Wallick (1976) collected soil CO2 samples in the semi-arid Tucson Basin. Sampling sites included desert grasslands, grassy mounds, and desert with mesquite, dry scrub, and grassy vegetation at elevations ranging from less than 3000 up to 5000 feet above MSL. The study area was a suspected recharge area within the Tuscon basin. Samples in the study were obtained by pumping soil gas into a hollow bore sealed with a silicone rubber septum. After purging the hollow bore of contaminated air the soil gas was pumped and expelled into an evacu ated storage flask. C02 was extracted by conden sation in a liquid nitrogen-cooled trap. The tech nique was compared with knowns (Wallick, 1 976) . Results appear to indicate minimal atmospheric con tamination. Again, results appear to be accurate, but would not be expected to coincide with those 83 found in the recharge zones on the NTS, since the ^^^ironmental factors differ so widely from those found on the NTS. 5.3.4 Radiocarbon Results Radiocarbon analyses, including 613c ratios, were conducted on twelve water samples from throughout the study area in order to determine ages of the samples. Table 5.3 contains the results from these analyses. Uncorrected radiocarbon ages ranged from 10,150 to >39,920 years before present for well waters sampled. Two spring waters sampled had uncorrected radiocarbon ages of <780 and 1,855 years before present. As previously described, radiocarbon age dates may be corrected to account for isotope fractionation as the carbon travels from one reservoir to another. The correction term where / £ 1 3r _ 5 1 3p ’ ^sample______rock P rock (Ingerson and Pearson, 1964) is reduced to TABLE 5.3 RADIOCARBON RESULTS Activity Sample a14Cxl00 Uncorrected S13 C * Corrected Samp 1 e Site No. 614C(°/oo) A (dpm/g C) (PMC) Age B.P.(yrs) (°/oo) a ***C Age B.P.(yrs) We II J - 13 NTS-88 707 ± 5 3.973 29.3 10,150±210 -7.8 0.450 6,590+710 -730 Test Well A NTS-90 944 ± 4 .759 05.6 23,830t790 -8.9 0.076 21,400+1210 -730 -1190 Test Wei 1 2 NTS-91 900 ± 4 1.356 10.0 !9,040t470 -11.2 0.107 I8,500±830 -460 U 19c NTS-93 928 ± 4 .976 07.2 21,760t620 -1 1.6 0.074 21,500+980 -600 -960 Wei 1 8 NTS-94 748 ± 5 3.417 25.2 1 1,400t240 -11.3 0.268 10,900+600 -250 -610 Ue 1 fad NTS-95 932 ± 4 .922 06.8 2 2 , 220+670 -8.7 0.094 19,600+1110 -620 -1090 Wei 1 3 NTS-99 796 ± 5 2.766 20.4 13,140+300 -7.1 0.345 8,800+830 -290 -860 Wei 1 4 CJ-4 802 ± 5 2.685 19.8 13,390+310 -10.9 .218 12,600+670 -300 -680 Well C-l CJC-I >992 .108 0.8 >39,920±280 -3.8 .025 >30,400+1240 -1370 Ue 1 5d CJ-15d 936 ± 4 .868 06.4 22,730+690 -4.1 .187 13,800+1590 -660 -1660 Cane Spring NTS-104 201 ± 8 10.834 79.9 1,855+95 -8.7 1.102 recent White Rock Sp. NTS-105 <90 12.340 91.0 <780+5 -1 1.2 .975 recent -6 * Adjusted assuminq S33C = -12.0 °/oo pI ants 8 5 a 1 h ( <5 1 3C m plants S 13c sample based on the assumption that S13Crock = 0 °/oo (Payne, 1972). The average 513C ratio obtained from samples in this study was -0.5°/oo. Although this value tends to validate the above assumption, it should be reemphasized that <513c ratios for carbonate rock cores in the study area ranged from +4.1 to -2.5°/oo, a range of 6.6°/oo. Given such a range, if flow within a particular aquifer could be clearly identified, a more accurate correction could be made by using the <$13c value appropriate to that aquifer. The most readily available source of carbon within the soil zone has been C02 soil gas. In this study 513c ratios measured in soil gas averaged -20.5 °/oo which is heavier than, but near the previously accepted -20 °/oo to -25 °/oo 613Cplants correction (Payne, 1972). How ever, examination of the 6^3C ratios found in waters from tuffaceous aquifers where only negligible carbonate sources, < 1 percent, are available (Noble et al, 1968) shows that the average 533C for those waters was -11.2 /oo. The most plausible explanation for this apparent dilution may be found in the 613C ratios found in the soil. As previously stated, 513c for soil sampled in the Pahute Mesa recharge area was -3.8 °/oo. Assuming equal contribution of the 86 average ^ C soil gas and ^ 3C soil, an average available S13C is -12.2 °/oo, very near the average of -11.2 °/oo found in water from the tuffaceous aguifers. Calculation of an undiluted 613c for the soil zone in the modern water found in White Rock Spring yields a value of -12.3 °/oo based on a sample containing 91 percent modern carbon. Jacobson (1984) obtained similar results, 5l3c=>12 °/oo, in a study of recharge waters in the nearby Spring Mountains. In addition, Wallick (1976) proposed a model in which he assumed simultaneous dissolution of soil gas ( 1 kC = 100% modern and 613C = -14 °/oo) and calcite from erosion of older alluvial surface on the mountain flanks (11+C=‘25% modern and 51 3C a-3.8°/oo producing a <$13C in the ground- water system a-11°/oo. Based on the above information, a 513c plants correc tion factor of -12°/oo was chosen for this study. The corrected radiocarbon ages, which appear in Table 5.3, range from recent waters in Cane Spring and White Rock Spring to <30,400 years before present in Well C-1 . An additional factor to be considered in correction of the radiocarbon ages is that Well Ue15d and Well C-1 had tritium in them when sampled for this study. This indicates that mixing is taking place between "modern" and "ancient water in these aquifers. This infers that the water in these aquifers prior to "modern" dilution is actually older 87 than the calculated ages. Further discussion of the mixing phenomena is found in the Tritium Section. Rightmire (1967) observed a trend toward 5 ^ ratios in caliche deposits becoming more negative (lighter carbon) with increasing age of caliche deposits in Texas. He hypothesized that the variations were correlated with pedological-climatic changes over the past 25,000 years. He felt that the data indicated a decrease in the influence of plant-derived C02 toward the present. One might expect an inverse relationship as waters exchange carbonate with soil or limestone. No such trend was observed in samples from this study. 