THE HYDROGEOLOGIC FRAMEWORK 

I AND GEOCHEMISTRY OF THE 

COLUMBIA PLATEAU AQUIFER SYSTEM, 

WASHINGTON, OREGON, AND IDAHO

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1413-B
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The Hydrogeologic Framework 

and Geochemistry of the 

Columbia Plateau Aquifer System, 

Washington, Oregon, and Idaho

ByK.]. WHITEMANJJ. VACCAROJ.B. GONTHIER, andH.H. BAUER

REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1413-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government.

Library of Congress Cataloging-in-Publication Data

The hydrogeologic framework and geochemistry of the Columbia Plateau aquifer system, Washington, Oregon, and 

Idaho / by K.J. Whiteman ... [et al.].

p. cm. (Regional aquifer system analysis Columbia Plateau, Washington-Oregon ; ch. B) (U.S. 

Geological Survey professional paper ; 1413-B) 

Includes bibliographical references.

1. Groundwater Columbia Plateau. I. Whiteman, K. J. II. Series. III. Series: U.S. Geological Survey 

professional paper ; 1413-B. 

GB1020.H49 1993

553.7'9'09797 dc20 93-23010

CIP

For sale by Book and Open-File Report Sales, U.S. Geological Survey 

Federal Center, Box 25286, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started in 

1978 following a congressional mandate to develop quantitative appraisals of 

the major ground-water systems of the United States. The RASA Program 

represents a systematic effort to study a number of the Nation's most 

important aquifer systems, which in aggregate underlie much of the country 

and which represent an important component of the Nation's total water 

supply. In general, the boundaries of these studies are identified by the 

hydrologic extent of each system and accordingly transcend the political 

subdivisions to which investigations have often arbitrarily been limited in the 

past. The broad objective for each study is to assemble geologic, hydrologic, 

and geochemical information, to analyze and develop an understanding of the 

system, and to develop predictive capabilities that will contribute to the 

effective management of the system. The use of computer simulation is an 

important element of the RASA studies, both to develop an understanding of 

the natural, undisturbed hydrologic system and the changes brought about in 

it by human activities, and to provide a means of predicting the regional 

effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in a series 

of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number, 

and where the volume of interpretive material warrants, separate topical 

chapters that consider the principal elements of the investigation may be 

published. The series of RASA interpretive reports begins with Professional 

Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Robert M. Hirsch 

Acting Director

CONTENTS

Abstr&ct «» « - - - - «

Introduction - » « »»» - » ' » «

Purpose and scope

Previous investigations

Physical setting 

Physiography

Water-resource and economic development 

Hydrogeologic framework

Columbia River Basalt Group

Geologic structures

Internal structure of basalt flows

Page

Bl

1

2

2

2

2

2

4

7

8

11

11

14

16

22

29

Hydrogeologic framework Continued 

Geology Continued

Basalt rock mechanics 

f±y Q.rOl 0 §y "*"" «»«""«««""» "- «««« "" «

Relation between geologic and hydrologic

Ix £LTXl6 \VO IM£S ~~~~~~~«« »««« » »» »«»» 

Hydraulic characteristics 

Recharge and discharge 

Ground-water development 

Regional flow system 

Effects of development 

\jGOCilGlillS try -.« .»« « - 

Chemical evolution of the ground water 

Water-quality characteristics 

Summary and conclusions 

Page

B30

30

30

32

40

50

50

61

65

65

66

68

71

ILLUSTRATIONS

FIGURE 1. Map showing location of the Columbia Plateau aquifer system and physiographic subprovince boundaries 

2. Map showing mean annual precipitation in the Columbia Plateau, 1956-77 - 

3-6. Graphs showing:

3. Mean monthly distribution of precipitation at 103 weather stations, 1956-77 -

4. Mean minimum, mean, and maximum daily air temperatures at 89 weather stations, 1956-77 

5. Number of farms with irrigated lands and average farm size, 1949-82 

6. Population of the Columbia Plateau area, 1900-80 

7. Map showing generalized surficial geology and stratigraphic chart for the Columbia Plateau 

8. Map showing extent and thickness of overburden where its thickness is generally 50 feet or more 

9. Generalized geologic sections through the Columbia Plateau 

10-18. Maps showing:

10. Thickness of the Grande Ronde Basalt and older basalts 

11. Altitude of the top of the Grande Ronde Basalt 

12. Thickness of the Wanapum-Grande Ronde interbed 

13. Thickness of the Wanapum Basalt and interbedded sediments 

14. Altitude of the top of the Wanapum Basalt 

15. Thickness of the Saddle Mountains-Wanapum interbed 

16. Thickness of the Saddle Mountains Basalt and interbedded sediments --

17. Altitude of the top of the Saddle Mountains Basalt 

18. Major geologic structures within the Columbia Plateau 

19. Generalized diagram showing a typical basalt flow in the Columbia River Basalt Group 

20. Chart showing correlation of geologic framework with hydrologic framework 

21. Sketch of generalized ground-water-flow pattern in the Columbia Plateau aquifer system 

22. Map showing relation of the hydrologic study area, the areal extent of the Columbia River Basalt Group, and 

the Columbia Plateau Regional Aquifer-System Analysis study area 

23. Graph showing frequency distribution of hydraulic-conductivity data for the overburden aquifer 

24. Map showing areal distribution of hydraulic conductivity for the overburden aquifer 

25. Graph showing frequency distribution of lateral hydraulic conductivities for the three basalt units 

26. Graph showing frequency distribution of thickness of the Columbia Plateau aquifer system 

27. Graphs showing frequency distribution of thickness for the three basalt units 

Page

B3

5

8

8

11

11

12

15

18

19

20

21

23

24

25

26

27

28

30

33

34

35

36

37

38

39

40
VI CONTENTS

FIGURE 28. Schematic diagram showing the conceptual model of the energy balance for evapotranspiration 

29. Schematic diagram showing the conceptual model of the water balance used in the deep-percolation model 

30-34. Maps showing:

30. Land-use classification of the Columbia Plateau, 1975 

31. Estimates of recharge in each of 53 selected basins 

32. Distribution of estimated recharge under predevelopment (1850's) conditions 

33. Distribution of estimated recharge under current (1980's) conditions 

34. Distribution of estimated recharge under predevelopment (1850's) and current (1980's) conditions in

cLTl cLxlCL ZOU6 « -- -- - - ~ - -- -- « «-. -- «. «--« --- »- - - " »«--- -- «-

35. Bar graph showing total irrigated acreage on the Columbia Plateau, 1949-82 

36-44. Maps showing:

36. Ground-water pumpage from the overburden aquifer, 1984 

37. Ground-water pumpage from the Saddle Mountains unit, 1984 

38. Ground-water pumpage from the Wanapum unit, 1984 

39. Ground-water pumpage from the Grande Ronde unit, 1984 

40. Total ground-water pumpage from the Columbia Plateau aquifer system, 1984

41. Water table in the overburden aquifer representing conditions during the spring of 1983 

42. Water-level contours for the Saddle Mountains unit, spring 1985 

43. Water-level contours for the Wanapum unit, spring 1985 

44. Water-level contours for the Grande Ronde unit, spring 1985-- -- 

45. Hydrographs showing seasonal water-level fluctuations for selected piezometers 

46. Map showing water-level changes in the Wanapum unit from predevelopment (1850's) to 1985 

47. Hydrographs of water levels in selected wells, showing long-term water-level changes 

48. Graphs showing relation of chemical water type in the Saddle Mountains unit to well depth and overburden

tillC.KIj.6SS "-"-"- --- -- - « « - » - --" *" « «« " -" « - »»« » ««

49. Bar graphs showing relation of chemical water type in the Wanapum unit to well depth, dissolved-oxygen

concentration, and overburden thickness 

PAGE

B42

43

44

45

46

47

49

50

51

52

53

54

55

56

58

59

60

62

63

64

68

 69

TABLES

TABLE 1. Mean annual precipitation at selected weather stations, 1956-77 

2. Mean air temperature data from selected weather stations, 1956-77 

3. Reservoirs in the study area having storage capacity greater than 40,000 acre-feet 

4. Rock-mechanics data for the Columbia River Basalt Group -

5. Summary of selected estimates of storage coefficient for the Columbia Plateau aquifer system 

6. Computed long-term, averaged monthly water budget for a semiarid zone and a temperate zone 

7. Summary of selected water chemistry for the three basalt units -

Page

B6

9

10

31

41

48

67

METRIC CONVERSION FACTORS AND VERTICAL DATUM

Multiply inch-pound unit

inch (in.)

foot (ft)

mile (mi)

square foot (ft2)

acre

square mile (mi2)

acre-foot (acre-ft)

foot per day (ft/d)

cubic foot per second (ft3/s)

gallon per minute (gal/min)

ton, short

pound per square inch (lb/in2)

pound per cubic inch (lb/in3)

By

25.4

0.3048

1.609

0.0929

0.4047

2.59

0.001233

0.3048

0.02832

0.06308

0.9072

70.31

27.68

To obtain metric unit

millimeter

meter

kilometer

square meter

hectare

square kilometer

cubic hectometer

meter per day

cubic meter per second

liter per second

megagram

gram per square centimeter

gram per cubic centimeter

to change degrees Fahrenheit (°F) to degrees Celsius (°C): °C = 5/9 (°F-32) 

to change degrees Celsius (°C) to degrees Fahrenheit (°F): °F = 9/5 °C+32

Sea Level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 a geodetic datum 

derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Sea Level Datum of 1929."
REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

THE HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY

OF THE COLUMBIA PLATEAU AQUIFER SYSTEM,

WASHINGTON, OREGON, AND IDAHO

By KJ. WHITEMAN, J J. VACCARO, J.B. GONTHIER, and H.H. BAUER

ABSTRACT

The Columbia Plateau aquifer system underlies about 

50,600 square miles in parts of Washington, Oregon, and Idaho. 

The aquifer system is a major source of water for municipal, 

industrial, domestic, and irrigation uses. About 828,270 acrefeet of water was pumped in 1984, 85 to 90 percent of which 

was used to irrigate about 0.5 million acres of croplands. An 

additional 1.3 million acres of croplands were irrigated with 

surface water.

The Columbia Plateau aquifer system consists of waterbearing Miocene basalt of the Columbia River Basalt Group, 

minor amounts of Miocene sedimentary rocks interlayered with 

the basalt, and Miocene to Holocene sediments overlying the 

basalt. The basalts are underlain by sedimentary, igneous, and 

metamorphic rocks older than the Columbia River Basalt 

Group, dating from Precambrian to early Tertiary age. The 

most important geologic units in the aquifer system are three 

formations belonging to the Yakima Basalt Subgroup of the 

Columbia River Basalt Group: from oldest to youngest, the 

Grande Ronde, Wanapum, and Saddle Mountains Basalts. The 

average total thickness of the basalts is 3,300 feet, with a 

maximum thickness exceeding 10,000 feet in the central part of 

the plateau.

For study purposes, the aquifer system was divided into 

seven hydrogeologic units the overburden aquifer, the Saddle 

Mountains unit, the Wanapum unit, the Grande Ronde unit, 

two confining units between the basalt units, and a basement confining unit. The basalt units include the interbedded sediments.

Lateral hydraulic conductivity of the aquifer materials varies widely, reflecting the heterogeneous nature of the aquifer 

system. Estimated hydraulic conductivity values for the overburden aquifer range from 0.02 to 150,000 feet per day, and for 

the basalt units, from 0.005 to 6,100 feet per day.

Discharge from the aquifer system occurs mainly as seepage 

to surface-water bodies in topographic lows, as pumpage of 

ground water, and as springs and seeps along canyon, coulee, 

and valley walls. Except for the ground-water pumpage, discharge cannot be accurately quantified. Recharge, which was 

estimated by using a daily water-budget model, is about 6,000 

cubic feet per second for predevelopment (1850's) conditions and 

about 9,490 cubic feet per second for current (1980's) conditions.

Water levels in the uppermost basalt unit and in the overlying sediments tend to parallel the land surface, and ground 

water moves generally" from topographic highs to topographic

lows. Ground water in each hydrogeologic unit generally flows 

from the peripheral boundary of each unit toward major surfacewater bodies, principally the Columbia, Snake, and Yakima 

Rivers. Geologic structures such as faults and folds modify this 

flow pattern. Ground-water pumpage has caused water levels to 

decline more than 150 feet locally, and imported surface water 

applied for irrigation has caused water levels to rise as much 

as 300 feet in parts of the area.

Ground-water development began about 1890. Pumpage has 

increased from an estimated 55,690 acre-feet in 1945, to 

177,970 acre-feet in 1960, and to a peak of about 939,770 acrefeet by 1979.

The water in the basalts is generally suitable for most uses. 

The dominant water type is calcium magnesium bicarbonate, 

followed by sodium bicarbonate water type. Dissolved-solids 

concentrations increase down gradient and range from 69 to 

1,100 milligrams per liter. Nitrogen concentrations range from 

0.1 to 54 milligrams per liter and average about 3.7. Nitrogen 

concentrations in ground water are greater in areas irrigated 

by surface water than in other areas.

INTRODUCTION

The Columbia Plateau aquifer system underlies 

the Columbia Plateau of central and eastern Washington, north-central and northeastern Oregon, and 

a small part of northwestern Idaho (fig. 1) for a 

total area of about 50,600 mi2 . The aquifer system 

consists of Miocene basalt belonging to the Columbia River Basalt Group, Miocene sedimentary rocks 

interlayered with the basalt, and Miocene to Holocene sediments overlying the basalts. The aquifer 

system is a major source of water for municipal, 

industrial, domestic, and irrigation uses. Concurrent with ground-water usage, imported surface 

water is used for irrigation in several areas of the 

plateau. Use of surface water for irrigation has 

caused ground-water-level rises of as much as 300 

ft in some areas; water levels have declined more 

than 150 ft in areas of ground-water pumpage, and

Bl
B2 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

the chemical quality of ground water has changed 

in irrigated areas. An improved understanding of 

the aquifer system, especially the movement and 

direction of ground-water flow, is needed to fully 

address these concerns.

PURPOSE AND SCOPE

The Columbia Plateau aquifer system is one of 

several regional aquifers selected for study as part 

of the U.S. Geological Survey's Regional AquiferSystem Analysis (RASA) Program. The objectives of 

the Columbia Plateau study are to describe (1) the 

hydrogeologic framework, (2) the hydrologic characteristics of the hydrogeologic units, (3) the area's 

water budget, (4) the ground-water and surfacewater interaction, and (5) the water-quality characteristics and water-rock interactions that occur in 

the study area. In order to provide the analytical 

capabilities for assessment of management alternatives and to allow a better understanding of the 

ground-water flow system, a numerical model that 

simulates ground-water movement has been 

constructed.

This report documents the following information 

collected from the study: (1) the physical, cultural, 

and economic settings, (2) the geologic framework, 

(3) the hydrologic characteristics of major geohydrologic units, (4) some components of the water 

budget, (5) the regional ground-water flow system, 

and (6) the geochemistry of the aquifer system.

PREVIOUS INVESTIGATIONS

Numerous geologic, hydrologic, and hydrogeologic investigations within or including the 

Columbia Plateau have been done. These investigations have laid the foundation for the work completed during this study. Smith (1901, 1903a, b, c) 

conducted early geologic mapping on the plateau 

and suggested stratigraphic nomenclature for the 

basalts. His work was confined to the area of the 

Columbia Lava delineated by Russell (1893, 1897). 

Later investigators who expanded the knowledge of 

the geology and nomenclature of the basalts 

included Pardee and Bryan (1926), Fuller (1931), 

Waters (1955, 1961), Mackin (1961), Grolier and 

Foxworthy (1961), Bingham and Walters (1965), 

Schmincke (1965, 1967a, b), Swanson (1967), 

Bingham and Grolier (1966), and Diery and McKee 

(1969). Starting in the early 1970's, geologic investigations on the plateau were many and diverse. 

The stratigraphic nomenclature report of Swanson

and others (1979c) gives a good background on 

these investigations. Finally, the work of Swanson 

and others (1979a, b, 1981) was the basis for the 

geologic work completed during this study.

Early water-resources investigations included the 

studies of Calkins (1905), Waring (1913), 

Schwennesen and Meinzer (1918), Piper (1932), and 

Taylor (1948). Since the mid-1950's, numerous investigations have been completed on the plateau. Some 

of the more important reports and investigations are 

referred to in subsequent sections of the present 

report.

ACKNOWLEDGMENTS

The State of Washington Department of Ecology 

assisted the U.S. Geological Survey during the water-level-data collection phase of this RASA project 

and cooperated with the Geological Survey in determining the rate and distribution of groundwater pumpage. In addition, previous studies made 

cooperatively by the Department of Ecology and 

the Geological Survey provided a foundation for the 

geology and water-quality results summarized in 

this report. The cooperation of numerous residents 

of the Columbia Plateau who have permitted the 

Geological Survey to measure water levels and 

collect water samples from their wells is also 

appreciated.

PHYSICAL SETTING

The Columbia Plateau lies within the Columbia 

intermontane physiographic province (Freeman and 

others, 1945). It is bordered by the Cascade Range 

on the west, by the Okanogan Highlands on the 

north, and by the Rocky Mountains on the east; its 

southern boundary is defined more by the extent of 

the Columbia River Basalt Group than by any 

physiographic feature. The Columbia Plateau is 

drained by the Columbia River and its major tributaries the Snake, Yakima, John Day, Umatilla, 

Spokane, Klickitat, and Deschutes Rivers. Although physiographers refer to it as a plateau, the 

Columbia Plateau is in reality both a structural 

and a topographic basin with its lowest point near 

Pasco, Wash. (fig. 1).

PHYSIOGRAPHY

The Columbia Plateau is underlain everywhere 

by massive basalt flows having an estimated composite thickness of about 14,000 ft at the plateau's
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B3

low point near Pasco, Wash. The characteristics of 

the older rocks overlain by the Columbia River 

Basalt Group are distinguishable only at exposures 

in the highlands surrounding the plateau. In the

interior of the province, the lithology, structure, 

and topography of the prebasalt rocks cannot be 

readily determined because the rocks are buried beneath the thick accumulation of lava. Sedimentary

122° 121 C 120° 119° 118° 117° 116°

- r ', I >#*

YAKIMA

BELT tstn

SUBPROVINCE

L_

I MORROW ,

1 j\ / C^tSLfcJE j \

GILLIAM ; o ^ '. MOUNTAINS

20 40 60 80 MILES

0 40 80 120 KILOMETERS

EXPLANATION

COLUMBIA BASIN IRRIGATION PROJECT

 COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

- - - - PHYSIOGRAPHIC SUBPROVINCE BOUNDARY INDEX MAP OF STUDY AREA 

FIGURE 1. Location of the Columbia Plateau aquifer system and physiographic subprovince boundaries.
B4 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

deposits overlie the basalt over large areas of the 

plateau, exceeding 1,200 ft in thickness in the 

Yakima River valley and 2,000 ft in the Grande 

Ronde valley near La Grande, Oregon.

The Columbia Plateau was divided into three informal physiographic subprovinces by Myers and 

Price (1979) the Yakima Fold Belt, Blue Mountains, and Palouse subprovinces (fig. 1). The 

Yakima Fold Belt includes most of the western half 

of the plateau north of the crest of the Blue Mountains and is characterized by a series of ridges and 

basins. The Palouse subprovince occupies the 

northeast quarter of the plateau in Washington, 

north of the Blue Mountains, and extends eastward 

into Idaho. It consists of nearly undeformed basalt 

with a gentle southwest slope, on which a rolling 

topography of loessal hills is developed. The Blue 

Mountains subprovince comprises all the Columbia 

Plateau in Oregon and Washington south and east 

of the Blue Mountains, including a series of folds 

extending into Idaho near Lewiston. This 

subprovince is characterized by higher plateaus, 

deeply dissected by many streams.

The topography in central Washington, commonly referred to as the "channeled scablands," 

was produced during Pleistocene time. Catastrophic floods, resulting from the breakup of glacial ice dams that impounded large lakes in 

western Montana and northern Idaho, carved spectacular erosional features into the basalt plateau. 

Floodwaters stripped away overlying sediments 

and left behind deep canyons and coulees, rugged 

cliffs and buttes, large gravel bars, and giant ripple 

marks that measure 20 to 30 ft in height. Thick 

layers of sediment were deposited in low areas 

where floodwaters spread, slowed, and ponded. 

These slack-water deposits approach a thickness of 

300 ft at several localities.

The types and amounts of natural vegetation 

found on the Columbia Plateau are largely dependent 

on conditions of precipitation and land-surface altitudes. In the central part of the plateau, where the 

land surface ranges from 350 to 2,000 ft above sea 

level and the precipitation ranges from 7 to 15 in/yr, 

the vegetation is principally sagebrush and grasslands, and there are few perennial streams. At altitudes ranging from 2,000 to 3,500 ft, the vegetation 

is typical of semiarid climates and includes both 

grasslands and forest. These areas generally receive 

from 15 to 25 in. of precipitation annually. Where altitudes range from 3,500 to 6,000 ft, forest lands predominate and small perennial streams in deep 

canyons are common. The mountains bordering the 

Columbia Plateau locally receive more than 100 in. of

precipitation per year. The mountainous topography 

is typically rugged and steep with a patchwork of 

barren rock and conifer forests.

CLIMATE

Most of the Columbia Plateau is semiarid and 

receives less than 15 in. of precipitation annually. 

Mean annual precipitation ranges from about 7 in. 

in the center of the study area to more than 45 in. 

in the surrounding forested mountains. From the 

east slope of the Cascade Range, at about 2,000 ft 

altitude, to the westernmost extent of the study 

area, the mean annual precipitation is as much as 

100 in. Precipitation is greater in the Cascade 

Range to the west than at similar altitudes in the 

Blue Mountains to the southeast. The mean annual 

precipitation for the Columbia Plateau for the 

period 1956 to 1977 (Nelson, 1991) is shown in figure 2, and information for the weather sites is 

given in table 1.

