SUMMARY OF THE COLUMBIA PLATEAU

REGIONAL AQUIFER-SYSTEM ANALYSIS,

WASHINGTON, OREGON, AND IDAHO

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Summary of the Columbia Plateau 

Regional Aquifer-System Analysis, 

Washington, Oregon, and Idaho

fiyJ.J. VACCARO

REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1413-A
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, 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.

Reston, Virginia 1999

Library of Congress Cataloging in Publication Data

Vaccaro, J.J.

Summary of the Columbia plateau regional aquifer-system analysis, Washington, Oregon, and Idaho/ by John J. Vaccaro.

p. cm. (Regional aquifer-system analysis Washington, Oregon, Idaho) (U.S. Geological Survey professional paper; 1413-A) 

Includes bibliographical references. 

Supt. of Docs, no.: I 19.16:1413-A

1. Groundwater Columbia Plateau. 2. Water quality Columbia Plateau. I. Title. II. Series. III. Series: U.S. Geological Survey professional paper; 1413-A 

QE75.P9 no. 1413-A 

[GB1020]

557.3 s dc21 98-38920 

[551.49'09795 CIP

ISBN 0-607-90291-4

For sale by U.S. Geological Survey, Branch of Information Services, Box 25286,

Federal Center, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (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 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 

beginning with Professional Paper 1400.

Charles G. Groat 

Director

CONTENTS

	Page

Forward............................................................................................ Ill

Abstract............................................................................................ Al

Introduction..................................................................................... 2

Purpose and scope ..................................................................... 2

Physical setting.......................................................................... 4

Hydrogeologic framework ............................................................... 6

Geologic setting.......................................................................... 6

Sedimentary units............................................................... 8

Basalt units.......................................................................... 10

Imnaha and Picture Gorge Basalt................................ 10

Grande Ronde Basalt.................................................... 11

Wanapum Basalt........................................................... 11

Saddle Mountains Basalt.............................................. 11

Structural features.............................................................. 12

Aquifer system........................................................................... 12

Hydraulic characteristics.......................................................... 13

Flow system............................................................................... 16

Recharge..................................................................................... 22

Page

Discharge................................................................................... 22

Ground-water development............................................................ 29

Regional ground-water flow............................................................ 29

Regional flow model................................................................... 29

Predevelopment land-use conditions........................................ 31

Current land-use conditions...................................................... 33

Effects of historical water-development practices......................... 35

Effects of potential water-management alternatives.................... 41

Equilibrium conditions.............................................................. 42

Columbia Basin Irrigation Project expansion, 1983-85

pumpage................................................................................ 44

Columbia Basin Irrigation Project expansion, reduced

pumpage................................................................................ 45

Ground-water quality...................................................................... 45

Water-quality characteristics.................................................... 46

Geochemical model.................................................................... 48

Selected references.......................................................................... 49

ILLUSTRATIONS

Page

FIGURES 1-3A. Maps showing:

1. Location of Columbia Plateau aquifer system, physiographic subprovince boundaries, and major

physiographic features........................................................................................................................................... 3

2. Relation of extent of the Columbia River Basalt Group to the Columbia Plateau Regional AquiferSystem Analysis study area and the hydrologic study area ................................................................................ 5

3A. Generalized surficial geology for the Columbia Plateau...................................................................................... 7

SB. Stratigraphic chart for the Columbia Plateau........................................................................................................................ 8

4.-12. Maps showing:

4. Major geologic structures within the Columbia Plateau...................................................................................... 9

5. Water-table altitude and direction of ground-water flow for the overburden aquifer, representing

conditions during spring 1983, for selected areas ................................................................................................ 17

6. Water-level contours and direction of ground-water flow for the Saddle Mountains unit, spring 1985............ 19

7. Water-level contours and direction of ground-water flow for the Wanapum unit, spring 1985......................... 20

8. Water-level contours and direction of ground-water flow for the Grande Ronde unit, spring 1985.................. 21

9. Location of 53 basins, or zones, for which recharge was estimated using a daily deep-percolation model....... 23

10. Distribution of estimated recharge for current (1980's) land-use conditions...................................................... 25

11. Distribution of estimated discharge for current (1980's) land-use conditions.................................................... 27

12. Ground-water pumpage from the Columbia Plateau aquifer system, 1984 ....................................................... 30

13.-14. Schematic diagrams showing:

13. The model-calculated water budget for predevelopment (1850's) land use conditions, Columbia Plateau

aquifer system......................................................................................................................................................... 32

14. The model-calculated water budget for current (1980's) land-use conditions, Columbia Plateau aquifer

system..................................................................................................................................................................... 34

15. Map showing model-calculated water-level changes in the Wanapum unit from predevelopment to present (1980's)..... 36

16. Hydrographs of selected wells showing long-term water-level changes................................................................................ 38

17. Map showing calculated water-level changes in the Wanapum unit from 1985 to equilibrium conditions, based on

current water-management strategies.................................................................................................................................... 43
VI

TABLE

CONTENTS

TABLES

Page

1. Selected hydrogeologic information for the Columbia Plateau aquifer system............................................................................. 14

2. Hydraulic characteristics of hydrogeologic units in the Columbia Plateau aquifer system, derived from the regional

ground-water-flow model.................................................................................................................................................................. 15

3. Summary of estimated recharge and data used for predevelopment and current land-use conditions, Columbia

Plateau aquifer system....................................................................................................................................................................^ 24

4. Ground-water pumpage by study unit from the Columbia Plateau, Washington, Oregon, and Idaho, 1945 to 1984................. 26

5. Calculated water budget for the predevelopment and time-averaged simulations for the Columbia Plateau aquifer system.. 28

6. Calculated water budget for the predevelopment and time-averaged simulations for layers in the gound-water model

of the Columbia Plateau aquifer system.......................................................................................................................................... 28

7. Model-calculated ground-water discharge, estimated recharge, and average streamflows for drainage basins with

streamflow records, Columbia Plateau aquifer system .................................................................................................................. 40

8. Model-calculated ground-water discharge to selected stream reaches, Columbia Plateau aquifer system................................. 41

9. Model-calculated changes in the regional ground-water flow system resulting from simulation of potential watermanagement alternatives, Columbia Plateau aquifer system ....................................................................................................... 44

10. Summary of selected water chemistry information for the three basalt units, Columbia Plateau aquifer system.................... 46

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

inch (in.)

foot (ft)

mile (mi)

acre

square foot (ft2 )

square mile (mi 2 )

cubic mile (mi 3 )

inch per year (in/yr)

acre-foot (acre-ft)

foot per mile (ft/mi)

foot per year (ft/yr)

foot per day (ft/d)

foot per second (ft/s)

square foot per second (ft2/s)

cubic foot per second (ft3/s)

gallon per minute (gal/min)

ton

pound per square inch (lb/in.2 ) 

pound per cubic inch (lb/in.3 )

25.4

0.3048

1.609

0.4047

0.0929

2.59

4.168

25.4

0.001233

0.3048

0.3048

0.3048

0.3048

0.0929

0.02832

0.6308

0.9072

70.3

27.68

millimeter

meter

kilometer

hectare

square meter

square kilometer

cubic kilometer

millimeter per year

cubic hectometer

meter per mile

meter per year

meter per day

meter per second

square meter per second

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 (NGVD 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

SUMMARY OF THE COLUMBIA PLATEAU

REGIONAL AQUIFER-SYSTEM ANALYSIS,

WASHINGTON, OREGON, AND IDAHO

BY J. J. VACCAKO

ABSTRACT

In 1982, the U.S. Geological Survey began a study of the Columbia 

Plateau aquifer system as part of its Regional Aquifer-System Analysis 

program. This report summarizes the results of the Columbia Plateau 

Regional Aquifer-System Analysis.

The study area, for which most of the physiographic, climatic, cultural, economic, and geologic information were presented in a series of 

reports, covers about 50,600 square miles of the 63,200 square miles 

underlain by the Columbia River Basalt Group. The study area for the 

hydrologic analysis covers about 32,700 square miles of the study area.

The Columbia Plateau aquifer system includes, from youngest to 

oldest: (1) the overburden, a collective term used in this study for all 

materials overlying the Columbia River Basalt Group; (2) a minor 

amount of sediment interlayered with the basalt; and (3) a large thickness of basalt belonging to the Columbia River Basalt Group, which is 

the most extensive and hydrologically important geologic unit in the 

aquifer system. This unit consists of five formations; the Saddle Mountains, Wanapum, and Grande Ronde Basalts are the principal formations of the aquifer system. Prebasalt rocks that underlie the plateau 

are the lower boundary to the aquifer system. The basaltic lavas make 

up more than 99 percent of the volume of the aquifer system. These 

basalts have an average thickness of 3,300 feet and an estimated maximum thickness of about 16,000 feet.

The aquifer system has been divided into three confining units and 

four aquifer units. The three confining units are the Saddle MountainsWanapum interbed, the Wanapum-Grande Ronde interbed, and the 

prebasalt rocks. The four aquifer units are the overburden aquifer, the 

Saddle Mountains unit, the Wanapum unit, and the Grande Ronde 

unit.

The overburden materials consist of fluvial consolidated to unconsolidated deposits of lacustrine, volcanic, and eolian origin whose 

lithology ranges from clay to gravels and shale to conglomerate. Most 

of these deposits generally have a much larger hydraulic conductivity 

than the basalts and, where saturated, make up a water-table aquifer 

called the overburden aquifer.

The Saddle Mountains Basalt constitutes less than 2 percent of the 

volume of the basalts, and, depending on geographic location, it overlies the Saddle Mountains-Wanapum interbed, the Wanapum Basalt, or 

the Grande Ronde Basalt. The Saddle Mountains Basalt and its intercalated sediments is called the Saddle Mountains unit.

A sedimentary interbed, the Saddle Mountains-Wanapum interbed, is commonly present between the Wanapum Basalt and the overlying Saddle Mountains Basalt and is considered a confining unit for 

this study. The Wanapum Basalt and its intercalated sediments (called

the Wanapum unit) range in thickness from 0 to 1,300 feet and compose 

about 6 percent of the volume of the basalts.

A sedimentary interbed, the Wanapum-Grande Ronde interbed, 

underlies part of the Wanapum Basalt and overlies part of the Grande 

Ronde Basalt. This unit is considered a confining unit for this study. 

The Grande Ronde Basalt underlies most of the plateau and constitutes 

more than 85 percent of the volume of the basalts. This formation and., 

its intercalated sediments is called the Grande Ronde unit. For modeling and descriptive purposes, this unit has been divided into the upper 

and lower Grande Ronde. The prebasalt "basement" rocks are considered the base of the regional flow system and are called the basement 

confining unit.

For the overburden aquifer, lateral hydraulic conductivity values 

derived from specific-capacity data range from 2.9xlO~7 to l.ZxlO"1 foot 

per second, and regional values derived from the ground-water flow 

model range from 5.0xlO~7 to 1.3xlO~2 foot per second. Lateral hydraulic conductivity values derived from specific-capacity data for the 

basalt units range from 5.8x10"8 to 6.1xlO~2 foot per second and values 

from the ground-water model range from l.OxlO"6 to l.OxlO"4 foot per 

second. Model-derived vertical hydraulic conductance values range 

from 4.5xlO~13 to l.Oxl0~5 foot per second per foot. Estimates of vertical 

hydraulic conductivity were calculated using the vertical hydraulic 

conductance values and thickness of units. The estimated median 

value of the vertical hydraulic conductivity of the overburden aquifer 

is about 2.1xlO~5 foot per second, and of the basalt, about 1.5x10 foot 

per second. Calculated ground-water velocities range from 10"4 to 20 

feet per day. The median velocity in the overburden aquifer is about 2 

feet per day, and in the basalt units about 0.2 foot per day.

Ground-water movement in the overburden aquifer is from 

uplands to discharge points along stream courses. The potentiometric 

surface in the basalt units, where they are not overlain by younger 

units, roughly parallels the land surface, and movement of water is 

toward surface-drainage features. The water movement in the basalt 

units also follows the regional dip of the basalt, and in structurally 

complex areas the water moves downward from the axis of anticlines 

toward structural lows in synclines. Water in the uppermost basalt 

flow is unconfined and becomes semiconfined-to-confined with depth. 

Over most of the plateau, the vertical component of flow is generally 

downward, except in the proximity of discharge areas.

The long-term estimate of recharge for predevelopment (1850's) 

conditions is about 6,566 cubic feet per second (4,750,000 acre-feet or 

2.72 inches per year) and for current (1980's) conditions is about 10,205 

cubic feet per second (7,385,000 acre-feet or 4.24 inches per year). Discharge from the ground-water system, excluding pumpage, is mainly

Al
A2 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

to surface-water features and to springs and seeps along canyon and 

coulee walls.

Ground-water pumpage for the Columbia Plateau was about 

56,000 acre-feet in 1945, 178,000 acre-feet in 1960, and increased to a 

peak of about 940,000 acre-feet by 1979. About 828,278 acre-feet of 

water was pumped from the aquifer system in 1984 from an estimated 

3,500 high-capacity wells. Between 85 and 90 percent of the pumped 

water was used to irrigate nearly 500,000 acres.

Water levels have risen to near land surface under about 1.2 million irrigated acres due to the application and infiltration of surface 

water. The largest rises are in the Columbia Basin Irrigation Project, 

where rises have exceeded 300 feet. Water-level declines resulting from 

ground-water pumping for irrigation began in the 1960's. The declines 

continue today and have exceeded 200 feet in some parts of the central 

plateau.

A ground-water flow model was constructed for predevelopment 

and current land-use conditions. Regional flow for current land-use 

conditions was simulated by using a time-averaged approach. Simulation indicates that from predevelopment to current conditions, 

recharge has increased about 3,640 cubic feet per second because of 

surface-water irrigation. An additional 187 cubic feet per second of 

water was obtained from loss in aquifer storage during 1983-85. The 

increase has been balanced by an increase in leakage to rivers (1,050 

cubic feet per second), leakage to drains (1,650 cubic feet per second), 

and ground-water pumpage (1,135 cubic feet per second). Most of the 

increase in recharge enters the overburden aquifer (3,083 cubic feet per 

second).

The changes in distribution and rates of recharge and pumpage 

through time have caused changes in water levels. The median waterlevel rise in the overburden aquifer has been about 12 feet, which has 

resulted in the saturation of about 32 cubic miles of sediments (an 

increase of water in storage of about 10 million acre-feet) throughout 

an additional area of about 1,600 square miles. Declines in the overburden have been local and small. There has been a median rise of about 

20 feet (average of 65 feet) in the Saddle Mountains unit, which has saturated about 23 cubic miles of the unit (an increase of water in storage 

of about 1.6 million acre-feet) throughout an additional area of about 

839 square miles. Water-level declines have been relatively small and 

local. Water levels in the Wanapum unit have risen more than 300 feet, 

with a median of 10 feet. Declines in the Wanapum unit range from 1 to 

more than 200 feet and the median is about 9 feet. The largest declines 

have been in the central part of the plateau in Washington; on the 

southern slope of Horse Heaven Hills; near Umatilla, Oreg.; and in the 

Walla Walla River basin. In the upper Grande Ronde, water-level rises 

have a median of about 14 feet, and declines a median of about 6 feet. 

The water-level changes in this unit have been in excess of 200 feet in 

some locations. The largest rises have occurred in the Quincy basin as a 

result of surface-water irrigation, and the largest declines have been in 

the central plateau in Washington and near Umatilla, Oreg.

The model was used to simulate the long-term changes in the 

regional flow system resulting from continuation of current (1980's) 

water-development practices. Under these practices, the overburden 

aquifer generally would be unaffected, and the basalt aquifers would 

experience declines generally less than 200 feet. The effects would be 

largest in the Wanapum unit, where declines would extend over 400 

square miles, and next largest in the Saddle Mountains unit. Declines 

in the Grande Ronde unit would not be as large or as widespread and 

generally would be less than 75 feet. The areas most affected would be 

in the central plateau in Washington; near Butter Creek, Oreg.; and on 

the Horse Heaven Hills. Additionally, parts of the Saddle Mountains 

unit and Wanapum unit may desaturate.

Four simulations were done to estimate the effects of the proposed 

expansion of the Federal Columbia Basin Irrigation Project, which 

receives water from the Columbia River. For each of the two phases of 

the proposed expansion, pumpage was held constant at 1984-85 rates, 

and pumpage was reduced proportionately according to expansion 

area. Water-level rises of more than 200 feet would occur in part of the 

aquifer system underlying and adjacent to the expansion area. Additional recharge to the aquifer system resulting from the infiltration of 

the applied surface water was estimated to be about 974 cubic feet per 

second. The expansion would result in resaturation of areas that were 

calculated to become desaturated under current water-development 

practices. Significant rises would cover a broad area extending over 

some 600 square miles. The study unit most affected by the expansion 

would be the Wanapum unit. Water levels over a broad area would be 

near or at land surface under this management strategy, and thus a 

regional drain system probably would be needed.

Ground water in the basalt units is generally of good quality and 

suitable for most uses. The dominant water type in the three basalt 

units is calcium magnesium bicarbonate; sodium bicarbonate is the 

next most prevalent type, and calcium magnesium sulfate chloride is 

the least prevalent type. Sodium bicarbonate waters typically are in 

deeper downgradient locations, indicating that sodium concentrations 

in the ground water increase with ground-water residence time. Nitrogen concentrations greater than 2.0 milligrams per liter are found in 

water in basalt in areas where the overburden aquifer is thin and where 

surface water is used for irrigation. Concentrations of nitrogen greater 

than 10 milligrams per liter have been found in water from the overburden aquifer in areas of surface-water irrigation.

INTRODUCTION

The Columbia Plateau aquifer system is located in 

the Columbia Plateau of central and eastern Washington, north-central and eastern Oregon, and a small part 

of northwestern Idaho (fig. 1). The aquifer system 

underlies an area of about 50,600 mi , and consists of a 

large thickness of Miocene basalt of the Columbia River 

Basalt Group, small thicknesses of Miocene sedimentary rocks interlayered with the basalt, and Miocene to 

Holocene sedimentary deposits overlying the basalt. 

The aquifer system is the major source of water for 

municipal, industrial, domestic, and irrigation uses. 

Concurrent with ground-water use, imported surface 

water is used for irrigation in several areas of the plateau. There are about 1.7 million acres of irrigated croplands and about 7.5 million acres of nonirrigated 

croplands on the Columbia Plateau. About 1.2 million 

acres of the irrigated croplands are irrigated using surface water and about 0.5 million acres are irrigated 

using ground water.

An estimated 1.5 million acres of rangeland could be 

cropped profitably if water supplies were available, and 

an additional 2.0 million acres of nonirrigated cropland 

could be converted to larger yield crops if water were 

available for irrigation. Conversely, the decline in water 

levels in much of the area of ground-water withdrawal 

threatens the continuation of the ground-water irrigation.

PURPOSE AND SCOPE

The U.S. Geological Survey initiated a Regional 

Aquifer-System Analysis (RASA) program in 1978 in 

response to congressional concerns about the availabil-
INTRODUCTION A3

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EXPLANATION

Columbia Basin Irrigation Project 

Odessa-Lind pumping center 

Columbia Plateau aquifer system study area OREGON

 Boundary of physiographic subprovince LOCATION OF STUDY AREA 

FIGURE 1. Location of Columbia Plateau aquifer system, physiographic subprovince boundaries, and major physiographic features.
A4 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

ity and quality of the Nation's ground water (Sun, 

1986). The Columbia Plateau aquifer system was chosen 

as one of the regional aquifers to be studied in this program. In order to meet the overall RASA program objectives, it was necessary to describe the following items 

for the Columbia Plateau: (1) the geologic framework, 

(2) hydrologic characteristics of individual hydrogeologic units, (3) the area's water budget, (4) the groundwater/surface-water flow system, and (5) the waterquality characteristics and water-rock interactions that 

occur in the study area. In order to provide the analytical capabilities necessary to assess management alternatives and to obtain a better understanding of the 

ground-water system, a numerical model that simulates 

ground-water movement was constructed.

This report, Chapter A of Professional Paper 1413, 

summarizes the results of the Columbia Plateau 

regional aquifer-system analysis. Chapter B (Whiteman 

and others, 1994) describes the physical, cultural, and 

economic setting, the geologic framework, the hydrologic characteristics of major hydrogeologic units, the 

components of the water budget, and the regional 

ground-water flow system, and presents a brief overview of the water-quality characteristics and geochemistry of the aquifer system. The hydrology of the 

regional aquifer system on the basis of simulating 

regional flow using a ground-water flow model is 

described in Hansen and others (1994) and Bauer and 

Hansen (in press). Steinkampf and Hearn (1996) 

describe the geochemistry of the aquifer system.

