Prepared in cooperation with the

U.S. DEPARTMENT OF ENERGY

NEVADA OPERATIONS OFFICE under

INTERAGENCY AGREEMENT DE-AI08-96NV11967

Analysis of Water Levels in the

Frenchman Flat Area, Nevada Test Site

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 00-4272
Analysis of Water Levels in the

Frenchman Flat Area, Nevada Test Site

By Daniel J. Bright, Sharon A. Watkins, and Barbara A. Lisle

U.S. GEOLOGICAL SURVEY

Carson City, Nevada

2001

Prepared in cooperation with the

U.S. DEPARTMENT OF ENERGY

NEVADA OPERATIONS OFFICE under

INTERAGENCY AGREEMENT DE-AI08-96NV11967

Water-Resources Investigations Report 00-4272
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

Any use of trade names in this publication is for descriptive purposes

only and does not constitute endorsement by the U.S. Government

For additional information Copies of this report can be

contact: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Information Services

333 West Nye Lane, Room 203 Building 810

Carson City, NV 89706-0866 Box 25286, Federal Center

Denver, CO 80225-0286

email: GS-W-NVpublic_info@usgs.gov

http://nevada.usgs.gov
CONTENTS III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction............................................................................................................................................................................ 1

Purpose and Scope ..................................................................................................................................................... 3

Hydrogeology............................................................................................................................................................. 3

Acknowledgments...................................................................................................................................................... 5

Water-Level Fluctuations....................................................................................................................................................... 5

Climate and Earth Tides............................................................................................................................................. 5

Precipitation.................................................................................................................................................... 5

Barometric Pressure........................................................................................................................................ 9

Earth Tides...................................................................................................................................................... 9

Seismic Activity ......................................................................................................................................................... 9

Underground Nuclear Testing .................................................................................................................................... 11

Ground-Water Withdrawal ......................................................................................................................................... 12

Water-Level Measurements ................................................................................................................................................... 17

Periodic Measurements .............................................................................................................................................. 26

Continual Measurements............................................................................................................................................ 26

Water-Level Adjustments ...................................................................................................................................................... 26

Barometric Pressure ................................................................................................................................................... 26

Water Density............................................................................................................................................................. 28

Borehole Deviation .................................................................................................................................................... 30

Land-Surface Altitude................................................................................................................................................ 31

Analysis of Water Levels....................................................................................................................................................... 32

Statistical Analysis Methods ...................................................................................................................................... 32

Trend Analysis Results............................................................................................................................................... 33

Alluvial Aquifer.............................................................................................................................................. 35

Volcanic Aquifer............................................................................................................................................. 36

Carbonate Aquifer .......................................................................................................................................... 39

Quartzite Confining Unit ................................................................................................................................ 41

Summary ............................................................................................................................................................................... 41

References Cited .................................................................................................................................................................. 42

FIGURES

1. Map showing location of Nevada Test Site, and Frenchman Flat, Mercury Valley, and Yucca Flat

Hydrographic Areas, southern Nevada .................................................................................................................. 2

2. Map showing surface distribution of rocks in the Frenchman Flat area, Nevada Test Site, Nevada.......................... 4

3-13. Graphs showing for selected areas on the Nevada Test Site:

3. Cumulative departure from mean monthly precipitation at Yucca Flat station and monthly precipitation

at Mercury, well WW-5b, and Yucca Flat stations for selected periods during 1958–97 ................................. 8

4. Barometric pressure and water levels at well WW-5a for 1996 and barometric pressure at Desert Rock

station near Mercury, Nevada, for 1985–96 ...................................................................................................... 10

5. Monthly withdrawals for selected wells in the Frenchman Flat area .................................................................. 13

6. Total annual withdrawals for wells in the Frenchman Flat area .......................................................................... 18

7. Periodic water-level measurements and associated linear-regression line for selected wells in the

Frenchman Flat area .......................................................................................................................................... 19

8. Continual water levels in wells SM-23, WW-5a, and WW-4a ............................................................................ 27

9. Temperature of water samples collected from selected wells in the Frenchman Flat area.................................. 29

10. Water levels in observation well WW-5a and withdrawal from water-supply wells WW-5b and WW-5c

from September through December 1997 ......................................................................................................... 35

11. Water levels in wells UE-5n and RNM-2s and withdrawals from wells RNM-2s, WW-5b, and UE-5c ............ 37
IV Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

12. Water-level altitudes in water-supply well WW-4 and observation well WW-4a for January–March 1993....... 38

13. Lagged water levels in wells TW-F and TW-3, cumulative departure from mean monthly precipitation at

Yucca Flat station, and withdrawal from water-supply wells WW-C1, WW-C, and Army-1 in

carbonate-rock aquifer....................................................................................................................................... 40

TABLES

1. Well-completion, water-level, and water-use information for wells in the Frenchman Flat area, Nevada Test Site ........ 6

2. Underground nuclear tests in the Frenchman Flat area, Nevada Test Site ........................................................................ 12

3. Annual water withdrawal from water-supply wells and test well RNM-2s in the Frenchman Flat area,

Nevada Test Site, 1951–97 ............................................................................................................................................. 16

4. Mean, minimum, and maximum water levels and land-surface altitudes for wells in the Frenchman Flat area,

Nevada Test Site ............................................................................................................................................................. 25

5. Water-level adjustments for borehole deviation in selected wells in the Frenchman Flat area, Nevada Test Site............ 30

6. Results of trend analysis of water levels for wells in the Frenchman Flat area, Nevada Test Site ................................... 34

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

degrees Fahrenheit per 100 ft 0.549 degrees Celsius per 100 meters

foot (ft) 0.3048 meter

foot per mile (ft/mi) 0.1894 meter per kilometer

foot per year (ft/yr) 0.3048 meter per year

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

million gallons per year (Mgal/yr) 3.785 million liters per year

pound per square inch per year (lb/in2/yr) 6.895 kilopascal per year

Temperature: Degrees Fahrenheit can be converted to degrees Celsius by using the formula °C = 0.556(°F – 32).

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called “Sea-Level

Datum of 1929”), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada.
Abstract 1

Abstract

Analysis of water levels in 21 wells in the

Frenchman Flat area, Nevada Test Site, provides

information on the accuracy of hydraulic-head calculations, temporal water-level trends, and potential causes of water-level fluctuations. Accurate

hydraulic heads are particularly important in

Frenchman Flat where the hydraulic gradients are

relatively flat (less than 1 foot per mile) in the alluvial aquifer. Temporal water-level trends with

magnitudes near or exceeding the regional hydraulic gradient may have a substantial effect on

ground-water flow directions.

Water-level measurements can be adjusted

for the effects of barometric pressure, formation

water density (from water-temperature measurements), borehole deviation, and land-surface altitude in selected wells in the Frenchman Flat area.

Water levels in one well were adjusted for the

effect of density; this adjustment was significantly

greater (about 17 feet) than the adjustment of

water levels for barometric pressure, borehole

deviation, or land-surface altitude (less than about

4 feet).

Water-level measurements from five wells

exhibited trends that were statistically and hydrologically significant. Statistically significant

water-level trends were observed for three wells

completed in the alluvial aquifer (WW-5a, UE-5n,

and PW-3), for one well completed in the carbonate aquifer (SM-23), and for one well completed in

the quartzite confining unit (Army-6a).

Potential causes of water-level fluctuations

in wells in the Frenchman Flat area include

changes in atmospheric conditions (precipitation

and barometric pressure), Earth tides, seismic

activity, past underground nuclear testing, and

nearby pumping. Periodic water-level measurements in some wells completed in the carbonate

aquifer indicate cyclic-type water-level fluctuations that generally correlate with longer term

changes (more than 5 years) in precipitation.

Ground-water pumping from the alluvial aquifer at

well WW-5c and pumping and discharge from

well RNM-2s appear to cause water-level fluctuations in nearby observation wells. The remaining

known sources of water-level fluctuations do not

appear to substantially affect water-level changes

(seismic activity and underground nuclear testing)

or do not affect changes over a period of more than

1 year (barometric pressure and Earth tides) in

wells in the Frenchman Flat area.

INTRODUCTION

The Nevada Test Site (NTS) is located in Nye

County, southern Nevada (fig. 1). The Frenchman Flat

area, for purposes of this report, includes parts of

administrative areas 5, 6, 11, 22, 23, and 27 in the

southern part of NTS. These administrative areas are

within the Frenchman Flat, Yucca Flat, and Mercury

Valley Hydrographic Areas1. The Frenchman Flat

Hydrographic Area is a topographically closed basin

surrounded by low-lying mountains that, to the south,

separate this area from the Mercury Valley Hydrographic Area and, to the north, separate it from the

Yucca Flat Hydrographic Area. These hydrographic

areas are in the Death Valley ground-water flow system, a regional system of about 15,000 mi2 in the

southern part of the Great Basin geographic province.

Water levels in wells in the Frenchman Flat area,

an area of previous underground nuclear testing,

have been measured since the 1950’s when the first

1 Formal hydrographic areas in Nevada were delineated systematically by the U.S. Geological Survey and Nevada Division of

Water Resources in the late 1960's (Rush, 1968; Cardinalli and

others, 1968) for scientific and administrative purposes. The official hydrographic-area names, numbers, and geographic boundaries continue to be used in Geological Survey scientific reports

and Division of Water Resources administrative activities.

Analysis of Water Levels in the Frenchman Flat Area,

Nevada Test Site

By Daniel J. Bright, Sharon A. Watkins, and Barbara A. Lisle
2 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 1. Location of Nevada Test Site, and Frenchman Flat, Mercury Valley, and Yucca Flat Hydrographic Areas,

southern Nevada.

EXPLANATION

Precipitation station

Nevada Test Site boundary

Administrative-area boundary within Nevada Test Site–Area number is indicated

Base prepared by U.S. Geological Survey from digital data, 1:100,000 1979-89

Universal Transverse Mercator projection, Zone 11

Shaded-relief base from 1:250,000 - scale Digital Elevation Model; 

sun illumination from northwest at 45 degrees above horizon.

116° 45' 115° 30'

37° 30' 

36° 15' 

Hydrographic-area boundary

0 10 20 30 40 Kilometers

0 10 20 30 Miles

Yucca

Flat

NEVADA

CALIFORNIA

Spring Mountains

Spotted Range

25

6

19

18

20

3

29

30 1

9

12

7

2

15

4

17

22

16

8

14 11

10

Frenchman

Flat 

5

23

27

26

South 

Ridge

LINCOLN COUNTY

LINCOLN COUNTY

NYE COUNTY

NYE COUNTY

CLARK COUNTY

CLARK COUNTY

Area of Figure 2

Mercury Valley

NEVADA

Nevada

Test Site

Pahute Mesa

Rainier

Mesa

CALIFORNIA
INTRODUCTION 3

water-supply wells were constructed in this area. In

Frenchman Flat, water levels generally indicate the

existence of relatively flat hydraulic-head gradients

(less than 1 ft/mi) in the alluvial aquifer. Determination

of ground-water flow direction in areas of flat hydraulic-head gradients requires accurate water-level measurements. The accuracy of these measurements is

affected by barometric pressure, formation water density (from water-temperature measurements), borehole

deviation, and land-surface altitude. In addition, water

levels that vary with time can be analyzed for trends,

particularly those trends with magnitudes that exceed

the regional hydraulic gradient and may have a substantial effect on ground-water flow directions. Determining accurate water-level measurements and

temporal water-level trends will aid ongoing studies

concerned with the direction of ground-water flow in

these areas and the potential transport of radionuclides.

Purpose and Scope

Temporal trends of water-level measurements

from 1954 to 1998 are presented for selected wells in

the Frenchman Flat area, Nevada Test Site. Water-level

measurements from 21 wells in Frenchman Flat, Mercury Valley, and the southernmost part of Yucca Flat

(fig. 2) were compiled and quality assured to (1) provide water-level adjustments for potential causes of

water-level fluctuations, (2) determine if statistically

and hydrologically significant water-level trends exist,

and (3) determine, if possible, the causes of water-level

trends or cyclic-type water-level fluctuations. Waterlevel adjustments for potential causes of water-level

fluctuations such as precipitation, barometric pressure,

formation water density, borehole deviation, and landsurface altitude are presented for wells with available

data. Causes of water-level trends were determined by

statistical correlation and by qualitative comparisons of

temporal data.

Hydrogeology

Erosion of the surrounding mountains has

resulted in the accumulation of more than a thousand

feet of alluvial deposits in some areas of Frenchman

Flat and Mercury Valley (Winograd and Thordarson,

1975, p. C37; USGS data files, Las Vegas, Nev.). Volcanic rocks underlie the alluvium in the southern part

of Yucca Flat and the northern and western parts of

Frenchman Flat and, where exposed, form the surrounding low-lying mountains (fig. 2; Laczniak and

others, 1996, pl. 2). Carbonate rocks primarily underlie

the alluvium in the eastern and southeastern parts of

Frenchman Flat and form much of the surrounding

mountains in these areas. Clastic rocks are less abundant, but crop out in areas east and south of Mercury

Valley.

For purposes of this report, stratigraphic units in

the Frenchman Flat area (Laczniak and others, 1996,

fig. 4) were divided into four hydrogeologic units.

From oldest to youngest, these units include: Paleozoic

clastic rocks that form the quartzite confining unit,

Paleozoic limestone and dolomite that form the carbonate aquifer, Tertiary ash-flow tuff that forms the volcanic aquifer, and Tertiary and Quaternary sand and

gravel (valley fill) that form the alluvial aquifer. The

quartzite confining unit and overlying carbonate aquifer are regionally extensive hydrogeologic units that

occur beneath the volcanic and alluvial aquifers

throughout NTS.

The primary hydrogeologic units occurring in the

open intervals of wells in the Frenchman Flat area are

listed in table 1. For the 21 wells evaluated in this study,

10 wells are completed in the alluvial aquifer, 2 wells

in the volcanic aquifer, 2 wells in alluvial and volcanic

aquifers, 6 wells in the carbonate aquifer, and 1 well in

the quartzite confining unit. The shallowest water level

in a well occurs in the alluvial aquifer at about 681 ft

below land surface (well WW-5b); the deepest water

level occurs in the carbonate aquifer at more than 1,700

ft below land surface (well TW-F).