The temporal distribution of annual precipitation is similar throughout the study area. The 

mean monthly precipitation, based on data for 103 

weather stations (fig. 3), is greatest in December 

and January and least in July (Nelson, 1991). Typically, about 83 percent of the precipitation occurs 

during October through May, when air temperatures are less than the yearly average. Approximately 42 percent of the total annual precipitation 

falls from November through January. Winter 

snowfall ranges from 8 to 20 in. in the central pla«- 

teau and from 70 to 300 in. at higher altitudes in 

the Cascade Range and Blue Mountains.

Mean air temperature data for the period 1956 

to 1977 at 89 weather stations located throughout 

the Columbia Plateau are shown in table 2. The 

mean daily minimum, maximum, and average air 

temperatures at these weather stations for the period 1956 to 1977 are shown in figure 4. Minimum 

temperatures range from about 3°C in the low-lying areas to about -3°C in the higher altitudes, 

and maximum temperatures range from about 19°C 

in the central plateau to about 12°C in the mountainous areas. Mean daily temperature fluctuations 

range from 8°C in winter to 20°C in summer. The 

seasonal extremes of temperature vary by about 

40°C between winter lows and summer highs.

The percentage of sunshine increases from 10 percent in the winter to 50 percent in the spring and 

fall, and to 75 percent in the summer. In response to 

the climate variations, the growing season ranges 

from about 220 days at Walla Walla, Wash., to less than 

100 days in the Cascade Range and Blue Mountains.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B5

122° 121 C 120° 119° 118° 117° 116°

LINCOLN

48°

47°

46°

45°

V_/' ~v £ w/

MALHEUR

WASHINGTON 

^ V BOISE

20 40 60 80 MILES

40 80

I 

120 KILOMETERS

EXPLANATION

 25 LINE OF EQUAL MEAN-ANNUAL PRECIPITATION Interval, in 

inches, is variable

41 WEATHER STATION AND REFERENCE NUMBER Station data 

given in table 1

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

FIGURE 2. Mean annual precipitation in the Columbia Plateau, 1956-77. (Modified from Nelson, 1991.)
B6 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

TABLE 1. Mean annual precipitation at selected weather stations, 1956-77 (from Nelson, 1991)

Weatherstation 

reference Index 

number number 

(see fig. 2)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

35-197

35-265

35-858

35-897

35-1028

35-1765

35-1924

35-2440

35-2597

35-2672

35-3038

35-3250

35-3402

35-3827

35-3847

35-4003

35-4161

35-4411

35-4622

35-5545

35-5593

35-5610

35-5711

35-5734

35-6468

35-6540

35-6546

35-6634

35-8000

35-8407

35-8726

35-8746

35-8985

35-9068

35-9219

45-217

45-294

45-668

45-969

45-1350

45-1400

45-1504

45-1586

45-1690

45-1691

45-1767

45-1968

45-2007

45-2030

45-2505

45-2542

45-2614

45-3183

45-3226

45-3502

45-3512

45-3529

45-3546

45-3883

45-4077

45-4154

45-4338

45-4394

Weather 

station

Antelope

Arlington

Boardman

Bonneville Dam

Brightwood

Condon

Cove

Dufur

Elgin

Enterprise

Fossil

Gibbon

Government camp

Heppner

Hermiston 2 S.

Hood River Exp. Sta.

lone 18 S.

Kent

La Grande

Mikkalo 6 W.

Milton Freewater

Minam 7 NE.

Monument 2

More

Parkdale 2 SSE.

Pendleton Exp. Sta.

Pendleton WSO AP

Pilot Rock 1 SE.

Spout Spgs Ski Lodge

The Dalles

Ukiak

Union Exp. Sta.

Walla Walla 13 ESE.

Wasco

Weston 5 ESE.

Appleton

Asotin 14 SW.

Bickleton

Bumping Lake

Chelan

Chief Joseph Dam

Cle Elum

Colfax 1 NW.

Connell 1 W.

Connell 12 SE.

Coulee Dam 1 SW.

Dallesport FAA AP

Davenport

Dayton 1 WSW.

Ellensburg

Eltopia 8 WSW.

Ephrata FAA AP

Glenwood 2

Goldendale 2 E.

Harrington 5 S.

Harrington 4 ENE.

Hartline

Hatton 9 ESE.

Ice Harbor Dam

Kahlotus 5 SSW.

Kennewick

La Crosse

Lake Cle Elum

Station 

altitude 

(feet)

2,680

285

300

60

1,065

2,830

2,920

1,330

2,655

3,790

2,650

1,740

3,980

1,950

624

500

2,130

2,720

2,755

1,550

970

3,615

1,995

1,870

1,890

1,487

1,492

1,720

5,035

102

3,355

2,765

2,400

1,264

3,200

2,336

3,500

3,000

3,440

1,120

820

1,930

1,955

1,020

1,078

1,700

240

2,460

1,557

1,480

700

1,259

1,850

1,800

2,170

2,266

1,910

1,430

368

1,550

390

1,480

2,250

Location

Longitude Latitude 

(decimal degree)

120.7167

120.2000

119.7000

121.9500

122.0167

120.1833

117.8000

121.1333

117.9167

117.2667

120.2167

118.3667

121.7500

119.5500

119.2833

121.5167

119.8500

120.7000

118.0833

120.3500

118.4167

117.6000

119.4167

120.7167

121.5833

118.6333

118.8500

118.8167

118.0500

121.2000

118.9333

117.8833

118.0500

120.7000

118.3333

121.2667

117.2500

120.3000

121.3000

120.0333

119.6500

120.9500

117.3833

118.8833

118.7667

119.0000

121.1500

118.1500

118.0000

120.5500

119.1667

119.5167

121.2833

120.7667

118.2500

118.1833

119.1000

118.6500

118.8667

118.6000

119.1000

117.8833

121.0667

44.9167

45.7167

45.8333

45.6333

45.3667

45.2333

45.3000

45.4500

45.5667

45.4333

45.0000

45.7000

45.3000

45.3500

45.8167

45.6833

45.3167

45.2000

45.3167

45.4667

45.9500

45.6833

44.8167

45.4833

45.5000

45.7167

45.6833

45.4833

45.7500

45.6000

45.1333

45.2167

46.0000

45.5833

45.8000

45.8167

46.2000

46.0000

46.8667

47.8333

48.0000

47.1833

46.8833

46.6667

46.5000

47.9500

45.6167

47.6500

46.3167

46.9667

46.4000

47.3167

46.0000

45.8167

47.4167

47.4833

47.6833

46.7500

46.2500

46.5833

46.2167

46.8167

47.2444

Annual 

precipitation 

(inches)

12.23

8.56

7.87

75.64

87.89

13.40

16.32

11.57

24.25

12.82

13.80

23.93

88.26

13.29

8.57

30.59

11.60

11.12

17.26

10.19

13.20

26.82

13.12

10.58

44.97

15.68

11.73

13.63

35.38

13.51

16.77

13.74

41.77

11.01

26.09

31.50

19.20

13.93

36.90

10.31

9.45

24.65

19.29

7.58

9.45

10.08

12.75

15.10

18.16

9.47

8.09

7.11

35.06

16.39

12.18

12.82

10.38

9.79

9.07

10.43

7.35

13.33

37.27
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B7

TABLE 1. Mean annual precipitation at selected weather stations, 1956-77 (from Nelson, 1991) 

Continued

Weatherstation 

reference Index 

number number 

(see fig. 2)

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

45-4406

45-4414

45-4679

45-4971

45-5231

45-5325

45-5326

45-5387

45-5613

45-5659

45-5688

45-5832

45-6039

45-6215

45-6610

45-6747

45-6768

45-6789

45-6880

45-7015

45-7038

45-7059

45-7180

45-726

45-7342

45-7727

45-7938

45-7956

45-8009

45-8207

45-8442

45-8931

45-8959

45-9012

45-9058

45-9079

45-9082

45-9200

45-9238

45-9465

Weather 

station

Kachess

Keechleus

Lind 3 NE.

Mansfield 7 W.

McNary Dam

Methow 2

Methow 2 S.

Mill Creek Dam

Moses Lake

Mt. Adams Ranger Sta.

Moxee City 10 E.

Nespelem 2 S.

Odessa

Othello 6 ESE.

Pomeroy

Priest Rapids Dam

Prosser 4 NE.

Pullman 2 NW.

Quincy 1 S.

Richland

Rimrock Reservoir

Ritzville 1 SSE.

Rosalia

St. John

Satus Pass 2 SSW.

Smyrna

Spokane WSO AP

Sprague

Stampede Pass WSCMO

Sunnyside

Tieton-Headwork S.

Walla Walla WSO CI

Wapato

Waterville

Wellpinit

Wenatchee Exp. Sta.

Wenatchee FAA AP

Whitman Mission

Wilbur

Yakima WSO AP

Station 

altitude 

(feet)

2,270

2,475

2,630

2,500

361

1,160

1,170

1,175

1,070

1,960

1,550

1,090

1,540

1,190

1,810

460

903

2,545

1,274

373

2,730

1,830

2,400

1,945

2,610

560

2,356

1,920

3,958

747

2,280

949

841

2,620

2,490

800

1,229

632

2,160

1,064

Location

Longitude Latitude 

(decimal degree)

121.2000

121.3389

118.5833

119.8000

119.3000

120.0000

120.0167

118.2667

119.3000

121.5333

120.1667

118.9833

118.6833

119.0500

117.6167

119.9000

119.7500

117.2000

119.8500

119.2667

121.1333

118.3667

117.3667

117.5833

120.6500

119.6667

117.5333

117.9833

121.3333

120.0000

121.0000

118.3333

120.4167

120.0667

118.0000

120.3500

120.2000

118.4500

118.7000

120.5333

47.2667

47.3222

47.0000

47.8167

45.9500

48.0000

48.1000

46.0833

47.1000

46.0000

46.5167

48.1333

47.3333

46.8000

46.4667

46.6500

46.2500

46.7667

47.2167

46.3167

46.6500

47.1167

47.2333

47.1000

45.9500

46.8333

47.6333

47.3000

47.2833

46.3167

46.6711

46.0333

46.4333

47.6500

47.9000

47.4333

47.4000

46.0500

47.7500

46.5667

Annual 

precipitation 

(inches)

52.84

69.03

9.18

10.54

7.33

10.59

10.93

17.82

7.46

43.64

7.79

12.68

9.72

7.82

15.44

6.67

7.68

21.95

7.95

6.55

24.72

11.20

16.98

15.06

19.28

7.87

16.61

14.75

94.53

6.44

20.26

15.91

7.82

10.38

15.78

11.69

10.75

15.56

11.14

9.14

CULTURAL SETTING

Lewis and Clark explored parts of southern 

Washington and northern Oregon along the Snake 

and Columbia Rivers in 1805; in the decade that 

followed, two more groups one led by David 

Thompson and the other by Gabriel Frachere 

explored the entire length of the Columbia River. 

What these early explorers found in the plateau 

country was a semiarid land, home to an estimated 

14,000 Indians. In the 1850's, the U.S. Government 

signed numerous treaties with the Indians in eastern Washington and Oregon, establishing reservations and opening up lands for settlement.

Settlements soon became communities and cities 

that supplied services to growing industries on the 

plateau, particularly the agriculture industry.

Large dams and surface-water storage reservoirs 

were developed on the Columbia River system beginning in 1939 to meet the demands of this expanding agricultural region. Reservoirs in the 

study area with storage capacities greater than 

40,000 acre-ft are listed in table 3. The reservoirs 

on the Columbia and lower Snake Rivers alone 

have the potential to store more than 43 million 

acre-ft of water. The stored water is used primarily 

for hydroelectric power production, irrigation, navigation, and flood control.
E8 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

25

20

15

10 

O

JAN FEE MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

FIGURE 3. Mean monthly distribution of precipitation at 103 

weather stations, 1956-77 (from Nelson, 1991).

WATER-RESOURCE AND ECONOMIC DEVELOPMENT

The cultural and economic development of the 

Columbia Plateau has depended heavily on the 

availability of water and on the ability to store and 

redistribute water from the Columbia River and its

major tributaries. Irrigation began as early as the 

1840's in the Yakima River valley, where settlers 

experimented with a wide variety of crops. Transportation was greatly improved in the late 1800's, 

when three railroad systems were built across the 

Columbia Plateau. Large land-grant acreages given 

to the railroads served to attract settlers, encourage exportation of crops, and promote investments 

in irrigation and in agriculture-related businesses. 

Numerous towns sprang up, some almost overnight. In the early 1900's, the lumber and agricultural industries grew steadily. Small-grain 

production on dryland farms and dairy and poultry 

farming were especially profitable because these 

enterprises did not need large quantities of water.

The region's dry summer climate forced the early 

settlers to develop water supplies for irrigation 

wherever possible. Most early attempts to form and 

finance irrigation districts and water-user associations failed. By the 1930's, economic growth was 

relatively low because of the 1929 depression and 

severe droughts that occurred after 1912 and again 

in the 1930's. Those who survived these hardships 

lived along surface-water bodies or in areas where 

ground water was available at shallow depths. A 

notable exception to this pattern of hardship was 

the Yakima River basin, where reservoirs, diversion dams, and canals were constructed during the 

period 1892-1933. These water projects ensured 

that irrigation water was available, and thus

I I I I I I I I I I I I I I I I I I I I

15 29 43 57 71 85 99 113 127 141 155 169 183 197 211 225 239 253 267 281 295 309 323 337 351 365

CALENDAR DAY

FIGURE 4. Mean minimum, mean, and maximum daily air temperatures at 89 weather stations, 1956-77.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B9 

TABLE 2. Mean air temperature data from selected weather stations, 1956-77

Station

Mean air temperature, 

in degrees Celsius

Minimum Maximum Average Station

Mean air temperature, 

in degrees Celsius

Minimum Maximum Average

Antelope

Arlington

Boardman

Bonneville Dam

Condon

Cove

Dufur

Elgin

Enterprise

Fossil

Government Camp

Heppner

Hermiston 2 S.

Hood River Exp. Sta.

Kent

La Grande

Mikkalo 6 W.

Milton Freewater

Minam 7 NE.

Monument 2

Moro

Parkdale 2 SSE.

Pendleton Exp. Sta.

Pendleton WSO AP

Pilot Rock 1 SE.

The Dalles

Ukiak

Union Exp. Sta.

Walla Walla 13 ESE.

Appleton

Bickleton

Bumping Lake

Chelan

Chief Joseph Dam

Cle Elum

Colfax 1 NW.

Connell 1 W.

Coulee Dam 1 SW.

Dallesport FAA AP

Davenport

Dayton 1 WSW.

Ellensburg

Eltopia 8 WSW.

Ephrata FAA AP

Goldendale 2

2.84

5.99

5.27

6.65

2.19

1.02

2.07

.74

-1.53

1.11

.86

3.67

4.65

4.42

2.64

1.86

4.86

5.98

-2.62

1.44

3.29

3.87

3.17

5.61

3.11

6.06

-1.80

2.06

2.14

2.53

2.60

-.38

4.57

3.78

1.37

2.45

3.57

4.29

5.99

1.56

4.21

2.12

4.07

5.01

3.57

16.69

19.03

18.46

15.86

15.43

15.61

17.29

16.68

14.47

16.66

10.32

17.12

18.54

16.14

15.29

16.00

17.12

18.45

13.74

17.98

15.46

14.53

17.63

17.61

17.99

18.37

15.18

15.38

14.91

14.08

14.33

12.32

15.52

16.34

14.32

15.55

17.91

15.37

17.96

14.45

16.99

15.51

17.57

16.57

16.18

9.77

12.51

11.86

11.26

8.81

8.32

9.68

8.71

6.47

8.88

5.59

10.39

11.59

10.28

8.97

8.93

10.99

12.22

5.56

9.72

9.38

9.20

10.40

11.61

10.55

12.21

6.69

8.72

8.52

8.31

8.47

5.97

10.04

10.07

7.84

9.00

10.73

9.83

11.98

8.01

10.60

8.82

10.82

10.79

9.87

Hartline

Hatton 9 ESE.

Ice Harbor Dam

Kennewick

La Crosse

Lake Cle Elum

Kachess

Keechleus

Lind 3 NE.

Mansfield 7 W.

McNary Dam

Methow 2

Moses Lake

Mt. Adams Ranger Sta.

Moxee City 10 E.

Nespelem 2 S.

Odessa

Othello 6 ESE.

Pomeroy

Priest Rapids Dam

Prosser 4 NE.

Pullman 2 NW.

Quincy 1 S.

Richland

Rimrock Reservoir

Ritzville 1 SSE.

Rosalia

St. John

Satus Pass 2 SSW.

Smyrna

Spokane WSO AP

Sprague

Stampede Pass WSCMO

Sunnyside

Tieton-Headwork S.

Walla Walla WSO CI

Wapato

Waterville

Wellpinit

Wenatchee Exp. Sta.

Wenatchee FAA AP

Whitman Mission

Wilbur

Yakima WSO AP

2.58

3.08

5.67

5.80

2.95

1.43

1.41

.58

2.87

3.53

6.57

2.95

2.83

1.89

2.23

1.25

2.14

3.64

3.84

6.90

3.63

2.64

2.88

5.78

.35

2.27

2.27

2.34

2.46

4.41

2.91

1.64

.85

3.87

.84

7.11

3.73

3.46

2.36

3.38

3.75

5.46

2.48

2.47

15.85

17.36

18.71

18.82

16.73

12.51

12.29

10.86

17.18

15.57

18.21

15.87

16.48

15.17

16.12

16.20

17.27

16.97

17.08

18.66

17.50

14.18

16.74

19.40

13.34

15.97

14.31

15.77

15.27

18.43

14.03

15.86

7.41

18.51

13.72

17.60

17.28

15.42

14.69

15.89

15.84

17.78

15.59

16.18

9.22

10.22

12.18

12.31

9.84

6.97

6.85

5.72

10.03

9.55

12.39

9.41

9.66

8.53

9.18

8.73

9.71

10.31

10.46

12.78

10.57

8.41

9.81

12.59

6.85

9.12

8.29

9.06

8.87

11.42

8.47

8.75

4.13

11.18

7.28

12.36

10.51

9.43

8.53

9.64

9.80

11.62

9.04

9.32

economic growth in this part of the plateau has 

been steady.

The start of the Columbia Basin Irrigation 

Project (CBIP) (see fig. 1) in 1933 and construction 

of the Hanford Nuclear Reservation (located in 

northern Benton County, Wash.) in the 1940's 

brought about a large influx of construction workers and associated service industries. Water from 

the Grand Coulee Equalization Reservoir became 

available for irrigation in 1952, and by 1972 more 

than 0.5 million acres in Franklin, southern Grant, 

and eastern Adams Counties were being irrigated 

by this project. More than 60 types of crops were

being produced commercially, including fruits, vegetables, and seeds. Major crops included hay and 

seed, sugar beets, corn, potatoes, and wheat. Currently (1980's), about 1.3 million acres of croplands 

are irrigated with surface water.

A rapid and intensive expansion of deep-well irrigation practices took place in areas not served by 

the CBIP starting around 1950, although earlier 

ground-water development had occurred in areas 

scattered throughout the plateau. Some of the most 

intensive early development of ground water was 

in the Yakima River basin and near Walla Walla, 

Wash. As ground-water pumpage increased, water
BIO REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

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HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM Bll

levels in the pumped areas declined. In central 

Washington, declines over the past 25 years locally 

have exceeded 150 ft (Cline, 1984). An estimated 

1.5 million acres of land in Douglas, Lincoln, 

Grant, Adams, Franklin, Garfield, and Whitman 

Counties could be cropped profitably if water supplies were available (Pacific Northwest River 

Basins Commission, 1971). Only a relatively small 

part of the available land in this so-called dry belt 

has been put into irrigation at present (1987).

Some parts of the Columbia Plateau, where 

ground water is the principal water source, receive 

sufficient precipitation to support a dryland farming economy. In areas where the soils are not suitable for croplands, the predominant economic 

activity is sheep and cattle ranching.

The number of farms with irrigated lands and 

the average farm size for the period 1949 to 1982 

are shown in figure 5. Overall, there has been a 

steady increase in irrigated acreage throughout the 

Columbia Plateau (see fig. 35 in "Ground-Water 

Development" section) and a trend toward fewer 

but larger farms (fig. 5) (U.S. Department of Commerce, 1982). There has been a change in these 

trends over the last decade, reflecting financial 

hardships that are seriously affecting the owners of 

intermediate-sized farms. Large-farm operators are 

better able to survive difficult financial periods, 

and owners of small farms often work outside jobs 

to supplement farm income.

Population trends of the Columbia Plateau (fig. 

6) correspond to changes in economic conditions. 

Population increases from 1900 to 1910 reflect the 

influx of settlers attracted by the availability of 

lands made accessible by the newly completed railroads. Population leveled out in response to slower

1,800

1,600

1,400

1,200

1,000

16

15

13 -

11

10

1945 1950 1955 1960 1965 1970 1975 1980 1985

FIGURE 5. Number of farms with irrigated lands and average 

farm size, 1949-82 (U.S. Department of Commerce, 1982).

1,200

c/5 1,000 

Q

800

600

400

200

1900 1910 1920 1930 1940 1950 1960 1970 1980 

FIGURE 6. Population of the Columbia Plateau area, 1900-80.

economic growth between 1910 and 1930. Construction of the CBIP, water-power projects, and the 

Hanford Nuclear Reservation contributed to the 

steep rise in population in the 1940's. Irrigation 

water made available by CBIP and through drilling 

of deep wells in the basalts spurred growth from 

the 1950's through the 1970's. The area had a slow 

rate of increase in population from 1960 to 1970, 

although there was a net decrease in population of 

approximately 15,000 people in Adams, Grant, and 

Lincoln Counties in Washington. During this period, Larson Air Force Base at Moses Lake, Wash., 

was closed, Titan Missile Base construction in eastern Washington was terminated, and construction 

of irrigation facilities in Washington decreased.

HYDROGEOLOGIC FRAMEWORK

An understanding of the geologic framework of 

the Columbia Plateau aquifer system has become 

increasingly important in recent years, not only 

because of questions concerning ground-water 

availability and quality, but also because of proposals to use the U.S. Department of Energy's 

Hanford Nuclear Reservation as a potential highlevel nuclear-waste repository site. The information 

on rock types their distribution, thickness, hydrologic properties, and structural characteristics is 

important to these issues.

