Prepared in cooperation with Public Utility District No. 1 of Chelan County

Conceptual Model of Hydrologic and Thermal Conditions of the 

Eastbank Aquifer System near Rocky Reach Dam, 

Douglas County, Washington

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2008–5071
Cover: Downstream view of Columbia River upstream of Rocky Reach Dam near 

Wenatchee, Washington. The Eastbank Aquifer system is located in the river-terrace 

deposit in the center-left of the picture on the front cover. Photograph by Marijke 

van Heeswijk, U.S. Geological Survey, January 27, 2008.
Conceptual Model of Hydrologic and 

Thermal Conditions of the Eastbank Aquifer 

System near Rocky Reach Dam, Douglas 

County, Washington

By Marijke van Heeswijk, Stephen E. Cox, Raegan L. Huffman, and Christopher A. 

Curran

Prepared in cooperation with Public Utility District No. 1 of Chelan County

Scientific Investigations Report 2008–5071

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

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natural hazards, and the environment:

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U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

van Heeswijk, Marijke, Cox, S.E., Huffman, R.L., and Curran, C.A, 2008, Conceptual model of hydrologic and thermal 

conditions of the Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington: U.S. Geological 

Survey Scientific Investigations Report 2008–5071, 66 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Description of Study Area ...................................................................................................................4

Previous Investigations........................................................................................................................5

Well-Numbering System......................................................................................................................6

Methods of Investigation .............................................................................................................................6

Water-Quality Sampling Procedures.................................................................................................6

Laboratory Analytical Procedures.....................................................................................................7

Hydrogeology .................................................................................................................................................7

Geologic Setting....................................................................................................................................7

Hydrogeologic Units.............................................................................................................................7

Hydrology .....................................................................................................................................................16

Aquifer Conditions Before and After Construction of Rocky Reach Dam.................................16

Sources of Ground-Water Recharge and Discharge ...................................................................16

Historical Ground-Water Discharge................................................................................................19

Ground-Water Pumpage...........................................................................................................19

Ground-Water Seepage Through the Subsurface Cutoff Wall ..........................................21

Historical Ground- and Surface-Water Levels ..............................................................................22

Reliability of Historical Water-Level Measurements...........................................................22

Ground-Water Levels on July 18, 2007 ...................................................................................24

Prior to Cessation of Ground-Water Pumping .............................................................25

Two Hours after Cessation of Ground-Water Pumping..............................................25

Historical Ground- and Surface-Water Temperatures.................................................................28

Reliability of Historical Water-Temperature Measurements..............................................29

Trends in Water Temperatures ................................................................................................30

Vertical Temperature Profiles.........................................................................................32

Spatial Patterns ................................................................................................................34

Time Lags ..................................................................................................................34

Annual Temperature Ranges ................................................................................39

Annual Temperature Extremes ..............................................................................39

Water Quality.......................................................................................................................................42

Spatial Patterns..........................................................................................................................43

Conceptual Model of Hydrologic and Thermal Conditions...................................................................47

Data Needs ..................................................................................................................................................49

Summary .......................................................................................................................................................49

Acknowledgments ......................................................................................................................................51

References Cited..........................................................................................................................................51

Appendix 1. Hydrogeologic Cross Sections of the Eastbank Aquifer System, Douglas 

County, Washington.......................................................................................................................53

Appendix 2. Summary of Down-Hole Camera Surveys of Selected Wells of the Eastbank 

Aquifer System, Douglas County, Washington, December 11–13, 2007................................59

Appendix 3. Natural-Gamma Logs of Selected Wells of the Eastbank Aquifer System, 

Douglas County, Washington, December 13, 2007....................................................................65
iv

Figures

Figure 1. Map showing location of Eastbank Aquifer system and vicinity, Douglas

County, Washington ........................................................................ 2

Figure 2. Map showing locations of the Eastbank Hatchery, subsurface cutoff wall,

wells, weirs, river-monitoring site, and U.S. Geological Survey gaging station,

Douglas County, Washington............................................................... 3

Figure 3. Graphs showing mean monthly precipitation and mean monthly minimum and

maximum air temperatures for the Wenatchee climate station (site 459074),

Chelan County, Washington, 1971–2000................................................... 5

Figure 4. Diagram showing well-numbering system used in Washington ..................... 6

Figure 5. Schematic hydrogeologic cross section through the south-central part of the

Eastbank Aquifer system, Douglas County, Washington .............................. 8

Figure 6. Map showing thickness of the Clay Confining Unit, Eastbank Aquifer system,

Douglas County, Washington............................................................... 9

Figure 7. Map showing altitude of the top of bedrock, Eastbank Aquifer system,

Douglas County, Washington............................................................... 10

Figure 8. Map showing thickness of the Lower Aquifer, Eastbank Aquifer system,

Douglas County, Washington............................................................... 11

Figure 9. Map showing wells that are currently (2008) completed in the Eastbank

Aquifer system and hydrogeologic units to which they are open, Douglas

County, Washington ........................................................................ 13

Figure 10. Map showing water-level and temperature monitoring network, Eastbank

Aquifer system, Douglas County, Washington .......................................... 17

Figure 11. Map showing potentiometric surface of the Lower and Combined Aquifers 

for post-dam, predevelopment conditions, Eastbank Aquifer system, Douglas

County, Washington, 8:30 a.m., July 19, 1977 ............................................. 18

Figure 12. Graphs showing annual mean and quarterly mean pumpage from the RW 

and CT well fields, Eastbank Aquifer System, Douglas County, Washington,

1990–2006 .................................................................................... 20

Figure 13. Graph showing instantaneous discharge through the North and South Weirs

and total instantaneous discharge, Eastbank Aquifer System, Douglas

County, Washington, 1977–2006............................................................ 22

Figure 14. Graph showing daily mean water levels recorded by the monitoring network

of the Eastbank Aquifer system, Douglas County, Washington, and daily

water levels recorded at midnight by USGS gaging station 12453679, Chelan

County, Washington, January 1991 – September 2006 ................................. 23

Figure 15. Map showing potentiometric surface of the Lower and Combined Aquifers

prior to the shutdown of pumping wells, Eastbank Aquifer system, Douglas

County, Washington, July 18, 2007......................................................... 26
v

Figure 16. Map showing potentiometric surface of the Lower and Combined Aquifers 

2 hours after shutdown of pumping wells, Eastbank Aquifer system, Douglas

County, Washington, 3 p.m., July 18, 2007 ................................................ 27

Figure 17. Graph showing daily median water temperatures recorded by the monitoring

network of the Eastbank Aquifer system, Douglas County, Washington, 2006 ...... 28

Figure 18. Graph showing daily river water temperatures recorded at midnight at the

forebay of Rocky Reach Dam and at probe RIV of the monitoring network 

of the Eastbank Aquifer system, Douglas County, Washington, 

March 25, 2003 – August 15, 2007 ......................................................... 30

Figure 19. Graph showing annual minimum, maximum, and mean temperature of the

Columbia River near the Eastbank Aquifer system, Douglas County,

Washington, 1991–2007 ..................................................................... 32

Figure 20. Selected vertical temperature profiles in wells CD6, CD47, and TH8 of the

Eastbank Aquifer system, Douglas County, Washington, 1989–2008 .................. 33

Figure 21. Graphs showing time lag between annual minimum and maximum temperatures 

in the Columbia River at probe RIV and in wells of the monitoring network of the 

Eastbank Aquifer system, Douglas County, Washington, 1991–2007 .................. 35

Figure 22. Map showing spatial distribution of trends in time lags between annual

minimum and maximum temperatures measured in the Columbia River at

probe RIV and in wells of the monitoring system of the Eastbank Aquifer

system with probes in the Lower or Combined Aquifers, 1991–98, and time

lags between annual maximum temperatures in the river and wells in 1991,

1999, and 2006, Douglas County, Washington .......................................... 40

Figure 23. Graphs showing ratio of annual temperature range between wells of the

monitoring network of the Eastbank Aquifer system and the Columbia River 

at probe RIV for wells with temperature probes at the depth of the Upper

Aquifer or Clay Confining Unit and the Lower Aquifer or Combined Aquifer,

Douglas County, Washington, 1991–2006 ................................................ 41

Figure 24. Graph showing annual maximum temperature in wells of the monitoring

network of the Eastbank Aquifer system and the Columbia River at probe 

RIV, Douglas County, Washington, 1999–2006 .......................................... 42

Figure 25. Maps showing spatial distribution of water-quality sampling sites and

selected water-quality constituents in the Columbia River and Eastbank

Aquifer system, Douglas County, Washington, August 20–22, 2007 .................. 44

Figure 26. Map showing generalized horizontal ground-water flow directions and fluxes

for current (2008) conditions of the Lower and Combined Aquifers of the

Eastbank Aquifer system, Douglas County, Washington .............................. 48

Figures—Continued
vi

Tables

Table 1. Hydrogeologic-unit names and terminology used in this study and previous

studies, Eastbank Aquifer system, Douglas County, Washington ..................... 8

Table 2. Transmissivities and storativities of the Lower Aquifer, Eastbank Aquifer

system, Douglas County, Washington ................................................... 12

Table 3. Summary information for wells completed in the Eastbank Aquifer system,

Douglas County, Washington............................................................... 14

Table 4. Differences between water levels measured manually and those recorded by

the monitoring network, Eastbank Aquifer system, Douglas County,

Washington, February 2006 and July 2007................................................ 24

Table 5. Comparison of temperature measurements by probes in selected wells of the

monitoring network of the Eastbank Aquifer system and two thermometers,

Douglas County, Washington, September 12, 2007 .................................... 31

Table 6. Summary of temperature trends in the Eastbank Aquifer system, Douglas

County, Washington, 1991–2007............................................................ 38

Table 7. Physical properties and concentrations of bacterial cells and selected

dissolved constituents in ground-water and surface-water samples,

Eastbank Aquifer System, Douglas County, Washington, August 20–22, 2007 ...... 46
vii

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2

) 

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2

) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

Hydraulic conductivity

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

Transmissivity*

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d) 

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

°F=(1.8×°C)+32.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Datums

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

(NGVD 29), unless otherwise noted. 

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

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

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Abstract 

The Lower and Combined Aquifers of the Eastbank 

Aquifer system, located in a river-terrace deposit along the 

Columbia River near Rocky Reach Dam, Washington, are 

primarily recharged by the Columbia River and provide water 

to the Eastbank Hatchery and the regional water system 

servicing the cities of Wenatchee, East Wenatchee, and parts 

of unincorporated Chelan and Douglas Counties. In 2006, 

mean annual pumpage from the aquifers by the hatchery and 

regional water system was about 43 and 16 cubic feet per 

second, respectively. Reportedly, temperatures of ground water 

pumped by the hatchery have been increasing, thereby making 

water potentially too warm for salmonid fish production. An 

evaluation of hourly ground-water and river temperatures 

from January 1991 through August 2007 indicates increasing 

interannual trends in temperatures in most of the Lower and 

Combined Aquifers from 1999 through 2006 that correspond 

to increasing trends in the annual mean and annual maximum 

river temperatures during the same period of 0.07 and 0.17°C 

per year, respectively. There were no trends in the annual 

minimum river temperatures from 1999 through 2006, and 

there were no trends in the annual minimum, mean, and 

maximum river temperatures from 1991 through 1998 and 

from 1991 through 2007. Increases in river temperatures from 

1999 through 2006 are within the natural variability of the 

river temperatures.

Most of the Lower and Combined Aquifers reached 

thermal equilibrium—defined by constant time lags between 

changes in river temperatures and subsequent changes in 

ground-water temperatures—during 1991–98. The only 

exceptions are the Combined Aquifer north of the well field 

of the regional water system, which had not reached thermal 

equilibrium by 2006, and the Lower Aquifer west of the 

well fields of the hatchery and the regional water system, 

which reached thermal equilibrium prior to 1991. Because 

most of the Lower and Combined Aquifers were in thermal 

equilibrium from 1999 through 2006 and seasonal pumpage 

patterns were relatively stable, reported trends of increasing 

temperatures of water pumped by the hatchery well field 

are most likely explained by increasing trends in river 

temperatures. Most of the water pumped by the hatchery well 

field recharges in an area west to southwest of the well field 

about 2 months prior to the time it is pumped from the aquifer. 

The northern extent of the hatchery well field may pump some 

colder water from a bedrock depression to the north and west 

of the well field. The conceptual model of hydrologic and 

thermal conditions is supported by analyses of historical water 

temperatures, water-level data collected on July 18, 2007, and 

dissolved-constituent and bacterial concentrations in samples 

collected on August 20–22, 2007.

Introduction 

The Eastbank Aquifer system is located in sedimentary 

deposits east of and adjacent to Rocky Reach Dam, which is 

a run-of-the-river hydroelectric dam on the Columbia River 

north of Wenatchee and East Wenatchee, Washington (fig. 1). 

Construction of the dam began in 1956 and the dam is owned 

and operated by Public Utility District No. 1 of Chelan 

County (PUD). By the time the dam was put into commercial 

operation in 1961, the water level of the Columbia River was 

raised from a natural low water level of about 610 ft (Stone 

and Webster Engineering Corporation, 1959) to a full-pool 

level of 707 ft. This rise formed a lake called Lake Entiat, 

which extends from Rocky Reach Dam upstream to Wells 

Dam (fig. 1). The water-level rise of the Columbia River 

similarly increased the saturated thickness of the Eastbank 

Aquifer system. As part of dam construction, a subsurface 

cutoff wall was constructed in the aquifer system (fig. 2) to 

minimize seepage around the eastern extent of Rocky Reach 

Dam and prevent destabilization of the east bank. This cutoff 

wall in effect acts as a “subsurface dam” and helps maintain 

elevated ground-water levels in the Eastbank Aquifer system 

to the north of the cutoff wall. The result is that the drop in 

ground-water levels from north to south of the cutoff wall 

is similar to the drop in river water levels from upstream to 

downstream of Rocky Reach Dam. 

Conceptual Model of Hydrologic and Thermal Conditions 

of the Eastbank Aquifer System near Rocky Reach Dam, 

Douglas County, Washington

By Marijke van Heeswijk, Stephen E. Cox, Raegan L. Huffman, and Christopher A. Curran
2 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 1. Location of Eastbank Aquifer system and vicinity, Douglas County, Washington.

tac08-0189_fig01

47°

55'

120°25' 120°20' 120°15' 120°10' 120°05' 120° 119°55' 119°50'

47°

50'

47°

45'

47°

40'

47°

35'

47°

30'

47°

25'

Base from U.S. Geological Survey digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Chelan

Wenatchee

Entiat

East Wenatchee

Waterville

Wenatchee

River

Swakane Creek

Lake Chelan

Entiat

Lake

Entiat Lake

Roaring Creek

Mud

Creek

Entiat

River

Rock

 Island

Creek

Beaver Creek

 Douglas

Creek

Chelan

R.

Columbia

River

Columbia River

Antoine Creek

WASHINGTON

Figure

location Cascade Range

0

0

10 MILES

10 15 KILOMETERS

5

5

OKANOGAN CO

CHELAN CO

GRANT CO

CHELAN CO

DOUGLAS CO

DOUGLAS CO

CHELAN CO

Columbia

River

US

2

US

2

US

2

US

2

US

97

US

2

US

97

US

97

US

97

ALT

97

ALT

97

ALT

97

ALT

97

US

97

SR

285

SR

28

SR

971

SR

172

SR

172

SR

28

US

97

SR

150

Wells Dam

Rocky

Reach

Dam

Lincoln

Rock

State

Park

Study

area

Lake

Chelan

Dam

Turtle

Rock

Island

Study

area
Introduction 3

Figure 2. Locations of the Eastbank Hatchery, subsurface cutoff wall, wells, weirs, river-monitoring site, and U.S. 

Geological Survey gaging station, Douglas County, Washington.

tac08-0189_fig02

120°18' 120°17'30" 120°17' 120°16'30"

47°

32'

30"

47°

31'

30"

47°

32'

Well, weir, or river site and

Subsurface cutoff wall

Approximate park boundary 

RW4

Eastbank Hatchery

USGS gaging station and No.

Land-surface contour—Shows

 altitude of ground surface. 

 Contour interval 20 feet. 

 Datum is NAVD 88 

720

12453679

 site name

EXPLANATION

720

740

760

760

720

740

760

740

US

2

US

97

0

0 500 1,000 1,500 FEET

100 200 300 400 METERS

Rocky

Reach

Dam

boat

Lincoln Rock ramp COLUMBIA RIVER

State Park

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

LR well field

RW well field

SW well field

North Weir

South Weir

TH6

TH5

TH4

TH2

RIV

CT2

TH7 TH9

TH1

CD10

CD8 CD6

12453679

North Weir

South Weir

LR1

LR2-E

LR2-W

RW3

RW4

RW2

RW1

CT1

CT3

CT4

TH8 TH7

CD47

SW14

SW13

SW11

12453679

CT well field
4 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

The primary use of the Eastbank Aquifer system 

is to supply water for an on-site fish hatchery called the 

Eastbank Hatchery (fig. 2), and the regional water system 

serving the cities of Wenatchee, East Wenatchee, and parts 

of unincorporated Chelan and Douglas Counties. In 2006, 

mean annual pumpage from the regional water system was 

about 16 ft3/s and mean annual pumpage from the Eastbank 

Hatchery was about 43 ft3/s. The regional water system pumps 

water from the RW well field—wells RW1, RW2, RW3, and 

RW4 (fig. 2) and serves more than 65,000 people through 

about 26,000 connections (M. Cockrum, City of Wenatchee, 

written commun., 2008). As the population of the service area 

continues to grow, the regional water system may need to 

pump more water in the future to serve additional customers. 

The hatchery pumps water from the CT well field—wells 

CT1, CT2, CT3, and CT4 (fig. 2). The secondary use of the 

Eastbank Aquifer system is to supply irrigation water for 

Lincoln Rock State Park (LR well field—wells LR1, LR2-E, 

and LR2-W; fig. 2), a small quantity of industrial water to 

lubricate turbines of the Rocky Reach Hydroelectric Project 

(wells SW13 and SW14 of the SW well field; fig. 2), and 

a small quantity of irrigation water for miscellaneous sites 

outside Lincoln Rock State Park (well SW11 of the SW well 

field; fig. 2).

The Eastbank Hatchery is owned by the PUD and 

operated by the Washington Department of Fish and Wildlife. 

The hatchery forms part of the Anadromous Fish Agreement 

and Habitat Conservation Plans that allow the PUD to 

operate the Rocky Reach and Rock Island Hydroelectric 

Projects under license agreements with the U.S. Federal 

Energy Regulatory Commission (FERC). The hatchery helps 

compensate for losses of sockeye, spring and summer Chinook 

salmon, and summer steelhead (Public Utility District No. 1 of 

Chelan County, 2007a). Successful operation of the hatchery 

relies on access to relatively cool ground water, preferably 

not exceeding 13°C (Ian Adams, Public Utility District No. 1 

of Chelan County, written commun., 2008). Ground-water 

temperatures are reported to have increased in recent years. 

If these increases continue, the PUD would either need a 

different approach for supplying appropriate water to the 

hatchery or alternative solutions for meeting its hatchery 

obligations. 

To help understand why the ground-water temperatures 

may have been increasing and to determine the data needs for 

possible future evaluations of aquifer-system management 

alternatives that maintain sufficiently cool ground water for 

the successful production of fish in the Eastbank Hatchery, 

the PUD requested that the U.S. Geological Survey (USGS) 

conduct a study of the Eastbank Aquifer system. The objective 

of this study is to improve the understanding of the hydrologic 

and thermal conditions of the Eastbank Aquifer system and the 

processes that affect those conditions. The objective was met 

by evaluating available hydrologic, water-temperature, and 

related information, identifying data gaps, collecting new data, 

and developing an updated data-collection program.

Purpose and Scope

This report documents the development of a conceptual 

model of hydrologic and thermal conditions of the Eastbank 

Aquifer system near Rocky Reach Dam, Douglas County, 

Washington, and the need for additional data and analyses to 

improve the understanding of the Eastbank Aquifer system. 

Information used to develop the conceptual model includes 

reports that document the design and construction of the 

subsurface cutoff wall east of Rocky Reach Dam (Stone 

and Webster Engineering Corporation, 1959), analyses of 

the hydrology and hydrogeology of the Eastbank Aquifer 

system (CH2M Hill, 1977 and 1988; Water & Environmental 

Systems Technology, Inc., 1990), vertical temperature 

profiles of the ground-water system (Water & Environmental 

Systems Technology, Inc., 1990), and numerical models of the 

Eastbank Aquifer system that simulate hydrologic and thermal 

conditions starting in 1989–90 (Water & Environmental 

Systems Technology, Inc., 1990 and 1998). Additional 

information evaluated include hourly river and aquifer water 

levels and water temperatures collected by the PUD in a 

monitoring network since 1990, miscellaneous data from PUD 

files, historical ground-water pumpage from wells supplying 

the regional water system and Eastbank Hatchery, and 

water-level, water-temperature, and other water-quality data 

collected during 2007–08 as part of this study.

Description of Study Area

The study area is located in Douglas County, Washington, 

in a river-terrace deposit along the east side of the Columbia 

River about 8 mi north of Wenatchee (fig. 1). The study area, 

which covers about 150 acres, includes Lincoln Rock State 

Park and the area to the south, including a subsurface cutoff 

wall constructed as part of Rocky Reach Dam. The dam is 

located at river mile (RM) 473.7 and creates Lake Entiat 

(fig. 1), which ranges in altitude from a normal low pool of 

703 ft to a normal full pool of 707 ft (Public Utility District 

No. 1 of Chelan County, 2007b). The Columbia River drainage 

area upstream of Rocky Reach Dam is about 88,000 mi2

and drains parts of Washington, Idaho, and Montana; 

and British Columbia, Canada. Mean discharge at Rocky 

Reach Dam for the period of record (October 1961 through 

September 2006) is 113,900 ft3/s with a maximum discharge 

of about 535,000 ft3/s on June 10, 1961, and a minimum 

daily discharge of 25,100 ft3/s on November 11, 1973 (U.S. 

Geological Survey, 2007).

The subsurface of the study area consists of coarse- and 

fine-grained sediments deposited along the east side of the 

Columbia River Valley on top of metamorphic bedrock. This 

bedrock forms the base beneath Rocky Reach Dam and crops 

out along the west bank of the river. East of the study area, 

metamorphic bedrock is overlain by Columbia River flood 

basalts that form the Columbia Plateau. The topography of 

the study area has low relief, with an average altitude of about 
Introduction 5

740 ft (fig. 2). Bedrock on the west and east sides of the 

river steeply rises to altitudes exceeding 2,400 and 2,000 ft, 

respectively, within 1 mi of the study area.