Lateral ground-water movement beneath the

Frenchman Flat area primarily occurs within the carbonate aquifer (Laczniak and others, 1996, p. 26). The

direction of ground-water flow in this region of the carbonate aquifer generally is from the northeast to southwest (fig. 2). Within the overlying alluvial and volcanic

aquifers, lateral ground-water flow occurs from the

margins to the center of the basin, and downward into

the carbonate aquifer (Laczniak and others, 1996, p.

28). The hydraulic-head gradient in most areas of the

alluvial aquifer in Frenchman Flat is relatively flat (less

than 1 ft/mi; Winograd and Thordarson, 1975, p. C60),

except near water-supply and (or) test wells (table 1).

Hydraulic heads in the only two wells completed

in the volcanic aquifer (wells WW-4, WW-4a; fig. 2)

are anomalously high — more than 300 ft higher than

hydraulic heads in the alluvial or carbonate aquifers.

Elevated water levels in these wells may be due, in part,

to an extension of an inferred hydraulic barrier formed

by the Cane Springs Fault Zone (fig. 2) occurring to the
4 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 2. Surface distribution of rocks in the Frenchman Flat area, Nevada Test Site, Nevada. (Modified from

Laczniak and others, 1996, fig. 4 and pl. 1.)

ARMY-6a

TW-F

TW-3

WW-C

SM-23

WW-C1

ARMY-1

UE-5c PW-1

PW-2

PW-3

WW-5a

WW-5c

WW-5b

RNM-2UE-5n

RNM-1

RNM-2s

UE-11a

WW-4

WW-4a

MERCURY

Mercury

Valley

Frenchman

Flat

Nevada Test Site 

Boundary 

Cane Springs Fault Zone

Mercury

Highway

4 7

10

6 9

8

5

36° 57' 30''

Yucca Flat

36° 30' 

115° 45' 

0

0 2

2

4 6 Kilometers

4 6 Miles

116° 07' 30"

BM-MERC5

BM-15A

BM-F370

BM-P328 3

2 1

Valley fill

Volcanic Rock

Carbonate Rock

Clastic Rock

PW-2 Well open to alluvial aquifer

WW-4 Well open to volcanic aquifer

TW-F Well open to carbonate aquifer

ARMY-6a Well open to quartzite confining unit

UE-5c Well open to alluvial and volcanic aquifers

WELL AND IDENTIFIER

General direction of regional 

 ground-water flow

Hydrographic-area boundary

1 UNDERGROUND NUCLEAR TEST AND IDENTIFIER–

 NTS test designations are listed in table 2 

EXPLANATION

BENCHMARK AND IDENTIFIER–Benchmark

 for survey of land-surface altitudes. Identifier from NTS

 Bechtel Nevada data files ( Rick Remington, Bechtel Nevada,

 written commun., 1997)

Base modified from U.S, Geological Survey, 1980.

BM-F370 
WATER-LEVEL FLUCTUATIONS 5

southeast and downgradient from the two volcanicaquifer wells (Winograd and Thordarson, 1975, p.

C60). Reported water-level altitudes in the carbonate

aquifer north of the inferred barrier (Winograd and

Thordarson, 1975, fig. 31), however, do not appear elevated relative to water-level altitudes in the carbonate

or alluvial aquifers south of the inferred barrier.

Acknowledgments

This report is prepared in cooperation with the

U.S. Department of Energy under Interagency Agreement DE-AI08-96NV11967. Meteorological data were

provided by Doug Soulé of the National Oceanic and

Atmospheric Administration. Land-surface altitudes

presented in this report were determined from globalpositioning-system data collected and evaluated by

Armando Robledo, U.S. Geological Survey.

WATER-LEVEL FLUCTUATIONS

Many natural processes and human activities can

cause water levels in wells to fluctuate. Natural processes that cause water-level changes in wells are climate (precipitation and atmospheric pressure), Earth

tides, and seismic activity (earthquakes). Human activities known to affect water levels in wells at NTS are

underground nuclear testing and ground-water withdrawal.

Climate and Earth Tides

Changes in precipitation, atmospheric (barometric) pressure, or Earth tides can cause cyclic water-level

fluctuations in wells. The frequency of the cyclic fluctuations differs for each of these natural processes. Precipitation cycles typically occur on annual or seasonal

frequencies, barometric-pressure cycles range from

annual to diurnal frequencies, and Earth-tide cycles

occur at semi-diurnal and diurnal frequencies.

Precipitation

In addition to the annual or seasonal frequency of

precipitation, periods of more than 5 years of lesser- or

greater-than-normal precipitation have intermittently

occurred in southern Nevada. These periods of lesseror greater-than-normal precipitation have been, in

some areas of southern Nevada, a cause of cyclic

water-level fluctuations in wells and of long-term

water-level trends (Dettinger and Schaefer, 1995,

p. 198).

Cumulative departure from mean monthly precipitation for Yucca Flat station (fig. 3; Doug Soulé, 

National Oceanic and Atmospheric Administration,

written commun., 1998) show the long-term dry and

wet periods for this area of the NTS (fig. 3A). Decreasing cumulative departure periods in figure 3A indicate

lesser-than-normal (dry) precipitation conditions;

increasing cumulative departure periods indicate

greater-than-normal (wet) precipitation conditions.

Decreasing cumulative departures occurred from the

late 1950’s to about 1969 and increasing departures

occurred from 1969 to about 1988. From 1988 to 1997,

cumulative departure data suggest shorter periods of

lesser- or greater-than-normal precipitation conditions.

Recharge to the alluvial aquifer generally is a

function of precipitation, evapotranspiration, surface

topography, and the thickness, vertical permeability,

and heterogeneity of the unsaturated zone. Averageannual precipitation at stations in Mercury, Frenchman

Flat (well WW-5b), and Yucca Flat (fig. 1) ranges from

4.85 inches to 6.66 inches (figs. 3B-3D). Relatively low

annual precipitation, high air temperatures, high evapotranspiration rates, and a thick unsaturated zone of

more than 600 ft below land surface suggest that precipitation in the Frenchman Flat area is not a likely

source of water-level fluctuations in wells completed in

the alluvial aquifer. For example, an analysis of soilwater chemistry (Tyler and others, 1996, p. 1487) at

wells PW-1, PW-2, and PW-3 in Frenchman Flat indicate that recharge has not occurred in this area since the

last two glacial maxima, about 20,000 and 120,000

years before present when the climate was considerably wetter and cooler.

In areas where the downward movement of

ground water occurs through fractured rock, the potential for cyclic fluctuations in wells due to precipitation

may be greater than that of the alluvial aquifer. In the

volcanic and carbonate aquifers, for example, recharge

through fracture systems in areas where fractured formations outcrop might provide a mechanism for precipitation-induced water-level fluctuations to occur in

wells completed beneath relatively thick unsaturated

zones. Lehman and Brown (1996) reported cyclic

water-level fluctuations in wells completed in the volcanic aquifer near Yucca Mountain where the unsaturated-zone thickness generally is greater than 1,000 ft.

Lehman and Brown (1996, p. 10) concluded that the
6 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site Table 1. Well-completion, water-level, and water-use information for wells in the Frenchman Flat area, Nevada Test Site—Continued Local well name USGS site identification number 1 Latitude (degrees, minutes, seconds) Longitude (degrees, minutes, seconds) Depth of well (feet) Year of completion Hydrogeologic unit Type of water-level measurement Use of well 

Mercury Valley Army-1 363530116021401 36°35′30′′ 116°02′14′′ 1,953 1962 carbonate periodic water-supply 

Army-6a 363437116010801 36°34′37′′ 116°01′08′′ 1,228 1955 quartzite confining unit periodic observation 

SM-23 363905116005801 36°39′05′′ 116°00′58′′ 1,332 1996 carbonate periodic

continual

observation 

Frenchman Flat

PW-1 365105115565801 36°51′06′′ 115°56′58′′ 839 1992 alluvium periodic observation 

PW-2 365152115565701 36°51′52′′ 115°56′57′′ 920 1992 alluvium periodic observation 

PW-3 365201115581601 36°52′01′′ 115°58′16′′ 955 1992 alluvium periodic observation 

RNM-1 364928115580101 36°49′28′′ 115°58′01′′ 3999 1974 alluvium periodic observation 

RNM-2 364923115575701 36°49′23′′ 115°57′57′′ 935 1974 alluvium periodic observation 

RNM-2s 364922115580101 36°49′22′′ 115°58′01′′ 1,156 1974 alluvium periodic test well/observation 

TW-3 364830115512601 36°48′30′′ 115°51′26′′ 1,516 1962 carbonate periodic observation 

TW-F 364534116065902 36°45′34′′ 116°06′59′′ 3,400 41962 carbonate periodic observation 

UE-5c 365011115584702 36°50′11′′ 115°58′47′′ 2,682 51964 volcanic/alluvium periodic water-supply 

UE-5n 364915115574101 36°49′15′′ 115°57′41′′ 1,687 1976 alluvium periodic observation 

UE-11a 365259115571601 36°52′59′′ 115°57′16′′ 1,400 71965 volcanic/alluvium periodic observation 

WW-4 365418116012601 36°54′18′′ 116°01′26′′ 1,479 1981 volcanic periodic

continual

water-supply 

WW-4a 365412116013901 36°54′12′′ 116°01′39′′ 1,516 1990 volcanic periodic

continual

water-supply/observatio

WW-5a 364635115572901 36°46′35′′ 115°57′29′′ 910 1951 alluvium periodic

continual

water-supply/observatio

WW-5b 364805115580801 36°48′05′′ 115°58′08′′ 900 1951 alluvium periodic water-supply 

WW-5c 364708115574401 36°47′20′′ 115°57′49′′ 1,200 1954 alluvium periodic water-supply 

Table 1. Well-completion, water-level, and water-use information for wells in the Frenchman Flat area, Nevada Test SiteDepth of well: Depth to bottom of open interval of borehole or to bottom of perforated interval of well at time of completion.Periodic data type: Water levels measured by wire-line, steel tape, or electric tape.Continual data type: Water levels measured by pressure transducer.Water levels: Period of record for water levels used for trend analysis (see section titled “Analysis of Water Levels” in text).Withdrawal: Period of record for annual water withdrawal (years with zero withdrawal not included);

—, not applicable.
WATER-LEVEL FLUCTUATIONS 7

Southern Yucca Flat

WW-C 365508116003501

365508116003502

36°55′08′′

36°55′08′′

116°00′35′′116°00′35′′

1,701 1961 carbonate periodic water-supply 

WW-C1 365500116003901 36°55′07′′ 116°00′34′′ 1,707 1962 carbonate periodic water-supply 

1 The U.S. Geological Survey system for site identification is based on the latitude-longitude grid. Each site is identified by a unique 15-digit number: The first six 

and seconds of latitude; the next seven digitis denote degrees, minutes, and seconds of longitude; and the last two digits are the sequence number of the well or test hole wand longitude. The assigned number is retained as a permanent identifier even if a more precise latitude and longitude are later determined. To determine the geographic latitude and longitude coordinates should be used rather than the site identifier.

2 Withdrawal data missing for 1972–82.3 Equals depth to bridge plug inside casing.4 Original well completed in 1961 to a depth of 1,871 ft; well deepened to a depth of 3,400 ft in 1962.5 Well recompleted with new perforated interval in April 1966.6 Withdrawal data missing for 1968–82.7 Well recompleted (borehole cleaned for geophysical logging) in October 1982.8 Trend analysis not performed due to short period of record (from December 1992 to March 1993).

Table 1. Well-completion, water-level, and water-use information for wells in the Frenchman Flat area, Nevada Test Site—Continued

Local

well name

USGS site

identification number 1

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Depth

of well

(feet)

Year of

completion

Hydrogeologic

unit

Type of

water-level

measurement

Use of

well
8 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 3. Cumulative departure from mean monthly precipitation at Yucca Flat station and monthly precipitation at

Mercury, well WW-5b, and Yucca Flat stations for selected periods during 1958–97, Nevada Test Site. (Data from Doug

Soulé, National Oceanic and Atmospheric Administration, written commun., 1998.)

1950 1960 1970 1980 1990 2000

0

2

4

6

0

2

4

6

0

2

4

6

20

10

0

10

20

Mercury station

Well WW-5b station

Yucca Flat station

Yucca Flat station

Average annual 

precipitation 5.73 inches 

Average annual 

precipitation 4.85 inches 

Average annual 

precipitation 6.66 inches 

MONTHLY PRECIPITATION, IN INCHES

CUMULATIVE DEPARTURE 

FROM MEAN MONTHLY 

PRECIPITATION, IN INCHES

A.

B.

C.

D.
WATER-LEVEL FLUCTUATIONS 9

period of cyclic water-level fluctuations in these wells

was 2–3 years and suggested that these fluctuations

may be the result of recharge from precipitation. However, a subsequent study of water-level fluctuations in

the same wells near Yucca Mountain (Graves and others, 1997, p. 69) concluded that the 11-year water-level

record used by Lehman and Brown (1996) was not sufficient to determine if a 2- to 3-year period of cyclic

water-level fluctuations was present.

Barometric Pressure

Water-levels in numerous wells completed in

confined or semi-confined aquifers at NTS fluctuate in

response to changes in barometric pressure. Water

levels in well WW-5a in the central part of Frenchman

Flat, for example, illustrate this relation (fig. 4A).

Water levels respond inversely to barometric-pressure

changes, with an increase in barometric pressure causing a decrease in the water level. The magnitudes of

short-term (less than 10 days) water-level fluctuations

in wells vary throughout the year but commonly have a

maximum amplitude of about 1 ft during the winter

season when changes in barometric pressure are greatest.

Water-level fluctuations in wells due to barometric-pressure changes probably are not a significant

cause of long-term water-level trends at NTS. Barometric-pressure changes occur at Desert Rock station

near Mercury (fig. 4B; National Climatic Data Center,

National Oceanic Atmospheric and Administration,

unpublished data accessed May 6, 1999, on the World

Wide Web at URL <http://www.ncdc.noaa.gov>) on an

annual frequency with maximum pressures during the

winter months. Linear regression of the long-term

barometric-pressure records yields a slope of +0.0003

lb/in2

/yr, which in equivalent units of head is about

+0.0007 ft/yr. This rate of change is less than waterlevel measurement error and could not be detected in

long-term water-level trends.

Earth Tides

Earth tides are caused by the gravitational forces

exerted on the Earth’s surface by the sun and the moon.

