Groundwater Conditions During 2009 and 

Changes in Groundwater Levels from 1984 to 

2009, Columbia Plateau Regional Aquifer System, 

Washington, Oregon, and Idaho

Scientific Investigations Report 2010–5040

U.S. Department of the Interior

U.S. Geological Survey

U.S. Geological Survey Groundwater Resources Program
Cover: Lower left: Photograph of irrigation well in the vicinity of Toppenish, Washington. 

(Photograph taken by Karen Payne, U.S. Geological Survey, 2009.)

Center foreground: Photograph of “Pullman’s Great Artesian Well,” in the vicinity of 

Pullman, Washington. (Image by Artopho Studios, circa 1910, courtesy of Manuscripts, 

Archives, and Special Collections, Washington State University Libraries, PC2-10-44. 

Used with permission.)

Lower right: Photograph of vicinity of Mosier, Oregon with Mt. Hood in the distance. 

(Photograph taken by Jonathan Haynes, U.S. Geological Survey, 2007.)

Background: Photograph of Frenchman’s Coulee in the vicinity of Quincy, Washington. 

(Photograph taken by Peter Prehn, private citizen, 2008. Used with permission.)
Groundwater Conditions During 2009 and 

Changes in Groundwater Levels from 1984 to 

2009, Columbia Plateau Regional Aquifer System, 

Washington, Oregon, and Idaho

By Daniel T. Snyder and Jonathan V. Haynes

U.S. Geological Survey Groundwater Resources Program

Scientific Investigations Report 2010–5040

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Snyder, D.T., and Haynes, J.V., 2010, Groundwater conditions during 2009 and changes in groundwater levels from 

1984 to 2009, Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho: U.S. Geological Survey 

Scientific Investigations Report 2010–5040, 12 p., http://pubs.usgs.gov/sir/2010/5040/
iii

Figures

Figure 1. Map showing long-term water level changes in selected wells, Columbia

Plateau Regional Aquifer System, Washington, Oregon, and Idaho .................. 3

Contents

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

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

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

Hydrogeologic Setting...................................................................................................................................2

Study Methods ...............................................................................................................................................4

Sources of Data.....................................................................................................................................4

Generalized Groundwater-Elevation Maps ......................................................................................4

Development of Groundwater-Level Change Maps........................................................................6

Changes in Groundwater Conditions and Groundwater Levels.............................................................6

Groundwater Configuration ................................................................................................................6

Water-Level Changes...........................................................................................................................8

Acknowledgments.........................................................................................................................................9

References Cited............................................................................................................................................9

Appendix A. Records of Selected Wells in the Columbia Plateau Regional Aquifer System ........11

Plates

Plate 1. Structural Regions of the Columbia Plateau Regional Aquifer System, Washington, 

Oregon, and Idaho

Plate 2. Locations of wells and estimated groundwater levels for the Overburden unit, 

Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho, 

spring 2009

Plate 3. Locations of wells and estimated groundwater levels for the Saddle Mountains unit, 

Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho, 

spring 2009

Plate 4. Locations of wells and estimated groundwater levels for the Wanapum unit, 

Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho, 

spring 2009

Plate 5. Locations of wells and estimated groundwater levels for the Grande Ronde unit, 

Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho, 

spring 2009

Plate 6. Groundwater-level changes for the Overburden unit, Columbia Plateau Regional 

Aquifer System, Washington, Oregon, and Idaho, spring 1984 to spring 2009

Plate 7. Groundwater-level changes for the Saddle Mountains unit, Columbia Plateau 

Regional Aquifer System, Washington, Oregon, and Idaho, spring 1984 to 

spring 2009

Plate 8. Groundwater-level changes for the Wanapum unit, Columbia Plateau Regional 

Aquifer System, Washington, Oregon, and Idaho, spring 1984 to spring 2009

Plate 9. Groundwater-level changes for the Grande Ronde unit, Columbia Plateau Regional 

Aquifer System, Washington, Oregon, and Idaho, spring 1984 to spring 2009
iv

Conversion Factors and Datums

Multiply By To obtain

foot (ft) 0.3048 meter (m)

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

meter (m) 3.281 foot (ft) 

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2) 

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88). Vertical coordinate information for historical data collected and stored as National 

Geodetic Vertical Datum of 1929 (NGVD 29) has been converted to NAVD 88 for this publication. 

Conversion between NAVD 88 and the commonly used NGVD 29 varies spatially; however, over 

most of the study area the following conversion can be used: 

NGVD 29 = NAVD 88 –3.6 feet.

This conversion generally is accurate within about ± 0.5 feet for 95 percent of the study area. 

The reader is directed to either the National Geodetic Survey Web site for VERTCON at http://

www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html or the U.S. Army Corps of Engineers Web site 

for Corpscon at http://crunch.tec.army.mil/software/corpscon/corpscon.html for more accurate 

conversions.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 

Horizontal coordinate information for historical data collected and stored as North American 

Datum of 1927 (NAD 27) has been converted to NAD 83 for this publication. Conversion between 

NAD 83 and the commonly used NAD 27 varies spatially, and the difference in lateral positions 

can be greater than 300 feet. For assistance with conversions, the reader is directed to either 

the National Geodetic Survey Web site for NADCON at http://www.ngs.noaa.gov/TOOLS/

Nadcon/Nadcon.html or the U.S. Army Corps of Engineers Web site for Corpscon at http://

crunch.tec.army.mil/software/corpscon/corpscon.html.

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

Tables

Table 1. Change in groundwater levels in wells in the Columbia Plateau Regional

Aquifer System, Washington, Oregon, and Idaho, from spring 1984 to spring

2009 .......................................................................................... 8
Groundwater Conditions During 2009 and Changes in 

Groundwater Levels from 1984 to 2009, Columbia Plateau 

Regional Aquifer System, Washington, Oregon, and Idaho

By Daniel T. Snyder and Jonathan V. Haynes

Abstract

Groundwater elevations in three basalt units and one 

unconsolidated hydrogeologic unit in the Columbia Plateau 

Regional Aquifer System were measured and evaluated to 

provide a regional overview of groundwater conditions in 

spring 2009. Water levels for the Saddle Mountains unit, the 

Wanapum unit, the Grande Ronde unit, and for the overlying 

Overburden unit were measured in 1,752 wells during spring 

2009 by the U.S. Geological Survey (USGS) and 10 other 

Federal, State, Tribal, and local agencies, including 66 wells 

located and measured by the USGS specifically for this 

study. These data were analyzed to determine the presence 

of spatial correlation of groundwater levels with distance 

and direction from each other. Groundwater flow in the 

Palouse Slope structural region showed evidence of being 

more continuous relative to groundwater flow in the Yakima 

Fold Belt, where the geologic complexity may contribute to 

compartmentalization of groundwater flow. This information 

was used to interpolate the generalized groundwater elevations 

for each of the basalt hydrogeologic units and to provide 

information on regional flow. 