The RASA study area, for which most of the physiographic, climatic, cultural, economic, and geologic 

information were described in this study, covers about 

50,600 mi2 of the 63,200 mi2 underlain by the Columbia 

River Basalt Group (fig. 2). The hydrologic study area 

(fig. 2), for which the hydrologic information was analyzed and presented, encompasses about 32,700 mi2 of 

the RASA study area and is the boundary for the 

ground-water flow model.

The information collected and analyzed in the 

Columbia Plateau RASA is documented in 30 reports. 

These reports, prepared by the U.S. Geological Survey, 

are listed in the Selected References section at the end of 

this report and describe major components of the aquifer system. An overview of the Columbia Plateau RASA 

was described by Vaccaro (1986a; 1986b). The geologic 

framework for the Washington part of the study was 

described by Drost and Whiteman (1986), for the Oregon part of the study by Gonthier (1990), and for the 

complete study area by Drost and others (1990). The 

ground-water flow system and water-level changes 

were described by Bauer and others (1985), Whiteman 

(1986), and Lane and Whiteman (1989). Estimates of 

ground-water pumpage were made by Collins (1987),

Cline and Knadle (1990), and Cline and Collins (1992). 

Ground-water recharge and climatic variability were 

evaluated by Bauer and Vaccaro (1986; 1987a; 1987b; 

1990), Vaccaro and Bauer (1987; 1990), and Vaccaro 

(1991). Nelson (1991) described the surface-water 

resources of the study area. Water-quality characteristics and geochemistry were evaluated by Hearn and 

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

(1989), and Steinkampf and Hearn (1996). The construction and use of a regional ground-water flow model and 

a description of the hydrology of the study area were 

discussed by Bauer and Hansen (in press), Hansen 

(1993a; 1993b), and Hansen and others (1994). The 

description of the hydrology is for both predevelopment and current land-use conditions. Predevelopment 

land-use conditions are assumed to represent the 1850's, 

the latest period on the plateau without water-development practices. Current land-use conditions represent 

the period 1983-85. For the construction of the groundwater flow model, the predevelopment conditions were 

simulated as steady-state and the current conditions 

were simulated as time-averaged (1983-85). The basic 

data compiled, gathered, and analyzed during this 

study were documented by Lane (1988a and 1988b) and 

Wagner and Lane (1994).

PHYSICAL SETTING

The Columbia Plateau lies in 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 by the extent of the Columbia River Basalt 

Group rather than by any physiographic feature (fig. 2). 

The Columbia Plateau is drained by the Columbia River 

and its major tributaries the Snake, Yakima, John Day, 

Umatilla, Spokane, Klickitat, and Deschutes Rivers.

The Columbia Plateau is underlain everywhere by 

massive basalt flows with an estimated composite maximum thickness of about 16,000 ft near its structural and 

topographic low near Pasco, Wash. The characteristics 

of the older rocks overlain by the Columbia River Basalt 

Group are distinguishable only at exposures in the 

ighlands surrounding the plateau. Sedimentary 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, Oreg.

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
INTRODUCTION A5

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

I -- x I BRITISH GPI4JMBL

CANADA"- \ (

UNITED STATES

WASMNGTON

OREGON v

0 20 40 60 80 MILES

! Ill I III

' |

0 40 80 120 KILOMETERS

46'

45'

44'

43'

Base modified from U.S. Geological Survey digital data, 1:2,000,000,1998, 

and Canadian Geological Survey digital data, 1:5,000,000,1995

EXPLANATION 

Columbia River Basalt Group

 Boundary of Columbia Plateau Regional Aquifer-System 

Analysis study area

- Boundary of hydrologic study area

FIGURE 2. Relation of extent of the Columbia River Basalt Group to the Columbia Plateau Regional Aquifer-System Analysis study area

and the hydrologic study area.
A6 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

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 most of the Columbia Plateau in 

Oregon and Washington south and east of the Blue 

Mountains, including a series of folds extending a few 

miles into Idaho near Lewiston. It is characterized by 

higher plateaus, deeply dissected by many streams.

The topography in central Washington, referred to 

as the "channeled scablands," was produced during 

Pleistocene time. Catastrophic floods, resulting from the 

breakup of glacial ice dams impounding large lakes in 

western Montana and northern Idaho, carved spectacular erosional features into the basalt plateau. Floodwaters stripped away overlying sediments and plucked 

large blocks of basalt, leaving behind deep canyons and 

coulees, rugged cliffs and buttes, large gravel bars, and 

giant ripple marks measuring 20 to 30 ft in height. Thick 

layers of sediment were deposited in low areas where 

flood waters spread, slowed, and ponded.

The types and amounts of natural vegetation found 

on the Columbia Plateau are determined largely by precipitation and land-surface altitudes. Mean annual precipitation ranges from about 6 inches in the center of the 

study area to more than 45 inches in the surrounding 

forested mountains. 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 6 to 15 

inches per year, the vegetation is principally sagebrush 

and grasslands and there are few perennial streams. At 

higher altitudes (2,000 to 3,500 ft), vegetation is more 

typical of semiarid climates and includes both grasslands and forest. These areas generally receive from 15 

to 25 inches of precipitation per year. Where altitudes 

range from 3,500 to 6,000 ft and precipitation ranges 

from 25 to 50 inches per year, forest lands predominate 

and small perennial streams in deep canyons are common. Precipitation is greater in the Cascade Range to 

the west than at similar altitudes in the Blue Mountains 

to the southeast. The mountainous topography is typically rugged and steep with a patchwork of barren rock 

and conifer forests at the land surface.

The mean monthly precipitation is greatest in 

December or January and least in July (Nelson, 1991). 

Typically, 85 percent of the precipitation occurs from 

October through May. Approximately 38 percent of the 

total annual precipitation falls from November through 

January. Winter snowfall ranges from 8 to 20 inches in

the central plateau and from 70 to 300 inches at higher 

altitudes in the Cascade Range and Blue Mountains.

The lowest mean monthly minimum temperatures 

range from 3°C in the low-lying areas to -3°C in the 

higher altitudes, and the highest mean monthly maximum temperatures range from 19°C in the central plateau to 13°C in the mountainous areas. Mean daily 

temperature fluctuations range from 8°C in winter to 

20°C in summer. The seasonal extremes of daily temperature vary by about 40°C between winter lows and 

summer highs.

HYDROGEOLOGIC FRAMEWORK

GEOLOGIC SETTING

The Columbia Plateau aquifer system includes, from 

youngest to oldest: (1) the overburden, a collective term 

used in this study for all materials (from Miocene to 

Holocene age) overlying the Columbia River Basalt 

Group; (2) a minor amount (in most areas) of Miocene 

sediment interlayered with the basalt; and (3) a large 

thickness of Miocene basalt belonging to the Columbia 

River Basalt Group. The Columbia River Basalt Group 

is the surficial geologic unit throughout 80 percent of 

the plateau (fig. 3A). Pre-Columbia River Basalt Group 

rocks underlie the plateau and are presumed to consist 

primarily of less permeable rocks that form the lower 

boundary to the aquifer system. These are sedimentary, 

igneous, and metamorphic rocks that range from the 

Precambrian through early Tertiary age. Little is known 

about the geologic nature and distribution of these rock 

types in the central plateau because few wells have been 

drilled through the basalt. However, the distribution of 

these older rocks is well defined along the margins of 

the plateau where the basalt thins and the older rocks 

are exposed or are at shallow depths.

Basaltic lavas that make up the bulk of the Columbia 

Plateau aquifer system were extruded over an interval 

of 12 million years during the Miocene Epoch between 

17 and 6 million years ago, from north-northwest-trending fissures as much as 90 miles long, located chiefly in 

northeastern Oregon and southeastern Washington 

(Hooper, 1982; Swanson and others, 1975). Flows from 

these fissures covered about 63,200 mi2 of eastern and 

parts of western 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 the 12-million-year interval.

Prebasalt topography in the fissure areas had considerable relief; early lava flows, therefore, filled narrow
HYDROGEOLOGIC FRAMEWORK A7

122° 121 C 120° 119C 118° 117°

> -1 .MONTANA

46

45

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

Overburden 

^^ Columbia River Basalt Group, undivided

^H Saddle Mountain Basalt 

^H Wanapum Basalt

Grande Ronde Basalt 

^H Imnaha Basalt

Boundary of Columbia Plateau aquifer system 

study area

Contact

FIGURE 3A Generalized surficial geology for the Columbia Plateau. (Modified from Drost and others, 1990).
A8 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

GEOLOGIC FRAMEWORK

BASALT STRATIGRAPHY

HOLOCENE MIOCENE to 

MIOCENE

Upper Miocene

ocene

^ 

CD 

-o

T3 

^

Lower Miocene

Precambrian Lower toTertiary

COLUMBIA RIVER BASALT GROUP

DDCD3 RIVER SUBGROUP YAKIMA

Q) 0n

Mountains Saddle

Basalt

Wanapum Basalt

Grande 

Ronde 

Basalt

ture 

rge 

salt

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 Rapis Member 

Roza Member 

Frenchman Springs Mem 

Eckler Mountain Member

Magnetostratigraphic 

units

Basement rocks (pre-Columbia

3er

N2 

R 2 

NT

Ri

T

No

Ro

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 MountainsWanapum Interbed

WanapumGrande Ronde Interbed

River Basalt Group)

HYDROLOGIC 

FRAMEWORK

STUDY UNIT

E CD

£05

£'^ 

0" 

CO

3

CO

<u

CD 

D_

CD

!Q 

E 3 

o 

o

Overburden 

aquifer

Saddle Mountains 

unit

Confining unit

Wanapum unit

Confining unit

Grande Ronde 

unit

Basement confining 

unit

MODEL 

LAYERS

Layer 

1

Layer 

2

Layer 

3

Layer 

4

Layer 

5

FIGURE 35. Stratigraphic chart 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.

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 steam 

explosions that shattered the basalt and formed pillow 

lava complexes and structural irregularities.

Warping and folding of the plateau increased late in 

the eruptive cycle, forming the Frenchman Hills anticline, the Horse Heaven Hills anticline, the Dalles-Umatilla syncline, the Blue Mountains uplift, and numerous 

other geologic structures (fig. 4). 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 in places 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 tectonic folding, 

uplift, and faulting.

SEDIMENTARY UNITS

Sedimentary interbeds are more common in the 

younger basalt than in the older units, 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 have 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. Thus, the greater thicknesses of overburden are in 

the western part of the study area near the Cascade 

Range.
HYDROGEOLOGIC FRAMEWORK A9

122° 121° 120° 119° 118° 117° 116°

48°

47°

46°

45°

20 40 60 80 MILES

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION 

Fault Relative displacement unknown r 

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

Boundary of Columbia Plateau aquifer 

system study area

 - Boundary of physiographic subprovince

 J Syncline Shows trace of trough plane 

FIGURE 4. Major geologic structures within the Columbia Plateau. (Modified from Drost and others, 1990).
A10 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

Overburden is a composite unit of all rock materials 

50 ft or greater in thickness that overlie the Columbia 

River Basalt Group, and is an important source of 

ground water. The thickness of the overburden ranges 

from 50 to more than 2,000 ft, and the thickest deposits 

occur in structural basins and in areas adjacent to the 

Cascade Range.

The overburden includes fluvial consolidated to 

unconsolidated deposits of lacustrine, volcanic, and 

eolian origin ranging from Miocene to Holocene age. 

The sediments and sedimentary rocks from the many 

different formations across the plateau are lithologically 

diverse, ranging from clay to gravels and shale to conglomerate. In Oregon, several of the major formations 

within the overburden have been named The Dalles 

Group by Farooqui and others (1981). Other major formations composing the overburden are the Ellensburg, 

Latah, Ringold, and Palouse.

Sedimentary deposits belonging to the Ellensburg 

Formation are interbedded with the basalt and also 

overlie it in the western and central parts of the plateau. 

They consist of weakly lithified fluvial sand and gravel 

with some lahars and sand, silt, and clay.

In the northeastern part of the plateau and within 

the Spokane River drainage, beds of the Latah Formation 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 granitic and metamorphic basement rocks of the region.

In the Walla Walla River, Quincy, and Pasco basins, 

the sediments overlying the basalt are part of the Ringold Formation. The Miocene-Pliocene Ringold Formation 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 sometimes 

includes a gravel-and-conglomerate facies.

Structural basins on the plateau margin south of the 

Columbia River in Oregon contain sediments that overlie the basalt and are folded with it. 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.

The Grande Ronde valley in northeastern Oregon is 

a major graben, filled with more than 2,000 ft of fluviolacustrine deposits, interfingering alluvial fan deposits, 

and alluvial deposits.

The Cordilleran ice sheet that covered the northern 

and northwestern parts of the plateau left extensive 

deposits of till, stratified drift, and ice-contact materials, 

especially in the northern and northwestern parts of the 

plateau. 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 late Pleistocene time 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. Deposits formed 

during the floods were poorly sorted, clast-supported, 

and open-work gravels intermixed with sand and gravels. These flood-gravels were deposited by high-energy 

flood currents in and along scabland channels, in depositional basins, and in the Columbia River east of The 

Dalles. Slackwater deposits formed in peripheral areas 

of basins in the central part of the plateau. Slackwater 

deposits are interbedded silt and sand with a minor 

amount of gravel and are known as the Touchet Beds 

(Flint, 1938).

Eolian deposits of fine loess of Pleistocene age cover 

much of the plateau and reach thicknesses of as much as 

250 ft, but generally are much thinner. The thickest 

deposits are found in the Palouse region 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.

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 predominately of fine to medium windblown sand, are found in Oregon and in central Grant 

County in Washington.

BASALT UNITS

The thickest, most extensive, and hydrologically 

most important geologic unit in the Columbia Plateau 

aquifer system is the Columbia River Basalt Group, a 

unit that has been subdivided into five formations and 

numerous members (fig. 3B). The five formations, from 

oldest to youngest, are the Imnaha Basalt, Picture Gorge 

Basalt, Grande Ronde Basalt, Wanapum Basalt, and the 

Saddle Mountains Basalt. Of these, the principal formations in the Columbia Plateau aquifer system are part of 

the Yakima Basalt Subgroup of the Columbia River 

Basalt Group. The generalized occurrence of these three 

formations is shown on figure 3A, and the accompanying diagram, figure 3B, lists the members within each 

formation.

Imnaha and Picture Gorge Basalt

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. 3A). The Picture 

Gorge Basalt is exposed only in north-central Oregon, 

mostly within the John Day basin south of the Blue
HYDROGEOLOGIC FRAMEWORK All

Mountains uplift, where it is locally interlayered with 

Grande Ronde Basalt and is in part coeval with it.

The Imnaha and Picture Gorge Basalts are not considered important units in the regional aquifer system 

because of their limited extent and their occurrence at 

the edges of the plateau areas. 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 on plate figure 3A.

Grande Ronde Basalt

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 consists of perhaps as many as 131 

individual flows (Tolan and others, 1987). 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. In the center of the plateau, the total 

thickness of pre-Wanapum basalts exceeds 14,000 ft 

(Drost and others, 1990).

Sedimentary interbeds within the Grande Ronde 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 top of this formation is marked by a zone of 

weathering and (or) a sedimentary interbed 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). Minor nomenclature problems of this 

type were avoided in this study by referring to the 

interbeds according to their typical stratigraphic position within the basalt; for example, the WanapumGrande Ronde interbed. The Wanapum-Grande Ronde 

interbed is most extensive and thickest in the northern 

part of the plateau, where it ranges from 0 to 100 ft 

locally, but averages about 25 ft (Drost and others, 

1990). 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 absent.

Wanapum Basalt

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 edge of the plateau, the Wanapum Basalt overlies 

the prebasalt rock material. The Wanapum Basalt 

includes about 33 separate basalt flows (Tolan and others, 1987). 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 any interbedded sediments ranges between 0 

and 1,300 ft, with the greatest thickness in the Pasco 

basin. 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 part, it is overlain by younger geologic units.

A sedimentary interbed the Saddle MountainsWanapum interbed is commonly present between the 

Wanapum Basalt and the overlying Saddle Mountains 

Basalt. This interbed is generally 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 coarse-grained materials. Thickness of the Saddle 

Mountains-Wanapum interbed averages about 50 ft, but 

generally ranges between 0 and 200 ft (Drost and others, 

1990).

Saddle Mountains Basalt

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, important components of the regional aquifer system. 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, erosion, 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.
A12 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

The thickness of the Saddle Mountains Basalt flows, 

together with any interbedded sediments, ranges from 

0 to more than 800 ft. Maximum thickness occurs in the 

Yakima valley and the area south of Hanford, Wash. In 

one area in Oregon, the interbeds make up about 50 percent of the total thickness; however, this is not the case 

in most of the area.

STRUCTURAL FEATURES

Geologic structures within the plateau are diverse 

and range from simple homoclines to sharp folds with 

structural relief of up to several thousand feet. Major 

faults generally are associated with anticlinal folds and 

range from steep normal faults to low-angle reverse 

faults. The structural complexity of the Columbia Plateau (fig. 4) is indicated by the major geologic structures 

(Drost and others, 1990). Complex structure is a major 

geologic control on the movement of ground water 

within the aquifer system.

The Palouse subprovince is structurally simple and 

is underlain by basalt flows that dip less than 5 degrees 

toward the southwest. Superimposed on the southwesterly dipping basalt are a few broad, open, northwesttrending folds with amplitudes of only a few tens of 

feet.

The dominant feature of the Yakima Fold Belt subprovince is a series of narrow, asymmetrical anticlinal 

ridges, east-west to northwesterly trending and east 

and southeasterly plunging, 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.

In Oregon south of the Columbia Hills, the basalt 

dips toward the axis of The Dalles-Umatilla syncline, 

which 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 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 region 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 lineaments with no apparent displacement.

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 some geologic 

structures.

AQUIFER SYSTEM

The primary factors controlling the occurrence, 

movement, availability, and quality of ground water in 

the Columbia Plateau aquifer system are the hydrologic 

characteristics of the geologic units underlying it, the 

climate, and water-supply development practices. In 

order to address these factors within such a complex 

aquifer system, it was necessary to conceptualize and 

relate the geologic and hydrologic frameworks into a 

simpler system, or conceptual model. This concept then 

provided a basis for investigating the hydraulic characteristics, the ground-water recharge and discharge, and 

ground-water chemistry, and for modeling the groundwater flow in the regional aquifer system.

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 

generally are 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 sediments 

and sedimentary rocks forming the overburden are considered a single unit, the overburden aquifer.

The movement of water through basalt is governed 

by several factors related to the individual basalt flows. 

These factors include the topographic surface over 

which basalts flowed; the erosional processes that 

occurred before, during, and after extrusion; presence 

of water on the paleosurface; the deposition of interbeds; tectonic activity; and diagenetic processes. As a 

result, basalt is an extremely heterogeneous aquifer unit 

that transmits water most readily through the broken 

vesicular and scoriaceous interflow zones that commonly make up 5 to 10 percent of the thickness of an 

individual basalt flow. The interflow zones are separated by the less transmissive and more coherent flow 

centers consisting of the entablature and colonnade in
HYDROGEOLOGIC FRAMEWORK A13

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 quite 

large over the region. Vertical movement of ground 

water varies because of the structure of individual lava 

flows and the hydraulic characteristics of the interbeds.

The lithology of sedimentary interbeds between 

basalt flows within a formation varies from shales to 

sand and gravels. Except in the Saddle Mountains 

Basalt, most interbeds within formations are of limited 

extent. The interbeds between formations are fairly 

extensive laterally, but are thin when compared with 

basalt formations. These interbeds can be locally transmissive and function as aquifers, but in general they 

probably impede vertical movement of water. Waterlevel and well-log data suggest that the interbeds generally can be regarded as semiconfining to locally confining layers that transmit small quantities of water 

laterally.

The conceptual ground-water model developed for 

the study area divides the aquifer system into seven 

hydrogeologic units the overburden aquifer, three 

aquifer units in the permeable basalt rock, two confining units, and the basement confining unit (see fig. 3B). 