GEOLOGY

The Columbia Plateau regional aquifer system 

defined in this report includes, from youngest to
B12 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121° 120° 119° 118° 117° 116°

46° -

45° 

20 40 60 80 MILES

OVERBURDEN

COLUMBIA RIVER BASALT GROUP, 

UNDIVIDED

Saddle Mountains Basalt

40 80 120 KILOMETERS

EXPLANATION

Wanapum Basalt

Grande Ronde Basalt 

Imnaha Basalt 

NOT MAPPED

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

CONTACT

FIGURE 7. Generalized surficial geology (A) and stratigraphic chart (JB) for the Columbia Plateau. (Modified from Drost and 

others, 1990.) Magnetostratigraphic units: N, normal polarity; R, reverse polarity; T, transition polarity; units numbered 

sequentially from oldest to youngest.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B13

oldest, (1) Holocene to Miocene overburden, a collective term used in this study for all materials 

overlying the Columbia River Basalt Group, (2) minor sedimentary units of Miocene age interlayered 

with the basalts, and (3) a large thickness of 

Miocene basalt belonging to the Columbia River 

Basalt Group. The discussions that follow summarize the geologic characteristics and are based on 

previous work completed during this project by 

Drost and Whiteman (1986), Gonthier (1990), and 

Drost and others (1990). A generalized surficial 

geology map and stratigraphic chart for the 

plateau is presented in figure 7. Pre-Columbia 

River Basalt Group rocks underlie the plateau and 

are presumed to consist primarily of less permeable 

rocks that form the lower hydrogeologic boundary 

to the aquifer system. These are sedimentary, igneous, and metamorphic rocks that range in age from 

Precambrian through early Tertiary.

Basaltic lavas that make up the bulk of the 

Columbia Plateau aquifer system were extruded 

during the Miocene Epoch between 17 and 6 million years ago from north-northwest-trending 

fissures as much as 90 mi long chiefly in northeastern Oregon and southeastern Washington (Hooper, 

1982). Flows from these vents covered about 63,200 

mi2 of eastern Washington, northern Oregon, and 

western Idaho to an average total thickness of 

3,300 ft. About 95 percent of the basalt was 

extruded in episodic eruptions during the first 3 

million years of that interval. An estimate of the 

duration and flow rate of a single large eruption of 

the basalt (Swanson and others, 1975) suggests 

that a fissure about 90 mi long spewed fluid lava

GEOLOGIC FRAMEWORK

BASALT STRATIGRAPHY

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Picture

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Basalt

Imnaha

Basalt

Lower Monumental Member

Ice Harbor Member

Buford Member

Elephant Mountain Member

Pomona Member

Esquatzel Member

Weissenfels Ridge Member

Asotin Member

Wilbur Creek Member

Umatilla Member

Priest Rapids Member

Roza Member

Frenchman Springs Member

Eckler Mountain Member

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SEDIMENT STRATIGRAPHY

Sediments of Miocene through

Holocene age {glaciofluvial, fluvial,

lacustrine, eolian, and ash fall

materials). Locally includes sediments

of the Palouse, Latah, Ringold, and

Ellensburg Formations, and the Dalles

Group (Farooqui and others, 1981).

Saddle Mountains-Wanapum Interbed

Wanapum-Grande Ronde Interbed

Basement rocks (pre-Columbia River Basalt Group)

FIGURE 7. Continued.
B14 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

at a rate of 0.24 mi3 from each 0.6 mi of vent over 

a duration of about 7 days. The basalt in that 

eruption flowed about 186 mi west and covered a 

vast area of the plateau. It is assumed that many 

of the flows in the Columbia River Basalt Group 

were of similar or larger magnitude because some 

flows extend to the Pacific Ocean, more than 340 

mi from their known vents (Hooper, 1982).

Prebasalt topography in the vent areas had considerable relief; early lava flows, therefore, filled 

narrow prebasalt valleys and gradually smoothed 

out the Miocene landscape. Later flows spread in 

thin sheets across a flat, west-sloping paleosurface 

having a few minor warps. It is likely that water 

was present on this paleosurface, and the interaction between the water and overriding molten lava 

caused rapid chilling and shattering of the basalt, 

pillow lava complexes, and structural irregularities 

from steam explosions within an individual lava flow.

Warping and folding of the plateau increased 

late in the eruptive cycle, forming the Frenchman 

Hills, Horse Heaven Hills, The Dalles-Umatilla 

syncline, Blue Mountains uplift, and numerous 

other geologic structures discussed later in this report. A more detailed account of the structural evolution of the Columbia Plateau has been presented 

by Barrash and others (1983). Because these tectonic activities were mostly in the western and 

southern plateau, late basalt flows tended to be 

confined to the central part of the plateau and 

were restricted to narrow canyons near the plateau 

margin. These younger flows have been buried 

under sediments in many areas and are usually 

more continuous areally than older basalt flows, 

which have been thinned by erosion, cut by streams, 

and affected by folding, uplift, and faulting.

Sedimentary interbeds are more common in the 

younger basalt and were deposited in shallow lake 

basins on the warped basalt surface between eruptive phases. Eruption of basalt ceased some 6 million years ago, but folding, erosion, and deposition 

of sediments has continued. The Cascade Range 

has been the principal source of large quantities of 

sediments and volcaniclastics, which have been 

transported by air and water and deposited in adjacent areas, reflecting the greater thicknesses of 

overburden seen in the western part of the plateau. 

Erosion is now the dominant process affecting the 

Columbia Plateau.

OVERBURDEN

In this report, overburden is the term used to 

describe a composite unit consisting of all rock

materials 50 ft or more in thickness that overlie 

the Columbia River Basalt Group and are important sources of ground water. The thickness of the 

overburden ranges from 50 to more than 2,000 ft, 

with the thickest deposits occurring in structural 

basins and in areas adjacent to the Cascade Range 

(fig. 8). The overburden exceeds a thickness of 

2,000 ft in the Grande Ronde Valley near La 

Grande, Oreg., 1,200 ft in the Ahtanum Valley 

near Yakima, Wash., and 1,000 ft in the Toppenish 

Valley near Toppenish, Wash.

The overburden includes consolidated to unconsolidated deposits of fluvial, lacustrine, and volcanic origin ranging from Miocene to Holocene age. 

The sediments and sedimentary rocks are lithologically diverse, ranging from clay to gravels and 

shale to conglomerate from many different formations across the plateau; however, in any one area, 

only a few formations may be present. In Oregon, 

several major formations within the overburden 

have been assigned to the Dalles Group by 

Farooqui and others (1981), and this term is used 

in this report. Other major formations composing 

the overburden are the Ellensburg, Latah, Ringold, 

and Palouse. Although these formations were not 

mapped or studied individually during this study, 

they are described briefly below.

Sedimentary deposits belonging to the Ellensburg 

Formation of Miocene age are interbedded with the 

basalt and also overlie it in the western and central 

part of the plateau. The deposits that overlie the 

basalt are thickest and coarsest along the west 

edge of the plateau and become finer toward the 

east, reflecting a Cascade Range source. They consist of weakly lithified fluvial sand and gravel with 

some lahars and sand, silt, and clay. They occur 

chiefly in the Yakima River valley and are folded 

with the underlying Columbia River Basalt Group 

(Myers and Price, 1979). In the Yakima River valley, the Ellensburg Formation reaches thicknesses 

of several hundreds of feet.

In the northeastern part of the plateau and 

within the Spokane River drainage, beds of the 

Latak Formation of Miocene age are interbedded 

with and overlie the basalt. These sediments consist mostly of finely laminated siltstone with some 

claystone, the composition of which reflects the 

pre-Columbia River Basalt Group granitic and 

metamorphic basement rocks of the region. Although the Latah Formation is as much as 1,500 ft 

thick in places, it is generally much thinner and is 

found mostly beyond the edges of the basalt plateau.

In the structural basins near Pasco, Quincy, and 

Walla Walla, Wash., the sediments overlying the
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B15

122 118° 117° 116°

46° 

45° 

0 20 40 60 80 MILES

i I i I i I i

40 80 120 KILOMETERS

OVERBURDEN THICKNESS, 

IN FEET

50-200 

200-400

EXPLANATION

400-600

600-800

400-800

More than 800

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

APPROXIMATE BOUNDARY OF 

OVERBURDEN Dashed where 

inferred; queried where uncertain

FIGURE 8. Extent and thickness of overburden where its thickness is generally 50 feet or more. (Modified from Drost and others,

1990.)
B16 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

basalt are part of the Ringold Formation. The 

Ringold Formation is of Pliocene age and includes 

sediments of both fluvial and lacustrine origin. It is 

at least 500 ft thick in these basins and consists 

predominantly of fine sand and silt, but also 

includes a gravel and conglomerate facies at one 

locality (Myers and Price, 1979).

Structural basins on the plateau margin south of 

the Columbia River in Oregon contain sediments 

that overlie the basalt and are folded with it; these 

have been assigned to the Dalles Group of Miocene 

and Pliocene age by Farooqui and others (1981). 

The sediments consist of coarse- to fine-grained fluvial deposits, lahars, and volcaniclastic materials 

that reflect source areas in the nearby uplands on 

the plateau margin. In The Dalles area (fig. 8), 

these units reach thicknesses of several hundreds 

of feet and are deeply eroded.

The Grande Ronde Valley in northeastern Oregon 

(fig. 8) is a major graben, filled with more than 2,000 

ft of fluviolacustrine deposits, interfingering alluvialfan deposits, and alluvial deposits. Materials in 

these deposits are primarily fine-grained siltstone 

and claystone at depth, whereas the upper few 

hundred feet or less contain some sand and gravel.

The Cordilleran ice sheet that covered the northern and northwestern part of the plateau left extensive deposits of till, stratified drift, and ice 

contact materials, especially in that area. Alpine 

glaciers from the Cascade Range and the Wallowa 

Mountains also reached the plateau margin and 

left deposits.

Catastrophic flooding of the Columbia Plateau 

took place during the late Pleistocene when ice 

dams in western Montana and northern Idaho were 

breached, allowing enormous volumes of water to 

flood what is now eastern and central Washington 

and to rush along the lower Snake River and the 

lower Columbia River (Bretz, 1923a, b). Deposits 

formed during the flood(s) were of two main types: 

(1) a "flood-gravel facies" deposited by high-energy 

flood currents in and along scabland channels, in 

depositional basins, and in the Columbia River east 

of The Dalles, and (2) a "slack-water facies" formed 

in peripheral areas of basins in the central part of 

the plateau. Flood-gravel deposits consist of poorly 

sorted, clast-supported, open-work gravels deposited as gravel bars; also present are gravel and intermixed sand and gravels. Slack-water deposits 

are interbedded silt and sand and minor gravel and 

are known as the Touchet Beds (Flint, 1938).

Eolian deposits of fine loess of Pleistocene age 

cover much of the plateau up to altitudes between 

2,700 and 3,200 ft and reach thicknesses of as

much as 250 ft, but generally are much thinner. 

The thickest deposits are found in the area surrounding the Palouse River in the eastern part of 

the study area and are part of the Palouse Formation. At least four different ages of loess deposits 

are present on the Columbia Plateau. The loess 

deposits are not shown on figure 8 because they 

are generally unsaturated.

Unconsolidated alluvial deposits of Quaternary 

age occur along most major streams and consist of 

gravel, sand, silt, and clay. Dune-sand deposits of 

Quaternary age, consisting predominantly of fineto medium-grained windblown sand, are found in 

Oregon and in central Grant County in Washington.

COLUMBIA RIVER BASALT GROUP

The thickest, most extensive, and hydrologically 

most important geologic unit in the Columbia 

Plateau aquifer system is the Columbia River 

Basalt Group of Miocene age, a unit that has been 

subdivided into five formations and numerous 

members (fig. IB). The five formations, from oldest 

to youngest, are the Imnaha Basalt, Picture Gorge 

Basalt, Grande Ronde Basalt, Wanapum Basalt, 

and Saddle Mountains Basalt. The Imnaha Basalt 

and the Picture Gorge Basalt crop out chiefly east 

and south of the study area.

The Imnaha Basalt is found in northeastern 

Oregon and adjacent Washington and Idaho, where 

it is exposed chiefly in the valleys of the Imnaha, 

Snake, Salmon, and Clearwater Rivers (fig. 7A). 

The Imnaha Basalt consists mostly of phyric flows 

with coarse-grained plagioclase. It unconformably 

overlies pre-Tertiary metamorphic and plutonic 

rocks and was extruded on a rugged erosional 

surface with more than 1,600 ft of local relief 

(Swanson and others, 1979a). About 1,600 ft of 

basalt is exposed at the type locality, where the 

base of the formation is not exposed.

In this study, the Picture Gorge Basalt has not 

been distinguished from the rest of the Columbia 

River Basalt Group and is included within either 

the Grande Ronde Basalt or the undivided category 

in figure 7A. The Picture Gorge Basalt is exposed 

only in north-central Oregon, mostly within the 

John Day Basin south of the Blue Mountains uplift, where it is locally interlayered with Grande 

Ronde Basalt and is in part coeval with it. The Picture Gorge Basalt reaches a maximum known 

thickness of 2,600 ft and consists of mostly finegrained plagioclase in phyric and some aphyric 

flows. Source vents for the Picture Gorge Basalt 

are east of Kimberly in the John Day Basin (fig.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B17

7A). The Imnaha and Picture Gorge Basalts are not 

considered important units in the aquifer system 

because of their limited extent and their occurrence 

at the edges of the study area.

The principal geologic formations in the Columbia 

Plateau aquifer system are part of the Yakima 

Basalt Subgroup of the Columbia River Basalt 

Group. These formations, from oldest to youngest, 

are the Grande Ronde, Wanapum, and Saddle 

Mountains Basalts. The generalized occurrence of 

these three formations is shown in figure 7A, and 

the accompanying stratigraphic chart (fig. IB) lists 

the members within each formation. Differentiating 

these members by extent and thickness was not 

within the scope of the present study but will be 

included in the following discussion. Two generalized geologic sections across the Columbia Plateau 

indicate the relative extents and thicknesses of the 

overburden and the three principal basalt formations (fig. 9).

The Grande Ronde Basalt underlies most of the 

plateau and pinches out at its margin. It is the 

most extensive of the three major formations, constituting 85 to 88 percent of the total volume of the 

Columbia River Basalt Group (Reidel, 1982; Tolan 

and others, 1987). The Grande Ronde Basalt probably consists of as many as 131 individual flows 

(Tolan and others, 1987). It is conformable with the 

Imnaha and Picture Gorge Basalts where they are 

in contact. Swanson and others (1979b, c, 1981) 

subdivided the Grande Ronde Basalt, using observed magnetic properties (N, normal magnetic 

polarity; R, reversed; and T, transitional), into four 

distinct magnetostratigraphic units because of the 

general absence of other distinguishing lithologies 

or chemical differences (fig. 7). The magnetostratigraphic units were named by Swanson and 

others (1979c) as Rx, Np R2 , and N2 , where the polarity and the polarity intervals were numbered 

sequentially from oldest to youngest, beginning 

with the top of the Imnaha Basalt (fig. IB). However, this method could not be used where the 

Grande Ronde was covered. Most Grande Ronde 

flows are fine-grained aphyric rocks with microphenocrysts of plagioclase and clinopyroxene. 

Olivine is generally present as a groundmass constituent and makes up less than 0.5 percent of the 

flow volume. Few drill holes on the plateau penetrate the total basalt thickness; thus, little is 

known about the complete thickness of the Grande 

Ronde Basalt except at the edges of the plateau, 

where the basalts are relatively thin and pinch out 

against older rocks. The combined thickness of the 

Grande Ronde Basalt and older basalts is shown in

figure 10. In most places, the Grande Ronde Basalt 

constitutes the entire thickness of the basalt. 

Locally, the Picture Gorge, Imnaha, or basalts 

older than the Columbia River Basalt Group may 

be included in the thicknesses shown. In the center 

of the plateau, the total thickness of pre-Wanapum 

basalts probably exceeds 10,000 ft. Sedimentary 

interbeds within the Grande Ronde Basalt are 

rare, generally only a few feet thick and of limited 

lateral extent. Where present, they vary in grain 

size from clay to gravel. Interbeds apparently are 

more common near the plateau margin.

The altitude of the top of the Grande Ronde 

Basalt has been contoured in areas where it is 

overlain by younger basalt or overburden materials 

(fig. 11). The top of this formation is marked by a 

zone of weathering and (or) a sedimentary iriterbed 

separating it from the overlying Wanapum or 

Saddle Mountains Basalts. Over most of the area, 

this sedimentary interbed is the Vantage Member 

of the Ellensburg Formation; however, in the 

northeastern part of the plateau, the sedimentary 

interbed in the same stratigraphic position is 

assigned to the Latah Formation (Swanson and 

others, 1979c). To avoid nomenclature problems of 

this type during this study, the interbeds are 

named on the basis of their typical stratigraphic 

position within the basalt for example, the 

Wanapum-Grande Ronde interbed. The WanapumGrande Ronde interbed is most extensive and 

thickest in the northern part of the plateau (fig. 

12), where its thickness ranges from 0 to 100 ft 

locally but averages about 25 ft. It consists chiefly 

of claystone and siltstone, with minor sand and 

gravel and sandstone beds. It is thinner to the 

south, and in the central plateau little is known 

about its extent. A thin saprolite commonly marks 

the interval in areas where the interbed is missing. 

In the absence of either the interbed or the saprolite, the contact between the Grande Ronde Basalt 

and overlying Wanapum Basalt is difficult to identify without information on minerals.

The Wanapum Basalt overlies the Grande Ronde 

Basalt and is the second most voluminous and extensive basalt formation in the Columbia River 

Basalt Group. It composes about 6 percent of the 

total volume of the basalts. Along part of the 

northeastern and eastern edges of the plateau, the 

Wanapum Basalt overlies the prebasalt rock. The 

Wanapum Basalt includes as many as 33 separate 

basalt flows (Tolan and others, 1987) consisting of 

medium-grained, olivine-bearing, slightly to moderately plagioclase-phyric basalt relatively high in 

iron and titanium oxides. It has been subdivided
B18 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121° 120° 119° 118° 117° 116° 115°

48°

47°

46°

45°

I I I I

EXPLANATION

____ GEOLOGIC UNIT 

O Overburden

S Saddle Mountains Basalt

W Wanapum Basalt

[ G j Grande Ronde Basalt

| B I Pre-Columbia River Basalt Group 

rocks

 ? GEOLOGIC CONTACT Queried 

where inferred

50 100 MILES

J_____I

I I I

0 50 100 KILOMETERS

9,000

VERTICAL SCALE GREATLY EXAGGERATED

50 MILES

I ' ' ' ' I

0 50 KILOMETERS

FIGURE 9. Generalized geologic sections through the Columbia Plateau (from Drost and others, 1990).
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B19

122° 121' 119 118° 117° 116°

GII.LIAM

SHERMANf T 2,439

f ^->n ~*H. { WASHINGTON / | 

I - __ * j || J

46° -

45'

40 80 120 KILOMETERS

EXPLANATION

THICKNESS OF GRANDE RONDE AND OLDER A 541 Basalt underlain by sediments or sedimentary 

BASALTS Number is thickness, in feet rock

V 454 Basalt underlain by igneous rock Basalt ranges from about 8,000 to 14,000 feet 

and is underlain by sediments COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 10. Thickness of the Grande Ronde Basalt and older basalts. (Modified from Drost and Whiteman, 1986.)
B20 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 120 116°

HIGHLANDS \ ^ ) £

o^j v^os

I*NGt''" 0lJ' U' ^

46° -

45° -

120 KILOMETERS

EXPLANATION

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 «oo STRUCTURE CONTOUR Shows altitude of top of Grande Ronde 

Basalt in areas where it is buried by younger materials. Contour 

interval 800 feet. Datum is sea level

APPROXIMATE BOUNDARY OF GRANDE RONDE BASALT Dashed 

where inferred

FIGURE 11. Altitude of the top of the Grande Ronde Basalt. (Modified from Drost and others, 1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B21

into four members on the basis of petrography and 

magnetic polarity. They are, from oldest to youngest, the Eckler Mountain, Frenchman Springs, 

Roza, and Priest Rapids Members. The Eckler

Mountain Member is found in southeastern Washington and northeastern Oregon, and is of limited 

areal extent. The three younger members are widespread on the plateau in Washington, but only the

122° 119 118° 117° 116°

PTND

I ORIELLE ' BONN! R

46° -

45° -

THICKNESS OF WANAPUM-GRANDE RONDE 

INTERBED, IN FEET Queried where unknown

0-50 

50-100

40 80 120 KILOMETERS

EXPLANATION

More than 100

No thickness data available

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 12.-^-Thickness of the Wanapum-Grande Ronde interbed. (Modified from Drost and others, 1990.)
B22 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

Frenchman Springs Member is widespread in 

Oregon. The Roza Member contains evenly distributed plagioclase phenocrysts, averaging more than 

5 millimeters (mm) in size, that make it an easily 

recognized and important marker bed on the plateau. Sedimentary interbeds are more abundant in 

the Wanapum Basalt than in the Grande Ronde 

Basalt but generally are thin and localized.

The combined thickness of the Wanapum Basalt 

flows and interbedded sediments is shown in figure 

13. Thickness ranges between 0 and 1,300 ft, with 

the greatest thickness in the Yakima Fold Belt 

subprovince (fig. 1). The Wanapum Basalt is exposed extensively or is covered by a veneer of sedimentary deposits in the northeastern and southern 

parts of the plateau. In the central and western 

parts, it is overlain by younger geologic units. The 

altitude of the top of the Wanapum Basalt where it 

is buried under younger geologic units is shown in 

figure 14.

A sedimentary interbed is commonly present 

between the Wanapum Basalt and the overlying 

Saddle Mountains Basalt. This interbed, the 

Saddle Mountains-Wanapum interbed, is equivalent to the Beverly Member of the Ellensburg Formation. The Saddle Mountains-Wanapum interbed 

consists chiefly of clay, silt, claystone, or siltstone. 