Water-level change maps were constructed for the 

three basalt hydrogeologic units and the Overburden 

(unconsolidated) unit. Groundwater levels measured in 

spring 1984 and 2009 in 470 wells were compared. Small to 

moderate groundwater-level declines were measured in most 

wells, although declines greater than 100 ft and as great as 

300 ft were measured in many wells. Essentially unchanged 

groundwater levels were measured in other wells. Of the 

wells measured in 1984 and 2009, water levels declined in 

83 percent of the wells, and declines greater than 25 ft were 

measured in 29 percent of all wells. The groundwater-level 

changes were greatest in the deeper hydrogeologic units. Mean 

groundwater-level changes ranged from a 7 ft decline for 

the Overburden unit to a 51 ft decline for the Grande Ronde 

unit. The average annual rates of groundwater-level change 

for the 25-year period ranged from a 0.3 ft/yr decline for the 

Overburden unit to a 2.0 ft/yr decline for the Grande Ronde 

unit. 

Groundwater level declines were identified throughout 

the Columbia Plateau, but areas with large and widespread 

declines were located in the central northern part of the study 

area, in parts of the Yakima River basin in Washington, in the 

Pullman-Moscow area in Washington and Idaho, and in parts 

of the Umatilla River basin in Oregon. These declines are in 

areas known to rely heavily on groundwater for irrigation and 

other uses.

Introduction

The Columbia Plateau Regional Aquifer System 

(CPRAS) covers about 44,000 mi2 within the Columbia River 

basin in southeastern Washington, northeastern Oregon, 

and western Idaho (pl. 1). The population of the region is 

more than 1.3 million people (2000 census) and important 

agricultural industry has developed despite its arid to semi-arid 

climate and limited access to surface-water resources. 

Groundwater availability in the aquifers of the area is 

therefore a critical water-resource management issue because 

the water demand for agriculture, economic development, and 

ecological needs is high. 

The primary aquifers of the CPRAS are basalts of the 

Columbia River Basalt Group and the overburden, consisting 

of overlying basin-fill sediments. Groundwater availability 

issues in the basin include (1) widespread water-level declines 

associated with development of groundwater resources for 

irrigation and other uses, (2) reduction in base flow to rivers 

and associated effects on stream temperature and water 

quality, and (3) current and anticipated effects of global 

climate change on recharge, base flow, and, ultimately, 

groundwater availability. 

The U.S. Geological Survey (USGS) Groundwater 

Resources Program began a study of the CPRAS in 2007 with 

the broad goals of characterizing the hydrologic status of the 

system, identifying trends in groundwater storage and use, and 

quantifying groundwater availability (U.S. Geological Survey, 

2008). The study approach includes documenting changes in 

the status of the system, quantifying the hydrologic budget for 
2 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

the system, updating the regional hydrogeologic framework, 

and developing a groundwater-flow simulation model for the 

system. The simulation model will be used to evaluate and 

test the conceptual model of the system and later to evaluate 

groundwater availability under alternative development and 

climate scenarios.

Purpose and Scope

The scope and objectives of this report are to 

characterize current (2009) groundwater conditions within 

each of the primary basalt aquifers and to evaluate changes 

in groundwater levels since the last regional synoptic 

measurement in 1984 (Whiteman, 1986; Vaccaro, 1999) 

through the presentation of maps of groundwater elevation and 

water-level change for the hydrogeologic units in the CPRAS. 

Regional assessment of water-level data from the CPRAS 

is necessary to document regional water-level conditions 

and to develop a broad view of the effects of groundwater 

development and management in the sustainability and 

availability of water supply in the region. This information 

is useful to delineate areas of water-level changes due to 

withdrawals, irrigation recharge, or climate and to identify 

areas with substantial data gaps that may preclude effective 

management of groundwater resources.

Hydrogeologic Setting

Overviews of the geology and hydrology of the 

Columbia Plateau presented in this section summarize detailed 

descriptions in reports that describe the groundwater flow 

system, including its boundaries, hydraulic characteristics, 

and components of recharge and discharge (Vaccaro, 1999); 

discuss the hydrology based on numerical modeling (Bauer 

and Hansen, 2000); and discuss the thickness, extent, and 

lithology of hydrogeologic units within the CPRAS (Kahle 

and others, 2009).

The Columbia Plateau is an intermontane basin between 

the Rocky Mountains and the Cascade Range filled mostly 

with Cenozoic basalt and sediment. The Columbia River 

Basalt Group consists of a series of basalt flows that erupted 

during various stages of the Miocene Age, 17 million to 

6 million years ago. More than 300 flows have been identified 

and individual flows range in thickness from 10 ft to more 

than 300 ft (Tolan and others, 1989; Drost and others, 1990). 

Soils derived from flows or sediments deposited on the surface 

of a flow were sometimes preserved, creating sedimentary 

interbeds between flows. The CPRAS occurs in an area of 

several structural regions (pl. 1). The geologic properties 

of these structural regions may influence groundwater flow 

through compartmentalization (the creation of distinct 

zones within an aquifer with limited interconnectivity) 

of the hydrogeologic units. The presence and importance 

of compartments in the CPRAS has been recognized and 

discussed in numerous studies (for example Newcomb, 

1959; Porcello and others, 2009). Groundwater-level data 

analyzed for this study, however, were insufficient to evaluate 

compartmentalization fully.

The largest structural regions in the CPRAS consist of 

the Yakima Fold Belt and the Palouse Slope, which occupy 

the Columbia River basin. The Yakima Fold Belt includes the 

western and central parts of the Columbia River basin and 

consists of a series of anticlinal ridges and synclinal valleys 

trending roughly east-west (Reidel and others, 2002). Folds 

and faults within this region affect groundwater movement 

by offsetting or altering permeable interflow zones to create 

effective barriers to flow (Drost and others, 1990; Reidel and 

others, 2002). The Palouse Slope in the eastern part of the 

basin is much less deformed and has a gently southwestward 

dipping slope. The other structural regions within the CPRAS 

are the Blue Mountains, a composite anticlinal structure that 

forms the southeastern extent of the Columbia River basin, 

and the Clearwater Embayment, which marks the eastward 

extent of the CPRAS along the foothills of the Rocky 

Mountains.

