Statistical Stationarity of Sediment Interbed 

Thicknesses in a Basalt Aquifer, Idaho National 

Laboratory, Eastern Snake River Plain, Idaho

Scientific Investigations Report 2008-5167

U.S. Department of the Interior

U.S. Geological Survey

DOE/ID-22204

Prepared in cooperation with the U.S. Department of Energy
Cover: Photograph of sediment core, corresponding natural gamma 

log, and sediment thickness distributions with time. (Courtesy of John 

Welhan, Idaho Geological Survey).
Statistical Stationarity of Sediment 

Interbed Thicknesses in a Basalt Aquifer, 

Idaho National Laboratory, Eastern Snake 

River Plain, Idaho

By Caleb N. Stroup, Department of Geosciences, Idaho State University, John A. 

Welhan, Idaho Geological Survey, and Linda C. Davis, U.S. Geological Survey

Prepared in cooperation with the U.S. Department of Energy

Scientific Investigations Report 2008–5167

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Stroup, C.N., Welhan, J.A., and Davis, L.C., 2008, Statistical stationarity of sediment interbed thicknesses in a basalt 

aquifer, Idaho National Laboratory, eastern Snake River Plain, Idaho: U.S. Geological Survey Scientific Investigations 

Report 2008–5167, 20 p.
iii

Contents

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

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

Purpose and Scope .............................................................................................................................2

Previous Work .......................................................................................................................................2

Statistical Analysis ......................................................................................................................2

Interpreted Stratigraphy.............................................................................................................4

Composite-Unit Stratigraphy .....................................................................................................5

Data Acquisition and Methods....................................................................................................................5

Data Collection......................................................................................................................................5

Analysis Approach................................................................................................................................6

Statistical Analysis of Sedimentary Interbed Thickness .......................................................................9

Tests of Spatial Stationarity: Composite Units 2–7..........................................................................9

Tests of Temporal Stationarity ............................................................................................................9

Interbed Thicknesses Inferred from Natural-Gamma Logs...........................................................9

Summary and Conclusions.........................................................................................................................17

Acknowledgments.......................................................................................................................................17

References Cited..........................................................................................................................................17

Appendix A. Development of Database ..................................................................................................19
iv

Figures

Figure 1. Map showing location of the study area, major topographic features, and

ground-water flow model boundaries within the Idaho National Laboratory,

Idaho .......................................................................................... 3

Figure 2. Map showing locations of wells included in this study and in the studies of

Anderson and Liszewski (1997) and Welhan and others (2006), in the study

area, Idaho National Laboratory, Idaho................................................... 4

Figure 3. Graph showing thickness and depth to the base of all sedimentary interbeds

observed in this study, Idaho National Laboratory, Idaho .............................. 7

Figure 4. Graphs showing frequency distribution of individual sedimentary interbed

thicknesses among three groups of composite-stratigraphic units, Idaho

National Laboratory, Idaho ............................................................... 8

Figure 5. Map showing locations of two geographic groups of coreholes used in tests

of spatial stationarity, Idaho National Laboratory, Idaho .............................. 10

Figure 6. Graphs showing frequency distributions of individual sedimentary interbed

thicknesses within composite stratigraphic units 2–7 from two geographic

groups of coreholes, Idaho National Laboratory, Idaho .............................. 11

Figure 7. Graphs showing frequency distributions of individual sedimentary interbed

thickness for composite units 2–3, 4–5, and 6–7, Idaho National Laboratory,

Idaho .......................................................................................... 12

Figure 8. Graphs showing frequency distributions of individual sedimentary interbed

thicknesses among two groups of interbeds from nearby boreholes, from this

study and from the study of Anderson and Liszewski (1997), Idaho National

Laboratory, Idaho ........................................................................... 14

Figure 9. Graphs showing frequency distributions of individual sedimentary interbed

thicknesses among two groups of interbeds, from this study based only on

natural-gamma logs and from the study of Anderson and Liszewski (1997),

Idaho National Laboratory, Idaho ......................................................... 16
v

Tables

Table 1. Summary of composite stratigraphic units and time spans as defined by

Anderson and Liszewski (1997), Idaho National Laboratory, Idaho .................. 5

Table 2. Summary of available lithologic, natural-gamma, and photographic log

sources and logged intervals from coreholes used in this study, Idaho

National Laboratory, Idaho ............................................................... 5

Table 3. List of boreholes with defined composite unit stratigraphy near new

coreholes analyzed in this study, Idaho National Laboratory, Idaho. ............... 6

Table 4. Results of nonparametric tests of similarity of sediment thickness medians,

variances, and distribution shapes between two geographic groups of

coreholes, Idaho National Laboratory, Idaho .......................................... 11

Table 5. Results of nonparametric tests of similarity of median sediment thicknesses

between three composite unit groups, Idaho National Laboratory, Idaho ......... 11

Table 6. Results of nonparametric tests of similarity of median sediment thicknesses

between various composite unit groups within composite units 2–7, Idaho

National Laboratory, Idaho ............................................................... 13

Table 7. Boreholes from which stratigraphic information was compiled by Anderson

and Liszewski (1997) and compared with information gathered from new

coreholes in this study, Idaho National Laboratory, Idaho ........................... 13

Table 8. Results of nonparametric tests of similarity of sediment thickness medians,

variances, and distribution shapes between two independent data sets,

Idaho National Laboratory, Idaho.......................................................... 14

Table 9. Results of nonparametric tests of similarity of sediment thickness medians,

variances, and frequency distribution shapes, Idaho National Laboratory,

Idaho .......................................................................................... 15

Table 10. Results of nonparametric tests of similarity of sediment thickness medians,

variances, and distribution shapes between two independent data sets

interpreted from natural-gamma logs, Idaho National Laboratory, Idaho ............ 16
vi

Conversion Factors, Datums, and Abbreviations and 

Acronyms

Conversion Factors

Multiply By To obtain

foot (ft) 0.3048 meter (m)

foot per day (ft/d) 0.3048 meter per day (m/d)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8.

Datums

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29). 

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

Abbreviations and Acronyms

Abbreviation or 

Acronym Definition

DOE U.S. Department of Energy

ESRP eastern Snake River Plain

INL Idaho National Laboratory

INTEC Idaho Nuclear Technology and Engineering Center

Ka Thousand years

K-S Kolmogorov-Smirnov two sample test of similarity of distribution shape

K-W Kruskal-Wallis test for similarity of multiple medians 

L Levene’s test of similarity of variances

M-W Mann-Whitney test for similarity of two medians

PDF Portable Document Format

RWMC Radioactive Waste Management Complex

USGS U.S. Geological Survey
Statistical Stationarity of Sediment Interbed 

Thicknesses in a Basalt Aquifer, Idaho National 

Laboratory, Eastern Snake River Plain, Idaho

By Caleb N. Stroup1, John A. Welhan2, and Linda C. Davis3

Abstract

The statistical stationarity of distributions of sedimentary 

interbed thicknesses within the southwestern part of the 

Idaho National Laboratory (INL) was evaluated within 

the stratigraphic framework of Quaternary sediments and 

basalts at the INL site, eastern Snake River Plain, Idaho. 