For the conceptual model, the three basalt aquifer units 

are the Saddle Mountains, Wanapum, and Grande 

Ronde Basalts and their intercalated sediments. In the 

southeastern part of the study area, the Imnaha Basalt 

and any intercalated sediments are included with the 

Grande Ronde unit. These basalt units are distinguished from basalt formations by being referred to in 

this study as "units"; for example, the Wanapum Basalt 

and interbeds are referred to as the Wanapum unit. The 

confining units are equivalent to the Saddle MountainsWanapum and the Wanapum-Grande Ronde interbeds. 

The basement confining unit consists of the prebasalt 

"basement" rocks that generally have much lower permeabilities than the basalts and are considered the base 

of the regional flow system.

The grouping of several overburden formations and 

100 or more individual basalt flows (representing large 

thicknesses) into a system of seven hydrogeologic units 

greatly limits the conceptual and numerical model's 

ability to deal with local phenomena. Part of this limitation was met by further dividing the Grande Ronde unit 

into an upper Grande Ronde and a lower Grande

Ronde. The upper Grande Ronde was defined as about 

the top 2,000 feet of the Grande Ronde unit. This division facilitated numerical modeling of the system and 

provided a better understanding and description of the 

explored basalt system. Therefore, information is presented in places in the following sections for the upper 

and lower Grande Ronde rather than the Grande Ronde 

unit. Selected hydrogeologic information for the aquifer 

system is presented in table 1.

HYDRAULIC CHARACTERISTICS

Estimates of the range and distribution of lateral 

hydraulic conductivity, transmissivity, vertical hydraulic conductance, specific yield, storage coefficient, and 

stream-leakance coefficients were made for this study 

because these estimates are required for understanding 

the occurrence, movement, quality, and availability of 

ground water. The lateral hydraulic conductivity analyzed in this study is a depth-integrated average value, 

representative over a study-unit thickness. Similarly, 

the vertical conductance represents the effective combined vertical hydraulic conductivity of two units and 

interbeds divided by a representative thickness.

Lateral hydraulic conductivity values for each study 

unit initially were estimated from drillers' specificcapacity data using the methods presented by Ferris 

and others (1962) and by Theis (1963). In this method, a 

vertically averaged lateral hydraulic conductivity for 

the depth of well penetration is derived, and the value 

includes the effects of the vertical movement of water. 

That is, estimated lateral hydraulic conductivities represent the integrated effects of water moving both horizontally and vertically through the entire open interval 

of a well, including all parts of a lava flow or flows and 

any intercalated sediments for the basalt units.

Initial estimates of lateral hydraulic conductivity of 

the overburden aquifer derived from specific-capacity 

tests were generally for basins. The values for the eastern part of the study area were represented by typical 

values for loess, the dominant sediments. The specificcapacity data were used in the ground-water model to 

derive regional estimates, which range from about 

2.9xlO~7 to 1.7 ft/s and have a median lateral hydraulic 

conductivity of about 2.8xlO~3 ft/s. Fifty percent of the 

values about the median lie in the range 5.2X10"4 to 

1.2xlO~2 ft/s, and only 3 of the 871 values were greater 

than 4.0X10"1 ft/s. The model-derived values range

7 O

from 5.0x10 to 1.3x10 ft/s and have a median of 

about S.OxlO"4 ft/s. Table 2 presents some descriptive 

statistics of the regional values derived from groundwater modeling.
A14 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

TABLE 1. Selected hydrogeologic information for the Columbia Plateau aquifer system

COLUMBIA RIVER BASALT GROUP

Volume

Areal extent

Areal extent within RASA Columbia Plateau study area

Areal extent within hydrologic study area

39,300 cubic miles 

63,200 square miles 

50,600 square miles 

32,688 square miles

Study unit within hydrologic study area1

Overburden 

aquifer

Saddle 

Mountains 

unit

Wanapum 

unit

Grande 

Ronde 

unit

Area saturated (square miles)

Predevelopment conditions 

Current (1980's) conditions

10th percentile 

Median

90th percentile

2,908 

4,509

75 

190

570

4,909

5,748

Thickness (feet)

20 

370

710

20,540 

20,540

30 

530

1,000

32,500 

32,500

805 

3,000

8,085

Areal extent of outcrops (square miles)

Predevelopment conditions 

Current (1980's) conditions

Predevelopment conditions 

Current (1980's) conditions

2,908 

4,509

137 

169

3,041 

2,990

Volume (cubic miles)

339 

362

14,745 

13,251

1,700 

1,700

11,984 

11,938

23,950 

23,950

Area of water-level changes2 (square miles)

Declines

Rises

110

2,850

340

3,210

7,450

3,930

8,460

8,340

1 Based on data gridded for model grid system that is discussed later in this report.

~ Model-calculated changes of more than 10 feet from predevelopment to current conditions. Calculated changes are described later in this report.

In general, aquifer tests of the cased wells in the 

basalt yield site-specific values of hydraulic conductivity that are representative of a single zone. To obtain an 

understanding of both the range in hydraulic conductivity values for the entire basalt sequence in the study 

area and of the effects of geologic structures, numerous 

aquifer tests in widely distributed cased wells would be 

needed. This need could not be met because most wells 

finished in the Columbia River Basalt Group are 

uncased, aquifer-test data are sparse and inconsistent, 

and there is a lack of information about the effects of 

vertical leakage. Therefore, specific-capacity data were 

used to estimate initial hydraulic conductivity values. 

The estimated values, about a thousand for all three 

basalt units, then were used in the ground-water flow 

model to derive regional estimates.

Estimates derived from specific-capacity data for the 

basalt values range from 5.8xl(T8 to 6.1xl(T2 ft/s and 

have a median of 5.9xl(T5 ft/s. Seventy-five percent of 

the lateral hydraulic conductivity values are less than 

S.OxKT4 ft/s, and 75 percent are larger than 1.2xl(T5 ft/ 

s. The Saddle Mountains, Wanapum, and Grande 

Ronde units have median lateral hydraulic conductivity 

values of 2.8xlO~5, 6.0xl(T5, and 5.7xl(T5 ft/s, respectively. The smaller median hydraulic conductivity of the 

Saddle Mountains unit is attributed to the thicker and 

more numerous intercalated sedimentary interbeds, 

generally lacking in the Wanapum and Grande Ronde 

units. Model-derived values for the basalt units (table 2) 

range from l.OxKT6 to l.OxKT4 ft/s. Median values for 

the Saddle Mountains and Wanapum units are 1.6x10 

and 3.0xlO~5 ft/s, respectively. The model-derived 

median lateral hydraulic conductivity is 1.6xl(T5 ft/s 

for the upper Grande Ronde and 1.4xl(T5 ft/s for the 

lower Grande Ronde.

The wide range in hydraulic conductivity reflects 

the heterogeneous nature of the basalt. The largest calculated hydraulic conductivity values are probably due 

to local geologic structure, thickening of interflow 

zones, thinning of individual lava flows, or to the presence of pillow lava complexes (Swanson, 1967) that 

increase the hydraulic conductivity. Wells for which 

many of these large values were estimated are close to 

wells for which small hydraulic conductivity values 

were estimated, demonstrating the localized occurrence 

of these values. Observed physical variations in 

exposed lava flows suggest that, within a single flow, 

the lateral and vertical hydraulic conductivity values
HYDROGEOLOGIC FRAMEWORK A15

TABLE 2. Hydraulic characteristics ofhydrogeologic units in the Columbia Plateau aquifer system, derived from the regional ground-water flow model

Lateral hydraulic conductivity, in feet per second 

(values in parentheses derived from specific-capacity data)

Hydrogeologic unit

Overburden aquifer

Saddle Mountains unit

Wanapum unit

Grande Ronde unit 

Upper Grande Ronde

Lower Grande Ronde

Median.

4.98X10"4 

(2.78xlO"3)

1.62xlO"5 

(2.76x10"*)

S.OlxlO"5 

(6.02xlO~5)

1.61xlO~5 

(5.70xlO~5)

1.45xlO"5

Mean

1.14xlO"3 

(9.53xlO"2)

1.48xlO~5 

(6.48xlO~5)

3.73x10"* 

(7.60X10"4)

2.62xlO"5 

(5.77X10"4)

2.30xlO"5

Minimum

4.98xlO"7 

(2.86xlO"7)

1.97xlO"5 

(8.12x10"*)

l.OlxlO"6 

(8.12x10"*)

l.SOxlO"6 

(5.78x10"*)

l.lOxlO"6

Maximum

1.27xlO"2 

(1.73x10°)

S.OlxlO"5 

(2.19xlO"2)

9.03xlO"5 

(6.07xlO~2)

9.98xlO~5 

(2.92xlO~2)

7.44xlO"5

Transmissivity, in feet squared per second

Hydrogeologic unit

Overburden aquifer

Saddle Mountains unit

Wanapum unit

Grande Ronde unit 

Upper Grande Ronde

Lower Grande Ronde

All units combined

Median

5.79xlO"2

3.70xlO"3

8.45xlO"3

1.97xlO"2

S.llxlO"2

3.85xlO~2

Mean

2.13X10"1

5.29xlO"3

1.55xlO"2

4.25xlO"2

8.51xlO"2

1.35x10"'

Minimum

2.60xlO"5

2.80xlO"5

5.00x10*

4.80X10"4

5.52X10"4

4.80X10"4

Maximum

3.12x10°

2.29xlO"2

l.OSxlO"1

1.84x10"'

4.80x10"'

3.48x10°

Vertical hydraulic conductance, in feet per second per foot

Hydrogeologic unit

Overburden aquifer

Saddle Mountains unit

Wanapum unit

Grande Ronde unit 

Upper Grande Ronde

Median

2.63x10^

2.12x10""

6.02xlO"12

4.98x10""

Mean

1.25x10*

1.09xlO"9

3.66xlO"10

4.10xlO"n

Minimum

2.00xlO"12

S.OOxlO"13

S.OOxlO"13

4.5xlO"13

Maximum

l.OlxlO"5

3.54x10*

2.70x10"*

4.98x10""

should exhibit a large range. For example, cascading 

water in many uncased wells is attributed to the relative 

ease with which water moves horizontally along interflow zones. Thus, the hydraulic conductivity in interflows is mainly due to primary features such as flow 

breccia, vesicles, and clinkers rather than to the fracture 

assemblage; whereas, in the entablature and colonnade, 

the hydraulic conductivity is mainly due to fractures 

and joint systems developed during cooling processes 

and tectonic activity.

Modeling studies (F. A. Packard, U.S. Geological 

Survey, written commun., 1987; Davies-Smith and others, 1988; William Meyer, U.S. Geological Survey, written commun., 1985) suggest that, within a basalt unit, 

the vertically averaged lateral hydraulic conductivity 

for some geologic structures, such as faults, may be as 

small as 1CT9 to 10~8 ft/s. There are two possible explanations for this the offsetting of interflow zones 

through faulting, which produces low-conductivity 

fault breccia and gouge material at that interface (as 

described by Newcomb, 1965, 1969; and Stearns, 1942), 

and the closing of pore space through deposition of secondary minerals. Values derived from the application of 

the ground-water model in this study suggest that, for 

some structures, typically faults and fault-associated 

anticlines, lateral conductivity can be reduced by about 

two orders of magnitude.

Transmissivities of the study units and of the total 

aquifer system were estimated for the area within the 

ground-water model boundaries. The transmissivities 

of the total aquifer system range from 4.8X1CT4 to 3.5 

ftVs (square feet per second), with an estimated 

median of about 3.8xlO~2 ft2 /s (table 2). The estimated 

median values for the five aquifers, from youngest to
A16 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

oldest, are 5.8x10~% 3.7xlO~3, 8.4x10~% 2.0x10~% and 

3.1x10 ftvs; maximum values range from 2.3xlO~2 to 

3.1 ft2 /s.

Vertical hydraulic conductivity values of the basalts 

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 2xlO~12 

to 5xlO~9 ft/s. The range of the ratio of horizontal to 

vertical hydraulic conductivity has been estimated to be 

from about 5,000:1 to 100:1 (Hansen and others, 1994; F. 

A. Packard, U.S. Geological Survey, written commun., 

1987; Lum and others, 1990; A. J. Hansen, U.S. Geological Survey, written commun., 1986). Vertical hydraulic 

conductivity values were not estimated directly in this 

study. Instead, vertical hydraulic conductance was estimated. These values were derived during model calibration on the basis of proportionality factors, 

thickness, and lateral hydraulic conductivity. These 

regionalized values integrate the hydraulic characteristics of all overburden sediments and basalt flows and 

intercalated sediments, and generally approximate an 

effective vertical hydraulic conductivity divided by a 

representative thickness. Table 2 shows that the median 

values are, from youngest to oldest, 2.6xlO~8, 2.1xlO~n, 

6.0xlO~12, and S.OxlO"1 * 1/s (feet per second per foot, or 

per second); basalt values range from 4.5xlO~13 to 

3.5x10 1/s, and overburden values range from 2.0x 

10-12 tol.OxlO-5 l/s.

Vertical hydraulic conductivity estimates based on 

the model-derived values of vertical conductance 

showed that the median value for the overburden aquifer is about 2.1xlO~5 ft/s, or about an order of magnitude smaller than the lateral hydraulic conductivity. 

The vertical hydraulic conductivity of the basalt units 

varied widely and has a median of about 1.5xlO~8 ft/s. 

This median value is, in turn, about three orders of 

magnitude smaller than the median lateral conductivity 

of basalt units. The larger vertical hydraulic conductivity values estimated during this study are probably due 

to the following reasons: (1) Unlike the previous investigations, most of the Palouse subprovince was included 

in this study, and the northeastern part encompasses 

most of the structurally unaffected basalt area; (2) the 

total thickness of the basalt units was modeled in this 

study, resulting in a smaller effective vertical hydraulic 

conductance and a larger effective vertical hydraulic 

conductivity; (3) the boundaries in this study generally 

extended to the basalt's lateral extent or an equivalent 

no-flow boundary; and (4) better hydraulic head control 

were available from more wells in the Wanapum and 

Grande Ronde units allowed for improved assessment 

of vertical gradients.

The potential range in the storage coefficient was 

estimated for the basalt units on the basis of selected 

published values of storage coefficients for the Columbia Plateau and on model simulations. Values for the 

overburden aquifer were estimated from selected published values.

The estimated storage coefficient values for the overburden materials range from 0.0002 to 0.2 and generally 

represent the specific yield. Storage coefficient values 

for the basalt range from 10~7 to 10~2 and represent a 

range of aquifer conditions including confined conditions where the values approach the expansibility of 

water, leaky artesian conditions, and water-table conditions with low porosity. Analysis of ground-water-level 

declines in conjunction with ground-water pumpage 

suggests that long-term regional values are about the 

same for all basalt units and probably range from 0.005 

to 0.05. A value of 0.04 was used as the estimate for the 

time-averaged ground-water model simulation.

Stream-leakance coefficients represent proportionality factors for estimating the flux of water between the 

aquifer system and streams. These factors are multiplied by the difference in hydraulic head between a 

stream and the unit the stream resides in, to obtain an 

estimate of the flux. The coefficients, derived and 

regionalized during model calibration, range from 0.1 

to 11.0 ftVs. The median coefficient was about 1 ftVs, 

and about 70 percent of the coefficients were equal to 

the median.

FLOW SYSTEM

The occurrence, movement, and availability of 

ground water in the Columbia Plateau are controlled by 

the aquifer system's geometry and hydraulic characteristics, and the distribution and rates of ground-water 

recharge and discharge, including changes caused by 

water-development practices. A description of the 

regional flow system and how it relates to these factors 

has been discussed by Bauer and others (1985), Whiteman (1986), Lane and Whiteman (1989), Whiteman and 

others (1994), and Hansen and others (1994).

The altitude of the water table in the overburden 

aquifer for Washington and Oregon is shown on figure 

5. The overburden materials compose a water-table 

aquifer in the Quincy, Pasco, Yakima River, Walla Walla 

River, and Umatilla River basins. The direction of 

ground-water flow is toward discharge points along 

surface-water features in these basins. Water in the 

overburden aquifer is in direct hydraulic connection 

with water in the immediately underlying basalt unit. 

Within the U.S. Bureau of Reclamation's Columbia 

Basin Irrigation Project (CBIP), much of the overburden
HYDROGEOLOGIC FRAMEWORK A17

122° 121° 120° 119° 118° 117° 116°

48°

47°

46°

45°

jORIFJJLE 1 ' BONNFR- ' LINCOLN '

: ''H J~f'^\ \lJf\ . X*x ^,- i ' ;- ... MONT'AN'/

VALLEY 

80 MILES

r

120 KILOMETERS

I_______

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

? Approximate extent of overburden aquifer Dashed where 

approximately located. Queried where unknown

I Area saturated due to irrigation 

- Direction of ground-water flow

 400 ? Water-table contour Shows approximate altitude of water table.

Queried where inferred. Contour interval 200 feet. Datum is sea level

 Boundary of Columbia Plateau aquifer system study area

FIGLRE 5 Water-table altitude and direction of ground-water flow for the overburden aquifer, representing conditions during spring

1983, for selected areas. (Modified from Bauer and others, 1985).
A18 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

was unsaturated prior to the importation of Columbia 

River water for irrigation. The overburden is saturated 

now in those areas and stores large quantities of water. 

The water levels reflect the application and infiltration 

of surface water and represent a dynamic equilibrium 

with only small, local declines caused by withdrawal 

and small rises resulting from increased recharge due to 

the infiltrating surface water used for irrigation.

Spring 1985 water-level contours and direction of 

ground-water flow in the three basalt units are shown 

on figures 6-8. 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 head distribution for that unit insofar as the 

data permitted. The contours are greatly generalized 

and present a simplified picture of the true, complex 

three-dimensional flow system.

The potentiometric surface in the Saddle Mountains 

unit (fig. 6) closely parallels the land surface where 

there is little or no overburden. Lateral ground-water 

flow in this basalt unit is generally toward major surface-drainage features, but small and intermediatesized streams also receive base flow from the Saddle 

Mountains unit. This ground-water flow pattern holds 

true for the Wanapum and Grande Ronde units (figs. 7 

and 8) 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 movement in both the Wanapum and 

Grande Ronde units closely parallels the southwest 

regional dip of the basalt. Regional discharge is to the 

Columbia and Snake Rivers. In the Yakima Fold Belt 

subprovince, ground water generally moves downward 

from the anticline axes toward the streams and rivers 

lying in the intervening synclines. Ground-water movement in the Blue Mountains subprovince is similar, 

closely paralleling the land surface in areas of high 

relief and moving downward from the anticline axes to 

streams and rivers. Ground-water movement in the 

low-relief areas parallels the dip of the basalt, but varies 

locally due to geologic structure and ground-water 

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 southcentral part of the plateau, water-level contours appear 

to be less influenced by surface-drainage features, and 

consequently have a smoother form. An example of this 

is in the Quincy basin, where ground-water movement 

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 

movement in the underlying Grande Ronde unit, however, is unaffected by these land-surface features, 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 it is more than 

about 500 ft thick, the water-level contours in the lower 

part of the Grande Ronde unit tend to be smoother and 

indicate smaller gradients; that is, the lower part of the 

unit is hydrologically similar to the buried units. This 

has been noted in Douglas County, Wash., and in the 

high-relief areas of the Blue Mountains.

In most of the study area, water-table conditions 

exist in the uppermost basalt flows, whereas water in 

the deeper basalt is generally semiconfined. Finegrained, tight interbeds and some basalt flow centers 

are semiconfining beds to the underlying flows. On the 

basis of water-level data and model analysis, it appears 

that over most of the plateau the vertical component of 

flow is downward except near discharge areas; exceptions to this pattern occur near geologic structures and 

areas with significant ground-water pumpage.

Large water-level gradients (100 to 300 feet per mile) 

are shown on the flanks of the Blue Mountains, Horse 

Heaven Hills, Frenchman Hills, Rattlesnake Hills, and 

Saddle Mountains anticlines (figs. 4, 7 and 8). Waterlevel 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 structural gradients.

Since the mid-1960's, pumping ground water for irrigation has disturbed the regional pattern of groundwater flow. For example, in the area of Connell, in Franklin County, Wash., and northward toward the area 

between Odessa and Lind (fig. 7), a large, upgradient 

bending or flexure of the contours, typical of lowered 

water levels, can be seen. A similar upgradient contour 

flexure attributed to pumping is evident in the Umatilla 

River basin in Oregon.

The effects of increased recharge because of waterdevelopment practices on the water-level configuration 

are shown by the downgradient contour flexure just 

east of Othello (fig. 7), between the 1,000- and 800-foot 

contours, where the CBIP's large East Low Canal straddles the downgradient flexures.