Generalized hydrogeologic units recognized in this 

investigation, listed in order of generally increasing age, 

include Overburden, Saddle Mountains, Wanapum, and 

Grande Ronde. The hydrogeology was simplified by grouping 

the Mabton and Vantage Interbeds into the Saddle Mountains 

and Wanapum units, respectively. The Overburden unit 

consists predominantly of undivided, unconsolidated to 

semi-consolidated sedimentary deposits ranging from Miocene 

to Holocene in age (Drost and others, 1990). These include 

many types of deposits of local and (or) regional extent 

including fluvial, glaciofluvial, eolian, and volcanoclastic 

deposits that can range in thickness from 0 to 1,300 ft. The 

Saddle Mountains hydrogeologic unit consists mostly of 

the Saddle Mountains Basalt and interbed members and is 

the least extensive and youngest formation of the Columbia 

River Basalt Group. Most of the unit is in the west-central 

part of the study area, with less continuous occurrences in the 

Blue Mountains and eastward into Idaho. Thickness of the 

Saddle Mountains unit can range from 0 to about 1,000 ft. The 

Wanapum hydrogeologic unit, composed mostly of basalt and 

interbed members of the Wanapum Basalt, is in the northcentral part of the study area. Much of the unit lies beneath 

the Overburden and Saddle Mountains units. Thickness of the 

Wanapum unit ranges from 0 to about 1,200 ft. The Grande 

Ronde hydrogeologic unit is the oldest and most extensive 

of the basalt units. This unit underlies most of the study area, 

except for an area along the southern boundary of the CPRAS 

in Oregon and along the eastern edge of the aquifer system in 

Idaho. The Grande Ronde unit contains the basalt and interbed 

members associated with the Grande Ronde Basalt. Thickness 

of the unit is largely unknown, but may be greater than 

15,000 ft near the central part of the basin (Reidel and others, 

2002).
Hydrogeologic Setting 3

Seasonal fluctuations of groundwater levels, due to 

recharge from precipitation, irrigation, or canals, or due 

to discharge to rivers or wells, are typical in the surficial 

or shallow aquifers of the CPRAS, although this also has 

Figure 1. Long-term water level changes in selected wells, Columbia Plateau Regional Aquifer System, Washington, 

Oregon, and Idaho. All hydrographs are at same scale.

been observed in deeper, non-surficial units. Long-term 

groundwater levels in the CPRAS, however, have been 

undergoing substantial changes since the 1930s (fig. 1). 

tac09-0411_fig01

Walla

Walla

Yakima

Kennewick

Spokane

The

Dalles

Pullman

Moses

Lake

Pendleton

O R E G O N

I D A H O

WA S H I N G T O N

SNAKE

RIVER

COLUMBIA RIVER

Yakima River Grande Ronde River

4

2

1

5

6

8

7 9

3

3

0

50

100

150

200

250

1950 1960 1970 1980 1990

Well identification No. 

470519119550801

Depth: 243 feet

Average rate of change: +5.5 feet/year

Well identification No. 

WDOE-ERO170

Depth: 507 feet

Average rate of change: 

-8.3 feet/year

100

1980 1990 2000 2010

150

200

250

300

350

400

1940 1950 1960 1970 1980 1990 2000 2010

0

50

100

150

WATER LEVEL

WATER LEVEL

WATER LEVEL

Well identification No.

PBAC WSU Test Well

Depth: 145 feet 

Average rate of change: -1.3 feet/year

150

1980 1990 2000 2010

200

250

300

350

400

450

WATER LEVEL

Well identification No. 

463118120003401

Depth: 1,703 feet

Average rate of change: 

-10.3 feet/year

Well identification No.

465700118510001

Depth: 258 feet

Average rate of change: -5.0 feet/year

0

1960 1970 1980 1990

50

100

150

200

250

300

Well identification No. 

455631118231901

Depth: 528 feet

Average rate of change: 

-2.2 feet/year

1960 1970 1980

50

100

150

200

WATER LEVEL

Well identification No. 

454031121224001

Depth: 553 feet

Average rate of change: 

-4.0 feet/year

1970 1980 1990 2000 2010

-100

-50

0

50

100

WATER LEVEL

Well identification No. 

464028119101601

Depth: 498 feet

Average rate of change: 

+6.2 feet/year

0

1960 1970 1980 1990

50

100

150

200

250

300

WATER LEVEL WATER LEVEL

Well identification No. 

453934118491701

Depth: 1,500 feet

Average rate of change:-2.2 feet/year

1960 1970 1980 1990 2000 2010

100

150

200

250

300

WATER LEVEL

Note: Water level values are in

feet below land surface.

EXPLANATION

Grande Ronde unit

Wanapum unit

Well location— 

number is map 

reference number 

on plate 1.
45 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System roundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

Groundwater level declines due to pumping have caused 

many wells to go dry, which required deepening of these wells 

to remain productive. Rises in groundwater due to recharge 

from canals and irrigation have created concerns of potential 

water logging of crops. Continued monitoring is needed to 

further evaluate human- or climate-induced changes to the 

groundwater system.

Study Methods

The method of analysis used to evaluate the configuration 

(shape or form) of the current (2009) groundwater surface 

in the CPRAS units relied on water-level data from wells 

measured in spring 2009. These data were used with 

statistical methods to determine the presence of spatial 

correlation of groundwater levels with distance and direction 

from each other. This information was used to interpolate 

the groundwater elevations between observations for each 

hydrogeologic unit. The change in groundwater levels between 

1984 and 2009 was determined by computing the change in 

water-level elevations from wells with observations in 1984 

and 2009, and analyzing these changes for spatial patterns to 

aid in interpolation.

Sources of Data

The spring 2009 groundwater-levels for the CPRAS were 

synoptic (collected simultaneously) sets of measurements 

of the depth to water in wells representative of a single 

hydrogeologic unit as part of routine monitoring. In addition 

to the water levels measured by the USGS, data were 

provided by the U.S. Department of Energy, Oregon Water 

Resources Department, Confederated Tribes of the Umatilla 

Indian Reservation, Washington Department of Ecology, 

South Columbia Basin Irrigation District, Walla Walla Basin 

Watershed Council, Palouse Basin Aquifer Committee, 

East Columbia Basin Irrigation District, and Bureau of 

Reclamation. These agencies provided well information and 

water-level data collected during late winter and early spring 

2009, prior to the typical start of significant pumping for 

agriculture. The spatial distribution of the wells measured 

in the existing monitoring networks was analyzed and 

determined to be insufficient for understanding groundwater 

levels in large areas of each of the hydrogeologic units. 