As the relative configuration of the sun, moon, and

Earth change, gravitational fields fluctuate and cause

corresponding deformations in the Earth’s crust.

Crustal deformation caused by Earth tides can affect

aquifer pore pressure, which can result in water-level

fluctuations in wells. Five principal Earth tides are

strong enough to cause measurable water-level fluctuations in wells (O’Brien, 1997, p. 61). These five principal Earth tides induce water-level fluctuations at

semi-diurnal and diurnal frequencies.

The amplitude of Earth-tide induced water-level

fluctuations in wells near NTS generally is less than

about 0.40 ft, which in comparison to other sources is

relatively small. Analysis of water levels in wells 20–

50 mi south and southeast of NTS indicated that Earth

tides caused water-level fluctuations with amplitudes

from 0.0004 to 0.056 ft (Kilroy, 1992, table 5). Reported amplitudes of water-level fluctuations due to Earth

tides in wells near Yucca Mountain are as high as 0.40 ft

(Geldon and others, 1998, p. 12). Because of the small

and consistent amplitude of Earth-tide induced

water-level fluctuations, Earth tides are not a likely

source of long-term water-level trends at NTS.

Seismic Activity

From 1950 to 1998, 526 earthquakes of

magnitude 4 or greater were documented at or

near NTS (Seismological Laboratory, University

of Nevada, Reno, unpublished data accessed September 10, 1998, on the World Wide Web at URL

<http://www.seismic.unr.edu>). Only 33 of these earthquakes occurred after 1992, the year the moratorium on

nuclear testing was established. Consequently, many of

these earthquakes likely were associated with nuclear

testing in the Pahute Mesa and Yucca Flat areas of NTS

(fig. 1) where most of the earthquake epicenters were

recorded.

Water-level fluctuations in response to earthquakes are relatively common phenomena in wells

completed in confined aquifers (Todd, 1980). Generally, high frequency (a continual chart recorder or measurement of less than 1 per second) water-level

measurements are necessary for detecting seismically

induced water-level fluctuations in wells. Periodic

water-level measurements generally are not sufficient

for detecting dynamic earthquake-induced fluctuations, but may be adequate for monitoring long-term

effects on water levels after a seismic event has

occurred.

Continual water-level measurements in wells

near Yucca Mountain showed a response to the Landers

(magnitude 7.5), Big Bear (magnitude 6.6), and Little

Skull Mountain (magnitude 5.6) earthquakes that

occurred between June 28 and June 29, 1992. The

earthquake epicenters were about 15 to 190 mi away
10 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 4. (A) Barometric pressure (BP) and water levels (WL) at well WW-5a for 1996 and (B) barometric pressure at Desert RoMercury, Nevada, for 1985–96, Nevada Test Site. (Data from Doug Soulé, National

Oceanic and

Atmospheric Administration,

w

1988.)

1984 1986 1988 1990 1992 1994 1996 

12.513.013.5

OCTOBER NOVEMBER DECEMBER

12.813.013.213.413.6 

Linear regression line slope = +0.0003pounds per square inch per year

BAROMETRIC PRESSURE, IN POUNDS PER SQUARE INCH

Desert Rock stationWell WW-5a

Linear-regression line

A.

B.

WL

BP
WATER-LEVEL FLUCTUATIONS 11

from the wells at Yucca Mountain. Water-level fluctuations in response to these earthquakes ranged in amplitude from about 2 to 35 inches (O’Brien, 1993, p. 8).

However, continual water-level measurements at 15-

minute intervals in well WW-4a, located about the

same distance from the earthquake epicenters as the

wells at Yucca Mountain, did not show any response to

these earthquakes. Water levels in this well are strongly

influenced by pumping in nearby well WW-4 and the

pumping most likely masked any potential water-level

response. Well WW-4a was the only well in the Frenchman Flat area in June 1992 instrumented for continual

water-level measurements.

Water levels were monitored in well SM-23 at 15-

minute intervals from June 1996 to June 1997, and in

well WW-5a at 5-minute intervals from June 1996 to

December 1997. During these periods, seven earthquakes of magnitude 4.0 to 5.0 occurred within

approximately a 125-mi radius of Frenchman Flat (no

earthquakes of magnitudes greater than 5.0 were

recorded during this period). Water-level records for

these two wells did not show any response to these

earthquakes. A lack of water-level response may be due

to numerous factors. For example, barometric pressure

at well SM-23 or nearby pumping at well WW-5a may

have obscured an earthquake-induced water-level

response. Additionally, a lack of response in these

wells may be due to the long distance or small magnitude of the seismic event.

The long-term effects of seismic activity on water

levels may include elevated or depressed water-level

altitudes. Typically, seismically induced water-level

fluctuations equilibrate with pre-earthquake altitude

(Ferris and others, 1962), but cases have been reported

where a new equilibrium water-level altitude has been

established. For example, the response of water levels

differed in wells near Yucca Mountain after the

June 28–29, 1992, earthquakes—both elevated and

depressed water-level fluctuations were observed and

water levels in one well did not return to the pre-earthquake altitude more than 3 years later (Graves and others, 1997, fig. 39). Water-level measurements in wells

in the Frenchman Flat area do not indicate any general

shifts to a new elevated or depressed equilibrium as a

result of seismic activity.

Underground Nuclear Testing

Prior to the moratorium on nuclear testing in September 1992, a reported 828 underground nuclear tests

were detonated at NTS (U.S. Department of Energy,

1994). Most underground tests were detonated in

Yucca Flat, Rainier Mesa, and Pahute Mesa (fig. 1).

Ten nuclear tests were detonated in the Frenchman Flat

area between 1965 and 1971 (table 2). Three tests were

detonated in the central part of basin (in the vicinity of

the RNM and UE-5n wells) and seven tests northeast of

well PW-3 (fig. 2) near the border of NTS. These tests

were detonated in the alluvial or volcanic aquifers

overlying the regional carbonate aquifer (Laczniak,

1996, p. 23).

Similar to the effects of earthquakes, nuclear detonations may cause short-term dynamic water-level

fluctuations in wells and (or) long-term effects of elevated or depressed water-level altitudes. The detection

of short-term water-level fluctuations in wells requires

high-frequency monitoring instrumentation or many

manual measurements shortly after the test. These measurements, however, were not collected from wells in

the Frenchman Flat area during the period of underground nuclear testing between 1965 and 1971.

Long-term effects of underground nuclear testing

on water levels typically include lowered (depressed)

levels within the chimney region (borehole “rubble”

area above the detonation) of the nuclear test and elevated levels outside the chimney region (Laczniak and

others, 1996, p. 44). Documented decreases in water

levels within the chimney region can be up to hundreds

of feet (Laczniak and others, 1996, p. 44). Lowered

water levels in the chimney region have been attributed

to increased drainage through the more porous rubble

and to the expulsion of water by the explosion.

Although highly pulverized rock typically extends

radially outward from the chimney region, zones nearest the chimney region after a test often become less

permeable than the native (pre-shot) rock. This reduction in permeability is due to tight compaction induced

by the compressional shock wave generated by the test

and to the local injection of radioactive molten rock

along fractures.

Lowered water levels in well RNM-1 in central

Frenchman Flat are likely due to the long-term effects

of a nuclear detonation. Well RNM-1 was drilled as a

re-entry hole into the chimney region of the 1965

Cambric underground nuclear test (Nimz and

Thompson, 1992, p. 7). During the period of water-
12 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

level measurements in well RNM-1 (1975–77), the

average water-level altitude was more than 50 ft below

the average water levels in nearby wells RNM-2 and

RNM-2s. The lag in water-level recovery in well

RNM-1 to levels measured in nearby wells may be the

result of a post-shot, low permeability zone that often

forms adjacent to the chimney region.

Water-level data for Frenchman Flat are too

sparse to determine elevated water-level altitudes from

comparing pre- and post-shot potentiometric surfaces.

However, recent (1996) water-level measurements

indicate that the difference in water-level altitudes

between wells in the central and northeastern parts of

Frenchman Flat is less than 3 ft. The minimal difference in water-level altitudes between wells in these

areas suggests that elevated water levels currently do

not exist in wells within the Frenchman Flat testing

areas.

Ground-Water Withdrawal

Ground-water withdrawals from the Frenchman

Flat area have been made by 10 production wells.

Monthly and annual withdrawal data, however, are

incomplete. Excluding well RNM-2s, limited monthly

withdrawal data are available for 1958–67 but are not

available for 1968–82. Complete monthly withdrawal

data are available for 1983–97 (fig. 5). Annual withdrawal data are not available for all wells from 1972

to 1982 except wells UE-5c and RNM-2s. For well

UE-5c, annual withdrawal data are not available for

1964–66 and for 1968–82. Annual withdrawal data are

available for well RNM-2s for 1975–91. Annual withdrawals are summarized for each production well in

table 3 and for each aquifer in figure 6.

Available withdrawal data (table 3) indicate an

upward trend in water use in the Frenchman Flat area

from an average use of about 130 Mgal/yr for 1951–71

to about 430 Mgal/yr for 1983–97. Since 1989, the year

of peak water use (based on existing data), water use

has decreased. Ground-water withdrawals in 1996–97

are the lowest since 1961. Relatively low ground-water

withdrawals since 1989 coincide with the general

decrease in operational activities at NTS following the

ban on nuclear testing in 1992.

Ground water in Frenchman Flat, during years in

which data are available, primarily has been pumped

from wells RNM-2s, WW-5b, WW-5c, UE-5c, WW-4,

and WW-4a. Test well RNM-2s was pumped from

1975 to 1991 for a radionuclide migration experiment

and the remaining wells have been pumped for water

supply (table 1). In Mercury Valley, ground-water

withdrawal has been from water-supply well Army-1

and in southern Yucca Flat from water-supply wells

WW-C and WW-C1.

Previous investigations in the Frenchman Flat

area indicate that ground-water withdrawal from some

water-supply wells appears to affect water levels in

nearby wells. For example, a tracer experiment at wells

WW-C and WW-C1 (fig. 2) showed a direct hydraulic

Table 2. Underground nuclear tests in the Frenchman Flat area, Nevada Test Site

[Sources of data: U.S. Department of Energy (1994) and Drellack (1995). Symbol: <, less than]

Local well

number

Cross-reference

number

(fig. 2)

Test name

Depth

of hole

(feet)

Detonation

Depth

(feet) Date Yield

(kilotons)

Central Frenchman Flat

U-5a 1 Wishbone 628 574 Feb. 18, 1965 <20

U-5b 2 Diluted Waters 675 632 June 16, 1965 <20

U-5e 3 Cambric 1,000 967 May 14, 1965 .75

Northeast Frenchman Flat

U-5i 4 Derringer 2,124 837 Sept. 12, 1966 7.8

U-5k 5 Milk Shake 905 868 Mar. 25, 1968 <20

U-11b 6 Pin Stripe 980 970 Apr. 25, 1966 <20

U-11c 7 New Point 835 785 Dec. 13, 1966 <20

U-11e 8 Diana Moon 835 794 Aug. 27, 1968 <20

U-11f 9 Minute Steak 910 868 Sept. 12, 1969 <20

U-11g 10 Diagonal Line 1,155 867 Nov. 24, 1971 <20
WATER-LEVEL FLUCTUATIONS 13

1950 1960 1970 1980 1990

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

Well WW-5a

Well WW-5b

MONTHLY WITHDRAWAL, IN MILLION GALLONS

Data not available

1964-66 and 1968-82

Well WW-5c

Well UE-5c

Data not available

1968-82

Data not available

1968-82

Data not available

1951-57 and 1968-70

1998

Figure 5. Monthly withdrawals for selected wells in the Frenchman Flat area, Nevada Test Site. Monthly withdrawal data not

available for some years in which annual withdrawal data are available.
14 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

1960 1970 1980 1990

0

5

10

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

40

Well RNM-2s

Well WW-4

MONTHLY WITHDRAWAL, IN MILLION GALLONS

Well WW-4a

Data not available

1981-82

1998

Figure 5. Continued.
WATER-LEVEL FLUCTUATIONS 15

1960 1970 1980 1990

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

Well Army-1

Well WW-C

MONTHLY WITHDRAWAL, IN MILLION GALLONS

Well WW-C1

Data not available

1968-82

Data not available

1962 and 1968-82

Data not available

1968-82

1998

Figure 5. Continued.
16 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Table 3. Annual water withdrawal from water-supply wells and test well RNM-2s in the

Frenchman Flat area, Nevada Test Site, 1951-97—Continued

Water withdrawal (million gallons)

Year Army-1 RNM-2s UE-5c WW-4 WW-4a WW-5a WW-5b WW-5c WW-C WW-C1 Total

1951 — — — — — 19.7 120.3 — — — 30.0

1952 — — — — — 19.7 120.3 — — — 30.0

1953 — — — — — 19.7 120.3 — — — 30.0

1954 — — — — — 19.7 120.3 218.1 — — 48.1

1955 — — — — — 19.7 120.3 218.1 — — 48.1

1956 — — — — — 19.7 120.3 218.1 — — 48.1

1957 — — — — — 19.7 120.3 218.1 — — 48.1

1958 — — — — — 7.2 26.3 20.2 — — 53.7

1959 — — — — — 9.8 17.9 12.8 — — 40.5

1960 — — — — — 12.7 21.7 19.6 — — 54.0

1961 — — — — — 19.5 37.2 22.1 4.9 — 83.7

1962 4.2 — — — — 34.5 66.1 72.9 37.4 16.2 231.3

1963 2.7 — — — — 23.8 23.3 69.5 43.0 31.5 193.8

1964 30.7 — ND — — 19.5 30.8 48.3 56.9 70.6 256.8

1965 25.4 — ND — — 9.8 23.2 58.0 30.9 39.1 186.4

1966 47.3 — ND — — 16.6 35.9 56.6 34.0 76.0 266.4

1967 56.1 — 16.5 — — 14.7 9.0 43.6 28.9 34.0 202.8

1968 52.7 — ND — — 16.2 10.4 59.5 81.0 26.9 246.7

1969 78.1 — ND — — 5.7 6.8 39.9 95.6 36.4 262.5

1970 69.4 — ND — — 3.5 23.6 41.1 62.4 18.3 218.3

1971 96.1 — ND — — 0 8.1 44.2 83.4 20.4 252.2

1972 ND — ND — — ND ND ND ND ND ND

1973 ND — ND — — ND ND ND ND ND ND

1974 ND ND ND — — ND ND ND ND ND ND

1975 ND 36.7 ND — — ND ND ND ND ND 36.7

1976 ND 171.5 ND — — ND ND ND ND ND 171.5

1977 ND 179.8 ND — — ND ND ND ND ND 179.8

1978 ND 321.2 ND — — ND ND ND ND ND 321.2

1979 ND 325.2 ND — — ND ND ND ND ND 325.2

1980 ND 300.7 ND — — ND ND ND ND ND 300.7

1981 ND 300.0 ND ND — ND ND ND ND ND 300.0

1982 ND 312.9 ND ND — ND ND ND ND ND 312.9

1983 56.8 309.5 1.3 24.1 — 0 32.2 42.1 27.7 37.6 531.3

1984 82.1 305.9 2.4 48.4 — 0 57.9 58.7 31.2 23.3 609.9

1985 41.6 283.8 5.0 42.9 — 0 67.8 47.1 19.4 29.0 536.6

1986 34.9 301.7 3.5 28.2 — 0 58.5 64.0 17.3 30.1 538.2

1987 34.7 315.3 8.4 28.2 — 0 50.5 50.3 7.2 22.3 516.9

1988 53.1 310.2 8.8 46.7 — 0 57.5 67.8 17.4 24.8 586.3

1989 114.4 311.6 3.2 192.0 — 0 0 35.4 31.6 28.1 716.3

1990 126.0 233.1 0 68.2 0 0 0 38.4 29.7 23.3 518.7

Table 3. Annual water withdrawal from water-supply wells and test well RNM-2s in the