5.4 TRITIUM Ten wells were sampled for the purpose of this study. Enriched tritium analyses were run on all samples. Seven of the samples were enriched to detection limits of 2 TU. All of these samples had tritium levels of <2 TU. the remaining three samples were enriched to detection limits of 5 TU. One of these samples had <5 TU. Wells C-1 and Ue15d had tritium levels of 10.2 TU and 15.6 TU respectively. See Table 5.4 for analytical results. Any tritium level above approximately 5 TU indicates that post-bomb water has been introduced into the system. Several inferences can be made to explain the presence of 88 TABLE 5.4 TRITIUM RESULTS Sample Date Concentration Detection Location Sampled (TU) Limit (TU) Well J-13 6/21/82 <2. 2. ± 1 . Well A 6/22/82 <2. 2.± 1 . Well 2 6/22/82 <2. 2. ± 1 . Well 8 6/22/82 <2. 2.1 1 . Well U19c 6/22/82 <2. 2.±1. Well Ue16d 6/29/82 <2. 2. ± 1 . Watertown Well 3 7/29/82 <2. 2.±1. Well C-1 9/27/83 10.2 5.1 3. Well Ue15d 9/27/83 15.6 5.13. Well 4 9/27/83 . <5. 5.1 3. modern water from these wells. First, it might be inferred that these are samples of modern origin. Secondly, these samples might represent a mixture of modern water with dead water. The third possibility is that the samples might contain contamination from underground nuclear testing. The second scenario is preferred for the following reasons. Both wells produce from Paleozoic aquifers. Well C—1 is perforated in the Carrara Formation, a Cambrian lime stone unit. Well Ue15d is slotted in the Wood Canyon Formation, which includes Lower Cambrian fractured quartzite and dolomite. Radiocarbon dating gives respective uncor rected ages of >39,920 years and 22,728 years before present (Table 5.3) . Further evidence for mixing is found upon review of periodic data (U.S. EPA, 1981). During the period January 1973 through January 1981, tritium levels in Ue15d fluctu- • • • • • • • • m i i i i i i______I 0 5 10 15 20 25 30 35 CORRECTED RADIOCARBON AGES (Y B P X 1000) Figure 5.5 Tritium Versus Corrected Radiocarbon Ages 90 ated between <2 TU and 19 TU. During the period January 1973 through July 1981, tritium levels in Well C-1 fluctu ated between <2 TU and 30 TU. Although the tritium level in Well J-13 was below the detection limit of 2 TU on June 21, 1982, U.S. EPA (1981) data show fluctuations between 1 TU and 14 TU for the period July 1974 through August 1981. Appendix 5 provides a summary of these periodic tritium data, along with temperature and specific conductance data. Examination of these data appears to reinforce the apparent periodicity of the tritium samples and therefore evidence of mixing modern water with deep regional systems. Fluctuations in both specific conductance and temperature occur with a similar periodicity to that observed in the tritium samples. Although measurement errors might have occurred on occasion, simple measurement errors could not account for the periodicity of the temperature fluctuations. Such temperature fluctuations can be found in relatively shallow, local aquifers, but are not expected in deep regional systems. Similarly, specific conductance is expected to remain relatively constant in deep systems. Again, simple sampling or analytical error cannot account for observed temporal variations in the specific conduc tance. Nor would underground nuclear testing be expected to be the source of the observed temperature and specific con ductance fluctuations. The fluctuations in all three 91 parameters are most reasonably explained by the periodic introduction of modern water into the deep system. Mechanisms for tritium fluctuations have been explored. Hydraulic connection between aquifers is not only possible, evidence has been presented for such connection. Winograd (1962) introduced hydraulic evidence for the possibility of Cenozoic discharge into the Paleozoic aquifer in Yucca Flat. Grove et al. (1969) also refer to possible dilution of water in Paleozoic rocks by downward drainage through Quaternary and Tertiary rocks. Claassen (1983) proposed that overlying valley fill aquifers could have been recharged by snowmelt flowing in or near present-day Forty-mile Canyon stream channels. If this were to have occurred in the past, the possibility exists that this process might be continuing at the present during periods of runoff. The possibility of improperly cased wells also exists. Surface drainage along the well bore could contaminate the well in the immediate vicinity of the casing. However, this possibility seems unlikely since the volume of available modern water would be low with respect to the volume available in the aquifer, particularly qiven that these wells have been pumped moder ately to heavily. Appendix 6 provides a summary of tritium analyses con ducted by various investigators in and near the study area. Clebsch (1961) presents further evidence for mixina between perched and regional aquifers. Tritium analyses from his 92 study reveal tritium levels of 34 TU and 36 TU from Whiterock Spring and Tunnel U12e.05 respectively, both sources which are near the Rainier Mesa recharge area. In that study, Clebsch (1961) argues that the absence of phreatophytes and sprinq discharges infers that much of the perched water reaches the main aquifer. He further argues that any perched water would have to be in the system less than 40 years in order for a measurable tritium concentra tion to occur in the regional aquifer. Jacobson (1984) reported tritium concentrations of 30.6 TU and 27.3 TU in water samples from the Spring Mountains, Kyle Canyon vicinity. Both of these samples had recent radiocarbon age dates which is what would be expected in the recharge areas. Dinwiddie and Weir (1979) reported a tritium level of 37 TU from Well Uel6d in water produced from the interval 81-830 feet below land surface. Three possible hypotheses are offered for this anomaly. 1. The sample was jetted with air. This may have caused atmospheric contamination during sampling. 2. The sample may represent a composite of "modern" perched waters and "ancient" waters from the Paleozoic Tippipah Limestone. 3. The water in the section sampled may have been con taminated by releases from underground nuclear testing. 