Seasonal water-level fluctuations in the overburden 

aquifer and basalt units vary widely because of several 

factors: (1) annual climatic variations in precipitation 

and temperature; (2) topographic location as it relates to 

precipitation variations and geologic conditions; (3) the 

storage capacity of the rock materials; and (4) irrigation 

practices. Seasonal water-level changes in the overburden materials are generally less than 10 ft, but may be as 

much as 20 ft in alluvial sediments in the western part 

of the study area. Hydrographs of U.S. Geological Survey observation wells located in Washington typically
HYDROGEOLOGIC FRAMEWORK A19

122° 121 C 120° 119° 118° 117° 116°

48°

47 C

46°

45°

'VALLEY

0 20 40 60 80 MILES

i I i I i I i I

120 KILOMETERS

I______

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

! Approximate extent of Saddle Mountains unit Dashed where inferred 

^^^H Generalized area where unit saturated due to irrigation

Area where unit is unsaturated 

< Direction of ground-water flow

 400 ? Water-level contour Shows approximate altitude of water level. 

Queried where inferred. Contour interval, in feet, is variable. 

Datum is sea level

Boundary of Columbia Plateau aquifer system study area

FIGURE 6, Water-level contours and direction of ground-water flow for the Saddle Mountains unit, spring 1985.

(Modified from Lane and Whiteman, 1989).
A20 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

122° 121 C 120° 119° 118° 117° 116°

48C

1 SKAGVT

SNOHOMIShT

V

FERRY i- ;

PChlD I" 

ORELLE | BONNER-- LINCOLN

U'~IV ~^

- X CL^t'fltfV* '

CHFi V,

A -W,A S H

 Ji: ' .KING; -

47C

UJ>

« 

^ < --,5

PIF.ROS- .

-7.W. Vl --1 ,_\

-~- S |i ', 

C; 

 K ," 

!JEW!S ,^'

46°

45°

SKM

LACKA'-n'S

M.\U«i> , '^--!

. ^

JVN r'« /

" VT 40 60

LAMfc X

V : .'-h

\L __ , ' 0

' VALLEY

80 MILES

_|

40

i

80 120 KILOMETERS

i ____

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

? Approximate extent of Wanapum unit Dashed where 

approximately located. Queried where inferred

< Direction of ground-water flow

BOO ? Water-level contour Shows approximate altitude of water level. 

Queried where inferred. Contour interval, in feet, is variable. 

Datum is sea level

 Boundary of Columbia Plateau aquifer system study area

FIGURE 7. Water-level contours and direction of ground-water flow for the Wanapum unit, spring 1985.

(Modified from Lane and Whiteman, 1989).
HYDROGEOLOGIC FRAMEWORK A21

122° 121° 120° 119° 118° 117° 116°

48°

47°

46°

45°

PCND I 

ORBEUJE I - BONNER-

/ LANE DESCHUTESj CROOK VL./ i

$(

20 40 60

I

\ 

40

\^ 

80

'.W.-J.-W

" )? - ' ;' V ' VALLEY

80 MILES

i I n

120 KILOMETERS

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

; Approximate extent of Grande Ronde unit Dashed where 

approximately located

<'"" "" Direction of ground-water flow

 900 ? Water-level contour Shows approximate altitude of water level. 

Queried where inferred. Contour interval, in feet, is variable. 

Datum is sea level

 Boundary of Columbia Plateau aquifer system study area

FIGURE 8. Water-level contours and direction of ground-water flow for the Grande Ronde unit, spring 1985.

(Modified from Lane and Whiteman, 1989).
A22 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

show water-level fluctuations of less than 10 ft in the 

shallower basalt units (Cline, 1984; Whiteman and others, 1994).

RECHARGE

Recharge to the aquifer system is primarily from 

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

lakes, and reservoirs. Recharge from precipitation is 

controlled by both daily and annual climatic variations 

and is thus highly variable both temporally and spatially. Recharge, as discussed in this report, does not 

include leakage from rivers, lakes, and reservoirs. These 

items are considered a separate water-budget component and are discussed in the Regional Ground-Water 

Flow section.

Recharge was estimated by Bauer and Vaccaro 

(1990) on a daily basis for 53 basins or zones (fig. 9) by 

applying a daily energy-soil-water balance model 

(Bauer and Vaccaro, 1987b). The model computes deep 

percolation of water for a control volume that includes 

vegetation, if any, covering the land surface down to the 

daily maximum prevalent root depth; or, for the case of 

unvegetated areas, down to the depth of the soil or 5 ft, 

whichever is less (Bauer and Vaccaro, 1987b). The modeled areas were discretized into rectangular cells over 

which the daily calculations were made. The daily estimates then were used to arrive at a long-term estimate 

of recharge for both predevelopment and current landuse conditions. The 22-year period of record from 1956 

to 1977 was used to estimate recharge for most of the 

basins or areas, a period that exhibited reasonable climatic variation.

Estimates of recharge and other pertinent information for the 53 zones under predevelopment and current 

land-use conditions are given in table 3. The areas 

included most of the irrigated croplands and most of 

the area where annual precipitation is less than 11 in/yr. 

The hydrologic study area (fig. 2) was divided into the 

same cells used for the ground-water model, 2.5 minutes of latitude by 2.0 minutes of longitude (about 2.8 

by 1.7 miles). The recharge estimates for each cell in the 

53 zones then were aggregated to those ground-water 

model cells. Recharge was estimated for the cells in the 

remainder of the hydrologic area through the use of a 

polynomial regression equation that related the 22-year 

average annual precipitation to the estimated predevelopment recharge for each of the cells in each modeled 

area (about 30,000 data values).

The plateau-wide, long-term, time-averaged estimate of recharge for predevelopment land-use conditions is about 6,566 ft /s, or 2.7 in/yr, and for current

(1980s) land-use conditions about 10,205 ft3 /s (4.24 in/ 

yr). Thus, recharge has been increased by about 3,639 

ft3 /s (1.5 in/yr) due to the infiltration of irrigation 

waters.

The estimates of recharge for current (1980's) landuse conditions are presented in figure 10. The estimates 

include some small changes in local areas that were 

derived during the calibration of the ground-water flow 

model (Hansen and others, 1994). The most apparent 

fact that can be ascertained from figure 10 is the large 

range (0.0 to more than 50 in/yr) and areal variability of 

the values. The areas of extensive surface-water irrigation can also be easily identified in the central plateau 

and along the Yakima River.

DISCHARGE

Discharge from the ground-water system, excluding 

ground-water pumpage, is mainly to surface-water 

bodies and springs and seeps along canyon and coulee 

walls. Lesser quantities of ground water discharge to 

the atmosphere as evapotranspiration. It is difficult to 

determine the actual discharge because of the large 

streamflow quantities, numerous impoundments, and 

streamflow regulation in the large rivers. Additionally, 

flow in the many small perennial and ephemeral 

streams and the diffuse nature of the seepage are not 

easily measured.

The location and quantity of discharge from the 

ground-water system was estimated for some smaller 

surface-water bodies and for ground-water pumpage. 

Average long-term ground-water discharge to a stream 

is termed "base flow" and can be quantified by the lowflow characteristics of a stream. Low-flow characteristics vary widely over the study area, and are discussed 

by Nelson (1991). The discharge to some of the smaller 

surface-water bodies estimated from the "base flow" 

accounts for about 26 percent, or 2,600 ft3 /s, of the current recharge. This estimated discharge to some of the 

smaller surface-water bodies was used as a calibration 

check for the ground-water model. Estimates of discharge as ground-water pumpage (table 4) account for 

some 11 percent of the current estimate of recharge. The 

regional distribution and rate of discharge excluding 

pumpage were estimated using the ground-water 

model (Hansen and others, 1994), and are presented for 

current conditions on figure 11. The ground-water discharge is also presented in tables 5 and 6, which show 

the model-calculated regional water budget. Figure 11 

and tables 5 and 6 together provide a summary of the 

estimated ground-water discharge for the Columbia 

Plateau aquifer system.
HYDROGEOLOGIC FRAMEWORK A23

122° 121° 120° 119° 118° 117° 116°

48°

47°

46°

45°

A -r\ ,,

-^ ' . SNOHOMiSH< ^ ' v. >^ X

/ ^ /--^ tfe,Ya'y / > ^ Fofhofe % '-f . T| -^

' ~\ , /* \J|L V^SJ X^A ' L Bll , Rewrooir , k 39 l^

, \HERCE // ^1^ri^y ^ ^T^S%^a^r> , /

I - '' \ T **JLf?^e='-'i qj*-- -^ _

 I , -' -21 » \»&£Z**£* iH^M/.

^a #/v ^

 , 10

~-/S f . __i * -, ^--r^l-T /AN 1 ..,

rf~LAm ~^x DESCHUTES ! - -=-. , ' S } 

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972

EXPLANATION

 Boundary of Columbia Plateau aquifer system study area

 Boundary of regional aquifer system ground-water model

 Boundary of recharge simulation zone

14 Recharge simulation zone reference number as given in table 3

FIGURE 9. Location of the 53 basins, or zones, for which recharge was estimated using a daily deep-percolation model

(From Bauer and Vaccaro, 1990).
A24 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

TABLE 3. Summary of estimated recharge and data used for predevelopment and current land-use conditions, Columbia Plateau aquifer system

(from Bauer and Vaccaro, 1990)

[Values in inches per year]

Zone 

reference 

number 

(see figure 9)

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

Average 

precipitation

7.29

8.91

9.34

6.61

8.77

8.64

8.26

6.95

7.64

7.93

7.76

7.41

8.19

7.95

6.98

8.31

8.09

12.05

10.09

9.19

17.27

22.75

22.32

6.94

10.33

12.61

12.54

10.05

21.80

10.09

8.69

7.78

11.12

10.24

8.94

10.26

24.30

8.24

22.42

8.15

8.04

9.12

9.04

8.61

18.28

21.06

16.49

20.96

12.93

37.65

11.35

11.34

8.93

Average 

current 

irrigation

23.74

.32

.29

0

0

.67

0

.23

6.50

0

0

22.02

9.86

7.20

2.73

4.30

5.31

.13

0

1.48

.08

1.83

0

2.51

1.54

.77

.27

.11

0

1.62

3.92

30.15

17.43

3.59

3.96

0

0

6.82

0

18.64

21.02

1.99

1.97

26.68

.37

0

.84

0

5.20

.28

.66

.15

23.84

Average 

potential 

evapotranspiration

43.06

35.93

39.92

42.45

36.14

37.32

39.43

41.89

38.92

40.25

41.49

41.72

42.15

42.82

40.56

40.56

41.19

40.47

40.71

41.04

36.16

28.69

36.13

44.24

43.43

41.32

41.32

39.09

37.45

41.64

42.49

41.41

34.73

43.09

44.78

40.00

27.92

44.9

34.5

40.41

41.71

44.55

42.47

39.91

38.75

38.51

42.98

36.21

40.13

35.72

41.21

41.85

37.60

Average actual 

evapotranspiration

Predevelopment

6.74

7.62

7.75

6.09

7.54

7.66

6.62

6.61

7.24

7.39

7.24

7.28

7.66

7.36

6.52

7.71

7.39

8.64

8.57

7.49

9.92

10.58

14.05

9.19

8.92

10.24

10.24

8.75

14.37

8.41

7.91

7.11

8.33

8.89

8.23

8.93

11.71

8.06

16.03

7.32

7.13

8.14

9.04

8.09

12.33

12.64

12.89

15.59

11.45

15.08

11.15

10.01

8.03

Current

18.56

7.83

7.97

6.09

7.54

8.07

6.66

6.73

12.47

7.47

7.28

22.11

15.13

11.56

9.23

10.68

11.54

8.75

8.54

8.77

10.00

11.65

14.05

11.64

10.68

11.13

10.90

9.10

14.94

9.71

10.81

19.08

18.71

12.01

10.68

9.32

11.71

13.89

16.54

16.30

17.10

9.76

11.02

25.10

13.18

12.98

13.91

14.84

14.53

15.53

11.81

9.58

20.73

Average stream 

discharge

Surface 

runoff

*0.06

.10

M3

*.07

*0

.12

.19

*0

.10

*0

*0

.07

*0

.14

.16

*.16

*.40

2.44

1.26

.76

3.61

3.56

2.82

.13

*0

.29

.65

.07

4.30

*.22

*0

*.05

*0

*.25

.28

*.ll

3.32

.10

2.39

*.21

*0.04

*.07

*0

*0

3.16

2.11

2.40

2.57

*.02

10.05

*0

.46

*0

Base 

flow

0

0

0

0

0

0

0

0

0

0

0

0

0

0

.04

0

0

1.29

1.20

.06

3.15

5.08

3.55

0

0

.32

.25

0

1.70

0

0

0

0

0

0

0

9.24

0

2.28

0

0

0

0

0

1.54

4.06

1.86

0

0

24.47

0

0

0

Average recharge

Predevelopment

0.43

1.25

1.37

.38

1.18

.66

1.31

.30

.43

.45

.44

.15

.47

.23

.13

.39

.26

1.30

.83

.87

5.39

10.52

6.01

.57

1.36

2.30

1.68

1.16

3.51

1.42

.73

.58

2.74

1.04

.24

1.17

10.65

.13

4.13

.57

0.82

0.84

.01

.44

3.30

6.79

1.53

2.98

1.45

15.06

.29

.90

0.84

Current

12.27

1.35

1.45

.38

1.18

.93

1.29

.29

1.56

.41

.43

7.26

2.83

2.83

.66

1.78

1.50

1.33

.87

1.16

5.39

11.11

6.00

.51

1.20

2.11

1.35

1.01

2.97

1.81

1.79

18.71

9.72

1.58

1.86

.85

10.65

1.21

2.79

10.07

11.89

1.30

.01

10.33

2.93

6.50

1.55

3.65

3.33

15.19

.29

1.63

11.15

* Stream runoff assumed to be zero from all land surfaces within the area; however, the presence of surface-water bodies results in surface-runoff output for those areas during model simulations.
HYDROGEOLOGIC FRAMEWORK A25

122° 121 C 120° 119° 118° 117° 116°

48°

47°

46°

45°

Pf-JND

ORIELLE ' , BONNER ' "

^ ...MONTANA 

'

MARION r1 -#:^4- 

--^. .-- > j,. *~»- *

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972 EXPLANATION 

Recharge, in inches per year

0.02-0.5

0.5-1.0

1.0-2.0

2.0-5.0

5.0-10.0 

10.0-52.2 

Model grid 

Boundary of model 

Boundary of Columbia Plateau aquifer system study area

FIGURE 10. Distribution of estimated recharge for current (1980's) land-use conditions.
A26 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

TABLE 4. Ground-water pumpage by study unit from the Columbia Plateau, Washington, Oregon, and Idaho, 1945 to 1984 (from Cline and Collins, 1992)

[Values in acre-feet per year]

Water-yielding unit

1945

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1950

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1955

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1960

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1965

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1968

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1970

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

Washington

9,040

13,270

1,970

23,490

47,770

14,650

26,160

3,390

38,830

83,039

22,280

41,850

4,010

46,900

115,040

31,630

51,820

4,890

48,210

136,550

49,890

80,070

5,980

53,100

189,040

80,200

131,390

9,090

62,190

283,070

87,910

141,530

11,160

75,420

316,020

Oregon

450

4,200

810

2,460

7,920

1,440

8,330

570

4,000

14,340

4,990

12,030

960

6,760

24,740

11,850

19,400

1,890

8,280

41,420

14,960

22,300

2,180

11,600

51,040

22,660

27,030

2,480

15,690

67,860

31,400

30,800

2,690

22,980

87,870

Water-yielding unit

1973

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1975

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1977

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1979

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1982

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1983

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

1984

Grande Ronde

Wanapum

Saddle Mountains

Overburden

TOTAL

Washington

106,080

184,130

11,900

108,300

410,410

149,920

200,830

12,320

137,580

500,650

213,230

265,130

18,580

189,610

686,550

248,350

320,960

21,710

191,640

782,660

239,330

297,680

23,590

190,930

751,530

192,800

268,960

23,130

181,150

666,040

205,390

271,480

23,720

680,930

Oregon

36,530

32,600

2,870

28,070

100,070

44,270

38,200

3,550

30,960

117,580

58,780

44,680

4,030

30,930

138,420

62,820

57,010

4,250

33,030

157,110

60,490

58,110

4,260

32,380

155,240

55,930

54,980

4,780

31,570

147,260

55,800

54,990

4,670

147,340
HYDROGEOLOGIC FRAMEWORK A27

122° 121 C 120° 119° 118° 117° 116°

1 SKAGIT-.

. ' V H/GHIAWOS ORIELLE I ', BONNERx 

i" .'\

LINCOLN '.

48°

47°

46°

45°

VV __ -'"

60

' VALLfcY 

80 MILES

\ 

40

I 

80 120 KILOMETERS

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972 EXPLANATION 

Discharge, in inches per year

0.0-0.1 

0.1-1.0 

1.0-2.0

ftW Model grid

 Boundary of model

 Boundary of Columbia Plateau aquifer system study area

FIGURE 11. Distribution of estimated discharge for current (1980's) land-use conditions.
A28 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

TABLE 5. Calculated water budget for the predevelopment and timeaveraged simulations for the Columbia Plateau aquifer system 

(from Hansen and others, 1994, in preparation)

[Values in cubic feet per second]

Water-budget 

component

Recharge 

Leakage from rivers 

Change in storage

TOTAL IN

Leakage to rivers 

Leakage to drains 

Leakage to seepage faces 

Pumpage

TOTAL OUT

Predevelopment 

simulation 

(P)

6,566.5 

553.6 

0.0

7,120.1

2,753.9 

3,944.8 

425.5 

0.0

7,124.2

Timeaveraged 

simulation 

(TA)

10,205.0 

556.7 

186.6

10,948.3

3,804.5 

5,595.5 

422.6 

1,134.7

10,957.3

Difference 

(TA-P)

3,638.5 

3.1 

186.6

3,828.2

1,050.6 

1,650.7 

-2.9 

1,134.7

3,833.1

TABLE 6. Calculated water budget for the predevelopment and time-averaged simulations for layers in the ground-water model

of the Columbia Plateau aquifer system

[Values in cubic feet per second]

Water-budget component

Recharge

Leakage from rivers

Leakage from overlying layers

Leakage from underlying layers

Change in storage

TOTAL IN

Predevelopment simulation 

Layer 1

1

119.3

452.3

0.0

578.2

0.0

1,149.8

2

132.6

11.5

25.9

503.0

0.0

673.0

3

2,184.7

45.0

137.1

708.1

0.0

3,074.9

4

4,131.1

44.8

730.7

423.0

0.0

5,329.6

5

0.0

0.0

421.4

0.0

0.0

421.4

Time-averaged simulation 

Layer1

1

3,202.4

407.0

0.0

733.8

0.0

2

576.7

8.7

224.6

560.9

11.7

3

2,267.8

69.5

574.6

685.4

111.8

4

4,160.6

71.5

936.4

425.8

63.1

5

0.0

0.0

423.1

0.0

0.0

4,343.2 1,382.6 3,709.1 5,657.4 423.1

Leakage to rivers

Leakage to drains

Leakage to seepage faces

Leakage to overlying layers

Leakage to underlying layers

Pumpage

TOTAL OUT

912.2

148.4

13.9

0.0

81.5

0.0

1,156.0

180.3

29.9

1.6

369.1

88.5

0.0

669.4

522.4

877.5

329.0

620.2

723.6

0.0

3,072.7

1,139.0

2,889.1

80.9

800.0

421 .4

0.0

5,330.4

0.0

0.0

0.0

423.0

0.0

0.0

423.0

1,882.5

1,670.1

16.2

0.0

499.9

285.1

4,353.8

274.9

225.2

14.4

503.9

320.8

39.7

1,378.9

531.4

812.3

312.2

685.6

914.9

449.2

3,705.6

1,115.8

2,888.5

79.8

790.5

423.1

360.8

5.658.5

0.0

0.0

0.0

425.8

0.0

0.0

425.8

Layer 1, overburden aquifer; Layer 2, Saddle Mountains unit and confining unit; Layer 3, Wanapum unit and confining unit; Layer 4, upper Grande Ronde unit; Layer 5, lower Grande 

Ronde unit
GROUND-WATER DEVELOPMENT A29

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 then 

increased rapidly from about 1965 to 1979 (table 4). 