Lesser amounts of sand, sand and gravel, and 

sandstone are reported; available data do not indicate any pattern to the distribution of these coarsegrained materials. The thickness of the Saddle 

Mountains-Wanapum interbed is shown in figure 

15 (Drost and others, 1990); it averages about 50 ft 

but generally ranges between 0 and 200 ft. The 

thickest section, about 250 ft, is found north of 

Yakima, Wash.

The Saddle Mountains Basalt, the youngest 

basalt formation in the Columbia River Basalt 

Group, consists of 10 members (Swanson and others, 

1979d) and about 19 flows (Tolan and others, 

1987). Of these members, only three are regional in 

extent, and therefore they are important components of the regional aquifer system. They are, in 

ascending order, the Umatilla, Pomona, and 

Elephant Mountain Members. Other members of 

the Saddle Mountains Basalt represent volumes of 

basalt that are either small in extent or are found 

as remnants of intracanyon flows in the Snake 

River canyon or as fillings in ancestral canyons 

(Swanson and others, 1979a). The Saddle Mountains Basalt constitutes less than 2 percent of the 

total volume of the Columbia River Basalt Group. 

The Saddle Mountains Basalt was extruded during 

a period of accelerated tectonic activity, canyon

cutting, waning volcanism, and deposition of sedimentary interbeds between eruption periods of the 

major members. Each of the major basalt members 

generally consists of only one or two basalt flows. 

Depending on geographic location, the Saddle 

Mountains Basalt overlies either the Saddle Mountains-Wanapum interbed, the Wanapum Basalt, or 

the Grande Ronde Basalt.

Chemically, the Saddle Mountains Basalt is the 

most diverse of the basalt formations. The 

Umatilla Member is chemically distinct and is consistently finer grained than all other flows of the 

Columbia River Basalt Group. The Pomona Member is sparsely phyric, and the Elephant Mountain 

Member is fine grained and aphyric. In the area 

around the Grande Ronde valley, units mapped by 

Swanson and others (1979b, 1981) as andesite have 

been included in the Saddle Mountains Basalt.

The thickness of the Saddle Mountains Basalt 

flows and any interbedded sediments ranges from 0 

to more than 800 ft (fig. 16). Maximum thickness 

occurs in the Yakima River valley and the area 

south of Hanford, Wash. In one area in Oregon, it 

was estimated that the interbeds make up about 50 

percent of the total thickness; however, this is not 

the case in most of the area. The altitude of the top 

of the Saddle Mountains Basalt where it is buried 

under younger rocks is shown in figure 17.

GEOLOGIC STRUCTURES

Geologic structures within the plateau are diverse and range from simple homoclines to sharp 

folds with structural relief of as much as several 

thousand feet. Major faults generally are associated with anticlinal folds and range from steep 

normal faults to low-angle reverse faults. Major 

geologic structures within the plateau, simplified 

from the work of Drost and others (1990), Drost 

and Whiteman (1986), and Gonthier (1990), are 

shown in figure 18. The discussion of structures 

that follows is by geographic regions or subprovinces wherein the types of structural deformation appear to be grossly similar.

The Palouse subprovince is structurally simple 

and is underlain by basalt flows that dip less than 

5° toward the southwest. Superimposed on the 

southwesterly dipping basalt are a few broad, open, 

northwest-trending folds with amplitudes of only a 

few tens of feet. Northwest-trending topographic 

lineaments are present in the Palouse that may 

represent fracture zones along which the rock is 

more readily eroded. No offset or displacement 

along them has been identified.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B23

122° 121 C 120° 119° 118° 117° 116°

UNCOI.N

48°

47°

46°

45°

BOISF.

20 40 60 80 MILES 

1,1,1,1

THICKNESS OF WANAPUM 

BASALT AND INTERBEDDED 

SEDIMENTS, IN FEET Queried 

where unknown

0-400 

400-600

40 80 120 KILOMETERS

EXPLANATION

600-800

800-1,000

More than 1,000

No thickness data available

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

APPROXIMATE BOUNDARY OF 

WANAPUM BASALT Dashed 

where inferred

FIGURE 13. Thickness of the Wanapum Basalt and interbedded sediments. (Modified from Drost and others, 1990.)
B24 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 116°

N - Ps .v^-cowfct

20 40 60 80 MILES

46° 

45° -

120 KILOMETERS

EXPLANATION

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 400 STRUCTURE CONTOUR Shows altitude of top of Wanapum 

Basalt in areas where it is buried by younger materials. Queried 

where uncertain. Contour interval 400 feet. Datum is sea level

 APPROXIMATE LIMIT OF WANAPUM BASALT Dashed where 

inferred

FIGURE 14. Altitude of the top of the Wanapum Basalt. (Modified from Drost and others, 1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B25

122° 120° 119 118° 117° 116°

46° -

45° 

20 40 60 80 MILES

THICKNESS OF SADDLE MOUNTAINS-WANAPUM 

INTERBED, IN FEET Queried where uncertain

0-50

50-100

100-200

40 80 120 KILOMETERS

EXPLANATION

More than 200

SADDLE MOUNTAINS-WANAPUM INTERBED 

BOUNDARY

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 15. Thickness of the Saddle Mountains-Wanapum interbed. (Modified from Drost and others, 1990.)
B26 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 120° 119° 118° 117° 116°

48 C

47C

46°

45C

PEND I LINCOLN 

jORIELLEl BONNER ' ~

>

I SHOSHONE \

I *

Ni2* .Creek - '

^ ^C^- 1 ^/^.---A. x i A -7/v^> * A ^,

O REGiO N

BOISE

20 40 60 80 MILES

1,1,1,1

THICKNESS OF SADDLE 

MOUNTAINS BASALT 

AND INTERBEDDED 

SEDIMENTS, IN FEET

0-200 

200-400

40 80 120 KILOMETERS

EXPLANATION

400-600 

600-800 

More than 800

Insufficient data for contouring; 

however, thicknesses are 

generally under 200 feet

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

APPROXIMATE LIMIT OF SADDLE 

MOUNTAINS BASALT Dashed 

where inferred

FIGURE 16 Thickness of the Saddle Mountains Basalt and interbedded sediments. (Modified from Drost and others, 1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B27

122° 121 C 120° 119° 118° 117° 116°

PEND 

I ORIELLE I BONNER

PUm LI D

20 40 60 80 MILES

45° -

0 40 120 KILOMETERS

EXPLANATION

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 400 STRUCTURE CONTOUR Shows altitude of top of Saddle Mountains 

Basalt in areas where it is buried by younger materials. Queried 

where uncertain. Hachures indicate depression. Contour interval 

400 feet. Datum is sea level

APPROXIMATE LIMIT OF SADDLE MOUNTAINS BASALT Dashed 

where inferred

FIGURE 17. Altitude of the top of the Saddle Mountains Basalt. (Modified from Drost and others, 1990.)
B28 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 120° 119° 118° 117° 116°

48°

47°

46°

45°

 H I N G T O N

PALOUSE'-WTEMANSUBPROVINCE '

WASCO YAKIMA

FOLD BELT GUI JAM 

SUBPROVINCE

*-^NV MOUNTAINS- WT 

WH! /-SUBPROVINCE

VALLEY

* 1 *

f' ^-^ 

f WASHINGTON / I

\ i, ^-^ I r

N r

BOISIi

20 40 60 80 MILES

40 80 120 KILOMETERS 

EXPLANATION

FAULT Relative displacement unknown

STRIKE-SLIP FAULT Arrows show 

relative horizontal movement

ANTICLINE Shows trace of crestal 

plane. Dashed where inferred

MONOCLINE Abrupt increase in dip 

in direction of arrows

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

PHYSIOGRAPHIC SUBPROVINCE 

BOUNDARY

 I SYNCLINE Shows trace of trough plane 

FIGURE 18. Major geologic structures within the Columbia Plateau. (Modified from Drost and others, 1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B29

The dominant feature of the Yakima Fold Belt 

subprovince is a series of narrow, asymmetrical 

anticlinal ridges, trending east-west to northwest 

and plunging east and southeast, that are generally separated by broad, flat-floored synclinal valleys. From south to north, the most prominent 

anticlinal ridges are the Columbia Hills, Horse 

Heaven Hills, Toppenish Ridge, Ahtanum Ridge, 

Rattlesnake Hills, Yakima Ridge, Umtanum Ridge, 

and Manastash Ridge. At the eastern ends of those 

ridges, each ridge intersects or is sharply deflected 

in a southeasterly direction along a 125-mi-long 

zone that extends between Cle Elum and Wallula, 

Wash. This zone is a segment of a larger lineament 

known as the Olympic-Wallowa lineament that 

extends northwest-southeasterly between the 

Olympic Mountains in northwestern Washington 

(more than 100 mi from the study area) and the 

Wallowa Mountains in northeastern Oregon.

Principal anticlinal ridges in the Yakima Fold 

Belt subprovince range in length from 35 to 150 

mi. In general, folds in this subprovince are asymmetrical, with amplitudes ranging from nearly flat 

to overturned. Large segments of some folds are 

cut by low-angle reverse faults that parallel the 

ridges. Reverse faults cut both limbs of some anticlines and form box folds. This style of folding persists north of the 125-mi zone between Cle Elum 

and Wallula, but the folds diminish in amplitude. 

The east-west and northwest-southeast fold trend is 

crossed at right angles by sinuous folds trending 

northeast, one of which is the Beezley Hills anticline.

In Oregon, south of the Columbia Hills, the 

basalt dips toward the axis of The Dalles-Umatilla 

syncline; this syncline roughly follows the south 

shore of the Columbia River and forms a broad, 

asymmetrical synclinal basin. The south limb of 

the syncline is formed by gently north-dipping | 

basalt that forms the north flank of the Blue 

Mountains anticline. Pre-Columbia River Basalt 

Group rocks that form the core of the Blue Mountains are exposed in a few places. The dip slope is 

crossed by gentle monoclinal flexures; by broad, 

open, small-amplitude folds; and by one or two narrow bands of tight asymmetrical folds. These fold 

types trend east-west to northeasterly, roughly parallel to the axis of the nearb}^ major structure, the 

Blue Mountains anticline. A series of lineaments 

trending northwest, narrow fold belts, and faults 

with minor strike-slip displacements crosses the 

southwest part of the fold belt and adds a prominent structural grain to the region. Collectively, 

the geologic structures in the Yakima Fold Belt 

subprovince suggest that the folds were formed in

a stress field in which the maximum stress was 

oriented in the north-south direction (Reidel, 1984).

The eastern part of the Blue Mountains subprovince was the vent area for much of the Columbia River Basalt Group flows. It is a rugged, 

uplifted area consisting of remnants of a plateau 

surface and deeply dissected canyons with up to a 

few thousand feet of local relief. The most prominent structural feature is the broad-crested Blue 

Mountains anticline and a belt of asymmetrical 

folds that diverge easterly from its northeastern 

end. The crestal area of the anticline is crossed by 

numerous northwest-trending high-angle normal 

faults, as well as by lineaments with no apparent 

displacement. Southeast of this crestal area, centered near La Grande, Oreg., is a major graben 

bounded by normal faults with a similar northwestern trend. The area south of the Blue Mountains anticline and west of the graben is marked by 

northwest- to west-trending, broad, open, lowamplitude folds and, in places, by somewhat similarly 

trending normal faults. East of the graben, the principal structures are widely spaced normal faults.

Numerous linear, northwest/southeast-trending, 

en echelon basalt feeder-dike complexes have been 

identified in the southeastern part of the plateau 

in both Washington and Oregon. Similar dike complexes are believed to be covered by younger basalt 

in these areas and possibly elsewhere. Although 

they are not strictly a geologic structure, their 

effects on the movement of ground water are similar to those of geologic structures. The feeder dikes 

are commonly a few to several feet wide and many 

miles long, and generally they are vertical to steeply 

dipping. They tend to crosscut older basalt flows and 

generally consist of dense, fine-grained basalt.

INTERNAL STRUCTURE OF BASALT FLOWS

Individual flows of the Columbia River Basalt 

Group range in thickness from a few inches to 

more than 300 ft (Swanson and others, 1979c). The 

internal structure of a typical flow consists of four 

sections the flow top, the entablature, the colonnade, and the flow base (fig. 19). The flow top 

(called the interflow zone where superimposed with 

the base of an overlying flow) generally is vesicular 

basalt with scoria and clinker. The entablature 

consists of small-diameter columns in fan-shaped 

arrangements. Hackly joints are common, and the 

upper part of the entablature is commonly vesicular. The colonnade is made up of nearly vertical 

three- to eight-sided columns bounded by cooling 

joints. The columns average 3 ft in diameter and
B30 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

25 ft in length. Columns commonly are crosscut by 

systems of nearly horizontal joints, and a vesicular 

zone is commonly present at the base of the colonnade. The base of the flow generally has a thin 

zone of glassy basalt and may be marked by a zone 

of pillow basalt. These four sections are usually 

recognizable in individual basalt flows; however, 

the degree of development of jointing in each section 

varies markedly, both laterally within flows and vertically among them. Colonnades and entablatures 

range from poorly to well developed; typically, if one 

is well developed, the other is barely recognizable.

BASALT ROCK MECHANICS

For regional ground-water investigations, the 

most important rock properties are porosity, density, bulk and Young's modulus of elasticity, and 

permeability. Laboratory data are available within 

the study area for these five properties. Laboratory

Flow top and base

of overlying flow

form interflow zone

Vesicular 

top

PillowPalagonite 

Complex

Vesicular 

base

Chilled base and 

"incipient pillows"

Palagonite 

Pillow

FIGURE 19. Generalized diagram showing a typical basalt flow 

in the Columbia River Basalt Group. (Modified from Swanson 

and Wright, 1978.)

values of permeability from core samples probably 

are not representative of the fractured basalts; 

however, initial estimates of hydraulic conductivity 

based on specific-capacity data are presented in the 

section "Hydraulic Characteristics." Similarly, laboratory values of bulk and Young's modulus are not 

presented because they were made for core 

samples, and may have little relation to the values 

of the composite skeletal structure of the basalt 

flows. Information on porosity and density for the 

Columbia River Basalt Group (Sublette, 1986) are 

summarized in table 4. Most of the data are from 

laboratory tests and investigations on the Hanford 

Nuclear Reservation site in central Washington.

The porosity of basalt is dependent on chemical 

composition of the basalt, temperature of extrusion, 

rate of cooling, flow thickness, and degree of 

diagenesis that the basalt has undergone. In discussing the hydrogeology of volcanic rocks, Wood 

and Fernandez (1988) reported that, on the basis of 

a worldwide sampling of volcanic rocks, basalts 

have total porosities ranging from 1 to 70 percent 

and that effective porosities have a much smaller 

range than the total porosities, averaging less than 

5 percent. According to Wood and Fernandez 

(1988), the bulk density of vesicular basalts ranges 

from 0.083 to 0.090 lb/in3 , and that of dense 

basalts from 0.098 to 0.105 lb/in3 , with an average 

grain density of 0.105 lb/in3 . These values are similar to those given in table 4. An average porosity of 

about 4 percent is indicated by the density values; 

thus, the higher porosity values in table 4 indicate 

that fracturing has increased the porosity, as suggested by Wood and Fernandez (1988).

HYDROLOGY

The primary factors controlling the occurrence, 

movement, and availability of ground water in the 

Columbia Plateau are the hydrologic characteristics of the geologic units underlying it, the climate, 

and water-supply development practices. The following sections describe the hydrologic framework 

of the Columbia Plateau aquifer system and, where 

appropriate, relate the hydrology to the geologic, 

climatic, and cultural characteristics that affect the 

availability and quality of ground water.

RELATION BETWEEN GEOLOGIC AND HYDROLOGIC 

FRAMEWORKS

The geologic characteristics of the rock materials 

underlying the Columbia Plateau are varied and 

complex because of formational, emplacement, and
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B31

TABLE 4. Rock-mechanics data for the Columbia River Basalt Group (from Sublette, 1986) 

[Density values given in pounds per cubic inch; porosity given in percent]

Intraflow structure

Flow-top and vesicular zone 1 

Representative value 

Number of samples 

Entablature and colonnade 1 

Representative value - ----- -

Entablature2

Grain 

density

0.104 

0.097-0.101 

33

0.104 

0.102 0.101

113

0.107 

0.100 0.115

Bulk 

density

0.084 

0.065-0.10 

171

0.102 

0.092-0.104 

360

0.101 

0.087-0.109

Effective 

porosity

14.45 

1.60-41.60 

163

1.85 

0.20-12.40 

356

1.73 

0.10 5.30

Total 

porosity

20.98 

7.20-35.80 

32

2.85 

0.00-13.00 

106

6.23 

0.40-13.70

1Based on samples from wells located within a small area of the Hanford Nuclear Reservation. 

2Based on samples from wells scattered throughout the Hanford Nuclear Reservation and on reports from 

various investigations.

diagenetic processes. In order to define the occurrence, movement, and quality of ground water 

within such a complex geologic system, it is necessary to conceptualize and relate the geological and 

hydrological frameworks into a simpler system, or 

a conceptual model, that provides a basis for evaluating the hydraulic characteristics, the groundwater recharge and discharge, and the movement 

of ground water in the Columbia Plateau aquifer 

system. In order to accomplish this task, the following aspects need to be considered: the relation 

of the overburden in the hydrologic framework, the 

flow of ground water through the basalt, the relation 

of the sedimentary interbeds, and the effect of geologic structures on the movement of ground water.

Most of the lowlands of the plateau are basins in 

which the Columbia River Basalt Group is overlain 

by sediments and sedimentary rocks. These rocks 

range from shales and clays to conglomerate and 

gravel, but they are generally coarse grained and 

permeable in their upper sections and finer grained 

and less permeable at depth. They transmit water 

readily and constitute a water-table aquifer where 

they are saturated. The average hydraulic conductivity can be several orders of magnitude larger 

than that of the basalt.

The movement of water through basalts is governed by numerous factors that affect the nature of 

individual flows. These factors include the topographic surfaces over which the basalts flowed; the 

erosional processes that occurred before, during, 

and after extrusion; the deposition of interbeds; 

tectonic activity; and diagenetic processes. For 

example, lava flows that fill valleys and canyons 

could leave a smooth surface for extrusion of later 

flows. These later flows might have extensive lateral continuity, but the earliest flows would be 

localized. Tectonic activity, basin subsidence, and 

formation of folds can distort emplaced lava flows 

and affect the distribution of subsequent flows. 

Moving water can erode flows, ponding water can 

quench solidifying flows, and lava flowing into 

standing water can form porous pillow-palagonite 

complexes. Thus, the lateral continuity, thickness, 

and composition of individual flows (particularly 

interflow zones) are highly varied. The degree of 

variation in the entablature and colonnade of a 

flow further complicates the understanding of 

water movement in the basalts.

The basalt is an extremely heterogeneous aquifer unit that transmits water most readily through 

the broken vesicular and scoriaceous interflow 

zones that commonly constitute 5 to 10 percent of 

the thickness of an individual basalt flow (fig. 19). 

The interflow zones are separated by the less 

transmissive and more massive entablature and 

colonnade (fig. 19), in which the fractures are more 

or less vertical. Lateral ground-water movement in 

the entablature and colonnade is probably negligible when compared with the volume of water that 

moves laterally through the interflow zones. This is 

because movement of water in the entablature and 

colonnade is controlled by fractures and joint 

systems, whereas movement of water in the interflow zones is controlled by primary features such 

as flow breccia, clinkers, and vesicles. Vertical 

movement of ground water between interflow zones 

is much less per unit area than lateral movement 

but is large over the entire aquifer area. Vertical 

movement of ground water varies because of the 

structure of individual flows and the hydraulic 

characteristics of the interbeds.
B32 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

The lithology of sedimentary interbeds between 

basalt flows within a formation varies from shales 

to sands and gravels. Except in the Saddle Mountains Basalt, most interbeds within the basalt formation are of a very limited extent. The interbeds 

between the basalt formations are fairly extensive 

laterally but are thin when compared with basalt 

formations. These interbeds may be locally transmissive and function as aquifers, but in general 

they probably impede the vertical movement of 

water. Water levels and well-log data suggest that 

the interbeds generally act as semiconfining to locally confining layers that transmit small amounts 

of water laterally. This conclusion is further supported by the fact that, locally, lateral hydraulic 

conductivities of the interbeds are much smaller 

than those of the interflow zones.

Newcomb (1961, 1969) discussed the effect of 

tectonic structures on ground-water flow in the 

basalt. In an analysis of the flow system in an area 

near The Dalles, Oreg., he postulated that tight 

anticlinal folding of basalt formed breccia and fault 

gouge between individual lava flows in the axial 

region of the fold that decreased the permeability 

of the basalt in the axial region, thus impeding 

ground-water flow across the axis. It is also possible that feeder dikes, individually or in series, 

could impede ground-water movement, especially if 

oriented transversely to the hydraulic gradient. 

Lack of observation wells and pumping centers 

near the axis of folds or feeder dikes makes it difficult to assess their control on the movement of 

ground water.

The relation between the geologic framework 

and the hydrologic framework that provides a basis 

for the study of a regional flow system is shown in 

figure 20. This relation provides a simpler system 

for study and is the foundation for the conceptual 

model for describing ground-water flow in the 

Columbia Plateau aquifer system. Thus, for study 

purposes, the aquifer system was divided into 

seven units the overburden aquifer, three basalt 

units, and three confining units (fig. 20).

The sediments and sedimentary rocks forming 

the overburden are considered a single unit. Because of the large difference in hydraulic conductivity between the overburden and the basalt, the 

unit is considered a separate aquifer, herein 

referred to as the overburden aquifer.

The basalt aquifers can be described only generally because of the number and complexity of individual basalt flows and the lack of data to define 

them in detail. The combining of 100 or more individual basalt flows into study units has been done

by following a division similar to that of the 

Yakima Basalt Subgroup. This subgroup and its 

intercalated sediments were divided into three 

basalt study units: the Saddle Mountains unit, the 

Wanapum unit, and the Grande Ronde unit (fig. 