The climate of the study area exhibits characteristics of 

both maritime and continental climates (National Oceanic 

and Atmospheric Administration Western Regional Climate 

Center, 2007a). The prevailing wind direction is from the 

southwest or west, which brings in the remnants of humid 

air masses generated over the Pacific Ocean after their flow 

has been impeded by the Cascade Range. Extreme summer 

and winter temperatures occur when the wind direction shifts 

to the north and east and continental air flows into the area 

(National Oceanic and Atmospheric Administration Western 

Regional Climate Center, 2007a). Generally, summers in 

the study area are warm and dry and winters are cold and 

also relatively dry. During the most recent climate-normal 

period (1971–2000) at the National Weather Service climate 

station in nearby Wenatchee (site 459074), the mean 

monthly precipitation ranged from 0.3 in. in July to 1.5 in. in 

December and the mean monthly minimum and maximum 

air temperatures ranged from -4.9 and 1.7°C in January, 

respectively, to 16.1 and 31.0°C in July, respectively (National 

Oceanic and Atmospheric Administration Western Regional 

Climate Center, 2007b; fig. 3). Mean annual precipitation 

was 9.1 in. and mean annual minimum and maximum air 

temperatures were 5.4 and 16.9°C, respectively.

Except for irrigated lawns, shrubs, and trees in Lincoln 

Rock State Park and limited additional sites, the study area is 

sparsely vegetated with primarily grasses and shrubs that have 

adapted to local conditions.

Previous Investigations

As part of the design process for Rocky Reach Dam in 

the 1950s, geotechnical engineering surveys and hydrologic 

assessments were conducted in and near the study area. 

Results of this work near the subsurface cutoff wall (fig. 2) 

were summarized by Stone and Webster Engineering 

Corporation (1959) when they described the design and 

construction of the subsurface cutoff wall. The feasibility of 

using the Eastbank Aquifer system as a public water supply 

for the Wenatchee urban area was investigated by R.W. Beck 

and Associates (1973) and included an aquifer assessment by 

Robinson and Noble, Inc. Subsequently, Robinson and Noble, 

Inc. conducted a more detailed aquifer assessment that was 

reported by CH2M Hill (1977) as part of a predesign study 

of the regional water system. The study included descriptions 

of the installation and testing of well RW1, the first well 

of the regional water system. CH2M Hill documented the 

installation and testing of wells RW2, RW3, and RW4 (1979; 

as reported by Water & Environmental Systems Technology, 

Inc., 1990) and wells CT1, CT2, CT3, and CT4 (1988). CH2M 

Hill (1988) also presented results of seismic-refraction and 

electrical-resistivity surveys of the Eastbank aquifer system 

and parts of a draft report dated 1987 that included detailed 

hydrogeologic cross sections of the system (appendix 1).

Water & Environmental Systems Technology, Inc. 

(1990) analyzed the feasibility of using the Eastbank Aquifer 

system as a source of water for the Eastbank Hatchery 

over the long term by considering both the availability and 

temperature of ground water. As part of this analysis, they 

developed numerical ground-water models to help evaluate 

the hydrologic and thermal conditions of the ground-water 

system in 1989–90 and possible future conditions. The first of 

these models was a finite-difference ground-water flow model, 

MODFLOW (McDonald and Harbaugh, 1988), that was used 

to verify the conceptual model of the flow system and refine 

aquifer properties. The second model was a finite-element 

model, CFEST (Gupta and others, 1987), that was used to 

assess hydrologic and thermal conditions in 1989–90 and 

evaluate possible future conditions for different combinations 

of river temperature and seasonal pumping. Water & 

Environmental Systems Technology, Inc. (1990) also designed 

a network for monitoring river and aquifer water levels and 

water temperatures. Data from this network collected by 

the PUD since 1990 were used by Water & Environmental 

tac08-0189_fig03

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

20

30

40

50

60

70

80

90

100

0

10

-10

20

30

40

AIR TEMPERATURE, IN DEGREES CELSIUS

AIR TEMPERATURE, IN DEGREES FAHRENHEIT

0

0.5

1.0

1.5

2.0

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

PRECIPITATION, IN INCHES

Maximum

Mean monthly temperature

Mean monthly precipitation

Minimum

Figure 3. Mean monthly precipitation and mean monthly 

minimum and maximum air temperatures for the Wenatchee 

climate station (site 459074), Chelan County, Washington, 

1971–2000. 
6 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Systems Technology, Inc. to verify the previously developed 

CFEST model (Water & Environmental Systems Technology, 

Inc., 1998). The model was subsequently used to assess 

possible impacts on the hydrologic and thermal conditions of 

the Eastbank Aquifer system, assuming increased pumping 

by the regional water system to accommodate a possible 

expansion of the system’s service area to include East 

Wenatchee (Water & Environmental Systems Technology, 

Inc., 1998). The expansion of the service area and the increase 

in pumping took place in 2001.

Well-Numbering System

In Washington, the USGS assigns wells identifiers that 

describe their locations with respect to township, range, 

section, and tract. For example, number 24N/20E-35G01 

(fig. 4) indicates that the well is in township 24 North (N) and 

Range 20 East (E) of the Willamette base line and meridian. 

The number immediately following the hyphen indicates 

the section (35) within the township; the letter following the 

section gives the tract within the section, as shown in figure 4. 

The two-digit sequence number (01) following the letter 

indicates that the well was the first inventoried by USGS 

personnel in that tract. The nominal size of a section is 1 mi2

and the nominal size of a tract is 40 acres. In the study area, 

sections and tracts may deviate from their nominal sizes 

because they do not have standard rectangular shapes.

Methods of Investigation 

All available monitoring and pumping wells in the study 

area were inventoried by the USGS and their locations were 

determined using a hand-held GPS unit. Altitudes of wells 

were based on a survey conducted by Horton Dennis & 

Associates, Inc. in 1998 (S. Dilly, written commun., 2007) and 

spot-checked and expanded on by PUD surveyors. Surveyed 

altitudes were reported to the nearest 0.01 ft and, for the 

purpose of this study, were considered accurate to ±0.05 ft. 

Water levels were measured using an electrical or steel 

tape that was read to the nearest 0.01 ft. Water levels were 

considered accurate to ±0.1 ft. Vertical temperature profiles 

in wells were measured using a recently verified electrical 

tape and water temperatures were read to the nearest 0.1°C. 

The time of all measurements was recorded in local time, 

which is either Pacific Standard Time or Pacific Daylight 

Time, depending on the time of year. Continuous water 

levels measured during several hours on July 18, 2007, were 

made using electrical and steel tapes that had been verified 

to give the same results. The times of the continuous waterlevel measurements were read from cellular phones that 

were verified to match the times recorded by the continuous 

monitoring network run by the PUD within 1 minute.

Willamette

Meridian

Willamette Base Line

SECTION 35

24N/20E-35G01 D C AB

E F G H

M L K J

N P Q R

R. 20 E.

T.

24

 N.

123456

7 12

18 13

19 24

30 25

31 32 33 34 35 36

W A S H I N G T O N

Figure 4. Well-numbering system used in Washington.

Water-Quality Sampling Procedures

All ground-water samples, with the exception of 

the sample collected from well TH4, were collected 

following protocols described by Wilde (1999) in 

order to ensure representative samples of ground water. 

Clean-sampling protocols, as described by Wilde 

and others (2002), were used to process the samples. 

Sampling equipment consisted of polyethylene tubing 

with Teflon® or stainless-steel fittings that were 

attached to a faucet at the well head. The tubing was 

then connected directly to a flow chamber to monitor 

physical properties (water temperature, pH, specific 

conductance, and concentrations of dissolved oxygen) 

and through a splitter to provide either raw or filtered 

water samples. Existing pumps were active in all wells 

that were sampled except for well TH4. An equivalent 

volume of purge water had already been pumped 

during the previous 24 hours, therefore, the sampling 

equipment was flushed with ground water and samples 

were collected after ensuring that physical properties 

measured in the flow chamber had stabilized. All lines 

and processing equipment that came in contact with 

the sample water after the point of attachment to the 

well discharge structure were composed of Teflon®, 

polyethylene, or stainless steel. Ground-water samples 

were pumped directly through a line or a filtration 

cartridge into sample bottles and samples were preserved 
Hydrogeology 7

or stored on ice and shipped for analysis to the USGS National 

Water Quality Laboratory (NWQL) in Denver, Colorado and 

Pacific Analytical Laboratory in Corvallis, Oregon. Because 

there was no pump in well TH4, a 2-L Kemmerer© sampler 

was lowered into the well to obtain a grab sample of water 

from the upper 10 ft of the perforated interval. The sampler 

was retrieved from the well and water was then pumped from 

the Kemmerer© sampler with a peristaltic pump and processed 

like all other samples. The Columbia River sample was 

collected with the Kemmerer© bottle near the location labeled 

RIV in figure 2. The sampler was lowered through the water 

column to about 3 ft above the riverbed before the sampling 

mechanism was triggered. Water from the Kemmerer©

bottle was withdrawn from the sampler using a peristaltic 

pump and processed like the ground-water samples. Aseptic 

techniques were used in the collection of samples for bacterial 

enumeration. 

Laboratory Analytical Procedures

Laboratory analyses were performed for common 

ions and bacteria enumeration. Water samples for the 

analysis of nitrate plus nitrite were received at the NWQL 

and stored at less than 4°C prior to analysis. Samples were 

analyzed for nitrate plus nitrite using a cadmium reductiondiazotization colorimetric method described by Fishman 

(1993). Samples were analyzed for chloride and sulfate using 

ion chromatography (Fishman and Friedman, 1989); calcium, 

magnesium, sodium, and iron were analyzed using inductively 

coupled plasma (Fishman, 1993); and potassium was analyzed 

using flame atomic absorption (Fishman and Friedman, 1989). 

Manganese was analyzed using inductively coupled plasma 

detected with a mass spectrometer (ICP/MS) (Faires, 1993). 

Variability in reported concentrations due to variability in 

laboratory analytical processes was expected to be less than 

2 percent. 

Bacterial enumerations were done using fluorescent 

counting techniques (Hurst and others, 1997). Bacterialenumeration samples were sent to Pacific Analytical 

Laboratory in Corvallis, Oregon, where enumerations were 

conducted using Moleculer Probes BacLight viability and 

counting stains with a fluorescent microscope. The 95-percent 

confidence interval for enumerations provided by the 

laboratory was about 10 percent.

Hydrogeology 

The subsurface of the study area consists of 

unconsolidated sedimentary layers with a wide range of 

hydraulic conductivities. These layers are deposited on top 

of bedrock to form two aquifers separated by a confining 

unit, which is absent in the northwestern part of the study 

area. An aquifer is a hydrogeologic unit that contains 

sufficient saturated permeable material to yield significant 

quantities of water to wells or springs, and a confining unit 

is a hydrogeologic unit of distinctly less permeable material 

bounding one or more aquifers. The lower aquifer, which is in 

direct contact with the Columbia River, is the source of water 

for the regional water system, the Eastbank Hatchery, and 

irrigation and industrial uses.

Geologic Setting

Rocky Reach Dam and the Eastbank Aquifer system are 

located in a canyon incised into Late Cretaceous metamorphic 

bedrock of biotite gneiss (Tabor and others, 1987). The canyon 

has been eroded by the ancestral Columbia River and multiple 

catastrophic outburst floods from glacial Lake Missoula during 

the Pleistocene age. Estimates of the discharge of those floods 

are on the order of 600 million ft3

/s (O’Connor and Baker, 

1992). Large gravel deposits have formed inside the Columbia 

River valley from the accumulation of up to boulder-sized 

sediments deposited by the catastrophic floods at locations of 

channel widening or downstream of bedrock promontories, 

such as Turtle Rock Island located about 1 mi northeast of 

the study area (fig. 1). In the Columbia River valley south 

of Wenatchee, catastrophic-flood discharges from Moses 

Coulee deposited sufficient sediment to create temporary flood 

backwater and a lake that deposited fine-grained, lacustrine 

sediments. Cycles of catastrophic flooding and lake formation 

deposited the glacio-fluvial gravels and varved clays that 

make up the aquifers and confining unit, respectively, of the 

Eastbank Aquifer system.

Hydrogeologic Units

Previous studies (Stone and Webster Engineering 

Corporation, 1959; CH2M Hill, 1977 and 1988; and Water & 

Environmental Systems Technology, Inc., 1990) determined 

that at river levels following the completion of Rocky Reach 

Dam, the Eastbank Aquifer system consists of two highly 

permeable, sand-and-gravel aquifers separated by a confining 

unit. A schematic hydrogeologic cross section through the 

south-central part of the Eastbank Aquifer system is shown in 

figure 5. In this study, the lower confined aquifer is referred 

to as the Lower Aquifer and the upper unconfined aquifer is 

referred to as the Upper Aquifer. Previous studies have used 

different names and terminology for the hydrogeologic units 

(table 1). The confining unit, which consists of varved clays 

and is referred to as the Clay Confining Unit in this study, 

generally thins towards the north, west, and east and is absent 

in the northwestern part of the study area (fig. 6; Water & 

Environmental Systems Technology, Inc., 1990). Where the 

Clay Confining Unit is absent, the Lower and Upper Aquifers 

merge to form the Combined Aquifer, which is unconfined.
8 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

tac08-0189_fig05

Permeable units Less permeable units Bedrock

Upper Aquifer

Full-pool level

of Lake Entiat

Natural low water level

prior to construction

of Rocky Reach Dam

Lower Aquifer

Clay Confining Unit

Bedrock

Columbia River / Lake Entiat

Northwest Southeast

NOT TO SCALE

US

2

US

97

Modified from Robinson and Noble, Inc., as 

reported by CH2M Hill (1977).

Figure 5. Schematic hydrogeologic cross section through the south-central part of the Eastbank Aquifer system, Douglas County, 

Washington.

Table 1. Hydrogeologic-unit names and terminology used in this study and previous studies, Eastbank Aquifer system, Douglas County, 

Washington.

[–, not named]

Hydrogeologic unit Source

Lower Aquifer Upper Aquifer Combined Aquifer Clay Confining Unit This study

Eastbank Aquifer – Eastbank Aquifer – Water & Environmental Systems Technology, Inc. (1990)

deep aquifer shallow aquifer combined aquifer aquitard CH2M Hill (1988)

The Eastbank Aquifer system lies on top of crystalline 

bedrock, which has an undulating surface as shown in 

figure 7 (Water & Environmental Systems Technology, Inc., 

1990). Near the RW wells near the center of the study area, 

the altitude of the top of the bedrock is less than 340 ft. 

This is lower than approximated on the hydrogeologic cross 

sections by CH2M Hill (1988; appendix 1) but is based on 

interpretations of seismic-refraction data reported by CH2M 

Hill (1988). Water & Environmental Systems Technology, Inc. 

(1990) relied on indirect methods to estimate the altitude of 

the top of bedrock near the center of the study area because 

none of the RW wells was drilled to bedrock. It is estimated 

that there may be up to about 200 ft of sedimentary material 

about which little is known between the bottom of the RW 

wells and the top of bedrock (appendix 1). In the eastern part 

of the study area bedrock is shallower and truncates the Lower 

Aquifer. Water & Environmental Systems Technology, Inc. 

(1990) cautions, however, that well coverage in the eastern 

part of the study area is sparse and thus the interpretation of 

the subsurface is less certain. The resulting thickness of the 

Lower Aquifer in the study area, including the Combined 

Aquifer, ranges from 0 ft to more than 300 ft (fig. 8; Water & 

Environmental Systems Technology, Inc., 1990). It is not 

known how far north the Lower Aquifer extends beyond the 

study area.

During construction of Rocky Reach Dam, Stone and 

Webster Engineering Corporation (1959) determined on the 

basis of a dye-tracer study that the hydraulic conductivities 

of the Lower Aquifer near the subsurface cutoff wall are on 

the order of 14,000 to 22,000 ft/d. Hydraulic conductivity is 

a measure of the ease with which water can move through a 

material. The horizontal hydraulic conductivity of an aquifer is 

related to the transmissivity of an aquifer according to

 ,

where

is transmissivity, in feet squared per day,

is horizontal hydraulic conductivity, in feet per

day, and

is thickness of the aquifer, in feet.

h

h

T Kb

T

K

b

= (1)
Hydrogeology 9

Figure 6. Thickness of the Clay Confining Unit, Eastbank Aquifer system, Douglas County, Washington.

tac08-0189_fig06

120°17'30" 120°17'

47°

32'

30"

47°

32'

EXPLANATION

Line of equal thickness of clay confining 

 unit—From Water & Environmental Systems 

 Technology, Inc. (1990). Interval 20 feet

20

RW4 Well or river site and site name

Subsurface cutoff wall

COLUMBIA RIVER

0

60

80

20

100

100

120

120

140

140

140

160

140

160

160

160

180

60

100

80

100

100

100

120

60

80

80

120

120

120

100

140

40

0

60

80

20

40

0

0

500 1,000 1,500 FEET

100 200 300 400 METERS

LR1

LR2-E

LR2-W

TH6

TH5

TH4

TH2

RIV

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH9 TH8 TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
10 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 7. Altitude of the top of bedrock, Eastbank Aquifer system, Douglas County, Washington.

LR1

LR2-E

LR2-W

TH6

TH5

TH4

TH2

RIV RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH8 TH9 TH7

TH1

CD47

CD10

SW14

SW13

SW11

CD8 CD6

120°18' 120°17'30" 120°17' 120°16'30"

47°

32'

30"

47°

31'

30"

47°

32'

EXPLANATION

Bedrock contour—Shows altitude of bedrock 

 surface (from Water & Environmental Systems 

 Technology, Inc.,1990). Contour interval 

 20 feet. Datum is National Geodetic Vertical 

 Datum of 1929

Well or river site and site name

540

RW4

Subsurface cutoff wall

COLUMBIA RIVER

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

580

500

500

500

500

580

600

600

500

700

700

400

800

400

340

800

480

560

620

540

540

600

600

600

560

700

460

520

0

0 500 1,000 1,500 FEET

100 200 300 400 METERS
Hydrogeology 11

Figure 8. Thickness of the Lower Aquifer, Eastbank Aquifer system, Douglas County, Washington.

tac08_0189_fig8

LR1

LR2-E LR2-W

TH6

TH5

TH4

TH2

RIV

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH9 TH8 TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

120°17'30" 120°17'

47°

32'

30"

47°

32'

EXPLANATION

Line of equal thickness of Lower 

 Aquifer (includes Combined 

 Aquifer)—From Water & 

 Environmental Systems Technology, 

 Inc. (1990). Interval 20 feet

20

RW4 Well or river site and site name

Subsurface cutoff wall

COLUMBIA RIVER

0

20

100

100

200

200

300

0

0

0

0

100

0

0

0

500 1,000 1,500 FEET

100 200 300 400 METERS

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
12 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Transmissivity is defined as the volume of water per unit time 

that will flow through a unit width of an aquifer perpendicular 

to the flow direction in response to a unit hydraulic head 

gradient. Another important aquifer parameter, the storativity, 

is defined as the volume of water an aquifer releases from, or 

takes into, storage per unit area of aquifer per unit change in 

head. Transmissivities and storativities of the Lower Aquifer 

calculated from aquifer tests performed between 1973 and 

1990 in different parts of the study area ranged from 37,000 

to 1.7 million ft2/d and from 0.0021 to 0.12, respectively 

(table 2). Results from aquifer tests of the CT well field (wells 

CT1, CT2, CT3, and CT4) described by CH2M Hill (1988) 

are not included in table 2 because they were reported as 

apparent transmissivities and storativities due to interference 

of the aquifer tests by intermittent pumping by the regional 

water system and other complications. The transmissivities 

and storativities of the Lower Aquifer indicate that it is a 

highly permeable, leaky confined aquifer with recharge 

entering the aquifer primarily from the Columbia River 

(Water & Environmental Systems Technology, Inc., 1990). 

In a numerical model of the Eastbank Aquifer system, Water 

& Environmental Systems Technology, Inc. (1990) achieved 

the best results by simulating hydraulic conductivities in 

the Lower and Upper Aquifers of 9,500 and 6,700 ft/d, 

respectively.

The interpretation of the hydrogeologic framework of 

the Eastbank Aquifer system in previous studies is based 

primarily on lithologic and geophysical logs of wells and 

borings. Although many well logs were available for use in 

this study, a significant number were not available and either 

no information was known about certain wells or only limited 

information was known from descriptions by previous studies. 

To learn more about these wells and also to ascertain the 

condition of all accessible wells currently (2008) in the study 

area, downhole-camera surveys and natural-gamma logs were 

made of selected wells in December 2007. A description of 

the downhole-camera surveys is included in appendix 2 and 

the natural-gamma logs are included in appendix 3. Several 

wells that existed when previous studies were conducted have 

since been abandoned or destroyed and were not available in 

this study. Wells that are currently (2008) in the study area 

and the hydrogeologic units the wells are open to are shown in 

figure 9; known information for these wells is summarized in 

table 3.

Table 2. Transmissivities and storativities of the Lower Aquifer, Eastbank Aquifer system, Douglas County, Washington.

[Locations of wells are shown in figure 2. Abbreviations: ft2/d, foot squared per day; –, not available]

General area

Transmissivity (ft2/d) Storativity (dimensionless)

Source

Range Final 

estimate Range Final estimate

South of well CD47 and north 

of subsurface grout wall

470,000–1,200,000 670,000 – – Robinson and Noble, Inc. (as reported by 

R.W. Beck and Associates, 1973)

North of well CD47 500,000–1,700,000 630,000 0.0021–0.0054 0.0032 Robinson and Noble, Inc. (as reported by 

CH2M Hill, 1977)

RW well field (wells RW1, 

RW2, RW3, and RW4)

250,000–380,000 320,000 0.021–0.12 0.06 CH2M Hill (1979; ranges as reported by 

Water & Environmental Systems Technology, 

Inc., 1990; final estimates as reported by 

CH2M Hill, 1988)

Entire study area north of 

subsurface grout wall

37,000–650,000 – 0.007–0.095 – Water & Environmental Systems Technology, 

Inc. (1990)
Hydrogeology 13

Figure 9. Wells that are currently (2008) completed in the Eastbank Aquifer system and hydrogeologic units to which 

they are open, Douglas County, Washington.

tac08-0189_fig09

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

EXPLANATION

Well and name

Well open to:

Open-end well

 (no perforations)

Subsurface cutoff wall

Upper Aquifer

Lower Aquifer

Combined Aquifer

Clay Confining Unit

Unknown

CT3

COLUMBIA RIVER

CD10

TH6

TH5

TH8

CD8

LR2-W

TH4

CT3

TH9

TH7

TH1

CD47

LR1

LR2-E

TH2

RW3

RW4

RW2

RW1

CT1

CT2

CT4

CD6

SW14

SW13

SW11

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
14 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington Table 3. Summary information for wells completed in the Eastbank Aquifer system, Douglas County, Washington. [Locations of wells are shown in figure 2. USGS well No.: See figure 4 for explanation of well-numbering system. Latitudes and longitudes of the wells are on file with the U.S. Geological Survey. Completion date of well: Source of information is well log or first mention in previous studies. Altitude of land surface: Datum is National Geodetic Vertical Datum (NGVD 29). Depth of well: Source of information is well log unless otherwise noted. Type of log available in this study: C, down-hole camera; D, driller’s; G1, natural gamma from previous studies; G2, natural gamma from this study; L, lithology. Abbreviations: USGS, U.S. Geological Survey; –, not available] Local well name USGS well No. Completion date of well Hydrogeologic unit to which well is open Altitude of land surface (feet) Depth of well (feet) Primary use of water since completion of Rocky Reach Dam Type of log available in this study Remarks CD6 24N/20E-35Q06 1972 or earlier; probably 1957 or earlier Lower Aquifer 744.7 216 Monitoring C, G2, L Open-end well (no perforations). CD8 24N/20E-35R01 1957 or earlier Clay Confining Unit 724.0 231 Monitoring

L Open-end well (no perforations). Well may be open to a sand 

lens connected to the Lower Aquifer based on cross section A-A' by Stone and Webster Engineering Corporation (1959); the water-level response to the 2-hour shutdown of pumping on July 18, 2007; and the fact that this well is used to monitor the integrity of the subsurface cutoff wall.