Therefore, the monitoring network data were supplemented 

with measurements from wells specifically selected for this 

study. Wells were selected from those measured during the 

1984 USGS synoptic water-level investigation (Vaccaro, 

1999) on the basis of the primary hydrogeologic unit to 

which the wells were open (a screened or open part of the 

well through which water enters—referred to as the open 

interval) and their proximity to areas of sparse data for the 

corresponding hydrogeologic unit. Priority was given to wells 

with water-level measurements from spring 1984 to facilitate 

the comparison of water levels between 1984 and 2009. 

Sixty‐six of these supplemental wells that fit these selection 

criteria were identified and located, and water levels were 

measured in early spring 2009 by the USGS (pls. 2, 3, 4, and 

5; appendix A). The number of wells measured during spring 

2009 from all sources totaled 1,752 and were apportioned 

between the hydrogeologic units as follows: Overburden, 984 

wells; Saddle Mountains, 118 wells; Wanapum, 288 wells; and 

Grande Ronde, 362 wells.

The water-level change analysis evaluated water-level 

data from spring 1984 obtained from the USGS and eight 

other agencies. Of the 1,752 wells measured in spring 2009, 

corresponding water levels had been measured in 470 wells 

in spring 1984. The 1984 water-level measurements were 

apportioned between the hydrogeologic units as follows: 

Overburden, 197 wells; Saddle Mountains, 50 wells; 

Wanapum, 87 wells; and Grande Ronde, 136 wells (pls. 6, 7, 

8, and 9; appendix A).

Information on land-surface elevation was needed 

to determine groundwater elevation from depth-to-water 

information. Land-surface elevations for many wells were 

provided by the agencies that measured the well. For the 

remaining wells, land-surface elevations were estimated 

as the median land-surface elevation using a 10-m lateral 

resolution Digital Elevation Model (DEM) (U.S. Geological 

Survey, 1999) within a 100-ft radius of the reported location 

of the well to account for uncertainty with regard to the exact 

location of wells used in the study (appendix A).

The hydrogeologic units to which the wells were open 

were determined on the basis of assignments made by the 

agencies that provided the well data. For wells with no 

assigned hydrogeologic unit, open-interval information 

was compared with estimated unit-top elevations from a 

three-dimensional hydrogeologic framework model (E.R. 

Burns, U.S. Geological Survey, written commun., 2009) 

and was assigned to a specific unit if that unit comprised 

75 percent or greater of the open interval (appendix A). If 

no units comprised 75 percent or greater of the open interval 

(multi-unit) or if information was insufficient to determine the 

hydrogeologic unit (unit unknown) then the water level from 

the well was excluded from all analyses.

Generalized Groundwater-Elevation Maps

Generalized groundwater-elevation maps for the 

three basalt hydrogeologic units were developed from the 

2009 water-level data using a three-stage geostatistical 

process (Bossong and others, 1999, p. 25–29; Davis, 2002, 

p. 258–259). A similar map for the Overburden unit was not 

developed because the 2009 data density was insufficient to 

develop reliable surfaces of groundwater elevation for the 
Study Methods 5

isolated and discontinuous areas over which thick overburden 

deposits generally occur. The first stage of the process 

involved estimating the regional groundwater-elevation 

trend for each unit for the entire CPRAS extent using a 

regression-smoothing technique called locally weighted 

scatterplot smoothing (LOESS). The groundwater elevation 

estimated using the regional trend surface at the location of 

each well was subtracted from the groundwater elevation 

measured at the well. The surface represented by the residuals 

(remainders) is the configuration of the groundwater surface 

without the regional influence. The second stage consisted 

of variography (analysis of the correlation of measurements 

with distance and direction) using the groundwaterelevation residuals within defined structural regions for each 

hydrogeologic unit to determine trends in the groundwater 

surface due to the hydrogeologic conditions within the regions. 

The third stage was the interpolation of the groundwaterelevation residuals for each hydrogeologic unit using kriging 

(a statistical method of data analysis and interpolation), with 

the required kriging parameters determined by the variography 

analysis.

The advantage of kriging, variography, and regional 

trend removal is that smaller scale structure of the data is 

revealed and preserved in areas where data are sufficiently 

dense, whereas the regional trend provides an indication of the 

general tendency of groundwater elevation and flow direction 

in areas where data are sparse or nonexistent. Because the 

2009 water-level data were relatively sparse in many parts 

of the CPRAS, only the generalized configurations of the 

groundwater surfaces for the basalt units could be reliably 

determined for the entire study area. These generalized 

water‐level configurations are shown on plates 3–5 using color 

shading rather than elevation contours to indicate that the 

maps are simplifications of the large and complex actual flow 

system. Generalized directions of groundwater flow derived 

from this analysis and depicted on maps were modified 

on the basis of detailed maps of regional and subregional 

groundwater levels that better illustrate groundwater flow 

directions that are available for many parts of the CPRAS 

(Whiteman, 1986; Whiteman and others, 1994; Vaccaro, 1999; 

and Vaccaro and others, 2009).

Because the CPRAS includes several distinctive 

structural regions (pl. 1) with markedly different densities 

of folds and faults that may be impediments to groundwater 

flow, an analysis was done to determine whether the spatial 

correlation between groundwater levels differed within these 

structural units for each hydrogeologic unit. This process 

included variography, which provides statistical measures of 

the degree of correlation between a groundwater measurement 

and other groundwater measurements based on the distance 

and direction that separates them. Typically, wells that are 

closer together in the same aquifer have similar water levels 

and respond similarly to stresses. As distance between 

wells increases, however, the similarity of measured values 

generally decreases. On the other hand, if a flow barrier 

exists between two closely spaced wells due to folds, faults, 

or changes in lithology that affect the hydraulic properties 

of the aquifers, then the hydraulic response to a given stress 

may be different in each well. The presence of a large number 

of flow barriers will shorten the correlation distance, and the 

absence of barriers will result in a larger average distance 

of correlation. Variography provides an objective way of 

evaluating the average distance over which groundwaterelevation measurements may be used to make an estimate 

of groundwater elevation at another, non-measured location, 

although the results are heavily dependent on having data 

available throughout the defined structural region. 

The CPRAS was divided by geographic or structural 

regions on the basis of significantly different variography to 

improve the estimates of groundwater elevation developed 

using the kriging analysis. The structural regions used for 

analysis during this study were modified from Reidel and 

others (2002) and initially included the Yakima Fold Belt, 

Palouse Slope, Blue Mountains, and Clearwater Embayment. 