Frenchman Flat area, Nevada Test Site, 1951–97

[ND, no data (withdrawal data not available); —, well not yet drilled. Total, annual withdrawal for available data]
WATER-LEVEL MEASUREMENTS 17

connection between the two wells, which are about 100

ft apart and completed in the carbonate aquifer (Isaac

Winograd and Lewis West, U.S. Geological Survey,

written commun., 1962). A hydraulic connection

between wells WW-5a and WW-5c can be inferred

from similarities in water-level changes, specific

capacity, and water chemistry (Claassen, 1973, p. 38).

Wells WW-5a and WW-5c are about 1 mile apart and

completed in the alluvial aquifer.

WATER-LEVEL MEASUREMENTS

Water levels in wells in the Frenchman Flat area

were measured periodically by manual methods and

(or) continually (5- or 15-minute measurement intervals) by pressure transducers. Periodic water-level

measurements for 21 wells in the Frenchman Flat area

are shown in figure 7. The mean, minimum, and maximum static water levels in these wells are summarized

in table 4. Continual water-level measurements for

three wells in Mercury Valley, Frenchman Flat, and

southern Yucca Flat are shown in figure 8.

Water levels in pumping wells at NTS (table 1)

generally were not measured for at least 24 hours after

pumping to allow the water level in the well to return to

the pre-pumping level. A water-level measurement 24

hours after pumping stops may better represent a staticaquifer condition. A water-level measurement within

24 hours of pumping may represent a non-static or

recovering aquifer condition. The actual time for water

levels in pumping wells to fully recover to a pre-pumping level is, in part, a function of the hydraulic conductivity of the aquifer, the efficiency of the well, and the

magnitude of the water-level drawdown in the well.

Therefore, the water-level recovery time in wells at

NTS varies and may extend beyond 24 hours; as a

result, pumping-well water-level measurements may or

may not represent static-aquifer conditions. Waterlevel measurements in pumping wells known to be

affected by or likely affected by recent pumping are

noted in the hydrographs shown in figure 7.

Water-level measurements made immediately

after the well was drilled may not represent static-aquifer conditions. The time required for water levels to

equilibrate varies but depends on the type of drilling

fluid, the well-developing techniques, and on the permeability of the formation contributing water to the

well. Anomalous water-level measurements collected

in the same year that the borehole was drilled are noted

in the hydrographs shown in figure 7.

Also noted in figure 7 are water levels affected by

oil in the well and “anomalous” water-level measurements. Water levels in wells in the Frenchman Flat area

have been affected by oil only in well TW-3. Waterlevel measurements for this well from 1964 to 1997

likely represent the depth below land surface to the top

of the oil column in the well. The thickness of the oil

column in well TW-3 has been estimated to be less than

1.5 ft (U.S. Geological Survey data files, Las Vegas,

Nev.) Anomalous measurements indicate water levels

that differ from previous or more recent measurements

for unknown reasons. For purposes of this report,

anomalous measurements include statistical outliers—

water-level measurements that fall outside the 95-

percent confidence interval computed for the waterlevel trend analysis (see “Statistical Analysis Methods”

section).

1991 109.9 154.6 4.5 70.7 0 0 0 28.8 27.7 23.8 420.0

1992 139.4 0 5.3 84.5 0 0 0 61.1 14.8 30.3 335.4

1993 110.2 0 7.3 75.4 .2 0 29.8 63.2 22.2 9.4 317.7

1994 76.9 0 6.5 53.0 21.5 0 55.2 46.8 16.5 6.1 282.5

1995 24.1 0 7.1 16.2 30.9 0 87.7 44.3 4.2 13.9 228.4

1996 17.7 0 6.2 15.5 32.2 0 47.8 35.0 0 31.4 185.8

1997 11.4 0 6.3 14.1 46.0 0 42.6 27.2 0 28.6 176.2

1 Equals average annual withdrawal for 1951–57.

2 Equals average annual withddrawal for 1954–57.

Table 3. Annual water withdrawal from water-supply wells and test well RNM-2s in the

Frenchman Flat area, Nevada Test Site, 1951-97—Continued

Water withdrawal (million gallons)

Year Army-1 RNM-2s UE-5c WW-4 WW-4a WW-5a WW-5b WW-5c WW-C WW-C1 Total
18 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 6. Total annual withdrawals for wells in the Frenchman Flat area, Nevada Test Site.

1950 1960 1970 1980 1990 2000

0

200

400

600

800

0

200

400

600

800

0

200

400

600

800

0

200

400

600

800

Alluvial aquifer 

Includes available data for wells WW-5a, WW-5b, WW-5c, UE-5c,

and RNM-2s 

Volcanic aquifer 

Includes available data for wells WW-4 and WW-4a

Carbonate aquifer 

Includes available data for wells Army-1, WW-C, and WW-C1

Total withdrawals 

Includes available data for wells completed

in the alluvial, volcanic, and carbonate aquifers

ANNUAL WITHDRAWAL, IN MILLION GALLONS
WATER-LEVEL MEASUREMENTS 19

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

740

720

700

680

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

1,000

900

800

700

600

1992 1993 1994 1995 1996 1997 1998

715

710

705

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

715

705

695

Well WW-5a

Well WW-5c

Well WW-5c

Well WW-5a

WATER LEVEL, IN FEET BELOW LAND SURFACE

EXPLANATION

Area enlarged

below

Water level used for trend analysis

Scale for water levels

enlarged below

Water level used for trend analysis

of wells WW-5a (1996-97), 

Linear regression line

Water level possibly affected by drilling

Water level affected by pumping/recovery

Water level affected by oil in well

UE-5n (1991-97), and Anomalous water level 

RNM-2s (1994-97)

Figure 7. Periodic water-level measurements and associated linear-regression line for selected wells in the

Frenchman Flat area, Nevada Test Site.
20 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

1993 1994 1995 1996 1997

890

889

888

887

1993 1994 1995 1996 1997

841

840

839

1993 1994 1995 1996 1997

772

771

770

1970 1975 1980 1985 1990

815

810

805

800

1950 1960 1970 1980 1990 2000

730

710

690

670

Well UE-5c

Well PW-3

Well PW-2

Well PW-1

WATER LEVEL, IN FEET BELOW LAND SURFACE

Well WW-5b

Figure 7. Continued.
WATER-LEVEL MEASUREMENTS 21

1970 1975 1980 1985 1990 1995 2000

745

735

725

715

1974 1976 1978 1980 1982 1984 1986

730

725

720

715

1975 1976 1977 1978

795

790

785

780

1991 1992 1993 1994 1995 1996 1997 1998

708

706

704

702

1975 1980 1985 1990 1995 2000

710

705

700

695

Well RNM-1

Well RNM-2

Well RNM-2s

Well UE-5n

WATER LEVEL, IN FEET BELOW LAND SURFACE

Well UE-5n

Area enlarged

below

Figure 7. Continued.
22 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

1990 1991 1992 1993 1994 1995 1996 1997 1998

860

850

840

830

820

1990 1991 1992 1993 1994 1995 1996 1997 1998

840

835

830

1982 1984 1986 1988 1990 1992 1994 1996 1998

860

850

840

830

820

1991 1992 1993 1994 1995 1996 1997

1,134

1,132

1,130

1,128

1965 1970 1975 1980 1985 1990 1995 2000

1,150

1,140

1,130

1,120

Well WW-4

Well WW-4

Well WW-4a

Well UE-11a

WATER LEVEL, IN FEET BELOW LAND SURFACE

Well UE-11a

Area

enlarged below

Scale enlarged

on next page

Area enlarged

below

Figure 7. Continued.
WATER-LEVEL MEASUREMENTS 23

1996 1997 1998 1999

1,166

1,165

1,164

1960 1965 1970 1975

1,550

1,545

1,540

1960 1965 1970 1975

1,620

1,570

1,520

1960 1965 1970 1975 1980

1,550

1,545

1,540

1,535

1990 1991 1992 1993 1994 1995 1996 1997 1998

838

837

836

835

834

Well WW-C1

Well WW-C1

Well SM-23

Well WW-4a

WATER LEVEL, IN FEET BELOW LAND SURFACE

Well WW-C

Scale enlarged

below

Figure 7. Continued.
24 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

1,035

1,030

1,025

1995 1996 1997 1998 1999

787

786

785

784

1960 1965 1970 1975 1980 1985 1990 1995 2000

795

790

785

780

1960 1965 1970 1975 1980 1985 1990 1995 2000

1,740

1,735

1,730

1960 1965 1970 1975 1980 1985 1990 1995 2000

1,107

1,102

1,097

Well Army-1

Well Army-1

Well Army-6a

WATER LEVEL, IN FEET BELOW LAND SURFACE

Area enlarged

below

Well TW-3

Well TW-F

Figure 7. Continued.
WATER-LEVEL MEASUREMENTS 25

Table 4. Mean, minimum, and maximum water levels and land-surface altitudes for wells in the Frenchman Flat area, Nevada

Test Site

[Period of record for mean, minimum, and maximum water levels based on “water levels used for trend analysis” data shown in figure 7. Number of

measurements: number indicates periodic water-level measurements by wire line, steel tape, or electric tape; continual water-level measurements by pressure

transducer. Previously estimated altitude of land surface data from USGS files; GPS and previously estimated land-surface altitudes referenced to the

National Geodetic Survey of 1929. Abbreviation: GPS, Global Positioning System. All water-level values rounded to 0.1 foot]

Local well

name

Water level Land surface (feet)

Period of record Number of

measurements

Mean Minimum

(deepest)

Maximum

(shallowest)

GPS altitude

Previously

estimated

altitude

Difference

in GPS and

previously

estimated

altitude

(feet below land surface)

Mercury Valley

Army-1 1962–97 25 785.8 791.2 783.6 3,153.50 3,153.30 0.20

Army-6a 1958–97 27 1,031.3 1,033.0 1,028.4 1 3,446.22

1 Land-surface altitude from USGS level survey. A nearby surveyed benchmark was not available for level survey; therefore, GPS altitude at well

Army-1 was used for level-survey benchmark at well Army-6a.

3,445.00 1.22

SM-23 1996–97 15 1,164.6 1,164.8 1,164.5 3,543.35 3,543.40 -.05

SM-23 Oct 1996 to

July 1997

continual 1,164.7 1,164.9 1,164.4

Frenchman Flat

PW-1 1993–96 73 771.1 771.3 770.8 ( 2)

2 GPS land-surface altitude survey was in error; previously estimated land-surface altitude at well PW-1 from first-order level survey (Brian Dozier,

Bechtel Nevada, written commun., 1997).

3,178.24 ( 2)

PW-2 1993–96 60 840.0 840.3 839.7 3,246.41 3,246.52 -.11

PW-3 1993–96 78 889.1 889.4 888.5 3,295.47 3,295.62 -.15

RNM-1 1975–77 5 787.9 789.0 786.0 3,135.03 3,136.40 -1.37

RNM-2 1974–85 7 724.1 727.8 718.8 3,128.76 3,131.73 -2.97

RNM-2s 1974–93 35 725.6 728.4 720.3 3 3,131.25

3 GPS land-surface altitude survey was in error; altitude shown in table from USGS level survey. A nearby surveyed benchmark was not available for

level survey; therefore, GPS altitude at well RNM-1 was used for level-survey benchmark at well RNM-2s.

3,133.00 -1.75

RNM-2s 1994–97 8 723.5 723.6 723.4

TW-3 1963–97 20 1,103.8 1,104.9 1,101.8 3,484.10 3,484.00 .10

TW-F 1962–97 27 1,735.6 1,737.1 1,733.8 4,140.82 4,142.70 -1.88

UE-5c 1971–87 6 807.1 810.5 805.4 3,216.14 3,216.00 .14

UE-5n 1977–91 43 704.8 706.1 702.9 3,112.38 3,112.20 .18

UE-5n 1991–97 38 704.5 705.2 703.3

UE-11a 1991–96 23 1,131.7 1,132.6 1,130.5 3,538.19 3,538.00 .19

WW-4 1983–97 26 835.3 837.2 829.0 3,604.12 3,601.50 2.62

WW-4a 1990–97 26 835.6 836.8 834.6 3,604.24 3,605.67 -1.43

WW-4a Aug. 1991 to

Mar. 1993

continual 835.8 838.2 834.6

WW-5a 1959–95 34 709.1 714.1 695.7 3,092.47 3,093.00 -.53

WW-5a 1996–97 22 711.6 712.3 710.9

WW-5a 1996–98 continual 711.8 712.5 710.3

WW-5b 1959–91 14 683.8 688.8 681.4 3,092.80 3,092.10 .70

WW-5c 1954–93 23 702.1 729.8 689.1 3,081.42 3,081.00 .42

Southern Yucca Flat

WW-C 1961–75 13 1,542.9 1,545.4 1,537.0 3,924.06 3,921.00 3.06

WW-C1 1962–72 14 1,544.3 1,548.0 1,542.0 3,923.50 3,921.00 2.50

Mean of absolute difference in GPS values 1.08
26 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Periodic Measurements

Periodic water-level measurements at NTS have

been collected by the U.S. Geological Survey (USGS)

since 1951 and are maintained in the USGS National

Water Information System (NWIS). Periodic waterlevel measurements are collected using steel tapes,

electric tapes, or electric-cable units (wire-line or ironhorse devices; Wood and Reiner, 1996). Water-level

measurements prior to 1996 typically were made with

electric cable units; after 1996, most measurements

were made with electric tapes (Fenelon, 2000, p. 8).