Since 1979, pumpage has decreased somewhat, owing 

in part to higher electrical costs for pumping the water 

and lower prices for crops. Pumpage of ground water 

from the Columbia Plateau is estimated to have been 

56,000 acre-ft in 1945, 178,000 acre-ft in 1960, and to 

have increased to a peak of about 940,000 acre-ft by 1979 

(table 4; data from Cline and Collins, 1992). By 1983, 

pumpage had dropped to about 813,000 acre-ft.

Estimates of ground-water pumpage for 1984 have 

been made for this study by Collins (1987) for the Oregon part of the Columbia Plateau, and by Cline and 

Knadle (1990) for the Washington part and a small part 

of Idaho (fig. 12). About 828,270 acre-ft of ground water 

was pumped from the regional aquifer system in 1984 

from an estimated 3,500 high-capacity wells. Between 

85 and 90 percent was used for irrigation of nearly onehalf million acres of cropland, and the remainder was 

used for public supply and industry. The relatively 

small quantity of ground water used for domestic purposes and other uses, such as stock watering, was not 

estimated in this analysis.

Of the total 1984 ground-water pumpage (fig. 12) 

from the regional aquifer system, 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 are near Hermiston, Oreg., and in three centers in Washington the 

Odessa-Lind pumping center, the Quincy basin, and 

southern Franklin County (see fig. 1 for locations).

REGIONAL GROUND-WATER FLOW

The regional ground-water flow system is described 

on the basis of results from a three-dimensional finitedifference model of ground-water flow. The model of 

the Columbia Plateau aquifer system was constructed 

(Hansen and others, 1994; Bauer and Hansen, in press) 

in order to obtain a better understanding of the groundwater flow system and the regional hydrology, and to 

provide the analytical capabilities necessary to assess 

ground-water management alternatives. The model of 

McDonald and Harbaugh (1988) as modified by Hansen 

(1993) was used to solve the ground-water flow equations.

REGIONAL FLOW MODEL

The hydraulic characteristics (model parameters) 

were estimated initially for the steady-state predevelopment conditions. The model then was calibrated to 

time-averaged conditions for current land use. These 

current conditions represent the average hydrologic 

conditions for the period from spring 1983 to spring 

1985 and approximate a steady-state condition. For the 

time-averaged simulations, the time-dependent term in 

the ground-water flow equation becomes a change-instorage term and is added to recharge term. This results 

from integrating the equation with respect to time over 

some time interval and, thus, the time-dependent term 

becomes equal to the average head change for a model 

cell over the averaging period divided by the time interval and multiplied by the estimated storage coefficient. 

The model parameters derived from the calibrated 

time-averaged model then were used in the steady-state 

model to calculate a predevelopment water-level configuration, areal distribution of ground-water discharge, and a regional water budget for the aquifer 

system. The calculated predevelopment and time-averaged water levels and water budget were compared to 

obtain an understanding of the effects of historic waterdevelopment practices. The time-averaged model then 

was used to assess some simple management strategies. 

The calibration and use of the regional flow model provided insight and increased understanding of the 

regional hydrology.

The model grid system used for these analyses consisted of five layers (fig. 3B) and 17,374 active cells (624 

for the overburden aquifer and 16,750 for the basalt 

units) for the predevelopment model, and 17,899 active 

cells (969 for the overburden aquifer and 16,930 for the 

basalt units) for the time-averaged model. The average 

cell dimensions were about 1.5 mi east to west and 2.8 

mi north to south. More cells were needed for the timeaveraged model because 525 previously unsaturated 

cells became saturated as a result of the delivery, application, and infiltration of surface water used for irrigation during the years of development (Hansen and 

others, 1994).

The regional ground-water flow system is highly 

complex because of the geometry of the aquifer system, 

variability in recharge, geologic structure, presence and 

location of major and minor stream courses, configuration of individual basalt flows, diagenetic processes, 

sediment deposition, and tectonic activity. Lateral 

hydraulic conductivity varies locally and varies as 

much as five orders of magnitude regionally; the average value for the basalts is about four orders of magnitude larger than the upper limit for rock materials that 

are considered 'tight' (Neuzil, 1986). Model-derived ver-
A30 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

122° 121° 120° 119° 118° 117° 116°

48°

47C

46°

45°

MAIilON 

V^- ,_4 CJ

 "T

 s o/ to

/ T

1JNN ' O ?.-.--:1

T-'

i VVL ' DK-CHUTKS ROOK

L-^J V V > T

120 KILOMETERS

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972 EXPLANATION 

Pumpage, in inches per year

Less than 0.1

0.1-0.2

0.2-0.5

0.5-1.0

1.0-2.0 

2.0-18.0 

Model grid 

Boundary of model 

Boundary of Columbia Plateau aquifer system study area

FIGURE 12. Ground- water pumpage from the Columbia Plateau aquifer system, 1984.
REGIONAL GROUND-WATER FLOW A31

tical hydraulic conductance varies up to eight orders of 

magnitude regionally and appears to average about 10~ 

1/s. Estimates of effective vertical hydraulic conductivity average about 1CT6 ft/s and range from about 1CT 

10 to 1(T2 ft/s.

Calculated ground-water velocities range from 1CT4 

to about 20 ft/d and generally decrease with depth 

within the aquifer system. Median estimated velocities 

for the five model layers are, from youngest to oldest, 2 

ft/d, 0.2 ft/d, 0.4 ft/d, 0.2 ft/d, and 0.1 ft/d (Hansen 

and others, 1994). The median velocities indicate that 

ground-water residence time for short flow paths (less 

than 10 mi) are on the order of a few months to 250 

years; for intermediate flow paths (10 to 30 mi), 250 to 

500 years; and for long flow paths (more than 30 mi) the 

residence time is 500 to more than 5,000 years. The long 

flow paths and slow ground-water movement in the 

deep basalts allow for the geochemical evolution of the 

flowing ground waters and precipitation of secondary 

minerals; this, in turn, affects the hydraulic characteristics of the basalts and, subsequently, the rate and quantity of ground-water movement.

PREDEVELOPMENT LAND-USE CONDITIONS

The model-calculated water budget for predevelopment land-use conditions (tables 5 and 6 and fig. 13) 

shows that, of the estimated 33,000 ft3 /s of precipitation 

that fell within the ground-water model boundaries, 

about 6,566 ft3 /s, or 20 percent (2.72 in/yr), became 

ground-water recharge. About 119 ft3 /s (0.55 in/yr) 

entered the overburden aquifer, 133 ft3 /s (0.58 in/yr) 

entered the Saddle Mountains unit, 2,185 ft3 /s (2.0 in/ 

yr) entered the Wanapum unit, and 4,131 ft3 /s (4.7 in/ 

yr) entered the upper Grande Ronde. Much of the 

recharge followed short flow paths within local flow 

systems and discharged as baseflow to small streams 

and as seeps and springs along canyon and coulee 

walls.

Of the 1,074 ft3 /s that discharged from the overburden aquifer, about 50 percent was water from underlying basalt units. About 71 ft3 /s of the discharge from 

the Saddle Mountains unit was water received from the 

overburden aquifer and the underlying Wanapum unit. 

About 840 ft3 /s of the water that discharged from the 

Wanapum unit was ground water received from other 

units and about 1,154 ft3 /s of the upper Grande Ronde 

discharge was water that had moved through other 

units.

Before water-development practices began, the saturated part of the overburden aquifer covered about 

2,910 mi2 (volume of about 140 mi3). The saturated 

deposits were located in structural basins along river

and stream courses. In these areas, typified by low precipitation, this unit received about 119 ft3 /s (0.56 in/yr) 

of recharge or less than 2 percent of the aquifer system's 

recharge. However, the unit was active hydrologically 

because it overlies regional and subregional discharge 

areas. Thus, about 15 percent of the ground water discharged through the overburden aquifer. Ground-water 

movement was from the uplands to lowlands in the 

basins and subsequently to rivers and streams, the altitude of which is the major control on the ground-water 

movement.

The predevelopment saturated part of the Saddle 

Mountains unit covered about 4,910 mi2 (volume of 

about 340 mi3), of which about 3,040 mi2 cropped out. 

The unit received about 133 ft3 /s (0.59 in/yr) of 

recharge where it cropped out. Movement of ground 

water in this unit is controlled primarily by topography 

and geologic structure, and secondarily by the heads in 

the overburden aquifer (which overlies about 38 percent 

of the unit) and the altitude of the Columbia and 

Yakima Rivers.

The Wanapum unit covers about 20,540 mi2 (volume 

of about 1,700 mi3), representing about 63 percent of the 

area within the modeled region, and about 14,750 mi2 of 

the unit crops out. This outcrop area received an estimated direct recharge from precipitation of 2,185 ft3 /s 

(2.0 in/yr), only about 24 percent of which reached the 

regional discharge area located along the Columbia and 

Snake Rivers. The remaining water in the unit discharged along short to intermediate flow paths and to 

the other units. Topography, geologic structure, and 

surface-water features control the movement of water 

within this unit. In the western part of the Palouse subprovince, individual basalt flows in the Wanapum unit 

appear to be laterally continuous and have small vertical hydraulic conductivity. Throughout much of the 

remainder of the area, the unit appears to be hydraulically well-connected to overlying units and has a highly 

variable connection to the underlying upper Grande 

Ronde. The lateral hydraulic conductivity is small in the 

high-relief areas of the Yakima Fold Belt and in other 

structurally complex areas, and is large throughout 

much of the remainder of the unit's extent.

Flow paths within the Wanapum unit are short and 

terminate at surface-water features within the Blue 

Mountains subprovince. In the Yakima Fold Belt, flow 

paths originate in topographic highs, generally anticlines where lateral hydraulic head gradients are large 

(100-200 ft/mi), and terminate along major rivers in the 

intervening synclinal valleys where hydraulic gradients 

are low (10-20 ft/mi).

r\

The upper Grande Ronde covers about 32,500 mi , 

or all but about 190 mi2 of the modeled area; the unit is 

absent in the periphery of the northeastern part of the
A32 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

119.3

452.3 ^>

912.2^

11.5^-

180.3 <

45.0 ^

522.4 <

44.8^

1, 139.0 <

R

R

R

T O) C

^

o'S

0 "~ "t

^1

i >

fT)

00 

0

"A-t 

o

i

>

O 

O

k

>

CD

1 [

3 ^>13.9

. 141

) ^>_

p|

 * 00 

DO

r

' 1

1

1

O

f

9t

1.4

13

G

D

>1.6

.29.9

> 2,184.7

«,

CMrG >329.0

D x' W4,131.1

Y G > 80.9

^

,^ D > 2,889.1

I |

Model 

layer 

number

1

2

3

4

5

Hydrogeologi 

unit

Overburden 

unit

Saddle 

Mountains 

unit

Wanapum 

unit

Grande Ron 

unit

0) 

Q. 

Q.

I 

O

EXPLANATION

Water budget Units are cubic feet per second

119.3 

^J Recharge

452.3 ^^ Leakage from rivers

912.2 <^1 Leakage to rivers

13.9 G £> Leakage to general-head boundaries

148.4 D£> Leakage to drains

°?

in Downward flow |;

A § Upward flow 

I <n

FIGURE 13. The model-calculated water budget for predevelopment (1850's) land-use 

conditions, Columbia Plateau aquifer system (From Hansen and others, 1994).

area. Thirty-seven percent of its surface area is exposed 

at the land surface and received about 4,131 ft3 /s (4.7 

in/yr) of recharge, of which about 73 percent discharged locally along short- to intermediate-length flow 

paths. About 28 percent of the recharge reached 

regional discharge areas. Topography, geologic structure, and surface-water features control the movement 

of ground water where the unit crops out. In the subsurface, the movement of ground water is controlled by the 

Wanapum unit's head configuration and dip. Over 

much of the area where the upper Grande Ronde is buried, the hydraulic head gradient is low or uniform and 

does not appear to be controlled by structural features 

as much as in the younger units. The upper Grande 

Ronde does not appear to be less permeable than overlying units; its lateral hydraulic conductivity values are 

similar to those of the Wanapum unit. However, like the 

Wanapum unit, it has lower lateral hydraulic conductivities in the Yakima Fold Belt and in other structurally 

complex areas.

The lower Grande Ronde covers about 20,110 mi2, or 

62 percent of the modeled area. It contains about 13,400 

mi of saturated rock material, which is 52 percent of

the total volume of predevelopment saturated aquifer 

within the ground-water model boundary. This model 

layer was chosen to represent the deeper flow within 

the regional aquifer system, and there is almost no 

regional hydrogeologic information pertaining to it. The 

layer receives water from and gives water solely to the 

upper Grande Ronde. The lateral hydraulic conductivity assigned to the lower Grande Ronde is based on the 

distribution and magnitude of lateral hydraulic conductivity in the upper Grande Ronde and the assumption 

that the basalts would be less permeable with depth 

(Hansen and others, 1994). Although the lower unit covers a large area and includes an extensive volume of 

rock and ground water, only about 422 ft3 /s of ground
REGIONAL GROUND-WATER FLOW A33

water is estimated to be moving through it. For comparison, the lower Grande Ronde's volume is 100 times 

greater than that of the saturated overburden aquifer 

during predevelopment times, but the quantity of water 

moving through it is only 37 percent of that moving 

through the overburden aquifer.

CURRENT LAND-USE CONDITIONS

The calculated water budget for the time-averaged 

simulation (tables 5 and 6 and fig. 14) shows that about 

10,205 ft3 /s (4.24 in/yr) of recharge enters the groundwater system, an increase of 3,640 ft3 /s (1.52 in/yr) 

from predevelopment conditions. The additional 

recharge is mainly due to the delivery, application, and 

infiltration of applied irrigation water. About 3,202 ft3 /s 

(9.6 in/yr) enters the overburden aquifer (an increase of 

about 3,083 ft3 /s), 577 ft3 /s (2.6 in/yr) enters the Saddle 

Mountains unit (a 444 ft3 /s increase), 2,268 ft3 /s (2.3 in/ 

yr) enters the Wanapum unit (an 83 ft3 /s increase), and 

4,161 ft3 /s (4.7 in/yr) enters the upper Grande Ronde (a 

30 ft3 /s increase; see table 6).

There is about 400 mi3 of water in storage in the 

aquifer system under current land-use conditions; as a 

comparison, Franklin D. Roosevelt Lake, created by the 

construction of Grande Coulee Dam, has about 2.8 mi3 

of water in storage. However, owing to the control 

exerted by the hydraulic characteristics and geometry 

of the aquifer system, the fact that much of the recharge 

is discharged locally in short flow paths, and based on 

the observed water-level declines and relative age of the 

ground water, all the recharge cannot be considered 

water available for use. Usable storage in the aquifer 

system, based on the estimated predevelopment to current decrease in storage (about 2,400 ft3 /s), is on the 

order of 0.5 to 1 mi3.

Of the total recharge to all units, about 5,595 ft3 /s 

(55 percent) discharges to drains and about 3,804 ft3 /s 

(37 percent) discharges to rivers (table 5). Discharge 

through seepage-face boundaries is only 4 percent of 

the recharge and is about the same as under predevelopment conditions. Pumpage is about 1,135 ft3 /s, or 

about 11 percent of the recharge. Two interrelated facts 

can be noted here: overall discharge exceeds recharge 

by 7 percent, and, because ground-water pumpage 

locally exceeds the sum of recharge and ground-water 

inflow, water levels have declined locally The leakage 

from rivers and the decrease in storage provide for the 

excess discharge. Although these two quantities are 

small, they are important locally as sources of water. 

For example, the decrease in storage from spring 1983 

to spring 1985 amounts to about 16 percent of the 

ground-water pumpage. Along parts of Crab Creek and

within the Odessa-Lind pumping center, river leakage 

and decrease in storage provide water for ground-water 

irrigation. Similarly, leakage from the Umatilla River in 

Oregon locally appears to supply water for groundwater pumpage.

About 110 percent of the recharge to the overburden 

aquifer discharges to drains and rivers. Leakage from 

rivers and from underlying basalts supplies an additional 1,144 ft3 /s of water to the overburden aquifer 

(table 6). The leakage of water from the overburden 

aquifer to underlying basalts is about 500 ft3 /s. Thus, 

the difference between the quantity of water moving 

into and out of the bottom of the overburden aquifer 

indicates that only about 7 percent of the overburden 

discharge from the aquifer system is flow received from 

underlying basalt units. About 7 percent of the total 

overburden aquifer discharge is ground-water pumpage.

Of the approximately 577 ft3 /s (2.6 in/yr) of 

recharge to the Saddle Mountains unit, about 47 percent 

discharges locally and the remainder discharges along 

intermediate-length flow paths or moves to other units. 

Leakage to overlying and underlying layers exceeds the 

leakage from those layers to the Saddle Mountains unit 

by about 39 ft3 /s. Pumpage from the Saddle Mountains 

unit amounts to only about 7 percent of the recharge. 

However, pumpage is locally important, as can be seen 

by the change in storage (table 6), which is about 30 percent of the pumpage.

The Wanapum unit receives about 2,268 ft3 /s (2.2 

in/yr) of recharge, of which about 48 percent discharges 

locally, slightly less than under predevelopment conditions. About 12 percent of the Wanapum unit's total discharge is pumpage, and about 43 percent is discharge to 

other layers. The change in storage is about 25 percent 

of the Wanapum unit's pumpage. Leakage to seepageface boundaries (part of the local discharge) from the 

Wanapum unit, although only about 14 percent of 

recharge, is nearly 70 percent of the pumpage and is, 

thus, an important budget item. The Wanapum unit has 

a net loss of water to the overlying overburden aquifer 

and Saddle Mountains unit of about 111 ft3 /s, which is 

about 373 ft3 /s less than under predevelopment conditions. There is a net loss to the upper Grande Ronde of 

about 230 ft3 /s, which is about 215 ft3 /s more than 

under predevelopment conditions.

The upper Grande Ronde discharges about 2,970 

ft3 /s locally along short-to intermediate-length flow 

paths; this is about 51 percent of the unit's total discharge and about 70 percent of its recharge. The 

ground-water pumpage for the upper Grande Ronde 

unit is only about 6 percent of its discharge. In comparison to the Wanapum unit, the upper Grande Ronde's 

larger ground-water storage reservoir and greater lat-
A34 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

407.0

1,882.5

8.7^

274.9

69.5

531.4

71.5

1,115.8

3,202.4

V

R

R

R

R

°> o °* 00 OOC 1 l& Oi ZbO.I CM

If) A J 4-

ID ^

"t

LT)

I i

i

-4HCO

iri

o

39.7

>

00 

LO

k

>

>

CO 

CM

I

^

Si 1

G

D

>16.2

1,670.1

^V576-7

 rv. G >14.4

 ^i °

I./ CM 99R 9 

00 ^ZZO.Z

0

449.2

'

*t

1

>

I u p- 2,267.8

ID IB ^

111.8 5;

I

G > 312.2 

812.3

D > ^4,160.6 oi G>79-8

360.8 ,S 63- 1 D >2,889.5

T

Model 

layer 

number

1

2

3

4

5

Hydrogeologi 

unit

Overburden 

unit

Saddle 

Mountains 

unit

Wanapum 

unit

Grande Rond

unit

o>

Q. 

Q.

13

o> 

1

3,202.4

EXPLANATION 

Water budget Units are cubic feet per second

Recharge

407.0 ^-^ Leakage from rivers 

1882.5 <1 Leakage to rivers 

16.2 G P> Leakage to general-head boundaries 

1870.1 D[~> Leakage to drains

11.7

Downward flow

Upward flow

Pumpage

Rate of change in storage

285.1

FIGURE 14. The model-calculated water budget for current (1980's) land-use 

conditions, Columbia Plateau aquifer system (From Hansen and others, 1994).

eral ground-water inflow in areas of pumpage have 

resulted in smaller water-level declines. Thus, the loss 

in storage is only about 17 percent of the pumpage and 

2 percent of the recharge. Pumpage is compensated for 

primarily by vertical leakage from the overlying 

Wanapum unit and secondarily from decrease in storage, increase in recharge, and increase in leakage from 

rivers (table 6).

The water budget and flow system for the lower 

Grande Ronde are similar to those under predevelopment conditions; differences mainly relate to local 

changes in lateral head gradient and the vertical head 

gradient between it and the upper Grande Ronde.

The total quantity of ground water that moves 

between layers is about 4,565 ft3 /s, or about 45 percent 

of the time-averaged recharge (fig. 14). The remaining 

55 percent of recharge remains in the unit it enters and 

discharges along short flow paths within local flow systems and along intermediate- to regional-length flow 

paths. Although ground-water travel times are both relatively large and increase with depth, the quantity of 

water moving between layers indicates an active flow 

system.