The extent of these structural regions (pl. 1) was modified 

on the basis of recent modeling of the extent and thickness 

of the hydrogeologic units and the geologic structures that 

form geologic compartments that may influence groundwater 

levels (E.R. Burns, U.S. Geological Survey, written commun., 

2009). The Blue Mountains and Clearwater Embayment 

structural regions were subsequently eliminated from the 

analysis because few of the spring 2009 groundwater-level 

measurements were within these regions. The arc-shaped 

Yakima Fold Belt is generally composed of long east-west 

trending valleys separated by fold-fault pairs defining the 

valley ridgetops (E.R. Burns, U.S. Geological Survey, written 

commun., 2009). Compared to the Yakima Fold Belt, the 

Palouse Slope is less deformed, with relatively few faults and 

less intense folding. On the basis of the significant difference 

in variography between the Palouse Slope and Yakima Fold 

Belt, whenever data from a specific hydrogeologic unit 

were sufficiently dense in each of these structural regions, 

water-level data within the regions were kriged separately. 

Kriging was used for interpolation of the 

groundwater-level residuals using a lateral grid size of 

1,000 ft. Kriging is based on a geostatistical theory predicated 

on the observation that values of spatially distributed data 

commonly are correlated—values at nearby locations are more 

highly correlated than values at distant locations (Alley, 1993, 

p. 87). Parameters for the kriging analysis were selected on 

the basis of the variography analysis and used to interpolate 

groundwater levels for each hydrogeologic unit by structural 

region. The regional trend, estimated using LOESS, and 

the kriged residuals, representing the configuration of the 

groundwater surface without the regional influence, were 

subsequently added together to produce the generalized 

groundwater-elevation maps for each hydrogeologic unit.
67 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System roundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

The estimated groundwater-elevation surfaces for each 

basalt hydrogeologic unit were compared to land-surface 

elevation to identify areas where artesian conditions 

(potential groundwater elevations greater than land-surface 

elevation) were indicated. Artesian conditions are common in 

selected areas within the CPRAS; however, the interpolated 

groundwater surface indicated that artesian conditions were 

in some areas where no data are available to support their 

presence, or that the magnitudes of the predicted artesian 

levels were deemed unreasonable. A small number of such 

areas occur along the edges of each hydrogeologic unit, where 

few data exist to constrain the interpolation or in topographical 

depressions or incised canyons where land-surface elevation 

decreases rapidly and no data are available for areas within the 

depression or along the canyon to guide the interpolation. In 

these situations, the interpolated groundwater elevations were 

modified such that the mapped groundwater elevations would 

not exceed the maximum artesian levels observed within each 

unit. The maximum artesian levels are 50, 225, and 300 ft 

above land-surface for the Saddle Mountains, Wanapum, and 

Grande Ronde, respectively.

The estimated groundwater-elevation surfaces for each 

basalt hydrogeologic unit also were compared to surfaces 

representing the estimated unit-top elevations from a 

three-dimensional hydrogeologic framework model (E.R. 

Burns, U.S. Geological Survey, written commun., 2009) to 

identify potentially unsaturated areas. On the basis of these 

comparisons, several areas within the Saddle Mountains and 

Wanapum Units may be unsaturated. These areas generally 

are associated with higher land-surface elevations where 

depths to water are greater and unit thicknesses are thinner. 

Because of the uncertainty associated with the estimates of the 

groundwater and unit-top elevations, these areas are retained 

on the groundwater-elevation maps.

Development of Groundwater-Level 

Change Maps

Groundwater levels measured during spring 1984 

and spring 2009 were compared for 470 wells to evaluate 

water-level changes for each of the hydrogeologic units and 

to construct groundwater-level change maps. The annualized 

rates of water-level change for the 25-year period between 

measurements were calculated for each well. This average 

rate of change based on only two measurements represents 

a long-term net change in water levels; the sign and rate of 

change in any particular year could be different and may not 

be representative of recent trends in water-level changes. 

The groundwater-level changes presented are for wells at 

specific locations and may not be representative of conditions 

throughout the CPRAS. 

Changes in Groundwater Conditions 

and Groundwater Levels

The accuracy of the groundwater-elevation maps depends 

on various factors pertaining to the quality, quantity, and 

spatial distribution of the data, the method of interpolation, 

and the hydrogeologic properties and stresses within the 

aquifers. Therefore, the maps of groundwater elevation are 

approximations whose accuracy is limited by the availability 

of data. Data density is insufficient to support their use for 

local or site-specific purposes. These maps are intended to 

provide a regional overview of groundwater conditions in the 

CPRAS during spring 2009. 

Groundwater Configuration

The configurations of the groundwater-elevation surface 

in the Saddle Mountains, Wanapum, and Grande Ronde 

units during spring 2009 are shown in plates 3, 4, and 5. 

The generalized groundwater-level maps provide a means 

to estimate regional-scale groundwater flow direction in that 

groundwater moves from areas of high to low water-level 

elevations. However, the groundwater flow system is 

three-dimensional and consists of vertical and horizontal 

components of flow that may change with depth in the flow 

system forming complex flow paths. The overall direction 

of groundwater flow for each of the basalt units is toward 

the major groundwater discharge areas, consisting primarily 

of parts of the Columbia River but also including parts of 

the Snake and Yakima Rivers. Data density was insufficient 

to quantify the local directions of groundwater flow, such 

as in structural basins embedded within the Yakima Fold 

Belt, although where units occur at or near land surface, 

groundwater flow generally is expected to be toward streams 

and rivers that occupy the lowest points in the CPRAS and to 

follow surface drainage patterns. Additionally, groundwater 

withdrawals from major pumping centers or widespread 

recharge from irrigation or canals may produce local to 

regional variations that may not be reflected in the maps.

Configuration of the groundwater-elevation surfaces 

for the three basalt units generally compare well with 

groundwater-elevation surface maps constructed for the 

three basalt units by Whiteman (1986) on the basis of water 

levels from spring 1984. The maps by Whiteman (1986) 

exhibit greater detail because they incorporate a more 

comprehensive set of data consisting of a larger set of wells 

and a variety of ancillary data including water levels from 

years other than 1984, surface-water features, and land-surface 

topography. The areas where groundwater elevations from 

1984 (Whiteman, 1986) and those from 2009 differ (where 

sufficient data were available for both dates) are most often 

associated with groundwater-level declines due to pumping 

since 1984 (see section titled “Water-Level Changes”).
Changes in Groundwater Conditions and Groundwater Levels 7

The groundwater-surface configuration for the Saddle 

Mountains unit is similar to that of land surface (pl. 3). 

The highest groundwater elevations exceed 2,000 ft are in 

eastern Klickitat County, Washington, where the highest 

land-surface elevations occur within the extent of the unit. 

The lowest groundwater elevations below 500 ft are in two 

low-lying areas along the Columbia River, along the border 

between Franklin and Benton Counties, Washington, and near 

the junction of Benton County and Morrow and Umatilla 

Counties, Oregon. However, due to the distribution of 

available data it is difficult to ascertain the overall directions 

of groundwater flow in the Saddle Mountains unit with much 

certainty, with the exception of flow that occurs southeastward 

along the axes of some valleys in the Yakima Fold Belt. 