The thicknesses of 122 sedimentary interbeds observed in 

11 coreholes were documented from lithologic logs and 

independently inferred from natural-gamma logs. Lithologic 

information was grouped into composite time-stratigraphic 

units based on correlations with existing composite-unit 

stratigraphy near these holes. The assignment of lithologic 

units to an existing chronostratigraphy on the basis of nearby 

composite stratigraphic units may introduce error where 

correlations with nearby holes are ambiguous or the distance 

between holes is great, but we consider this the best technique 

for grouping stratigraphic information in this geologic 

environment at this time. 

Nonparametric tests of similarity were used to evaluate 

temporal and spatial stationarity in the distributions of 

sediment thickness. The following statistical tests were applied 

to the data: (1) the Kolmogorov-Smirnov (K-S) two-sample 

test to compare distribution shape, (2) the Mann-Whitney 

(M-W) test for similarity of two medians, (3) the KruskalWallis (K-W) test for similarity of multiple medians, and 

(4) Levene’s (L) test for the similarity of two variances.

Results of these analyses corroborate previous work 

that concluded the thickness distributions of Quaternary 

sedimentary interbeds are locally stationary in space and time. 

The data set used in this study was relatively small, so the 

results presented should be considered preliminary, pending 

incorporation of data from more coreholes.

1

Department of Geosciences, Idaho State University, Pocatello, Idaho 83209.

2

Idaho Geological Survey, Department of Geosciences, Idaho State 

University, Pocatello, Idaho 83209.

3

U.S. Geological Survey, Idaho National Laboratory Project Office, P.O. Box 

2230, Idaho Falls, Idaho 83415. 

Statistical tests also demonstrated that natural-gamma 

logs consistently fail to detect interbeds less than about 2–3 ft 

thick, although these interbeds are observable in lithologic 

logs. This should be taken into consideration when modeling 

aquifer lithology or hydraulic properties based on lithology.

Introduction

The eastern Snake River Plain (ESRP) aquifer, 

Idaho’s largest fresh-water source, lies within the ESRP 

mafic volcanic province. Pahoehoe basalt and intercalated 

sediments make up most of the aquifer, with andesite 

and rhyolite as minor components. Transmissivities and 

hydraulic conductivities in the aquifer range over six orders 

of magnitude, and linear ground-water flow velocities are 

as much as 10 ft/d (Ackerman, 1991; Anderson and others, 

1999). Recent ground-water flow modeling has shown that 

these hydraulic properties are sensitive to the proportion of 

sediment intercalated within the basalt.

Analysis of sedimentary occurrences by Welhan and 

others (2006) indicated that the abundance of sediment relative 

to basalt was statistically stationary: the local medians and 

variances of sediment abundance do not vary in response to 

spatial trends, either geographically or time-stratigraphically. 

Evidence of this was used to justify the application of 

the kriging interpolation method for modeling sediment 

abundance in the aquifer. Nonstationary data can be kriged by 

accounting for a trend, but more importantly, the absence of a 

trend reveals one of the underlying properties of the geologic 

system (in this case, a relatively constant sedimentation rate 

over the entire study area for at least the past 800 thousand 

years [Ka]).
2 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

Testing for stationarity is relatively straightforward. 

In this study, as in the work of Welhan and others (2006), 

nonparametric tests of similarity were applied because the 

distributions were non-normal and variably skewed. The tests 

evaluate the degree of statistical similarity between paired and 

multiple sample populations, in terms of their similarity in 

shape, medians, and variances.

Numerous well borings, geophysical and lithologic 

logging records, and drill cores have been collected in the INL 

region to help define the geohydrologic regime in this part 

of the ESRP aquifer (fig. 1). Improved understanding of the 

subsurface stratigraphy has led to increasingly sophisticated 

conceptual and digital models of the aquifer and of groundwater flow and contaminant transport at various spatial 

scales. A subregional-scale flow model (approximately 25 

by 75 mi; fig. 1) is currently being tested and refined at the 

U.S. Geological Survey (USGS) INL Project Office. Relative 

sediment abundances within the aquifer have been shown 

through model calibration to significantly affect hydraulic 

conductivity values. A more realistic model of the spatial and 

stratigraphic variability of sediment may be required to further 

refine the ground-water flow model. 

This study was undertaken by the USGS, in cooperation 

with the U.S. Department of Energy, to test fundamental 

assumptions, namely spatial and temporal stationarity, of a 

geostatistical model of sediment abundance at INL that was 

developed by Welhan and others (2006). Any future groundwater flow model calibrations will hinge on the accuracy and 

reliability of such models, and this study was designed to test 

statistical assumptions in the sediment abundance model. The 

study also was designed to identify problems or biases in data 

sets that could affect subsequent studies of a larger scope, 

such as the subregional scale ground-water flow model being 

developed by the USGS (Ackerman and others, 2006). 

Purpose and Scope 

This report describes the results of statistical tests that 

were used to evaluate the conclusion of Welhan and others 

(2006) that sedimentary interbeds at INL are distributed in 

a statistically stationary manner, in a spatial and a temporal 

sense, using new and more detailed data available subsequent 

to their study. Welhan and others used stratigraphic data 

interpreted from geophysical logs of 333 wells to demonstrate 

that sediment abundances of the stratigraphic units below 

the water table appear to be statistically invariant in different 

areas of the INL and through geologic time. The data used 

in this study are of higher quality than those used by Welhan 

and others (2006) because detailed lithologic logs of drill 

cores were available to compliment interpretations based on 

natural-gamma logs by confirming the existence, position, and 

thickness of sedimentary interbeds.

The lithologic information used in the previous study 

of Welhan and others (2006) was based only on naturalgamma log interpretations, so the reliability and quality of 

the stratigraphic data were unknown; therefore, this study 

also evaluated the accuracy of the lithologic information 

that can be obtained solely from natural-gamma logs. High 

quality stratigraphic data compiled from lithologic logs 

in this study were compared with stratigraphic inferences 

based only on geophysical logs to determine if the naturalgamma logs consistently failed to identify interbeds less than 

about 2–3 feet thick. The relative effort required to interpret 

geophysical data in conjunction with lithologic logs versus 

natural-gamma logs alone was also evaluated. 

Stratigraphic data, including 122 sedimentary interbeds, 

from 11 coreholes within the INL boundary were entered 

into a stratigraphic database. The 11 holes included eight 

“USGS series” holes and three “Middle series” holes. All new 

holes are in the southwestern part of the INL. Stratigraphic 

information was gathered using lithologic, photo, and naturalgamma logs.

Previous Work

Geophysical logging has been the primary method for 

characterizing lithologies and distinguishing sediment from 

basalt in the subsurface at the INL (Barraclough and others, 

1976; Anderson, 1991; Anderson and Liszewski, 1997). Drill 

cores have been selectively analyzed for properties such as 

geochronology, paleomagnetism, and bulk geochemistry 

(Kuntz and others, 1980; Anderson and others, 1997). 

Systematic interpretation of these and other data sets has 

led to the development of a stratigraphic framework and a 

conceptual model of ground-water flow in the ESRP aquifer 

(Ackerman and others, 2006). Recent work has focused on 

characterizing the geostatistical distribution of sediment within 

the aquifer to aid in future model calibrations (Welhan and 

others, 2006).

Statistical Analysis

Welhan and others (2006) modeled the distribution of 

sediment in the aquifer to better understand the variability 

in hydraulic conductivity within the aquifer and to increase 

the accuracy of simulation made with the subregional-scale 

ground-water flow model being developed by the USGS INL 

Project Office. A main conclusion drawn from their work was 

that sediment abundance (relative to basalt) in the aquifer is 

spatially and temporally stationary (statistically invariant). 

