Surface-Water/Ground-Water Interaction of the Spokane River

and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and

Washington

National Water-Quality Assessment Program

Water Resources Investigations Report 03-4239

U.S. Department of the Interior

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

U.S. Geological Survey

Surface-Water/Ground-Water Interaction of the Spokane 

River and the Spokane Valley/Rathdrum Prairie Aquifer, 

Idaho and Washington

by Rodney R. Caldwell and Craig L. Bowers

Water-Resources Investigations Report 03-4239

Helena, Montana

October 2003
U.S. Department of the Interior

GALE A. NORTON, Secretary

U.S. Geological Survey

Charles G. Groat, Director

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

descriptive purposes only and does not imply endorsement by the

U.S. Government

For additional information write to:

District Chief

U.S. Geological Survey

3162 Bozeman Avenue

Helena, MT 59601-6456

Copies of this report can be purchased from:

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Box 25286, Federal Center

Denver, CO 80225-0286

Information regarding the National Water-Quality Assessment (NAWQA) Program is available on the 

Internet via the World Wide Web using the URL:

http://water.usgs.gov/nawqa
FOREWORD iii

FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and 

timely scientific information that helps enhance and 

protect the overall quality of life, and facilitates effective management of water, biological, energy, and 

mineral resources (http://www.usgs.gov/). Information 

on the quality of the Nation’s water resources is of 

critical interest to the USGS because it is so integrally 

linked to the long-term availability of water that is 

clean and safe for drinking and recreation and that is 

suitable for industry, irrigation, and habitat for fish and 

wildlife. Escalating population growth and increasing 

demands for the multiple water uses make water availability, now measured in terms of quantity and quality, 

even more critical to the long-term sustainability of 

our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy (http://water.usgs.gov/nawqa/). Shaped by and 

coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is 

designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the 

conditions changing over time? How do natural 

features and human activities affect the quality of 

streams and ground water, and where are those effects 

most pronounced? By combining information on 

water chemistry, physical characteristics, stream 

habitat, and aquatic life, the NAWQA Program aims to 

provide science-based insights for current and 

emerging water issues and priorities. NAWQA results 

can contribute to informed decisions that result in 

practical and effective water-resource management 

and strategies that protect and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 

of the Nation’s most important river basins and aquifers, referred to as Study Units (http://water.usgs.gov/ 

nawqa/nawqamap.html). Collectively, these Study 

Units account for more than 60 percent of the overall 

water use and population served by public water 

supply, and are representative of the Nation’s major 

hydrologic landscapes, priority ecological resources, 

and agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally 

consistent study design and methods of sampling and 

analysis. The assessments thereby build local knowledge about water-quality issues and trends in a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multi-scale 

approach helps to determine if certain types of waterquality issues are isolated or pervasive, and allows 

direct comparisons of how human activities and 

natural processes affect water quality and ecological 

health in the Nation’s diverse geographic and environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace 

metals, and aquatic ecology are developed at the 

national scale through comparative analysis of the 

Study-Unit findings (http://water.usgs.gov/nawqa/ 

natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant science so that the most recent and available 

knowledge about water resources can be applied in 

management and policy decisions. We hope this 

NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The NAWQA Program recognizes that a 

national assessment by a single program cannot 

address all water-resource issues of interest. External 

coordination at all levels is critical for a fully integrated understanding of watersheds and for cost-effective management, regulation, and conservation of our 

Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, and 

information from other Federal, State, interstate, 

Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Associate Director for Water
CONTENTS v

CONTENTS

Page

Foreword................................................................................................................................................................................ iii

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

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

Purpose and Scope....................................................................................................................................................... 5

Acknowledgments ....................................................................................................................................................... 5

Description of Study Area ..................................................................................................................................................... 6

Physiography, Land Use, and Climate......................................................................................................................... 6

Hydrogeologic Setting................................................................................................................................................. 6

Study Design and Methods.................................................................................................................................................... 7

Well Inventory ............................................................................................................................................................. 9

Monitoring Wells......................................................................................................................................................... 9

Streamflow and Calculated Losses.............................................................................................................................. 9

Water-Level, River-Stage, Water-Temperature, and Specific Conductance Monitoring............................................. 9

Water-Quality Sample Collection and Analysis .......................................................................................................... 12

Quality Assurance/Quality Control ............................................................................................................................. 13

Surface-Water/Ground-Water Interaction.............................................................................................................................. 14

Conceptual Model........................................................................................................................................................ 14

Spokane River Streamflow Losses .............................................................................................................................. 15

Ground-Water Levels and Flow Directions ................................................................................................................. 18

Water Temperature....................................................................................................................................................... 23

Water Chemistry .......................................................................................................................................................... 24

Specific Conductance ........................................................................................................................................ 25

Major Ions.......................................................................................................................................................... 25

Trace Elements .................................................................................................................................................. 30

Stable Isotopes................................................................................................................................................... 38

Temporal Variability in Water Chemistry.......................................................................................................... 39

Summary................................................................................................................................................................................ 41

References Cited.................................................................................................................................................................... 42

Appendix ............................................................................................................................................................................... 47

FIGURES

Figures 1-4. Maps showing:

1. Location of Northern Rockies Intermontane Basins Study Unit, Montana, Idaho,

and Washington ................................................................................................................................. 3