A detailed groundwater elevation and flow direction map 

constructed for the Saddle Mountains unit (as well as the 

Wanapum, Grande Ronde, and Overburden units) in the 

Yakima River basin using water-level data from 2001 is 

presented in Vaccaro and others (2009).

The groundwater-surface configuration for the 

Wanapum unit is roughly a circular depression centered 

southwest of Pasco, Washington, with a slight northeast to 

southwest elongation and a probable outlet that follows the 

Columbia River to the west (pl. 4). With few exceptions, 

the highest groundwater elevations exceeding 2,000 ft occur 

along the eastern and northeastern extents of the unit. The 

groundwater-elevation surface generally slopes concentrically 

inward toward the Columbia and Snake Rivers, reaching 

minimum elevations of less than 400 ft from the northern 

end of Benton County extending southeastward to Pasco, 

Washington, and then extending southwestward to the 

northeast corner of Gilliam County, Oregon. The general 

directions of groundwater flow are southwestward from the 

margin of the Palouse Slope radially towards the Columbia 

River in the vicinity of Pasco, northward from the Oregon 

side to the Columbia River, and southeastward along the 

axes of valleys in the Yakima Fold Belt toward the Yakima or 

Columbia Rivers.

The configuration of the groundwater surface for the 

Grande Ronde unit is generally trough shaped, elongated 

from northeast to southwest in the Pasco, Washington, area 

and then along a more east-west trend along the Columbia 

River downstream of Pasco (pl. 5). The highest groundwater 

elevations occur along the southern, northwestern, and eastern 

extents of the unit with elevations exceeding 2,000 ft. With 

few exceptions, the groundwater-elevation surface slopes 

concentrically inward toward the Columbia and Snake Rivers, 

reaching minimum elevations of less than 200 ft along the 

Columbia River between The Dalles, Oregon, and Pasco, 

Washington. However, data from the central and deepest part 

of the Grande Ronde unit are sparse or nonexistent leading 

to high uncertainty in this area. The general directions of 

groundwater flow are similar to those for the Wanapum unit, 

with overall directions of flow moving radially from the 

margins of the unit toward the center of the CPRAS or the 

Columbia River.

The variography analysis indicated that the maximum 

range or distance that the groundwater level at a location in 

the Saddle Mountains unit (that is primarily within the Yakima 

Fold Belt) could be correlated with the level in another 

location is about 40 mi along a northwest-southeast direction, 

but only about 13 mi along a northeast-southwest direction. 

This difference in range by direction is because the correlation 

is determined not only by the distance between observations, 

but also by the direction from one observation to another. For 

example, water levels in wells along valleys are similar for 

much greater distances than across valleys, over ridges, and 

into adjacent valleys. This phenomenon is known as geometric 

anisotropy and may be explained by the presence of hydraulic 

barriers (such as those imposed by the faulted ridge tops in the 

Yakima Fold Belt) or by differences in stresses with direction 

(such as recharge from precipitation, irrigation, and canals, or 

discharge due to pumping). 

The area of the Wanapum unit primarily extends across 

the Yakima Fold Belt and Palouse Slope structural regions. 

The interpolation of groundwater levels was performed 

separately for each region and then combined to create a 

map of groundwater levels. Analyses of the Yakima Fold 

Belt observations yielded a low geometric anisotropy, with a 

range of about 13 mi along a northwest-southeast direction 

and 11 mi along a northeast-southwest direction. The Palouse 

Slope data showed no anisotropy and a range of about 36 mi.

The extent of the Grande Ronde unit includes large parts 

of the Yakima Fold Belt and Palouse Slope structural regions. 

Variography indicated that groundwater-level correlations 

within these two regions are substantially different. Within 

the Yakima Fold Belt, correlations extend about 38 mi along 

a northeast-southwest direction, with a slight anisotropy, 

resulting in correlations extending about 32 mi in a 

northwest-southeast direction. Within the Palouse Slope, the 

range is about 61 mi in a north-south direction, with a slight 

anisotropy indicating a range of about 51 mi in an east-west 

direction. 

Overall, the variography analysis was consistent with 

previously known groundwater flow features in the study 

area. The generally short ranges in the Yakima Fold Belt 

structural region indicate that the geologic complexity 

due to the large number of folds and faults contributes to 

compartmentalization of the groundwater flow system. 

The long ranges in the Palouse Slope result from the fewer 

number of faults and folds and indicate that the groundwater 

flow system is more continuous in this much less deformed 

structural region. The orientation of the greatest correlation of 

groundwater levels for the Saddle Mountains and Wanapum 

units within the Yakima Fold Belt is consistent with the dip of 

the valleys for which sufficient data are available. However, 

the sparse clusters of data relative to geological structures 

affect the results presented. As a result, the data are supportive 

and consistent with the geologic model, but the unqualified use 

of the parameters described above is not recommended when 

making predictions of groundwater elevations. 
89 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System roundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

Vertical head differences, calculated as the difference 

in groundwater elevations between an upper and lower 

hydrogeologic unit, give an indication of the magnitude and 

direction of vertical gradients that may influence the vertical 

component of flow. Accurate head differences depend on the 

availability of wells that are open to individual hydrogeologic 

units and are in close proximity (ideally within the same 

drill hole if properly constructed). Because of the limited 

availability of this type of data for the three basalt units, only 

generalized vertical head differences that were calculated by 

subtracting the estimated water-level surface from one unit 

from the estimated water-level surface from the underlying 

unit are discussed. Vertical head differences between the 

Saddle Mountains and Wanapum units indicate that downward 

gradients may exist in the Saddle Mountains unit in many 

of the upper elevation areas. Upward gradients may be in 

several low-lying areas, including along much of the length 

of the Columbia River and in some valleys of eastern Yakima 

County, Washington. Vertical head differences between the 

Wanapum and Grande Ronde units show no clear spatial 

patterns possibly as a result of limited data, pumping within 

either unit, or vertical compartmentalization that may be 

limiting vertical flow between the units (Porcello and others, 

2009).

The depth to water in the basalt units was estimated 

from the groundwater-elevation maps by subtracting the 

groundwater elevation from the land-surface elevation 

(maps of these calculated estimates are not shown). All three 

basalt units have a modest to strong correlation of depth to 

water with land-surface elevation, especially where the units 

are present at the surface. The correlation is strongest for 

the Saddle Mountains unit. Depth to water was generally 

shallowest in low-lying or deeply incised valleys and deepest 

in the higher land-surface elevation and mountainous areas. 