9 3 Evidence points to the last hypothesis as the most probable. This interval also had elevated levels of Gross « and Gross B radiation which may be products of nuclear testing. Dinwiddie and Weir (1979) also reported an elevated tritium concentration of 43 TU in Well Ue16f in the Paleozoic Eleana Formation interval 1293-1414 feet below land surface. The third explanation provided above may also apply in this instance since elevated Gross 11 and Gross B counts were also detected in this sample. Benson et al's. (1983) overall reported results ranged from < .6 TU to < 68 TU. However, it is impossible to make inferences about the presence or absence of recent water in the analyses from Well Ue-25b-1 dated 9/1/81 (<62 TU), Well USWH-5 dated 7/3/82 and 7/26/82 (both <62 TU), Well J-12 dated 3/26/71 (<68 TU) and Well J-13 dated 6/21/82 (<68 TU) because any tritium level above 5 TU would infer presence of modern water. Since steady state background tritium levels range from 5-20 TU with an increase between 1952 and 1963 of 2 to 3 orders of magnitude (Gat, 1980), tritium samples should be enriched and analyzed to levels of 2 to 5 TU in order to obtain meaningful results. Sample enrichment is particularily necessary in order to obtain meaningful temporal data, because subtle signals can be obscured in unenriched samples. 94 Benson et al. (1983) reported tritium concentrations of 11 TCJ's in two separate samples from Well Ue-29a-2 located in Forty-Mile Wash. Claassen (1983) hypothesized recharge during runoff events in the vicinity of Forty-Mile Canyon during past pluvial periods. The presence of tritium in those samples may indicate that such recharge may not only have occurred during past pluvial events, but may still be continuing today. Benson et als' (1983) radiocarbon results for these two samples appears to contradict the tritium data, having uncorrected apparent radiocarbon ages of 3,800 years before present and 4,100 years before present or 62.3 and 60 percent modern radiocarbon, respectively. The most likely explanation for this anomaly is the presence of both recent and ancient waters; e.g. mixing of the two. 5.5 STABLE ISOTOPE CHEMISTRY Samples from thirteen wells within the study area were analyzed for the stable isotope ratios of <5180 and <5d in k order to aid in fingerprinting the water. Results of <5180 and <5D analyses appear in Table 5.5. Additional analyses (Jacobson, 1984; Winograd and Pearson, 1976; Dinwiddie and Weir, 1979; Benson et al., 1983; Claassen, 1983) were incorporated into this study (Appendix 7) . 95 TABLE 5.5 STABLE ISOTOPE RESULTS Date Sample Site Sampled <$1 80 ±. 3 °/oo <$D ±1 °/oo Well J-13 6/21/82 -12.7 - 96 Test Well A 6/22/82 -13.0 -107 Test Well 2 6/22/82 -13.2 -102 Well U1 9c 6/22/82 -14.1 -109 Well 8 6/22/82 -12.9 -101 Well Ue 1 6d 6/29/82 -12.4 - 96 Well Ue 1 6d 5/25/82 -13.5 -106 Army Well 1 6/21/82 -13.1 - 99 Well 5c 6/21/82 -13.4 -108 Well C 6/22/82 -13.3 -106 Well 4 9/27/83 -12.6 - 94 Well C-1 9/27/83 -12.8 -102 1 VO Well Ue15d 9/27/83 -14.1 VO -14.2 1 5d values for samples collected for this study ranged from -94 °/oo to -109 °/oo. 5D values for all analyses ranged from -93 °/oo to -109 °/oo. «180 values for samples from this investigation ranged from -12.4 °/oo to -14.2 °/oo. 6180 values for all analyses considered ranged from -11.5°/oo to -14.9°/oo. Results of analyses from this study are plotted on Figure 5.6. The analytical uncertainty for these data was 96 + • 3 °/oo for ^ 0 and + 1 °/oo for ^D. With the excep tion of one sample, from Well Ue15d, the data closely paralleled the Craig Meteoric Water Line of Sd = 8 6 1 80 + 10. The equation developed for these data was <5d = 9.2 <518o + 18.4 with a correlation coefficient of .83 using a least squares linear regression. These samples show a shift which indicates recharge at mid to high elevations or during precipitation events ranging from snowfall to rainfall. Other researchers in southern Nevada near the NTS have obtained similar results. Hess (1986) has developed a meteoric water line for southern Nevada whch closely parallels the Craig Meteoric Water Line. There is a slight evaporative shift in the lighter samples (Figure 5.6). For instance, the water from Well 5C appears to have an evaporative shift from recharge such as that found in the sample from Ul9c. Water from Well A appears to continue along the same slope indicating an even greater evaporative shift. Wells 4 and J-13 appear to have been recharged at a relatively lower elevation or during summer precipitation and appear to have undergone little or no evaporation. Well Ue16d was sampled on two separate dates, May 25, 1982, and June 29, 1982. These samples show a shift which appears to indicate recharge having come from different elevations, mid-elevation similar to that of Well 4 and Well s d(SMOW)%© F igure 5.6Oxygen Versus HydrogenIsotopes from this Study 98 J-13 and from higher elevation or perhaps from seasonally variable precipitation events. Well Ue15d has an unexpected deuterium shift. An obvious explanation is that this may be due to analytical error. It is felt that this water should be resampled and a comparison made to evaluate whether these are valid data. The remainder of the data are clustered tightly in the mid to high elevation recharge range, and show insignificant evaporation effects. Similar trends are found in overall results of all available analyses from in and near NTS (Figure 5.7). The elevation shift for all samples is nearly identical to the shift found in the samples from this study. However, there is a more pronounced range in overall <5 0 values. Two samples in particular differ from the overall trend. The sample from Ue16f had reported values of <$d = -14.9 °/oo and So = -13.5 and 61 80 = -106 °/oo in two separate samples. Since Ue16f penetrates the same aquifers as Ue16d, it is felt that the reported results for Ue16f may be in error. The differences in the two samples from Ue16d may be explained by the fact that the well is producing from both the Tippipah and the Eleana formations. The recharge sources of the water in these formations may vary. The s D(SMOW)%o - 0 8 Figure 5.7Oxygen Versus HydrogenIsotopes from In andHear NTS I 100 amount of pumping prior to sampling may have had an effect on which formation the samples were drawn from. The sample from Tule Spring Well had values of <5d = -11.5 °/oo and <518o = -100 °/oo. This appears to be an evaporative shift. However, this data point- is not shown in Figure 5.7, since the well is located a considerable distance from other sampling points. Comparison of this data point with others similarly located would be more instructive than to overemphasize its significance with respect to regional flow on the NTS. 101 > 6.0 CONCLUSION 6.1 OVERVIEW Regional groundwater flow is from the north and north east of the study area toward the proposed regional dis charge area near Ash Meadows in the