This fundamental assumption allowed Welhan and others 

(2006) to krige borehole data as two-dimensional spatial 

data, characterize the geographic distribution of sediment 

abundance, and parameterize hydraulic conductivity with 

respect to individual flow model layers (Welhan and others, 

2006, p. 13–15).
Introduction 3

Figure 1. Location of the study area, major topographic features, and ground-water flow model boundaries within the 

Idaho National Laboratory, Idaho. 

idtac08-0226_Figure 01

0 20 KILOMETERS

0 20 MILES

10

10

113°30’ 113° 112°30’

44°

43°

43°30’

Atomic

City

Arco

Howe

Mud 

Lake

Terreton

PIONEER MOUNTAINS

LOST RIVER RANGE

LEMHI RANGE

SNAKE

RIVER

Big

Lost

River

Mackay

Reserviour Little

lost River

Birch Creek

Camas

Creek

Mud 

Lake

Study area

Figures 2 and 5 

location

Big 

Southern 

Butte

Middle

Butte East

Butte

EASTERN SNAKE RIVER PLAIN

20

20

26

93

26

93

33

28

Base from U.S. Geological Survey digital data, 1:24,000 and 1:100,000

Albers Equal-Area Conic projection Standard parallels 42°50’N and 

44°10’N, central meridian 113°00’W

Datum is North American Datum of 1927

EASTERN

SNAKE

RIVER

PLAIN

IDAHO NATIONAL

LABORATORY

BOISE

TWIN FALLS POCATELLO

IDAHO

FALLS

IDAHO

EXPLANATION

Idaho National Laboratory boundary

Model boundary

Ground-water flow model boundary
4 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

Interpreted Stratigraphy

Because fewer than 10 percent of all boreholes on the 

INL have been cored, almost all stratigraphic correlation 

analyses have relied on geophysical and geochemical 

indicators. Early subsurface stratigraphic work in the area 

of the Radioactive Waste Management Complex (RWMC) 

(Barraclough and others, 1976) used predominantly 

geophysical logs to characterize sedimentary interbeds and 

individual basalt-flow groups (defined as packages of flows 

derived from a single shield volcano). Studies conducted 

by Anderson and coworkers (Anderson and Lewis, 1989; 

Anderson, 1991; Anderson and Bowers, 1995; Anderson and 

Bartholomay, 1990) resulted in the first and most carefully 

documented stratigraphic framework for the INL subsurface. 

This work characterized subsurface lithologic variability and 

offered stratigraphic correlations across the INL on the basis 

of natural-gamma log records that had been calibrated to 

available core properties. Interpreted subsurface stratigraphy 

from 333 boreholes across the INL and vicinity (fig. 2) 

5 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000 and 1:100,000

Albers Equal-Area Conic projection Standard parallels 42°50’N and 

44°10’N, central meridian 113°00’W

Datum is North American Datum of 1927

0

0 5 MILES

Big Lost

River

26

20

33 LOST RIVER RANGE

EXPLANATION

Idaho National Laboratory boundary

New well analyzed in this study

Well included in the study of Anderson and Liszewski (1997) 

 and Welhan and others (2006)

Well from the study of Anderson and Liszewski (1997) from

 which stratigraphy was compared with new wells

USGS 106

USGS 134

113°10' 113° 112°50'

43°30'

43°35’

43°40'

OW-2

EBR I

USGS 106

CFA 2

USGS 85 CFA LF 3-11

USGS 76

TRA 08

Site 19

EFS Well

Highway #3

USGS 98

USGS 39 USGS 57

USGS 123

USGS 134

USGS 132

USGS 131

USGS 129 USGS 127

USGS 128

USGS 133

MIDDLE 2051

MIDDLE 1823

MIDDLE 2050A

USGS 130

Radioactive Waste

Management Complex

Figure 2. Locations of wells included in this study and in the studies of Anderson and Liszewski (1997) and Welhan and others 

(2006), in the study area, Idaho National Laboratory, Idaho.
Data Acquisition and Methods 5

were compiled into a database (Anderson and others, 1996; 

Anderson and Liszewski, 1997). These data were used by 

Welhan and others (2006) to analyze and geostatistically 

model sediment abundances in the aquifer beneath the INL.

Composite-Unit Stratigraphy

Anderson and Liszewski (1997) proposed a stratigraphic 

classification based on groups of units of similar age to show 

principal subsurface stratigraphic features. They grouped 

individual basalt and sedimentary units into 14 composite 

stratigraphic units, each made up of 5 to 90 individual 

stratigraphic units of similar age (Anderson and Liszewski, 

1997, p. 14, table 4). 

Composite units recognized in the subsurface of the 

INL are summarized in table 1. Composite unit 1, the 

youngest, consists of 78 basalt-flow groups and as many as 12 

sedimentary interbeds. Composite unit 14, the oldest, consists 

of 4 identified basalt-flow groups and 1 sedimentary interbed. 

The decreasing number of individual units within successively 

older composite units may be either the result of larger and 

less-frequent volcanic eruptions or possibly a function of the 

decreasing availability of borehole data with depth on which 

to base stratigraphic correlations. Composite units 2–7 are the 

primary focus of this study because the ESRP aquifer is hosted 

primarily in these units within the study area. Composite units 

8–14 were grouped together and evaluated as a single sample 

because of the limited number of deep coreholes, resulting 

in small sample size and the difficulty of making individual 

composite-unit assignments. 

Data Acquisition and Methods

Stratigraphic data were collected from multiple sources 

and used to test hypotheses of statistical similarity of the 

frequency distributions of sediment interbed thickness. Data 

were collected from several sources and by various methods, 

and were analyzed by a selected suite of statistical tests. 

Data Collection

Subsurface stratigraphic information for boreholes in this 

study was derived from lithologic data and natural-gamma 

geophysical logs. Independent stratigraphic interpretations 

based on only natural-gamma logs and interpretations 

based on a combination of natural-gamma and lithologic 

log information were catalogued in a spreadsheet database 

(appendix A). Unless otherwise specified, “interbed thickness” 

data in this report refers to what are considered the most 

accurate inferences of thicknesses derived from a combination 

of lithologic and natural-gamma log information. 

Lithologic logs from “USGS series” holes 127 through 

134 were obtained from the USGS INL Project Office in 

electronic format (table 2). Lithologic information from holes 

designated Middle 2050a and Middle 2051 was obtained 

from photographic logs of recovered core. Visual distinction 

between sediment and basalt in the core-box photographs was 

fairly straightforward. Lithologic information for hole Middle 

1823 was available only from a depth of 500 ft to 1,654 ft 

(Mazurek, 2005); the first 500 ft of the hole were not cored 

(table 2). Natural-gamma logs were provided by the USGS 

INL Project Office for all coreholes in this study and were the 

only type of geophysical data used in this analysis. 

Composite 

stratigraphic unit

Approximate time span 

of the unit (Ka)

1 5–250

2 250–350

3 350–440

4 440–515

5 515–580

6 580–650

7 650–800

8–14 800–1,800

Table 1. Summary of composite stratigraphic units and time 

spans as defined by Anderson and Liszewski (1997), Idaho 

National Laboratory, Idaho.