CD10 24N/20E-35Q01 1959 or earlier; 

probably 1957 or earlier

__ 733.6 230 Monitoring

L Well may be open to the Lower Aquifer based on cross section 

A-A’ by Stone and Webster Engineering Corporation (1959); the water-level response to the 2-hour shutdown of pumping on July 18, 2007; and the fact that this well is used to monitor the integrity of the subsurface cutoff wall.

CD47 24N/20E-35Q02 1959 or earlier; 

probably 1957 or earlier

Lower Aquifer 746.6 245 Monitoring C, G2, L

CT well field

CT1 24N/20E-35K10 November 1987 Lower Aquifer 747.7 206 Hatchery

D

CT2 24N/20E-35Q04 November 1987 Lower Aquifer 748.1 204 Hatchery

D

CT3 24N/20E-35Q03 December 1987 Lower Aquifer 749.9 213 Hatchery

D

CT4 24N/20E-35K11 January 1988 Lower Aquifer 747.9 203 Hatchery

D

LR well field

LR1 24N/20E-35H04 after 1977 and 

before 1988

Combined Aquifer 750 – Irrigation – Altitude of land surface is ±10 ft.

LR2-E 24N/20E-35H01 after 1977 and 

before 1988

Combined Aquifer 770 157 Irrigation – Altitude of land surface is ±10 ft. Depth of well estimated from 

hydrogeologic cross section by CH2M Hill (1988).

LR2-W 24N/20E-35H02 after 1977 and 

before 1988

Combined Aquifer 770 – Irrigation – Altitude of land surface is ±10 ft; Chelan County PUD notes 

indicate this well is 140 ft deep.

RW well field

RW1 24N/20E-35K07 July 1977 Lower Aquifer 742.7 219 Public Supply

D

RW2 24N/20E-35K08 July 1979 Lower Aquifer 747.6 226 Public Supply

D

RW3 24N/20E-35K09 June 1979 Lower Aquifer 746.8 230 Public Supply

D

RW4 24N/20E-35H03 June 1979 Lower Aquifer 737.8 179 Public Supply

D
Hydrogeology 15

Local well 

name

USGS 

well No.

Completion 

date of well

Hydrogeologic 

unit to which

well is open

Altitude of 

land surface 

(feet)

Depth of 

well 

(feet)

Primary use of 

water since 

completion 

of Rocky 

Reach Dam

Type of log 

available in 

this study

Remarks

SW well field

SW11 24N/20E-35Q05 1959 or earlier Lower Aquifer 726.9 – Irrigation –SW13 24N/20E-35K12 1959 or earlier Lower Aquifer 740.3 176 Irrigation/Dam –SW14 24N/20E-35K13 1959 or earlier Lower Aquifer 737.8 – Irrigation/Dam –TH1 24N/20E-35K05 1977 Lower Aquifer 748.1 190 Monitoring D, G1TH2 24N/20E-35K06 1977 Lower Aquifer 741.4 225 Monitoring C, D, G1, G2TH4 24N/20E-35K02 1977 Lower Aquifer 723.8 170 Monitoring C, D, G1TH5 24N/20E-35G01 July 1987 Upper Aquifer 713.1 47 Monitoring C, DTH6 24N/20E-35G02 July 1987 Combined Aquifer 727.6 134 Monitoring C, D, G2TH7 24N/20E-35K01 July 1987 Lower Aquifer 723.8 176 Monitoring C, DTH8 24N/20E-35K04 November 1987 Lower Aquifer 747.8 255 Monitoring C, D Open-end well (no perforations).TH9 24N/20E-35K03 October 1987 Lower Aquifer 743.2 211 Monitoring C, D

Table 3. Summary information for wells of the Eastbank Aquifer system, Douglas County, Washington.—Continued[Locations of wells are shown in figure 2. USGS well No.: See figure 4 for explanation of well-numbering system. Latitudes and longitudes of the wells are on file with the U.S. Geological Survey. Completion date of well: Source of information is well log or first mention in previous studies. Altitude of land surface: Datum is National Geodetic Vertical Datum (NGVD 29). Depth of well: Source of information is well log unless otherwise noted. Type of log available in this study: C, down-hole camera; D, driller’s; G1, natural gamma from previous studies; G2, natural gamma from this study; L, lithology. Abbreviations: USGS, U.S. Geological Survey; –, not available]
16 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Hydrology 

The Lower Aquifer of the Eastbank Aquifer system has 

been used as a water source for the Eastbank Hatchery and the 

regional water system since the 1980s. Historical water-level 

and water-temperature data and water-quality data collected 

in 2007 were analyzed to evaluate how pumping of the Lower 

Aquifer has affected its hydrologic and thermal conditions. 

The source of the historical data is a monitoring network 

operated by the PUD (fig. 10) that has measured hourly water 

levels and temperatures in 12 wells and 1 river site from 1990 

to the present (2008). The network was designed by Water & 

Environmental Systems Technology, Inc. (1990) as part of 

a long-term aquifer test that was completed in 1990. The 

continuous records from January 1991 through August 2007 

were used in this study.

Aquifer Conditions Before and After 

Construction of Rocky Reach Dam

Prior to the construction of Rocky Reach Dam, when the 

Columbia River was a free-flowing river in the study area, 

the natural low water level of the river was 610 ft (Stone and 

Webster Engineering Corporation, 1959). The water level in 

the Lower Aquifer was likely similar to the river level, so the 

Lower Aquifer was probably largely unconfined and only 

partially saturated (fig. 5). The Upper Aquifer is presumed to 

have been unsaturated entirely, except for a possible seasonal, 

perched unconfined aquifer above the Clay Confining Unit. 

Once construction of Rocky Reach Dam was completed and 

the hydroelectric project became operational in 1961, the 

natural water level was raised by almost 100 ft to normal pool 

levels ranging from 703 to 707 ft (Public Utility District No. 1 

of Chelan County, 2007b). This raised the water level in the 

Eastbank Aquifer system such that the Lower Aquifer became 

confined and the Upper Aquifer became partially saturated 

to form an unconfined aquifer (fig. 5). Water levels are 

maintained in the Upper and Lower Aquifers by the subsurface 

cutoff wall that extends to bedrock. This wall consists of a 

clay curtain across the Upper Aquifer and a grout curtain 

across the Lower Aquifer. Ground water that seeps through 

the subsurface cutoff wall from the Lower and Upper Aquifers 

is captured by drains and flows through the North and South 

Weirs (fig. 2). Seepage around and through the subsurface 

cutoff wall likely is not all captured by the drains (G. Yow, 

Public Utility District No. 1 of Chelan County, written 

commun., 2008).

Potentiometric-surface maps of the Lower Aquifer prior 

to the construction of Rocky Reach Dam, which show the 

altitude at which water levels would have stood in tightly 

cased wells, were not available for this study. However, in 

July 1977, prior to pumping of the Eastbank Aquifer system 

by the regional water system and the Eastbank Hatchery, 

and years following the decline of ground-water levels to 

facilitate dam construction, Robinson and Noble, Inc. (as 

reported by CH2M Hill, 1977) prepared a potentiometricsurface map of the Lower and Combined Aquifers (fig. 11). 

This map demonstrates that prior to extensive pumping of 

the aquifer system, water levels in the Lower and Combined 

Aquifers were lower than the water level in the river, and the 

primary ground-water flow direction generally was parallel 

to the river from northeast to southwest (fig. 11). The sparse 

water-level data also support an alternative interpretation 

of a more dominant ground-water flow component from 

the west-northwest along the western extent of the Lower 

and Combined Aquifers than shown in figure 11. The 

interpretation shown in figure 11 is reasonable, however. The 

potentiometric surface shown in figure 11 can be considered 

a map of post-dam, pre-development water levels, as it 

represents static water levels prior to the start of extensive, 

approximately continuous pumping of the Eastbank Aquifer 

system since 1983.

Sources of Ground-Water Recharge and 

Discharge

The sources of ground-water recharge to the Eastbank 

Aquifer system are flow from the Columbia River, recharge 

from precipitation, and recharge from irrigation. The mean 

annual recharge from precipitation is small, because the 

mean annual precipitation is only 9.1 in. and potential 

evapotranspiration is large (the mean annual reference 

evapotranspiration is 44.5 in. at AgriMet weather station 

MASW in Manson, Washington, located about 25 mi northnortheast of the study area [Bureau of Reclamation, 2008]). 

In a ground-water recharge study of the Yakima River basin, 

about 75 mi south of the study area, Vaccaro and Olsen 

(2007) estimated mean annual ground-water recharge rates 

of less than 0.5 in. in parts of the lower basin with similar 

mean annual precipitation and temperatures as the study area 

and with similarly short vegetation. A regression equation 

developed by Bauer and Vaccaro (1990) for estimating 

recharge to the Columbia Plateau regional aquifer system, 

which is located just to the east of the study area, was used to 

estimate a mean annual recharge of 0.65 in. to the Eastbank 

Aquifer system. However, because the study area has thin to 

no soils and because the surficial geology consists of very 

coarse gravels, mean annual recharge may be larger. In the 

northern part of the U.S. Department of Energy Hanford Site, 

about 80 mi south-southeast of the study area, Bauer and 

Vaccaro (1990) simulated mean annual recharge from 23 to 

39 percent of precipitation with a median of 35 percent of 

precipitation in areas with coarse sediments and no vegetation 

(J. Vaccaro, U.S. Geological Survey, written commun., 2008). 
Hydrology 17

Figure 10. Water-level and temperature monitoring network, Eastbank Aquifer system, Douglas County, Washington.

tac08-0189_fig10

TH6

North Weir

South Weir

LR1

LR2-E

LR2-W

TH5

TH4

TH2

RIV

TH8 TH9

TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

EXPLANATION

Well, weir, or river site and name

Subsurface cutoff wall

Site monitored continuously

LR1

COLUMBIA RIVER

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
18 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 11. Potentiometric surface of the Lower and Combined Aquifers for post-dam, predevelopment conditions, 

Eastbank Aquifer system, Douglas County, Washington, 8:30 a.m., July 19, 1977. Well LR1 was called well CD46 in 1977. 

tac08-0189_fig11

702.76

702.36

702.08

702.12

702.31

LR1 LR2-E

LR2-W

TH5

TH4

TH2

702.56

TH8

TH9

TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

705.8

702.7

702.6

702.5

702.4

702.3

702.2

702.1

702.0

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

TH3

TH3

EXPLANATION

Subsurface cutoff wall

Extent of Lower and Combined Aquifers—Modified from Water &

 Environmental Systems Technology, Inc. (1990)

Direction of ground-water flow

Well and name—Italicized number is measured water level, in feet

River water level, in feet—Mean water level measured at USGS gaging station

 12453679 from 8 to 9 a.m., July 19, 1977. Gaging station location is shown in figure 2 

697

702.56

Potentiometric contour—Modified from Robinson and Noble, Inc., as reported by 

 CH2M Hill (1977). Shows altitude at which water level would have stood in tightly

 cased wells, 8:30 a.m., July 19, 1977. Contour interval 0.1 foot. 

 Datum is National Geodetic Vertical Datum of 1929

705.8

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

COLUMBIA RIVER
Hydrology 19

The median percentage applied to the study area results in a 

mean annual recharge of 3.2 in. However, because there is 

vegetation in the study area, actual recharge from precipitation 

is likely less than 3.2 in. Irrigation is limited to lawn, shrub, 

and tree irrigation in small parts of the study area and is 

considered a negligible source of recharge. Thus, the only 

significant source of recharge to the Eastbank Aquifer system 

is the Columbia River.

Current (2008) sources of ground-water discharge from 

the Eastbank Aquifer system are ground-water pumping from 

the Lower Aquifer and ground-water seepage around and 

through the subsurface cutoff wall. Although ground-water 

discharge from the Lower Aquifer to the Columbia River may 

have been significant prior to the construction of Rocky Reach 

Dam, it is presumed to be currently (2008) non-existent. 

Historical Ground-Water Discharge

After the completion of Rocky Reach Dam in 1961 and 

the complete and partial saturation of the Lower and Upper 

Aquifers, respectively, the Eastbank Aquifer system was not 

used as a significant resource until 1983, when the regional 

water system came on-line. This was followed by use of the 

aquifer system by the Eastbank Hatchery, which started in 

1989. (Lincoln Rock State Park, which uses the Eastbank 

Aquifer system for limited irrigation, started pumping ground 

water sometime after an agreement was signed with the PUD 

in April 1980.) In addition to ground-water pumping, ground 

water also has been removed from the aquifer system by 

seepage around and through the subsurface cutoff wall.

A history of ground-water pumping was reconstructed 

using daily flow-meter records for the RW wells provided by 

the City of Wenatchee (M. Cockrum, written commun., 2007) 

and seasonal records for the CT and LR wells provided by the 

Eastbank Hatchery and PUD, respectively (S. Dilly, Public 

Utility District No. 1 of Chelan County, written commun., 

2007). Mostly semi-annual records of discharge through the 

North and South Weirs, representing seepage through the 

subsurface cutoff wall, were provided by the PUD (I. Adams, 

written commun., 2007).

Ground-Water Pumpage

The annual mean pumpage from the RW well field was 

computed from 1990 through 2006 based on records provided 

by the City of Wenatchee (M. Cockrum, written commun., 

2007; fig. 12A) for years with at least 11 months of data. From 

1990 through 2000, annual mean pumpage was relatively 

constant, with a mean annual pumpage of 10.7 ft3

/s. In 2001, 

the service area of the regional water system was expanded to 

include the City of East Wenatchee and pumpage increased 

about 40 percent to a mean annual pumpage of 15.0 ft3/s 

from 2002 through 2006, excluding 2003. A breakdown of 

pumpage into quarterly mean pumpage by the RW well field 

shows that regional water system pumpage is largest in the 

summer (July–September) and generally smallest in the winter 

(January–March; fig. 12B). Quarterly pumpage is only shown 

for quarters with 3 months of data.

The annual mean pumpage from the CT well field was 

computed from 1991 through 2006 using data provided by the 

Eastbank Hatchery, including seasonal estimates of pumpage 

and run-time information for the wells (S. Dilly, Public Utility 

District No. 1 of Chelan County, written commun., 2007; 

fig. 12A). Data conflicted for part of 1998. Data available 

initially indicated an annual pumpage of 42.0 ft3/s and data 

available later indicated an annual pumpage of 43.2 ft3/s. 

The initial data were used in this study and are shown in 

figure 12. Over the years, the hatchery used different methods 

to estimate pumpage from the CT well field. Prior to 1999, 

pumpage estimates were based on the run time and nominal 

pumping rate of each CT well, which is 12.5 ft3

/s. From 1999 

until November 10, 2001, pumpage estimates were based on 

flow measurements over damboards at the end of hatchery 

ponds, and from November 10, 2001 through 2005, pumpage 

was measured by a flow meter. Based on the available data, 

it appears that by 2006, pumpage was again estimated based 

on the run time and nominal pumping rate of each CT well. 

The mean annual pumpage from 1999 through 2001, which 

was almost entirely based on damboard measurements, was 

36 percent less than the mean annual pumpage during the 

10-year period including 1994 through 1998 and 2002 through 

2006 (26.7 ft3/s versus 41.4 ft3/s, respectively). Because there 

was no known change in operations of the hatchery between 

1999 and 2001 (S. Dilly, Public Utility District No. 1 of 

Chelan County, oral commun., 2007), the pumpage estimates 

based on damboard measurements were assumed to be in 

error. Instead, new pumpage estimates were computed based 

on the run time and nominal pumping rate of each CT well. 

This increased the estimate of mean annual pumpage from 

1999 through 2001 by 41 percent to 37.6 ft3/s (fig. 12). 

The information provided by the Eastbank Hatchery 

notes that around the time the flowmeter was installed in late 

2001, wells of the CT well field received maintenance that 

increased the peak capacity of the well field by about 5 ft3

/s 

and restored the well field to close to its nominal capacity 

of 50 ft3/s. The maximum pumpage from the CT well field 

prior to well maintenance was reported to be 43 ft3

/s, but it is 

not known how long the wells had been pumping at reduced 

capacity. The maximum pumpage from the CT well field 

measured by the flow meter was 48.5 ft3/s in 2003 and 47 ft3/s 

from 2004 through 2005. This information indicates that 

pumpage estimates for the CT well field based on the run time 

and nominal pumping rate of individual wells may be too high 

by as much as about 15 percent prior to 2002 and by as much 

as about 6 percent in 2006. The percentage of overestimation 

of pumpage prior to 2002 would depend on how long the CT 

wells had been pumping at reduced capacity.
20 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 12. Annual mean and quarterly mean pumpage from the RW and CT well fields, Eastbank Aquifer System, Douglas 

County, Washington, 1990–2006.

tac08_0189_fig12

B. Quarterly mean pumpage from RW well field

C. Quarterly mean pumpage from CT well field

1990 1992 1994 1996 1998 2000 2002 2004 2006

1990 1992 1994 1996 1998 2000 2002 2004 2006

A. Annual mean pumpage from RW and CT well fields

5

10

15

20

25

5

10

15

20

25

30

35

40

45

50

55

10

15

20

25

30

35

40

0.10

0.15

0.20

0.25

0.30

0.35

0.40

45

50

PUMPAGE, IN CUBIC FEET PER SECOND

1990 1992 1994 1996 1998 2000 2002 2004 2006

1990 1992 1994 1996 1998 2000 2002 2004 2006

QUARTERLY PUMPAGE AS A FRACTION

OF ANNUAL PUMPAGE FROM CT 

WELL FIELD, DIMENSIONLESS

D. Quarterly pumpage from CT well field

RW well field

CT well field

January–March

April–June

July–September

October–December
Hydrology 21

A breakdown of pumpage from the CT well field into 

quarterly mean pumpage (fig. 12C) and quarterly pumpage 

as a fraction of annual pumpage (fig. 12D) shows that the 

seasonal pumpage pattern has changed over time. Since 1994, 

summer (July–September) pumpage generally has increased, 

although the annual mean pumpage has remained relatively 

constant and increases expressed as a fraction of annual 

pumpage (fig. 12D) generally occurred prior to 1999. Winter 

(January–March) pumpage generally decreased from 1994 

until about 2002. Starting in 2001, summer pumpage exceeded 

winter pumpage, except in 2006. From 1999 through 2006, the 

overall seasonal pumpage patterns were relatively stable. The 

seasonal pumpage patterns of the CT well field differ from 

the RW well field because pumpage from the CT well field is 

determined by fish-production needs of the Eastbank Hatchery 

and pumpage from the RW well field is determined by publicsupply needs. In 2006, the mean annual pumpage from the CT 

and RW well fields was about 43 and 16 ft3

/s, respectively. 

Other well fields in the study area are the SW and LR 

well fields, and pumpage from these well fields is negligible 

compared to pumpage from the RW and CT well fields. The 

original purpose of the SW well field was to lower groundwater levels during construction of Rocky Reach Dam. Since 

completion of the dam, two wells of the SW well field (SW13 

and SW14) have continued to be pumped at a combined rate 

of about 80 gal/min or about 0.2 ft3/s to lubricate turbines 

at Rocky Reach Dam and one well, SW11, has been used 

seasonally to irrigate small parts of the study area. Pumpage 

from the SW11 well is unknown but it is assumed to be 

negligible. The LR well field provides water for irrigation of 

Lincoln Rock State Park. The well field has been in operation 

since about 1980 and the wells are pumped several hours 

per day for about 6 months per year. Pumpage data for 2004 

through 2006 (S. Dilly, Public Utility District No. 1 of Chelan 

County, written commun., 2007) show that the mean annual 

pumpage from the LR well field is about 0.14 ft3/s. It is 

assumed that mean annual pumpage has remained relatively 

constant from the LR well field since the start of its operation 

and from the SW well field since the start of its use for 

irrigation and turbine lubrication. 

Ground-Water Seepage Through the Subsurface 

Cutoff Wall

Ground-water seepage through the subsurface cutoff 

wall that was captured by drains has been measured in the 

North and South Weirs since July 1, 1977 (I. Adams, Public 

Utility District No. 1 of Chelan County, written commun., 

2007; fig. 13). Weir stage is recorded by a strip-chart recorder 

and converted to discharge using the stage-discharge rating 

curve for the weir. Prior to 1989, weir discharge was recorded 

monthly and starting in 1989, weir discharge was mostly 

recorded semi-annually. Other than a note indicating that 

the weirs were recalibrated sometime between late 2001 and 

late 2002, the only other historical calibration information 

available to this study was from K. deRubertis and others 

(written commun., 2007) stating that measurements made 

on February 24, 2006, correlated with the recorded values. 

At 8:43 a.m. on July 17, 2007, measured stage of the water 

in the box of the North Weir was 0.36 ft and recorded stage 

was 0.335 ft. These values are close (within 7 percent of each 

other) and so both the North and South Weirs were assumed to 

be accurately recording weir stage. A more detailed analysis 

of the weir recordings was beyond the scope of this study.

 Seepage from the Lower Aquifer is assumed to flow 

through the North Weir and seepage from the Upper Aquifer 

is assumed to flow through the South Weir. This assumption 

is based on the significant decrease in discharge that occurred 

in the North Weir after October 1987 (fig. 13) that coincided 

with the installation of the CT well field. No other information 

is available to support this assumption and it is possible each 

weir captured a combination of seepage from the Lower and 

Upper Aquifers.