Amargosa Desert. Inconsistencies exist between the proposed regional flow path and the various geochemical parameters examined during the course of this study (Figure 6.1). In the western portion of the study area the proposed regional flow is from the northwest to the south and southwest. Specific conductance increases from 154 umhos/cm in Well U19c in the north to 190 Mmhos/cm in Well 8 to 276 umhos/cm in Well j-13, the southwesterly most sampling point. Specific conductance is expected to increase as residence time along the flow path increases, therefore, this trend corresponds to expected changes along the flow path. However, the radiocarbon data show the opposite trend from that which would be expected. Uncorrected radiocarbon ages show that the water in Well U19c is 21,757 years old, the water in Well 8 is 11,396 years old, and the water in Well J-13 is 10,150 years old. Stable isotope data range from Sd = -109 °/oo and S18o = -14.1 °/oo in Well U19c to <$d = -96 °/oo and S180 = -12.7 °/oo in Well J-13, with Well 8 having intermediate values of Sd = -101 °/oo and S18o = -12.9 °/oo. F gr 61 Comparison 6.1 igure CofKCl.d An. (VBP x 10O0I H.«d III xbox. M8L A 10001 I Sp.clllc Conducl.nc. 100| fPrmtr Eautd n hs Study this in Evaluated ofParameters 103 Similar inconsistencies occur in the eastern portion of the study area. The proposed regional groundwater flow path is generally from the east and northeast toward the south west . Specific conductance in Well Ue15d is 682 umhos/cm, increasing to 1050 umhos/cm and 1082 umhos/cm in Wells C and C-1 respectively, and then decreasing to 420 umhos/cm in Well 4 and 532 umhos/cm in Army Well 1. Again, the uncor rected radiocarbon ages fluctuate alonq the proposed flow path with water from Well Ue15d dated at 22,730 years before present, Well C-1 aqed > 39,920 years before present and Well 4 aged 13,390 years before present. 518o data for these wells ranged from -14.1 °/oo in Well Ue15d to -12.8 °/oo and -12.6 °/oo in Wells C-1 and 4, respectively. Respective <$D ratios were -99 °/oo, 102 °/oo, and -94 °/oo. Tritium was below detection limits in eight of the ten samples analyzed for this study. Wells C-1 and Ue15d had levels of 10.2 and 15.6 TU respectively. This is an indi cation that younq water was present in samples which had ancient radiocarbon ages (Figure 6.2). As shown m Appendix 5, temporal fluctuations in tritium, specific conductance, and temperature have occurred in Wells Ue15d, C-1, and J-13 during the years 1973 through 1981 for which analyses were available. Claassen (1973) shows similar variations with time. 104 The results of this study lead to the following con clusions . 1. Major ion, stable isotope, and radioisotope analyses all indicate that mixing is taking place among the aquifers within the study area. Such mixing may occur by any or all of the mechanisms stated below: a. Mixing may occur by vertical flow where local ized potentiometric head differences occur (Blankennaael and Weir, 1973; Dinwiddie and Weir, 1979). b. Migration from one aquifer to another may occur where lateral discontinuities exist (Winograd and Doty, 1980). c. Migration through open well bores may occur. Well construction data obtained from Fenix and Scisson, Inc. and other reports (Dinwiddie and Weir, 1979; Moore, 1962; Blankennagel and Weir, 1973) tend to show no cement plugs isolating aquifers in normal NTS well construction. Several of the wells sampled durina the course of this study produce from more than one inter val (Appendix 4). 2. Major ion chemistry, as shown in Section 6.2, indicates three major water types, sodium bicar bonate dominant, calcium bicarbonate dominant, and 105 i sodium-calcium bicarbonate waters which indicates mixing of the first two types. 3. Temporal fluctuations in major ion chemistry as well as temperature and tritium occur in samples from wells which produce from deep aquifers. Discussion of possible explanations for this fluctuation follows: a. Sampling errors - The possibility exists that either contamination of samples occurred or that sampling locations were improperly identi fied throughout the period during which samples have been analyzed in the study area. Atmos pheric contamination of samples might account for tritium fluctuations, but would not account for fluctuations in major ion chemistry. Temperatures are obtained at the well head. Fluctuations in temperature could not have been caused by contamination subsequent to sample collection. In the case of the samples obtained for this study, particular care was taken to avoid contamination as outlined in the Field Methods section. Improper identification of samples seems unlikely. EPA personnel had a set sampling route. Although it is not impossible that labeling errors or misidentification of samples 106 may have occurred on occasion, the presence of tritium from any well would remain unexplained. Samples from this study were positively identi fied . b. Analytical errors - The possibility exists that analytical errors were made on occasion. Arguments, similar to those used in (a) above, are used against the probability of analytical errors explaining the observed fluctuations. In addition, it should be noted that fluctuations have been shown in two investiga tions in addition to this study (Claassen, 1973; U.S. EPA, 1981). c. Fluctuations are real - The third possibility is that the fluctuations are real. If the assumption is made that temporal fluctuations occur in deep regional aguifers a mechanism for this phenomenon must be found. Two possible explanations follow. Precipitation events may cause drainage from the surface down the well bore. Examina tion of well records shows that Well Ue15d is cemented from the surface to 1735 feet below land surface. Well C-1 is cemented to 914 feet below land surface. Well J-13 is cemented from the surface to 435 feet below land surface. It would appear doubtful that the well bore could act as a conduit in these wells. In addition, these wells were pumped until temperatures were stabilized before samples were taken for this study. Under these circumstances it would appear unlikely that localized drainage could account for the observed fluctuations. Precipitation is being rapidly transported from the surface to the saturated zone and then to the proximity of the deeper aquifers. As pointed out in the Climate Section, the annual evapotranspiration