The accuracy of the electric tapes and cable units are

affected by mechanical stretch, thermal expansion, or

damage. To maintain instrument accuracy, tape and

cable units have been calibrated annually against a

2,000-ft reference steel tape since at least 1968, when

Garber and Koopman (1968, p. 6) reported its use as a

calibration standard. The reference steel tape was calibrated in 1997 by the National Institute of Standards

and Technology and showed a measurement error of

less than about 0.20 ft at a depth of 2,000 ft. Tape and

cable units are calibrated at different water-level depths

to within 0.10 percent of the reference-tape measurement and assigned an instrument correction factor. At

the time of measurement, the depth-to-water reading is

adjusted using the appropriate steel tape or cable unit

correction factor.

Continual Measurements

Continual water-level data in the Frenchman Flat

area for period of records of at least nine months are

available for wells WW-4a (1991–93), SM-23 (1996–

97), and WW-5a (1996–97; fig. 8). Water-level measurements at these wells were recorded every 5 or 15

minutes using submersible pressure transducers and

electronic data loggers. The transducer and data-logger

systems were calibrated by recording transducer output

at known depths of submergence. Manual water-level

measurements were made when transducers were

installed and removed from service to reference the

depth of submergence to land surface, and during the

period of continual measurements to assure proper

operation and accurate data collection. The procedure

for calibrating pressure transducers is outlined by

La Camera and Locke (1997, p. 15).

WATER-LEVEL ADJUSTMENTS

Adjustments of periodic and continual waterlevel measurements are presented for the effects

of barometric pressure, water density (from watertemperature measurements), borehole deviation,

and land-surface altitude. These adjustments are

not required for the analysis of long-term waterlevel trends for selected wells in this report, but may be

critical for future calculations of hydraulic heads.

Barometric Pressure

Water-level measurements shown in figure 8 for

wells SM-23 and WW-5a were adjusted for the effects

of barometric pressure prior to evaluating the hydrographs for significant water-level trends. Water-level

adjustments were determined from hourly barometricpressure measurements collected at each well during

the same period as the continual water-level measurements.

A graphical procedure (Brassington, 1988, p. 83)

was used to adjust water levels for the effects of barometric pressure. As outlined by Brassington (1988), the

graphical procedure includes:

(1) determining a constant barometric efficiency

of the aquifer at each well. Barometer efficiency is the

change in water level divided by the change in barometric pressure, expressed in equivalent units of

hydraulic head as a percent,

(2) multiplying the change in barometric pressure

between two successive measurements by the barometric efficiency, and

(3) adding the amount calculated in (2) to the

water-level measurement if successive barometricpressure measurements increased, or subtracting

the amount calculated in (2) if successive barometricpressure measurements decreased.

This adjustment for barometric pressure is based

on a constant barometric efficiency that represents an

average value for the period of record. Some error in

the water-level adjustment, therefore, may be introduced in shorter-term periods (for example, daily,

monthly, or seasonal periods of the hydrograph) when

the constant barometric efficiency used in the graphical

procedure differs from the true barometric efficiency.

The slope of adjusted water levels, therefore, may be

slightly different over short intervals of the hydrograph

than the slope of water levels adjusted using a variable

barometric efficiency; however, the beginning and ending adjusted water levels would be equivalent.
WATER-LEVEL ADJUSTMENTS 27

Figure 8. Continual water levels in wells SM-23 (1996–97), WW-5a (1996–98), and WW-4a

(1991–93), Nevada Test Site.

1991 1992 1993

838

836

834

1996 1997 1998

713

712

711

710

709

WATER LEVEL, IN FEET BELOW LAND SURFACE

1996 1997

1,165.0

1,164.5

1,164.0

Water levels uncorrected for barometric pressure

Water levels corrected for barometric pressure

Linear regression line

EXPLANATION

Well SM-23

Well WW-5a

Well WW-4a

B.

C.

A.

J A S O N D J F M A M J J A S O N D 

J A S O N D J F M A M J J A S O N D J F M A M J 

 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 

Minimum water level at 838.2 ft
28 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

A second limitation of the procedure is that the

absolute value of the adjusted water level is a function of

the initial barometric pressure. Therefore, a change in

the initial barometric pressure causes a “shift” in the

absolute value of the adjusted water level. However, the

relative change in adjusted water levels (the slope or

trend of the hydrograph) is unaffected.

The barometric efficiencies of the aquifers at

observation wells SM-23 (86 percent) and WW-5a (64

percent) were substantially higher than at observation

well WW-4a (about 1 percent). Water-level adjustments

for the effects of barometric pressure in wells SM-23 and

WW-5a (fig. 8), therefore, resulted in hydrographs that

contain lower amplitude water-level fluctuations (figs.

8A and 8B). Because of a low barometric efficiency,

water levels in well WW-4a were not adjusted for the

effects of barometric pressure (fig. 8C). A water-level

response in well WW-4a to barometric pressure likely is

masked by the effect of pumping from nearby well

WW-4.

Water Density

Variation in water density (from water-temperature

measurements) in the study area may affect the accuracy

of hydraulic-head measurements. Water density and

temperature are inversely related and as water temperature increases, water density decreases. The water level

in wells with anomalously high water temperature will

be higher than water of lower temperature in nearby

wells open to the same aquifer and pressure conditions.

The average temperature of water samples collected from wells in the Frenchman Flat area with available data (Perfect and others, 1994; Rose and others,

1997) is about 94°F for wells open to the carbonate aquifer (excluding well TW-F) and about 75°F for wells open

to the alluvial and volcanic aquifers and quartzite confining unit (fig. 9). The average water temperature in well

TW-F (147°F) for water samples collected since the well

was deepened and completed in the carbonate aquifer in

1962 (Perfect and others, 1994) is substantially higher

than in other wells open to the carbonate aquifer. The

depth of well TW-F is 3,400 ft, which is more than 1,400

ft deeper than other wells completed in the carbonate

aquifer with available temperature data (wells WW-C,

WW-C1, TW-3, and Army-1). The greater depth of well

TW-F, however, does not completely account for the

high temperature in this well. For example, assuming a

geothermal gradient of 0.014°F per foot (the average

gradient estimated for the Pahute Mesa area; Pottoroff

and others, 1987, p. 3), a 2,000-foot increase in the depth

of well TW-3 to a depth equal to that of well TW-F

would cause a corresponding increase in water temperature of about 28°F. However, water temperatures in well

TW-F are almost 50°F higher than temperatures in well

TW-3. The anomalous trend of decreasing temperature

with increasing depth for the carbonate-aquifer wells

shown in figure 9 (not including well TW-F) also illustrates that factors other than depth, such as geologic

structure, likely are important in controlling water temperature.

Although temperature likely is the most important

factor affecting water density in well TW-F, other factors

such as a relatively high dissolved-solids concentration

or the compressibility of water caused by pressure from

the overlying water column can influence water density.

However, the relatively low dissolved-solids concentrations of water in well TW-F (less than about 550 milligrams per liter between 1962–80; Perfect and others,

1994) would not significantly affect water density. Additionally, based on standard relations between water density, pressure, and temperature, Winograd (1970, p. 24)

concluded that the effect of pressure on water density in

well TW-F is minor in comparison to the effect of temperature.

An adjustment for the effect of water density on

water levels in well TW-F was determined using a procedure applied by Winograd (1970). Using this procedure, the density of the water column in well TW-F is

adjusted to a standard density that best represents the

average density of the water column in nearby wells

completed in the carbonate aquifer. The following equation, modified from Winograd (1970, p. 23), was used to

adjust water levels in well TW-F to a standard density:

WCcorrected = (DTW/Dcarb) * WCuncorrected (1)

where WCcorrected is the corrected length of the water

column between the static water

level and the top of the open interval, in feet;

WCuncorrected is the uncorrected length of the water

column between the mean static

water level and the top of the open

interval, in feet;

DTW is the density of 144°F water in well

TW-F, in grams per cubic centimeter

(g/cm3

) = 0.98207 g/cm3 (Chemical

Rubber Publishing Co., 1985, p.

F-10); and

Dcarb is the standard density of 94°F water

= 0.99425 g/cm3 (Chemical Rubber

Publishing Co., 1985, p. F-10).
WATER-LEVEL ADJUSTMENTS 29

The magnitude of the water-level adjustment

using equation 1 depends on the length of the water column to be corrected and on the ratio of the density of

water in well TW-F and the standard density. For this

report, the length of the water column is based on 1,414

ft of water between the mean static water level in the

well for 1962–97 (1,736 ft below land surface) and the

top of the open interval (3,150 ft below land surface).

The density of water in well TW-F (DTW) is based on

the average temperature of the water column (144°F)

determined from a borehole geophysical temperature

log (Winograd, 1970, p. 24). The average temperature

of water in wells TW-3, WW-C, WW-C1, and Army-1

(94°F) was used to determine the standard density.

The average temperature of water in these wells was

determined from pumped water samples because borehole geophysical temperature logs were not available.

Solving equation 1 for WLcorrected, the length of the

water column would be 1,396.7 ft, resulting in a

decrease in water level of 17.3 ft. This adjustment is

about 15 percent larger than the 15 ft adjustment determined by Winograd (1970, p. 24) using a standard density based on a temperature of 100°F.

Equation 1 can be used to estimate the effect, if

any, of temporal changes in water temperature and

associated density on water-level fluctuations in well

TW-F. For example, the maximum difference in water

levels in well TW-F between 1962 and 1997 was about

60 70 80 90 100 110 120 130 140 150 160

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Alluvial aquifer

Volcanic aquifer

Carbonate aquifer

Quartzite confining unit

EXPLANATION

Principal aquifer or confining unit contributing water to well–

Well TW-F

WATER SAMPLE TEMPERATURE, IN DEGREES FAHRENHEIT

DEPTH OF WELL, IN FEET BELOW LAND SURFACE

Figure 9. Temperature of water samples collected from selected wells in the Frenchman Flat area, Nevada

Test Site.
WATER-LEVEL ADJUSTMENTS 31

3.5 ft (fig. 7). During this period, four temperature

measurements of water samples collected from well

TW-F indicate a maximum change of less than 2°F.

Assuming that these temperature measurements are

representative of the average water column temperature in well TW-F, a 2°F rise in average temperature

from 144° to 146°F, would result in a new water density (DTW) of 0.98149 g/cm3. Solving equation 1 for

WLcorrected, the length of the water column would be

1,395.9 ft — an increase in the water-level adjustment

from 17.3 ft to 18.1 ft. A rise in water temperature of

2°F in well TW-F, therefore, would cause a corresponding rise in water level of about 0.8 ft, or about 23

percent of the maximum water-level change observed

during this period.

Borehole Deviation

Most boreholes deviate slightly from true vertical

during drilling. If a gyroscopic or “borehole deviation”

survey was made during geophysical logging of the

borehole, measured water levels can be adjusted to represent the true vertical water-level depth below land

surface. Borehole deviation surveys were completed in

about half of the wells drilled in the Frenchman Flat

area.

Three water-level adjustments were developed

using linear equations based on measured cumulative

borehole deviation across a selected depth interval

(table 5). If a complete deviation survey was available,

linear equations were developed to adjust water levels

Table 5. Water-level adjustments for borehole deviation in selected wells in the Frenchman Flat area, Nevada Test Site

Borehole-deviation survey: Complete results, data available for entire borehole; limited results, data for horizontal displacement at bottom of borehole

only; depth interval, equals depth interval used to determine linear equation.

Type of water-level adjustment: Adjustment 1, based on a borehole deviation survey (BDS) depth interval that bounds historic water levels; adjustment 2,

based on a BDS depth interval from top to bottom of borehole; adjustment 3, no BDS data available; therefore, based on a depth interval from top to bottom

of borehole and the horizontal displacement and deviated depth at the bottom of the borehole.

Mean water-level depth: Equals mean water level for period of record based on “water levels used for trend analysis data” shown in figure 7.

Water-level adjustment: Vertical water-level depth (Vd) computed for measured water-level depth (Md) equal to mean water-level depth. Adjustment

equals difference between Vd and mean water-level depth, rounded to nearest 0.01 foot.

Local well

name

Borehole-deviation survey Type of

adjustment

Linear equation used

for adjustment

Water-level

Results Depth interval

(feet)

Mean depth

(feet)

Adjustment

(feet)

Mercury Valley

Army-1 limited 0–1,946 3 Vd = Md * 0.99923 785.8 0.61

Frenchman Flat

PW-1 complete 770–775 1 Vd = Md * 0.99800 + 1.27 771.1 .27

PW-1 complete 0–823 2 Vd = Md * 0.99960 771.1 .31

PW-2 complete 835–845 1 Vd = Md * 0.99900 + 0.17 840.0 .67

PW-2 complete 0–878 2 Vd = Md * 0.99915 840.0 .71

PW-3 complete 885–890 1 Vd = Md - 0.06 889.1 .06

PW-3 complete 5–924 2 Vd = Md * 0.99994 889.1 .05

TW-F complete 1,725–1,750 1 Vd = Md * 0.99960 + 0.49 1,735.6 .20

TW-F complete 50–1,875 2 Vd = Md * 0.99984 + 0.01 1,735.6 .27

UE-5c complete 800–825 1 Vd = Md - 0.02 807.1 .02

UE-5c complete 0–2,360 2 Vd = Md * 0.99998 807.1 .02

UE-11a complete 1,125–1,150 1 Vd = Md * 0.99960 + 0.36 1,131.7 .09

UE-11a complete 0–1,370 2 Vd = Md * 0.99985 1,131.7 .17

WW-4 complete 800–1,000 1 Vd = Md - 0.05 835.3 .05

WW-4 complete 0–1,000 2 Vd = Md * 0.99995 1 835.3 .04

Southern Yucca Flat

WW-C limited 0–1,540 3 Vd = Md * 0.99959 1,542.9 .63

WW-C1 complete 1,525–1,550 1 Vd = Md * 0.98480 +19.21 1,544.3 4.26

WW-C1 complete 25–1,707 2 Vd = Md * 0.99541 + 0.11 1,544.3 6.98

1 Calculated from deviation survey records of borehole inclination angles and depths.
WATER-LEVEL ADJUSTMENTS 31

that were based on (1) a depth interval that bounds

historic water level measurements (adjustment 1) or

(2) a depth interval from the top to the bottom of the

deviation survey (adjustment 2). If a limited deviation

survey was available (true-vertical depth data not available), the linear equation developed was based on a

depth interval from the top to the bottom of the borehole (adjustment 3). For adjustment 3, the true-vertical

depth at the bottom of the borehole was determined

from the horizontal displacement and deviated (measured) depth of the borehole.