20). Each unit includes the intercalated sediments 

within the basalt formation. Additionally, in the 

southeastern part of the study area, the Imnaha 

Basalt is included in the Grande Ronde unit. The 

term "unit" or "units" is used to distinguish them 

from the basalt formations, which formally do not 

include the intercalated sediments.

The Saddle Mountains-Wanapum and 

Wanapum-Grande Ronde interbeds are two of the 

confining units. Because these units are thin, 

locally missing, of a smaller lateral extent than the 

basalt units they overlie, and at some locations 

consist of rock materials that are at least as permeable as the basalts, they are not formally 

named. They simply have been called confining 

units for the division of the aquifer system that 

relates the geologic and hydrologic frameworks in 

this study. The prebasalt basement rocks generally 

have much lower permeabilities than the basalts 

and are considered to be the base of the regional 

aquifer system. These basement rocks are called 

the basement confining unit.

The conceptual model of the ground-water flow 

in the Columbia Plateau aquifer system, based on 

the relation between the geologic and hydrologic 

frameworks, is shown in figure 21. The area for 

which the hydrologic framework information in the 

following sections is presented is limited to about 

32,800 mi2 of the study area. This hydrologic study 

area also represents the boundaries of the numerical ground-water-flow model constructed during 

this study. The relation between the hydrologic 

study area, the areal extent of the Columbia River 

Basalt Group (which extends beyond the boundary 

of the described aquifer system), and the Columbia 

Plateau RASA study area is shown in figure 22.

HYDRAULIC CHARACTERISTICS

Most of the lateral hydraulic conductivity values 

discussed in this report are depth-integrated average values that represent the general hydraulic 

characteristics of the entire study-unit thickness. 

Vertical hydraulic conductivities are largely 

unknown. Application of aquifer testing methods 

for estimating vertical hydraulic conductivity of the 

basalts is difficult and prone to error. However, 

where fine-grained interbeds are present, the 

interbeds control vertical ground-water movement,
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B33

and vertical hydraulic conductivity then can be 

estimated on the basis of the hydraulic characteristics of the interbed lithology. Otherwise, vertical 

hydraulic conductivities may only be estimated by 

numerical ground-water-flow model simulation. 

Such estimates represent the integrated effects of 

the basalt flows and the confining unit, if present, 

between two units.

The initial values of lateral hydraulic conductivities for each basalt unit were estimated from drillers' specific-capacity data using the combined 

method of Theis (1963) and of Ferris and others 

(1962). In this method, the Theis equation is used 

to calculate transmissivity, which is the product of 

the hydraulic conductivity and the saturated thickness and is "equal to an integration of the hydraulicconductivity values across the saturated part of the 

aquifer perpendicular to the flow paths" (Lohman

and others, 1972). However, the transmissivity calculated from specific-capacity data was assumed to 

be the product of the hydraulic conductivity and 

the thickness of the aquifer open to the wells. This 

transmissivity was then divided by the length of 

the open section or screened interval in a well to 

obtain a vertically averaged lateral hydraulic conductivity at that interval. The lateral hydraulic 

conductivity value estimated on the basis of 

specific-capacity data is probably high because of 

the effects of the vertical flow of water within the 

interval.

The vertically averaged lateral hydraulic conductivity of the overburden aquifer at any given location is dependent on the distribution of the 

materials that compose the aquifer. The types of 

sediment present in the overburden (discussed previously in the "Overburden" subsection) range from

GEOLOGIC FRAMEWORK

BASALT STRATIGRAPHY

MIOCENE

| Miocene Uppr ocene 

T3 

T3

Lower Miocene

c 

o ro

O '-P (O

 i ;R <-> 0) a,

£

BASALT GROUP \ RIVER 

COLUMBI/

SUBGROUP YAKIMA BSALT 

Saddle Mountains Basalt

Wanapum Basalt

Grande 

Ronde 

Basalt

Picture j Gorge ' 

Basalt !

Imnaha 

Basalt

Lower Monumental Member 

Ice Harbor Member 

Buford Member 

Elephant Mountain Member 

Pomona Member 

Esquatzel Member 

Weissenfels Ridge Member 

Asotin Member 

Wilbur Creek Member 

Umatilla Member

Priest Rapids Member 

Roza Member 

Frenchman Springs Member 

Eckler Mountain Member

 j= R2 

I RI

s T

nj i"Q 5

SEDIMENT STRATIGRAPHY

Sediments of Miocene through 

Holocene age (glaciofluvial, fluvial, 

lacustrine, eolian, and ash fall 

materials). Locally includes sediments 

of the Palouse, Latah, Ringold, and 

Ellensburg Formations, and the Dalles 

Group (Farooqui and others, 1981).

Saddle Mountains-Wanapum Interbed

Wanapum-Grande Ronde Interbed

Basement rocks <pre-Columbia River Basalt Group)

HYDROLOGIC FRAMEWORK

STUDY UNIT

E

 4-"

CO

** 'D

C7

D 

CO

 4-"

CO

o_

en

Columbi

Overburden aquifer

Saddle Mountains 

unit

Confining unit

Wanapum unit

Confining unit

Grande Ronde 

unit

Basement confining unit

FIGURE 20. Correlation of geologic framework with hydrologic framework. See figure 7 for explanation of magnetostratigraphic units.
B34 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

fine to coarse materials. Estimates of lateral hydraulic conductivity made from specific-capacity 

data were supplemented with data from previous 

studies by Tanaka and others (1974), MacNish and 

Barker (1976), Bolke and Skrivan (1981), Prych 

(1983), H.H. Bauer (U.S. Geological Survey, written 

commun., 1984), and B.W. Drost (U.S. Geological 

Survey, written commun., 1988). Estimates from 

previous studies were based on specific-capacity data, 

aquifer tests, and numerical ground-water-flow modeling. The frequency distribution of the lateralhydraulic-conductivity data for the overburden 

aquifer is shown in figure 23. The values range 

from about 0.02 to 150,000 ft/d, with a median lateral hydraulic conductivity of about 240 ft/d. Fifty 

percent of the values about the median lie in the 

range 45 to 1,000 ft/d. The areal distribution of 

hydraulic conductivity for the overburden aquifer is 

presented in figure 24. This distribution is based 

on specific-capacity data, and thus values might be 

high; in areas with no data, lower values (1 to 5 ft/d), 

representative of loess, were assumed to be the 

best estimate.

Ideally, estimates of aquifer conductivities are 

made by conducting tests on wells that fully

penetrate the aquifer of interest and that are 

cased off above and below that aquifer zone. Because of the variability in hydraulic conductivities 

caused by folds, faults, basalt-flow thickness, and 

intercalated sedimentary material, many hundreds 

of such aquifer tests would be necessary to delineate properly the hydraulic-conductivity distribution throughout the basalt part of the aquifer 

system. Relatively few such aquifer tests have 

been made. Indeed, cased wells completed in 

basalt on the plateau are rare. However, a large 

number of specific-capacity values for domestic, 

irrigated, and municipal wells are available from 

which hydraulic conductivities can be estimated. 

Generally, these wells are uncased in the basalt, 

and estimated hydraulic conductivities represent 

vertically integrated values over the entire penetration interval in the basalt. Therefore, some 

hydraulic conductivities may represent only a part 

of an aquifer at a particular location, whereas 

others may represent composite hydraulic conductivities over parts of two or more aquifers. Because 

of the similarity between basalt aquifers in structurally similar areas, this was not considered to be 

a serious problem.

SW NE

Overburden aquifer

Saddle Mountains unit 

Confining unit 

Wanapum unit

Confining unit

Grande Ronde unit

EXPLANATION

Direction of ground-water flow

FIGURE 21. Generalized ground-water-flow pattern in the Columbia Plateau aquifer system*
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B35

The frequency distribution of the estimated 0.005 to 6,100 ft/d and have a median of about 5 ft/d.

lateral hydraulic conductivities for the three basalt Seventy-five percent of the hydraulic conductivity

units is shown in figure 25. The values range from values are less than about 26 ft/d, and 25 percent

125° 124° 123° 122° 121 C 120° 119° 118° 117° 116°

49°

48C

47°

46C

45°

44C

0 20 40 60 80 MILES

I i I. i I . I .1

I ' I ' I ' I

0 40 80 120 KILOMETERS

EXPLANATION

 BOUNDARY OF HYDROLOGIC STUDY AREA

 BOUNDARY OF COLUMBIA RIVER BASALT GROUP

 BOUNDARY OF COLUMBIA PLATEAU REGIONAL 

AQUIFER-SYSTEM ANALYSIS STUDY AREA

FIGURE 22. Relation of the hydrologic study area, the areal extent of the Columbia River Basalt Group, and the Columbia Plateau

Regional Aquifer-System Analysis study area.
B36 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

are less than about 1 ft/d. The Saddle Mountains, 

Wanapum, and Grande Ronde units have median 

hydraulic-conductivity values of 2.4, 5.2, and 4.9 ft/d, 

respectively. The smaller median hydraulic conductivity of the Saddle Mountains unit is attributed to 

the thicker and more numerous intercalated sediments, which are generally not present in the 

Wanapum and Grande Ronde units. In the center 

of the plateau, these sediments are generally fine 

grained and less permeable.

The wide range in lateral hydraulic conductivity 

reflects the heterogeneous nature of the basalts. 

The largest estimated hydraulic conductivities 

probably are due to local geologic structure, to 

thickening of interflow zones, or to the presence of 

pillow-palagonite complexes (Swanson, 1967). Many 

wells with large hydraulic-conductivity values are 

close to wells from which small values were estimated. This indicates the high degree of heterogeneity in the hydraulic conductivity. Observed 

physical variations in exposed flows indicate that, 

within a single flow, a wide range of lateral (and 

vertical) hydraulic-conductivity values would exist. 

For example, cascading water in many uncased 

wells is attributed to the relative ease with which 

water moves horizontally along interflow zones. 

Thus, the water flows from a higher head interflow

zone to a lower head interflow zone through the 

borehole of a well. The hydraulic conductivity in 

interflows is probably dependent on primary features such as flow breccia, clinkers, and vesicles, 

whereas in the entablature and colonnade the hydraulic conductivity is mainly due to fractures and 

joint systems developed during cooling processes 

and tectonic activity. Lateral hydraulic conductivity may be much larger than estimated from 

specific-capacity data for some zones because these 

estimates represent the entire uncased penetrated 

intervals.

Lateral hydraulic conductivity of basalts also 

may be affected by faults. Recent modeling studies 

(William Meyer, U.S. Geological Survey, written 

commun., 1985; F.A. Packard, U.S. Geological 

Survey, written commun., 1987; Davies-Smith and 

others, 1988) indicate that within a hydrogeologic 

unit of basalt the vertically averaged lateral hydraulic conductivity along faults might be as low as 

0.003 ft/d. There are two possible explanations for 

this the offsetting of interflow zones through 

faulting, which produces low-hydraulic-conductivity 

fault breccia and gouge material at that interface, 

as described by Stearns (1942) and Newcomb (1965, 

1969); and the closing of pore space through deposition of secondary minerals along the fault plane.

EXPLANATION

MINIMUM QUARTILES 

25 50 75 -3.7

'0.023 H I h

MAXIMUM

11.9 i LOGARITHM (BASE e) FEET PER DAY

150,000' FEET PER DAY

Number of sample points is 871

LLJ

tr

o io z

°S 

5E 

> °-

^

LLI

a

50

40

w0

to0

10

o " 

-3.7

0.023

11.9

150,000

240

-3 -2 -1 23456 

LOGARITHM (BASE e) FEET PER DAY

10 11 12

-0.018 0.05 0.14 0.37 1.0 2.7 7.4 20.1 55 148 403 1,096 2,980 8,103 22,030 59,874 162,750

FEET PER DAY 

HYDRAULIC CONDUCTIVITY

FIGURE 23. Frequency distribution of hydraulic-conductivity data for the overburden aquifer.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B37

122° 12V 119 118° 117° 116°

/ I

^S H I N GT O ML -

\

) -

I D A H\O

MARION - g , ~" 

cr.

46° -

45° 

20 40

_L

60

_L

80 MILES

J

I 

40 80 120 KILOMETERS 

EXPLANATION

HYDRAULIC CONDUCTIVITY, IN FEET 

PER DAY 100-2,000 

More than 2,000 

Unknown

COLUMBIA PLATEAU AQUIFER SYSTEM 

STUDY BOUNDARY

APPROXIMATE LIMIT OF OVERBURDEN 

UNIT Dashed where inferred; queried 

where uncertain

FIGURE 24. Areal distribution of hydraulic conductivity for the overburden aquifer.
B38 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

Large local variation in lateral hydraulic conductivities and the lack of data in many areas preclude areal mapping of these estimated hydraulic 

conductivities of the basalt units. Results from 

previous modeling studies (Luzier and Skrivan, 

1975; Bolke and Skrivan, 1981; Davies-Smith and 

others, 1988) indicate that small values of hydraulic conductivity probably are the principal factor 

controlling the regional movement of ground water 

in the basalts.

The potential range in transmissivity values can 

be estimated by using the distribution of thickness 

of the aquifer system and the estimated hydraulicconductivity values. The frequency distribution of

the entire thickness of the Columbia Plateau aquifer system is shown in figure 26. The thickness 

values were determined on the basis of grid-block 

sizes of 2.5 minutes of latitude (about 2.8 mi) by 

2.0 minutes of longitude (about 1.6 mi). The area of 

each grid block is about 4.6 mi2. Application of the 

grid-determining procedure is to smooth local 

variation to produce a spatially averaged distribution of the aquifer thickness. Multiplying the minimum, median, and maximum values of aquifer 

thickness by the respective minimum, median, and 

maximum values of hydraulic conductivity gives a 

potential range in values and an approximate 

median value of the transmissivity of the aquifer

EXPLANATION

MINIMUM 

, -5.3 0.09,

QUARTILES 

25 50 75

3.2

MAXIMUM 

7.8 , LOGARITHM (BASE e) FEET PER DAY

1 0.0005 1.1 J 23.9 2,522' FEET PER DAY

All basalt units, estimated on the basis of 1,395 specific capacity tests 

Grande Ronde unit, estimated on the basis of 446 specific capacity tests 

Wanapum unit, estimated on the basis of 461 specific capacity tests 

Saddle Mountains unit, estimated on the basis of 116 specific capacity tests

50

o 40

uz 30

20

1)

a

£ 10

-5.3 0.09

0. D05 1.1 

-4.96 0.08

0.007 1.1

1.6

4,9

1.7 

5.2

3.2 7.8

23.9 2,522

3.3 8.6

26.6 5,244

-4.96

0.007

-0.62

0.54

.88 

2.4

2.8

15.7

7.5

1,892

-5.3 0.06

0.005 1.05

1.6 

5.1

3.3 87

26.35 6,1001

-6

0.002

-4 -2 024 

LOGARITHM (BASE e) FEET PER DAY

10

0.02 0.14 1 7.4 55

FEET PER DAY 

HYDRAULIC CONDUCTIVITY

403 2,980 22,030

FIGURE 25. Frequency distribution of lateral hydraulic conductivities for the three basalt units.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B39

system. The potential range of transmissivities is 

from 0.5 to 114 million ft2/d (feet squared per day), 

with an approximate median of about 17,000 ft2/d.

Vertical hydraulic-conductivity values of the 

basalt study units are largely unknown. Estimates 

made during numerical ground-water-modeling 

studies (MacNish and Barker, 1976, p. 5; Prych, 

1983, p. 35; F.A. Packard, U.S. Geological Survey, 

written commun., 1987) range from 0.5 x 10~3 to 

3.5 ft/d, depending on the degree of fracturing and 

on the presence of pillow-palagonite complexes 

(Swanson, 1967) or geologic structures. The ratio of 

horizontal to vertical hydraulic conductivity has 

been estimated to be about 1,000:1 to 100:1 (W.E. 

Lum, U.S. Geological Survey, written commun., 

1986; A.J. Hansen, U.S. Geological Survey, written 

commun., 1986; F.A. Packard, U.S. Geological 

Survey, written commun., 1987).

Storage coefficients were not directly estimated 

because of the lack of data and the nature of the

basalts. However, the potential range of storage 

coefficients of the three basalt units was estimated 

on the basis of the specific storage (Ss).

The specific storage (Sg) was described by Jacob 

(1940) on the basis of the assumption that if the 

compressibility of the skeleton of the aquifer is 

small in comparison with the expansibility of 

water, then the Jacob concept can be described by 

the following equation:

5 = or = Gyp

where 0 is the porosity, y is the specific weight of 

water, Ew is the bulk modulus of elasticity of 

water, and p is the compressibility of water (l/Ew). 

Using a value of porosity of 0.04 (previously discussed in the "Basalt Rock Mechanics" section), the 

compressibility of water of 3.3 x 10~6 in2/lb, and 

specific weight of water of 0.434 Ib in.~2 ft"1 , the 

specific storage was calculated to be 6 x 10~8 ft"1 .

EXPLANATION

MINIMUM QUARTILES MAXIMUM 

25 50 75

Estimated on the basis of 7,016 gridded data points

40

35

30

25

20

q 15

10

1,670 3,260 6,500

100 18,700

3456 

THICKNESS, IN THOUSANDS OF FEET

18.7

FIGURE 26. Frequency distribution of thickness of the Columbia Plateau aquifer system.
B40 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

The storage coefficient of each basalt unit was then 

estimated by multiplying specific storage by the 

estimates of the unit's thickness (fig. 27). The 

estimated minimum, median, and maximum values 

of storage coefficient of each basalt unit are 

summarized below.

Basalt unit

Storage coefficient 

Minimum Median Maximum

Saddle Mountains..... 1.2xlO~6 2.2xlO~5 7.8xlO"5

Wanapum................... 1.8xlO~6 3.2xlO~5 9.9xlO"5

Grande Ronde............ 6.0xlO~6 l.SxKT4 l.lxlO"3

These estimated values are within the range of storage coefficients estimated by other investigators, 

which are summarized in table 5. The overburden 

aquifer, being a water-table aquifer, has a specific 

yield that ranges from 0.0002 to 0.2, as determined 

from aquifer tests and model simulations (table 5).

RECHARGE AND DISCHARGE

Recharge to the aquifer system is primarily from 

precipitation and applied irrigation water, and secondarily from surface-water bodies, such as canals, 

rivers, and reservoirs. Discharge from the aquifer 

system, excluding pumpage, is mainly to the river 

systems and, in lesser quantities, to springs and 

seeps along canyon and coulee walls and by evapotranspiration. It is difficult to determine the actual 

discharge to rivers because of the large streamflow, 

numerous impoundments, and streamflow regulation. This, in turn, makes any analysis of groundwater recharge based on streamflow measurements 

tenuous and subject to large errors. Recharge is 

also controlled by both daily and annual climatic 

variations and, thus, is highly variable both temporally and spatially. The areal variation in recharge

tu

35

25

20

15

10

1- 5

m n cj 0

GC

£ 35

[j 30

CJ

Z 25

LLJ °

GC

0 20

CJ

0 15

LL

o

> 10

CJ

LLJ 5

13

LLJ 0 

GC" 35

30

25

20

15

10

5

n

1 1 1

-

-

!_

-

-

-

-

r\ 1,300 feet maximum Estimated on the basis of

20 feet minimum 1,229 gridded data points

370 feet median

 -

1

-

-

-

-

-

-

_

D 1,650 feet maximum Estimated on the basis of

30 feet minimum 4,414 gridded data points

-

-

-

-

-

530 feet median

1

-

-

-

_

-

-

-

^ 18,300 feet maximum Estimated on the basis of

100 feet minimum 6,977 gridded data points

u 3,000 feet median

-

-

i

-

^H

0 -^ * -° -° 1 2 3 4 5 6 7 

^J

THICKNESS, IN THOUSANDS OF FEET

FIGURE 27. Frequency distribution of thickness for the (A) Saddle Mountains unit, (B) 

Wanapum unit, and (C) Grande Ronde unit.

18.7
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B41 

TABLE 5. Summary of selected estimates of storage coefficient for the Columbia Plateau aquifer system

Geologic unit

Fluvial

Glaciofluvial

Ringold Formation

Touchet Beds

Glaciofluvial

Overburden

Ringold Formation

Glaciofluvial 

Basalt

Basalt

Basalt

Basalt 

Basalt

Basalt

Basalt

Basalt 

Basalt

Basalt

Hydrogeologic unit

Overburden aquifer

......do 

......do 

......do 

......do -

......do 

......do 

......do 

Wanapum unit

Composite Saddle 

Mountains unit and 

Wanapum unit 

Grande Ronde unit

Mainly Wanapum unit

Wanapum unit

Wanapum unit and 

Grande Ronde unit

Composite of Wanapum 

unit and Grande Ronde 

unit

Saddle Mountains unit, 

Wanapum unit, and 

Grande Ronde unit

Saddle Mountains unit 

Not determined

Wanapum unit and 

Grande Ronde unit

Storage coefficient 

or specific yield

0.20

0.03-0.2

0.0002

0.1

0.06-0.2

0.06

0.1

0.15

1.2 x 10-4 

2.2 x 10~5

3.2 x lO-2 

5.2 x 10-4

4.7 x 10-4 

9.0 x 10~5 

4.75 x 10~3

2.0 x 10~4

6 x 10~4 

1.4 x 10-6

1.5 x 10-3 

2.0 x lO-3 

6.0 x 10~3

1.0 x 10~2 

1.0 x lO-3

2.5 x 10~3

3.1 x 10~2 

1.9 x lO-3 

4.6 x 10~4 

5.0 x 10~5

7.6 x 10~4 

to 

3.0 x 10~5

Method1 of 

determination

Model

AT

AT

Model

AT

AT

AT, Model

AT, Model 

AT

Model 

Model

AT

AT

AT

Model

Model

AT, Model 

AT

AT

References

Bolke and Skrivan, 1981

Newcomb and others, 1972

Do.

Prych, 1983

Bierschenk, 1959

Do.

Tanaka and others, 1974

Do.

Eddy, 1976 

Do.

A. Smith, U.S. Geological Survey, written 

commun., 1984

Do.