potential in the study area is up to a magnitude higher than the average annual precipitation. As further pointed out, precipitation comes as snowfall or as intense summer thundershowers. Winograd and Thordarson (1975) have characterized the water movement through the lava-flow aquifer and welded-tuff aquifer as being controlled by primary and secondary fractures (Appendix 1). Field obser vation of drainage through fractures was made on September 27, 1983, on Pahute and Rainier Mesas. Intense thundershowers had reportedly passed through the area on September 25, 1983. In the depression from which soil sample CJCAL-4 was taken where the soil cover was 108 shallow, 1-4 inches, and relatively sandy, drainage had occurred. In a swale less than a quarter mile away where the soil profile was up to a foot deep and apparently more clay-rich, there was water left standing. These depressions where both underlain by highly fractured welded tuff. Further observa tions of drainage through ash-flow tuff was made at a road cut on Pahute Mesa on the same day. Both vertical and horizontal fractures were prominant in this unit. Rapid seepage was observed from both the horizontal and vertical fractures. These observations have lead to the conclusion that considerable infiltration can occur rapidly through fractured bed rock where soil profiles are such that rapid infiltration can take place. These observations appear to provide a mechanism for rapid movement of recharge to deeper aquifers. For example, producing aquifers in Wells J—13, C—1, and Ue15d are all overlain by tuffaceous units which could act as conduits through which fracture flow could occur. This recharge mechanism appears to be further supported by the stable isotopic evi- 109 dence which indicates that little evaporation has taken place. 4. Radiocarbon age corrections are based upon 613c data obtained by sampling various media with which reaional ground water might have come in contact. Soil gas has been thought to be the primary source of carbonate dilution within the soil zone. However, results of this study indicate that 613c in qround water rapidly approaches -12.0°/oo, considerably heavier than the -18.7°/oo to —24.2°/oo found in soil gas within the study area. This has led to a belief that use of 613c ratios for the term 513C plants should not be based upon soil aas measurements alone. 613c , plants might more appropriately be referred to as the 613c of the recharge zone, since it appears to be representative of the entire recharge environment, not only that of vegetation within that zone. The correction factors used in this study based upon site specific measurements are -12.0°/oo for 6l3cplants and 0°/°o for 5l3crock* 6.2 PROPOSALS FOR FURTHER STUDY The results of this study point to several areas of inadequate or incomplete data. Following are several recom- 110 mendations for future work which might further the under standing of this complex flow system. 1. Whenever possible, complete hydrologic profile should be made as wells and test holes are drilled. Minimum information to be obtained should include hydraulic data, geochemical data, stable and radio isotope data, and lithologic data. 2. A systematic temporal sampling program should be established for specified wells to further under standing of temporal fluctuations within the regional flow system. 3. New hydrologic data should be incorporated as available. Sampling should be extended to points beyond the boundaries of the NTS and to new wells within the boundaries of the NTS as they are drilled. 4. A drilling program which would provide sampling points where data are currently unavailable should be instituted. 5. Further mechanistic studies of carbonate dissolu tion processes should be undertaken to provide a clearer picture of appropriate <513C correction factors for radiocarbon dating. 6. Further studies of both saturated and unsaturated flow through fractured media should be conducted in—situ in rock units found on the NTS. Ill 13 10 ^ C content of caliche samples is variable between samples and within individual samples. A con trolled mechanistic study might provide a clearer understanding of the solution—dissolution processes which lead to the variation in 513c content. 112 REFERENCES Allaway, W.G., C.B. Osmond, J.H. Troughton, 1974, Environ mental regulation of qrowth, photosynthetic pathway and carbon isotope discrimination ratio in plants capable of crassulacean acid metabolism, in Mechanisms of regu lation of plant growth: Royal Soc. of New Zealand, Bull. 12, pp. 195-202. Baertschi, P., 1941, Relative abundances of oxygen and car bon isotopes in carbonate rocks: Nature, v. 168, pp. 288-289. Beatley, J.C., 1974, Effects of rainfall and temperature on the distributioin and behavior of Larrea tridentata: Ecology, Vol. 44, pp. 245-261. 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Maximum Thickneaa Hydrogeologlc Water-bearing Characteristic* and extent of Saturation3 Major Lithology ( foot) Unit System Stratigraphic Unit fflcient of trenemieslbl 11ty ranges Tro* 1,000 to Alluvial fan, fluvial, 2,000 Valley-rill Quaternary and Holocene, Valley rill 35,000 gpd par ft| average coefficient of lntaratltial fanglomerate , lakebed, aquifer Tertiary | Plelatocene, permeability ranges Tor > to 70 tpd per aq ft| eatu- and mudflow depoalta and ratad only beneath atructurally doepaat parta of Yucca P Hoc one Flat and Frenchman Flat. Wator movement controlled by primary (cooling) and aec- Baaalt flows, dense and Baaalt of Kiwi Heea ondary fractures and poaalbly by rubble between flows; vn alcular______2 ,00 0 Lava-flow intercryatalline porosity and permeability negligible; Rhyolite of Shoshone Rhyolite flows qulfer estimated coefficient of trenemiseibility rangea from Mountain______500 to 10,000 gpd per ft; aaturated only beneath east- Basalt of Skull Baaalt flowa central JackBUO Flate.