Mean discharges in the North Weir were 5.4 ft3

/s from 

July 1977 through October 1987 and 3.1 ft3/s from November 

1987 through December 1998. This means that the long-term 

mean seepage from the Lower Aquifer through the subsurface 

cutoff wall decreased by 2.3 ft3/s or 43 percent. In contrast, 

discharge in the South Weir, and thus seepage from the Upper 

Aquifer through the subsurface cutoff wall, was relatively 

constant during the same time period, showing an increase of 

0.7 ft3/s or about 13 percent, from 5.4 to 6.1 ft3/s.

 The first wells of the CT well field were completed in 

November 1987, followed by CT3 in December 1987 and CT4 

in January 1988 (table 3). Even though the Eastbank Hatchery 

did not become operational until July 1989 and expanded to 

full operations by about November 1989 (I. Adams, Public 

Utility District No. 1 of Chelan County, written commun., 

2008), it is postulated that the CT well field started pumping 

as soon as wells were installed and that this explains the 

decrease in seepage from the Lower Aquifer. 

From 2004 through 2006, the mean total discharge 

through the North and South Weirs was 8.4 ft3

/s. This indicates 

that from 2004 through 2006, the mean annual ground-water 

pumpage from the Eastbank Aquifer system was about seven 

times the measured portion of the mean annual ground-water 

seepage through the subsurface cutoff wall. 
22 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 13. Instantaneous discharge through the North and South Weirs and total instantaneous discharge, Eastbank 

Aquifer System, Douglas County, Washington, 1977–2006.

tac08-0189_fig13

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

YEAR

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

Recorder

recalibrated

North Weir

Total discharge

South Weir

Historical Ground- and Surface-Water Levels

Water levels have been measured hourly in 12 wells and 

1 river site by the PUD since 1990 (fig. 10) for the purpose 

of monitoring hydrologic conditions of the Eastbank Aquifer 

system. Daily means of the hourly water levels for January 1, 

1991 through September 30, 2006, are shown in figure 14. In 

addition to the continuous, hourly measurements, occasional 

manual water-level measurements have been made to verify 

the continuous measurements.

Reliability of Historical Water-Level 

Measurements

The historical hourly water levels have been measured 

using sealed probes that measure both water levels and water 

temperature (see Water & Environmental Systems Technology, 

Inc., 1990, for a detailed description of the instrumentation). 

Because the probes are not vented to the atmosphere, changes 

in atmospheric pressure are recorded as apparent changes in 

water levels, even if the actual water levels did not change 

in response to changes in atmospheric pressure. Without 

corrections for atmospheric effects, errors between actual 

and recorded water levels by non-vented probes may be on 

the order of inches to feet (Wardwell, 2007). Other sources 

of error in the recorded water-level data are instrument 

drift, possible incomplete information about the timing of 

probe replacements, and noise that resulted from spliced 

transmission cables that had to be repaired. Probes were 

replaced in case of obvious instrument failure (D. Davies, 

Public Utility District No. 1 of Chelan County, oral commun., 

2007).

To be able to correct for instrument drift and other 

possible sources of error, manual water-level verification 

measurements are needed at regular intervals throughout 

the year for comparison to recorded water levels. The first 

water-level verification measurements since the start of the 

monitoring network in 1990 known to this study were made 

in July 1998, when the monitoring network was recalibrated. 
Hydrology 23

tac08-0189_fig14

2000 1999 1998 1997 1996 1995 1994 1993 1992 1991

690680

2001 2005 2004 2003 2002 2006

715710705700695685

YEAR

TH5TH6 CT3

LR2-W

TH4TH7

TH8

CD47

TH9RIV

CD8CD10

TH1

USGS gaging station 12453679 

WATER LEVEL, IN FEET ABOVE NATIONAL GEODETIC VERTICAL DATUM 0F 1929 (NGVD 29) Monitoring network recalibrated

Figure 14. Daily mean water levels recorded by the monitoring network of the Eastbank Aquifer system, Douglas County, Washington, and daily water levels recorded at midnight by USGS gaging station 12453679, Chelan County, Washington, January 1991 – September 2006.
24 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

This recalibration resulted in significant shifts in some 

recorded water levels at that time (fig. 14). (Sudden rises in 

water levels during the spring of the mid-1990s correspond 

to seasonal reductions in pumping by the CT wells.) The next 

known verification measurements were made in February, 

2006 (K. deRubertis and others, written commun., 2007) 

followed by periodic measurements made by this study from 

July 2007 through January 2008. Differences between water 

levels measured manually in February 2006 (K. deRubertis 

and others, written commun., 2007) and July 2007 and those 

recorded by the monitoring network are summarized in 

table 4. Other than the outlier of 9.51 ft, the differences in 

the measurements range from -2.39 to 3.39 ft. Because few 

verification measurements have been made over the period 

of record of the monitoring network, there is significant 

uncertainty in the historical continuous water-level data.

To evaluate the accuracy of the long-term record of the 

river probe (RIV in fig. 14), river water levels measured by 

the monitoring network were compared to river water levels 

recorded by USGS gaging station 12453679 (period of record 

July 25, 1975 to the present [2008]). The gaging station is 

located along the west bank of the river at the forebay of 

Rocky Reach Dam (fig. 2). The gaging station measures 

hourly water levels but only measurements at midnight are 

reported by the USGS (fig. 14). Recorded water levels are 

verified at regular intervals with manual measurements and 

the water-level record is adjusted accordingly. A comparison 

of the water-level record of the USGS station and the probe 

labeled RIV shows that probe RIV has been subject to a steady 

downward instrument drift of about 3 ft since 1990. Probes 

in wells of the monitoring network are of the same type and 

it is likely that they have drifted also, but the magnitude and 

direction of their drifts over the life of the monitoring network 

cannot be determined due to a lack of manual water-level 

measurements.

The pre-development potentiometric surface measured 

in the Eastbank Aquifer system in 1977 (fig. 11) shows that 

potentiometric gradients in the study area are small and thus 

accurate water-level measurements are required to be able to 

use the historical continuous water-level data for analyses of 

long-term changes in the aquifer system. The uncertainty of 

the historical continuous water-level data is too large for this 

purpose and so these data were not further analyzed in this 

study.

Ground-Water Levels on July 18, 2007

To make equipment repairs at the Eastbank Hatchery, 

the PUD scheduled a shutdown of the CT well field from 1 to 

3 p.m. on July 18, 2007. Because a complete shutdown of 

all CT wells is rare, the opportunity was used to schedule a 

shutdown of all significant pumping wells in the study area 

and to measure water levels before and after the shutdown. 

Arrangements were made with the City of Wenatchee and 

Lincoln Rock State Park to simultaneously shut down the 

RW and LR well fields. In addition, the PUD shut down 

wells SW13 and SW14, and only continued to pump about 

20 gal/min from well SW11. From about 9 a.m. until about 

5 p.m. on July 18, 2007, the recording frequency of the 

monitoring network was increased from once per hour to once 

per minute and a team of PUD and USGS personnel made 

multiple manual water-level measurements from about 10 

a.m. until shortly after 3 p.m. River water levels measured at 

USGS gaging station 12453679 were nearly stable between 

10 a.m. and 3 p.m., ranging from 704.33 ft at 10 a.m. to 

704.59 ft at 1 p.m. Water levels were not measured in the LR 

and SW wells because they were not accessible, and water 

levels were not measured in well CD6 because it had not been 

located at the time. In addition, before pumping ceased, water 

levels were not measured in pumping wells except for one 

measurement in well RW4. The water-level data were used 

to document the ground-water flow pattern of the Lower and 

Combined Aquifers before and after the shutdown of pumping.

Table 4. Differences between water levels measured manually 

and those recorded by the monitoring network, Eastbank Aquifer 

system, Douglas County, Washington, February 2006 and July 

2007.

[Locations of wells are shown in figure 2. USGS well no.: See figure 4 for 

explanation of well-numbering system. Latitudes and longitudes of the wells 

are on file with the U.S. Geological Survey. Difference between manually 

measured and recorded water levels: negative values indicate that manually 

measured water levels are lower than recorded water levels, and positive 

values indicate that they are higher. February 6-8, 2006: Values computed 

from data provided by K. deRubertis and others (written commun., 2007). 

July 18, 2007: Values are medians of differences computed from multiple 

measurements between 11:00 a.m. and 3:30 p.m., Pacific Daylight Time. 

Abbreviations: USGS, U.S. Geological Survey; –, not available]

Local 

well name

USGS 

well No.

Difference between manually 

measured and recorded water 

levels (feet)

February 6–8, 2006 July 18, 2007

CD8 24N/20E-35R01 0.01 2.57

CD10 24N/20E-35Q01 -2.39 3.39

CD47 24N/20E-35Q02 .4 1.22

CT3 24N/20E-35Q03 .72 .79

LR2-W 24N/20E-35H02 .53 –

TH1 24N/20E-35K05 – –

TH4 24N/20E-35K02 9.51 1.96

TH5 24N/20E-35G01 .7 1.30

TH6 24N/20E-35G02 -.08 -.29

TH7 24N/20E-35K01 .66 1.07

TH8 24N/20E-35K04 -.36 .42

TH9 24N/20E-35K03 .23 1.08
Hydrology 25

During the shutdown, the water-level probe in well 

TH1 was not working properly and the water level in well 

TH9 did not respond to the shutdown of pumping. The 

lack of response in well TH9 is considered anomalous and 

remains unexplained. A slug test was performed in well TH9 

to determine if the well was isolated from the aquifer due 

to clogging of its perforations. However, changes in water 

levels induced by the slug test dissipated quickly and thus 

the well perforations were not clogged. A subsequent downhole camera survey of well TH9 revealed that it contained a 

1-inch inner-diameter PVC pipe at depth attached to a heavy 

object that was presumed to be a pump. An attempt to remove 

the pipe and pump was unsuccessful (see appendix 2 for 

additional detail).

Prior to Cessation of Ground-Water Pumping

Multiple water levels measured manually prior to the 

shutdown of pumping wells were averaged, plotted, and 

contoured to create a potentiometric-surface map of the Lower 

and Combined Aquifers (fig. 15). At the time, wells CT1, 

CT2, CT3, CT4, RW2, RW4, LR1, LR2-W, SW11, SW13, and 

SW14 were pumping. The nominal pumping rate of each CT 

well was 12.5 ft3

/s, and wells RW2 and RW4 were pumped 

at rates of 18.5 and 22.3 ft3/s, respectively. The combined 

pumping rates of the LR and SW wells were estimated to 

be 0.3 and 0.2 ft3/s, respectively. Figure 15 shows that with 

four CT and two RW wells pumping, a cone of depression 

surrounds the RW field and another cone of depression 

surrounds the CT well field. The cone of depression of the 

CT well field widens towards the south because some ground 

water drains through the subsurface cutoff wall. The cones of 

depression of the RW and CT well fields intersect and create 

a ground-water divide along an approximately east-west 

line going through the general area between wells RW1 and 

TH8. Based on the potentiometric contours, the horizontal 

ground-water flow direction is approximately radial towards 

the pumping wells with source water originating along 

the aquifer boundary with the Columbia River (fig. 15). A 

steep potentiometric gradient exists between the river and 

the western extent of the Lower and Combined Aquifers, 

indicating that the bottom of the Columbia River is blanketed 

with materials of lower permeability than the sediments of the 

Lower and Combined Aquifers. An aquatic habitat study of 

Lake Entiat confirmed the presence of fine-grained sediments 

at the bottom of the Columbia River near the study area 

(Duke Engineering & Services, Inc., 2001). The layer of finegrained sediments impedes ground-water recharge from the 

Columbia River but it does not prevent it, as demonstrated by 

the potentiometric-surface maps (figs. 11 and 15). In addition 

to the approximately radial horizontal ground-water flow 

toward the pumping wells, ground water also flows towards 

the subsurface cutoff wall. The majority of flow to the CT well 

field may come from the small embayment northeast of and 

adjacent to Rocky Reach Dam (fig. 15). The aquatic habitat 

study mapped large cobble and gravel at the bottom of the 

embayment (Duke Engineering & Services, Inc., 2001), which 

is riprap that was put at the bottom of the embayment after 

it was excavated as part of the construction of Rocky Reach 

Dam. 

Two Hours after Cessation of Ground-Water Pumping

Following the shutdown of the pumping wells at 1 p.m., 

multiple water levels were measured manually in monitoring 

wells and wells that were previously pumping. The manual 

measurements continued until shortly after 3 p.m., when the 

pumping wells that were shut down at 1 p.m. were turned back 

on. The last set of manual water-level measurements that were 

made from 3 to 26 minutes before 3 p.m. were extrapolated to 

3 p.m. to obtain a set of estimated water levels that represented 

the potentiometric surface 2 hours after the start of water-level 

recovery. For wells that are part of the monitoring network, 

extrapolations of manual water-level measurements were 

based on the water-level recovery pattern recorded every 

minute by the monitoring network; for wells that are not 

part of the monitoring network, extrapolations were made 

visually based on trends in multiple manual water-level 

measurements. Water-level adjustments ranged from -0.1 to 

0.5 ft with a median adjustment of 0.1 ft. Figure 16 shows that 

after 2 hours of water-level recovery, the cones of depression 

surrounding the RW and CT well fields remain, although 

the potentiometric gradients are less steep. Excluding waterlevel recoveries of 0 ft in well TH9 and 8.7 ft in well RW4, 

the water levels recovered from 0.8 ft in well TH5 to 4.7 ft in 

well CD47, with a median recovery of 4.1 ft. The water levels 

recorded every minute by the monitoring network indicated 

that although recovery had slowed down after 2 hours, 

complete recovery was not achieved. Complete recovery 

would be expected to return the potentiometric surface to 

the predevelopment conditions measured on July 19, 1977 

(fig. 11). Based on the pattern of the water-level contours, 

the horizontal ground-water flow directions after 2 hours of 

recovery were still similar to the flow directions prior to the 

shutdown of the pumping wells. 
26 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 15. Potentiometric surface of the Lower and Combined Aquifers prior to the shutdown of pumping wells, 

Eastbank Aquifer system, Douglas County, Washington, July 18, 2007.

tac08-0189_fig15

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

EXPLANATION

Subsurface cutoff wall

Well pumping

Extent of Lower and Combined Aquifers—Modified from Water & Environmental Systems Technology, Inc. (1990)

Direction of ground-water flow

Well and name—Italicized number is measured water level, in feet. Values in parentheses represent water levels for the

 Upper Aquifer, Clay Confining Unit, or an unknown unit

704.5

695.1

TH2

Potentiometric contours prior to shutdown of pumping wells—Shows altitude at which water level would have stood

 in tightly cased wells (July 18, 2007). Dashed where approximately located. Contour interval, in feet, is variable.

 Datum is National Geodetic Vertical Datum of 1929

River water level, in feet—Mean water

 level measured at USGS gaging station

 12453679 from 10 a.m. to 1 p.m.,

 July 18, 2007. Gaging station

 location is shown in figure 2 

704.5

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

694.7

LR1

LR2-E

TH2

RW3

RW4

RW2

RW1

CT2

CD6

SW14

SW13

SW11

CD10

TH6

TH5

TH8

CD8

LR2-W

CT3

TH9

TH7

TH1

CD47

TH4

CT1

CT4

COLUMBIA RIVER

697.0

695.0

693.0

693.0

695.0

694.7

694.5

691.0

(693.1) (694.5)

694.3

694.8 694.6

695.1

694.7

689.9

696.7

(698.5)

695.1

695.0

694.7
Hydrology 27

Figure 16. Potentiometric surface of the Lower and Combined Aquifers 2 hours after shutdown of pumping wells, 

Eastbank Aquifer system, Douglas County, Washington, 3 p.m., July 18, 2007. 

tac08-0189_fig16

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

EXPLANATION

Subsurface cutoff wall

Well pumping

Extent of Lower and Combined Aquifers—Modified from Water & Environmental Systems Technology, Inc. (1990)

Direction of ground-water flow

Well and name—Italicized number is measured water level, in feet. Values in parentheses represent water levels for the

 Upper Aquifer, Clay Confining Unit, or an unknown unit 699.2

TH2

Potentiometric contours 2 hours after shutdown of pumping wells—Shows altitude at which water level would have 

 stood in tightly cased wells (3 p.m., July 18, 2007). Dashed where approximately located. Contour interval 0.4 foot.

 Datum is National Geodetic Vertical Datum of 1929

River water level, in feet—Mean water

 level measured at USGS gaging station

 12453679 from 1 to 3 p.m.,

 July 18, 2007. Gaging station

 location is shown in figure 2 

704.5

Well recently pumping

704.5

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

699.4

TH2

RW3

RW4

RW2

RW1

CT1

CT2

CT4

CD10

TH6

TH5

TH8

CD8

CT3

TH9

TH7

TH1

CD47

TH4

LR1

LR2-E

CD6

SW14

SW13

SW11

LR2-W

COLUMBIA RIVER

(698.8)

699.0

699.0

(699.3)

699.2

699.1

698.9

698.9

699.0

699.1

699.1

698.7

699.2

698.5

698.6

698.6

699.6

(701.9)

699.4

698.6

699.0

699.0

(697.6)
28 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Historical Ground- and Surface-Water 

Temperatures

Water temperatures have been measured hourly in 12 

wells and 1 river site by the PUD since 1990 for the purpose 

of monitoring thermal conditions of the Eastbank Aquifer 

system. The river probe (RIV in fig. 10), which also measures 

the water level of the river, is in a PVC pipe draped along 

the bottom of the river, about 200 ft offshore. Hourly water 

temperatures measured in the monitoring-network wells 

represent temperatures at particular depths and do not provide 

vertical temperature profiles. Daily median temperatures were 

computed from hourly temperatures for 2006 (fig. 17), which 

is an example of a typical 1-year period. The temperature 

records indicated that different wells have different annual 

temperature ranges and different time lags between changes 

in river temperatures and subsequent changes in well 

temperatures (fig. 17).

Water & Environmental Systems Technology, Inc. (1990) 

measured vertical temperature profiles in wells CD6, CD47, 

TH1, TH4, TH5, TH6, TH7, TH8, and TH9 at selected times 

between July 1989 and April 1990. These profiles indicated 

that there were significant vertical temperature gradients 

in the Eastbank Aquifer system that changed seasonally. In 

July 1987, CH2M Hill (1988) measured vertical temperature 

profiles in wells TH4, TH5, and TH6 but these data were not 

available to this study. In February 2006, K. deRubertis and 

others (written commun., 2007) measured vertical temperature 

profiles in the same wells as CH2M Hill and also wells CD8, 

CD10, CD47, LR2-W and TH7. This study measured vertical 

temperature profiles in wells CD10, TH1, TH4, TH6, TH7, 

and TH9 between August and September 2007 and started 

a network of monthly measurements of vertical temperature 

profiles in 12 wells (CD6, CD8, CD10, CD47, TH1, TH2, 

TH4, TH5, TH6, TH7, TH8, and TH9) in December 2007 that 

is now maintained by the PUD.

On August 20, 2007, 32 vertical temperature profiles 

were measured using CTD (conductivity-temperature-depth) 

casts in the Columbia River near the study area to determine if 

the river was thermally stratified in the area of likely groundwater recharge. Profiles were located in an approximately 

500-ft-wide band extending from the north shore near the boat 

ramp (fig. 2) to the shore along the embayment adjacent to 

Rocky Reach Dam. One profile was measured in the center 

of the river. Excluding two anomalous temperature profiles 

located near the outfall from the Eastbank Hatchery, negligible 

Figure 17. Daily median water temperatures recorded by the monitoring network of the Eastbank Aquifer system, Douglas County, 

Washington, 2006.

TH5

TH6

CT3

LR2-W

TH4

TH7

TH8

CD47

TH9

RIV

CD8

TH1

CD10

2

4

6

8

10

12

14

16

18

20

DAILY MEDIAN TEMPERATURE, IN DEGREES CELSIUS

JAN FEB MAR APR MAY JUNE JULY SEPT

2006

AUG OCT NOV DEC
Hydrology 29

temperature variation was measured. Water temperatures 

ranged from 19.0 to 19.5°C, with a median of 19.3°C and 

a standard deviation of 0.1°C. Previous temperature studies 

also showed a lack of both vertical and lateral stratification 

of the river near the study area. For example, in a series 

of approximately monthly vertical temperature-profile 

measurements from October 1999 through September 

2000 located in the center of the river approximately due 

west of well TH6, Parametrix, Inc. and Rensel Associates 

Aquatic Science Consultants (2001) measured a maximum 

temperature range of 0.32°C on July 14, 2000. Parametrix, 

Inc. and Thomas R. Payne & Associates (2002) recorded 

nearly constant temperatures in a temperature transect of the 

river adjacent to the study area in the morning and afternoon 

of September 2, 2001, except for a slight warming of the 

surface layer in the afternoon ranging from 0 to 1.3°C. Based 

on these data, thermal stratification of the Columbia River 

near the study area was insignificant and water temperatures 

measured at any nearby river location were representative of 

the temperature of water that recharged the Eastbank Aquifer 

system within about ±0.5°C. 

Reliability of Historical Water-Temperature 

Measurements

The historical hourly water temperatures were measured 

with the same sealed instruments used to measure water levels. 

Similar to the lack of manual measurements to verify water 

levels recorded by the monitoring network, there also was a 

lack of manual measurements to verify water temperatures 

recorded by the network. Temperature probes also are subject 

to failure, instrument drift, possible incomplete information 

about the timing of probe replacements, and the addition of 

noise due to transmission-cable repairs. However, watertemperature probes generally are more robust than water-level 

probes and their measurements are not affected by day to day 

changes in atmospheric pressure.

To evaluate the accuracy of the river probe (probe RIV), 

hourly river temperatures measured by the monitoring network 

were compared with hourly river temperatures measured at the 

forebay of Rocky Reach Dam (S. Hayes, Public Utility District 

No. 1 of Chelan County, written commun., 2007) for the time 

period of concurrent data, March 25, 2003 through August 

15, 2007. River temperatures are measured at the forebay for 

the purpose of monitoring fish habitat and the time series used 

in this study consisted of merged records of four separate 

temperature probes (S. Hayes, Public Utility District No. 1 

of Chelan County, written commun., 2007). Figure 18 shows 

that except for some scatter at the low-temperature range that 

represents several days in January 2007, there is a close match 

between the temperatures measured at midnight at the forebay 

and by probe RIV. Statistics based on all hourly data for the 

concurrent period show that the differences in temperature 

range from -0.7 to 2.1°C, with a median difference of 0.3°C 

and a standard deviation of 0.2°C. These results indicate that 

the temperature measurements of probe RIV since March 

2003 have been accurate within a comparable margin of error 

(generally less than 1°C) as may result from assuming that 

water temperatures measured at any nearby river location are 

representative of the temperature of water that recharges the 

Eastbank Aquifer system. In addition, because probe RIV has 

not been replaced since its installation in 1990, it is reasonable 

to assume that temperature measurements by probe RIV have 

been reliable since 1990.