[Abbreviation: Ka, thousand years]

Corehole

Lithologic log coverage Natural-gamma 

log coverage

Log source Depth below 

land surface (ft)

Depth below 

land surface (ft)

USGS 127 USGS PDF 15–598 4–576

USGS 128 USGS PDF 0–766 7–743

USGS 129 USGS PDF 0–779 3–732

USGS 130 USGS PDF 0–703 0–693

USGS 131 USGS PDF 0–809 3–726

USGS 132 USGS PDF 9–1,235 0–1,220

USGS 133 USGS PDF 0–812 7–746

USGS 134 USGS PDF 0–949 0–921

Middle 1823 Mazurek (2005) 500–1,650 6–1,593

Middle 2050A USGS photo log 76–1,427 0–1,413

Middle 2051 USGS photo log 127–1,179 0–1,170

Table 2. Summary of available lithologic, natural-gamma, and 

photographic log sources and logged intervals from coreholes 

used in this study, Idaho National Laboratory, Idaho.

[Abbreviations: PDF, Portable Document Format; USGS, U.S. Geological 

Survey; ft, foot]
6 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

Each lithologic unit encountered in a corehole was 

assigned to a composite stratigraphic unit by correlating the 

corehole’s stratigraphy with that of nearby holes in which a 

composite-unit stratigraphy had been previously defined by 

Anderson and Liszewski (1997). Boreholes that were used for 

this purpose are listed in table 3. Where direct correlation of 

individual units was difficult or ambiguous, a comparison of 

depth of interbed and depth of composite units in surrounding 

holes aided in composite unit assignment.

Five coreholes (USGS 129, USGS 130, USGS 133, 

USGS 134, and Middle 1823; fig. 2) terminated within 

a sedimentary interbed, thus providing only a minimum 

thickness estimate. Such interbeds were excluded from 

subsequent analysis. Such omission ensures that all thickness 

data used in this analysis are tied to best estimates of actual 

thicknesses. Considering the rarity of this occurrence (5 

interbeds of 122 observed), omission of these beds does not 

significantly affect the statistical tests. 

Corehole Borehole(s) used to 

assign composite unit designations

Approximate 

 distance apart

(ft)

USGS 127 USGS 130; USGS 106 5,150; 11,200 

USGS 128 CFA LF 3-11; USGS 85 95; 1,200

USGS 129 EBR I 1,500

USGS 130 CFA 2 1,450

USGS 131 USGS 106 6,600

USGS 132 OW-2 1,650

USGS 133 EFS Well 6,350

USGS 134 Site 19; USGS 98 8,850; 15,850

Middle 1823 USGS 76; TRA 08 3,500; 1,750

Middle 2050A USGS 57; USGS 76; 

USGS 39; USGS 123

3,850; 2,500; 2,750; 

4,200

Middle 2051 Highway 3 4,500

Table 3. List of boreholes with defined composite unit stratigraphy near 

new coreholes analyzed in this study, Idaho National Laboratory, Idaho. 

[Stratigraphy assigned in these holes by Anderson and Liszewski (1997) was used to make 

composite unit stratigraphic determinations in the new holes. Abbreviation: ft, foot]

Analysis Approach

Welhan and others (2006) concluded that the proportion 

of sediment relative to basalt in composite unit 1 was larger 

than that in other composite units. Composite unit 1 also tends 

to lack thin interbeds (less than about 10 feet) (figs. 3 and 4), 

which may be the result of relative volcanic quiescence over 

the past 200 Ka (Anderson and others, 1997; Champion and 

others, 2002; Welhan and others, 2006).

Welhan and others (2006) tested the frequency 

distribution of sediment abundance within individual 

composite units in 333 boreholes across the INL and 

concluded that these frequency distributions did not vary 

in a statistically significant manner among composite units 

2 through 7 (and less confidently, between composite unit 

groups 2–7 and 8–14) (Welhan and others, 2006, p. 12 

and 16). This study tests the stationarity of the frequency 

distribution of individual interbed thicknesses within a 

composite unit rather than the distribution of total sediment 

thickness in a composite unit. The term distribution will be 

used hereafter in the statistical sense (that is, synonymous with 

frequency distribution). 
Data Acquisition and Methods 7

idtac08-0226_INL-Basalts_Figure 03

0.01

0.1

1

10

100

1,000

0 200 400 600 800 1,000 1,200 1,400 1,600

DEPTH TO INTERBED BASE, IN FEET

THICKNESS, IN FEET

CU 1 CU 2-7 CU 8-14

n=16

n=88

n=13

n–Number of

 measurements

CU 1

CU –Composite Unit

CU 2-7

CU 8-14

Figure 3. Thickness and depth to the base of all sedimentary interbeds observed in this study, Idaho National Laboratory, 

Idaho. Shaded areas indicate the average depth to the base of composite-stratigraphic unit 1 and the maximum depth to the 

base of composite-stratigraphic unit group 2–7. 

The analyses conducted here differ from the approach 

taken by Welhan and others (2006) because of the small 

sample size of the new corehole data set. The analyses 

conducted here allow more refined tests of temporal 

stationarity because they consider more information about 

the statistics of individual rather than aggregate interbed 

thicknesses, whereas the approach taken by Welhan and 

others (2006) is better at testing spatial stationarity across 

time. The two approaches are equivalent if the relative rates 

of sedimentation and volcanism that affect sediment thickness 

distributions have been invariant in time and space. 

Nonparametric statistical tests of similarity were 

performed on distribution shapes, medians, and variances 

of interbed thicknesses to determine if the different sample 

populations displayed statistically significant differences or if 

they were statistically stationary. The Kolmogorov-Smirnov 

(K-S) two sample test was used to compare distribution shape 

(form, skewness, peakedness, and degree of tailing) among 

pairs of sample populations; the Mann-Whitney (M-W) test 

was used to determine similarity of two medians; the KruskalWallis (K-W) test was used to determine similarity of multiple 

medians; and Levene’s (L) test was used to determine the 

similarity of two variances.
8 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

idtac08-0226_Figure 04

30

20

10

0

30

20

10

0

0 20 40 60 80 100

56

Composite Unit 1

INTERBED THICKNESS, IN FEET

FREQUENCY

Composite Units 2−7

Composite Units 8−14

One value at 215

30

20

10

0

n = 16

Median = 15.25

Mean = 20.91

Variance = 187.45

n = 88

Median = 2.65

Mean = 6.28

Variance = 82.58

n = 13

Median = 13.00

Mean = 34.68

Variance = 3,709.28

n = number of measurements

Figure 4. Frequency distribution of individual sedimentary interbed thicknesses among three groups of 

composite-stratigraphic units, Idaho National Laboratory, Idaho.
Statistical Analysis of Sedimentary Interbed Thickness 9

Statistical Analysis of Sedimentary 

Interbed Thickness 

Nonparametric statistical tests of spatial and temporal 

stationarity of sediment interbed thickness distributions were 

performed and are discussed in the following sections.