The overburden aquifer has a net gain of about 234 

ft3 /s from underlying units. This water discharges both 

locally and to the major rivers. Upward flow to the 

overburden aquifer typically occurs at or near the 

regional discharge area.

About 1,610 ft3 /s of ground water moves between 

the Saddle Mountains unit and other units; this quantity is about 280 percent of its recharge. The Saddle 

Mountains unit loses about 279 ft3 /s to the overburden 

aquifer and gains about 234 ft3 /s from the underlying 

basalt units, resulting in a net loss of about 39 ft3 /s. 

Under predevelopment conditions, the unit had a net 

gain of about 71 ft3 /s from the other layers (table 6).
EFFECTS OF HISTORICAL WATER-DEVELOPMENT PRACTICES A35

About 2,860 ft3/s of ground water (126 percent of its 

recharge) moves between the Wanapum unit and other 

units. Of this quantity, about 1,260 ft3 /s is water gained 

from other units and about 1,601 ftVs is water lost to 

other units, or a net loss of water from the unit of about 

341 ft /s. About 45 percent of the gains are from overlying units and about 55 percent are from the upper 

Grande Ronde unit. Leakage to the overlying units and 

to the upper Grande Ronde is about 43 and 57 percent 

of the losses, respectively As a result, the overburden 

aquifer, Saddle Mountains unit, and upper Grande 

Ronde have a net gain from the Wanapum unit. The first 

two units receive most of the gain, mainly at or near the 

regional discharge area, and this gain is about 75 percent less than under predevelopment conditions. The 

upper Grande Ronde gains about 93 percent more than 

under predevelopment conditions.

About 2,576 ft3 /s of ground water (about 62 percent 

of its recharge) moves between the upper Grande 

Ronde and other units, about 8 percent more than under 

predevelopment conditions. As a result of changes in 

the regional flow system, the upper Grande Ronde has a 

net gain in ground water of about 149 ft3 /s; under predevelopment conditions, this unit had a net loss of 

about 68 ft3 /s.

The total simulated quantity of water moving 

through both the top and bottom of each aquifer unit 

(excluding recharge), from youngest to oldest, is about 

1,234 ft3 /s, 1,610 ft3 /s, 2,860 ft3 /s, 2,576 ft3 /s, and 850 

ft /s. The units listed in order of flow are Wanapum 

unit, upper Grande Ronde, Saddle Mountains unit, 

Overburden aquifer, and lower Grande Ronde, respectively. The upper three units are more active than under 

predevelopment conditions. For example, the overburden aquifer has about 574 ft3 /s more water moving 

between it and underlying units and the Saddle Mountains unit has 623 ft3 /s more water moving between it 

and other layers (table 6).

EFFECTS OF HISTORICAL WATERDEVELOPMENT PRACTICES

The aquifer system is a dynamic system that is constantly receiving and discharging water. When recharge 

to and discharge from the aquifer system are equal, the 

ground-water system is in equilibrium and water levels 

remain constant from year to year. If recharge exceeds 

discharge, water levels rise; if discharge exceeds 

recharge, water levels decline. Water-level changes, in 

turn, reflect changes in the quantity of ground water in 

storage. Excluding climatic effects, changes in recharge 

and discharge are caused by water-development practices.

Water-development practices include ground-water 

pumpage, application of most of the pumpage to croplands, delivery and application of surface water to croplands, alterations in land use (including the agricultural 

practice of fallowing nonirrigated croplands), and the 

construction of dams. The changes in recharge and discharge on the plateau caused by these practices, in turn, 

result in changes in water levels.

The net regional effect of water-development practices can be seen by comparing the information presented in table 5 for the regional aquifer system and in 

table 6 for the model layers. The largest single change in 

the regional water budget was an increase in recharge 

of about 3,640 ft3 /s (table 5). The increase is due to the 

infiltration of delivered and applied surface water. The 

increased recharge is more than balanced by leakage to 

rivers (29 percent of increased recharge), leakage to 

drains (45 percent of increased recharge), and groundwater pumpage (31 percent of increased recharge). Most 

of the increased recharge enters the overburden aquifer 

(about 84 percent) and a smaller quantity enters the 

Saddle Mountains unit (12 percent). Therefore, these 

two units have been affected most by increased 

recharge due to water-development practices. Correspondingly, the largest increases in leakage to rivers 

and drains occur within these two units. The changes in 

recharge and leakage to rivers and drains for the 

Wanapum unit and the upper Grande Ronde are minor 

compared with changes for the overburden aquifer and 

the Saddle Mountains unit. However, leakage to drains 

from the Wanapum unit has decreased by about 8 percent, whereas it increased for the rest of the system. This 

decrease represents a net loss of streamflow resulting 

from ground-water pumpage.

The flow between layers has been changed as a 

result of the increased recharge in the overburden aquifer and Saddle Mountains (table 6). The Wanapum unit 

now receives four times more water from these units 

because they overlie the Wanapum unit in the areas 

with the largest increases in recharge. Thus, the largest 

changes in water-budget components for the Wanapum 

unit occur in the quantity of water it receives from the 

overlying units and the additional water it provides to 

the upper Grande Ronde. The spatial distribution of 

these changes, combined with the effects of groundwater pumpage, has caused water-level changes.

The difference between model-calculated water levels for the time-averaged and the predevelopment simulations shows the simulated water-level changes that 

have occurred as a result of water-development practices. These model-calculated changes are in general 

agreement with data from local studies. Model-calculated water-level changes are shown on figure 15 for the
A36 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

122° 121° 120° 119° 118° 117° 116°

SKAGirr u| " ' I n MI> i"

JOKIELU; I tONNDfe' I LJNCOIJN'

48°

47°

46°

45°

 tm&ri^

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972 EXPLANATION

Water level change, in feet

Rise of more than 400

Rise of 300-400 

Rise of 200-300 

Rise of 100-200 

Rise of 0-100 

Decline of 0-100 

Decline of 100-200

Decline of 200-300

Decline of 300-400

Decline of more than 400 

Model cells calculated as desaturated 

Cells where aquifer is thin or absent-Not included in model 

Boundary of Wanapum unit as modeled 

Boundary of Columbia Plateau aquifer system study area

FIGURE 15. Model-calculated water-level changes in the Wanapum unit from predevelopment to present (1980's).
EFFECTS OF HISTORICAL WATER-DEVELOPMENT PRACTICES A37

Wanapum unit; the patterns of change are generally 

similar in the other units.

For the overburden aquifer, there has been a median 

water-level rise of about 12 ft. The rises have led to the 

saturation of about 32 mi3 of sediments (an increase of 

water in storage of about 10 million acre-ft). The overburden aquifer has been saturated throughout an additional 1,600 mi2 where the sediments previously were 

unsaturated. These changes were caused by the 

increased recharge, which in turn is a result of the infiltration of applied surface water to croplands; the surface-water application rate averages about 4 ft/yr on 

the plateau. The largest changes have occurred in the 

CBIP, where water-level rises are as much as 300 ft. 

Rises have not been as large in the extensively surfacewater-irrigated Yakima River basin because water levels 

were already near land surface and most of the overburden was already saturated in this basin. Thus, most 

rises there have been generally less than about 10 ft. 

Water-level declines have occurred in only a few locations within the overburden aquifer. The model indicates some local declines, on the order of 10 ft, in the 

Wenas Creek valley (tributary to the Yakima River). 

Declines of as much as 40 ft also are indicated along the 

eastern edge of the overburden aquifer in the Walla 

Walla River basin where the overburden aquifer is 

pumped. Throughout the remaining part of the Walla 

Walla River basin, water levels have risen 5 to 30 ft.

As with the overburden aquifer, throughout much of 

the extent of the Saddle Mountains unit water levels 

have risen; the average and median rise are about 65 

and 20 ft, respectively. The rises have, in turn, saturated 

about 23 mi (an increase of water in storage of about 

1.6 million acre-ft) of the Saddle Mountains unit, as well 

as an additional area of about 839 mi2 where the sediments previously were unsaturated. The largest rises 

have occurred within the lower CBIP north of Pasco, 

Wash., where rises have exceeded 300 ft. Rises have 

occurred throughout the extent of this unit where it 

underlies the valley floor in the Yakima River basin. 

Because water levels are near land surface, the rises in 

the Yakima basin have been smaller than those in the 

CBIP. However, larger rises, as much as 100 ft or so, 

have occurred where the overburden aquifer is thin or 

absent and in tributary valleys of the Yakima River. 

Rises also have occurred along the Columbia River in 

both Oregon and Washington between the Umatilla 

River and Willow Creek. Except for some places along 

the Columbia River where dams have an effect, the rises 

result from surface-water irrigation. Water-level 

declines have been small and local, mainly in small valleys within the Yakima Fold Belt.

The general effect of water development on the 

overburden aquifer and the Saddle Mountains unit has

been to raise the water-level altitudes throughout most 

of their extent. Declines in these units have been local 

and small. This is because little water is pumped from 

the Saddle Mountains unit, and the water pumped from 

the overburden aquifer is generally from areas of surface-water irrigation. In those areas, the pumpage typically is derived from stored water from irrigation 

recharge and water in streams, canals, and irrigation 

drains.

Water-level rises and declines in the Wanapum unit 

have been much more widespread (fig. 15). In areas of 

intensive surface-water irrigation, such as the Yakima 

River valley, CBIP, and parts of Oregon between the 

Umatilla River and Willow Creek, water levels have 

risen. These rises average about 55 ft (median of 10 ft) 

and range from 1 to more than 300 ft. The area affected 

by rises is some 6,600 mi2 (about 35 percent of the unit's 

area), although the area with rises greater than about 10 

ft is some 3,930 mi2. Water-level rises are smaller where 

the regional streams are near the top of the Wanapum 

unit. Rises are larger in upland areas where the top of 

the Wanapum unit is above the regional streams. In 

these areas, water levels in the Wanapum unit were 

already above the regional streams, increasing lateral 

head gradients due to the hydraulic characteristics of 

the rock materials.

The East Low Canal (fig. 1) marks the general 

boundary in the central plateau between water-level 

rises in the Wanapum unit to the west and water-level 

declines in the Wanapum unit to the east. Water levels 

began to rise with the completion of the canal and 

importation and application of Columbia River water in 

the early 1950's for the CBIP; in most areas 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. 16) illustrate this steady rise. The largest 

rises have occurred in the Quincy basin, as much as 300 

ft, and in areas southeast and northeast of Potholes Reservoir, as much as 150 ft.

Water levels declined in the Wanapum unit throughout about 13,400 mi2 (about 65 percent of the area); 

declines were greater than about 10 ft in about 7,450 

mi2. Water-level declines, resulting from pumping 

ground water for irrigation, began in the 1960's and are 

concurrent with the increase in irrigated acreage. The 

initial declines were in five areas: (1) western Adams 

and southern Lincoln Counties, Wash, (the Odessa-Lind 

pumping center), (2) Walla Walla River basin, Wash., (3) 

the Pullman-Moscow area in Washington and Idaho, (4) 

The Dalles, Oreg., and (5) the Hermiston, Oreg. area 

(fig. 1). Water levels began to decline in the Horse 

Heaven Hills in the early 1970's. Declines average about 

60 ft (median value of about 9 ft) and in places have 

exceeded 200 ft. The largest declines occur in the
A38 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

0

50

100

150

200

250

15N/45E-32N03 238 feet in Wanapum and Grande Ronde unit

300

i i i r

i i I i i I i i I i i I i i I i i I i i I i i I i i I i i I i i I i i I i i

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

YEAR 

19N/23E-34R01 234 feet in Wanapum unit

LU

S 50

cc

^

_r<? 100

LU O

rc > 150

LU >

h- O

5 m 200

LU 

LU

^ 250

 ^nn

i , | i , | , , | , , | , , | , , | , , | , , | , , | , , | , , | , , | , ,

-

: / -

, , l i , l , , l , , l , , i , , i , , i , , i , , i , , i , , i , , i , ,

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

YEAR 

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

u

LU

< 50

LL

CC

=3

_rj? 100

LU O

> z

LU<

o:^ 150

LU >

h- O

< -1

5 m 200

LU

LU

^ 250

300 

, , | i i | , , | , , | i , | , i | , , | , , | , , | , , | , , | , , | , ,

"

_ 

_ _

~~ - -r-"""^ ~~

^^*\ '\A /A/An

: X ~

 -^ 

 - ^. ~

 

", . 1 1 . 1 1 , 1 , , 1 , , 1 , , 1 . , 1 , , 1 , , 1 , , 1 , , 1 , , 1

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

YEAR

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

LU

< 50

LL

CC

_r<!? 100 ii i O

> z

LU <

a: d 150

LU >

h- O

< -1

5£ 200

LU 

LU

^ 250

 ann

. 1 1 . 1 1 1 1 1 1 1 1 II 1 1 1 1 1 < 1 < < , < 1 1 I I 1 I I 1 I 1 1 I 1

"

 

» ^

NiflrXT nflf !*' i / i i ' ii rA 1 ( i 1 ^

 ' U ' ^

n/i ^

 A/w A

A-i "''/ A j* * *

~ 1 * -

, , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , , 1 , ,

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

LOCATION OF WELLS

EXPLANATION 

19N/23E-34R01 Well number

A Non-static water level

Note: Water-level fluctuations due to pumping

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

YEAR

FIGURE 16. Hydrographs of selected wells showing long-term water-level changes.
EFFECTS OF HISTORICAL WATER-DEVELOPMENT PRACTICES A39

Odessa-Lind pumping center, within some of the valleys in the Yakima Fold Belt, on the south slope of Horse 

Heaven Hills, in the pumping center near Umatilla, 

Oreg., and in the Walla Walla River basin (fig. 15). The 

hydrographs of wells 15N/45E-32N03 and 17N/32E19E01 (fig. 16) illustrate some of these declines. In general, water levels in those areas continue to decline, and 

the size of the areas affected has increased with time. 

The rate of water-level decline, however, has decreased, 

at least in the central part of the plateau (Lane and 

Whiteman, 1989).

In several of these areas, the declines have been 

moderated by the rising water levels in nearby surfacewater irrigated areas. These rises have increased gradient, and thus supply additional water to the pumping 

centers. A good example of this is the narrow transition 

zone between water-level rises in the CBIP and waterlevel declines beginning just east of the East Low Canal 

and extending into the Odessa-Lind area. Simulation, 

using the predevelopment model, of the affects of the 

additional recharge resulting from the surface-water 

irrigation indicated a water-level rise of 10 to 100 ft over 

a large part of the Odessa-Lind pumping center.

The effects of water development on the upper 

Grande Ronde have been to raise water levels over 

about half of its area and to lower water levels over the 

remainder. Rises have averaged about 30 ft (median of 

about 14 ft) and declines have averaged about 35 ft 

(median of about 6 ft). Model-calculated rises and 

declines are in excess of 200 ft. The rises have occurred 

in the surface-water-irrigated areas and along the manmade reservoirs of the major rivers. The largest rises 

have occurred in the Quincy basin. Declines have 

occurred in areas of ground-water pumping, mainly 

centered in the Odessa-Lind area of Washington and the 

Umatilla area of Oregon. Smaller scale declines have 

occurred in the Pullman-Moscow area and in the Horse 

Heaven Hills area. Local declines have also occurred 

throughout the plateau.

Projected rises and declines in the lower Grande 

Ronde cannot be verified because there are no data. The 

model-calculated water-level changes are only a preliminary and coarse estimate of the effects of water development on the deep flow system. The largest modelcalculated rises, up to about 150 ft, are in the northwest 

Quincy basin. Smaller rises are indicated in other surface- water-irrigated areas and along the major rivers. 

Declines of as much as 170 ft are calculated for the 

Odessa-Lind area in Washington, and as much as 50 ft 

for the Umatilla, Oreg., area. The distribution of rises 

and declines for the lower Grande Ronde are similar to 

those for the upper Grande Ronde, but the magnitude 

of these changes is less. As with the upper Grande 

Ronde, declines in the lower Grande Ronde have spread

north and east from the Odessa-Lind area and the 

southern extent of declines is delineated by a narrow 

east-west strip of low hydraulic conductivity that 

extends eastward from the Saddle Mountains anticline 

to the vicinity of the mouth of the Palouse River.

Water-level rises and declines of more than a few 

feet affect regional patterns of ground-water movement. 

The dominant direction of ground-water movement 

across the northern half of the plateau prior to the 

development of an agriculture-based economy was simulated as south-westerward, from the northern and 

eastern plateau margins toward the Columbia and 

Snake Rivers. The complex pattern of flow in this area, 

mapped for the Wanapum unit (fig. 7) and simulated 

for current conditions, reflects the combined effects of 

water-level rises and declines.

The effects of water development in 27 selected 

basins (table 7) were analyzed through the model-calculated changes in ground-water discharge (Hansen and 

others, 1994). Ground-water discharge decreased in 

about half the basins; some of the decreases were small. 

Ground-water discharge in the other basins either 

remained about the same or increased in comparison to 

results for simulated predevelopment conditions. Largest decreases were in the Cow Creek, upper Crab Creek, 

Bowers Coulee, South Fork Palouse River, and Little 

Klickitat River basins. For example, ground-water discharge in Cow Creek basin decreased from about 41 ft3 / 

s under predevelopment conditions to about 23 ft /s 

under 1983-85 conditions. Similarly, the discharge in 

Crab Creek basin decreased by about 38 ft3 /s, from 63 

to 25 ft3 /s. Ground-water discharge increased in several 

of the basins, although only in Glade Creek, in Washington, was the percentage of increase large, from 0 to 

7.9 ft3 /s.

In the model analysis by Hansen and others (1994), 

ground-water discharge to 16 selected stream reaches 

was calculated (table 8). The model-calculated groundwater discharge to 7 of the 16 selected stream reaches 

has increased significantly due to water development. 

The seven reaches are the upper Columbia River, lower 

and upper Yakima River, lower Crab Creek, Walla Walla 

River, Naches River, and the Rocky Ford-Crab Creek. 

The upper Columbia River receives an additional 540 

ft3 /s of ground-water discharge when compared with 

predevelopment conditions. This increase is caused by 

the rise in water levels in CBIP. This quantity is insignificant when compared with the flow in the Columbia 

River. The upper Yakima River now is estimated to 

receive about 304 ft3 /s of ground-water discharge, an 

increase of about 118 ft3 /s. The calculated ground-water 

discharge to the lower Yakima River has increased from 

about 45 ft3 /s to about 425 ft3 /s. The model calculations 

indicate that the Yakima River now receives about 500
TABLE 7. Model-calculated ground-water discharge, estimated recharge, and average stream/lows for drainage basins with streamflow record

Columbia Plateau aquifer system (from Bauer and Hansen, in press)

[Values in cubic feet per second; Cr, Creek; R, River; S., South; Wash., Washington; Oreg., Oregon; CBIP, Columbia Basin Irrigation Project]

Total simulated discharge to basin (river + drain + seep

CBIP ex

Basin

Rebel Flat Cr.

Pine Cr.

Bowers Coulee

Glade Cr.

S. Fork Palouse R.

Alkali Flat Cr.

Alder Cr.

Dry Cr. 

Rock Cr., Wash.

Wilson Cr.

Cow Cr.

Naneum Cr.

Hawk Cr.

Union Flat Cr.

Crab Cr.

Foster Cr.

Willow Cr.

Douglas Cr. 

Rock Cr., Oreg. 

Asotin Cr.

Little Klickitat R.

Ahtanum Cr.

Touchet Cr.

Walla Walla R.

Satus Cr.

Tucannon R.

Umatilla R.

Drainage 

area, in 

square 

miles

79

66

992

427

125

158

254

52 

415

437

543

83

168

172

1,015

322

837

598 

515 

173

287

126

725

132

577

430

2,436

Estimated recharge

Predevelopment

17.6

4.4

74.0

5.2

18.3

26.9

19.3

16.7 

36.2

30.3

88.4

52.7

27.9

39.1

129.1

29.9

34.3

44.3 

58.5 

79.9

132.3

104.3

164.0

151.1

231.3

212.2

680.7

1983-85

17.6

4.4

77.5

22.1

18.3

26.9

21.7

14.7 

37.1

51.2

80.9

52.7

27.9

39.1

106.3

28.6

104.0

36.2 

58.5 

80.0

132.3

108.6

148.0

152.3

231.4

203.5

719.8

Streamflow1

Total

12.7

9.8

6.4

36.

--

17.0

25.2 

107.

14.5

24.

78.

--

35.

68.

--

31.

3.1 

54. 

78.

177.

78.

172.

325.

287.

197.