Similar temperature data were not available to verify 

the accuracy of temperature measurements by probes in 

wells of the monitoring network. Instead, probes were pulled 

from three wells (TH4, TH6, and TH7) and submerged in a 

water bath with two thermometers to obtain a representative 

comparison of temperature readings by the monitoring 

network (table 5). One thermometer was a Cole-Parmer®

reference thermometer calibrated against a National Institute 

of Standards and Technology (NIST) standard thermometer 

(INNOCAL test no. 22144) and the other thermometer was 

a 300-ft-long TLC (temperature-level-conductivity) probe 

made by Solinst®. The accuracy of the TLC thermometer 

was confirmed using a 4-point verification in the USGS 

laboratory in Tacoma, Washington, on July 31, 2007. The 

temperature probe of a fourth well (CD10) was checked in 

place by submerging the TLC thermometer into the well to the 

reported depth of the probe. The probe was not pulled from 

well CD10 because it was stuck. Side-by-side thermometer 

and monitoring-network probe comparisons in a water bath 

are considered more reliable because the method leaves no 

question that all instruments are measuring the same water and 

that the measurements are made simultaneously. The results 

of the temperature comparisons indicate that the monitoringnetwork probes for wells TH4, TH6, and TH7 measured 

temperatures within 0.3°C of the reference thermometer 

(table 5). The monitoring-network probe for well CD10 

measured temperature within 0.1°C of the TLC thermometer. 

Based on verifications of the subset of monitoring-network 

probes, bias and variability in temperature measurements for 

all monitoring-network probes were assumed to be less than 

0.5°C.

In February 2006, K. deRubertis and others (written 

commun., 2007) made in-place comparisons of temperatures 

recorded by all probes of the monitoring network, except the 

probe in well CD47, at reported probe depths. They found that 

temperatures matched within 0.5°C, except for probes in wells 

LR2-W and TH8 for which differences exceeded 1.5°C. Water 

temperatures recorded once per minute on July 18, 2007, 

indicated that several temperature probes of the monitoring 

network had noisy recordings (defined as large variability over 

short periods of time), including the temperature probes of 

wells LR2-W and TH8. The large temperature discrepancies 

reported by K. deRubertis and others (written commun., 

2007) for the probes in wells LR2-W and TH8 may therefore 

have resulted from small differences between the times the 

verification temperatures were read and the times the probe 

temperatures were recorded by the monitoring network. 
30 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

The limited verification data available for the temperature 

probes of the monitoring network indicate that many of the 

temperature probes may be making reliable temperature 

measurements and presumably have done so since they 

were installed or last replaced. Even if water temperatures 

recorded by the monitoring network cannot be relied on with 

great certainty due to limited verification data, the relative 

pattern of the historical temperature record is reliable and the 

recorded times of the annual minimum and maximum water 

temperatures are likely accurate within 1 day. 

Figure 18. Daily river water temperatures recorded at midnight at the forebay of Rocky Reach 

Dam and at probe RIV of the monitoring network of the Eastbank Aquifer system, Douglas County, 

Washington, March 25, 2003 – August 15, 2007.

tac08-0189_fig18

1

3

5

7

9

11

13

15

17

19

21

1 3 5 7 9 11 13 15 17 19 21

WATER TEMPERATURE AT PROBE RIV OF THE MONITORING NETWORK, IN DEGREES CELSIUS

WATER TEMPERATURE AT THE FOREBAY OF ROCKY REACH DAM, IN DEGREES CELSIUS

Line of equal temperature

Trends in Water Temperatures

Ground-water recharge transports heat from the Columbia 

River to the Eastbank Aquifer system, and each location in 

the aquifer system has an annual temperature record that 

mimics the annual temperature record of the river. Generally, 

with increasing distance from the river, the time lag between 

a change in river temperature and a subsequent change in 

well temperature increases and the annual temperature range 

decreases. The spatial and temporal patterns of ground-water 

temperatures may change as thermal and hydraulic conditions 

change in the river and/or aquifer system. Water temperatures 

measured by the monitoring network were analyzed to 

determine if and how patterns of ground-water temperatures in 

the Eastbank Aquifer system have changed. 
Hydrology 31

Hourly water temperatures measured by the monitoring 

network from January 1, 1991 through August 31, 2007, 

were simplified to time series of daily median temperatures. 

The entire record of daily values was analyzed to determine 

if there were trends in the time lags between changes in 

river and well temperatures. The part of the record starting 

in 1999 was analyzed to determine if there were trends in 

the annual minimum and maximum well temperatures and 

in the annual temperature ranges of wells with respect to 

the river. The well-temperature record prior to 1999 was not 

analyzed for trends in annual extreme temperatures and annual 

temperature ranges due to uncertainty in the data. An analysis 

of temperature trends in the Eastbank Aquifer system must 

consider both horizontal and vertical variability of groundwater temperatures. A limited number of vertical temperature 

profiles were available to illustrate the three-dimensionality of 

ground-water temperatures, but too few profiles were available 

to determine interannual trends in vertical temperature 

profiles.

Analyses of trends in time lags and annual temperature 

ranges help determine if the ground-water flow system 

is in thermal equilibrium. In this study, the ground-water 

flow system is defined to be in thermal equilibrium at a 

given location if the time lags between changes in river 

temperatures and subsequent changes in ground-water 

temperatures are constant at that location. The equilibrium is 

a dynamic equilibrium because temperatures vary throughout 

the year. When the ground-water flow system is in thermal 

equilibrium, the ratios of annual temperature ranges in the 

wells to annual temperature ranges in the river also should 

be constant at a given location. Because transport of heat 

is primarily by advection (flow of water) within 

aquifers and by conduction within confining units, 

and because transport by advection is faster than 

by conduction (Miller and Delin, 2002), decreasing 

trends in time lags and increasing trends in ratios 

are likely explained by increasing transport of heat 

by advection. This transport increases as groundwater fluxes increase due to increases in pumping 

and/or increases in hydraulic conductivities as fine 

sediments in the aquifers are removed or rearranged 

as a result of pumping and preferential flowpaths 

form.

Because the only significant source of recharge 

to the Eastbank Aquifer system is the Columbia 

River, it is important to know whether there have 

been trends in river temperature during the periods 

of analysis. Annual minimum, maximum, and 

mean river temperature measured by probe RIV 

(fig. 10) from 1991 through August 2007 is shown 

in figure 19. Straight-line linear regressions of each 

time series for the entire time period show that there 

are no statistically significant trends in the annual 

minimum, maximum, and mean river temperature 

Table 5. Comparison of temperature measurements by probes in selected 

wells of the monitoring network of the Eastbank Aquifer system and two 

thermometers, Douglas County, Washington, September 12, 2007.

[Locations of wells are shown in figure 2. USGS well No.: See figure 4 for explanation 

of well-numbering system. Latitudes and longitudes of the wells are on file with the 

U.S. Geological Survey. Monitoring-network probe: Geokon probe. Reference 

thermometer: Cole-Parmer reference thermometer calibrated against a National Institute 

of Standards and Technology standard thermometer. TLC: Solinst temperature-levelconductivity (TLC) meter probe, 300 feet long. Abbreviations: USGS, U.S. Geological 

Survey; –, not available]

Local 

well name

USGS 

well No.

Water temperature 

(degrees Celsius) Measurement 

type

Monitoringnetwork 

probe

Reference 

thermometerTLC

CD10 24N/20E-35Q01 12.3 – 12.4 in place

TH4 24N/20E-35K02 13.2 13.5 13.6 water bath

21.3 21.0 21.0

TH6 24N/20E-35G02 20.5 20.3 – water bath

TH7 24N/20E-35K01 24.2 24.3 24.6 water bath

at a confidence level of 95 percent. However, straight-line 

linear regressions of each time series starting in 1999 show 

that there are statistically significant trends in the annual 

mean and maximum river temperature at a confidence level 

of 95 percent, indicating a mean annual increase in the annual 

mean and maximum river temperature from 1999 through 

2006 of 0.07 and 0.17°C, respectively (fig. 19). There are no 

statistically significant trends in the annual minimum river 

temperature since 1999 at a confidence level of 95 percent, nor 

are there statistically significant trends in the annual minimum, 

maximum, and mean river temperature from 1991 through 

1998 at a confidence level of 95 percent.

The analysis of well-temperature records was based 

on the assumption that the water temperature measured at a 

given depth in a monitoring well was representative of the 

water temperature at the same depth in the ground-water 

flow system outside the well. This assumption is justified 

because convective flow, and thus temperature-controlled 

density stratification of the water column, is unlikely to occur 

in the monitoring wells analyzed in this study due to their 

small diameters (3 to 8 in.; Diment, 1967; Gillespie, 1995). 

Well CT3, which is a hatchery well with a temperature probe 

located about 85 ft above the top of the open interval, has a 

casing diameter of 26 in. for most of its depth. Due to its large 

diameter, density stratification may occur in well CT3 when 

it is not pumping. When the well is pumping, the temperature 

probe measures water temperatures that are likely affected 

both by the ambient temperature of the ground-water flow 

system outside the well and the temperature of pumped water 

moving through a pipe inside the well casing. Well CT3 was 
32 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 19. Annual minimum, maximum, and mean temperature of the Columbia River near the Eastbank Aquifer system, Douglas 

County, Washington, 1991–2007.

tac08-0189_fig19

0

2

4

6

8

10

12

14

16

18

22

20

24

WATER TE MPERATURE, IN DEGREES CELSIUS

1991 1992 1993 1994 1995 1996 1997 1999

YEAR

1998 2000 2001 2002 2003 2004 2005 2006 2007

Mean

Minimum

Maximum

Annual water temperature

Least-squares regression line of annual

 maximum temperatures, 1999–2006

Least-squares regression line of annual

 mean temperatures, 1999–2006

Slope=0.07; r 2=0.56

Slope=0.17; r 2=0.61

pumping the majority of the time, except during 1991 and 

1992. Annual temperature extremes measured in well CT3 

and that were used in the trend analyses were all measured 

when well CT3 was pumping, except for the annual maximum 

temperature in 1991 and the annual minimum temperatures 

in 1992, 1998, 2005, and 2006. Due to the poorly known 

variables that affect the temperature record of well CT3, there 

is greater uncertainty in the interpretation of the temperature 

records of well CT3 than the records of the monitoring wells. 

Vertical Temperature Profiles

Figure 20 shows selected historical vertical temperature 

profiles in three wells, CD6, CD47, and TH8, measured in 

1989–90 by Water & Environmental Systems Technology, 

Inc. (1990), in 2006 by K. deRubertis and others (written 

commun., 2007), and in 2007–08 by this study. Profiles were 

selected to illustrate the maximum temperature range that may 

occur in each hydrogeologic unit in each well. Although wells 

CD6 and TH8 had multiple temperature-profile measurements 

throughout 1989–90, none of the wells had a sufficient number 

of measurements to be sure that the annual temperature 

extremes had been measured.

The Upper Aquifer at well CD6 (fig. 20A), which is 

located near the shoreline and subsurface cutoff wall (fig. 15), 

has a temperature range that is almost identical to the 

temperature range of the river (fig. 19). In addition, the annual 

extreme temperatures in the river and Upper Aquifer at well 

CD6 occur at about the same time of year; usually the annual 

minimum and maximum river temperatures occur in February 

and August or September, respectively. Temperatures in the 

Upper Aquifer at the location of well CD6 track the river 

temperatures closely, because sediments of the Upper Aquifer 

near the well were highly disturbed during construction of 

Rocky Reach Dam and probably consist primarily of highpermeability backfill. The annual temperature range in the 

Lower Aquifer at well CD6 is smaller than that in the Upper 

Aquifer and the dates of annual high and low temperatures are 

different between the aquifers, with the Clay Confining Unit 

showing transitional patterns.
Hydrology 33

Figure 20. Selected vertical temperature profiles in wells CD6, CD47, and TH8 of the Eastbank Aquifer system, Douglas 

County, Washington, 1989–2008. Data for 1989–90 are from Water & Environmental Systems Technology, Inc. (1990) and data 

for 2006 are from K. deRubertis and others (written commun., 2007).

tac08-0189_fig20

B. CD47, top of perforated interval at about 560 feet

February 22, 1990

February 7, 2006 

December 11, 2007

January 28, 2008

August 22, 2007

TEMPERATURE, IN DEGREES CELSIUS

TEMPERATURE, IN DEGREES CELSIUS TEMPERATURE, IN DEGREES CELSIUS

August 16, 1989

August 31, 1989

November 7, 1989

December 11, 2007

January 28, 2008

August 22, 2007

April 12, 1990

A. CD6, open-end well (no perforations) and no temperature probe

C. TH8, open-end well (no perforations)

2 4 6 8 10 12 14 16 18 20 22

6

? ? ?

8 10 12 14 16 8 10 12 14 16 18

450

500

550

600

650

700

750

ALTITUDE, IN FEET ABOVE NGVD 29

450

500

550

600

650

700

750

ALTITUDE, IN FEET ABOVE NGVD 29

450

500

550

600

650

700

750

ALTITUDE, IN FEET ABOVE NGVD 29

Upper Aquifer

Hydrogeologic unit

Lower Aquifer

Bedrock

Clay Confining Unit

July 24, 1989

August 16, 1989

October 30, 1989

December 13, 2007

April 12, 1990

January 28, 2008

Temperature profile

 measured on:

Temperature profile measured on:

Altitude of temperature probe

Temperature profile

 measured on: Land surface Land surface

Land surface
34 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Wells CD47 and TH8 (figs. 20B and 20C) show complex 

vertical temperature profiles that are different from each 

other and well CD6, indicating that each location in the 

Eastbank Aquifer system has a set of unique, time-varying 

vertical temperature profiles. The temperature profile at each 

location at a given time is a function of the temperature and 

water level of the river; the proximity to the river, pumping 

wells, and subsurface cutoff wall; the rate and schedule of 

pumping; the horizontal and vertical hydraulic conductivities 

and thicknesses of the hydrogeologic units; and the thermal 

properties of the sediments of and the bedrock beneath 

the Eastbank Aquifer system. Even though the vertical 

temperature profiles of wells CD6, CD47, and TH8 differ, 

temperature changes across the confining units at each of these 

wells indicate that the flow systems of the Upper and Lower 

Aquifers are not tightly connected although there is a stronger 

connection at well TH8.

A comparison of the vertical temperature profiles of the 

Lower Aquifer of wells CD47 and TH8 shows that generally, 

the vertical temperature gradients are slightly larger in well 

TH8 than in well CD47 indicating slightly more flow in the 

upper part of the Lower Aquifer near well TH8. Well TH8 

has no perforated interval, so water inside its casing has likely 

equilibrated to the temperature of the surrounding aquifer by 

conduction. One possible explanation for the increased flow in 

the upper part of the Lower Aquifer is that it has a relatively 

larger horizontal hydraulic conductivity, although the driller’s 

log for well TH8 did not indicate a significant change in 

lithology from the upper to the lower parts of the Lower 

Aquifer. An alternative explanation for the increased flow in 

the upper part of the Lower Aquifer near well TH8 is that the 

well is very near the CT well field, and in particular near well 

CT4 (fig. 15). Well CT4 is open to the Lower Aquifer from an 

altitude of 549 to 575 ft and the open intervals for all wells of 

the CT well field range from 540 to 576 ft.

The smaller vertical temperature gradients in the lower 

part (below the altitude of the CT well field open intervals) 

of the Lower Aquifer of well TH8 during much of the year 

represent colder and thus denser water that probably is 

pumped by the CT well field at a lower rate than water in 

the upper part (within the altitude range of the CT well field 

open intervals) of the Lower Aquifer. The source of some 

of this colder water may be colder and denser water that 

settled locally in the bedrock depression north and west of 

well TH8 (fig. 7) and is captured by well CT4. The smaller 

vertical temperature gradients in the Lower Aquifer of well 

CD47 may result from mixing of water at and near the open 

interval because well CD47 is perforated below an altitude of 

about 560 ft. The mixing would result in more uniform water 

temperatures in the well that represent the average ambient 

ground-water temperatures near the perforated interval. 

Alternatively, mixing in well CD47 is minimal and the vertical 

temperature profile measured in the well reflects the vertical 

temperature profile of the ambient water temperatures. Vertical 

temperature profiles not shown for other monitoring wells 

with perforated intervals (for example, wells TH1, TH4, and 

TH7) include significant vertical temperature gradients (up to 

about 0.1°C/ft) adjacent to open intervals and so it is assumed 

that generally, vertical temperature profiles measured in 

monitoring wells with perforated intervals are representative 

of vertical temperature profiles of ambient temperatures.

The vertical temperature profiles in figure 20 also 

indicate that the depth at which a temperature probe is 

located substantially influences the ground-water temperature 

measurements. For example, a probe located in the upper 

part of the Lower Aquifer of well TH8 (fig. 20C) would 

measure a different temperature record than a probe located 

in the lower part of the aquifer, where the probe in well TH8 

has been located since the start of the monitoring network. 

Trend analyses of the temperature record of a probe that has 

remained at a constant depth through time can provide useful 

insights into the dynamics of the aquifer system.

Spatial Patterns 

Temporal trends in time lags between changes in river 

and ground-water temperatures; annual ranges in groundwater temperatures with respect to annual ranges in river 

temperatures; and annual extreme ground-water temperatures 

were analyzed spatially. 

Time Lags 

Time series of daily median water temperatures were 

used to estimate the time lag between a change in river 

temperature and the subsequent change in ground-water 

temperature at a given well. Particular focus was on the time 

lag between annual minimum and maximum temperatures. 

The time lags were estimated as the difference between the 

date of an annual extreme temperature in the river and the date 

of the subsequent annual extreme temperature in individual 

wells. Time lags did not exceed 1 year. The resulting annual 

time series of time lags of annual minimum and maximum 

temperatures are shown in figure 21. Time lags of wells 

in which the subsequent annual extreme occurred in the 

following year are plotted according to the year of the annual 

extreme in the river. Data are missing for years when welltemperature records had gaps or when the record was unclear 

when the annual minimum or maximum occurred.
Hydrology 35

Figure 21. Time lag between annual minimum and maximum temperatures in the Columbia River at probe RIV and in wells of the 

monitoring network of the Eastbank Aquifer system, Douglas County, Washington, 1991–2007.

tac08-0189_fig21_page1_A-D

Least-squares regression line of annual

 maximum temperatures

 1991–98

CT3, Clay Confining Unit D.

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

YEAR

CD47, Clay Confining Unit C.

0

40

80

120

160

200

240

280

320

360

199119931995199719992001200320052007

TIME LAG, IN DAYS

YEAR

CD10, Sand lens in Clay Confining Unit B.

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

r 2=0.85

CD8, Sand lens in Clay Confining Unit

Probe last replaced June 1998

r 2=0.84

A.

0

40

80

120

160

200

240

280

320

360

TIME LAG, IN DAYS

199119931995199719992001200320052007

Annual temperature

Minimum 

Maximum
36 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

tac08-0189_fig21_page2_E-H

TH5, Upper Aquifer H.

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

YEAR YEAR

Probe last replaced May 1998

TH4, Lower Aquifer G.

0

40

80

120

160

200

240

280

320

360

199119931995199719992001200320052007

TIME LAG, IN DAYS

TH1, Lower Aquifer F.

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

LR2-W, Combined Aquifer

r 2

=0.46

r 2

=0.79 

r 2=0.57

r 2=0.73 

E.

0

40

80

120

160

200

240

280

320

360

TIME LAG, IN DAYS

199119931995199719992001200320052007

Least-squares regression line of annual

 minimum temperatures

Least-squares regression line of annual

 maximum temperatures

Annual temperature

Minimum 

Maximum

1991–2007 

1999–2006

1991–2007 

1991–98

Figure 21.—Continued.
Hydrology 37

tac08-0189_fig21_page3_I-L

YEAR

r 2=0.78

r 2

=0.64

L.

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

TH8, Lower Aquifer TH9, Lower Aquifer

r 2=0.86

r 2

=0.57

YEAR

TIME LAG, IN DAYS

K.

199119931995199719992001200320052007

0

40

80

120

160

200

240

280

320

360

Probe last replaced December 1996

199119931995199719992001200320052007

40

80

120

160

200

240

280

320

360

0

TH7, Lower Aquifer

Probe last replaced May 1998 r 2

=0.73

r 2

=0.67

r 2

=0.31

J.

2007

r 2=0.45

r 2

=0.56

r 2

=0.53

r 2

=0.68

19911993199519971999200120032005

0

40

80

120

160

200

240

280

320

360

TIME LAG, IN DAYS

TH6, Combined Aquifer

Probe last replaced December 1996

I.

Least-squares regression line of annual

 minimum temperatures

Least-squares regression line of annual

 maximum temperatures

Annual temperature

Minimum 

Maximum

1991–2007 

1991–98

1991–2007 

1991–98

Figure 21.—Continued.
38 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Trends in the time series of time lags from 1991 through 

2007 were evaluated using straight-line linear regressions 

with each of the time series shown in figure 21. The results 

of the trend analyses are summarized in table 6, and trends 

of decreasing time lags that are statistically significant at 

a confidence level of 95 percent are shown in figure 21. A 

decreasing trend in time lags is indicated (table 6) if the trend 

is observed in the time lag for either the annual maximum 

or the annual minimum temperature. The results indicate 

that there were no decreasing trends in time lags in the 

Upper Aquifer and Clay Confining Unit. However, with the 

exception of wells TH1 and TH4, there were decreasing trends 

in time lags in the Lower and Combined Aquifers. The lack 

of decreasing trends in Lower Aquifer wells TH1 and TH4 

indicates that the thermal conditions of the Lower Aquifer near 

wells TH1 and TH4 have been in equilibrium for the pumping 

and aquifer conditions that have existed since 1991. Any 

decreases in time lags near wells TH1 and TH4 presumably 

would have occurred following activation of the CT and RW 

well fields, respectively, and prior to 1991.

Trends in the time series of time lags also were evaluated 

from 1991 through 1998 and from 1999 through 2006. The 

selected time periods were arbitrary, except that the period 

1999-2006 coincides with the period of analysis of annual 

well-temperature ranges described in section “Annual 

Temperature Ranges.” From 1991 through 1998, there were 

statistically significant decreasing trends at a confidence level 

of 95 percent in either the annual minimum or maximum 

temperatures in wells CD8 and CD10 in the Clay Confining 

Unit and all wells in the Lower and Combined Aquifers except 

wells TH1 and TH4 (table 6; fig. 21). (The temperature probes 

in wells CD8 and CD10 are adjacent to sand lenses near the 

Table 6. Summary of temperature trends in the Eastbank Aquifer system, Douglas County, Washington, 1991–2007.