______—— AeJi-flow tuff, moderately Ammonia Tanks Water rovarwint controlled by primary (cooling) and sec to dnnaaly wel(Wd| thin Himbar ondary Joints in densely welded part or ash-flow tuff| aah-fall tuff at beeo coo fflcient of tranamlaaibillty rangaa from 100 to Aeli-flow tuff, nonweldod Rainier Hoaa 100,00 gpd per ft| lntercryetalllno porosity and ash- to densely welded; thin Hember flow tuff, whoro present, haa relatively high lntoratl- anh-rr11 tuff at bneo Hoi dnd-tuf f tlal porosity (35-50 percent) and modest permeability Aeh-flow tuff, nonwoldod 300-350 aquifer live Canyon (2 g)d per eq ft) and may act as leaky aquitard; satu to densely welcted; thin Member rated only beneath atructurally deepest parts of Yucce, ash-fall tuff at base Frenchman and Jackass Flats. Tcnopah Spring Aeh-flow tuff, nonweldod Hcmber to densely welded; thin aah-f a 11 tuTf at base Coefficient of tranemlasibility rangea from 200 to Ash-fall turr and fluvially 1,000 odded-tuff Bedded tuff 1,000 gpd per ft; saturated only beneath structurally reworked tuff aquifer (Informal uilt) deepest parta of Yucca Flat, Frenchman riat and Jackaaa Flatai occur* locally below ash-flow tuff members of Paintbrush Tufr end below Crouea Canyon Member of Indian irall Formation. Water movement controlled by poorly connected fractures; Lava-flow and interflow Lava-flow interstitial porosity and permeability neqlialblei co turr wid breccia; locally aquitard efficient of tranamlaaibillty estimated leas than 500 hydrothermally altered gpd per ft; contains minor perched water in foothills between Frenchman flat and Jackaaa Flata. Wahmonle Formation Aah-fal 1 tuff, tuffaceoue 1,700 aandatone, and tuff brec cia, all lntorboddcd raccia flow, lithlc brec 2,00 0 cia and tuff breccia, in- tsrbadded with aah-fall Salyar Formation tuff, aandatone, ailt- Tertiary atone, clayatona - liL Grouna Canyon Aeh-flow tuff, densely Member wo lded______Tub Spring Aeh-flow tuff, non welded Ho* be r to welded ______Local informal Aeh-flow tuff, nonweldad to 2,00 0 oofficlsnt of tranamlsslbllity rangea from 100 to 200 uilta semi-welded aeh-flow tuff tuffaceoue aandatone, gpd par ft; Interstitial porosity is as hltfi aa 40 per cent, but interstitial permeability is negligible (6x alltatono, and clayatone all maaaivaly altered to IQ3 to 6xlQ5 gpd por aq rt) | owing to poor hydraulic connection of fractures, interstitial permeability prob zeolite or clay minerals ably controls regional groundwater movement; porches locally, minor welded tuff Turr minor quwititioa of water beneath foothills flanking near base; minor rhyolite aquitard 'alleys; Tully aaturated only beneath structurally deep and basalt ______est parte or Yucca Flat, Frenchman Flat, -nd -iiL Flatai G rou n a Canyon and Tub Soring ttaab.F. »r Indian R h yo lite flo -e and R h o llt e , non we 1 ded and Troll Formation may locally bo aquifers In northern 1—*- — l Turr of Cratar flat Anh-riow tuff, nonweldod to partly welded, ln- terbedded, with ash-fall tuff _____ Miocene 1,400 and Rocks of Pavlta Spring Tuffaceoua sandstone and Oligocene si ltstone claystonej freshwater limestone and conglomerate Oligocene Horae Spring formation Freshwater limestone, 1,000 conglomerate, tuff (A minor Complexly fractured but nearly lmpormeabla. Cretaceous to Granitic stocks C r and lor 1 to and quartz aquitard) Peraian monzonite In atocka , dikes , and allls______3,600 Upper Complexly fractured aquiferi coefficient of tranamieai- Permian and Tlpplpah Limestone Limestone carbonate b111ty estimated in range from 1,000 to 100,000 gpd par Pennaylvanlan aquifer ft; intarcryatalline poroalty and permeability negligi ble; saturated only beneath western ono-thlrd of Yucca Flat. Complexly fractured but nearly impermeable; coefficient Hlsaleaipplan Cleans Formation Argillite, quartzite, con 7,900 Upper or tranamlaaibillty estimated lass than 300 gpd par ft; and Devonian glomerate, conglomerate clastic limestone aquitard lntaratltial permeability negligible but owing to poor hydraulic connactlon of fraaturee probably controls groundwatar movement; aaturated only beneath waatern Yucca Flat and Jackaaa Flats, ______ Upper Davila Cats Limestone Limestone, diloalte, > 1,300 - 7 minor quartzite______> 1.325 Kiddle Nevada Formation 1,413 Devonian and Undifferentiated Silurian Uppsr Ely Sprlnoe Dolomite Eureka frjertzlta Quertzlta minor limestone 340 Complexly fractured aquifer which auppUea major aprlnga Limestone and silty 1,330 8 Antelope Valley throughout eastern Nevada; coefficient of trenamlaeibll- Llmqitone l imestone Lowor 1ty rangea from 1,000 to 1,100,000 gpd par rt| inter- Nlnemlla Formation Clayatone and llmeatona. Inter be dJou carbonate crystalline poroalty and pormeablUty negligible; solu tion caverns era present locally but regional ground l lmeatone > 900 aquifer water movement la controlled by fracture tranamlaalbll- Nopah Formation Dolomite, limestone 1,070 ty| aaturated beneath much of the study area. Smoky Member Hslfplnt Member Llmeatona, dolomite, el. Upper ty limestone 715 Dunderberg Shale Shale, minor llmaatone 225 Member______Bonanza King Formation Limestone, dolomite Banded Mountain minor slltstone 2,440 Hw"boc Papooaa Lake Member Llmaatone, dolomite minor alltntone____ 2.160 Carrara Formation Slltstone, limestone, ln- 1,050 terbedded. Upper 1050 ft predominantly llmoatone| lower 950 ft predominant ly slltstone Comp laxly fractured but nearly impermeable; supplies no Zabrlekle Quartzite Quartzite major aprlnga; coefficient of tranamlaaibillty laaa than Wood Canyon Formation Quartzite, alltatono, 2,285 Lower minor dolomite______clastic 1,000 gpd per ft| lntaratltial poroalty and permeability la negligible, but probably controls raglonal ground- Stir 1 lnq QiartzUe_ Quartzite, elltetnne 3.400 squltard(3) 3,200 water noveiwnt owing to poor hydraulic connactlon of Precenbrian Jolmnla Formation Quartzite, sandstone , a 1 It atom , minor lime- fractures; aaturated beneath moat of study area. atoi'a ami dolomite____ lCo.rricl.nt or lr.n..l..lblllty h> th. unit, gallon. por d.y por foot (gpd por rt) uldth of .qulferi co.rriciont or portability has tho unit, gallon, par d.y p.r square foot (gpd per aq ft) of aquifer. 120 2Iha thro. Hloceno wqu.no.. occur In ..p.r.U p.rt. or tl. t.glon. Ago corr.l.tlon. b.t.aon tho. u . uncrt.ln. Th.y M. placid v.rtlc.lly In tabl. to .p.w. llh. Noond.y(7) Dolo.lt., ohtcb undorll.. tin Johnnl. ror..tlon, 1. con.ldor.d p.rt of tho lont clootie .qult.nl. ut. 1 2 Goodwin Formation 121 eno W • Well U19c Watertown 3 • ■ CJCAL3-1 a NTS Rx1* * 2* 5 Nm tq T S -1ii« 1 6 J!.NTS" ^ flML Deep 103 L •Well Ue15d n riK 105CJCAL6-1 0White Rock Sp C JC A L5 -1,2 ■ aRM T deeQf Te| • Well 8 • Test Well 2 □ RMT 2 16d1,2,3 ••well Ue1Qd ■ U3C2 ■ N T S - 111 • Test Well A ■NTS-109 YL« TWC3 i # Weil C-1 CJCAL1-2■ ‘ Well < Well 4 • ■CJCAL2-2 ► Well J-13 QCane Sp ■ FF Well 5c 4 LEGEND • RADIOCARBON, TRITIUM. STABLE. MAJOR ION. - WELL WATER O RAOIOCARBON - SPRING WATER ▲ STABLE. MAJOR ION - WILL WATER ■ J l»C - OTHER MEDIA a j Q CARBONATE - OTHER MEDIA Ar1,2,3 — STUOY AREA BOUNOARY 8 C A L E o 3 0 .0 0 0 It APPENDIX 2 LOCATIONS OF NTS SAMPLING SITES 122 leno 14 APPENDIX 3. 