750.

Estimated 

baseflow

1.2

6.2

0.0

1.3

18.

1.2

1.2

7.1

37.

0.0

13.

46.

8.8

0.0

19.

2.0

0.0

0.0

7. 

44.

22.

46.

.8

230.

134.

129.

328.

Predevelopment

0.0

1.6

12.3

0.0

14.5

9.6

11.1

14.3 

21.9

16.9

40.9

23.2

25.9

24.2

62.8

30.9

64.9

43.8 

56.5

75.5

100.8

99.6

124.3

159.4

162.5

174.9

552.9

1983-85 

timeaveraged

0.0

2.0

2.7

7.9

8.6

9.5

9.6

12.0 

21.5

21.6

22.9

23.8

23.8

24.3

24.7

27.4

63.2

37.1 

54.6

75.3

79.0

102.3

109.1

160.7

164.2

168.7

555.6

Phase 1

1983-85 

equilibrium

0.0

2.0

1.0

6.4

8.6

9.4

7.8

12.0 

20.7

21.1

11.1

23.8

23.1

23.9

20.6

27.4

62.0

36.9 

54.1 

75.2

78.4

102.4

109.1

160.6

164.0

168.7

549.1

1983-85 

pumpage

0.0

2.0

7.3

6.4

8.6

9.4

7.8

12.0 

20.7

21.3

12.0

23.8

23.3

23.9

23.1

27.4

62.0

37.1 

54.1

75.2

78.4

102.4

109.1

160.6

164.0

168.7

549.1

Reduced 

pumpage

0.0

2.0

8.6

6.4

8.6

9.4

7.8

12.0 

20.8

21.5

12.6

23.8

23.4

23.9

23.4

27.4

62.0

37.1 

54.1 

75.2

78.4

102.4

109.1

160.7

164.0

168.7

549.2

1 Average values for periods of record during 1956-77.
EFFECTS OF POTENTIAL WATER-MANAGEMENT ALTERNATIVES A41

TABLE 8. Model-calculated ground-water discharge to selected stream reaches, Columbia Plateau aquifer system (from Bauer and Hansen, in press)

[Values in cubic feet per second; CBIP, Columbia Basin Irrigation Project]

CBIP expansion

Phase 1

Stream reach

Upper Columbia River 

Snake River

Lower Yakima River

Lower Columbia River

Upper Yakima River 

Klickitat River

Palouse River

Lower Crab Creek

Walla Walla River

Naches River

Rocky Ford-Crab Creek 

Grande Ronde River

Spokane River 

Deschutes River

John Day River 

Moses Coulee

Predevelopment

291.1 

491.7

45.3

383.9

185.4

217.2

160.4

76.3

72.1

54.7

10.8 

74.0

52.4 

47.4

42.5 

11.5

1983-85 

time-averaged

831.4

435.5

424.8

354.1

303.8

225.7

164.3

145.1

115.3

97.5

90.9 

74.0

51.5 

50.6

45.9 

9.8

1983-85 

equilibrium

827.1 

428.0

417.9

333.6

303.4

225.7

140.5

140.3

114.6

95.7

87.6 

74.0

51.4 

50.4

45.6 

9.2

1983-85 

pumpage

840.8 

433.0

418.2

333.7

303.4

225.7

142.6

144.6

114.8

95.7

98.5 

74.0

51.4 

50.4

45.6 

9.2

Reduced 

pumpage

842.6 

434.9

418.3

333.7

303.4

225.7

144.0

146.9

114.9

95.7

104.7 

74.0

51.4 

50.4

45.6 

9.2

Phases 1 and 2

1983-85 

pumpage

850.6 

449.0

418.9

333.8

303.4

225.7

150.1

152.2

115.3

95.7

103.1 

74.0

51.4 

50.4

45.6 

9.2

Reduced 

pumpage

857.4 

456.1

419.4

334.1

303.4

225.7

158.1

162.8

115.5

95.7

114.3 

74.0

51.4 

50.4

45.6 

9.3

ft3 /s more ground-water discharge than under predevelopment conditions. The increased ground-water discharge is due to return flows resulting from the 

infiltration of delivered and applied excess surface 

water. Much of this excess water flows through the 

overburden aquifer to drains that discharge to the 

Yakima River; that quantity is not included in the 500 

ft3 /s. The 500 ft3 /s is relied upon for meeting downstream water rights. Lower Crab Creek receives an 

additional 69 ft3 /s, as calculated by the model. The 

increase in ground-water discharge is from irrigation 

return flow from both CBIP and ground water from the 

rising water levels in the Wanapum unit. The simulated 

increase in ground-water discharge to the Walla Walla 

River was about 43 ft /s; the increase is due to surfacewater irrigation. The calculated ground-water discharge 

to the Naches River has increased from about 55 ft3 /s to 

98 ft3 /s, due to surface-water irrigation in the Naches 

River basin. Last, the Rocky Ford-Crab Creek area 

(defined as the area around Potholes Reservoir, fig. 1) 

has a calculated increase of about 80 ft3 /s (from 11 ft3 /s 

for predevelopment conditions to 91 ft3 /s). This 

increased discharge also is due to the application of surface water in the CBIP. Each of these seven stream 

reaches crosses part of the areas of calculated rises in 

water levels.

Generally, ground-water discharge to the stream 

reaches does not appear to have decreased significantly. 

However, decreases in discharge to streams have

occurred both in the selected basins analyzed and for 

some of the model drain cells not included in the basins.

EFFECTS OF POTENTIAL WATERMANAGEMENT ALTERNATIVES

The ground-water model was used principally to 

obtain a better understanding of the regional groundwater flow system and the relation between the various 

components of the flow system. However, five steadystate simulations also were completed to estimate the 

effects of potential water-management alternatives 

(Bauer and Hansen, in press).

The first simulation was made to estimate the longterm effects of the 1983-85 distribution of pumpage and 

recharge; the time-averaged model was used without 

the 1983-85 change-in-storage term. This simulation 

represents the long-term, 1983-85 equilibrium conditions under current water-management strategies.

The other four simulations were made to estimate 

the effects of the proposed further development (expansion) of CBIP. The expansion area covers most of the 

Odessa-Lind pumping center in Washington. The CBIP 

originally was authorized for the development of 

1,095,000 acres to receive Columbia River water; about 

556,000 acres currently are developed. Under the proposed expansion, the remaining 538,500 acres would be 

developed.
A42 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

On the basis of information from the Water Conservation Steering Committee (1987), the expansion would 

proceed in two phases, and there are several proposed 

alternatives for each phase. The existing Alternative A 

phase 1 (about 160,000 acres) and phase 2 (about 

378,500 acres) developments were chosen for simulation. Each phase of development (160,000 acres for 

phase 1 and 538,500 acres for phases 1 and 2) was simulated under an annual irrigation-application rate of 4.0 

ft/yr, the estimated average current operating rate for 

CBIP.

On the basis of the observed historical water-level 

rises in CBIP, it is estimated that drains would be 

needed at every model cell with new surface-water 

application; therefore, drains were added to all these 

model cells. Additionally, recharge to those cells caused 

by the infiltration of the surface water delivered and 

applied to croplands was estimated from the information presented in Bauer and Vaccaro (1990). Climate, 

and thus ground-water recharge, was assumed to be 

invariant, and because the simulations were steadystate, a time-history of the effects was not examined.

For two of the four simulations, phase 1 and phase 1 

plus 2, 1983-85 pumpage was kept the same. For the 

other two simulations the pumpage was reduced for a 

ground-water model cell in proportion to the percentage of area of the cell included in the proposed CBIP 

expansion. In order to isolate the effects of the proposed 

expansion of CBIP, the model results (discussed later in 

this section) were referenced to the calculated 1983-85 

equilibrium conditions.

EQUILIBRIUM CONDITIONS

The first simulation, representing the long-term 

effects of 1983-85 water-management strategies, indicated that the largest changes in the flow system would 

occur in the Wanapum unit. The water budget and 

water-level configuration calculated by the model for 

the overburden aquifer remained about the same; continued pumpage from this unit slightly decreased the 

quantity of water discharging from it to drains.

The effects on the Saddle Mountains unit were limited to the Yakima Fold Belt in the Moxee-Selah-Cold 

Creek tributary valleys and to the western part of Horse 

Heaven Hills. The water-level configuration and water 

budget would remain nearly the same throughout the 

remainder of the Saddle Mountains unit. For the areas 

in the Yakima Fold Belt, calculated water-level declines 

would exceed 100 ft and some areas would become 

unsaturated. This is due to the pumping from both the 

Saddle Mountains unit and the underlying Wanapum 

unit. The declines would extend throughout some 80

mi2, and the model calculated the desaturation of some 

160 mi2 of the unit. The model-calculated desaturated 

areas generally are areas where the unit is thin, presently is saturated, receives only a small quantity of 

recharge, and has little to no potential for lateral inflow 

(small upgradient contributing area).

The model-derived estimates of changes in water 

levels (all declines) from the 1983-85 simulation for the 

Wanapum unit (fig. 17) show that the largest declines 

would occur in the Odessa-Lind pumping center, near 

The Dalles, Oreg., near Butter Creek, Oreg., near Glade 

Creek, Wash., on the south slope of Horse Heaven Hills, 

and in the Moxee-Selah-Cold Creek tributary valleys 

within the Yakima Fold Belt; calculated declines in 

those areas are generally less than 200 ft, but exceed 500 

ft locally The areal extent of the declines is large: 1- to 

75-foot declines cover about 200 mi2; 75- to 150-foot 

declines, about 180 mi2; and model cells that desaturate, 

some 400 mi2. About 4 percent of the area of the 

Wanapum unit is affected by declines. In the OdessaLind pumping center alone, about 20 model cells were 

calculated as desaturating, indicating desaturation 

throughout 93 mi2 of the Wanapum unit (a decrease in 

storage of about 350,000 acre-feet of ground water).

Changes in the flow system in the Grande Ronde 

unit, resulting from continuing the 1983-85 pumpage 

from the aquifer system, occur principally in parts of 

the Odessa-Lind pumping center, near Butter Creek, 

Oreg., and near Glade Creek, Wash., on the Horse 

Heaven Hills. The water- level declines in the Grande 

Ronde unit in the Odessa-Lind area extend from south 

of Odessa to north of Connell and from about the East 

Low Canal in the west to Ritzville, Wash., in the east; 

this is about the same area of calculated declines for the 

Wanapum unit. Unlike the Wanapum unit, however, in 

only one model cell are calculated declines greater than 

75 ft. Declines ranging between 1 and 75 ft were calculated to include some 225 mi2. In one area in the western part of Horse Heaven Hills, the upper Grande 

Ronde was calculated as desaturating, but this is 

believed to have been caused by numerical instability in 

the model rather than by pumping in that area. The 

declines in the upper Grande Ronde are paralleled in 

the lower Grande Ronde, but they are neither as widespread nor as large in magnitude.

The model was used to calculate changes to the 

water budget of the aquifer system (table 9). The inflow 

changes are the loss of storage and an additional 20 ft3 / 

s of streamflow captured. The induced leakage from rivers is due to the lowering of water levels, caused by the 

current distribution and rate of ground-water pumping. 

Also, because continued pumping at the current rate 

causes areas to become desaturated, there was a net loss 

of about 40 ft3 /s of ground-water pumpage. It is esti-
EFFECTS OF POTENTIAL WATER-MANAGEMENT ALTERNATIVES A43

122° 121 C 120° 119° 118° 117° 116°

1-K.tv

rL.vo i

OPIK Li: ' BONNEf? LINCOLN

48° MONTANA

'" V - -x ^ -'' K i'j \ , !~.., 

N >.

S SANDERS 

<

%<t - -

ci \

47C

46°

45°

VALLEY

20 40 60 80 MILES

lil ~^ i I i I

\ ' r

40 80

n

120 KILOMETERS

Base modified from U.S. Geological Survey digital data, 

1:2,000,000,1972 EXPLANATION

Water level change, in feet

Decline of 0-10

Decline of 10-50 

Decline of 50-100 

Decline of 100-200 

Decline of 200-300 

Decline of 300-400 

Decline of more than 400

Model cells calculated as desaturated under 

current conditions

Model cells calculated as becoming desaturated 

under future equilibrium conditions

Cells where aquifer is thin or absent-Not included in model

Boundary of Wanapum unit as modeled

Boundary of Columbia Plateau aquifer system study area

FIGLRE 17. Calculated water-level changes in the Wanapum unit from 1985 to equilibrium conditions, 

based on current water-management strategies.
A44 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

TABI E 9. Model-calculated changes in the regional ground-water flow system resulting from simulation of potential water-management alternatives,

Columbia Plateau aquifer system (from Bauer and Hansen, in press)

[Values in cubic feet per second]

Water-budget 

component

Wells (change in storage) 

Recharge 

Leakage from rivers

TOTAL INFLOW

Wells

Leakage to rivers 

Leakage to drains 

Leakage to seepage faces

TOTAL OUTFLOW

Calculated 

water budget 

for time-averaged 

1983-85 simulation

187 

10,205

557

10,949

1,135

3,804 

5,596 

423

10,958

Time-averaged 

simulation

Simulated 

equilibrium 

conditions

-187 

0 

20

-167

-10

-78 

-47 

-2

-167

Calculated change from 

equilibrium conditions simulation

*Phase 1

1983-85 

pumpage

0 

330 

-13

317

9

32 

272 

3

316

Reduced 

pumpage

0 

330 

-24

305

-121

44 

377 

4

305

*Phases 1 and 2

1983-85 

pumpage

0 

974

-23

950

19

72 

858 

5

954

Reduced 

pumpage

0 

974

-38

935

-252

120 

1,060 

6

934

* Simulated phased expansion of CBIP (Columbia Basin Irrigation Project) with 4.0 feet per year surface-water irrigation application rate.

mated that the lowering of water levels would cause a 

decrease of 78 ft3 /s in leakage to rivers and a decrease 

of 47 ft3 /s of leakage to drains.

Model-calculated ground-water discharge to the 27 

selected basins would remain about the same in all but 

the Cow Creek basin and, to a lesser extent, Bowers 

Coulee (table 7). In Cow Creek basin, pumping would 

reduce ground-water discharge by about 52 percent. 

Similarly, model-calculated ground-water discharge to 

the 16 selected stream reaches would be virtually 

unchanged (table 8), and the largest change would be 

for the Palouse River.

To summarize, under the assumption of invariant 

climate, the continuation of the current (1983-85) waterdevelopment practices would cause water-level 

declines in all basalt units and only minor declines in 

the overburden aquifer. The declines in the Saddle 

Mountains unit would be confined to the Horse Heaven 

Hills and the tributary valleys in the Yakima Fold Belt. 

Declines in the Wanapum unit would be more widespread and of a much larger magnitude. The areas 

affected would be the Odessa-Lind pumping center, 

Horse Heaven Hills, an area near Butter Creek, Oreg., 

an area near The Dalles, Oreg., and some valleys in the 

Yakima Fold Belt. Because the current pumping rate 

would lower water levels if continued, some parts of 

the aquifer would desaturate, localized leakage would 

be induced from the streams (reduction in streamflow), 

and well yields would decline (in some cases the flow to 

wells would cease).

COLUMBIA BASIN IRRIGATION PROJECT 

EXPANSION, 1983-85 PUMPAGE

The simulations estimating the effects of the expansion of CBIP showed large water-level rises from equilibrium conditions. In the CBIP for the phase 1 

expansion, about 16 cells that desaturated with continuation of current (1980's) strategies (3 in the Saddle 

Mountains unit and 13 in the Wanapum unit) would not 

desaturate because of the additional 330 ft /s of 

recharge (table 9) resulting from the application of surface water for irrigation. This would allow for about 31 

ft3 /s of pumpage to be continued in those cells. Infiltration of the surface water would cause water levels to 

rise in the aquifer system. The rises in the overburden 

aquifer would be small because there is little overburden in the expansion areas. Water levels in the Saddle 

Mountains unit would rise to or near land surface along 

its eastern extent, throughout about 80 to 90 mi2. Calculated rises for the phase 1 expansion occurred principally in the Wanapum unit. Rises of 1 to 100 ft and of 

100 to 200 ft in the Wanapum unit would each encompass more than 200 mi2. Rises greater than 200 ft would 

encompass less than about 100 mi2. As a result of waterlevel rises, the leakage to rivers would increase by 

about 32 ft3 /s and leakage to drains would increase by 

about 272 ft3 /s. (Because the drains discharge to the rivers, the net effect of increased leakage to rivers and 

drains accounts for most of the increase in recharge.) 

Discharge at seepage faces, generally located at the 

margins of the units, would not be affected by the proposed expansion.
GROUND-WATER QUALITY A45

The expansion of both phases of CBIP would cause 

recharge to increase by about 974 ft3 /s (table 9). Streamflow in the rivers bordering CBIP would increase by 

about 40 ft3 /s in addition to the 32 ft3 /s increase under 

the phase 1 expansion. Drains would receive most (88 

percent) of the additional recharge water. With full 

development of CBIP, an additional 14 cells in the 

Wanapum unit that were simulated to desaturate under 

the phase 1 management strategy simulation would 

remain saturated (allowing for the continuation of the 

10 ft3 /s of pumpage). Water-level rises would encompass about three times the area under phase 1 alone. 

Additionally, areas of rises of more than 250 ft would 

increase, as would areas of water-level rises in the 

upper Grande Ronde, although these rises would still 

be generally less than 100 ft.

COLUMBIA BASIN IRRIGATION PROJECT 

EXPANSION, REDUCED PUMPAGE

For the phase 1 expansion but with a prorated 

reduction in 1983-85 ground-water pumping, pumpage 

was estimated to be reduced by about 121 ft3 /s (table 9). 

This results in a slightly different flow system than 

under the phase 1 expansion with continuation of 1983- 

85 pumpage. The inflow into the aquifer system (table 

9) would increase by about 305 ft3 /s. This is less than 

under the other phase 1 simulation because the large 

reduction in pumpage would allow water levels to rise 

further, resulting in less leakage from the rivers. The 

reduction in pumpage is compensated for principally 

by increased leakage to drains. Additionally, the reduction in pumpage allows more than 50 percent of the 

Wanapum unit cells that were desaturated under the 

other phase 1 simulation to remain saturated. Discharge 

to the 27 selected basins and 16 selected river reaches 

(tables 8 and 9) would remain about the same as under 

the other phase 1 simulation with 1983-85 pumpage.

Under the phase 1 and 2 expansion with reduced 

pumpage, there are large model-calculated changes in 

the water budget and flow system from equilibrium 

conditions and only small changes in the total inflow 

and outflow quantities from the phase 1 and 2 expansion with 1983-85 pumpage. Thus, the flow system 

remains about the same as under the phase 1 and 2 

expansion with 1983-85 pumpage. However, because 

the expansion area includes much of the Odessa-Lind 

pumping center that would be supplied with surfacewater sources, there would be a net reduction in pumpage of about 252 ft3 /s (a 20-percent decrease from equilibrium conditions). This would allow water levels to 

rise an additional 50 to 100 ft throughout about 160 mi2 

of both the Wanapum and upper Grande Ronde units.

These rises would result in an increase in discharge to 

drains of about 1,060 ft3 /s compared to equilibrium 

conditions, a 24-percent increase compared to the phase 

1 and 2 expansion with 1983-85 pumpage.

The calculated discharge to all but one of the 

selected basins and river reaches generally would be 

unchanged from equilibrium conditions. Only Bowers 

Coulee basin (zone number 27 on figure 9, and table 3) 

would have a large percentage of change in discharge. 

This basin is located within both the Odessa-Lind 

pumping center and the expansion area. About 30 percent of the increased leakage to drains under both phase 

1 and 2 expansion simulations would be within this 

basin. Under reduced pumpage, an additional 61 ft3 /s 

would discharge to drains in this basin, compared with 

the phase 1 and 2, 1983-85 pumpage simulation. Water 

levels would rise an additional 100 ft throughout much 

of this basin in both the Wanapum unit and the upper 

Grande Ronde.

GROUND-WATER QUALITY

One of the principal factors necessary for economic 

development of the Columbia Plateau is the availability 

of large quantities of ground water for irrigation. The 

suitability of water depends on its quality, and therefore 

an understanding of the processes that affect groundwater quality is important. Ground-water chemistry 

can significantly affect the hydrologic characteristics of 

the rock composing the aquifer system. The filling of 

fractures with mineral precipitates derived from chemically reactive volcanic glass (which usually has progressed farther in older volcanic rocks than in younger 

rock) decreases hydraulic conductivity. This is believed 

to be related to the rate of ground-water flow, the availability of the chemically reactive volcanic glass, and the 

relatively porous nature of volcanic rocks, which provides a large surface area per unit volume for contact 

with the water (Wood and Fernandez, 1988).