MacNish and Barker, 1976

Price, 1960 

LaSala and Doty, 1971

Luzier and Skrivan, 1975

F.A. Packard, U.S. Geological Survey, 

written commun., 1987

Tanaka and others, 1974

Oregon Water Resources Department, from 

A. Smith, U.S. Geological Survey, written 

commun., 1984

Tanaka and others, 1979

1Model, derived from numerical ground-water model; AT, derived from aquifer tests.

is an important factor in understanding the movement of water in the aquifer system.

Recharge was estimated on a daily basis for 53 

basins or zones in the study area by applying a 

model that computes daily values of deep percolation of water below the effective root zone (Bauer 

and Vaccaro, 1990). These daily estimates were 

used to estimate long-term recharge for both 

predevelopment (1850's) and current land-use conditions (a 1980's multiyear composite). The period 

of record used to estimate recharge for most of the 

basins or zones was the 22-yr period from 1956 to 

1977, a period that exhibited climatic variation.

The deep-percolation model is an energy-soilwater balance model developed during the study

and is documented in a report by Bauer and 

Vaccaro (1987). The conceptual models of the 

energy balance for evapotranspiration and the 

water balance used in the deep-percolation model 

are shown in figures 28 and 29. The model is used 

to compute deep percolation for each control volume or cell into which a zone is discretized. The 

cell includes vegetation covering the land surface 

down to the maximum prevalent root depth or, in 

the case of areas devoid of vegetation, the soil 

cover down to 5 ft or the total depth of the soil, 

whichever is less. The root zone or soil cover is 

divided into 6-in. layers, each with unique physical 

characteristics. The daily water budget is 

expressed as
B42 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

PROP = RO + EVINT + EVSM + EVSNW + PTR + 

RECH + AflVT + &SNW + ASM,

where 

PROP = precipitation and irrigation,

RO = surface runoff, 

EVINT = evaporation of moisture on the foliage

surface,

EVSM = evaporation from bare soil, 

EVSNW = evaporation from the snowpack,

PTR = transpiration,

RECH = water percolating beyond the root zone, 

&INT = change of moisture on the foliage surface, 

&SNW = change of snowpack, and 

ASM = change of soil water in the root zone.

The following data are required for each modeled 

zone to estimate recharge: daily streamflows, estimates of monthly base flow, daily precipitation, 

and maximum and minimum daily air temperatures. For each cell the following data are required: 

22-yr average annual values of precipitation, mean 

monthly maximum and minimum air-temperature 

lapse rates (a lapse rate is a temperature change 

with altitude), soil water-holding capacity, soil texture, topographic data (altitude-slope-aspect), landuse classification, and annual application rates of 

irrigation water.

Daily meteorological data were obtained from 

the U.S. Department of Commerce for 103 weather 

sites, 89 of which included daily air-temperature

data (see fig. 4 and tables 1 and 2). A 22-yr average annual precipitation map for the period 1956- 

77 was developed for the study by Nelson (1991) 

and is shown in figure 2. Regional monthly maximum and minimum air-temperature lapse rates 

were estimated by Bauer and Vaccaro (1990). Soil 

information was obtained from the U.S. Soil Conservation Service county soil maps. The various 

soil-type data were aggregated by physical characteristics into 24 soil categories. Slope and aspect 

for cells were computed from altitude data obtained 

from the U.S. Geological Survey as Digital Elevation Model (DEM) (Elassal and Caruso, 1983). 

Land-use classification data for 1975 (fig. 30) initially were obtained from T.A. Zimmerman 

(Battelle Northwest Laboratory, written commun., 

1984) and later were modified on the basis of 

Landsat data by Wukelic and others (1981). On the 

basis of information presented by Wukelic and 

others (1981) for 1979 and of field and map identification of irrigated croplands by D.R. Cline, M.E. 

Knadle, and C.A. Collins (U.S. Geological Survey, 

written commun., 1986) for the period 1983 to 

1985, additional irrigated lands were added to the 

irrigated lands shown in figure 30. Predevelopment 

land-use conditions were estimated from these data 

by assuming that, historically, dryland croplands 

were grasslands, irrigated croplands were sagebrush, and residential-commercial-urban development was sagebrush. Surface-water irrigation rates

EVAPOTRANSPIRATION

POTENTIAL EVAPOTRANSPIRATION 

= f (RADIATION, TEMPERATURE)

POTENTIAL SOIL 

TRANSPIRATION

ACTUAL SOIL 

EVAPORATION

POTENTIAL 

TRANSPIRATION

POTENTIAL CROP 

TRANSPIRATION

SENSIBLE HEAT AND 

REFLECTED RADIATION

ACTUAL 

TRANSPIRATION

EVAPORATION OF 

INTERCEPTED MOISTURE

FIGURE 28. Schematic diagram showing the conceptual model of the energy balance for evapotranspiration (from Bauer

and Vaccaro, 1987).
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B43

were based on data from Washington State Department of Ecology (1974) and ground-water-irrigation 

rates were reported by D.R. Cline, M.E. Knadle, 

and C.A. Collins (U.S. Geological Survey, written 

commun., 1985). A detailed description and analysis of the data can be found in Bauer and Vaccaro 

(1990).

The estimates of recharge in each of the 53 selected basins calculated by the deep-percolation 

model are shown in figure 31. Fifty basins were 

discretized into rectangular cells with cell areas 

ranging from 0.25 mi2 to 1.2 mi2. The remaining 

three basins were discretized with highly variable

cell sizes. The estimated recharge for each cell then 

was integrated into the 4.6-mi2 blocks discussed in 

the "Hydraulic Characteristics" section. Estimates 

of recharge for the remaining study area not included in the 53 basins were made by using a polynomial regression equation. The regression equation 

relates the 22-yr average annual precipitation to 

the estimated recharge modeled for the 53 selected 

basins. The 22-yr average annual precipitation values were interpolated to the remaining study area 

using digitized annual precipitation contours and a 

surface-fitting technique described in IMSL (1982). 

On the basis of the polynomial regression equation

PRECIPITATION

NO

TEMPERATURE

GREATER THEN

32 DEGREES FAHRENHEIT

SUBLIMATION

SNOW

I

SNOWPACK STORAGE

L.YES

EVAPORATION

RAIN

i

INTERCEPTION STORAGE

SNOWMELT REDUCED RAINFALL

\

SURFACE 

RUNOFF

MOISTURE INCIDENT 

TO GROUND SURFACE

SOIL EVAPORATION

AND 

TRANSPIRATION

SHALLOW

SUBSURFACE

RUNOFF

SOIL MOISTURE 1 

STORAGE IN 1 

ROOT ZONE 1

\ r

DEEP PERCOLATION

GROUND-WATER 

RECHARGE

FIGURE 29. Schematic diagram showing the conceptual model of the water balance used in 

the deep-percolation model (from Bauer and Vaccaro, 1987).
B44 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 120° 119° 118° 117° 116°

48C

47 C

46C

45°

GRLLE x x

! A / BONNERj

STEV>NS T^ v -J } r^\

0 20 40 60 80 MILES 

1,1,1,1,1

40

I 

80 120 KILOMETERS

DRYLAND AGRICULTURE

FOREST

SAGE

GRASS

EXPLANATION

AREA, IN 

SQUARE MILES

12,015

10,332

9,887

3,930

AREA, IN 

SQUARE MILES

IRRIGATED AGRICULTURE 3,366

COMMERCIAL/RESIDENTIAL 216

SAND/BARREN 197

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

FIGURE 30. Land-use classification of the Columbia Plateau, 1975 (from Wukelic and others, 1981, and from Bauer and Vaccaro, 1990).
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B45

and the interpolated annual precipitation values, 

recharge values for the remaining study area then 

were estimated. The resulting distributions of estimated recharge within the hydrologic study area 

under predevelopment conditions and current conditions are shown in figures 32 and 33, respectively.

122° 121 C 120° 119° 118° 117° 116°

48°

47 C

46C

45C

BOISE

20 40 

I

60

I

80 MILES

^ ESTIMATE OF AVERAGE RECHARGE, IN INCHES 

PER YEAR Upper number is predevelopment 

(1850's); lower number is current (1980's)

' I ^ T 

40 80 120 KILOMETERS

EXPLANATION

ZONE SHOWN IN DETAIL ON FIGURE 34

ZONE BOUNDARY

WATER BUDGET FOR ZONES A AND B SHOWN 

IN TABLE 6

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 31. Estimates of recharge in each of 53 selected basins (from Bauer and Vaccaro, 1990).
B46 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 119' 118° 117° 116°

PEND I I LJNCO!..\

IORIELLEJ BO\M;H V'' s

0 20 40 60 80 MILES

45° -

AVERAGE RECHARGE, 

IN INCHES PER YEAR

0-0.5

0.5-1.0

1.0-2.0

40 80 120 KILOMETERS 

EXPLANATION

2.0-5.0

5.0-10.0

10.0-28.6

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

FIGURE 32. Distribution of estimated recharge under predevelopment (1850's) conditions (from Bauer and Vaccaro, 1990).
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B47

122° 121 C 120° 119° 118° 117° 116°

PEND i I

f ORILLIJ; i BONNUR ' ~

\sf \

LINCOLN

48° S -

47°

46°

45°

BOISE

\ 

40

AVERAGE RECHARGE, 

IN INCHES PER YEAR

20 40 60 80 MILES

I . I i I

80 120 KILOMETERS 

EXPLANATION

2.0-5.0

5.0-10.0

10.0-52.2

COLUMBIA PLATEAU AQUIFER 

SYSTEM STUDY BOUNDARY

FIGURE 33. Distribution of estimated recharge under current (1980's) conditions (from Bauer and Vaccaro, 1990).
B48 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

TABLE 6. Computed long-term, averaged monthly water budget for a semiarid (A} and a temperate (~B) zone

[Values in inches]

Water-budget component1

Evaporation from:

Month

January

February

March

April

May

June

July

August

September

October

November

December

Annual

Zone2

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

Precipitation

1.00

2.85

.27

1.86

.29

2.16

.34

1.53

.18

1.56

.69

1.28

.30

.61

.30

.96

.22

1.06

.55

1.54

1.55

2.59

1.29

3.06

6.98

21.06

Surface3 

runoff

0.04

.48

.01

.34

.01

.30

.0

.19

.0

.19

.0

.12

.0

.03

.0

.02

.0

.02

.0

.03

.01

.09

.08

.30

.15

2.11

Intercepted 

moisture

0.18

.21

.11

.35

.20

.56

.21

.70

.13

.78

.28

.68

.13

.33

.20

.47

.13

.45

.25

.52

.33

.39

.16

.23

2.31

5.67

Bare 

soil

0.11

.06

.33

.13

.27

.24

.02

.26

.0

.15

.01

.08

.0

.02

.0

.03

.0

.06

.02

.06

.03

.04

.06

.04

.85

1.17

Snow

0.07

.13

.0

.05

.0

.05

.0

.01

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.03

.08

.10

.15

.37

Plant 

transpiration

0.04

.02

.26

.09

.67

.36

.85

.95

.45

1.51

.39

1.04

.21

.53

.05

.29

.10

.35

.09

.21

.06

.06

.03

.01

3.20

5.42

Recharge

0.07

1.47

.0

.99

.0

.98

.0

.37

.0

.19

.0

.11

.0

.03

.0

.07

.0

.13

.0

.28

.0

.87

.05

1.33

.12

6.82

Change in:

Intercepted 

moisture

0.0

-.02

.0

.0

.0

.0

.0

-.03

.0

-.01

.0

-.02

.0

.0

.0

.01

.0

.0

.0

.05

.02

.03

-.01

-.01

.01

.0

Snow

-0.05

.06

-.01

-.13

.0

-.12

.0

-.06

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.01

.0

.11

.13

.17

.07

.04

Soil 

moisture

0.54

.44

-.43

.04

-.86

-.21

-.74

-.86

-.40

-1.25

.01

-.73

-.04

-.33

.05

.07

-.01

.05

.19

.38

1.10

.97

.71

.94

.12

-.49

1See "Recharge and Discharge" section for description of budget components. 

2Zones outlined in figure 31.

3Values calculated using estimates of monthly baseflow; values are generally overestimates (larger) due to underestimates of and errors in 

monthly baseflow estimates. This results in conservative estimates of recharge.

The computed long-term, averaged, monthly 

water budget for a semiarid (A) and temperate (B) 

zone is shown in table 6 (see fig. 31 for locations). 

The distribution of recharge under both conditions 

in an arid zone (see fig. 31 for location) shows the 

large areal variation in recharge and the effects of 

irrigation, mainly surface-water irrigation (fig. 34). 

Recharge was found to be most sensitive to amount 

of total precipitation and to soil type; sandy-type 

soils allow for deeper percolation.

The plateau-wide, long-term, averaged estimate 

of recharge for predevelopment land-use conditions 

was about 6,000 ft3/s, most of which probably discharged to streams. The estimate of recharge for 

current land-use conditions is about 9,490 ft3/s. 

Thus, recharge was increased by about 3,490 ft3/s 

as a result of surface-water and ground-water irrigation and additional recharge on fallowed dryland 

croplands. About 33 percent of the additional

recharge (1,144 ft3/s) discharged as ground-water 

pumpage in 1984. The remainder, about 2,346 ft3/s, 

discharged to drains and streams and to the atmosphere as evapotranspiration. As an example of the 

development effects, some drains in the areas irrigated with surface water receive as much as 80 ft3/s 

of additional ground-water discharge, and ephemeral streams in the arid part of the plateau that 

historically flowed about 6 days a year now flow at 

least through the irrigation season (Nelson, 1991). 

One example is Equatzel Coulee, located in central 

Franklin County, which flows at about 50 ft3/s during the irrigation season. Discharge as additional 

evapotranspiration occurs mainly in the Satus and 

Toppenish River basins and in the Columbia Basin 

Irrigation Project area, where surface-water irrigation has caused the water levels to be at or near 

the land surface (Tanaka and others, 1974; Bolke 

and Skrivan, 1981; Prych, 1983).
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B49

120' 

47°00'

'00'

46°50'

PREDEVELOPMENT CONDITIONS

47°00'

46°50'

CURRENT CONDITIONS

02468 10 MILES 

I _______II I I 

I I I 

02468 10 KILOMETERS

EXPLANATION

AVERAGE RECHARGE, 

IN INCHES PER YEAR

0-0.1

0.1-0.5

0.5-1.0

1.0-2.0 

2.0-5.0 

MORE THAN 5.0

FIGURE 34 Distribution of estimated recharge under predevelopment (1850's) and current (1980's) conditions in an arid zone See

figure 31 for location of area.
B50 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

GROUND-WATER DEVELOPMENT

Ground-water pumpage on the Columbia Plateau 

was minimal during the early part of this century, 

increased moderately after World War II, and 

increased rapidly from about 1965 to 1979 in 

response to expanding use of ground water for irrigation. Since 1979, the pumpage has decreased 

somewhat, owing in part to higher electrical costs 

for pumping the water and lower prices for crops. 

The total irrigated acreage on the Columbia 

Plateau from 1949 to 1982 (U.S. Department of 

Commerce, 1982), shown in figure 35, generally 

reflects this pattern. Differences are due to 

changes in irrigation and pump technology. 

Pumpage of ground water from the Columbia 

Plateau has increased from an estimated 55,690 

acre-ft in 1945, to 177,970 acre-ft in 1960, to a 

peak of about 939,770 acre-ft in 1979 (D.R. Cline 

and C.A. Collins, U.S. Geological Survey, written 

commun., 1988). By 1983, pumpage had dropped to 

about 813,300 acre-ft.

Estimates of ground-water pumpage for 1984 

have been made during this study for the Oregon 

part of the Columbia Plateau (Collins, 1987) and 

for the Washington part and a small part of Idaho 

(Cline and Knadle, 1990). It was concluded from 

the study that a total of 828,270 acre-ft of ground 

water were pumped from the regional aquifer system in 1984 from an estimated 3,500 high-capacity 

wells. Between 85 and 90 percent of the pumpage 

was used for irrigation of nearly 0.5 million acres; 

the rest of the pumpage was used for public water 

supply and industrial uses. The relatively small

C/3 

LU

g 1,800

0 1,600

C/3 

Q

Z 1,400

C/3

0 1.200

I

z 1,000

LU

Cj 800

LU

o 600

uj 400

I 200

DC 

0

19

1 1 1

, 

r |

I

 |

 i

I I

, |

I

 |

I

I

pi -

-

-

-

45 1950 1955 1960 1965 1970 1975 1980 19

YEAR

FIGURE 35 Total irrigated acreage on the Columbia Plateau, 

1949-82 (after U.S. Department of Commerce, 1982).

quantity of ground water used for domestic purposes and other uses, such as stock watering, was 

not included.

Estimates of pumpage made during this study 

were based on one of the following three methods: 

(1) for wells equipped with flowmeters, pumpage 

data were directly available; (2) for wells with 

power-consumption data but no flowmeter, estimates of pumpage were made from a pumpagepower consumption relation derived from wells 

with flowmeter and power consumption data; and 

(3) for wells lacking flowmeter and power-consumption data, estimates were based on irrigated acreage, crop type, and water-application rates. In the 

State of Washington, information from published 

reports, field visits, population figures, remotesensing and Landsat scenes, water rights, an inventory of water suppliers, and well data were 

used to estimate pumpage where more specific data 

were lacking. More detailed information on the 

methods of determining ground-water pumpage for 

1984 is given by Collins (1987) and Cline and 

Knadle (1990).

Estimates of the areal distribution of 1984 

pumpage (see figs. 36-39) in each of the four studied 

hydrogeologic units were aggregated by quartertownship block. For wells that tap more than one 

unit, pumpage was divided proportionally according to the saturated thickness of each unit open to 

the well. Of the total 1984 ground-water pumpage 

from the regional aquifer system (fig. 40), about 32 

percent was from the Grande Ronde unit, 39 percent from the Wanapum unit, 3 percent from the 

Saddle Mountains unit, and 26 percent from the 

overburden aquifer. The greatest concentrations of 

pumpage occur near Hermiston, Oreg., and in three 

centers in Washington the Odessa subarea, the 

Quincy basin, and southern Franklin County.

REGIONAL FLOW SYSTEM

The occurrence, movement, and availability of 

ground water in the Columbia Plateau aquifer system are controlled by the geometry of the aquifer 

system, the hydraulic characteristics of the rock 

materials that make up the aquifer system, the 

distribution and rates of recharge and discharge, 

the development of the ground-water resource, and 

the application of irrigation water to croplands.

Water-level contours in the overburden aquifer 

for Washington and Oregon are shown in figure 41. 

The Washington data were collected and contoured for spring 1983 (Bauer and others, 1985). 

Oregon water-level data were collected by the
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B51

122 120° 119° 118° 117° 116°

IORIELLE I BONNER '

S H I N G T O N SPOKAM]

20 40 60 80 MILES

46° -

45° 

120 KILOMETERS

EXPLANATION

1984 PUMPAGE, IN ACRE-FEET; BLOCK SIZE IS I 

ONE QUARTER TOWNSHIP ^~

0-49 ^H

|____| 50-99

| | 100-499

| | 500-999

I I 1,000-1,999

2,000-3,999 

4,000-5,999 

6,000-8,999 

9,000-11,000

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 36. Ground-water pumpage from the overburden aquifer, 1984. (Modified from Collins, 1987, and from Cline and Knadle,

1990.)
B52 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121° 120° 119° 118° 117° 116°

LINCOLN'

48C

47 <

46C

45°

 r I \

/ s ) VA!-

BOISE

20 40 60 80 MILES

40 80 120 KILOMETERS

EXPLANATION

1984 PUMPAGE, IN ACRE-FEET; BLOCK SIZE IS I I 2 000-3 999 

ONE QUARTER TOWNSHIP '^^*

 4,000-5,999 |____| 0-49

[ | 50-99

| | 100-499

| | 500-999

I I 1,000-1,999

| | 6.000-8,999 

^ i 9,000-11,000

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 37. Ground-water pumpage from the Saddle Mountains unit, 1984. (Modified from Collins, 1987, and from Cline and

Knadle, 1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B53

122° 121° 120° 119° 118° 117° 116°

48C

47'

46C

45C

I j SPQKANE 

'< J - \ __ ->s.|

s^ ** ~^

s

\ HOOD 

\V. BIVER f

BOISE

20 40 60

I

80 MILES 

J

I 

40 80 120 KILOMETERS

EXPLANATION

1984 PUMPAGE, IN ACRE-FEET; BLOCK SIZE IS I 

ONE QUARTER TOWNSHIP ^^~

0-49 ^H 

50-99 I 

100-499 ^H 

500-999 

1,000-1,999

2,000-3,999 

4,000-5,999 

6.000-8.999 

9,000-11,000

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 38. Ground-water pumpage from the Wanapum unit, 1984. (Modified from Collins, 1987, and from Cline and Knadle,

1990.)
B54 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121° 120° 119° 118° 117° 116°

Bftfl cUa^ti K<c_^ v\

n ^ xolT^. n ^^^vXi *

W I «l-C^->i'itv, _1 i

20 40 

_L

60

J_

80 MILES 

J

I 

40 80 120 KILOMETERS

EXPLANATION

1984 PUMPAGE, IN ACRE-FEET; BLOCK SIZE IS I I 2 000-3 999 

ONE QUARTER TOWNSHIP '^^*

^^H 4,000-5,999 I____| 0-49

| | 50-99

| | 100-499

| [ 500-999

I I 1,000-1,999

| | 6,000-8,999 

 j^H 9,000-11,000

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 39. Ground-water pumpage from the Grande Ronde unit, 1984. (Modified from Collins, 1987, and from Cline and Knadle,

1990.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B55

120° 119° 118° 117° 116° 122° 121°

LINCOLN

48°

47 C

46C

45C

SHERMAM

S

n G RE G'G N

BOISE

20

J

40 60 80 MILES

40 80 120 KILOMETERS

EXPLANATION

1984 PUMPAGE, IN ACRE-FEET; BLOCK SIZE IS I I 2 000-3 999 

ONE QUARTER TOWNSHIP ' '

| | 0-49

| | 50-99

| | 100-499

[ | 500-999

| | 1,000-1,999

|____ 4,000-5,999

| | 6.000-8,999

^^| 9,000-11,000

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 40. Total ground-water pumpage from the Columbia Plateau aquifer system, 1984. (Modified from Collins, 1987, and from

Cline and Knadle, 1990.)
B56 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 120° 119 118° 117° 116°

"v " - *^S3*' NO PI-RCI-:

COLUMBIAN ^ HMBTON

) J V ^

^\ I»!IDAH\O

CE i ~~ \ , 

y--1 \\ / - J

?br > ~1

rCWAkLAWAlLA L

20 40 60 80 MILES

45° -

120 KILOMETERS

EXPLANATION

APPROXIMATE LIMIT OF OVERBURDEN AQUIFER Dashed 

where inferred

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 800 WATER TABLE CONTOUR Shows approximate altitude of water 

table. Queried where uncertain. Contour interval 200 feet. Datum 

is sea level

FIGURE 41. Water table in the overburden aquifer representing conditions during the spring of 1983. (Modified from Bauer and

others, 1985.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B57

U.S. Geological Survey Oregon District and interpreted by Joseph B. Gonthier (U.S. Geological Survey, written commun., 1986). Data in the Umatilla 

area were collected in spring 1983, but contours in 

The Dalles area are based on water-level measurements made in 1979. Because there is no evidence 

that a regional change in water levels in the overburden aquifer has occurred since that time, the 

1979 data are assumed to be representative of the 

1983 conditions. Where sediments are sufficiently 

thick, such as in the Quincy, Pasco, Yakima River, 

Walla Walla River, and Umatilla River basins, the 

overburden materials compose a water-table 

aquifer; otherwise, the materials are thin and (or) 

unsaturated and may not be an aquifer. The direction of ground-water flow is toward discharge 

points along major rivers that exist in these basins. 