Tests of Spatial Stationarity: Composite 

Units 2–7

To test for spatial stationarity, interbed thickness 

distributions from two geographically grouped sets of 

five coreholes were compared (Northeast Hole Group and 

Southwest Hole Group, fig. 5). Middle 1823 was excluded 

from this analysis because lithologic information was not 

available for much of composite units 2–7 in this corehole. All 

tests of similarity showed no statistically significant difference 

between these sample groups at the 95 percent confidence 

level, thereby supporting the hypothesis of spatial stationarity 

of distributions, medians, and variances of interbed 

thicknesses (fig. 6; table 4) within the area studied. P-values 

greater than 0.05 indicate a less than 5 percent probability that 

the tested populations actually differ in the property being 

tested and therefore violate the hypothesis of stationarity.

Tests of Temporal Stationarity

The hypothesis of temporal stationarity was tested by 

comparing sedimentary interbed thickness distributions 

between groups of composite units. A general grouping 

scenario using the three groups shown in table 5 (composite 

unit 1, units 2–7, and units 8–14) was used to test if particular 

stratigraphic intervals differ from others with respect to 

interbed thickness distributions (fig. 4, table 5). The K-W 

test of similarity of multiple medians and the M-W test of 

similarity of two medians shows thickness distributions of 

composite units 2–7 are statistically different from composite 

unit 1 and units 8–14 (table 5). These results corroborate 

the conclusions of Welhan and others (2006) regarding 

composite unit 1. They concluded that sediment abundances 

in composite unit 1 were higher than in other composite units. 

The data obtained in this study also indicate that interbeds in 

composite unit 1 tend to be thicker than those in composite 

units 2–7 (fig. 4, table 5), possibly because of relative volcanic 

quiescence during the past 200 Ka (Anderson and others, 

1997; Champion and others, 2002).

Although the results of this study corroborate the 

conclusions of Welhan and others (2006) regarding temporal 

stationarity among composite units 2–7, the new data obtained 

in this study on interbed thicknesses in composite units 

8-14 do not support their conclusion that median sediment 

content in composite units 2–14 does not statistically vary. 

The low p-values indicate that median interbed thicknesses 

in composite units 2–7 are statistically different than those 

in composite units 8–14 (table 5). Sample size, however, 

is small; more deep stratigraphic data would be needed to 

confirm this result.

Welhan and others (2006) inferred temporal stationarity 

among two groupings of composite units 2-7 (composite units 

2-5 and 6-7), not among individual composite units. The K-W 

test was used to analyze the similarity of medians among three 

grouping scenarios (fig. 7, table 6). Results indicate that the 

interbed distribution of composite units 2–3 is significantly 

different at the 95 percent confidence level, whereas the 

differences among other groups are not statistically significant 

(table 6). With the exception of composite units 2–3, interbed 

thicknesses among different groupings support the hypothesis 

of temporal stationarity across composite units 4–7. 

The apparent difference between composite units 2–3 

and 4–7 may be due to random variations arising from small 

sample size (Welhan and others, 2006) or it may reflect a real 

difference. More data are needed to determine if composite 

units 2 and 3, like composite unit 1, tend to have significantly 

thicker interbeds than older units. 

Interbed Thicknesses Inferred from 

Natural-Gamma Logs

Welhan and others (2006) used the data on Quaternary 

interbed thicknesses that Anderson and Liszewski (1997) 

interpreted solely from natural-gamma logs. Those data were 

compared with the interbed thickness data compiled in this 

study from a combination of lithologic and natural-gamma 

logs. The statistical distributions of interbed thicknesses in 

the eight USGS series coreholes (USGS 127 through 134), 

Middle 2050A, and Middle 2051 (fig. 2) were compared 

with the statistical distributions of interbed thicknesses in 10 

nearby boreholes analyzed by Anderson and Liszewski (1997) 

(table 7), using the same statistical tests described above (K-S, 

M-W, and L). Data from only 10 boreholes of Anderson and 

Liszewski (1997) were used so the number of borings from 

their analysis was equal to the number of new coreholes 

studied here. Only composite unit group 1–7 was analyzed 

because sample size from composite unit group 8–14 was 

small. 
10 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

idtac08-0226_Figure 05

5 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000 and 1:100,000

Albers Equal-Area Conic projection Standard parallels 42°50’N and 

44°10’N, central meridian 113°00’W

Datum is North American Datum of 1927

0

0 5 MILES

Big Lost

River

26

20

33 LOST RIVER RANGE

EXPLANATION

Idaho National Laboratory boundary

New well analyzed in this study

Boundary of geographic group of coreholes 

113°10' 113° 112°50'

43°30'

43°35’

43°40'

Northeast Hole Group

Southwest Hole

Group

USGS 134

USGS 132

USGS 131

USGS 129 USGS 127

USGS 128

USGS 133

MIDDLE 2051

MIDDLE 1823

MIDDLE 2050A

USGS 130

Radioactive Waste

Management Complex

USGS 134

Figure 5. Locations of two geographic groups of coreholes used in tests of spatial stationarity, Idaho National 

Laboratory, Idaho. 
Statistical Analysis of Sedimentary Interbed Thickness 11

idtac08-0226_Figure 06

30

20

10

0

0 10 20 30 40 50

Northeast hole group

Composite Units 2−7

INTERBED THICKNESS, IN FEET

FREQUENCY

Southwest hole group

Composite Units 2−7

30

20

10

0

n = 34

Median = 2.85

Mean = 6.63

Variance = 89.43

n = 46

Median = 1.95

Mean = 5.19

Variance = 73.81

n = number of measurements

Figure 6. Frequency distributions of individual sedimentary interbed thicknesses within composite 

stratigraphic units 2–7 from two geographic groups of coreholes, Idaho National Laboratory, Idaho. 

Composite units 2–7 

from geographic 

hole groups Test p-value

Number of 

measurements 

from samples

1 2 1 2

Southwest vs. Northeast

M-W 0.182 46 34

L 0.219 46 34

K-S 0.503 46 34

Table 4. Results of nonparametric tests of similarity of sediment 

thickness medians, variances, and distribution shapes between 

two geographic groups of coreholes, Idaho National Laboratory, 

Idaho. 

[See figure 5 for geographic group locations. Abbreviations: M-W, MannWhitney test of similarity of medians; L, Levene’s test of similarity of 

variances; K-S, Kolmogorov-Smirnov test of similarity of distribution shape; 

p-value, probability value; vs., versus] Groupings of 

composite 

units Test p-value

Number of 

measurements 

from samples

1 2 3 1 2 3

1 vs. 2–7 vs. 8–14 K-W 0.000 16 88 13

1 vs. 2–7 M-W 0.000 16 88

2–7 vs. 8–14 M-W 0.005 88 13

1 vs. 8–14 M-W 0.693 16 13

Table 5. Results of nonparametric tests of similarity of median 

sediment thicknesses between three composite unit groups, Idaho 

National Laboratory, Idaho.