513C RESULTS 5 1 3C Sample # Location Type (°/oo) YL Yucca Lake Playa Playa -1.0 -1.3 CJCAL8 Pahute Mesa Soil -3.8 FF Frenchman Flat Playa Playa -0.4 1 6d 1 Well Ue16d - 1122- Limestone core -2.5 1336 ft interval 1 6d2 Well Ue16d - 1 336- Limestone core + 1.1 1343 ft interval 1 6d3 Well Ue16d - 890-900 Limestone core + 4.1 *ft interval Ar 1 Army Well 1 - 1674— Limestone/ -1 . 1 1684 ft interval dolomite core Ar2 Army Well 2 - 982- Limestone/ -1 .8 1108 ft interval dolomite core Ar3 Army Well 1 - 1826— Limestone core -1 .6 1875 ft interval TWC3 Test Well C - 1331— Limestone core -1 .9 1339 ft interval U3C2 U3CN-5 - 2957-2960 Limestone/ + 0.1 ft interval quartzite core CJCAL1-2 C P Hogback Caliche -7.7 CJCAL2-2 Cane Spring Wash Caliche -6.5 -7.5 CJCAL3-1 Rainier Mesa Caliche CJCAL5-1 Rainier Mesa Caliche -7.9 -5.8 CJCAL5-2 Rainier Mesa Caliche -4.6 CJCAL6-1 Rainier Mesa Caliche -5.6 CJCAL7-2 Pahute Mesa Caliche -7.1 CJCAL9-2 Head of Silent Caliche Canyon 123 APPENDIX 3. (Continued) 613C Sample # Location Type (°/oo) RML Deep L RML Deep L Soil water -18.0 NTS-101 PT-3 Soil gas -18.8 NTS-103 RT-1 Soil gas -18.7 NTS-109 ST-1 Soil gas -24.2 NTS—111 TT-2 Soil gas -19.7 NTS— 116 RML Deep L Soil gas -21.2 NTS-88 Well J-13 Well water - 7.8 NTS-90 Test Well A Well water - 8.9 NTS-91 Test Well 2 Well water -1 1 .2 NTS-93 U1 9c Well water -1 1 .6 NTS-94 Well8 Well water -11.3 NTS-95 Ue 1 6d Well water - 8.7 NTS-99 Watertown Well 3 Well water - 7.1 CJ-4 Well 4 Well water -10.9 CJC-1 Well C-1 Well water - 3.8 CJ-15d Well Ue15d Well water - 4.1 NTS-104 Cane Spring Spring water - 8.7 NTS-105 White Rock Spring Spring water -11.2 RESEARCH INSTITUTE SAMPLING SITES APPENDIX 4. AQUIFER CHARACTERISTICS - DESERT Produci ng Land Surface Depth to Static Water Level Interva 1 E1evat i on Reference We 1 1 Des i gnat i on/ (ft below 1.s.) (ft above MSL) (ft below 1.s.) Nevada Coordinates Water Bearing Formation 786-1050 Moore (1962), 3154 787 Cambrian Windfall formation, Claassen (1972), Army Well 1 N670902, E684772 Smokey member 1360-1946 Fenix & Scisson Undifferentiated Paleozoic (1972) carbonates Claassen (1972), 690 800-1200 Tertiary and Quaternary 3081 Wei 1 5C Fenix & Scisson N742860, E705888 a 1 luv i urn (1972) Thordarson 925,9 1301-1386 Tertiary Paintbrush Tuff, 3218 (1983), Well J-13 Topopah Spring Member Claassen (1972), N749209, E579651 929.5 2690-3312 Tertiary Crater Flat Tuff, Fenix & Scisson Tram Un it (1974) Garber & Thordar 1544 1542-1620 Cambrian Carrara limestone 3921 son (1962), Test Wei 1 C N790083, E692061 Claassen (1972) Price & Thordar 1604 1604-1870 Tertiary and Quaternary 4006 Test Well A son (1961), N833000, E684000 a 1 1uv i um Fenix & Scisson (1972), Claassen (1972) Claassen (1972), 2416 1690-2560 Tertiary bedded and reworked 4470 Fenix & Scisson Test Wei 1 2 2416 2560-3422 N880000, E668720 tuff (no date) Ordovician Pogonip Group do 1omi te leno APPENDIX 4. (Continued) Land Surface Depth to Static Producing Water Level Interva 1 Well Designation/ El1evat i on (ft below l.s .) (ft below l.s .) Reference Nevada Coordinates Water Bearing Formation (ft above MSL) Claassen (1972), Test Wei 1 8 Tertiary Indian Trail, Split 5695 1068 1290-2010 Fenix & Scisson N879468, E609999 Ridge Member, vitrophyric (no date) ash-flow tuff and lava flow 2031-5490 Tertiary zeolitized bedded and 1088 reworked tuff 2345 2319-4231 Blankennagel & Ue-19c Tertiary Paintbrush Tuff, 7033 Weir (1972) N917000, E601027 Deadhorse Flat Tuff, Belted Range Tuff. 754.6 1309-1526 Dinwiddie & Weir Ue16d Paleozoic Permian (?) and Penn 4684.4 (1979) N844878, E646567 sylvanian Tippipah l.s. with interbedded argillite, s ilt- stone and sandstone 2116-2999 Paleozoic Mississippian, Eleana, 380.6 unit J, alternating quartzite and argi 1 1 ite 1 106.8 7-371 Schoff & Moore Watertown Well 3 Tertiary and Quaternary 4446 (1964) N914990, E742272 a 1 luv i um. 1542 1536-1650 Fenix & Scisson Wei 1 C-l Cambrian Carrara limestone 3921 (no date) N790011, E692132 941 941-1479 Fenix & Scisson Wei 1 4 Tertiary Piapi Canyon Group, 3601.58 (1981) N785038, E687934 Timber Mountain tuff, Rainier Mesa Member 66 7 1784-6001 Fenix & Scisson Well Ue15d Lower Cambrian, Wood Canyon, 4586 (no date) N895709, E682084 fractured quartzite and dolo- mite leno 126 leno APPENDIX 5. SUMMARY OF EPA ANALYSES 14 Sampling Temperature Spec. Cond. Concentration Well * Date (°C) (u) 3H (TU) Ue 1 5d 1/18/73 34 600 < 2 . 7/5/73 37 610 < 2 . 1/8/74 36 590 < 4. 7/9/74 36 625 < 3. 1/15/75 35 600 < 2 . 7/8/75 36 750 < 2 . 1/8/76 35 780 < 2 . 7/12/76 36 580 < 2 . 1/4/77 31 625 14. 6/8/77 32 1 000 < 3. 2/2/78 34 640 4. 7/19/78 38 650 .6 2/4/80 25 700 2 . 7/10/80 37 700 3. 1/6/81 27 725 19. • 30 . C-1 1/19/73 36 900 7/2/73 36 1075 31 . 1/8/74 38 875 12. 7/10/74 37 860 5. 1/14/75 36 900 22 . 16. 7/8/75 38 1115 1/8/76 37 1 150 14. 38 760 10 . 7/13/76 7. 1/4/77 38 950 6 . 6/13/77 38 1 180 37 1260 7. 2/2/78 3 . 7/19/78 34 1060 4. 2/22/79 37 1140 36 850 40 . 2/6/80 1 . 7/9/80 3 1 1060 32 850 3 . 1/31/81 3. 7/21/81 38 1 200 < 2. 265 J-13 7/1174 32 < 2. 8/13/74 32 260 310 < 2. 7/9/75 32 220 < 3. 8/13/75 32 2. 9/10/75 31 285 280 < 2 . 10/8/75 < 2. 1/7/76 270 240 < 2 . 2/4/76 256 < 2 . 3/3/76 300 < 4. 4/7/76 245 24. 5/12/76 340 < 2 . 6/1/76 310 < 2 . 7/14/76 127 leno 14 APPENDIX 5. (Continued) Sampling Temperature Spec. Cond. Concentration Well Date (°C) (w) 3H (TU) J-1 3 8/2/76 32 280 < 2. 9/8/76 32 250 < 2. 10/13/76 32 255 14. 11/3/76 32 • 275 3. 12/1/76 32 280 < 2. 1/5/77 32 275 < 3. 2/2/77 32 340 < 2. 3/2/77 31 280 < 3. 4/20/77 25 680 < 2. 5/11/77 28 320 < 2. 6/13/77 32 350 < 2. 7/7/77 32 290 < 2. 8/10/77 31 280 < 3. 9/7/77 30 320 < 2. 11/4/77 32 280 < 2. 12/7/77 31 280 < 2. 3/8/78 32.5 180 1 . 4/4/78 31 280 1 . 5/4/78 32 360 1 . 7/18/78 31 300 1 . 8/1/78 31 450 4. 9/19/78 31 200 1 . 10/19/78 31 225 1 . 11/21/78 29 240 1 . 12/19/78 31 225 3. 2/2/79 31 280 4 . 3/27/79 30 270 1 1 . 7/25/79 33 330 5. 8/24/79 32 320 1 . 10/23/79 31 315 < 1 . 12/4/79 31 265 < 1 . 1/17/80 31 270 3. 3/12/80 31 260 < 4. 1 . 5/6/80 28 320 8. 5/29/80 31 240 < 3. 6/26/80 32 280 7/10/80 32 255 < 3. 32 320 < 2. 9/10/80 9. 10/29/80 32 300 < 2. 11/21/80 32 325 1 1 . 12/22/80 32 275 32 245 < 4. 