To determine the adjusted water level, measured

and true-vertical depth data from the deviation survey

were substituted into a linear equation of the form:

WLadj = (WLm – Mtop)*(∆Vint/∆Mint)+Vtop, (2)

where WLadj is adjusted water level, in feet below

land surface;

WLm is measured water level, in feet below

land surface;

Mtop is measured top of selected depth interval

from borehole deviation survey, in feet

below land surface;

Vtop is true-vertical top of selected depth interval from borehole-deviation survey, in

feet below land surface;

∆Vint is difference in top and bottom of truevertical depth interval from borehole

deviation survey, in feet below land surface; and

∆Mint is difference in top and bottom of measured depth interval from borehole deviation survey, in feet below land surface.

For example, the borehole deviation survey for

well WW-C1 (U.S. Geological Survey data files, Las

Vegas, Nev.) shows that a measured depth interval of

1,525-1,550 ft below land surface can be used to bound

historic water-level measurements for this well (table

4). The corresponding true-vertical depths in the deviation survey at the top and the bottom of this interval

are 1,521.03 ft and 1,545.65 ft, respectively. Substituting these values into equation 2 gives the linear waterlevel adjustment for the depth interval that bound historic water levels (table 5):

WLadj = (WLm – 1,525 ft)*(24.62 ft/25.00 ft) +

1,521.03 ft . (3)

In reduced form, equation (3) becomes:

WLadj = (0.98480*WLm) + 19.21 ft . (4)

For adjusting historic water levels, adjustment 1

is more accurate than adjustments 2 or 3 because the

slope is averaged over a shorter depth interval. For

adjustments 2 and 3, some error is introduced by using

an average slope across the entire depth interval of the

deviation survey. However, adjustments 2 and 3 were

included to provide general adjustments if future water

levels in wells increase or decrease beyond the depth

interval of historic water levels used in adjustment 1.

Additional error to water-level adjustments for

borehole deviation may be caused by the accuracy of

the borehole deviation equipment in determining truevertical depth. For example, the accuracy of true-vertical depth data provided by the deviation instrument

used in wells PW-1, PW-2, and PW-3 was ± 0.5 ft (Reynolds Electric & Engineering Company, 1994, p. 4–

14). This potential error is substantially larger than the

actual water-level adjustment for these wells using the

mean static water level (table 4). Instrument accuracy

was not reported in available deviation survey records

and, therefore, the potential error in water-level adjustments for deviation in boreholes other than PW-1, PW2, and PW-3 is unknown.

Using the mean static water level (table 4), adjustments to measured water levels for borehole deviation

are less than 1 ft for all wells except well WW-C1 (table

5). Deviation survey results show that the difference

between the measured and vertical depth at the bottom

of well WW-C1 is more than 7 ft, resulting in a waterlevel adjustment of more than 4 ft.

Land-Surface Altitude

In December 1997, global positioning system

(GPS) measurements of land-surface altitude at well

locations in the Frenchman Flat area were collected by

the USGS. These measurements were collected to confirm or improve the accuracy of previously estimated

land-surface altitudes. Although land-surface altitudes

are not required for water-level trend and correlation

analyses, these data are critical when calculating waterlevel altitudes for potentiometric-surface maps. Accurate land-surface altitudes are particularly important in

Frenchman Flat, where small differences in waterlevel altitude exists for much of the alluvial aquifer

(Winograd and Thordarson, 1975, p. C60).
32 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

GPS measurements of land-surface altitude were

collected using a geodetic grade receiver. A differential

GPS procedure was used where one base-station

receiver was calibrated to a benchmark of known landsurface altitude while an additional receiver simultaneously collected satellite-transmitted data at one or

two well locations. Four benchmark locations of 1st and

2nd order accuracy (maximum relative error of less than

about 0.01 ft at the time of original survey) were used

for base stations (fig. 2). Satellite-transmitted data were

collected at benchmark and well locations for 1.5 to 2

hours. After the land-surface altitude was determined,

the location of the measuring point was marked at each

well. The GPS land-surface altitudes determined during this survey and previous survey estimates of altitude in the Frenchman Flat area are presented in table

4. A GPS survey was not completed at well Army-6a.

At wells PW-1 and RNM-2s, GPS land-surface altitudes were in error. As a result, land-surface altitudes at

wells Army-6a, PW-1, and RNM-2s were estimated

from level surveys.

Prior to completing the differential GPS surveys

at each well location, the accuracy of the GPS system

was checked by measuring the land-surface altitude at

the benchmark locations. During this accuracy check,

each benchmark alternately served as a base station of

known altitude while satellite data were collected at

two other benchmark locations. A GPS land-surface

altitude was determined for each benchmark and compared to the surveyed altitudes. Results of this survey

showed a maximum difference in GPS-derived altitude

of less than 0.07 ft from the known benchmark altitude.

The mean difference between previously surveyed land-surface altitudes and GPS-derived altitudes

(table 4) is about 1 ft. This mean difference is relatively

high considering the generally flat potentiometric surface in the alluvial aquifer in Frenchman Flat. The

mean altitude difference of about 1 ft is strongly influenced by differences of greater than 2 ft at wells

RNM-2, WW-4, WW-C, and WW-C1.

ANALYSIS OF WATER LEVELS

Water-level measurements for wells with available data in the Frenchman Flat area were evaluated to

determine (1) if statistically significant temporal trends

exist, (2) if water-level fluctuations between wells have

been similar over time, and (3) a possible cause for

observed trends or cyclic-type water-level changes.

Statistical Analysis Methods

Water-level trends are defined herein as statistically and hydrologically significant rises or declines in

the water level over time. Manual measurements collected for at least 1 year and (or) continual measurements collected for at least 9 months were used in the

trend analysis. For purposes of this report, water-level

records with 10 or less measurements were considered

sparse data sets. Statistical analysis of sparse data sets

typically result in a higher degree of uncertainty and,

therefore, are noted in this report.

Continual water-level records used for trend analysis were available for wells SM-23, WW-5a, and

WW-4a (fig. 8). Because water levels in wells SM-23

and WW-5a are affected by barometric pressure (see

“Water-Level Adjustments” section), the effect of

barometric pressure was removed from continual

water-level records for these wells prior to the trend

analysis.

Two statistical methods were applied in the trend

analysis, simple linear regression (ordinary least

squares method) and the Kendall-Theil method (Kendall’s tau rank correlation coefficient). The least

squares method was applied when water-level data

were collected from observation wells (table 1) and

changes in these data generally appeared linear.

Although water-level changes in wells may not be perfectly linear, particularly those changes affected by

nearby pumping, the least squares method provides a

reasonable estimate of the net rate of change in water

level over the period of record.

The least squares method (Helsel and Hirsch,

1992, p. 221–263) was applied using water level as the

dependent variable and time as the independent variable. The trend was considered statistically significant

if the slope of the regression line was significant at a

95-percent confidence interval. Significance of the

regression slope was tested using the t-distribution with

the null hypothesis being that the slope equalled zero;

that is, at the 95-percent confidence interval the slope

does not include zero.

Statistical measures of leverage and influence

were computed prior to applying the least squares

method to help qualitatively evaluate observations with

high leverage and (or) erratic water-level measurements (outliers). “Standardized” and “studentized”

residuals were used to detect outliers. The statistical

parameters “Cook’s D” and “DFFITS” were used to

evaluate the influence of outliers on water-level trends.
ANALYSIS OF WATER LEVELS 33

Outliers outside the 95-percent confidence level were

deleted from the water-level data set if the measurement was thought to be in error, particularly if the data

point was one of low influence. Outliers with high

influence were deleted from the data set only if the data

point was isolated in time and likely represented a different population than later or earlier water-level measurements (for example, water levels affected by

drilling).

Kendall’s tau rank correlation coefficient (Helsel

and Hirsch, 1992, p. 212) was applied when water-level

data were collected from water-supply wells (table 1)

because changes in these data may represent nonlinear

recovering water levels. Kendall’s tau also was applied

if a water-level record appeared to contain nonlinear

fluctuations (wells UE-5n and WW-5a) or appeared to

contain cyclic-type water-level fluctuations (wells

Army-1, TW-F, and TW-3).

Kendall’s tau is a robust test that indicates if a significant upward or downward change in water level has

occurred over the period of record, but does not imply

anything about the magnitude of the change in water

level or whether the change in water level is linear.

Where data are irregularly spaced or “clustered” in

time (for example, wells RNM-2s and Army-1), specific time periods may be over-represented on the overall trend because a higher number of data points per

unit time are used in the calculation relative to other

parts of the water-level record. A 95-percent confidence level was used in the test to determine a statistically significant upward or downward change in water

level.

Trends that were statistically significant were further analyzed for hydrologic significance. A trend was

considered hydrologically significant if the total

change in water level along the trend slope (regression

analysis) or the maximum water-level change over the

period of record (Kendall’s tau analysis) was greater

than three times the accuracy of the measurement

instrument. For manual water-level measurements,

three times the accuracy of the NTS reference steel tape

is 0.60 ft. For continual water-level measurements,

three times the accuracy of a submersible pressure

transducer at maximum recording pressure (15 lb/in2

)

is 0.02 ft. These values were arbitrarily selected, but

could indicate water-level trends that are worthy of

attention.

To help identify wells with similar hydrologic

responses and possible sources of water-level fluctuations, a correlation analysis was completed. Correlations were computed for water levels in nearby wells,

water levels and pumpage from nearby wells, and

water levels and precipitation. To determine the correlation between two variables the observations must be

paired in time. Correlations between water levels in

nearby wells typically were from the same day,

although sparse data often were matched by week or by

month. For most correlations involving pumpage or

precipitation, water-level data were lagged by day,

week, month, and (or) years. Gaps in the pumpage or

precipitation data sets were considered missing data

(rather than a value of zero). Water levels matched

against a gap in the pumpage or precipitation data set

were therefore deleted prior to the correlation analysis.

Correlations between periodic and continual data generally were matched using a single periodic value and

the mean value of the continual data for the same day.

The exceedance probability (p-value) associated

with the statistical parameters “Spearman’s rho” and

“Pearson’s r” (Helsel and Hirsch, 1992, p. 217–219)

was used to determine the significance of each correlation. Spearman’s rho is a nonparametric, rank correlation coefficient; Pearson’s r is a parametric, linear

correlation coefficient. Because many data sets used in

this analysis are not normally distributed, a greater

weight was placed on the parameter Spearman’s rho

than on the parameter Pearson’s r. Therefore, a correlation was considered statistically significant if the

p-value associated with Spearman’s rho was equal to or

less than 0.05. The correlation was considered statistically marginal if the p-value associated with Spearman’s rho was between 0.05 and 0.10 and statistically

not significant if the p-value was equal to or greater

than 0.10.

Trend Analysis Results

Water levels in five wells had both statistically

and hydrologically significant trends. Statistically significant trends were observed for three wells completed

in the alluvial aquifer (WW-5a, UE-5n, and PW-3), one

well completed in the carbonate aquifer (SM-23), and

one well completed in the quartzite confining unit

(Army-6a). The results of the trend analysis for 21

wells are presented in table 6. Linear-regression lines

for the water levels used in the trend analysis are shown

in figures 7 and 8.
34 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

1 Water-level measurements show cyclic-type fluctuations.

2 Water-level change of +0.21ft less than three times measurement error for periodic water-level data (0.60 ft).

3 Data set has 10 or less water-level measurements.

Table 6. Results of trend analysis of water levels for wells in the Frenchman Flat area, Nevada Test Site

Data type: Periodic, water levels measured by wire-line, steel tape, or electric tape; continual, water levels measured by pressure transducer.

Statistical technique applied: Kendall's tau, Kendall's rank correlation coefficient test; regression, simple linear regression test.

Statistical significance: Linear trend considered statistically significant if null hypothesis of t-distribution rejected at 95-percent confidence

interval. Nonlinear trend considered significant if the probability (p) value associated with Kendall's tau is less than 0.05 and the correlatation

coefficient (Kendall's tau) is greater than 0.50.

Linear trend: Indicates a general linear decrease (-) or increase (+) of water levels in the well over time.

Water-level change: Equals difference in beginning and ending water-level values along linear trend line (regression analysis) or difference

between the maximum and minimum water level over the period of record (Kendall's tau analysis); --, not applicable.

Hydrological significance: Statistically significant trends considered hydrologically significant if total change along linear trend slope (regression

analysis) or maximum water-level change over the period of record (Kendall's tau analysis) is greater than three times the accuracy of the

measurement instrument; up, significant water level rise; --, not applicable.