[Locations of wells are shown in figure 2. USGS well No.: See figure 4 for explanation of well-numbering system. Latitudes and longitudes of the wells are on 

file with the U.S. Geological Survey. Abbreviations: USGS, U.S. Geological Survey; X, not analyzed because too few or no data points; na, not applicable; –, 

not available]

Local 

well 

name

USGS 

well No.

Hydrogeologic 

unit at depth 

of temperature 

probe

Is indicated trend statistically significant at a 

confidence level of 95 percent?

Mean annual 

increase 

of annual 

maximum 

temperature, 

1999–2006 

(degrees 

Celsius)

Hydrogeologic 

unit to 

which well 

is open

Primary 

use of 

water since 

completion 

of Rocky 

Reach Dam

Decreasing time 

lag between annual 

minimum and/or 

maximum river and well 

temperatures

Increasing 

ratio of annual 

temperature 

range of 

well divided 

by annual 

temperature 

range of river, 

1999–2006

Increasing 

annual 

maximum 

well 

temperature, 

1999–2006 1991–

2007

1991–

98

1999–

2006

Temperature probe in Upper Aquifer or Clay Confining Unit

CD8 24N/20E-35R01 Sand lens in Clay 

Confining Unit

X Yes X X X X Clay Confining 

Unit

Monitoring

CD10 24N/20E-35Q01 Sand lens in Clay 

Confining Unit

No Yes No X No na – Monitoring

CD47 24N/20E-35Q02 Clay Confining 

Unit

No No No Yes Yes 0.12 Lower Aquifer Monitoring

CT3 24N/20E-35Q03 Clay Confining 

Unit

No No No X Yes .14 Lower Aquifer Hatchery

TH5 24N/20E-35G01 Upper Aquifer No No No No No na Upper Aquifer Monitoring

Temperature probe in Lower Aquifer or Combined Aquifer

LR2-W 24N/20E-35H02 Combined 

Aquifer

Yes Yes Yes Yes Yes 0.23 Combined 

Aquifer

Irrigation

TH1 24N/20E-35K05 Lower Aquifer No No No No Yes .26 Lower Aquifer Monitoring

TH4 24N/20E-35K02 Lower Aquifer No No No Yes Yes .22 Lower Aquifer Monitoring

TH6 24N/20E-35G02 Combined 

Aquifer

Yes Yes No Yes Yes .19 Combined 

Aquifer

Monitoring

TH7 24N/20E-35K01 Lower Aquifer Yes Yes No No Yes .18 Lower Aquifer Monitoring

TH8 24N/20E-35K04 Lower Aquifer Yes Yes No No No na Lower Aquifer Monitoring

TH9 24N/20E-35K03 Lower Aquifer Yes Yes No Yes Yes .19 Lower Aquifer Monitoring
Hydrology 39

base of the Clay Confining Unit that may be connected to 

the Lower Aquifer.) From 1999 through 2006, there were no 

statistically significant trends in time lags, except for well 

LR2-W (table 6; fig. 21). These results indicate that during 

1999-2006, the Lower and Combined Aquifers were in 

thermal equilibrium except for the Combined Aquifer near 

well LR2-W. The thermal equilibrium was reached prior to 

1991 in the Lower Aquifer near wells TH1 and TH4, and 

during 1991-98 in the remainder of the Lower and Combined 

Aquifers except for the Combined Aquifer near well LR2-W. 

The spatial distribution of decreasing trends in time lags 

of wells in the Lower and Combined Aquifers during 1991–98 

and the time lags of the annual maximum temperatures in 

1991, 1999, and 2006 are shown in figure 22. The distribution 

of time lags shows that as early as 1991, the time lag in well 

TH1 was significantly shorter than in wells TH7, TH8, and 

TH9, which is likely the result of a large ground-water flux 

from the Columbia River west-to-southwest of well TH1 to the 

CT well field. The short time lag in well TH1 as early as 1991 

is consistent with the lack of decreasing trends in time lags at 

the well during 1991–2007 and 1991–98 because the Lower 

Aquifer near the well had already reached equilibrium by 

1991. The same is not true for the Lower Aquifer near wells 

TH7, TH8, and TH9, which are located approximately along 

the ground-water divide between the CT and RW well fields 

(fig. 15). In 1991, 1999, and 2006 these wells showed a pattern 

of increasing time lags of the annual maximum temperatures 

with distance from the river (fig. 22). However, during 

1991-98, the time lags of the annual maximum temperatures 

decreased for all three wells (fig. 21J–L), ranging from a mean 

annual decrease of 7.0 days in well TH9 to 10.0 days in well 

TH8.

Annual Temperature Ranges 

The time series of daily median water temperatures 

were also used to determine if there were trends in the annual 

temperature ranges of ground water in wells compared to 

annual temperature ranges in the river. Time series of ratios of 

annual temperature ranges in the wells to annual temperature 

ranges in the river were computed and the results are shown in 

figure 23. Ratios for wells in which the corresponding annual 

temperature range spanned more than one calendar year are 

plotted according to the year of the annual extreme in the river. 

Data are missing for years when well-temperature records had 

gaps or when the record was unclear what the magnitude was 

of the annual minimum or maximum temperature.

Figure 23 indicates that the annual temperature-range 

ratios for well TH6 have been increasing since 1991. Straightline linear regressions were performed on each of the time 

series from 1999 through 2006, to determine quantitatively 

if there were trends in the time series of annual temperaturerange ratios. Values prior to 1999 were not included in the 

analysis because the monitoring network was recalibrated in 

July 1998, which may have affected the magnitude but not 

the timing of annual temperature extremes. The effects of the 

recalibration are indicated in figure 23 as offsets in 1998 in 

several of the time series of annual temperature-range ratios. 

Trends of increasing annual temperature-range ratios that are 

statistically significant at a confidence level of 95 percent are 

summarized in table 6. The results indicate that in the Lower 

and Combined Aquifers, the trends in the annual temperaturerange ratios support the 1999-2006 trends in the time lags 

for 4 of 7 wells (wells LR2-W, TH1, TH7, and TH8). For the 

remaining 3 wells in the Lower and Combined Aquifers (wells 

TH4, TH6, and TH9), trends in the annual temperature-range 

ratios indicate that the Lower and Combined Aquifers near 

those wells have not reached thermal equilibrium. However, 

it is assumed that the Lower and Combined Aquifers near 

wells TH4, TH6, and TH9 are in thermal equilibrium, 

because trends in time lags are more reliable than trends in 

annual temperature-range ratios. Trends in time lags are more 

reliable because time lags are estimated from the relative 

patterns (and thus timing) of temperature records that are 

likely accurate within 1 day, and annual temperature-range 

ratios are estimated from 4 temperature measurements with 

unknown error. The cumulative errors in annual temperaturerange ratios make the metric less reliable and may help explain 

discrepancies between results of the trend analyses for time 

lags and annual temperature-range ratios for some of the wells.

Annual Temperature Extremes

The time series of daily median water temperatures 

were also used to determine if there were trends in the annual 

minimum and maximum ground-water temperatures from 

1999 through 2006. No statistically significant trends were 

found in the annual minimum temperatures at a confidence 

level of 95 percent, but statistically significant trends of 

increasing annual maximum temperatures were found in 

all but 3 wells of the monitoring network (fig. 24). Annual 

maximum temperatures of wells in which the corresponding 

annual maximum temperature in the river occurred the 

previous calendar year are plotted according to the year of 

the annual maximum in the river. Data are missing for years 

when well-temperature records had gaps or when the record 

was unclear what the magnitude was of the annual maximum 

temperature. Mean annual increases in annual maximum 

temperatures from 1999 through 2006 ranged from 0.12°C 

in well CD47 to 0.26°C in well TH1 (table 6) and averaged 

0.19°C for all wells with statistically significant increases 

in annual maximum temperatures. The lack of an increasing 

trend in annual maximum temperatures in Lower Aquifer 

well TH8 may be due to heat attenuation with distance from 

the Columbia River that decreases the variability of annual 

maximum temperatures in this part of the aquifer that is 

minimally affected by pumping (fig. 20C). Alternatively, the 

lack of a trend could be due to a source of colder water that 

settled locally in the bedrock depression north and west of 

well TH8 (fig. 7) and is captured by pumping well CT4. 
40 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 22. Spatial distribution of trends in time lags between annual minimum and maximum temperatures 

measured in the Columbia River at probe RIV and in wells of the monitoring system of the Eastbank Aquifer system 

with probes in the Lower or Combined Aquifers, 1991–98, and time lags between annual maximum temperatures in the 

river and wells in 1991, 1999, and 2006, Douglas County, Washington. tac08-0189_fig22

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

North Weir

South Weir

COLUMBIA RIVER

96 / 21 / 28

LR1

LR2-E

LR2-W

TH5

TH4

TH2

RIV

TH8 TH9 TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

150 / 123 / 96 193 / 142 / 145

67 / 44 / 47

55 / 49 / 53

37 / 2 / 1

119 / 82 / 65

EXPLANATION

Subsurface cutoff wall

Statistically significant trend of decreasing 

 time lag of annual minimum or maximum 

 temperatures, 1991–98 (α=0.05)

No statistically significant trend of 

 decreasing time lag of annual minimum 

 or maximum temperatures, 1991–98 (α=0.05)

Well with time lag of annual 

 maximum temperature

 in 1991 / 1999 / 2006, in days

Well, weir, or river site and name LR1

96 / 21 / 28

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
Hydrology 41

Figure 23. Ratio of annual temperature range between wells of the monitoring network of the Eastbank Aquifer system and 

the Columbia River at probe RIV for wells with temperature probes at the depth of the Upper Aquifer or Clay Confining Unit 

and the Lower Aquifer or Combined Aquifer, Douglas County, Washington, 1991–2006.

tac08-0189_fig23

A. Temperature probe in Upper Aquifer or Clay Confining Unit

0

0.2

0.4

0.6

0.8

1.0

1991 1993 1995 1997 1999 2001 2003 2005

0

0.2

0.4

0.6

0.8

1.0

1991 1993 1995 1997 1999 2001 2003 2005

2007

2007

RATIO OF ANNUAL TEMPERATURE RANGE OF WELL DIVIDED

BY ANNUAL TEMPERATURE RANGE OF RIVER, DIMENSIONLESS 

B. Temperature probe in Lower Aquifer or Combined Aquifer 

TH5

CT3

CD47

CD8

CD10

Last replacement

 of probe in well

TH6

LR2-W

TH4

TH7

TH8

TH9

TH1

TH6

TH7

TH4

TH8

 CD8

Last replacement

 of probe in well

EXPLANATION

Well

EXPLANATION

Well
42 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 24. Annual maximum temperature in wells of the monitoring network of the Eastbank Aquifer system and the Columbia 

River at probe RIV, Douglas County, Washington, 1999–2006.

tac08-0189_fig24

10

11

12

13

14

15

16

17

18

19

20

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

ANNUAL MAXIMUM TEMPERATURE, IN DEGREES CELSIUS 

RIV

CD10

CD47

CT3

TH5

LR2-W

TH1

TH4

TH6

TH7

TH8

TH9

Temperature probe in river

EXPLANATION

Temperature probe in Upper Aquifer

 or Clay Confining Unit

Temperature probe in Lower Aquifer

 or Combined Aquifer

Solid line indicates a time series with a statistically 

significant trend of increasing annual maximum 

temperatures (α=0.05)

Dashed line indicates a time series with no statistically 

significant trend (α=0.05)

Increases in annual maximum ground-water temperatures 

cannot be larger than increases in annual maximum river 

temperatures. However, the mean annual increases in annual 

maximum ground-water temperatures in the Lower and 

Combined Aquifers from 1999 through 2006 ranged from 

0.18°C in well TH7 to 0.26°C in well TH1, whereas the 

increase was 0.17°C in the river; the discrepancy indicates 

that the trend analysis results in errors in the estimated mean 

annual increase in annual maximum temperatures of ±0.09°C. 

Although there is uncertainty in the magnitude of the mean 

annual increases in annual maximum river and ground-water 

temperatures, figure 24 and the trend analyses indicate that 

the river and most annual maximum well temperatures have 

generally been increasing from 1999 through 2006. Because 

there was no trend in the annual minimum well temperatures 

during the same period, the mean annual well temperatures 

will also have increased in most wells from 1999 through 2006 

although less than the annual maximum well temperatures.

Water Quality

Water-quality samples were collected from nine groundwater and one surface-water location in the study area on 

August 20–22, 2007, to measure the concentrations of selected 

water-quality constituents, including calcium, magnesium, 

sodium, potassium, bicarbonate, nitrate, chloride, sulfate, 

fluoride, and silica. The concentrations of these constituents 

are present in many natural waters and will vary largely 

due to the extent of interactions between the water and 
Hydrology 43

surrounding rock material (Hem, 1985). The objective of 

the sampling program was to evaluate the spatial variations 

in the concentration of these water-quality constituents and 

verify ground-water flowpaths between areas of ground-water 

recharge and discharge to and from the Lower Aquifer of the 

Eastbank Aquifer system.

The source of recharge to the Lower Aquifer is the 

Columbia River. Concentrations of water-quality constituents 

in Columbia River water typically are low compared to 

concentrations in ground water of the Columbia Plateau 

region (Bortleson and Cox, 1986; Turney, 1986). As ground 

water moves away from recharge areas through relatively 

unweathered aquifer material such as the sediments that 

make up the Lower Aquifer, it accumulates solutes from the 

dissolution of rock and mineral fragments (Drever, 1988). 

Conversely, particulate matter such as bacteria that is present 

in river water will be reduced by filtration from passage 

through the aquifer material. Thus, ground water at locations 

along a flowpath downgradient from a recharge area can 

be expected to have increasing concentrations of dissolved 

constituents and decreasing numbers of live bacterial cells.

Ground-water samples were collected from one well that 

supplies the regional water system (RW3), one well that is 

used to irrigate Lincoln Rock State Park (LR2-E), two wells 

that supply the Eastbank Hatchery (CT3 and CT4); three 

wells that are used for dam operations or irrigation (SW11, 

SW13, and SW14), and one monitoring well (TH4; fig. 25A). 

A sample also was collected from the North Weir, which is 

assumed to represent ground-water seepage from the Lower 

Aquifer through the grout curtain of the subsurface cutoff wall. 

In addition, one sample of Columbia River water was collected 

near the site where the PUD collects continuous river waterlevel and water-temperature data, labeled RIV in figure 25A.

Spatial Patterns

Concentrations of many of the analyzed constituents 

showed spatial patterns in the Lower Aquifer. Samples were 

collected nearly concurrently from wells SW13 and SW14 to 

establish a baseline of variability, which includes variability 

due to sampling, sample analysis, and localized spatial 

variability within the aquifer. Wells SW13 and SW14 are 

believed to have similar construction and are located within 

about 200 ft of each other. For many constituents (table 7), the 

laboratory analysis of samples from wells SW13 and SW14 

were nearly identical. Larger variations of more than 2 percent 

were reported for dissolved oxygen, nitrate, and the bacterial 

enumeration; the relative percent difference computed 

for nitrate and dissolved oxygen was 13 and 16 percent, 

respectively, and about 60 percent for bacterial enumeration. 

Smaller variations with a relative percent difference of 

less than 2 percent were reported for concentrations of 

alkalinity, calcium, magnesium, bicarbonate, chloride, 

potassium, sodium, silica, fluoride, and sulfate. This level 

of variation commonly is reported for analysis of duplicate 

environmental samples. As a result, differences in constituent 

concentrations greater than those observed between the 

samples for wells SW13 and SW14 were considered indicative 

of spatial variations in water quality of the Lower Aquifer. 

Concentrations of nitrate and dissolved oxygen were not used 

to assess spatial variation. 

Specific conductance is a measure of the ability of water 

to conduct an electric current and thus provides a general 

measure of the amount of dissolved matter in water. Specific 

conductance of the river sample was 127 μS/cm. A survey of 

32 vertical profiles distributed throughout the Columbia River 

near the study area conducted on the same day the river was 

sampled showed that the specific conductance in the river 

varied by less than 3 μS/cm. Specific conductance in ground 

water from wells near the shoreline and from wells near the 

center of the Lower Aquifer was in the range of 135 to 

148 μS/cm and 163 to 167 μS/cm, respectively. This indicates 

a pattern of lower concentrations of dissolved constituents 

near the river and larger concentrations near the center of the 

Lower Aquifer (fig. 25A). 

A similar pattern also was observed for individual 

dissolved constituents. Concentrations of all dissolved 

constituents, except sulfate, were smallest in the river sample 

and largest in ground-water samples from nearer the center 

of the Lower Aquifer. The largest concentrations of dissolved 

constituents were generally measured in wells CT4 or RW3 

with generally slightly smaller concentrations in LR2-E and 

the North Weir. Maps of the spatial distributions of specific 

conductance, potassium, silica, alkalinity, and chloride are 

shown in figures 25A through 25E. Silica (fig. 25C) and 

potassium (fig. 25B) show the most pronounced spatial 

variation, whereas spatial variation is more difficult to discern 

for sodium (fig. 25F). With few exceptions, this pattern was 

consistent among different constituents, including alkalinity 

(fig. 25D) and chloride (fig. 25E). For several constituents, 

such as sodium (fig. 25F), concentrations in ground water 

were larger than in surface water but did not show a consistent 

spatial pattern in relation to possible directions of groundwater flow. A generally northeast-southwest gradient of 

increasing concentrations of dissolved constituents in the 

direction of predevelopment ground-water flowpaths (fig. 11) 

was not observed. Instead, data generally indicate groundwater flowpaths from the western shoreline to the pumping 

centers in the CT and RW well fields.
44 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 25. Spatial distribution of water-quality sampling sites and selected water-quality constituents in the Columbia 

River and Eastbank Aquifer system, Douglas County, Washington, August 20–22, 2007.

tac08-0189_fig25A-C.

120°17'30" 120°17'

47°

32'

30"

47°

32'

7.54

4.14

10.6

8.71

8.14

7.49

10.9

North Weir

South Weir

LR1

LR2-W LR2-E

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1 CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

8.17

7.34 9.09

C. Silica, in milligrams

 per liter

COLUMBIA RIVER

120°17'30" 120°17'

47°

32'

30"

47°

32'

0.61

1.63

1.04 1.02

1.02

1.48

1.03

North Weir

South Weir

LR1

LR2-W LR2-E

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1 CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

1.02

1.20 1.61

COLUMBIA RIVER

B. Potassium, in 

 milligrams per liter

A. Specific conductance,

 in microsiemens per 

 centimeter

167

135 163

127

167

144

148

146

146

160

167

North Weir

South Weir

LR1

LR2-E LR2-W

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1 CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

120°17'30" 120°17'

47°

32'

30"

47°

32'

COLUMBIA RIVER

127

EXPLANATION

Subsurface cutoff wall

Sampling site—Number is concentration of

 selected dissolved constituents, bacterial

 cells, or value of physical properties. Units of 

 measurement are shown on each map 

TH4

0

0

500 1,000 FEET

200100 300 METERS

Well, weir, or river site and name

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)
Hydrology 45

tac08-0189_fig25 D-G

North Weir

South Weir

LR1 LR2-E

LR2-W

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1

CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

120°17'30" 120°17'

47°

32'

30"

47°

32'

450

1,500

88,000

470

1,300

360

390

800

290

<3

G. Counts of live bacterial cells

 per milliliter of water

COLUMBIA RIVER

120°17'30" 120°17'

47°

32'

30"

47°

32'

2.28 2.38

1.62

2.41

2.26

2.37

2.40

2.11

2.14

North Weir

South Weir

LR1

LR2-W

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1

CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

LR2-E

2.40

F. Sodium, in milligrams 

 per liter

COLUMBIA RIVER

COLUMBIA RIVER

120°17'30" 120°17'

47°

32'

30"

47°

32'

0.71

0.90

0.78 0.75

0.77

0.92

North Weir

South Weir

LR1

LR2-W LR2-E

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1

CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

0.74

0.74 0.84

0.75

COLUMBIA RIVER

120°17'30" 120°17'

47°

32'

30"

47°

32'

66

59 67

54

72

61

60

60

60

69

66

North Weir

South Weir

LR1

LR2-E LR2-W

TH5

TH4

TH2

RIV

TH9 TH8 TH7

TH1

CD47

CD6 CD10

SW14

SW13

SW11

CD8

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

TH6

D. Alkalinity (acid-neutralizing

 capacity), in milligrams 

 per liter as CaCO3

E. Chloride, in milligrams 

 per liter

Figure 25.—Continued.
46 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Bacterial concentrations are largest in the river and 

lowest in wells closer to the center of the Lower Aquifer 

(fig. 25G). In the sample from the well in Lincoln Rock State 

Park (LR2-E), no viable bacterial cells were observed above 

the detection limit of 3 cells per milliliter. The occurrence of 

fewer live bacterial cells in ground-water samples obtained 

at locations more distant from the surface-water source is 

consistent with the filtering effect resulting from movement 

of ground water through an aquifer matrix. As shown in 

figure 25G, live bacterial concentrations increased along the 

central axis from wells LR2-E to CT3, which is inconsistent 

with a ground-water flowpath from the northeast to the 

southwest. Generally, the live bacterial concentrations indicate 

ground-water flowpaths from the western shoreline to near 

the center of the Lower Aquifer. In well CT3, however, live 

bacterial concentrations are larger than those in wells near the 

shoreline, which may be related to the large pumping rate of 

the well, its proximity to the river, and preferential flowpaths 

from the river to the well. This interpretation is supported by 

dissolved constituent concentrations in well CT3, which were 

consistently smaller than those found in wells to the north and 

were similar to the more dilute concentrations in nearby wells 

adjacent to the river. 

The water-quality data indicate that the ground-water 

flowpaths that end in the CT well field predominantly 

originate along the shoreline west and southwest from the 

pumping wells. If the northeast-to-southwest ground-water 

flowpath present during predevelopment conditions were 

predominant, then well CT3, which is the most southerly 

well that pumps at a high rate, should have had the largest 

concentrations of dissolved constituents and the smallest 

concentration of live bacterial cells. However, the waterquality results show nearly the opposite and a very short 

flowpath is indicated for well CT3. Conversely, the lack of 

substantial live bacterial concentrations and the occurrence of 

relatively larger dissolved constituent concentrations in well 

LR2-E indicate that the flowpath from the river to the well is 

longer and/or less recharge from the river passes through that 

area. Ground-water seepage through the grout curtain of the 

subsurface cutoff wall appears to be a combination of water 

with both long and short flowpaths and is consistent with a 

collector drain integrating discharge from the Lower Aquifer 

along a 2,000-foot-long interface. 