1/22/81 1 . 2/12/81 32 240 32 230 4. 3/4/81 < 3. 4/29/81 32.5 380 31 280 1 . 5/20/81 1 . 6/30/81 33 335 32 290 1 . 7/22/81 1 . 8/20/81' 32 325 APPENDIX 6. TRITIUM ANALYSES Sampling Concentration Sampling Interval Analysis Sample Sources (T.U.) Location Date (ft below 1.s . ) <2 Composite Current Investigation Well J-13 6/21/82 <68 3/26/71 Composite Benson, et al. (1983) Composite Thordarson (1983) 6 5/25/64 <68 Composite Thordarson (1983) 4/21/69 See Appendix 5 various Composite U.S. EPA (1981) Current Investigation <2 Well A 6/22/82 Composite Current Investigation <2 Well 2 6/22/82 Composite Current Investigation <2 Well 8 6/22/82 Composite Current Investiaation <2 Well U19c 6/22/82 Composite <2 Composite Current Investigation Well Ue16d 6/24/82 37 5/23/77 81-830 Dinwiddie & Wier (1979) 81-2119 Dinwiddie & Wier (1979) <31 6/14/77 <31 6/19/77 1534-1750 Dinwiddie & Wier (1979) Current Investigation <2 Watertown Well 3 7/29/82 Composite Current Investigation 10.2 Well C-1 9/27/83 Composite <• 1 12/19/61 Composite Winograd & Pearson (1976 ) See Appendix 5 various Composite U.S. EPA (1981) 15.6 Composite Current Investigation Well Ue15d 9/27/83 See Appendix 5 various Composite U.S. EPA (1981) NJ> 00 ouai; APPENDIX 6. (Continued) Sampling Concentrat: Sampling Interval Analysis Sample s.) Sources (T.U.) Location Date (ft below 1. <4 Composite Current Investigation Well 4 9/27/83 <.5 Composite Clebsch (1961) Well 3 8/7/58 <.5 4/21/59 Composite Clebsch (1961) Clebsch (1961) <.5 Well 5A 2/26/59 Composite Clebsch (1961) <.5 Well 5C 2/26/59 Composite Composite Clebsch (1961) <.5 Well J-11 8/7/58 <.5 4/21/59 Composite Clebsch (1961) Clebsch (1961) <.5 Well 15S/49-14aal 1/28/59 Composite <62 Composite Benson et al. (1983) Well Ue-25b-1 9/1/81 (1983) <.6 7/20/82 2831-2871 Benson et al. Composite Benson et al. ( 1983) 11 Well Ue-29a-2 1/8/82 (1983) 1 1 1/15/82 Composite Benson et al. Benson et al. (1983) <6 USWH-1 10/20/80 1877-2254 2254-6001 Benson et al. (1983) <6 Benson et al. ( 1983) <3 USWH-4 5/17/82 Composite <62 Composite Benson et al. (1983) USWH-5 7/3/82 ( 1983) <62 7/26/82 Composite Benson et al. M ouaj APPENDIX 6. (Continued) Sampling Concentration Sampling Interval Analysis Sample Sources (T.U.) Location Date (ft below l.s.) Benson et al. (1983) <3 USWH-6 10/16/82 Composite Benson et al. (1983) <6 USWVH-1 2/11/81 Composite Composite Benson et al. (1983) <68 Well J-12 3/26/71 <3 various Composite U.S. EPA (1981) 680-840 Dinwiddie & Weir (1979) <31 Well Ue16f 8/20/77 43 9/25/77 1293-1414 Dinwiddie & Weir (1979) Composite Winograd & Pearson (1976) 0.2 Army Well 1 12/11/74 0.2 3/7/75 Composite Winograd & Pearson (1976) Corn Creek Ranch Winograd & Pearson (1976) 0.0 Well 3/13/75 Composite Jacobson, R.L. (1984) 30 .6 Rainbow Spring 1983 7182* Jacobson, R.L. (1984) 27.3 Highway Main Well 1983 6772* reported depths are in feet below 1 * elevation in feet above sea level, all other surface. oCO 4* ouaj; 131 ■teno 44 APPENDIX 7. STABLE ISOTOPE DATA FROM IN AND NEAR STUDY AREA S180 <5d s13c Sampling Point *Source (°/oo) (°/oo) (°/oo) Well J-13 1 -12.7 - 96 -7.8 Test Well A 1 -13.0 -107 -8.9 Test Well 2 1 -13.2 -102 -11.2 -11.6 Well U19c 1 -14.1 -109 -11.3 Well 8 1 -12.9 -101 -8.7 Well Uel6d 1 -12.4 - 96 -106 NA Well Uel6d 1 -13.5 - 99 NA Army Well 1 1 -13.1 -108 NA Well 5c 1 -13.4 -13.3 -106 NA Well C 1 -12.6 - 94 -10.9 Well 4 1 -12.8 -102 -3.8 Well C-l 1 -14.1 - 99 -4.1 Well Uel5d 1 -13.6 -103 -4.9 Fairbanks Sp. S.W. 2 -13.7 -102 -5.0 Crystal Pool 2 -13.6 NA -5.0 Devils Hole 2 -13.4 -102 -4.6 Big Spring 2 -13.6 NA -4.6 Amargosa Tracer Well #2 2 -14.9 -105 NA Well Uel6f 3 -13.4 - 99.5 -10.8 UE-25b#l 4 -13.4 -101 -10.4 UE-25b#l 4 -13.5 - 99.5 -8.6 UE-25b#l 4 -12.8 - 93.5 -12.6 UE-29a#2 4 -12.8 - 93 -13.1 UE-29a#2 4 132 3eno 44 APPENDIX 7. (Continued) 6180 6D S13C Sampling Point *Source (°/00) (°/oo) (°/oo) USWG-4 4 -13.8 -103 -9.1 USWH-1 4 -13.4 -103 . NA USWH-1 4 -13.5 -101 -11.4 USWH-4 4 -14.0 -104 -7.4 USWH-5 4 -13.6 -102 -10.3 USWH-6 4 -13.8 -106 -7.5 USWVH-1 4 -14.2 -108 -8.5 Well J-12 4 -12.8 - 97.5 -7.9 Well J-13 4 -13.0 - 97.5 -7.3 Rainbow Spring 5 -12.4 - 96 -9.8 Highway Main Well 5 -12.2 - 96 -10.1 -8.8 Gilbert Well 5 -12.7 - 98 -7.7 Mifflin Well 5 -12.6 -100 -7.9 Cortney Well 5 -12.1 - 96 - 98 -8.2 Adams Well 5 -12.7 - 98 -6.2 Holland Well 5 -12.6 -100 NA Tule Spring Well 5 -11.5 -102 NA 15S/49E-22dc 6 -12.8 -103 -7.1 16S/49E-5acc 6 -13.2 - 99.5 -6.8 16S/49E-8abb 6 -13.2 -13.4 -103 -7.3 16S/49E-9dcc 6 -12.6 -102 NA 16S/49E-18dc 6 -13.2 - 97.5 -5.2 16S/49E-16ccc 6 -13.1 -101 • NA 16S/49E-19daa 6 133 Reno 44 APPENDIX 7. (Continued) 5D 613C Sampling Point *Source (°/oo) (°/oo) (°/oo) 16S/48E--25aa 6 -13.0 -102 NA 16S/48E-36aaa 6 -12.6 - 98.5 NA 17S/48E-lab 6 -13.0 -104 NA 17S/49E-7bb 6 -12.7 -104 NA 00 » CN] —1 17S/49E-9aa 6 1 -105 NA 17S/49E-8ddb 6 -13.0 -102 NA 16S/50E-7bcd 6 -13.8 -105 NA 16S/49E-15aaa 6 -13.8 -105 -3.4 16S/49E-36aaa 6 -13.7 -104 -3.4 Hiko Spring 7 NA -114 NA 7 NA -113 NA 7 NA -113 NA NA Crystal Spring 7 NA -112 7 NA -113 NA 7 NA -112 NA NA Ash Srping 7 NA -110 7 NA -112 NA 7 NA -115 NA -102 NA Trout Spring 7 NA 7 NA -100 NA Cold Creek Spring NA 7 NA -105 7 NA -106 NA 7 NA -101 NA Indian Springs NA 7 NA -103 7 NA -104 NA 7 NA - 98 NA Corn Creek Ranch Well NA 7 NA - 97 7 NA -100 NA Manse Spring NA 7 NA -104 NA -103 NA Tule Springs Well 7 134 Reno 44 APPENDIX 7. (Continued) <$18o 5D d ^ C Sampling Point *Source (°/oo) (°/oo) (°/oo) Fairbanks Spring 7 NA -106 NA 7 NA -106 NA 7 NA -106 NA 7 NA -107 NA Crystal Pool 7 NA - 99 NA 7 NA - n o NA 7 NA -106 NA 7 NA -107 NA Indian Rock Spring 7 NA -107 NA 7 NA -110 NA 7 NA -104 NA 7 NA -107 NA NA Big Spring 7 NA -101 7 NA -107 NA 7 NA -107 NA NA Nevares Spring 7 NA -111 7 NA -109 NA -108 NA Texas Spring 7 NA NA Travertine Spring 7 NA -109 -101 NA Warm Spring 7 NA -100 NA Spring feeding Moapa 7 NA -101 NA Pederson's Warm Spring 7 NA NA 7 NA -100 7 -100 NA Iverson's Spring NA NA -111 NA Flag Srping 7 NA -124 NA Hot Creek Spring / NA -114 NA Well C-l / 7 NA -107 NA Well Army 1 NA 7 NA -106 135 Reno 44 APPENDIX 7. (Cont inued) S180 <5d s13c Sampling Point *Source (°/oo) (0/00) (°/oo) Well 5B 7 NA -110 NA Well J-12 7 NA -102 NA Nuclear Engr. Co. Well 7 NA -112 NA * Source 1 Current Investigation 2 Winogrand and Pearson, 1976 3 Dinwiddie and Weir, 1979 4 Benson, 1983 5 Jacobson, 1984 6 Claassen, 1983 7 Winograd and Friedman, 1972 ** NA: Not Analyzed •\