In the Columbia Plateau RASA study, the regional 

water-quality characteristics for the basalt units and the 

geochemical evolution of the ground water were 

assessed; the results are summarized below. Specific 

water-quality problems (except for the higher concentrations of sodium in some ground water withdrawn 

from the basalts) and the water-quality characteristics 

of the ground water in the overburden aquifer (which 

are complex due to human activities and the variations 

in overburden lithology) were not studied.
A46 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

WATER-QUALITY CHARACTERISTICS

Ground water in the basalt units generally is of good 

quality and suitable for most uses (Steinkampf, 1989). A 

summary of water chemistry in the three units is 

included as table 10. The dominant water type in all 

three units is calcium-magnesium bicarbonate (CaMg 

HCO3). Sodium bicarbonate (Na HCO3) is the next most 

prevalent type, and calcium-magnesium sulfate-chloride (CaMgSC^Cl) is the least prevalent water type. 

Sodium bicarbonate water typically occurs in deeper 

downgradient locations, due to the precipitation of calcium and magnesium and the release of sodium as a

result of longer ground-water residence time in the 

aquifer system.

In the Saddle Mountains unit, in areas of surfacewater irrigation and where the overburden is less than 

200 ft thick, water from shallow wells is of a calciummagnesium sulfate-chloride type. Dissolved-solids concentrations generally increase in a downgradient direction because of longer residence time in the aquifer, 

which effects the evolution of ground-water chemistry. 

The concentrations of dissolved solids may further 

increase because of recharge waters from irrigation with 

high solute concentrations. Nitrogen concentrations 

(nitrate plus nitrite as N) in ground water of 2.0 mg/L

TABLE 10. Summary of selected water chemistry information for the three basalt units, Columbia Plateau aquifer system (from Steinkampf, 1989)

[Values in milligrams per liter unless otherwise indicated] 

Saddle Mountains unit, 131 water analyses

Maximum Minimum Mean

Specific conductance (microsiemens

per centimeter at 25° Celsius)

Calculated dissolved solids

Sodium (Na)

Chloride (Cl)

Nitrate + Nitrite (NO3+NO2 , as N)

Silica (SiO2 )

Sulf ate (SO4 )

Temperature (°Celsius)

Dissolved oxygen (DO)

Calcium (Ca)

Magnesium (Mg)

Fluoride (F)

Bicarbonate (HCO3 )

Iron (Fe)

Potassium (K)

pH (standard units)

1,460

890

100

130

54

72

490

25.5

10.1

98

62

2.9

392

.79

13.0

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

18.36

4.5

38.28

19.4

.58

195.4

.03

6.9

a7.7

Wanapum unit, 410 water analyses

Specific conductance (microsiemens

per centimeter at 25° Celsius)

Calculated dissolved solids

Sodium (Na)

Chloride (Cl)

Nitrate + Nitrite (NO3+NO2 , as N)

Silica (SiO2 )

Sulf ate (SO4 )

Temperature (°Celsius)

Dissolved oxygen (DO)

Calcium (Ca)

Magnesium (Mg)

Fluoride (F)

Bicarbonate (HCO3 )

Iron (Fe)

Potassium (K)

pH (standard units)

Maximum

1,970

1,100

130

300

54

110

490

43.4

10.6

180

75

4.9

455

10

22.0

9.4

Minimum

85

69

2.4

.5

.1

10

.2

6.2

.1

.8

.01

.1

43

.003

.9

6.1

Mean

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
GROUND-WATER QUALITY A47

TABLE 10. Summary of selected water chemistry information for the three basalt units, Columbia Plateau aquifer system (from Steinkampf, 1989) Continued

[Values in milligrams per liter unless otherwise indicated] 

Grande Ronde unit, 283 water analyses

Maximum Minimum Mean

Specific conductance (microsiemens

per centimeter at 25° Celsius)

Calculated dissolved solids

Sodium (Na)

Chloride (Cl)

Nitrate + Nitrite (NO3+NO2 , as N)

Silica (SiO2 )

Sulfate (SO4 )

Temperature (°Celsius)

Dissolved oxygen (DO)

Calcium (Ca)

Magnesium (Mg)

Fluoride (F)

Bicarbonate (HCO3 )

Iron (Fe)

Potassium (K)

pH (standard units)

All basalt units,

Specific conductance (microsiemens

per centimeter at 25° Celsius)

Calculated dissolved solids

Sodium (Na)

Chloride (Cl)

Nitrate + Nitrite (NO3+NO2 , as N)

Silica (SiO2 )

Sulfate (SO4 )

Temperature (°Celsius)

Dissolved oxygen (DO)

Calcium (Ca)

Magnesium (Mg)

Fluoride (F)

Bicarbonate (HCO3 )

Iron (Fe)

Potassium (K)

pH (standard units)

830

510

90

45

15

110

100

36.7

10.2

88

38

4.9

455

10

13

9.4

824 water analyses

Maximum

1,970

1,100

130

300

54

110

490

43.4

10.6

180

75.0

4.9

455

10

22.0

9.4

85

94

4

.5

.1

29

.2

7.6

.1

.95

.13

.1

43

.003

1.1

6.7

Minimum

85

69

2.4

.5

.1

10

.2

6.2

.1

.8

.01

.1

43

.003

.9

6.1

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

Mean

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

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

or larger occur in areas where the overburden aquifer is 

thin and where surface water is used for irrigation. The 

recharging surface water transports large quantities of 

nitrogen derived from agricultural chemicals. The mean 

dissolved-solids concentration for the Saddle Mountains unit is about 340 mg/L (table 10).

The concentration of dissolved solids in the 

Wanapum unit averaged about 240 mg/L. For this 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 ground 

water are greater than 4.0 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 

about 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 

origin of this dissolved nitrogen is unknown, but agricultural chemicals are the most likely source. The vertical variation in nitrogen concentrations in the 

Wanapum unit is probably due either to variations in 

the direction of flow or to the possibility that nitrogen-
A48 REGIONAL AQUIFER-SYSTSM ANALYSIS COLUMBIA PLATEAU

enriched water has not reached the deeper depths at 

this time; the former is most likely.

The mean concentration of dissolved solids of water 

in the Grande Ronde unit is 234 mg/L and reflects concentrations of solutes generally smaller than in the 

other units. Sodium concentrations increase with 

ground-water 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 no measured concentrations were larger than 2.0 mg/L. This is 

probably because in the areas with intensive irrigation, 

the Grande Ronde unit is generally overlain by thick 

layers of the other basalts and, thus, the water chemistry in the Grande Ronde unit is not affected by irrigation.

GEOCHEMICAL MODEL

The chemical composition of water in the 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. Solute 

concentrations also are influenced by the hydrologic 

processes occurring in the system. These aspects were 

investigated by Steinkampf and Hearn (1996) and are 

briefly summarized below.

Rocks of the Columbia River Basalt Group consist 

primarily of labradorite (plagioclase feldspar), augite 

(pyroxene), and opaque metal oxides (commonly titanomagnetite) in a matrix of volcanic glass and cryptocrystalline material. The most common accessory 

minerals are apatite, olivine, and metallic sulfides. 

These are present in varying and 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 dissolution of rock by 

weakly acidic recharge waters and dissolution by 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 the semiconfined to confined aquifers where little or no oxygen penetrates from the atmosphere, carbonic acid usually is 

not generated. In such areas, silicate hydrolysis is the 

dominant dissolution process. Volcanic glass, a major 

component of the Columbia River Basalt, is the most 

reactive mineral. In decreasing order, cryptocrystalline 

intergrowths, olivine, pyroxene, and feldspar are the 

next most reactive.

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. Dissolution of minerals by carbonic acid increases the concentrations of all of those 

constituents and also increases ground-water pH. Silicate hydrolysis also increases the concentrations of solutes, and, because the hydroxyl ion is produced in the 

reaction, increases pH even more than does acidic dissolution. Increasing ground-water pH 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 

ground-water pH. Sodium and potassium are dissolved 

faster than they are removed. As dissolved sodium, 

potassium, and silica concentrations increase, the 

ground water eventually becomes supersaturated with 

clinoptilolite. Clinoptilolite, which incorporates dissolved sodium and potassium, then precipitates, consequently limiting the concentrations of sodium and 

potassium in the basalts.

Dissolved-silica concentrations are large in ground 

water from basalt 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 ground-water 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. The concentration of a trace element in solution
SELECTED REFERENCES A49

depends upon a variety of factors, many of which are 

difficult to quantify in natural systems. Concentrations 

of some 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 (that increase in 

concentration with increasing total concentration of dissolved solids) are usually controlled by availability of 

the element in the rock.

SELECTED REFERENCES

Ames, L.L., 1980, Hanford basalt flow mineralogy: Richland, Washington, Report INL-2847, Pacific Northwest Laboratory, 447 p.

Bauer, H.H., and Hansen, A.J., in press, Hydrology of the Columbia 

Plateau regional aquifer system, Washington, Oregon, and 

Idaho: U.S. Geological Survey Water-Resources Investigations 

Report 96-4106, 63 p.

Bauer, H.H., and Vaccaro, J.J., 1986, Model estimates of climatological 

variability on ground water: Conference on Climate and Water 

Management: A Critical Era, American Meteorological Society, 

Ashville, N.C., August 4-7,1986, p. 45^9.

___1987a, Estimation of the spatial and temporal distributions of 

evapotranspiration and deep percolation; Part I. The Model 

[abs.]: EOS, Transactions of the American Geophysical Union, v. 

68, no. 44, November 3,1987, p. 1,299.

___1987b, Documentation of a deep percolation model for estimating ground-water recharge: U.S. Geological Survey Open-File 

Report 86-536,180 p. 

_1990, Estimates of ground-water recharge to the Columbia Plateau regional aquifer system, Washington, Oregon, and Idaho, 

for predevelopment and current land-use conditions: U.S. Geological Survey Water-Resources Investigations Report 88-4108, 

37 p., 2 plates.

Bauer, H.H., Vaccaro, J.J., and Lane, R.C., 1985, Maps showing 

ground-water levels in the Columbia River Basalt and overlying 

material, spring 1983, southeastern Washington: U.S. Geological 

Survey Water-Resources Investigations Report 84-4360,4 sheets.

Benson, L.V., and Teague, L.S., 1982, Diagenesis of basalts from the 

Pasco Basin, Washington I. Distribution and composition of 

secondary mineral phases: Journal of Sedimentary Petrology, v. 

52, no. 2, p. 595-613.

Cline, D.R., 1984, Ground-water levels and pumpage in east-central 

Washington, including the Odessa-Lind area, 1967 to 1981: 

Washington State Department of Ecology, Water-Supply Bulletin 

no. 55, 34 p.

Cline, D.R., and Collins, C.A., 1992, Ground-water pumpage in the 

Columbia Plateau, Washington and Oregon, 1945 to 1984: U.S. 

Geological Survey Water-Resources Investigations Report 90- 

4085, 31 p., 5 plates.

Cline, D.R., and Knadle, M.E., 1990, Ground-water pumpage from the 

Columbia Plateau regional aquifer system, Washington, 1984: 

U.S. Geological Survey Water-Resources Investigations Report 

87-4135, 32 p., 1 sheet.

Collins, C.A., 1987, Ground-water pumpage from the Columbia Plateau regional aquifer system, Oregon, 1984: U.S. Geological Survey Water-Resources Investigations Report 86-4211, 21 p.

Davies-Smith, A., Bolke, E.L., and Collins, C.A., 1988, Geohydrology 

and digital simulation of the ground-water flow system in the 

Umatilla Plateau and Horse Heaven Hills area, Oregon and 

Washington: U.S. Geological Survey Water-Resources Investigations Report 87-4268, 70 p.

Drost, B.W., and Whiteman, K.J., 1986, Surficial geology, structure, 

and thickness of selected geohydrologic units in the Columbia 

Plateau, Washington: U.S. Geological Survey Water-Resources 

Investigations Report 84-4326,10 sheets.

Drost, B.W, Whiteman, K.J., and Gonthier, J.B., 1990, The geologic 

framework of the Columbia Plateau regional aquifer system, 

Washington, Oregon, and Idaho: U.S. Geological Survey WaterResources Investigations Report 87-4238,10 p., 10 sheets.

Farooqui, S.M., Beaulieu, J.B., Bunker, R.C., Stensland, D.E., and 

Thorns, R.E., 1981, Dalles Group: Neogene formations overlying 

the Columbia River Basalt Group in north-central Oregon: Oregon Department of Geology and Mineral Industries, Oregon 

Geology, v. 43, no. 10, p. 131-140.

Ferris, J.G., Knowles, D.B., Brown, R.H., and Stallman, R.W., 1962, 

Theory of aquifer test: U.S. Geological Survey Water-Supply 

Paper 1536-E, 174 p.

Flint, R.F., 1938, Summary of late-Cenozoic geology of southeastern 

Washington: American Journal of Science, v. 35, p. 223-230.

Freeman, O.W., Forrester, J.O., and Lupher, R.L., 1945, Physiographic 

divisions of the Columbia Intermontane Province: Association 

American Geographer Annals, v. 35, no. 2, p. 50-75.

Gonthier, J.B., 1990, Geology, structure, and thickness of hydrogeologic units in part of the Columbia Plateau, Oregon: U.S. Geological Survey Water-Resources Investigations Report 86-4001, 6 

sheets.

Hansen, A.J., 1993a, Archiving of source code for the finite-difference 

flow model and the post-processors and input and output files 

for the Columbia Plateau regional aquifer system, Washington, 

Oregon, and Idaho: U.S. Geological Survey Open-File Report 90- 

364, 9 p.

Hansen, A.J., 1993b, Modifications to the modular three-dimensional, 

finite difference, ground-water flow model used for the Columbia Plateau Regional Aquifer-System Analysis, Washington, 

Oregon, and Idaho: U.S. Geological Survey Open-File Report 91- 

532,162 p.

Hansen, A.J., Vaccaro, J.J., and Bauer, H.H., 1994, Ground-water flow 

simulation of the Columbia Plateau regional aquifer system, 

Washington, Oregon, and Idaho: U.S. Geological Survey WaterResources Investigations Report 91-4178, 81 p., 15 sheets.

Hearn, P.P., Steinkampf, W.C., Bortleson, G.C., and Drost, B.W, 1985, 

Geochemical controls on dissolved sodium in basalt aquifers of 

the Columbia Plateau, Washington: U.S. Geological Survey 

Water-Resources Investigations Report 84-4304,38 p.

Hooper, PR., 1982, The Columbia River Basalts: Science, v. 215, no. 

4539, p. 1,463-1,468.

Lane, R.C., 1988a, Selected ground-water information for the Columbia Plateau regional aquifer system, Washington and Oregon, 

1982-1985: Volume 1. Geohydrology: U.S. Geological Survey 

Open-File Report 88-182, 236 p.

___1988b, Selected ground-water information for the Columbia Plateau regional aquifer system, Washington and Oregon, 1982- 

1985: Volume 2. Water-levels: U.S. Geological Survey Open-File 

Report 88-183,136 p.

Lane, R.C., and Whiteman, K.J., 1989, Ground-water levels, spring 

1985, and ground-water level changes, spring 1983 to spring 

1985, in three basalt units underlying the Columbia Plateau,
A50 REGIONAL AQUIFER-SYSTEM ANALYSIS COLUMBIA PLATEAU

Washington and Oregon: U.S. Geological Survey WaterResources Investigations Report 88-4018,4 sheets.

Lindholm, G.F., and Vaccaro, J.J., 1988, Region 2 Columbia Lava Plateau, chapter 5, in Back, W., Rosenshein, J.S., and Seaber, P.R., 

eds., Hydrogeology, The Geology of North America: Volume 0-2: 

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of America, Boulder, Colorado, p. 37-50.

Lum, WE., Smoot, J.L., and Ralston, D.R., 1990, Geohydrology and 

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Water-Resources Investigations Report 89-4103, 73 p.

MacNish, R.D., and Barker, R.A., 1976, Digital simulation of a basalt 

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McDonald, M.G., and Harbaugh, A.W, 1988, A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water Resources Investigations, Book 

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Myers, C.W, and Price, S.M., 1979, Geologic studies of the Columbia 

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Nelson, L.M., 1991, Surface-water resources for the Columbia Plateau, 

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Neuzil, C.E., 1986, Ground-water flow in low-permeability environments: Water Resources Research, v. 22, no. 8, p. 1,163-1,195.

Newcomb, R.C., 1965, Geology and ground-water resources of the 

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___1969, Effect of tectonic structure on the occurrence of ground 

water in the basalt of the Columbia River Group of The Dalles 

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Prych, E.A., 1983, Numerical simulation of ground-water flow in 

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Reidel, S.P., 1982, Stratigraphy of the Grande Ronde Basalt, Columbia 

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Selected Series of U.S. Geological Survey Publications

Books and Other Publications

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS investigations and research.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of 

wide interest to professional geologists, hydrologists, and engineers. The series covers investigations in all phases of hydrology, including hydrogeology, availability of water, quality of 

water, and use of water.

Circulars are reports of programmatic or scientific information 

of an ephemeral nature; many present important scientific 

information of wide popular interest. Circulars are distributed 

at no cost to the public.

Fact Sheets communicate a wide variety of timely information 

on USGS programs, projects, and research. They commonly 

address issues of public interest. Fact Sheets generally are two 

or four pages long and are distributed at no cost to the public.

Reports in the Digital Data Series (DOS) distribute large 

amounts of data through digital media, including compact discread-only memory (CD-ROM). They are high-quality, interpretive publications designed as self-contained packages for viewing and interpreting data and typically contain data sets, 

software to view the data, and explanatory text.

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal USGS publications series. Copies are produced on request 

(unlike formal USGS publications) and are also available for 

public inspection at depositories indicated in USGS catalogs.

Open-File Reports can consist of basic data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories.

Maps

Geologic Quadrangle Maps (GQ's) are multicolor geologic 

maps on topographic bases in 7.5- or 15-minute quadrangle 

formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, 

surficial, or engineering geology. Maps generally include brief 

texts; some maps include structure and columnar sections only.

Geophysical Investigations Maps (GP's) are on topographic 

or planimetric bases at various scales. They show results of 

geophysical investigations using gravity, magnetic, seismic, or 

radioactivity surveys, which provide data on subsurface structures that are of economic or geologic significance.

Miscellaneous Investigations Series Maps or Geologic 

Investigations Series (I's) are on planimetric or topographic 

bases at various scales; they present a wide variety of format 

and subject matter. The series also incudes 7.5-minute quadrangle photogeologic maps on planimetric bases and planetary 

maps.

Information Periodicals

Metal Industry Indicators (Mil's) is a free monthly newsletter that analyzes and forecasts the economic health of five 

metal industries with composite leading and coincident 

indexes: primary metals, steel, copper, primary and secondary 

aluminum, and aluminum mill products.

Mineral Industry Surveys (MIS's) are free periodic statistical 

and economic reports designed to provide timely statistical data 

on production, distribution, stocks, and consumption of significant mineral commodities. The surveys are issued monthly, 

quarterly, annually, or at other regular intervals, depending on 

the need for current data. The MIS's are published by commodity as well as by State. A series of international MIS's is also 

available.

Published on an annual basis, Mineral Commodity Summaries is the earliest Government publication to furnish estimates 

covering nonfuel mineral industry data. Data sheets contain 

information on the domestic industry structure, Government 

programs, tariffs, and 5-year salient statistics for more than 90 

individual minerals and materials.

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in interpreting that performance. The Minerals Yearbook consists of 

three volumes. Volume I, Metals and Minerals, contains chapters about virtually all metallic and industrial mineral commodities important to the U.S. economy. Volume II, Area Reports: 

Domestic, contains a chapter on the minerals industry of each 

of the 50 States and Puerto Rico and the Administered Islands. 

Volume III, Area Reports: International, is published as four 

separate reports. These reports collectively contain the latest 

available mineral data on more than 190 foreign countries and 

discuss the importance of minerals to the economies of these 

nations and the United States.

Permanent Catalogs

"Publications of the U.S. Geological Survey, 1879-1961" 

and "Publications of the U.S. Geological Survey, 1962- 

1970" are available in paperback book form and as a set of 

microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" is

available in paperback book form (two volumes, publications 

listing and index) and as a set of microfiche.

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.