Table 7. Physical properties and concentrations of bacterial cells and selected dissolved constituents in ground-water and surfacewater samples, Eastbank Aquifer System, Douglas County, Washington, August 20–22, 2007.

[Locations of wells, weir, and river site are shown in figure 25. Abbreviations: CaCO3, calcium carbonate; N, nitrogen; μS/cm, microsiemens per centimeter; 

–, not measured; <, less than]

River CT3 CT4 RW3 SW11 SW13 SW14 TH4 LR2-E North Weir

Physical properties

Temperature (degrees Celsius) 19.4 13.4 10.4 12.7 16.1 16.2 16.2 18.4 10.9 15.4

Specific conductance (μS/cm) 127 144 167 163 146 146 148 135 167 160

pH (standard units) 7.5 7.4 7.3 7.5 7.2 7.5 7.3 – 7.3 7.6

Bacteria, per milliliter

Live bacterial cells 88,000 1,300 470 450 800 390 360 1,500 <3 290

Dead bacterial cells 54,000 7,700 1,000 1,700 380 610 330 730 <3 330

Dissolved constituents, in milligrams per liter

Dissolved oxygen – 5.5 3.9 6.0 3.8 4.5 5.3 – 3.7 8.0

Alkalinity, as CaCO3 54 61 72 67 60 60 60 59 66 69

Calcium 17.6 19.3 21.9 22.1 18.9 19.0 18.7 18.9 20.2 21.7

Magnesium 4.10 4.47 4.75 4.64 4.32 4.36 4.36 4.30 4.72 4.44

Sodium 1.62 2.26 2.41 2.38 2.40 2.40 2.37 2.28 2.14 2.11

Potassium .61 1.04 1.63 1.61 1.02 1.02 1.02 1.20 1.03 1.48

Bicarbonate 65 74 88 82 73 72 73 72 81 84

Nitrate plus nitrite, as N .04 .15 .16 .16 .14 .16 .14 .18 .14 .19

Chloride .706 .775 .900 .843 .749 .753 .739 .947 .915 .769

Sulfate 8.43 8.30 8.97 8.38 8.00 8.27 8.29 8.31 7.96 8.57

Fluoride .058 .066 .079 .097 .075 .076 .076 .068 .075 .080

Silica 4.14 7.54 10.60 9.09 8.71 8.14 8.17 7.34 10.90 7.49
Conceptual Model of Hydrologic and Thermal Conditions 47

Conceptual Model of Hydrologic and 

Thermal Conditions

The hydrogeologic framework of the Eastbank Aquifer 

system consists of the Upper and Lower Aquifers, which 

are highly permeable sand-and-gravel aquifers separated by 

the Clay Confining Unit (fig. 5). In the northwestern part of 

the study area (fig. 6), the Clay Confining Unit is absent and 

the Upper and Lower Aquifers merge to form the Combined 

Aquifer. The lower boundary of the Eastbank Aquifer system 

is crystalline bedrock that consists of biotite gneiss with 

low permeability. The bedrock has an undulating surface 

that forms a basin in the central part of the study area that 

is deepest near the RW well field (fig. 7). The Lower and 

Combined Aquifers in the eastern part of the study area 

are truncated by the bedrock surface (fig. 8) and the Clay 

Confining Unit and Upper Aquifer continue farther to the east, 

where they also are truncated by bedrock (fig. 5). The southern 

boundary of the aquifer system is a subsurface cutoff wall 

that is a partial barrier to ground-water flow from the Upper 

and Lower Aquifers. The northern and western boundaries of 

the aquifer system are the Columbia River. Along the western 

boundary, the Lower and Upper Aquifers are truncated by the 

river, and along the northern boundary, the Combined Aquifer 

extends beneath the river for an unknown distance to the north.

The Upper, Lower, and Combined Aquifers primarily are 

recharged by water from the Columbia River. Along most of 

the western boundary of the aquifers, ground-water recharge 

occurs across a layer of fine-grained, low-permeability 

sediments. Discharge from the aquifer system is ground-water 

pumpage from the Lower Aquifer and ground-water seepage 

from the Upper and Lower Aquifers around and through the 

subsurface cutoff wall.

During post-dam, predevelopment conditions, ground 

water generally flowed from the northeast to the southwest, 

approximately parallel to the river (fig. 11). With the onset of 

significant pumping from the Lower Aquifer by the RW well 

field in 1983 and the CT well field in 1989, two overlapping 

cones of depression have formed in the Lower and Combined 

Aquifers (fig. 15) and an approximately east-west trending 

ground-water divide has formed between them. The location 

of the ground-water divide probably varies slightly over time 

depending on which wells are pumping and at what rate. In 

2006, mean annual pumpage from the RW and CT well fields 

was about 16 and 43 ft3

/s, respectively. Pumpage from the SW 

well field from the Lower Aquifer and from the LR well field 

from the Combined Aquifer is small compared to pumpage 

from the RW and CT well fields and has a negligible effect 

on the ground-water flow system. Because of the hydraulic 

properties of the Clay Confining Unit, water levels in the 

Upper Aquifer are assumed to be relatively unaffected by 

pumping in the Lower Aquifer. Data do not exist, however, to 

confirm this assumption.

The cone of depression in the Lower and Combined 

Aquifers surrounding the RW well field draws water primarily 

from the west and secondarily from the north (fig. 26). An 

additional, smaller amount of water is drawn in from the 

south and east and, presumably, from beneath the wells. The 

cone of depression surrounding the CT well field draws water 

primarily from the west and southwest (fig. 26). An additional, 

smaller amount of water is drawn in from the north and 

east. Any water in the Lower Aquifer south of well CT3 not 

captured by pumping becomes seepage through the subsurface 

cutoff wall. Because of its proximity to the ground-water 

divide between the two cones of depression and because the 

location of the ground-water divide may shift as pumping 

patterns change, some of the water pumped by well CT4 may 

originate from a bedrock depression to the north and west.

Most of the Lower and Combined Aquifers have been 

in thermal equilibrium since 1999 and this equilibrium was 

reached during 1991–98. The only exceptions are the Lower 

Aquifer near wells TH1 and TH4, which reached thermal 

equilibrium prior to 1991, and the Combined Aquifer near 

well LR2-W, which had not reached equilibrium by 2006. 

At thermal equilibrium, the time lags between changes 

in river temperatures and subsequent changes in groundwater temperatures are constant at a given location and 

the ratios of annual temperature ranges in ground water to 

annual temperature ranges in the river also are constant at a 

given location. Because time lags and annual temperaturerange ratios vary in three dimensions, the Eastbank Aquifer 

system is a mosaic of different temperatures at any time of 

the year. Generally, however, time lags increase and annual 

temperature-range ratios decrease with distance from the river.

Mean annual minimum and maximum temperatures of 

source water in the Columbia River that recharges the aquifer 

system were 2.5 and 19.2°C, respectively, from 1991 through 

2006. Typically, the annual minimum temperatures occur in 

February and the annual maximum temperatures occur in 

August or September. From 1999 through 2006, there were 

statistically significant increasing trends in mean annual and 

annual maximum river temperatures but there were no trends 

in the annual minimum temperatures. The increases in river 

temperatures resulted in a corresponding increase in Lower 

and Combined Aquifer temperatures, except near well TH8. 

Temperatures in this well may not have increased because they 

represent a part of the Lower Aquifer minimally affected by 

pumping at a greater distance from the river or because nearby 

well CT4 may pump colder water that may have settled locally 

in the bedrock depression north and west of well TH8. There 

were no trends in the annual minimum, mean, and maximum 

river temperatures from 1991 through 1998 and from 1991 

through 2007. The mean annual increase in the annual mean 

and maximum river temperature from 1999 through 2006 was 

0.07 and 0.17°C, respectively.
48 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Figure 26. Generalized horizontal ground-water flow directions and fluxes for current (2008) conditions of the Lower 

and Combined Aquifers of the Eastbank Aquifer system, Douglas County, Washington.

tac08-0189_fig26

120°17'30" 120°17'

47°

32'

30"

47°

32'

0

0

500 1,000 FEET

100 200 300 METERS

RW3

RW4

RW2

RW1

CT1

CT3

CT2

CT4

North Weir

South Weir

LR1

LR2-E

LR2-W

TH6

TH5

TH4

TH2

RIV

TH8

TH9

TH7

TH1

CD47

CD6

CD10

SW14

SW13

SW11

CD8

U.S. Forest Service orthophoto, Rocky Reach Dam quad, August 2, 1998

Universal Transverse Mercator projection, Zone 10

Horizontal datum: North American Datum of 1927 (NAD 27)

COLUMBIA RIVER

EXPLANATION

General ground-water flow direction in the Lower and

 Combined Aquifers—Arrow lengths represent relative flux

General location of ground-water divide

Subsurface cutoff wall

Well of CT well field

Well of RW well field

Extent of Lower and Combined Aquifers—Modified from

 Water & Environmental Systems Technology, Inc. (1990)

TH4 Well, weir, or river site and site name
Summary 49

The dependence of the detection of river-temperature 

trends on the period of the record selected for analysis 

indicates that although mean annual river temperatures may 

increase during multi-year periods and these increases result in 

corresponding increases in the Lower and Combined Aquifers, 

the increases in river temperatures and thus ground-water 

temperatures over relatively short periods of time are within 

the natural variability of the river temperatures and decreases 

in mean annual river temperatures are likely during other 

multi-year periods.

Interannual trends in ground-water temperatures are 

controlled by interannual trends in river temperatures, 

interannual trends in seasonal pumpage patterns, and the 

extent of thermal equilibrium in the aquifer system. From 

1999 through 2006, seasonal pumpage patterns were 

relatively stable and most of the aquifer system was in thermal 

equilibrium; thus reported trends of increasing temperatures of 

water pumped by the CT well field are most likely explained 

by increasing trends in river temperatures.

Data Needs 

A numerical model of the Eastbank Aquifer system 

would be useful for evaluating potential future hydrologic 

and thermal effects of different ground-water pumping rates, 

timing, and locations. Specifically, a model would help 

determine if there may be pumping alternatives that can meet 

the water demand by the Eastbank Hatchery and the regional 

water system and also provide sufficiently cool water for the 

hatchery. Numerical modeling can be achieved by verifying 

and updating the numerical model of the Eastbank Aquifer 

system by Water & Environmental Systems Technology, 

Inc. (1990) or by constructing a new model. Updating or 

constructing a numerical model would benefit from the 

following data, collected over a period of at least a year:

1. Daily measurements of pumpage from the RW and CT 

wells.

2. Daily records of when wells were pumped.

3. Hourly measurements of the temperature of water pumped 

by the RW and CT wells.

4. Semi-annual or more frequent verification of hourly 

temperature measurements of water pumped by the RW 

and CT wells.

5. Monthly manual measurements of vertical temperature 

profiles and water levels in each monitoring well on 

the same day, including verification that pumpage data 

were collected during the previous 24 hours [(1) and 

(2)]. Although not critical, bi-monthly temperature 

measurements of the North and South Weirs would be 

helpful. 

6. Hourly measurements of temperature in the river and 

monitoring wells at constant depths.

7. Semi-annual or more frequent verification of hourly 

temperature measurements in the river and monitoring 

wells.

8. Hourly measurements of water levels in the river and 

monitoring wells using vented transducers.

9. Semi-annual or more frequent verification of hourly 

water-level measurements in the monitoring wells. As 

long as USGS gaging station 12453679 continues to 

record hourly water levels along the west bank of the 

river at the forebay of Rocky Reach Dam, additional river 

water-level verification measurements are not necessary.

10. Measurements of continuous discharge from the North 

and South Weirs.

11. Semi-annual or more frequent verification of weirdischarge measurements.

Regular verification and calibration of instruments and 

detailed records of the verification and calibration will ensure 

that reliable data are collected. Detailed records of instrument 

replacements and other significant events that may affect the 

pumpage, water-level, and water-temperature data may help 

explain possible data anomalies.

A numerical model of the Eastbank Aquifer system 

would be more reliable if detailed information were available 

about the source of the water flowing through the North and 

South Weirs and if the presence of a bedrock depression near 

the RW well field could be determined by drilling a new well. 

The depth to bedrock, the nature of the sediments above the 

bedrock, and the age and temperature of ground water in the 

depression could be evaluated as part of the drilling process.

Summary 

The Eastbank Aquifer system covers about 150 acres 

and is located in a river-terrace deposit along the east bank of 

the Columbia River near Rocky Reach Dam, about 8 miles 

north of Wenatchee, Washington. It consists of the Upper and 

Lower Aquifers, which are highly permeable sand-and-gravel 

aquifers separated by the Clay Confining Unit. Where the 

Clay Confining Unit is absent in the northwestern part of the 

study area, the aquifers merge to form the Combined Aquifer. 

The primary use of the Eastbank Aquifer system is to supply 

water from the Lower and Combined Aquifers to the Eastbank 

Hatchery and the regional water system, which serves more 

than 65,000 people in and near the cities of Wenatchee and 

East Wenatchee. The hatchery is owned by the Public Utility 

District No. 1 of Chelan County (PUD) and compensates 
50 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

for fish losses resulting from the Rocky Reach and Rock 

Island Hydroelectric Projects. The Eastbank Hatchery needs 

relatively cool water for successful operations and, reportedly, 

temperatures of ground water pumped by the hatchery have 

been increasing. The PUD asked the U.S. Geological Survey 

to conduct a study of the Eastbank Aquifer system to help 

understand why the ground-water temperatures may have 

been increasing and to determine data needs for possible 

future evaluations of aquifer-system management options 

that maintain sufficiently cool ground water for hatchery 

operations.

The Upper, Lower, and Combined Aquifers are primarily 

recharged by water from the Columbia River. Ground-water 

discharge occurs as seepage around and through a subsurface 

cutoff wall and ground-water pumping. The main pumping 

centers are the RW well field in the central part of the study 

area, which supplies the regional water system, and the CT 

well field in the south-central part of the study area, which 

supplies the hatchery. The RW and CT well fields became 

operational in 1983 and 1989, respectively. From 1990 

through 2000, annual mean pumpage from the RW well field 

was relatively constant, with a mean annual pumpage of 

10.7 ft3

/s. Pumpage increased by about 40 percent to a mean 

annual pumpage of 15.0 ft3/s from 2002 through 2006 due to 

an expansion of the service area to include the city of East 

Wenatchee. The mean annual pumpage from the CT well field 

probably has been relatively constant since 1994, although 

there is greater uncertainty in the historical pumpage estimate 

for the CT well field than the RW well field. In 2006, mean 

annual pumpage from the hatchery and regional water system 

was about 43 and 16 cubic feet per second (ft3/s), respectively. 

Ground-water levels measured on July 18, 2007 indicate 

that there are two overlapping cones of depression in the 

Lower and Combined Aquifers with an approximately eastwest trending ground-water divide between them. The cone 

of depression surrounding the RW well field draws water 

primarily from the west and secondarily from the north, while 

an additional, smaller amount of water is drawn in from the 

south, east, and probably from beneath the wells. The cone 

of depression surrounding the CT well field draws water 

primarily from the west and southwest, with an additional, 

smaller amount of water drawn in from the north and east. 

A spatial analysis of dissolved-constituent and bacterial 

concentrations in water sampled in nine wells and one river 

location in August 2007 was consistent with the ground-water 

flowpaths inferred from the July 18, 2007, water-level data. 

The PUD has measured hourly water levels since 

1990 in a monitoring network of 1 river site and 12 wells 

distributed throughout the Eastbank Aquifer system for the 

purpose of monitoring hydrologic and thermal conditions of 

the system. Because potentiometric gradients in the Lower 

Aquifer are small, the uncertainty in the historical waterlevel measurements was too large to use the data to analyze 

for possible trends in hydrologic conditions. The uncertainty 

in the historical water-temperature measurements was less, 

however, and these data were analyzed for trends in thermal 

conditions.

Analyses of interannual trends in time lags between 

changes in river temperatures and subsequent changes in 

ground-water temperatures showed that most of the Lower 

and Combined Aquifers have been in thermal equilibrium—

defined by constant time lags, since 1999 and the equilibrium 

was reached during 1991–98. The only exceptions are the 

Combined Aquifer near well LR2-W, which had not reached 

thermal equilibrium by 2006, and the Lower Aquifer near 

wells TH1 and TH4, which reached thermal equilibrium prior 

to 1991.

Analyses of interannual trends in river temperatures 

showed increasing trends in annual mean and maximum river 

temperatures from 1999 through 2006. The mean annual 

increase was 0.07°C for the annual mean and 0.17°C for the 

annual maximum river temperature. There were no trends in 

the annual minimum temperatures from 1999 through 2006, 

and there were no trends in the annual minimum, mean, and 

maximum river temperatures from 1991 through 1998 and 

from 1991 through 2007. The increases in river temperatures 

from 1999 through 2006 resulted in corresponding increases 

in Lower and Combined Aquifer temperatures, except near 

well TH8. The increases in mean annual river temperatures 

and thus ground-water temperatures over a relatively short, 

multi-year period are within the natural variability of the river 

temperatures and decreases in mean annual river temperatures 

are likely during other multi-year periods.

Interannual trends in ground-water temperatures are 

controlled by interannual trends in river temperatures, 

interannual trends in seasonal pumpage patterns, and the 

extent of thermal equilibrium in the aquifer system. From 

1999 through 2006, seasonal pumpage patterns were 

relatively stable and most of the aquifer system was in thermal 

equilibrium; thus reported trends of increasing temperatures of 

water pumped by the CT well field are most likely explained 

by increasing trends in river temperatures.

A numerical model could be used to evaluate if there may 

be pumping alternatives that can meet the water demand by 

the Eastbank Hatchery and the regional water system and also 

provide sufficiently cool water for the hatchery. Updating or 

constructing a numerical model would benefit from continued 

monitoring of the hydrologic and thermal conditions of the 

Lower Aquifer for at least 1 year. A numerical model would 

be more reliable if more detail were available about the source 

of the water flowing through the North and South Weirs and if 

the presence of a bedrock depression with possible cold-water 

storage near the RW well field could be confirmed. 
References Cited 51

Acknowledgments 

We thank the following PUD personnel for assistance 

with this study: Ian Adams, Dan Davies, and Sam Dilly for 

extensive assistance with compilation of data and information 

and help in the field, Travis Dolge, Tim Doneen, and Tom 

Whaley for help in the field, and Steve Hays for compilation 

of historical Rocky Reach Dam forebay temperatures. We also 

thank Mike Krautkramer and Jim Hay of Robinson, Noble, 

and Saltbush, Inc. for sharing data and information from their 

library, Kim deRubertis and Omar Fulton for sharing previous 

work, and Mike Cockrum, Regional Water Operator of the 

City of Wenatchee, for sharing historical pumpage data of the 

regional water system.

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Report 88-4108, 37 p.

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Miller, R.T., and Delin, G.N., 2002, Analysis of thermal data 

and nonisothermal modeling of short-term test cycles: U.S. 

Geological Survey Professional Paper 1530-B, 66 p. 

National Oceanic and Atmospheric Administration Western 

Regional Climate Center, 2007a, Climate of Washington: 

http://www.wrcc.dri.edu/narratives/WASHINGTON.htm, 

accessed December 21, 2007.

National Oceanic and Atmospheric Administration Western 

Regional Climate Center. 2007b, Wenatchee Washington 

(site 459074) NCDC 1971-2000 Climate Normals: 

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?wawena, 

accessed January 4, 2008.
52 Hydrologic and Thermal Conditions of the Eastbank Aquifer System near Rocky Reach Dam, Washington

Turney, G.L., 1986, Quality of ground water in the Columbia 

Basin, Washington, 1983: U.S. Geological Survey WaterResources Investigations Report 85-4320, 172 p.

U.S. Geological Survey, 2007, Water-resources data for the 

United States, Water Year 2006: U.S. Geological Survey 

Water-Data Report WDR-US-2006, site 12453700, accessed 

January 3, 2008, at http://pubs.water.usgs.gov/wdr2006.

Vaccaro, J.J., and Olsen, T.D., 2007, Estimates of groundwater recharge to the Yakima River Basin aquifer system, 

Washington, for predevelopment and current land-use and 

land-cover conditions: U.S. Geological Survey Scientific 

Investigations Report 2007-5007, version 1.1, 30 p.

Wardwell, D.A., 2007, Barometric effects on transducer data 

and groundwater levels in monitoring wells: October 2007 

presentation by In-Situ Inc., accessed January 23, 2008, at 

http://www.sdgs.usd.edu/esdwc/wardwell.pdf.

Water & Environmental Systems Technology, Inc., 1990, 

Eastbank Hatchery pumping test and analysis, final report: 

Prepared for Public Utility District No. 1 of Chelan County, 

Wenatchee, Washington, about 200 p. 

Water & Environmental Systems Technology, Inc., 1998, 

Eastbank aquifer hydrologic and thermal model report: 

Prepared for Public Utility District No. 1 of Chelan County, 

Wenatchee, Washington, about 150 p.

Wilde, F.D. (ed.), 1999, Collection of water samples: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, Book 9, Chapter A4, 231 p.

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T. 

(eds.), 2002, Processing of water samples: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

Book 9, Chapter A5, 180 p.

O’Connor, J.E., and Baker, V.R., 1992, Magnitudes and 

implications of peak discharges from glacial Lake Missoula: 

Geological Society of America Bulletin, v. 104, no. 3, 

p. 267-279.

Parametrix, Inc., and Rensel Associates Aquatic Science 

Consultants, 2001, Water quality monitoring report, 

Rocky Reach Reservoir Water Year 2000, Rocky Reach 

Hydroelectric Project: Prepared for Public Utility District 

No. 1 of Chelan County, Wenatchee, Washington, number 

of pages not known.

Parametrix, Inc., and Thomas R. Payne & Associates, 2002, 

Rocky Reach Reservoir temperature studies, Rocky Reach 

Hydroelectric Project: Prepared for Public Utility District 

No. 1 of Chelan County, Wenatchee, Washington, number 

of pages not known.

Public Utility District No. 1 of Chelan County, 2007a, 

Anadromous Fish Agreements and Habitat Conservation 

Plans, http://www.chelanpud.org/HCP/, accessed May 3, 

2007.

Public Utility District No. 1 of Chelan County, 2007b, 

Hydroelectric information for Columbia and Snake River 

Projects: Reported by the University of Washington at 

http://www.cbr.washington.edu/crisp/hydro/rrd.html, 

accessed December 21, 2007.