[Abbreviations: K-W, Kruskal-Wallis test for similarity of multiple medians; 

M-W, Mann-Whitney test of similarity of two medians; p-value, probability 

value; vs., versus]
12 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

idtac08-0226_Figure 07

30

20

10

0

30

20

10

0

0 10 20 30 40 50

Composite Units 2−3

INTERBED THICKNESS, IN FEET

FREQUENCY

Composite Units 4−5

Composite Units 6−7 30

20

10

0

n = 24

Median = 6.00

Mean = 9.11

Variance = 112.58

n = 31

Median = 1.70

Mean = 4.01

Variance = 39.85

n = 25

Median = 1.60

Mean = 5.04

Variance = 93.19

n = number of measurements

Figure 7. Frequency distributions of individual sedimentary interbed thickness for composite units 

2–3, 4–5, and 6–7, Idaho National Laboratory, Idaho.
Statistical Analysis of Sedimentary Interbed Thickness 13

Groupings of 

composite 

units Test p-value

Number of 

measurements 

from samples

1 2 3 1 2 3

2–3 vs. 4–5 vs. 6–7 K-W 0.001 24 31 25

2–3 vs. 4–5 M-W 0.003 24 31

4–5 vs. 6–7 M-W 0.891 31 25

2–3 vs. 6–7 M-W 0.004 24 25

2–4 vs. 5–7 M-W 0.166 47 33

2–5 vs. 6–7 M-W 0.174 55 25

Table 6. Results of nonparametric tests of similarity of median 

sediment thicknesses between various composite unit groups 

within composite units 2–7, Idaho National Laboratory, Idaho. 

[Abbreviations: K-W, Kruskal-Wallis test for similarity of multiple medians; 

M-W, Mann-Whitney test of similarity of two medians; p-value, probability 

value; vs., versus]

Distributions of interbed thicknesses from composite 

units 1-7 were quite different from those of the Anderson and 

Liszewski (1997) database, consistently showing a statistically 

significant difference in both the medians (M-W test) and the 

shapes (K-S test) of the distributions (fig. 8; table 8). These 

differences are due to the presence of relatively thin (~1-3 ft) 

interbeds that were distinguished in the new data set from 

lithologic logs, but not in the Anderson and Liszewski (1997) 

data set, and probably reflects the difference in data collection 

methods used in the two studies. Because both the medians 

and distribution shapes are statistically distinguishable, the 

similarity of variances demonstrated by the L test has no 

relevance to the overall similarity of these two samples.

By using lithologic logs in conjunction with geophysical 

logs to quantify interbed thicknesses, many more thin 

interbeds could be identified than could be inferred from 

natural-gamma signatures alone. The physical sensing 

limitation of natural-gamma sonde censors small features 

such as thin beds (Keys, 1997). Because the Anderson and 

Liszewski (1997) lithologic data were compiled using only 

natural-gamma logs, it is likely that their data are censored of 

these thin interbeds.

To test the hypothesis that the Anderson and Liszewski 

(1997) lithologic data are censored of thin interbeds, the 

interbed thickness data obtained in this study were artificially 

censored to varying degrees and compared to the data of 

Anderson and Liszewski (1997) (table 9). By excluding 

interbeds of thicknesses less than 2 ft, the statistical 

similarities between the two datasets increased such that they 

were not statistically different (table 9). By evaluating a range 

of censoring thresholds, it is possible to conclude that the 

thickness data of Anderson and Liszewski (1997) are censored 

at a threshold of between 1 and 2 feet with a 95 percent 

confidence level, and therefore are not representative of the 

statistical distribution of all interbed thicknesses.

Comparison holes for statistical tests, 

from Anderson and Liszewski (1997)

USGS 39

USGS 76

USGS 85

USGS 106

CFA LF 3-11

CFA 2

EBR 1

EFS Well

OW-2

Site 19

Table 7. Boreholes from which stratigraphic information was 

compiled by Anderson and Liszewski (1997) and compared with 

information gathered from new coreholes in this study, Idaho 

National Laboratory, Idaho. 
14 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

idtac08-0226_Figure 08

60

40

20

0

60

40

20

0

Composite Units 1−7; this study

FREQUENCY

Composite Units 1−7;

Anderson and Liszewski (1997)

0 20 40 60 80 100

INTERBED THICKNESS, IN FEET

n = 97

Median = 2.8

Mean = 7.76

Variance = 109.24

n = 74

Median = 8.50

Mean = 12.02

Variance = 124.63

n = number of measurements

Figure 8. Frequency distributions of individual sedimentary interbed thicknesses among two groups of 

interbeds from nearby boreholes, from this study and from the study of Anderson and Liszewski (1997), 

Idaho National Laboratory, Idaho. 

 Sedimentary interbed thicknesses 

of composite units 1–7 Test p-value

Number of measurements 

from samples

1 2 1 2

Anderson and Liszewski (1997) vs. This data set M-W 0.000 74 97

L 0.861 74 97

K-S 0.000 74 97

Table 8. Results of nonparametric tests of similarity of sediment thickness medians, variances, and 

distribution shapes between two independent data sets, Idaho National Laboratory, Idaho. 

[Selected data from Anderson and Liszewski (1997) interpreted from natural-gamma logs and data from this study 

gathered using both lithologic logs and natural-gamma logs. Abbreviations: M-W, Mann-Whitney test of similarity of 

medians; L, Levene’s test of similarity of variances; K-S, Kolmogorov-Smirnov test of similarity of distribution shape; 

p-value, probability value; vs., versus]
Statistical Analysis of Sedimentary Interbed Thickness 15

Table 9. Results of nonparametric tests of similarity of sediment thickness medians, variances, and 

frequency distribution shapes, Idaho National Laboratory, Idaho.

[Selected data from Anderson and Liszewski (1997) and data gathered in this study, with various degrees of artificial 

censoring. Abbreviations: M-W, Mann-Whitney test of similarity of medians; L, Levene’s test of similarity of variances; 

K-S, Kolmogorov-Smirnov test of similarity of distribution shape; p-value, probability value; vs., versus; >, greater than]

Sedimentary interbed thicknesses 

of composite units 1–7 Test p-value

Number of measurements 

from samples

1 2 1 2

Anderson and Liszewski (1997) vs. This data set

M-W 0.000 74 97

L 0.861 74 97

K-S 0.000 74 97

Anderson and Liszewski (1997) vs. This data set (> 1 foot)

M-W 0.014 74 73

L 0.687 74 73

K-S 0.000 74 73

Anderson and Liszewski (1997) vs. This data set (> 2 feet)

M-W 0.991 74 56

L 0.617 74 56

K-S 0.386 74 56

Anderson and Liszewski (1997) vs. This data set (> 3 feet)

M-W 0.050 74 46

L 0.603 74 46

K-S 0.103 74 46

Conversely, statistical comparisons of the new corehole 

data based solely on natural-gamma logs showed no 

statistically significant difference with the Anderson and 

Liszewski (1997) data (fig. 9; table 10). A few relatively thin 

(2–3 ft) interbeds were still observed with the new geophysical 

data, indicating that an unintentional bias may have been 

introduced because of pre-existing knowledge of the lithologic 

log information.

The analyses conducted here document the censoring 

effect of natural-gamma logs and indicate that detailed 

lithologic logs are essential for accurately interpreting 

subsurface interbed occurrences. Lithologic logs do not 

require significantly more effort to interpret than geophysical 

logs, and in fact may entail less effort overall. Drawbacks 

include potentially poor knowledge of the actual sediment 

recovery when coreholes are logged, together with the expense 

and infrastructural overhead involved with coring, logging, 

and core storage.
16 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

Table 10. Results of nonparametric tests of similarity of sediment thickness medians, 

variances, and distribution shapes between two independent data sets interpreted from 

natural-gamma logs, Idaho National Laboratory, Idaho. 