Local

well name Data type Period of record

Statistical

technique

applied

Statistical

significance

Linear trend

(feet per year)

Water-level

change

(feet)

Hydrologic

significance

Mercury Valley

Army-11 periodic 1962–97 Kendall's tau none not estimated -- --

Army-6a periodic 1958–97 regression significant -0.09 -3.64 significant

SM-23 periodic 1996–97 regression significant +.14 +.21 2

none

SM-23 continual Oct. 1996 to July 1997 regression significant +.19 +.15 significant

Frenchman Flat

PW-1 periodic 1993–96 regression none not estimated -- --

PW-2 periodic 1993–96 regression none not estimated -- --

PW-3 periodic 1993–96 regression significant +.21 +.76 significant

RNM-1 periodic 3

1975–77 regression none not estimated -- --

RNM-2 periodic 3

1974–85 regression none not estimated -- --

RNM-2s periodic 1974–93 Kendall's tau none not estimated -- --

RNM-2s periodic 3

1994–97 regression none not estimated -- --

TW-31 periodic 1963–97 Kendall's tau none not estimated -- --

TW-F1 periodic 1962–97 Kendall's tau none not estimated -- --

UE-5c periodic 3

1971–87 Kendall's tau none not estimated -- --

UE-5n periodic 1977–91 Kendall's tau none not estimated -- --

UE-5n periodic 1991–97 regression significant -.26 -1.51 significant

UE-11a periodic 1991–96 regression none not estimated -- --

WW-4 periodic 1983–97 Kendall's tau none not estimated -- --

WW-4a periodic 1990–97 Kendall's tau none not estimated -- --

continual Aug. 1991 to Mar. 1993 Kendall's tau none not estimated -- --

WW-5a periodic 1959–95 regression significant -.43 -15.33 significant

periodic 1996–97 regression significant +.67 +1.20 significant

continual Oct. 1996 to Jan. 1998 Kendall's tau significant not estimated 2.18 up

WW-5b periodic 1959–91 Kendall's tau none not estimated -- --

WW-5c periodic 1954–93 Kendall's tau none not estimated -- --

Southern Yucca Flat

WW-C periodic 1961–75 Kendall's tau none not estimated -- --

WW-C1 periodic 1962–72 Kendall's tau none not estimated -- --
ANALYSIS OF WATER LEVELS 35

Alluvial Aquifer

In the central part of Frenchman Flat, several

wells had statistically significant trends. The trend

analysis indicated that water levels in well WW-5a

declined at a rate of about 0.4 ft/yr for 1959–95 with a

total decrease in water level of more than 15 ft. The

trend analysis of the periodic and continual water-level

data for well WW-5a for 1996–98, however, indicates

a reversal of the long-term declining water-level trend.

From 1996 to 1998, water levels in well WW-5a

increased at a rate of about 0.7 ft/yr (table 6).

Water-level fluctuations in observation well

WW-5a appear to be related to pumping from nearby

water-supply well WW-5c (fig. 10). An increase

(decrease) in pumping from WW-5c causes a corresponding decrease (increase) in water levels in well

WW-5a. The correlation between water levels in obserSEPT OCT NOV DEC JAN

0

0.10

0.20

0.30

0.40

0

0.10

0.20

0.30

0.40

712

711

710

Well WW-5a

Well WW-5c

Well WW-5b

WATER LEVEL, IN FEET 

BELOW LAND SURFACE DAILY WITHDRAWAL, IN MILLION GALLONS

1997 1998

Figure 10. Water levels in observation well WW-5a and withdrawal from water-supply wells WW-5b and

WW-5c from September through December 1997, Nevada Test Site. Water levels corrected for

barometric pressure.
36 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

vation well WW-5a and pumping from water-supply

well WW-5c is supported by significant p-values for

Spearman and Pearson correlation coefficients.

The water-level response in well WW-5a to

pumping from well WW-5b appears to be either nonexistent or masked by the effect of pumping from well

WW-5c (fig. 10). In 1996, for example, water levels in

well WW-5a began to rise shortly after pumping from

well WW-5c stopped (November 1997; fig. 10). During the following 45 days, water-level fluctuations in

well WW-5a showed no correlation to pumping from

well WW-5b (p-values for Spearman and Pearson correlation coefficients were not significant). The distance

from well WW-5b to well WW-5a is about 2 mi and

probably contributes to the lack of a direct water-level

response in this observation well. Well WW-5c is about

1 mi from well WW-5a.

A statistically significant water-level trend was

determined for well UE-5n for 1991–97 (table 6). The

1991-97 period of record was selected for analysis

because pumping from nearby test well RNM-2s was

stopped in mid-1991. During 1991–97, water levels in

well UE-5n declined at a rate of about 0.3 ft/yr (fig. 7).

The frequency of water-level measurements for

well UE-5n were not sufficient to establish a long-term

correlation with pumping from well RNM-2s. A substantial quantity of water was continuously pumped

from well RNM-2s for radionuclide transport tests during 1975–91. Water-level fluctuations in well UE-5n

during this period did not decline but appear erratic.

For example, water levels increased in well UE-5n during 1983–86 even though pumping from test well

RNM-2s generally was constant (fig. 11A). Furthermore, after pumping from well RNM-2s stopped in

1991, water levels in well UE-5n continued to rise for

a few months and then declined. The water-level

response in well UE-5n from 1991 to 1997 generally

was opposite to the water-level response in test well

RNM-2s (fig. 11B).

The erratic water-level fluctuations in well UE-5n

may be a response to recharge of water discharged from

test well RNM-2s. The water pumped from test well

RNM-2s was discharged to an unlined channel near

well UE-5n and contained elevated concentrations of

tritium (IT Corporation, written commun., 1998).

Water in well UE-5n also has contained elevated concentrations of tritium, suggesting that discharged water

from well RNM-2s has recharged the alluvial aquifer

(IT Corporation, written commun., 1998). Declining

water levels in well UE-5n during 1991–97, therefore,

may represent the effect of dissipating recharge of

water previously discharged from well RNM-2s.

Similar to well RNM-2s, the frequency of waterlevel measurements in well UE-5n (fig. 11C) are not

sufficient to accurately determine the influence of

pumping from water-supply wells UE-5c or WW-5b.

On the basis of available data, however, changes in

pumping from wells UE-5c or WW-5b do not appear to

cause corresponding water-level changes in well

UE-5n. Correlations between water-level fluctuations

in well UE-5n and pumping from well WW-5b or well

UE-5c were not statistically significant.

The trend analysis indicated that water levels in

well PW-3 increased at a rate of about 0.2 ft/yr during

1993–96 (table 6). The cause of the increasing waterlevel trend (rising water levels in the well) in well

PW-3 is not clear. On the basis of soil-water chemistry

data, Tyler and others (1996) reported that recharge to

the alluvial aquifer at well PW-3 has not occurred since

the last glacial maxima, about 20,000 years before

present. Furthermore, water withdrawals from wells

UE-5c and WW-5b (fig. 5) for 1993–96 do not appear

to correlate with rising water levels in well PW-3

(p-values for Spearman and Pearson correlation coefficients were not significant). The rising water-level

trend in well PW-3 may be a response to cessation of

pumping in well RNM-2s in 1991. However, waterlevel measurements are not available to determine the

potentiometric surface in the area of well PW-3 prior to

1993.

Volcanic Aquifer

The long-term water-level trends for wells WW-4

and WW-4a, completed in the volcanic aquifer, were

not statistically significant. However, a comparison of

continual water-level records shows similar water-level

fluctuations (fig. 12). Water-levels collected in well

WW-4 during pumping coincide with declining water

levels in observation well WW-4a, and indicates that a

hydraulic connection likely exists between these wells.

About 3 months of continual water-level data are available for water-supply well WW-4 prior to pumping of

well WW-4a. The correlation between water-level fluctuations in these wells is supported by significant p-values for Spearman and Pearson correlation coefficients.
ANALYSIS OF WATER LEVELS 37

Figure 11. Water levels in wells UE-5n (1977–97) and RNM-2s (1974–97) and withdrawals from wells RNM-2s

(1975–91), WW-5b (1983–97), and UE-5c (1983–97), Nevada Test Site.

0

5

10

Withdrawal from water-supply well WW-5b (graph C)

Withdrawal from water-supply well UE-5c (graph C)

0

10

20

30

Withdrawal from test well RNM-2s (graphs A and B)

0

10

20

30

708

706

704

702

Water levels in observation well UE-5n (graphs A and C)

730

725

720

715

Water levels in test well RNM-2s (graph B)

1974 1978 1982 1986 1990 1994 1998

708

706

704

702

EXPLANATION

WATER LEVEL, IN FEET BELOW LAND SURFACE

MONTHLY WITHDRAWAL, IN MILLION GALLONS

A.

B.

C.
38 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 12. Water-level altitudes in water-supply well WW-4 and observation well WW-4a for January–March 1993, Nevada

Test Site.

JAN FEB MAR

2,768

2,769

2,770

2,771

2,772

2,730

2,740

2,750

2,760

2,770

2,780

2,790

2,800

Static 

water level

in waterPumping

water level

in water-supply

well WW-4

Missing water-level data

WATER-LEVEL ALTITUDE IN WATER-SUPPLY WELL WW-4, IN FEET ABOVE SEA LEVEL

WATER-LEVEL ALTITUDE IN OBSERVATION WELL WW-4A, IN FEET ABOVE SEA LEVEL

Water level in observation 

well WW-4a

supply well

WW-4

1993
ANALYSIS OF WATER LEVELS 39

Carbonate Aquifer

A significant trend of increasing water levels during 1996–97 was observed in well SM-23 (fig. 8), completed in the carbonate aquifer about 4 mi north of well

Army-1. Using continual water-level data, the analysis

showed an increasing trend of about 0.2 ft/yr for well

SM-23 from October 1996 to July 1997 (table 6).

Continual water measurements at observation

well SM-23 do not correlate with pumping from watersupply well Army-1 (p-values for Spearman and Pearson coefficients were not significant). This poor correlation may be due to (1) irregular daily pumping of well

Army-1, (2) a poor hydraulic connection between the

two wells, and (or), (3) the quantity of pumping from

well Army-1 being too small to affect water levels in

well SM-23. Well Army-1 contains almost 900 ft of

open interval, but well SM-23 is open to only 30 ft of

the carbonate aquifer. Pumping from well Army-1 generally has decreased since about mid-1994 when withdrawals were reduced by more than 50 percent (fig. 5).

These factors would likely produce either a lagged and

irregular water-level response or no water-level

response in well SM-23.

Statistically significant water-level trends for the

period of record were not observed for wells TW-F,

TW-3, or Army-1 (table 6). The absence of longer-term

trends for these wells may be due to the cyclic nature of

water-level fluctuations that are apparent on the hydrographs (fig. 7). Water levels in wells TW-F, TW-3 and

Army-1 generally declined during the 1960’s,

increased during the 1970–80’s, and again declined

during the 1990’s. Similar water-level fluctuations in

observation wells TW-F and TW-3 are supported by

statistical correlation (p-values for Spearman and Pearson coefficients were significant). Water-level fluctuations between these wells and well Army-1, however,

were not statistically significant. The lack of statistical

correlation with well Army-1 may be due to the uncertainty associated with recovering water levels in this

water-supply well.

Cyclic-type water-level fluctuations in wells

TW-F and TW-3 may be the result, in part, of precipitation-induced recharge, ground-water pumping, or

some combination of both causes. Infiltration of precipitation in higher altitude recharge areas near the

Frenchman Flat area, where fractured carbonate rocks

outcrop, might provide a mechanism for the observed

water-level fluctuations in these wells. Ground-water

flow through the carbonate aquifer largely is controlled

by fractures, which increase the permeability of the

rock unit (Laczniak and others, 1996, p. 27). Results of

aquifer tests at Yucca Mountain show that the permeability of fractured carbonate or volcanic rock typically

is several orders-of-magnitude greater than unfractured

rock (Luckey and others, 1996, p. 32). Regional

ground-water flow through the fractured carbonate

aquifer beneath the Frenchman Flat area (fig. 2) is

thought to originate to the east and southeast in the

Spotted Range, South Ridge, and Spring Mountains

(fig. 1) where carbonate rock crops out.

Comparison of water levels in wells TW-F and

TW-3 with long-term cycles of precipitation (cumulative monthly departure from mean precipitation) generally support precipitation-induced recharge as a source

of water-level fluctuations (fig. 13). Precipitation at

Yucca Flat station (fig. 1) was less than normal

(declined) in the 1960’s and early 1990’s and greater

than normal (increased) during the 1970–80’s. These

changes in precipitation generally where similar to

long-term changes of water levels in the carbonate

aquifer. Precipitation records at Yucca Flat station were

chosen because of the relatively long period of record

(1958–94). Long-term fluctuations in precipitation at

this station are similar to precipitation measured near

well WW-5b in Frenchman Flat and at Mercury (fig. 3),

and generally coincide with precipitation changes

reported for southern Nevada (Dettinger and Schaefer,

1995, fig. 3).

A statistically significant correlation was

observed between cumulative monthly departure from

mean precipitation and lagged water levels in well

TW-F; a marginal statistical correlation was observed

for well TW-3 (p-value associated with Spearman’s rho

equal to 0.06). Although the statistical analysis resulted

in more than one lagged time where water levels reasonably fit precipitation data, the most significant correlation occurred when water levels were lagged about

3 years behind precipitation (figs. 13A and 13B). A

lagged water-level response in these wells may represent the time interval for precipitation to (1) infiltrate in

higher-altitude areas some distance from the well, (2)

move as ground water through unsaturated fractured

rock to the water table, and (3) be observed as a confined-system (pressure) response (Davis and DeWiest,

1966, p. 46) at the well. Tritium age-dating of water

emanating from springs in the carbonate rocks of the

Spring Mountains and from tunnel seepage in volcanic

rock beneath Rainier Mesa (fig. 1) suggests that infiltration of precipitation-induced recharge in fractured
40 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Figure 13. Lagged water levels in wells TW-F and TW-3 (1962–97), cumulative departure from mean monthly precipitation

at Yucca Flat station (1958–94), and withdrawal from water-supply wells WW-C1, WW-C, and Army-1 in carbonate-rock

aquifer (1961–97), Nevada Test Site.

1960 1970 1980 1990 2000

0

100

200

300

Total annual withdrawal from wells WW-C, WW-C1, and Army-1

1,108

1,103

1,098

1,740

1,735

1,730

Water levels 

20

10

0

10

20

20

10

0

10

20

Departure from mean monthly precipitation (shifted 3 years)

WATER LEVEL, IN FEET BELOW LAND SURFACE

Data not available

1972-82

EXPLANATION

MONTHLY DEPARTURE FROM MEAN 

PRECIPITATION,IN INCHES

ANNUAL WITHDRAWAL, 

IN MILLION GALLONS 

A.

B.

C.

Direction of shifted precipitation data

Shifted precipitation data begins

on June 1,1958

Shifted precipitation data ends

on December 31, 1994

Well TW-3

Well TW-F
SUMMARY 41

rocks to depths of more than 1,000 ft may occur in a

time interval of less than 6 years (Clebsch, 1961, table

194.1; Winograd and others, 1998, p. 90).