R.W. Beck and Associates, 1973, Feasibility study, Wenatchee 

urban area regional water supply: Prepared for Public 

Utility District No. 1 of Chelan County, Wenatchee, 

Washington, about 150 p.

Stone and Webster Engineering Corporation, 1959, Report 

on East Bank grouted cutoff, Rocky Reach Hydroelectric 

Power Project: Prepared for Public Utility District No. 1 of 

Chelan County, Wenatchee, Washington, about 150 p.

Tabor, R.W., Frizzell Jr., V.A., Whetten, J.T., Waitt, R.B., 

Swanson, D.A., Byerly, G.R., Booth, D.B., Hetherington, 

M.J., and Zartman, R.E., 1987, Geologic map of the Chelan 

30-minute by 60-minute quadrangle, Washington: U.S. 

Geological Survey Geologic Investigations Series I-1661, 

1 plate.
Appendix 1 53

Appendix 1. Hydrogeologic Cross Sections of the Eastbank Aquifer System, 

Douglas County, Washington.

From CH2M Hill (1988)
54 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington Modified from CH2M Hill (1988) From CH2M Hill (1988)

1b.

CD6 CD10 CD8

Appendix 1.—Continued
Appendix 1 55

450400

350300

250200

Modified from CH2M Hill (1988)

TOP OF BEDROCK—Estimated from plate 2 by Water & Environmental Systems Technology, Inc. (1990) 

Bedrock contours of plate 2 are shown in figure 7 of this report. 

Appendix 1c

350300 300

450400

450

400

350

300

250200

Appendix 1.—Continued
56 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

Appendix 1.—Continued

Modified from CH2M Hill (1988)

450 450
Appendix 1 57

Appendix 1.—Continued

Modified from CH2M Hill (1988)

TOP OF BEDROCK—Estimated from plate 2 by Water & Environmental Systems Technology, Inc. (1990) 

Bedrock contours of plate 2 are shown in figure 7 of this report. 

750700650600550500450400350300

350 350750700650600550500450400300

450400350300

450400300
58 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

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Appendix 2 59

Appendix 2. Summary of Down-Hole Camera Surveys of Selected Wells of the 

Eastbank Aquifer System, Douglas County, Washington, December 11–13, 2007.

Well CD6; USGS Well No. 24N/20E-35Q06

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 11, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading 

was 1.5 feet. Camera-depth readings may thus be as much 

as 1.5 feet too large. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top of 

the camera unit and the sideward-looking camera lens is 1.68 

feet below the top of the camera unit.

Basic information about the well

Well CD6 was drilled to a depth of 216 feet in 1972 or earlier, 

and probably 1957 or earlier. A 6-inch-diameter steel casing 

was installed without perforations. The well is a monitoring 

well and does not have a pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 49.2 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 198.8 feet below TOC.

2. The well casing is in good condition with thin patchy 

scaling attached to the casing at all depths.

3. No perforations were seen. No animals were seen.

Well CD47; USGS Well No. 24N/20E-35Q02

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 11, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the metal manhole cover (TMMC) of the concrete vault 

that houses the well. The top of the metal manhole cover is 

6.70 feet above the top of the well casing (TOC), which is 

below land surface. After reaching the bottom of the well 

and bringing the camera back up, the camera-depth reader 

indicated a depth of 1.2 feet for the TMMC. The camera-depth 

readings may thus be as much as 1.2 feet too large. During 

the second part of the survey, when the camera moved from 

the bottom of the well to the top, the tripod from which the 

camera was suspended fell and it was put back up again. 

Depth readings on the movie represent the depth below 

TMMCs for the top of the camera unit. The downwardlooking camera lens is 2.03 feet below the top of the camera 

unit and the sideward-looking camera lens is 1.68 feet below 

the top of the camera unit.

Basic information about the well

Well CD47 was drilled to a depth of 245 feet in 1972 or 

earlier, and probably 1957 or earlier. A 6-inch-diameter steel 

casing was installed and perforations were added later at 

unknown depths across from the Lower Aquifer. The well is a 

monitoring well and does not have a pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 47.6 feet 

below TOC. The camera did not reach the bottom of 

the well, because the casing became too narrow due 

to protruding of scaling. Maximum depth reached 

was 186.9 feet below TOC.

2. The well casing is in good condition with scaling 

attached to the casing at all depths. The scaling 

is patchy and thin to a depth of approximately 

115.3 feet below TOC when it gradually became 

rougher and more three-dimensional. At 134 feet 

below TOC, there may have been flow. However, 

it was difficult to be certain because falling scaling 

was disturbing the water. By 169.5 feet below TOC, 

there was flow and the scaling was solid instead 

of patchy. By 179.8 below TOC, the scaling had 

become hummocky and protruded into the casing 

by about 0.25 inch. By 180.5 feet below TOC, the 

water became noticeably clearer, which had been 

murky until that depth. By 181.3 feet below TOC, 

the scaling was protruding as much as about 0.5 inch 

and there was flow. By 186.9 feet below TOC, the 

protrusions narrowed the casing to the point where 

the camera could not go down farther. Based on 

these findings, it is concluded that the perforated 

interval of this well starts at about 180 feet below 

TOC and extends to an unknown depth.
60 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

3. At 140.2 feet below TOC, a large piece of scaling 

extended across the casing, which broke into pieces 

after the camera went through it. This may have been 

a sliver of corroded casing.

4. Two different types of invertebrate animals were 

observed in this well, none of which have currently 

(2008) been sampled and identified. 

a. An arthropod that may be an amphipod without 

pigment was observed at a depth of 186.9 feet 

below TOC moving along the well casing from 

the center right across the top of the picture 

and disappearing on the left. This animal was 

different than those seen in well TH6 and may 

have been the same animal as the second, larger 

possible amphipod in well TH2. The animal was 

about 1 inch long. 

b. At the same depth, a second unidentified 

arthropod moved into view in the upper righthand corner. This animal was different than 

any of the animals seen in wells TH6 and TH2. 

It had no pigment, was about 1 inch long, 

had a large head and dark eyes, and generally 

resembled a damselfly nymph (T. DeVries, 

Burke Museum of Natural History and Culture, 

oral commun., 2008). The animal appeared to 

be carrying prey, possibly of the same species. 

A temperature profile of the water column was 

measured in well CD47 on December 11, 2007 

prior to the down-hole camera survey, with 

temperatures ranging from 11.9°C between 220 

and 230 feet below TOC to 14.4°C at 160 feet 

below TOC. At the depth the arthropods were 

seen, temperatures ranged from 13.0°C at 180 

feet below TOC to 12.7°C at 190 feet below 

TOC.

Video 1 of arthropod in well CD47 (http://pubs.usgs.gov/

sir/2008/5071/VideoCD47A.wmv). Arthropod is possible amphipod.

Video 2 of arthropod in well CD47 (http://pubs.usgs.gov/

sir/2008/5071/VideoCD47B.wmv). Arthropod generally resembles a 

damselfly nymph.

Well TH2; USGS Well No. 24N/20E-35K06

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 11, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading was 

1.5 feet. The camera-depth readings may thus be as much 

as 1.5 feet too large. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top of 

the camera unit and the sideward-looking camera lens is 1.68 

feet below the top of the camera unit.

Basic information about the well

Well TH2 was drilled to a depth of 225 feet. An 8-inchdiameter steel casing was installed, with perforations from 135 

to 220 feet. The well is a monitoring well and does not have a 

pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC. The 

camera survey described here was the second survey of well 

TH2 that was redone immediately following the first survey, 

which did not properly record. Well RW1, a public-supply 

well adjacent to well TH2, was pumping throughout the first 

and second surveys.)

1. The camera contacted the water surface at 45.3 feet 

below TOC, and was unable to go deeper than 

156.4 feet because of narrowing of the casing due to 

scaling. It is estimated that scaling protruded into the 

casing by about 1 inch at this depth.

2. The well casing is in good condition with scaling 

attached to the casing at all depths. The scaling 

is thin until about 136 feet below TOC, where it 

gradually starts to thicken and becomes hummocky. 

The increase in thickness of the scaling coincides 

with the start of the reported perforated zone, 

although no perforations were seen.
Appendix 2 61

3. Two different types of invertebrate animals were 

observed in this well, none of which have currently 

(2008) been sampled and identified. 

a. Arthropods that appear to be blind isopods 

without pigment were observed clinging to 

the well casing from 117.6 to 155.4 feet below 

TOC. The estimated length of the possible 

isopods is about 1 inch. 

b. At 132.7 and 113.3 feet below TOC, a second 

type of arthropod was observed that may be an 

amphipod. This animal was shorter than the 

possible isopods and moved faster. The possible 

amphipod seen at 113.3 feet below TOC was 

larger than the one seen at 132.7 feet below 

TOC. A temperature profile of the water column 

was measured in well TH2 on December 11, 

2007 prior to the first down-hole camera survey, 

with temperatures ranging from 10.5°C at 50 

feet below TOC to 15.1°C at 160 feet below 

TOC. At the depth range where arthropods 

were seen, temperatures ranged from 13.5°C 

at 110 feet below TOC to 15.1°C at 160 feet 

below TOC. Abundance of the possible isopods 

appeared to be unrelated to water temperature. 

Instead, abundance of the possible isopods 

appeared to be correlated with proximity to 

the perforated interval, presumably because 

water that is replenished is richer in oxygen and 

nutrients and thus can reasonably be expected 

to be preferred habitat for the possible isopods. 

The abundance of possible isopods in well TH2 

was less than in well TH6.

Video 1 of arthropod in well TH2 (http://pubs.usgs.gov/

sir/2008/5071/VideoTH2A.wmv). Arthropod is possible isopod. 

Video 2 of arthropod in well TH2 (http://pubs.usgs.gov/

sir/2008/5071/VideoTH2B.wmv). Arthropod is possible amphipod.

Video 3 of arthropod in well TH2 (http://pubs.usgs.gov/

sir/2008/5071/VideoTH2C.wmv). Arthropod is possible isopod.

Video 4 of arthropod in well TH2 (http://pubs.usgs.gov/

sir/2008/5071/VideoTH2D.wmv). Arthropod is possible amphipod.

Well TH4; USGS Well No. 24N/20E-35K02

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 12, 2007

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading was 

0.5 foot. The camera-depth readings may thus be as much 

as 0.5 foot too large. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top of 

the camera unit and the sideward-looking camera lens is 1.68 

feet below the top of the camera unit.

Basic information about the well

Well TH4 was drilled to a depth of 170 feet. An 8-inchdiameter steel casing was installed with perforations from 100 

to 168 feet. The well is a monitoring well and does not have a 

pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 27.2 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 161.0 feet below TOC.

2. The well casing is in good condition with scaling 

attached to the casing at all depths. The scaling is 

thin and patchy to about 50 feet below TOC, when 

the scaling starts to protrude more into the casing. 

By about 60 feet below TOC, the scaling is no longer 

patchy. The scaling continues to get thicker and 

more hummocky farther down. By about 110 feet 

below TOC, the scaling protrudes into the well by as 

much as about 1 inch. By about 100 feet below TOC, 

water is relatively clear except for suspended pieces 

of scaling.

3. One type of invertebrate animal was observed in this 

well, which has currently (2008) not been sampled 

and identified. Two arthropods that appear to be 

small amphipods without pigment were observed 

moving along the well casing at 101.4 and 130.1 feet 

below TOC. A temperature profile of the water 

column was measured in well TH4 on December 

12, 2007 prior to the down-hole camera survey, 

with temperatures ranging from 11.2 to 13.6°C 

throughout the well and ranging from 12.1 to 11.4°C 

from 100 to 130 feet below TOC.
62 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

Well TH5; 24N/20E-35G01

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 12, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top of 

the well casing (TOC). After reaching the bottom of the well 

and bringing the camera back up, the TOC reading was 0 foot. 

The camera depth readings were thus correct. Depth readings 

on the movie represent the depth below TOC for the top of the 

camera unit. The downward-looking camera lens is 2.03 feet 

below the top of the camera unit and the sideward-looking 

camera lens is 1.68 feet below the top of the camera unit.

Basic information about the well

Well TH5 was drilled in 1987 to a depth of 47 feet. An 8-inchdiameter steel casing was installed, with perforations from 25 

to 45 feet. The well is a monitoring well and does not have a 

pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 13.1 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 41.8 feet below TOC.

2. The well casing is in good condition with thin patchy 

scaling attached to the casing at all depths.

3. No flow was seen from the water surface to as deep 

as 34.3 feet below TOC. Flow may have been seen at 

38.3 feet below TOC and possibly also perforations 

in the casing. Perforations also may have been seen 

at 39.3 feet below TOC. Perforations were difficult 

to see due to scaling, murky water, and a fuzzy 

image. Water at bottom of the well is clear. No 

animals were seen.

Well TH6; USGS Well No. 24N/20E-35G02 

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 12, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading was 

-0.2 foot. The camera-depth readings may thus be as much 

as 0.2 foot too small. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top 

of the camera unit and the sideward-looking camera lens is 

1.68 feet below the top of the camera unit.

Basic information about the well

Well TH6 was drilled in 1987 to a depth of 148 feet and the 

hole was sealed below 134 feet. An 8-inch-diameter steel 

casing was installed, with perforations from 60 to 115 feet. 

The well is a monitoring well and does not have a pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 29.2 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 121.7 feet below TOC.

2. The well casing is in good condition with scaling 

attached to the casing at all depths. The scaling 

is thicker and hummocky where the casing is 

perforated. Maximum protrusion of scaling into the 

well is estimated to be about 0.5 inch.

3. Starting at about 59 feet below TOC, horizontal flow 

was observed in the well. This flow became stronger 

with depth, with strong currents from about 63 to 

about 72 feet below TOC. By 76 feet below TOC, 

the currents were weaker and by about 102 feet 

below TOC, there was no evidence of horizontal 

flow. In the zone of strong currents, the flow 

direction appeared to be spiraling.

4. From 103.6 to 105.6 feet below TOC, open vertical 

perforations were seen. Additional open vertical 

perforations were seen from 118.1 to 119.4 feet 

below TOC.

5. Three different types of invertebrate animals were 

observed in this well, none of which have currently 

(2008) been sampled and identified. 

a. Arthropods that appear to be blind isopods 

without pigment were observed clinging to the 

well casing from just below the water surface 

to the bottom of the well. The estimated length 

of the possible isopods is about 1 inch. The 

possible isopods were most numerous in parts 

of the well with strong currents, although the 

current at times knocked the animals from the 

casing. 

b. At the bottom of the well, a second type 

of arthropod was observed that may be an 

amphipod. This animal was about one-third the 

length of the possible isopods and moved faster.
Appendix 2 63

c. At the bottom of the well, two worms also were 

observed. One moved from its hiding place in 

the sediments and in doing so extended to a 

length of 5-6 times the length of the possible 

isopods. The possible amphipods were observed 

avoiding the moving worms. A temperature 

profile of the water column was measured in 

well TH6 on December 12, 2007 prior to the 

down-hole camera survey, with temperatures 

ranging from 8.5 to 9.2°C. Abundance of the 

possible isopods appeared to be unrelated to 

water temperature. Instead, abundance of the 

possible isopods appeared to be correlated with 

water flow, presumably because water that is 

replenished is richer in oxygen and nutrients and 

thus can reasonably be expected to be preferred 

habitat for the possible isopods.

Video 1 of arthropods in well TH6 (http://pubs.usgs.gov/

sir/2008/5071/VideoTH6A.wmv). Arthropods are possible isopods. 

Video 2 of arthropods and worms in well TH6 (http://pubs.usgs.

gov/sir/2008/5071/VideoTH6B.wmv). Arthropods are possible 

isopods and possible amphipods. 

Well TH7; USGS Well No. 24N/20E-35K01

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 12, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top of 

the well casing (TOC). No TOC reading was taken when the 

camera was brought back up and thus the error of the camera 

depth reading is not known. Depth readings on the movie 

represent the depth below TOC for the top of the camera unit. 

The downward-looking camera lens is 2.03 feet below the top 

of the camera unit and the sideward-looking camera lens is 

1.68 feet below the top of the camera unit.

Basic information about the well

Well TH7 was drilled in 1987 to a depth of 180 feet. An 

8-inch-diameter steel casing was installed to 176 feet, with 

perforations from 90 to 165 feet. The well is a monitoring well 

and does not have a pump.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 28.2 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 171.5 feet below TOC.

2. The well casing is in good condition, with scaling 

attached to the casing at all depths. The scaling 

is thin and patchy until a depth of about 80 feet 

below TOC, when it starts to become more threedimensional and less patchy. Scaling was protruding 

about 0.25 inch into the well at this depth. By about 

92 feet below TOC, the scaling had become thicker 

and hummocky. The thick and hummocky scaling 

continued until the bottom of the well and protruded 

as much as about 1 inch into the casing. Scaling in 

this well appeared to be harder than and did not flake 

off as easily as scaling seen in other wells of the 

monitoring network.

3. From 153 to 158 feet below TOC, vertical 

perforations were seen and water was very clear at 

this depth. Clear water was first noticed at a depth of 

132 feet below TOC and it continued to be clear to 

the bottom of the well.

4. As many as three different types of invertebrate 

animals were observed in this well, none of which 

have currently (2008) been sampled and identified. 

a. Arthropods that appear to be blind isopods 

without pigment were observed clinging to the 

well casing. Two possible isopods were seen in 

the well and perhaps a few more between depths 

of 88 to 146.1 feet below TOC. The estimated 

length of the possible isopods is about 1 inch.

b. A second and third type of arthropod was 

more numerous in this well and may have been 

amphipods of two different sizes. One size was 

about 1 inch and the other about one-third of 

an inch. Only a few specimens were seen at 

depths ranging from 94.5 to 114.4 feet below 

TOC. These animals move faster than the 

possible isopods. A temperature profile of the 

water column was measured in well TH7 on 

December 12, 2007, prior to the down-hole 

camera survey, with temperatures ranging from 

12.9 to 14.2°C throughout the well and ranging 

from 13.9 to 13.5°C from 90 to 150 feet below 

TOC. Abundance of the possible isopods and 

amphipods appeared to be related to proximity 

to the perforated interval.
64 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

Well TH8; USGS Well No. 24N/20E-35K04

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 13, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading was 

-0.6 foot. The camera-depth readings may thus be as much 

as 0.6 foot too small. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top 

of the camera unit and the sideward-looking camera lens is 

1.68 feet below the top of the camera unit.

Basic information about the well

Well TH8 was drilled in 1987 to a depth of 255.5 feet. A 

6-inch-diameter steel casing was installed to 255 feet and an 

8-inch-diameter steel casing to 217 feet without perforations. 

Currently (2008), only the 6-inch-diameter casing is visible 

above land surface. The well is a monitoring well and does not 

have a pump. 

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 52.4 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 258.1 feet below TOC.

2. The well casing is in good condition with thin 

scaling attached to the casing at all depths. The 

scaling is more three-dimensional and patchier in 

about the bottom 10 feet of the well.

3. At about 177.3 and 197.2 feet below TOC, casing 

sections were connected by some type of collar 

that was about 1–2 inches wide. Other casing 

connections were welded seams.

4. No flow was observed. No animals were observed.

Well TH9; USGS Well No. 24N/20E-35K03

Down-hole camera survey by Kevin D. Knutson, USGS, 

December 12, 2007.

Survey procedures

The depth reader for the camera was set to zero at the top 

of the well casing (TOC). After reaching the bottom of the 

well and bringing the camera back up, the TOC reading was 

0.1 foot. The camera-depth readings may thus be as much 

as 0.1 foot too large. Depth readings on the movie represent 

the depth below TOC for the top of the camera unit. The 

downward-looking camera lens is 2.03 feet below the top 

of the camera unit and the sideward-looking camera lens is 

1.68 feet below the top of the camera unit.

Basic information about the well

Well TH9 was drilled in 1987 to a depth of 211.5 feet. An 

8-inch-diameter steel casing was installed to 92.5 feet and a 

6-inch-diameter steel casing was installed from 85 to 211 feet, 

with perforations from 130 to 165 feet and 180 to 205 feet. 

The well is a monitoring well and does not have a working 

pump. During the camera survey, a 1-inch inner-diameter PVC 

pipe was encountered at depth attached to a heavy object that 

was presumed to be a pump. The presumed pump and attached 

pipe fell to the bottom of the well.

Summary of down-hole camera survey

(Depths shown in this section have been corrected for the 

position of the camera lens and are depths below TOC.)

1. The camera contacted the water surface at 41.9 feet 

below TOC, and the camera encountered sediments 

at the bottom of the well at 188.3 feet below TOC.

2. The top of the broken off 1-inch-inner-diameter PVC 

pipe is at 76 feet below TOC. The pipe runs all the 

way to the bottom of the well into the sediments.

3. At a depth of about 87.4 feet below TOC, the casing 

appeared to narrow and the camera started getting 

stuck more frequently.

4. The well casing is in good condition with scaling 

attached to the casing at all depths. The scaling is 

generally thin and patchy in places. It is notable that 

no particularly hummocky scaling was seen at any 

depth, perhaps indicating limited, if any flow in this 

well.

5. No perforations and no animals were seen. However, 

the image was poor because water was murky due 

to large amounts of suspended matter. The water 

seemed less murky near the bottom of the well, 

although it was difficult to be certain due to the large 

amount of falling and suspended matter in the well.
Appendix 3 65

Appendix 3. Natural-Gamma Logs of Selected Wells of the Eastbank Aquifer 

System, Douglas County, Washington, December 13, 2007.

Altitude of land surface 744.7 feet 746.6 feet 741.4 feet

TH6

727.6 feet

CD6 CD47 TH2

0

10

20

30

40

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70

80

90

DEPTH BELOW LAND SURFACE. IN FEET 100

110

120

130

140

150

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190

0

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230

170

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190

0

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0

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20 40 60 80

NATURAL GAMMA,

IN API UNITS

20 40 60 80

NATURAL GAMMA,

IN API UNITS

20 40 60 80

NATURAL GAMMA,

IN API UNITS

20 40 60 80

NATURAL GAMMA,

IN API UNITS
66 Hydrologic and Thermal Conditions, Eastbank Aquifer System near Rocky Reach Dam, Douglas County, Washington

This page intentionally left blank.
Manuscript approved for publication, April 30, 2008

Prepared by the USGS Publishing Network

Bob Crist

Bill Gibbs

Bobbie Jo Richey

Linda Rogers

Sharon Wahlstrom

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

Washington Water Science Center Director, 

U.S. Geological Survey, 934 Broadway — Suite 300

Tacoma, Washington 98402

http://wa.water.usgs.gov
van Heeswijk and others— Hydrologic and Thermal Conditions of the Eastbank Aquifer System, Douglas County, Washington—Scientific Investigations Report 2008–5071