Water in the overburden aquifer is in direct 

hydraulic connection with water in the immediately underlying basalt unit. Within the CBIP, 

much of the overburden was unsaturated prior to 

the importation of Columbia River water for irrigation. The overburden is now saturated in the CBIP 

areas, and the ground-water levels reflect the 

application of surface water for irrigation. Over 

most of the CBIP, the water-level configuration 

shown in figure 41 represents a dynamic equilibrium, with only small, localized declines caused by 

withdrawal of ground water, and small rises resulting from increased recharge due to infiltrating surface water used for irrigation.

Water-level contours for spring 1985 in the 

three basalt units are shown in figures 42-44. In 

general, changes of hydraulic head occur with 

depth at any given location, both within and between basalt units. The water-level contours 

drawn for a unit represent the vertically averaged 

areal hydraulic heads for that unit insofar as the 

data permitted. The contours are greatly generalized and present a simplified trend of hydraulic 

heads in a complex three-dimensional flow system. 

More detailed maps and a description of how 

these maps are constructed are discussed by 

Whiteman (1986) and Lane and Whiteman (1989).

The ground-water or potentiometric surface in 

the Saddle Mountains unit (fig. 42) approximately 

parallels the land surface where there is little or 

no overburden. Lateral flow in this basalt unit is 

generally toward major surface-drainage features, 

but small and intermediate-sized streams also derive flow from the Saddle Mountains unit. This 

type of ground-water flow also occurs in the 

Wanapum and Grande Ronde units (figs. 43, 44) 

where they are not overlain by younger basalts or

by a great thickness of overburden. In the Palouse 

subprovince, north of the Snake River, the regional 

ground-water flow in both the Wanapum and 

Grande Ronde units approximately parallels the 

southwest regional dip slope of the basalt. Regional 

discharge is to the Columbia and Snake Rivers. In 

the Yakima Fold Belt subprovince, ground-water 

flow generally is downward from the anticline axes 

toward the streams and rivers lying in the intervening synclines. The tighter and narrower the 

synclines, the more the ground water tends to be 

confined because the synclines resemble structurally closed basins. Ground-water flow in the Blue 

Mountains subprovince is similar to that in the 

Yakima Fold Belt, approximately paralleling the 

land surface in areas of high relief and moving 

downward from the anticline axes to streams and 

rivers. Ground-water flow in the low-relief areas 

parallels the dip slope of the basalt but varies locally 

owing to geologic structure or is altered by groundwater development.

Water levels in the deeply buried parts of the 

Wanapum and Grande Ronde units are significantly different from those in the overlying units. 

In the south-central part of the plateau, water levels appear to be less influenced by surface-drainage 

features, and consequently the potentiometric surface is smoother. This is due, at least in part, to 

the fact that most recharge to and discharge from 

the deeply buried basalt is through vertical leakage 

over broad areas to and from the overlying basalt 

or overburden materials, rather than by direct hydraulic connection with surface-water bodies or 

drainage features. An example of this is in the 

Quincy basin, where ground-water flow in the 

Wanapum unit {.which is at or near the land surface) is toward Moses Lake and Potholes Reservoir 

(located just south of Moses Lake). Ground-water 

flow in the underlying Grande Ronde unit, however, is unaffected by these surface-water bodies 

and is to the south, toward the Columbia River. 

Where the regional aquifer system consists mainly, 

if not completely, of the Grande Ronde unit and is 

more than 500 ft thick, the configuration of the 

potentiometric surface in the lower part of the 

Grande Ronde unit tends to be smoother, and the 

hydraulic gradient is flatter, similar to the buried 

units. This has been noted in Douglas County, 

Wash., and in the high-relief areas of the Blue 

Mountains. Lack of data precludes subdivision of 

the Grande Ronde unit in these locations, and, in 

general, most of the depth-averaged water levels, 

which are from shallower wells, do parallel the 

land surface.
B58 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121° 120° 119° 118° 117° 116°

,U S -

N - " "A?--" *J ^^^- ^ ^- 

COLUMB.AX J^R^O^^V

" ^±^"m<a^ ^B*' j±LL^^|fi.TK~-" 7 ; j.^.n.1. - G^VJ ,ov r«v^C

20 40 60 80 MILES 

I i I , I

0

r

40 80 120 KILOMETERS

EXPLANATION

! AREA WHERE SADDLE MOUNTAINS UNIT IS UNSATURATED

 COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 400 WATER-LEVEL CONTOUR Shows approximate altitude of water 

level. Queried where uncertain. Hachures indicate depression. 

Contour interval, in feet, is variable. Datum is sea level

APPROXIMATE LIMIT OF SADDLE MOUNTAINS BASALT Dashed 

where inferred

FIGURE 42 Water-level contours for the Saddle Mountains unit, spring 1985. (Modified from Whiteman, 1986, and from Lane and

Whiteman, 1989.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B59

122° 121 C 120° 119° 118° 117° 116°

48C

SKAGIT

SNOHOMISH

c

OKANOGAN

I FERRY V

HIGHLANDS )'?f

STEVENS PEND I 

ORIELLE ' BONNER |

LINCOLN

\

47°

46°

45°

r [ } 1 i x

< ^A

I WASHINGTON / 1

* I * *

VALLEY

i I

BOISE

0 20 40 60 80 MILES

I i I i I i I . I

40 80 120 KILOMETERS

EXPLANATION

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

4oo WATER-LEVEL CONTOUR Shows approximate altitude of water 

level. Queried where uncertain. Hachures indicate depression. 

Contour interval, in feet, is variable. Datum is sea level

APPROXIMATE LIMIT OF WANAPUM UNIT Dashed where inferred

FIGURE 43. Water-level contours for the Wanapum unit, apring 1985. (Modified from Whiteman, 1986, and from Lane and

Whiteman, 1989.)
B60 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

122° 121 C 120° 119° 118° 117° 116°

LINCOLN

48 C

47 C

46°

45°

VALLEY

( WASHINGTON 

_T MALHEUR

BOISE

20 40

I i I

60 80 MILES

40 80 120 KILOMETERS

EXPLANATION

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY BOUNDARY

 400 WATER-LEVEL CONTOUR Shows approximate altitude of water 

level. Queried where uncertain.Contour interval, in feet, is variable. 

Datum is sea level

APPROXIMATE LIMIT OF GRANDE RONDE UNIT Dashed where 

inferred

FIGURE 44. Water-level contours for the Grande Ronde unit, spring 1985. (Modified from Whiteman, 1986, and from Lane

and Whiteman, 1989.)
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B61

In most of the study area, water-table or unconfined conditions exist in the uppermost basalt 

flows, whereas water in the deeper basalt is generally confined. Fine-grained, tight interbeds, where 

present, and some basalt flow centers are confining 

beds to the underlying flows. The hydraulic connection between flows is sufficient to allow vertical 

movement of water between them. From the available water-level data it appears that over most of 

the plateau the vertical flow is downward except 

near discharge areas. The exceptions to this trend 

occur near geologic structures, such as anticlines 

and faults, and areas with high pumpages. According to Newcomb (1961), faulting in the basalt near 

Walla Walla and in the Cold Creek syncline near 

Yakima in Washington and southwest of The 

Dalles in Oregon has caused lateral-flow impediments, resulting in upward flow. F.A. Packard 

(U.S. Geological Survey, written commun., 1987) 

reports that in the central part of the Horse 

Heaven Hills, water in wells tapping the Wanapum 

unit is confined and flows at the surface, but approximately 2 mi downgradient to the southeast the water 

levels in wells tapping the Wanapum unit are about 

340 ft lower. This variation in water levels and 

change in direction of flow are caused by some impediment that is inferred to be a fault system. The 

vertical hydraulic gradient is upward northwest of 

this impediment and downward southeast of it.

Steep gradients are shown on the flanks of the 

Blue Mountains, Horse Heaven Hills, Frenchman 

Hills, Rattlesnake Hills, and Saddle Mountains 

anticlines (figs. 42, 43). Water-level data from locations on the flanks of anticlines and in other areas 

where the basalt is steeply dipping show lateral 

water-level gradients to be approximately equal to 

or slightly less than the dip slope of the basalts.

Since the mid-1960's, pumping for irrigation has 

altered the regional flow. For example, in the area 

of Connell and northward toward the Odessa-Lind 

area (fig. 43), an upgradient bending of the contours, typical of lowered water levels, can be seen. 

A similar trend of upgradient contours attributed 

to pumping is in the Umatilla River basin in 

Oregon.

The effects of induced recharge from irrigation 

canals on the potentiometric surface are shown by 

the downgradient trend of contour just east of 

Othello (fig. 43), between the 1,000- and 800-ft contours, where the large East Low Canal is located 

and is part of the CBIP.

Seasonal water-level fluctuations in the aquifer 

system vary widely, probably because of the following major factors: (1) variations in precipitation, (2)

storage capacity of rock materials, and (3) irrigation practices. Seasonal water-level changes in the 

overburden materials in the Satus Creek and 

Toppenish areas in Washington generally are less 

than 10 ft but may be as much as 20 ft in alluvial 

sediments (U.S. Geological Survey, 1975; Mundorff 

and others, 1977; Prych, 1983). Newcomb (1965) 

and Barker and MacNish (1976) have reported 

more than 30 ft of seasonal water-level changes in 

the overburden aquifer in the Walla Walla River 

basin. Hydrographs of U.S. Geological Survey observation piezometers located in Washington (fig. 

45) typically show seasonal water-level fluctuations 

of less than 10 ft in the shallower basalt units. 

However, water levels in deeply buried basalt flows 

fluctuate more than those of the shallower units 

(fig. 45). These larger fluctuations are due to the 

effects of pumpage. Several of the hydrographs in 

figure 45 show long-term water-level declines; 

these changes are discussed in more detail in the 

next section.

EFFECTS OF DEVELOPMENT

Water-level changes from predevelopment to the 

present (1985) are difficult to assess because of the 

complexity of the aquifer system, the lack of wellconstruction data, and the number of wells open to 

several aquifers. Nevertheless, a generalized map 

of water-level changes for the Wanapum unit was 

constructed (fig. 46). Similar patterns of change in 

water levels probably occur in other hydrogeologic 

study units as well, although the degree of change 

probably is less in the Grande Ronde unit.

The East Low Canal marks the general boundary in the central plateau between water-level rises 

in the Wanapum unit to the west and water-level 

declines to the east. Water-level rises began with 

the completion of the canal in the early 1950's, and 

in most areas the water levels had stabilized to a 

new equilibrium by the mid-1970's. The hydrographs 

of wells 14N/29E-27E01 and 19N/23E-34R01 (fig. 

47) indicate the rise of the water levels. The largest rises occurred in the Quincy basin, where water 

levels rose more than 300 ft, and in the area east 

of Potholes Reservoir, where water levels rose more 

than 150 ft.

Water-level declines resulting from pumping for 

irrigation began in the 1960's and are concurrent 

with the increase in irrigated acreage. The initial 

decline in water levels occurred in five areas: (1) 

western Adams and southern Lincoln Counties, 

Wash.; (2) Walla Walla River basin, Wash.; (3) the 

Pullman, Wash.-Moscow, Idaho, area; (4) The
B62 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

B o

L? 40

__ cc

LU to 90

i < i 40

>- § 190

x O l_ _i

LU CD 240

O I 

LU 290

LL

z 340

27N/26E-25D

i i i i i i i i i i i \ _, _ i i i

D01 

60

WN '

152 

WNGB

 _

-

 

D05 -

- /760 

S^ GR

i i i i i i i i i i i i i i i

25

24N/36E-16A

0^125 

X O

175 A08

122° 121° 120° 119° 1180 / 117° 116° 115

E01

317 

WNGR

EXPLANATION

24N/31E-16E WELL NUMBER

M02 - PIEZOMETER NUMBER

735

WNGR DEPTH TO BOTTOM OF 

PIEZOMETER, IN FEET BELOW 

LAND SURFACE

PIEZOMETER COMPLETED IN

WN Wanapum unit

GR

WNGR 

20N/33E-16E

Grande Ronde unit

Wanapum and Grande Ronde units

1971 1974 1977 1980 

YEAR

1983 1986 1971 1974 1977 1980 

YEAR

1983 1986

FIGURE 45. Seasonal water-level fluctuations for selected piezometers.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B63

Dalles, Oreg.; and (5) the Hermiston, Oreg., area. 15N/45E-32N03 and 17N/32E-19E01 (fig. 47) indiWater-level declines in the Horse Heaven Hills cate these water-level declines. In general, water

began in the early 1970's. The hydrographs of wells levels in the above five areas continue to decline,

122° 121 C 120° 119° 118° 117° 116°

LINCOLN

48C

47C

46C

45°

^ if ! 1 r. <x>>~J ' / { '

BOISE

20 40 60 80 MILES

1,1,1,1

WATER-LEVEL CHANGE, IN FEET Boundaries 

dashed where inferred

Rise of more than 100 

Oto 100

40 80 120 KILOMETERS 

EXPLANATION

Oto-100 

Decline of more than 100

COLUMBIA PLATEAU AQUIFER SYSTEM STUDY 

BOUNDARY

FIGURE 46. Water-level changes in the Wanapum unit from predevelopment (1850's) to 1985.
_r£ LU Q 

> Z°- > pi | d > m

0

50

100150

200250

19N/23E-34R01 234 feet in Wanapum unit 15N/45E-32N03 238 feet in Wanapum and Grande Ronde unit

< 50

LILTD 

-i 100LU D 

LU <tr > 150 

5 m 200

LU LU

i 250

1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 

YEAR

300

1949 1952 1955 1958 1961 1964 1967 1970 1973 1976^1979 1982 1985

YEAR

s

> LU> m

0

50

100

150200

250

17N/32E-19E01 258 feet in Wanapum unit

300

1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 

YEAR

0

50

100150

200

250300

14N/29E-27E01 498 feet in Wanapum unit

 v ' 1 I I ' ;i'^ ,,/i/ufin

I I . I

122° 121° 120" 119° 118° 117° 7116° 115

1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 

YEAR

EXPLANATION

19N/23E-34R01 WELL NUMBER

A NON-STATIC WATER-LEVEL 

Note: Water-level fluctuations due to pumping

W O5

OHHi"3 

H

 -3

O

s

£ 

w

g

9io

s

FIGURE 47. Hydrographs of water levels in selected wells, showing long-term water-level changes.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B65

and the size of the affected areas has increased 

with time (Luzier and others, 1968; Cline, 1984). 

The rate of water-level decline, however, has 

decreased, at least in the central part of the 

plateau, as evidenced by the hydrographs for wells 

24N/36E-16A08 and 21N/31E-10M02 (fig. 45). The 

largest water-level declines in the Wanapum unit 

had exceeded 150 ft in the Walla Walla River 

basin, the Horse Heaven Hills, the Hermiston area, 

and the central plateau.

Water-level rises and declines affect regional 

flow. Prior to development, the dominant direction 

of ground-water flow across the northern half of 

the plateau is assumed to have been southwesterly, 

from the northern and eastern plateau margins 

toward the Columbia and Snake Rivers. However, 

the 1985 potentiometric surface of the Wanapum 

unit reflects the effects of the development (fig. 43). 

In places, the ground-water flow changed direction; 

for example, in an area between Scootenay Reservoir and Connell in northern Franklin County, 

ground water now flows southeasterly instead of 

southwesterly.

GEOCHEMISTRY

One of the principal factors in the development 

of the Columbia Plateau is the availability of large 

quantities of ground water for irrigation. The suitability of water is dependent on the quality of the 

water. An understanding of the processes that 

affect and control the ground-water quality is important. Ground-water chemistry also can significantly affect the hydrologic characteristics of the 

rock comprising the aquifer system. The filling of 

fractures with mineral precipitates from chemically 

reactive volcanic glass (which usually progresses 

farther in older volcanic rocks than in younger 

rock) results in decrease of hydraulic conductivity. 

This is believed to be related to the rate of groundwater flow, the availability of the chemically reactive volcanic glass, and the relatively porous 

nature of volcanic rocks that results in a large surface area per unit volume to come into contact with 

the water (Wood and Fernandez, 1988). The sections that follow discuss evolution of the groundwater chemistry in the basalt, describe major 

water-quality characteristics of the three basalt 

study units, and discuss the effects of surface- and 

ground-water development on water chemistry. The 

information is summarized from Hearn and others 

(1985), Steinkampf and others (1985), Wood and 

Fernandez (1988), and Steinkampf (1989).

CHEMICAL EVOLUTION OF THE GROUND WATER

The chemical composition of water in the Columbia 

Plateau aquifer system depends on the composition 

and relative solubility of the rocks through which 

the water flows, the chemical composition of the 

recharge water, and the residence time of the 

water in the aquifer system.

Rocks of the Columbia River Basalt Group consist primarily of labradorite (plagioclase feldspar), 

augite (pyroxene), and opaque metal oxides (commonly titanomagnetite) in a glassy to cryptocrystalline matrix. The most common accessory minerals 

are apatite, olivine, and metallic sulfides. These 

minerals are present in varying and relatively 

minor amounts as intergrown and isolated crystals. 

The most abundant secondary minerals are a 

nontronitic smectite, quartz, clinoptilolite, and iron 

oxyhydroxides (Ames, 1980; Benson and Teague, 

1982; Hearn and others, 1985). The Grande Ronde, 

Wanapum, and Saddle Mountains Basalts are compositionally distinct, and individual flows within 

these units also can have distinct mineral compositions. On the basis of bulk compositions, Swanson 

and Wright (1978) described eight chemical types 

of basalt in the northern part of the plateau.

The primary means by which solutes are added 

to ground water in the basalt are (1) dissolution of 

rock by weakly acidic recharge waters and (2) silicate hydrolysis. The presence of a soil zone in the 

recharge area increases the dissolution capacity of 

the recharging water by carbon dioxide generation. 

Carbon dioxide is formed by the microbial oxidation of organic carbon and dissolves to carbonic 

acid. In areas devoid of a soil zone or vegetative 

cover, and in confined aquifers where little or no 

oxygen penetrates from the atmosphere, carbonic 

acid generally is not generated. In such areas, silicate hydrolysis is the dominant dissolution process. 

Volcanic glass, a major component of the Columbia 

River Basalt Group, is the most reactive mineral. 

It is relatively unstable and reacts rapidly because 

of the presence of large internal surface areas resulting from cooling fractures and devitrification 

(Jones, 1966). In decreasing order, cryptocrystalline 

intergrowths, olivine, pyroxene, and feldspar are the 

next most reactive minerals.

The most abundant solutes added to ground 

water by dissolution of the basalt are calcium, 

magnesium, iron, sodium, potassium, silica, sulfate, chloride, fluoride, and bicarbonate. The relative concentrations of each in ground water are 

determined by their availability in the rock, by 

water-rock reactions, and by reactions occurring
B66 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

after dissolution. Dissolution of minerals by carbonic acid increases both the concentrations of all 

of the above solutes and the pH values in ground 

water. Silicate hydrolysis also increases the concentrations of all solutes and, because the hydroxyl 

ion is produced in the reaction, increases pH more 

than does acidic dissolution. As ground-water pH 

rises, it eventually exceeds the stability limits of 

calcium carbonate, which can then precipitate calcite from solution, lowering calcium and magnesium levels and contributing to decreased iron 

concentrations, effectively buffering the groundwater pH. Sodium and potassium are primarily 

derived from volcanic glass and cryptocrystalline 

intergrowths and somewhat from plagioclase feldspar, and they are dissolved at a rate faster than 

that at which they are precipitated. As dissolved 

sodium, potassium, and silica concentrations increase, the ground water eventually becomes supersaturated with respect to clinoptilolite. The latter 

mineral, which incorporates dissolved sodium and 

potassium, then precipitates, therefore limiting the 

concentrations of sodium and potassium in water 

in the basalts.

Dissolved silica concentrations are large, on the 

order of 50 mg/L, in basaltic ground water because 

of the readily dissolved glassy material present. 

Silica levels are limited by the solubility of amorphous or opaline silica. The relatively large silica 

concentrations buffer the pH of the water, limiting 

the increase from the hydrolysis reaction to a pH of 

about 9.5.

Sulfate in ground water in the basalt has three 

likely sources. The first is the dissolution of accessory metallic sulfide minerals, such as pyrite, in 

the presence of dissolved oxygen. The second is the 

dissolution of anhydrite or gypsum from sedimentary interbeds interlayered with the basalt. Sulfate 

minerals in the interbeds are likely to be of either 

eolian or evaporative (caliche) origin. The third 

source is agricultural chemicals present in groundwater recharge. Sulfide has been found in some 

ground-water samples from the plateau and is 

probably derived from the microbial reduction of 

dissolved sulfate.