[Selected data from Anderson and Liszewski (1997) and data gathered in this study. Abbreviations: M-W, 

Mann-Whitney test of similarity of medians; L, Levene’s test of similarity of variances; K-S, KolmogorovSmirnov test of similarity of distribution shape; p-value, probability value; vs., versus]

 Sedimentary interbed thicknesses 

of composite units 1–7 Test p-value

Number of measurements 

from samples

1 2 1 2

Anderson and 

Liszewski (1997)

vs. This data set 

(interpreted from 

natural-gamma logs)

M-W 0.120 74 60

L 0.548 74 60

K-S 0.052 74 60

idtac08-0226_Figure 09

60

40

20

0

60

40

20

0

Composite Units 1−7; this study

(natural-gamma log interpretations)

FREQUENCY

Composite Units 1−7;

Anderson and Liszewski (1997)

0 20 40 60 80 100

INTERBED THICKNESS, IN FEET

n = 60

Median = 9.0

Mean = 11.25

Variance = 138.50

n = 74

Median = 8.50

Mean = 12.20

Variance = 124.63

n = number of measurements

Figure 9. Frequency distributions of individual sedimentary interbed thicknesses among two groups 

of interbeds, from this study based only on natural-gamma logs and from the study of Anderson and 

Liszewski (1997), Idaho National Laboratory, Idaho. 
References Cited 17

Summary and Conclusions

The stratigraphy of sedimentary interbeds from 11 

coreholes at the Idaho National Laboratory, Idaho, was 

interpreted using the best available lithologic and naturalgamma log information. This information was used to test 

hypotheses posed by earlier investigators regarding the spatial 

and temporal stationarity of aggregate interbed thickness 

distributions in the Quaternary basalt-dominated eastern 

Snake River Plain (ESRP) aquifer. A total of 122 sedimentary 

interbeds were observed in 11 subsurface borings using 

natural-gamma geophysical logs and lithologic core logs to 

identify the occurrence and thickness of interbeds beneath the 

southwestern part of the Idaho National Laboratory. 

The statistical analyses conducted in this study tested 

the stationarity of individual interbed thickness distributions 

rather than aggregate thicknesses as conducted by earlier 

investigators. The following statistical tests were applied 

to the data (1) the Kolmogorov-Smirnov (K-S) two-sample 

test to compare distribution shape, (2) the Mann-Whitney 

(M-W) test for similarity of two medians, (3) the KruskalWallis (K-W) test for similarity of multiple medians, and 

(4) Levene’s (L) test for the similarity of two variances. The 

results generally support the hypothesis that the frequency 

distribution of sedimentary interbed thicknesses in composite 

stratigraphic units designated 2 through 7 is temporally and 

spatially stationary (invariant). However, because sample size 

was small, the results should be considered preliminary until 

more high-quality corehole information becomes available. 

For example, the new data indicate that interbeds in composite 

units 2 and 3 may be thicker than those in units 4–7. The 

approach taken in this study (testing individual interbed 

thickness distributions) also might be applied to a data set 

developed for the INL by earlier investigators to explore 

more subtle aspects of statistical variability in a stratigraphic 

context, such as possible trends in the proportion of sediment 

relative to basalt in the uppermost part of the stratigraphic 

section. 

The composite unit stratigraphy developed for the Idaho 

National Laboratory in an earlier study provides a useful 

framework for grouping stratigraphic intervals and correlating 

stratigraphy in new boreholes with that of nearby existing 

holes. However, unique, laterally persistent marker horizons 

are rare and it can be difficult to correlate stratigraphic 

intervals and assign composite unit stratigraphy when holes 

are separated spatially. 

High quality lithologic logs greatly improve the ability to 

identify sedimentary interbeds in the ESRP aquifer, especially 

those that are relatively thin (less than 2–3 ft. thick). A 

combination of high-quality lithologic logs and natural-gamma 

logs provide a more confident characterization of aquifer 

lithology and stratigraphy. However, good quality stratigraphic 

data still can be obtained from geophysical logs alone when 

the presence of thin interbeds is not critical to the scope of the 

stratigraphic analysis.

Acknowledgments

The authors would like to thank Joseph Rousseau, 

Supervisory Hydrologist, USGS, for his support of this work. 

Paul Link, Professor of Geosciences, Idaho State University, 

Pocatello, Idaho, provided vision, encouragement, and 

informal reviews of early manuscripts that were fundamental 

to completion of this work. Mary Hodges, Geologist, 

USGS, provided valuable assistance in acquiring lithologic 

and geophysical data. This work was funded by the U.S. 

Department of Energy, Idaho Operations Office. 

References Cited

Ackerman, D.J., 1991, Transmissivity of the Snake River 

Plain aquifer at the Idaho National Engineering Laboratory, 

Idaho: U.S. Geological Survey Water-Resources 

Investigations Report 91-40058 (DOE/ID-22097), 35 p.

Ackerman, D.J., Rattray, G.W., Rousseau, J.P., Davis, L.C., 

and Orr, B.R., 2006, A conceptual model of ground-water 

flow in the eastern Snake River Plain aquifer at the Idaho 

National Laboratory and vicinity with implications for 

contaminant transport: U.S. Geological Survey Scientific 

Investigations Report 2006-5316 (DOE/ID-22198), 63 p.

Anderson, S.R., 1991, Stratigraphy of the unsaturated zone 

and uppermost part of the Snake River Plain aquifer at 

the Idaho Chemical Processing Plant and Test Reactors 

Area, Idaho National Engineering Laboratory, Idaho: U.S. 

Geological Survey Water-Resources Investigations Report 

91-4010 (DOE/ID-22095), 71 p.

Anderson, S.R., Ackerman, D.J., Liszewski, M.J., and 

Freiburger, R.M., 1996, Stratigraphic data for wells at and 

near the Idaho National Engineering Laboratory, Idaho: 

U.S. Geological Survey Open-File Report 96-248 (DOE/

ID-22127), 27 p. and 1 diskette.

Anderson, S.R., and Bartholomay, R.C., 1990, Use of natural 

gamma logs correlated to potassium-oxide content in 

determining the stratigraphy of basalt and sediment at the 

Idaho National Engineering Laboratory: Geological Society 

of America, Abstracts with Programs, 43rd Annual Meeting, 

Rocky Mountain Section, v. 22, n. 6, p. 1

Anderson, S.R., and Bowers, Beverly, 1995, Stratigraphy 

of the unsaturated zone and uppermost part of the Snake 

River Plain aquifer at Test Area North, Idaho National 

Engineering Laboratory, Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 95-4130 (DOE/

ID-22122), 47 p.
18 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

Anderson, S.R., Kuntz, M.A., and Davis, L.C., 1999, Geologic 

controls of hydraulic conductivity in the Snake River Plain 

aquifer at and near the Idaho National Engineering and 

Environmental Laboratory, Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 89-4065 (DOE/

ID-22142), 65 p.

Anderson, S.R. and Lewis, B.D., 1989, Stratigraphy of the 

unsaturated zone at the Radioactive Waste Management 

Complex, Idaho National Engineering Laboratory, Idaho: 

U.S. Geological Survey Water-Resources Investigations 

Report 89-4065 (DOE/ID-22080), 54 p.

Anderson, S.R., and Liszewski, M.J., 1997, Stratigraphy of 

the unsaturated zone and the Snake River Plain aquifer at 

and near the Idaho National Engineering Laboratory, Idaho: 

U.S. Geological Survey Water-Resources Investigations 

Report 97-4183 (DOE/ID-22142), 65 p.