Water-Level Changes

Small to moderate net groundwater-level declines 

between 1984 and 2009 were measured in most wells, 

although large declines greater than 100 ft and as great as 

300 ft and essentially unchanged groundwater levels were not 

uncommon (pls. 6, 7, 8, and 9; table 1). Of the wells measured 

in 1984 and 2009, water levels declined in 83 percent of 

the wells and declines greater than 25 ft were measured in 

29 percent of all wells. The magnitude of changes in water 

level depends on the change in storage within the aquifer, 

which is a function of the quantity of recharge or discharge 

added or removed from the aquifer and the storage properties 

of the aquifer.

The smallest change in groundwater levels in terms 

of maximum decline, maximum rise, and mean change 

was measured in the Overburden unit (pl. 6; table 1). The 

frequency distribution of water-level changes indicates that 

little change in water levels occurred in most areas, although 

some areas showed a tendency toward small groundwater 

declines and a few areas exhibited small groundwater rises. 

Of the wells measured in spring 1984 and spring 2009, 

water levels declined in 87 percent of the wells, although 

declines greater than 25 ft were measured in only 8 percent 

of the wells. Most of the wells measured in the Overburden 

unit as part of this analysis are located within the Hanford 

Site operated by the Department of Energy in northern 

Benton County, Washington. Water levels in the area of the 

Hanford Site showed little change except for the central or 

northwestern areas, which show small to moderate water level 

declines. These declines can be largely attributed to the 

substantial decrease in liquid effluent disposal at the Hanford 

Site during the 1990s (Pacific Northwest National Laboratory, 

2009). 

Most groundwater levels measured in the Saddle 

Mountains unit showed small declines, although large declines 

or small to moderate rises were indicated in some areas (pl. 7; 

table 1). Water levels declined in 68 percent of the wells and 

declines were greater than 25 percent in 16 percent of the 

wells. The magnitudes of the water-level changes were low 

relative to the other basalt hydrogeologic units. Spatial trends 

in water-level changes in the Saddle Mountains unit were 

difficult to discern due to the distribution of the data. An area 

of small groundwater-level declines was identified in the 

central area of the Hanford Site. Groundwater declines also 

were identified in the Yakima River basin. Small water-level 

rises were measured in the area along the northeast side of the 

Columbia River within the Palouse Slope.

Table 1. Change in groundwater levels in wells in the Columbia 

Plateau Regional Aquifer System, Washington, Oregon, and Idaho, 

from spring 1984 to spring 2009.

[Negative values indicate a decline in groundwater levels]

Hydrogeologic unit

Overburden Saddle 

Mountains Wanapum Grande Ronde

Number of wells 197 50 87 136

Change in groundwater level, in feet

Maximum decline -147 -244 -249 -298

Maximum rise 44 77 94 90

Mean change -7 -12 -33 -51

Annualized change in groundwater level, in feet per year

Maximum rate of 

decline

-5.9 -9.8 -9.9 -11.9

Maximum rate of 

rise

1.8 3.1 3.8 3.6

Mean rate of change -.3 -.5 -1.3 -2.0
References Cited 9

Groundwater levels in the Wanapum unit mostly showed 

small or moderate declines, with large declines (greater than 

100 ft) in a few areas (pl. 8; table 1). Between 1984 and 2009, 

water levels declined in 78 percent of the wells measured and 

declines greater than 25 ft were measured in 38 percent of the 

wells. Wells within the Yakima Fold Belt structural region 

generally had larger groundwater declines relative to the 

Palouse Slope. This may be the combined result of pumping 

and the increased compartmentalization of the groundwater 

system by geologic structures present in the Yakima Fold Belt. 

The largest concentration of declines was in the Yakima River 

basin, which corresponds to areas of heavy pumping within 

the Wanapum unit (Whiteman and others, 1994).

Groundwater levels changed in the Grande Ronde 

unit more than water levels in the other units in terms of 

maximum decline and mean change (pl. 9; table 1). Moderate 

declines in water levels were measured in most areas, with 

declines greater than 100 ft and some greater than 200 ft. 

Water levels declined in 87 percent of the wells, and declines 

greater than 25 ft were measured in 60 percent of the wells. 

Substantial rises in groundwater levels were measured in 

few wells. Groundwater declines were present in the Grande 

Ronde unit throughout much of the area where wells were 

measured. The largest concentrations of declines were in 

the central northern part of the study area that extends from 

western Lincoln County, Washington, southward into eastern 

Grant and southwestern Adams Counties, Washington. Large 

concentrations of declines also were measured in the part of 

the Umatilla River basin in northeast Morrow and western 

Umatilla Counties, Oregon, and in the Pullman, Washington, 

and Moscow, Idaho, area. These concentrations of declines in 

water levels correspond with areas of heavy pumping within 

the Grande Ronde unit (Whiteman and others, 1994).

This report provides a regional assessment of 

groundwater levels during spring 2009 based on an inventory 

of 1,752 wells in the Columbia Plateau of Washington, 

Oregon, and Idaho. Data included in the report are from field 

investigations and a compilation of published and unpublished 

well data from many agencies. Water-level change maps are 

presented for the Overburden, Saddle Mountains, Wanapum, 

and Grande Ronde units and indicate trends toward waterlevel declines in many areas since 1984. The distribution of 

wells monitored in spring of 2009 provide information on 

where additional monitoring would better define the response 

of the groundwater system to stresses such as pumping, 

irrigation, and climate.

Acknowledgments

The authors thank the many people that contributed 

their time and knowledge to help complete this study. We are 

grateful to the many well owners who have permitted access 

to their wells, well drillers who have diligently recorded and 

reported their findings, and the many people and agencies that 

collect, analyze, maintain, or disseminate the scientific data 

needed for studies of groundwater systems. The following 

agencies are noted for their special assistance with the 

collection of data used in this study: U.S. Department of 

Energy, Oregon Water Resources Department, Confederated 

Tribes of the Umatilla Indian Reservation, Washington 

Department of Ecology, South Columbia Basin Irrigation 

District, Walla Walla Basin Watershed Council, Palouse 

Basin Aquifer Committee, East Columbia Basin Irrigation 

District, Bureau of Reclamation, Franklin Conservation 

District, and the Columbia Basin Ground Water Management 

Area. USGS employees whose efforts contributed to the 

study include Erick Burns, Matt Ely, and Sue Kahle, whose 

statistical, modeling, and geologic expertise facilitated the 

interpretation of the data; Gregory Justin, Karen Payne, 

Danial Polette, Kevin Knutson, Rachel Peavler, Keith Hein, 

Peter Elliott, Tessa Harden, Annette Campbell, and Benjamin 

Johnson (volunteer) who assisted in the collection of field 

data to supplement the knowledge of the groundwater system; 

Leonard Orzol, Tiffany Jacklin, and Elisabeth Fasser whose 

skills greatly simplified access to existing data; David Morgan 

and Richard Dinicola for their guidance and support, and the 

many other USGS employees whose everyday efforts go to 

support this and many other studies.