Trace elements in the ground water also are 

derived from the weathering of minerals composing 

the rock matrix, and their concentrations in ground 

water are dependent on a variety of factors, many 

of which are difficult to quantify. Concentrations of 

some trace elements are controlled by the chemical 

characteristics of the ground water, whereas concentrations of others are a function of their availability in the basaltic rock. For example, the

concentrations of barium, calcium, fluorine, and 

iron are likely controlled by the chemical characteristics of the water and the solubilities of relevant secondary minerals such as barite, calcite, 

fluorite, and iron oxyhydroxides. In contrast, elements such as lithium, strontium, and boron 

(which increase in concentration with increasing 

total dissolved-solids concentration) are usually 

controlled by availability of the element in the 

rock.

WATER-QUALITY CHARACTERISTICS

The areal and vertical distribution of selected 

dissolved chemical constituents and physical 

properties of water from the Saddle Mountains, 

Wanapum, and Grande Ronde units have been 

mapped on the basis of analyzed water samples 

and discussed by Steinkampf (1989). A summary of 

water-chemistry statistics for the three basalt 

units, taken from Steinkampf (1989), is presented 

here as table 7. Ground water in the basalt units is 

generally of good quality and suitable for most 

uses. The dominant water type in all three units is 

calcium magnesium bicarbonate (CaMgHCO3 ), and 

sodium bicarbonate (NaHCO3) is the next most 

prevalent water type. Sodium bicarbonate waters 

typically occur in deeper downgradient locations. 

Similarly, the concentrations of dissolved solids 

generally are higher in downgradient locations or 

in deeper parts of the aquifer system. This is 

because of a larger residence time of water in the 

system, resulting from an increase in length of flow 

paths. Therefore, the similar areal trend in 

NaHCO3 and concentrations of dissolved solids 

indicates that sodium concentrations in the ground 

water increase with ground-water residence time.

In the Saddle Mountains unit where surfacewater irrigation occurs and where the overburden 

is less than 200 ft thick, water from shallow wells 

(less than 400 ft) is of a calcium magnesium sulfate 

chloride (CaMgSO4Cl) type (fig. 48). Dissolvedsolids concentrations generally increase in a downgradient direction owing to longer residence time of 

water in the aquifer system. In irrigated areas the 

concentration of dissolved solids may further be 

increased by contaminated infiltrating irrigation 

water. The infiltrating surface water transports 

large quantities of nitrogen derived from agricultural 

chemicals. Nitrogen concentrations (nitrate plus 

nitrite as N) in ground water of 2.0 mg/L or larger 

occur in areas where the overburden aquifer is thin 

and where surface water is used for irrigation.
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B67

TABLE 7. Summary of selected water chemistry for the three basalt units (from Steinkampf, 1989) 

[Values are in milligrams per liter unless otherwise indicated]

Maximum Minimum Mean

A. Saddle Mountains unit, 131 water analyses

Specific conductance (microeiemene 

per centimeter at 25°C).

Chloride (Cl) 

Nitrate+nitrite (NO3+NO2, as N) - 

Silica (SiO ) 

Sulfate (SO4) 

TPATnTMvrafn-rA (°C*} ..........__..__. .......

f*A 1 Pi i im f Pft 1 .........................

f 1 * * f^-m^i J A /f '\

Bicarbonate (HCO3) 

T_«« f tV \

Potassium (K) 

1,460 

890 

100 

130 

54 

72 

490 

25.5 

10.1 

98 

62 

2.9 

392 

.79 

13 

8.7

175 

140 

7.3 

1.3 

.1 

36 

.2 

8.6 

.1 

1.9 

.28 

.2 

108 

.003 

1.5 

7.0

498.2 

340.2 

34.5 

24.3 

4.8 

55.6 

53 

18.4 

4.5 

38.3 

19.4 

.58 

195.4 

.03 

6.9 

a7.7

B. Wanapum unit, 410 water analyses

Specific conductance (microeiemene 

per centimeter at 25°C).

Chloride (Cl) 

Nitrate+nitrite (NO3+NO2, as N) - 

Silica (SiO ) 

Sulfate (SO4) ________ 

Temperature (°C) 

Dissolved oxygen (DO) 

Pnlrinm (C*a\

"A^ncmAflinin fA^cr^ . .. ._..__....__._._

TTlnnriHt* J. 1 Uvl 1UC (ff~\ \ A / ...» . --- -........... ..

Bicarbonate (HCO3) 

Iron (Fe) ________________

PntciooiiTm (ff\

pH (units) 

1,970 

1,100 

130 

300 

35 

100 

290 

43.4 

10.6 

180 

75 

3.4 

406 

1.1 

22 

9.4

102 

69 

2.4 

7 

.1 

10 

.2 

6.2 

.1 

.8 

.1 

.1 

53 

.003 

.9 

6.1

402.5 

269.5 

28 

17.2 

3.7 

48.3 

29.3 

15.5 

5.2 

32.8 

14.8 

.5 

178.1 

.03 

4.9 

a7.4

Maximum Minimum Mean

C. Grande Ronde unit, 283 water analyses

Specific conductance (microsiemens 

per centimeter at 25°C).

Sodium (Na) 

Chloride (Cl) 

Nitrate+nitrite (NO3+NO2, as N) -

Silica (SiO2) __ 

Ciiilfnf-p C9O 1

Tomnorotnro fof^ ..... _ ... __ . . . .

Calcium (Ca) 

TTlnnriHp (TT1 _________________

Bicarbonate (HCO3) 

T-rrm fT?o"\

Potassium (K) 

pH (units) 

830 

510 

90 

45 

15 

110 

100 

36.7 

10.2 

88 

38 

4.9 

455 

10 

13 

9.4

85 

94 

4 

.5 

.1 

29 

.2 

7.6 

.1 

.95 

.13 

.1 

43 

.003 

1.1 

6.7

311.8 

234.1 

24.9 

7.1 

.96 

56.5 

21.8 

18 

3.3 

24.5 

10.7 

.6 

170.3 

.098 

4.7 

a7.6

D. All three basalt units, 824 water analyses

Specific conductance (microsiemens 

per centimeter at 25°C).

QndiiiTn (No ^ ................................

Chloride (Cl) 

Nitrate+nitrite (NO3+NO2, as N) -

Cilirn (SiO ^ 

OUliaie ^OvJ A ) .. -- - - - - - .... .- 

Temperature (°C) -

Pal/»inTYl (C^Q\

Magnesium (Mg) 

Bicarbonate (HCO3) 

Twvn fTTo^

Pntneeium (K) ..... _ . __ . __ ..... _ ... __ .

1,970 

1,100 

130 

300 

54 

110 

490 

43.4 

10.6 

180 

75 

4.9 

455 

10 

22 

9.4

85 

69 

2.4 

.5 

.1 

10 

.2 

6.2 

.1 

.8 

.1 

.1 

43 

.003 

.9 

6.1

385.6 

243 

40.4 

14.9 

2.9 

52.3 

30.1 

16.7 

4.5 

30.8 

14.1 

.53 

166.2 

.05 

5.1 

a7.5

aMean value represents the negative base-10 log of the average hydrogen ion concentration in moles per liter.

The mean concentration of dissolved solids in 

water in the Saddle Mountains unit is about 340 

mg/L (table 7).

In the Wanapum unit, calcium magnesium sulfate chloride waters are generally found in wells 

shallower than 400 ft, in areas where the overburden is less than 200 ft thick, and in areas 

where dissolved-oxygen concentrations in water are 

greater than 4.0 mg/L (fig. 49). The concentration 

of dissolved solids in the Wanapum unit had a 

mean of about 240 mg/L. Sodium concentrations 

greater than 25 mg/L are found in downgradient 

and discharge areas. Nitrogen concentrations are 

generally less than 2.0 mg/L in waters from wells 

deeper than 500 ft. Larger nitrogen concentrations, 

greater than 10 mg/L, are found in water from 

wells less than 300 ft deep and where the overburden is thin or absent generally in the central

part of the plateau. The source of this dissolved 

nitrogen is unknown, but agricultural chemicals 

are the most likely source. The observed vertical 

variations in the nitrogen concentrations in the 

Wanapum unit probably are due to ground-waterflow patterns or to the possibility that nitrogenenriched water has not reached the deeper depths 

at this time; the former is the most likely case.

The mean concentration of dissolved solids of 

water in the Grande Ronde unit is about 234 mg/L 

and reflects the generally smaller concentrations of 

most solutes in this unit than in the other units. 

Sodium concentrations increase with residence 

time, and the largest concentrations are found in 

samples from the deepest wells. In general, sodium 

concentrations are larger in the central part of the 

plateau. Dissolved nitrogen is not a significant 

constituent in the Grande Ronde unit, and few
B68 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

concentrations were larger than 2.0 mg/L. This is 

probably because the Grande Ronde unit is generally overlain by large thicknesses of the other 

basalts in the areas with intensive irrigation, and 

thus the water chemistry in the Grande Ronde unit 

is not affected by the infiltrating irrigation water.

100

80

60

CO Q

W (J

Si

40

20

EXPLANATION

WATER TYPE

|* \ Sodium bicarbonate (NaHCO3)

|| Calcium magnesium sulfate chloride 

(CaMgS04Cl)

|___ Calcium magnesium bicarbonate 

(CaMgHCO3)

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

DEPTH, IN FEET

B

100

80

60

U- UJ

O > 

w O

2°

< LU

^ 

UJ O

-1

UJ ^ 

40

20

-

~

-

-

1

1

1 1 1 1

 1 EXPLANATION

WATER TYPE

Imj Sodium bicarbonate (NaHCC^)

| _____ | Calcium magnesium sulfate chloride 

(CaMgSO4Cl)

Calcium magnesium bicarbonate 

(CaMgHC03)

,n n, , n, "

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

OVERBURDEN THICKNESS, IN FEET

FIGURE 48. Relation of chemical water type in the Saddle 

Mountains unit to (A) well depth and (B) overburden 

thickness (from Steinkampf, 1989).

SUMMARY AND CONCLUSIONS

The Columbia Plateau aquifer system underlies 

about 50,600 mi2 in parts of Washington, Oregon, 

and Idaho. The aquifer system is a major source of 

water in one of the Nation's important agricultural 

areas. About 3,500 high-capacity wells pumped 

water from the aquifer system to irrigate nearly 

0.5 million acres of cropland in 1984.

The aquifer system consists of thick, water-bearing 

basalts of the Columbia River Basalt Group of 

Miocene age, and water-bearing sediments and 

sedimentary rocks of Miocene to Holocene age, 

overlying and intercalated with the basalts. The 

sediments and sedimentary rocks overlying the 

Columbia River Basalt Group are considered a 

composite unit of rock materials, termed overburden, that includes fluvial consolidated to unconsolidated deposits of lacustrine, volcanic, and 

eolian sediments. The overburden constitutes a 

water-table aquifer where saturated and has larger 

hydraulic-conductivity values than those of the 

basalts.

The three basalt formations of the Yakima Basalt 

Subgroup of the Columbia River Basalt Group constitute the bulk of the aquifer system. They are, 

from oldest to youngest, the Grande Ronde, 

Wanapum, and Saddle Mountains Basalts. The 

Grande Ronde Basalt is the thickest and most extensive of the three and consists of as many as 131 

individual flows. The Wanapum Basalt overlies the 

Grande Ronde Basalt and is areally less extensive 

than the Grande Ronde Basalt; it consists of as 

many as 33 flows. The Saddle Mountains Basalt 

constitutes less than 2 percent of the total volume 

of the Columbia River Basalt Group and is limited 

areally to the central plateau.

The basalt forms an extremely complex, heterogeneous aquifer system with interflow zones that 

potentially function as small semiconfined to confined aquifers. The basalt transmits water most 

readily through these interflow zones, which represent about 5 to 10 percent of the total thickness of 

a typical basalt flow. Interflow zones are separated 

by less transmissive flow interiors with fractures. 

The density of fractures in the flow interiors differs 

greatly areally, and fractures are more vertically 

than laterally oriented. Ground-water flow in the 

flow interiors is probably vertical. Intercalated 

sediments within each formation range in lithologic 

character from shale to sands and gravels, and in 

most locations they are fine grained. Except in the 

Saddle Mountains Basalt, their thickness and 

extent are generally less than those of individual
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B69

basalt flows, and the total thickness of these intercalated sediments is much less than the total 

thickness of that basalt formation. The two sedimentary interbeds between the basalt formations 

are fairly extensive laterally but are thin when 

compared with the thickness of a basalt formation. 

These interbeds may be locally transmissive and 

function as aquifers. However, the nature of their

lithology indicates that they have low permeability 

and usually function as semiconfining or confining 

units.

A regional conceptual model that relates the geologic and hydrologic frameworks and provides a 

basis for evaluating the hydrologic system was 

developed during this study. In this model, the 

overburden is a water-table aquifer and is named

IUU

LU

H 80

z

MPLESWITHI 

i/ELL DPTH

O5 

O

CO Q

LL Ul

° < 40

CD ^

< ^

LU 

O

£ 20

Q.

n

1 1 1 1

-

-

|

EXPLANATION

i -

WATER TYPE 

1 | Sodium bicarbonate (NaHCO3>

[ | Calcium magnesium sulfate chloride 

(CaMgSO4Cl)

| ___ 1 Calcium magnesium bicarbonate 

(CaMgHCO3)

m^i

1

Hi in Hi-

-

i

IUU

Ul

f to 80

LU g 60 

o_ Q

CO £5

LL ul

So 40

< Ul

1- H 

Z <

Ul O

Si 20 Q- ~

n

-

-

-

-

1

,

1 1 1 1

EXPLANATION

WATER TYPE 

[~ | Sodium bicarbonate (NaHQ^)

PI Calcium magnesium sulfate chloride 

(CaMgSO4Cl)

I" __ ] Calcium magnesium bicarbonate 

(CaMgHCO3)

-

in rli_ i i

0-400 400-800 800-1,200 1,200-1,600 1,600-2,000 

DEPTH, IN FEET

0-200 200-400 400-600 600-800 800-1.000 

OVERBURDEN THICKNESS, IN FEET

B

100

80 -

60 -

°2 40

20 -

1 1 1 i i

EXPLANATION

WATER TYPE

~

_

-

^^^| Sodium bicarbonate (NaHCO3)

^^^| Calcium magnesium sulfate chloride

(CaMgSO4Cl)

| | Calcium magnesium bicarbonate 

(CaMgHC03)

7 n.n ^i r ,

;

0-2 2-4 4-6 6-8 8-10

DISSOLVED-OXYGEN CONCENTRATION, 

IN MILLIGRAMS PER LITER

FIGURE 49. Relation of chemical water type in the Wanapum unit to (A) well depth, (B) dissolved-oxygen concentration, and (C)

overburden thickness (from Steinkampf, 1989).
B70 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU, WASHINGTON-OREGON

the overburden aquifer. The basalt part of the 

aquifer system is subdivided into three units that 

correspond to the three basalt formations. Each 

unit includes the intercalated sediments but not 

the sedimentary interbeds between the basalt formations. The Saddle Mountains-Wanapum and 

Wanapum-Grande Ronde sedimentary interbeds 

are considered to be confining units. The prebasalt 

basement rocks generally have much lower permeability than the basalts. They are considered the 

bottom of the regional aquifer system and are 

named the basement confining unit. These six 

units compose the regional aquifer system.

The principal hydraulic characteristics of the 

aquifer system are hydraulic conductivity, specific 

yield, and storage coefficient. Specific-capacity data 

were used to estimate lateral hydraulic-conductivity 

values; for the overburden aquifer, the estimates 

were supplemented with data from previous studies. 

The median lateral hydraulic conductivity for the 

overburden aquifer was estimated to be about 240 

ft/d, with 50 percent of the values about the 

median ranging from 45 to 1,000 ft/d. Median 

values estimated for the three basalt units, youngest to oldest, are about 2, 5, and 5 ft/d. Values of 

hydraulic conductivity for all three basalt units 

range from 0.005 to 6,100 ft/d and have a median 

of about 5 ft/d.

The large range in hydraulic-conductivity values 

(from 0.02 to 150,000 ft/d) for the overburden aquifer is due to the lithologic variety. The large range 

in lateral hydraulic-conductivity values in the 

basalts reflects their heterogeneous nature. The 

hydraulic-conductivity values estimated on the 

basis of specific-capacity data are integrated values 

for the depth of well penetration and thus are 

assumed to be estimates for the entire thickness of 

each unit. However, because they are integrated 

quantities, the lateral hydraulic conductivity of a 

productive zone can be larger than the estimated 

values.

The potential range in transmissivity for the 

aquifer system was estimated on the basis of thickness estimates and hydraulic-conductivity values. 

The thickness estimates were derived on the basis 

of discretization of each unit into blocks. A thickness value for each block in each unit was estimated from the thickness contours developed 

during the study. The potential range in transmissivity values for the aquifer system was obtained 

by multiplying the minima, medians, and maxima 

of estimated block thicknesses and estimated 

hydraulic-conductivity values. The estimated transmissivity of the aquifer system ranges from about

0.5 to 114 million ft2/d, with a median of about 

17,000 ft2/d. The estimated values probably are 

overestimated; however, they should be within an 

order of magnitude.

Vertical hydraulic conductivity is largely unknown. Values estimated from earlier modeling 

studies range from 0.5 x 10~3 to 3.5 ft/d, depending 

on the degree of fracturing and on the presence of 

pillow-palagonite complexes or geologic structures. 

The ratio of lateral to vertical hydraulic conductivity was estimated to be 1,000:1 to 100:1.

Specific-yield values of the overburden aquifer 

were estimated on the basis of previous studies and 

range from 0.0002 to 0.2. The values of storage 

coefficient both obtained from earlier studies and 

estimated in this study for the basalt units range 

from 1.2 x 10~6 to 1.1 x 10'3 .

The total ground-water discharge from the aquifer system cannot be estimated accurately because 

of the large streamflow in the Columbia, Snake, 

and Yakima River systems. Estimates of groundwater recharge on the plateau were computed independently for both predevelopment (1850's) and 

current (1980's) land-use conditions using a daily 

deep-percolation model. The model is an energysoils-water balance model that computes deep percolation below the effective root zone. Fifty-three 

basins were selected for estimates of recharge. The 

recharge values calculated for these basins were 

then used to develop a polynomial regression relation between the 22-yr average annual precipitation and the estimated recharge values. This 

relation then was used to estimate recharge for the 

remaining study area not included in the 53 

selected basins.

The estimate of recharge for predevelopment 

conditions is about 6,000 ft3/s, and for current conditions is about 9,490 ft3/s. The areal distribution 

of recharge varies and depends on the timing and 

amount of precipitation, soil properties, land use, 

and topography.

Discharge from the aquifer system occurs principally as leakage to surface-water bodies and 

through springs and seeps along valley, canyon, 

and coulee walls. With the development of irrigated 

agricultural croplands, discharge also occurs as 

pumpage, increase in evapotranspiration in irrigated areas, and leakage to irrigation drains. 

About 67 percent (2,346 ft3/s) of the increased 

recharge under current conditions discharges to 

surface-water bodies, and the remainder discharges 

as pumpage.

An estimated 828,270 acre-ft of ground water 

was pumped from the Columbia Plateau in 1984
HYDROGEOLOGIC FRAMEWORK AND GEOCHEMISTRY OF THE COLUMBIA PLATEAU AQUIFER SYSTEM B71

from an estimated 3,500 high-capacity wells. Between 85 and 90 percent of the total pumpage was 

used for irrigation; the rest of the pumpage was 

used for public water supply and industrial uses. 

About 39 percent of the pumpage is from the 

Wanapum unit, 32 percent from the Grande Ronde 

unit, 26 percent from the overburden aquifer, and 

3 percent from the Saddle Mountains unit. The 

highest pumpage is found in the central plateau in 

Washington and near Hermiston, Oregon.

Water in each unit generally flows from the 

peripheral boundary of each unit toward major 

surface-water bodies, principally the Columbia, 

Snake, and Yakima Rivers. Water-level changes 

have occurred in response to expansion of irrigation activities. The importation of surface water to 

the Columbia Basin Irrigation Project area has 

caused water-level rises throughout the area between the East Low Canal and the Columbia River 

to the west. Water-level rises exceed 300 ft in the 

Quincy basin. Water-level declines in excess of 150 

ft have resulted from pumpage in several localities 

east and south of the Columbia Basin Irrigation 

Project and in Oregon.

Water in the aquifer system is generally suitable 

for most uses. The dominant water type is calcium 

magnesium bicarbonate, and sodium bicarbonate is 

the next most prevalent water type. Sodium bicarbonate waters typically occur in deeper downgradient locations in the aquifer system. Sodium 

concentrations increase with residence time in the 

aquifer system. Large nitrogen concentrations in 

ground water are observed in areas of surfacewater irrigation.

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potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or 

irregular areas at various scales. Pre-1971 maps show bedrock 

geology in relation to specific mining or mineral-deposit problems; 

post-1971 maps are primarily black-and-white maps on various 

subjects, such as environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolor or black-andwhite maps on topographic or planimetric bases presenting a wide 

range of geohydrologic data of both regular and irregular areas; 

principal scale is 1:24,000, and regional studies are at 1:250,000 

scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available 

under the conditions indicated below from the U.S. Geological 

Survey, Books and Open-File Reports Sales, Federal Center, Box 

25286, Denver, CO 80225. (See latest Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be 

purchased by mail and over the counter in paperback book form and 

as a set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be 

purchased by mail and over the counter in paperback book form and 

as a set of microfiche.

"Publications of the Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982,1983,1984,1985,1986, and for subsequent years since the last permanent catalog may be purchased by 

mail and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by 

mail and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback 

booklet form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" are available free of charge by mail or may 

be obtained over the counter in paperback booklet form only. Those 

wishing a free subscription to the monthly catalog "New Publications of the U.S. Geological Survey" should write to the U.S. 

Geological Survey, 582 National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, announcements, and publications may be incorrect. Therefore, 

the prices charged may differ from the prices in catalogs, announcements, and publications.