Anderson, S.R., Liszewski, M.J., and Cecil, L.D., 1997, 

Geologic ages and accumulation rates of basalt-flow groups 

and sedimentary interbeds in selected wells at the Idaho 

National Engineering Laboratory, Idaho: U.S. Geological 

Survey Water-Resources Investigations Report 97-4010 

(DOE/ID-22134), 39 p.

Barraclough, J.T., Robertson, J.B., Janzer, V.J., and Saindon, 

L.G., 1976, Hydrology of the solid waste burial ground, as 

related to the potential migration of radionuclides, Idaho 

National Engineering Laboratory: U.S. Geological Survey 

Open-File Report 76-471 (IDO 22056), 183 p.

Champion, D.E., Lanphere, M.A., Anderson, S.R., and 

Kuntz, M.A., 2002, Accumulation and subsidence of late 

Pleistocene basaltic lava flows of the eastern Snake River 

Plain, Idaho, in Link, P.K., and Mink, L.L., eds., Geology, 

hydrogeology, and environmental remediation—Idaho 

National Engineering and Environmental Laboratory, 

Eastern Snake River Plain, Idaho: Boulder, Colo., 

Geological Society of America, Special Paper 353, 

p.175–192.

Keys, W.S., 1997, A practical guide to borehole geophysics 

in environmental investigations: Boca Raton, La., Lewis 

Publishers, 176 p.

Kuntz, M.A., Dalrymple, G.B., Champion, D.E., and Doherty, 

D.J., 1980, Petrography and paleomagnetism of volcanic 

rocks at the Radioactive Waste Management Complex, 

Idaho National Engineering Laboratory, Idaho, with an 

evaluation of potential volcanic hazards: U.S. Geological 

Survey Open-File Report 80-388, 63 p. 

Mazurek, J.A., 2005, Genetic controls on basalt alteration 

within the Eastern Snake River Plain aquifer system: 

Pocatello, Idaho State University, M.S. thesis, 178 p.

Welhan, J.A., Farabaugh, R.L., Merrick, M.J., and Anderson, 

S.R., 2006, Geostatistical modeling of sediment abundance 

in a heterogeneous basalt aquifer at the Idaho National 

Laboratory, Idaho: U.S. Geological Survey Scientific 

Investigations Report 2006-5316 (DOE/ID-22201), 32 p.
Appendix A. Development of Database 19

Table A1. List of fields under which data were entered in the 

database with a brief description of each field. 

Field Name Description

Boring_name Name of core

X_ALB Albers projection coordinate

Y_ALB Albers projection coordinate

AltWell Altitude of top of well

DepthLog Depth of recorded well log

Source_Flag Data source: “1” if non-USGS, 

“2” if USGS

StratUnit_type Unit type: sediment or basalt

Composite_unit Composite unit number 

Confidence_Composite_unit Confidence in composite unit 

designation: high, medium, low

Alt_comp_unit Where confidence is low, alternative 

composite unit designation

Confidence_Thickness Confidence in thickness of unit: 

high, medium, low

DepthBase Depth of base of interbed unit

Thickness_Lith Thickness of interbed based 

only on lithologic log

Thickness_Geophys Thickness of interbed based 

only on geophysical logs

Thickness_Inferred Inferred thickness of interbed 

based on both lithologic and 

geophysical logs

Appendix A. Development of Database

Stratigraphic information interpreted from geophysical 

and lithologic logs was entered into a Microsoft ExcelTM 

spreadsheet. The spreadsheet was set up with Excel’s 

AutoFilter capability, which allowed data in each field to 

be easily queried, sorted, or filtered. The spreadsheet can be 

imported into Microsoft AccessTM. Stratigraphic data were 

entered into 14 individual fields. A field list with a brief 

description of each field is given in table A1.

Data flags were used if information was irrelevant 

or unavailable. An -888 flag was entered if no data were 

available. A -999 flag was used if an entry was irrelevant; for 

example, -999 was entered under the Thickness_Geophys field 

for all basalt units, because geophysical logs were not used to 

quantify basalt thicknesses. 

Locations of each well (Albers coordinates) and 

elevations to the top of the wells were obtained from a USGSINL shapefile of borings on the INL. The depth of the well log 

was entered as the deepest log recording from either lithologic 

or geophysical logs. For lithologies logged by USGS 

personnel, a flag value of 2 was entered in the Source_Flag 

field, and for coreholes logged by non-USGS personnel, a 1 

was entered. The general lithology (sediment or basalt) of each 

identified unit was entered under the StratUnit_type field.

Sediment interbeds were generally represented by 

higher natural-gamma signatures. A sedimentary interbed was 

interpreted to exist only where the width and height of naturalgamma spikes were distinct from background (basalt) levels. 

Boundaries between sediment and basalt were interpreted at 

the midpoints of the top and bottom shoulders of the naturalgamma interbed signal. 

A relative confidence flag (high, medium, or low) 

was entered under the Confidence_Composite_unit field to 

qualify the degree of confidence with which a composite 

unit assignment was made. The degree of confidence was 

qualitatively based (high, medium, or low) on the proximity 

of coreholes to boreholes with established composite unit 

stratigraphy and on how well composite units could be 

correlated between these and the new coreholes. Where 

confidence was low, an alternative composite unit designation 

was entered under the Alt_Comp_Unit field to record the next 

most likely designation. 

The depth to the base of each sedimentary or basalt 

unit (in feet below top of well), regardless of lithology, was 

entered under the DepthBase field. For holes with lithologic 

logs, the thickness of sedimentary interbeds interpreted only 

from lithologic logs was entered under the Thickness_Lith 

field. Only logged sediment thicknesses were considered. 

Missing intervals in lithologic logs due to poor core recovery 

did not contribute to this thickness, although in some cases, 

sediment likely existed but was not recovered. Sediment 

interbed thickness interpreted only from natural-gamma 

logs was entered under the Thickness_Geophys field. If no 

natural-gamma spike was observed corresponding to an 

interbed recognized in a lithologic log, a thickness value of 

0 was entered to record the failure of the geophysical log to 

detect the interbed. For holes with only geophysical logs, it 

was not possible to identify sedimentary interbeds that were 

not recorded by natural-gamma logs. In this situation, some 

fraction of interbeds presumably were not recorded. For 

holes with both lithologic and natural-gamma logs, the most 

likely interbed thickness was determined using lithologic and 

natural-gamma logs and entered under Thickness_Inferred. 

This represents the best quality thickness data available on the 

basis of both lithologic logs and natural-gamma signatures of 

interbeds. The relative confidence in the inferred thickness 

was entered under the Confidence_Thickness field. The 

degree of confidence (high, medium or low) was based on the 

explicitness of the base and top of interbeds as recorded by 

lithologic logs, geophysical logs, or both. 
20 Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho

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Manuscript approved for publication, September 5, 2008

Prepared by the USGS Publishing Network 

Bill Gibbs 

Debra Grillo

Bobbie Jo Richey

Sharon Wahlstrom

For more information concerning the research in this report, contact the 

Director, Idaho Water Science Center

U.S. Geological Survey, 230 Collins Road

Boise, Idaho 83702

http://id.water.usgs.gov
Stroup and others—Statistical Stationarity of Sediment Interbed Thicknesses in a Basalt Aquifer, Idaho National Laboratory, Idaho—Scientific Investigations Report 2008-5167