References Cited

Alley, W.M., 1993, Geostatistical models, in Alley, W.M., ed., 

Regional ground-water quality: New York, Van Nostrand 

Reinhold, p. 87-108.

Bauer, H.H., and Hansen, A.J., 2000, Hydrology of the 

Columbia Plateau regional aquifer system, Washington, 

Oregon, and Idaho: U.S. Geological Survey WaterResources Investigations Report 96-4106, 61 p. (Also 

available at http://pubs.er.usgs.gov/usgspubs/wri/

wri964106.)
101 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System roundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

Bossong, C.R., Karlinger, M.R., Troutman, B.M., and 

Vecchia, A.V., 1999, Overview and technical and practical 

aspects for use of geostatistics in hazardous-, toxic-, and 

radioactive-waste-site investigations: U.S. Geological 

Survey Water-Resources Investigations Report 98-4145, 

70 p. (Also available at http://pubs.er.usgs.gov/usgspubs/

wri/wri984145.)

Davis, J.C., 2002, Statistics and data analysis in geology (3d 

ed.): New York, John Wiley and Sons, 638 p.

Drost, B.W., Whiteman, K.J., and Gonthier, J.B., 1990, 

Geologic framework of the Columbia Plateau Aquifer 

System, Washington, Oregon, and Idaho: U.S. Geological 

Survey Water-Resources Investigations Report 87-4238, 

10 p., 10 sheets. (Also available at http://pubs.er.usgs.gov/

usgspubs/wri/wri874238.)

Kahle, S.C., Olsen, T.D., and Morgan, D.S., 2009, Geologic 

setting and hydrogeologic units of the Columbia Plateau 

Regional Aquifer System, Washington, Oregon, and Idaho: 

U.S. Geological Survey Scientific Investigations Map 3088, 

1 sheet. (Also available at http://pubs.er.usgs.gov/usgspubs/

sim/sim3088.)

Newcomb, R.C., 1959, Some preliminary notes on ground 

water in the Columbia River Basalt: Northwest Science, 

v. 33, no. 1, p. 1-18, accessed September 3, 2009, at http://

www.vetmed.wsu.edu/org_NWS/NWSci%20journal%20

articles/1950-1959/1959%20vol%2033/33-1/v33%20

p1%20Newcomb.PDF.

Pacific Northwest National Laboratory, 2009, Hanford Site 

environmental report for calendar year 2008: prepared for 

U.S. Department of Energy under Contract DE-AC05-

76RL01830; available from the National Technical 

Information Service, U.S. Department of Commerce, 

Springfield, Va., variously paged, accessed September 3, 

2009, at http://hanford-site.pnl.gov/envreport/2008/pnnl18427.pdf.

Porcello, J.J., Tolan, T.L., and Lindsey, K.A., 2009, 

Groundwater level declines in the Columbia River 

Basalt Group and their relationship to mechanisms for 

groundwater recharge—A conceptual groundwater system 

model, Columbia Basin Ground Water Management Area 

of Adams, Franklin, Grant, and Lincoln Counties: Othello, 

Washington: prepared by the Columbia Basin Ground Water 

Management Area of Adams, Franklin, Grant, and Lincoln 

Counties, June, 2009, 175 p., accessed September 3, 2009, 

at http://www.cbgwma.org/pdf/GWMA_Groundwater%20

Level%20Declines_%20TEXT_June%202009.pdf.

Reidel, S.P., Johnson, V.G., and Spane, F.A., 2002, Natural 

gas storage in basalt aquifers of the Columbia Basin, Pacific 

Northwest USA—A guide to site characterization: Pacific 

Northwest National Laboratory, Richland, Washington, 

variously paginated, accessed August 22, 2009, at http://

www.pnl.gov/main/publications/external/technical_reports/

PNNL-13962.pdf.

Tolan, T.L., Reidel, S.P., Beeson, M.H., Anderson, J.L., Fecht, 

K.R., and Swanson, D.A., 1989, Revisions to the estimates 

of the areal extent and volume of the Columbia River Basalt 

Group, in Reidel, S.P., and Hooper, P.R., eds., Volcanism 

and tectonism in the Columbia River flood-basalt province: 

Geological Society of America Special Paper 239, p. 1-20.

U.S. Geological Survey, 1999, National Elevation Dataset: 

U.S. Geological Survey Fact Sheet 148-99, 2 p. (Also 

available at http://erg.usgs.gov/isb/pubs/factsheets/fs14899.

html.)

U.S. Geological Survey, 2008, Ground-Water Availability 

Assessment for the Columbia Plateau Regional Aquifer 

System, Washington, Oregon, and Idaho: U.S. Geological 

Survey Fact Sheet 2008-3086, 2 p. (Also available at http://

pubs.er.usgs.gov/usgspubs/fs/fs20083086.)

Vaccaro, J.J., 1999, Summary of the Columbia Plateau 

Regional Aquifer-System Analysis, Washington, Oregon, 

and Idaho: U.S. Geological Survey Professional Paper 

1413-A, 51 p. (Also available at http://pubs.er.usgs.gov/

usgspubs/pp/pp1413A.)

Vaccaro, J.J., Jones, M.A., Ely, D.M., Keys, M.E., Olsen, 

T.D., Welch, W.B., and Cox, S.E., 2009, Hydrogeologic 

framework of the Yakima River basin aquifer system, 

Washington: U.S. Geological Survey Scientific 

Investigations Report 2009–5152, 106 p. (Also available at 

http://pubs.er.usgs.gov/usgspubs/sir/sir20095152.)

Whiteman, K.J., 1986, Ground-water levels in three basalt 

hydrologic units underlying the Columbia Plateau, 

Washington and Oregon, spring 1984: U.S. Geological 

Survey Water-Resources Investigations Report 86-4046, 

4 sheets. (Also available at http://pubs.er.usgs.gov/

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Appendix 11

Appendix A. Records of Selected Wells in the Columbia Plateau Regional 

Aquifer System

The appendix contains limited information for selected wells including identifier, location, elevation, construction, water levels, 

and hydrogeologic unit and is available in a Microsoft Excel spreadsheet at http://pubs.usgs.gov/sir/2010/5040/. 
12 Groundwater Conditions 2009, and Changes in Groundwater Levels 1984–2009, Columbia Plateau Regional Aquifer System

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