Because of missing withdrawal records for all

NTS water-supply wells, pumping from the carbonate

aquifer (wells Army-1, WW-C, and WW-C1) could not

be confirmed in this evaluation as a possible source of

water-level fluctuations in observation wells TW-F and

TW-3. Some evidence exists that pumping may influence water levels in these wells: pumping was relatively high in the late 1960’s, low in the late 1980’s, and

was again high in the early 1990’s, which generally

coincides with water-level fluctuations in these wells

(fig. 13C). Statistical correlations using available

pumping data were significant for well TW-F, but nonsignificant for well TW-3 (p-value associated with

Spearman correlation coefficient equal to 0.82).

Quartzite Confining Unit

A significant trend of decreasing water levels for

1958–97 was determined for observation well Army-6a

(fig. 7). Water levels in this well declined at a rate of

about 0.1 ft/yr for a total water-level change from 1958

to 1997 of 3.6 ft. The cause of the decline in water levels in this well is not clear. Water-level fluctuations do

not appear to correlate with pumping from water-supply well Army-1 (p-values associated with Spearman

and Pearson correlation coefficients were not significant). For example, water levels in well Army-6a do

not respond to a decrease in withdrawal from well

Army-1 in 1994 from more than 10 million gallons per

month to about 1 million gallons per month (fig. 5).

The water-level response in well Army-6a to pumping

from well Army-1, which is about 1.5 mi to the northwest (fig. 2), may be subdued, delayed, and (or) difficult to detect if a limited hydraulic connection exists

between the two wells. A limited hydraulic connection

may occur because the wells are open to different

hydrogeologic units. Well Army-6a is completed in the

quartzite confining unit that regionally underlies the

carbonate aquifer. Also, the interstitial permeability of

the quartzite confining unit typically is low (Winograd

and Thordarson, 1975, p. C42). Well Army-6a produces only a few gallons per minute when pumped

(Thordarson and others, 1967, table 1), indicating that

the permeability of the quartzite confining unit in this

area probably is low.

SUMMARY

Water-level measurements from 1954 to 1998

were compiled and quality assured for 21 wells in the

Frenchman Flat area. Water-level data were evaluated

to (1) provide water-level adjustments for potential

causes of water-level fluctuations, (2) determine if statistically and hydrologically significant water-level

trends exist, and (3) determine, if possible, the causes

of water-level trends or cyclic-type water-level fluctuations. Potential causes of water-level fluctuations in

the Frenchman Flat area of the Nevada Test Site

include changes in atmospheric conditions (precipitation and barometric pressure), Earth tides, seismic

activity, underground nuclear testing, and groundwater withdrawals.

Adjustments of periodic and continual waterlevel measurements for the effects of barometric pressure, water density (from water-temperature measurements), borehole deviation, and land-surface altitude

were determined for wells with available data. Continual water-level measurements for wells SM-23 and

WW-5a were adjusted for the effects of barometric

pressure and resulted in hydrographs that contain lower

amplitude water-level fluctuations. Relatively high

water temperature and associated low density significantly affect water levels only in well TW-F. The

water-level adjustment for well TW-F (adjusted to the

average water-sample temperature from wells completed in the carbonate aquifer) was about 17 ft. Waterlevel adjustment for the effects of borehole deviation

ranged from less than 0.1 ft to more than 4 ft. Based on

a differential global positioning system (GPS) survey

of land-surface altitudes (LSA) at wells included in this

study, the difference between previously recorded LSA

and GPS derived LSA ranged from 0.10 ft to slightly

more than 3 ft.

Water levels in five wells had statistically and

hydrologically significant linear trends. Statistically

significant trends were observed for three wells

(WW-5a, UE-5n, and PW-3) completed in the alluvial

aquifer, for one well (SM-23) completed in the carbonate aquifer, and for one well (Army-6a) completed in

the quartzite confining unit .

Water levels in observation well WW-5a declined

at a rate of about 0.4 ft/yr during 1959–95 and

increased at a rate of about 0.7 ft/yr during 1996–98.

Water-level fluctuations in well WW-5a appear to be

the result of pumping from nearby water-supply well

WW-5c (located about 1 mi from well WW-5a).
42 Analysis of Water Levels in the Frenchman Flat Area, Nevada Test Site

Water levels in observation well UE-5n declined

at a rate of about 0.3 ft/yr from 1991 to 1997. Waterlevel and water-chemistry data suggest that water discharged from test well RNM-2s has locally recharged

the alluvial aquifer near well UE-5n. Declining water

levels in well UE-5n from 1991 to 1997, therefore, may

represent the effect of dissipating recharge of water

previously discharged from well RNM-2s.

Water levels in observation well PW-3 increased

(rising water levels in the well) at a rate of about 0.2

ft/yr for 1993–96. The cause of rising water levels in

well PW-3 is not clear. Water-level fluctuations in this

well do not appear to correlate with pumping from

nearby water-supply wells (wells WW-5b and UE-5c).

Additionally, data on soil-water chemistry suggest that

precipitation-induced recharge has not occurred at well

PW-3 in the recent past.

Water levels in observation well SM-23, completed in the carbonate aquifer, increased at a rate of

about 0.2 ft/yr from October 1996 to July 1997. A significant correlation could not be established for this

period between water-level fluctuations at well SM-23

and pumping from water-supply well Army-1, located

about 4 mi south of well SM-23.

Water levels in observation wells TW-F and

TW-3 completed in the carbonate aquifer indicate the

occurrence of cyclic-type water-level fluctuations—

long-term periods (more than 5 years) when water levels decreased or increased. Visual and statistical correlation of water-level and precipitation data generally

were supportive of precipitation-induced recharge as

a possible source of long-term (1962–97), cyclic-type

water-level fluctuations in wells TW-F and TW-3. Statistically significant and marginal correlations were

observed between a 3-year lag in water levels in wells

TW-F and TW-3, respectively, and cumulative departure from mean monthly precipitation.

A significant trend of decreasing water levels for

1958–97 was determined for observation well Army6a. Water levels in this well declined at a rate of about

0.10 ft/yr. The cause of the steady decline in water levels in well Army-6a is not clear. Water levels in well

Army-6a do not correlate with pumping from watersupply well Army-1, which is about 1.5 mi to the northwest. The poor correlation may be due to a limited

hydraulic connection between the two wells, which

may subdue or delay the water-level response in well

Army-6a to pumping from well Army-1.

REFERENCES CITED

Brassington, R., 1988, Field hydrology: New York, Halsted

Press, 175 p.

Cardinalli, J.L., Roach, L.M., Rush, F.E., and Vasey, B.J.,

comps., 1968, State of Nevada hydrographic areas:

Nevada Division of Water Resources map, scale

1:500,000.

Chemical Rubber Publishing Co., 1985, Handbook of chemistry and physics (66th ed.): Boca Raton, Fla., CRC

Press, 2,370 p.

Claassen, H.C., 1973, Water quality and physical characteristics of Nevada Test Site water-supply wells: U.S.

Geological Survey Open-File Report 474-158, 145 p.

Clebsch, A., 1961, Tritium-age ground water at the Nevada

Test Site, Nye County, Nevada in Short Papers in the

Geologic and Hydrologic Sciences, Articles 147-292:

U. S. Geological Survey Professional Paper 424-C, p.

C122–C125.

Davis, S.N., and DeWiest, R.J.M., 1966, Hydrogeology:

New York, John Wiley, 463 p.

Dettinger, M.D., and Schaefer, D.H., 1995, Decade-scale

hydroclimatic forcing of ground-water levels in the

central Great Basin, eastern Nevada: Summer Symposium, American Water Resources Association, Honolulu, Hawaii, June 1995, p. 195–204.

Drellack, S.L., 1995, Selected stratigraphic data for drill

holes located in Frenchman Flat, Nevada Test Site:

Raytheon Services Nevada Report TSP:DGP:111:95,

70 p.

Fenelon, J.M., 2000, Quality assurance and analysis of water

levels in wells on Pahute Mesa and vicinity, Nevada

Test Site, Nye County, Nevada: U.S. Geological Survey

Water-Resources Investigations Report 00-4014, 68 p.

Ferris, J.G., Knowles, D.B., Brown, R.H., and Stallman,

R.W., 1962, Theory of aquifer tests: U.S. Geological

Survey Water-Supply Paper 1536-E, 174 p.

Garber, M.S., and Koopman, F.C., 1968, Methods of measuring water levels in deep wells: Techniques of Water

Resources Investigations of the United States Geological Survey, Chapter A1, Book 8, 23 p.

Geldon, A.L., Umari, A.M.A., Earle, J.D., Fahy, M.F., Gemmell, J.M., and Darnell, Jon, 1998, Analysis of a multiple-well interference test in Miocene tuffaceous rocks

at the c-hole complex, May-June 1995, Yucca Mountain, Nye County, Nevada: U.S. Geological Survey

Water-Resources Investigations Report 97-4166, 33 p.

Graves, R.P., Tucci, Patrick, and O’Brien, G.M., 1997, Analysis of water-level data in the Yucca Mountain area,

Nevada, 1985–95: U.S. Geological Survey WaterResources Investigations Report 96-4256, 140 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in

water resources: New York, Elsevier, 522 p.
REFERENCES CITED 43

Kilroy, K.C., 1992, Aquifer storage characteristics of Paleozoic carbonate rocks in southwestern Nevada estimated

from harmonic analysis of water-level fluctuations:

University of Nevada at Reno, unpublished Ph. D. dissertation, 77 p.

La Camera, R.J., and Locke, G.L., 1997, Selected groundwater data for Yucca Mountain region, southern Nevada

and eastern California, through December 1996: U. S.

Geological Survey Open-File Report 97-821, 79 p.

Laczniak, R.J., Cole, J.C., Sawyer, D.A., and Trudeau, D.A.,

1996, Summary of hydrogeologic controls on groundwater flow at the Nevada Test Site, Nye County,

Nevada: U.S. Geological Survey Water-Resources

Investigations Report 96-4109, 59 p.

Lehman, L.L., and Brown, T.P., 1996, Summary of State of

Nevada-funded studies of the saturated zone at Yucca

Mountain, Nevada: Burnsville, Minn., L. Lehman &

Associates, Inc., 44 p.

Luckey, R.R., Tucci, Patrick, Faunt, C.C., Ervin, E.M.,

Steinkampf, W.C., D’Agnese, F.A., and Patterson, G.L.,

1996, Status of understanding of the saturated-zone

ground-water flow system at Yucca Mountain, Nevada,

as of 1995: U.S. Geological Survey Water-Resources

Investigations Report 96-4077, 71 p.

Nimz, G.J., and Thompson, J.L., 1992, Underground radionuclides migration at the Nevada Test Site: Reynolds

Electrical & Engineering Co., Inc., Report DOE/NV346 UC-703, 17 p.

O’Brien, G.M., 1993, Earthquake-induced water-level fluctuations at Yucca Mountain, Nevada, June 1992: U.S.

Geological Survey Open-File Report 93-73, 12 p.

———1997, Determination of aquifer-system properties

based on the water-level frequency response to atmospheric loading and earth tides, Yucca Mountain,

Nevada: Colorado School of Mines, unpublished Master’s thesis, 280 p.

Perfect, D.L., Faunt, C.C., Steinkampf, W.C., and Turner,

A.K., 1994, Hydrochemical data base for the Death Valley region, California and Nevada: U.S. Geological

Survey Open-File Report, 13 p. (2 diskettes).

Pottorff, E.J., Erickson, S.J., and Campana, M.E., 1987,

Hydrologic utility of borehole temperatures in Areas 19

and 20, Pahute Mesa, Nevada Test Site: University of

Nevada, Desert Research Institute Publication 45060,

189 p.

Reynolds Electric & Engineering Company (REECo), 1994,

Site characterization and monitoring data from Area 5

pilot wells, Nevada Test Site, Nye County, Nevada:

U.S. Department of Energy, Nevada Operations Office,

DOE/NV/11432-74, 124 p.

Rose, T.P., Kenneally, J.M., Smith, D.K., Davisson, M.L.,

Hudson, G.B., and Rego, J.H., 1997, Chemical and isotopic data for groundwater in southern Nevada:

Lawrence Livermore National Laboratory Report

UCRL-ID-128000, 35 p.

Rush, F.E., 1968, Index of hydrographic areas in Nevada:

Nevada Division of Water Resources, Information

Report 6, 38 p.

Thordarson, William, Young, R.A., and Winograd, I.J.,

1967, Records of wells and test holes in the Nevada Test

Site and vicinity (through December 1966): U.S. Geological Survey Open-File Report TEI-872, 26 p.

Todd, D.K., 1980, Groundwater hydrology: New York, John

Wiley, 535 p.

Tyler, S.W., Chapman, J.B., Conrad, S.H., Hammermeister,

D.P., Blout, D.O., Miller, J.J., Sully, M.J., and Gianni,

J.M., 1996, Soil-water flux in the southern Great Basin,

United States—Temporal and spatial variations over

the last 120,000 years: Water Resources Research, v.

32, no. 6, p. 1481–1499.

U.S. Department of Energy, 1994, United States nuclear

tests, July 1945 through September 1992: U.S. Department of Energy, Nevada Operation Office, DOE/NV209 (rev. 14), 105 p.

Winograd, I.J., 1970, Noninstrumental factors affecting

measurement of static water levels in deeply buried

aquifers and aquitards, Nevada Test Site: Ground

Water, v. 8, no. 2, p. 19–28.

Winograd, I.J., and Thordarson, William, 1975, Hydrogeologic and hydrochemical framework, south-central

Great Basin, Nevada-California, with special reference

to the Nevada Test Site: U.S. Geological Survey Professional Paper 712-C, 126 p.

Winograd, I.J., Riggs, A.C., and Coplen, T.B., 1998, The relative contributions of summer and cool-season precipitation to ground water recharge, Spring Mountains,

Nevada, USA: Hydrogeology Journal, v. 6, p. 77–93.

Wood, D.B., and Reiner, S.R., 1996, Ground-water data for

1990–91 and ground-water withdrawals for 1951-91,

Nevada Test Site and vicinity, Nye County, Nevada:

U.S. Geological Survey Open-File Report 96-475, 78 p.