2. Location of Spokane Valley/Rathdrum Prairie aquifer and detailed study area of northern

Idaho and eastern Washington ........................................................................................................... 4

3. Location of monitoring wells and gaging stations in the detailed study area utilized in the

surface-water/ground-water interaction study of the Spokane Valley/Rathdrum

Prairie aquifer between Post Falls, Idaho, and Spokane, Washington............................................... 5

4. Generalized geology and ground-water flow directions of the Spokane Valley/Rathdrum

Prairie aquifer and surrounding basin-fill aquifers............................................................................ 8

5. Graph showing ground-water and Spokane River sample-collection dates and streamflow

of the Spokane River at Post Falls, Idaho, 1999-2001................................................................................ 12
vi Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley-Rathdrum Prairie Aquifer, Idaho and Washington

FIGURES—Continued

Page

Figure 6. Graph showing Spokane River streamflow and water temperature at Post Falls, Idaho,

and calculated streamflow losses between Post Falls, Idaho (station 12419000),

and Otis Orchards, Washington (station 12419500), water year 2001....................................................... 17

7. Map showing generalized water table of the Spokane Valley/Rathdrum Prairie aquifer

between Post Falls, Idaho, and Spokane, Washington ............................................................................... 18

8. Generalized hydrogeologic sections of the Spokane River channel and Spokane Valley/Rathdrum

Prairie aquifer showing selected monitoring wells including water levels and inferred water table ......... 20

9-12. Graphs showing:

9. Spokane River stage, water levels in representative wells, and calculated streamflow loss,

water year 2001................................................................................................................................. 22

10. Generalized hydrologic section showing temperature range of the Spokane River

measured at Post Falls, Idaho, and ground water from wells 11 through 16,

water year 2001................................................................................................................................. 23

11. Temperature record of the Spokane River measured at Post Falls, Idaho, and ground

water from wells 11 through 16, water year 2001 ............................................................................ 24

12. Temperature record of the Spokane River measured at Post Falls, Idaho, and ground

water from wells 1, 19, 21, and 22, water year 2001 ........................................................................ 25

 13. Map showing specific conductance of ground-water samples from the Spokane Valley/

Rathdrum Prairie aquifer, Idaho and Washington ...................................................................................... 27

14. Trilinear diagram showing major-ion composition of the Spokane River at Post Falls, Idaho,

and ground water from 25 monitoring wells from the Spokane Valley/Rathdrum Prairie

aquifer between Post Falls, Idaho, and Spokane Washington.................................................................... 28

15. Map of median dissolved-solids concentrations of samples collected from the Spokane River

at Post Falls, Idaho, and ground water classified as river-source, transitional, and regional

ground water in the Spokane Valley/Rathdrum Prairie aquifer, Idaho and

Washington, 1999-2001.............................................................................................................................. 29

16. Boxplots summarizing dissolved-solids concentrations of samples collected from the Spokane

River at Post Falls, Idaho (water years 1999 through 2001), and ground water identified

as river source, transitional, or regional (June 2000 through August 2001) from the

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington ............ 30

17. Boxplots summarizing dissolved concentrations of selected trace elements in samples

collected from the Spokane River at Post Falls, Idaho, and ground water identified

as river source, transitional, or regional from the Spokane Valley/Rathdrum Prairie

aquifer between Post Falls, Idaho, and Spokane, Washington, water year 2001 ....................................... 32

18. Map of dissolved zinc concentrations of samples collected from the Spokane River at

Post Falls, Idaho, and ground water from the Spokane Valley/Rathdrum Prairie aquifer

between Post Falls, Idaho, and Spokane, Washington, water year 2001.................................................... 33

19. Map of median dissolved arsenic concentrations of samples collected from the Spokane

River at Post Falls, Idaho, and ground water from the Spokane Valley/Rathdrum Prairie

aquifer between Post Falls, Idaho, and Spokane, Washington, water year 2001 ....................................... 34

20-24. Graphs showing:

20. Dissolved concentrations of cadmium, lead, and zinc in samples collected from the

Spokane River at Post Falls, Idaho, and ground water identified as river source

from the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho,

and Spokane, Washington, water year 2001 ..................................................................................... 35
Contents vii

FIGURES—Continued

Page

Figure 21. Median dissolved-solids and dissolved zinc concentrations of the Spokane River

measured at Post Falls, Idaho, and ground water from wells 11 through 16,

water year 2001................................................................................................................................. 37

22. Relation between δD and δ18O in water from the Spokane River and ground water

from the Spokane Valley/Rathdrum Prairie aquifer of Idaho and Washington

classified as river source, transitional, and regional based on concentrations 

of dissolved solids, 1999-2001.......................................................................................................... 38

23. δ18O of samples from the Spokane River at Post Falls, Idaho, ground water influenced

by recharge from the Spokane River, and regional ground water of the Spokane 

alley/Rathdrum Prairie aquifer, 1999-2001....................................................................................... 39

24. Dissolved-solids and zinc concentrations of the Spokane River at Post Falls, Idaho,

and ground water from selected monitoring wells within the Spokane Valley/Rathdrum

Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 1999-2001........................... 40

25. Graphs showing ground-water altitude and water temperature measured in 25 monitoring

wells within the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho,

and Spokane, Washington, water year 2001............................................................................................... 50

TABLES

Table 1. Selected site information for monitoring wells utilized in the surface-water/ground-water

interaction detailed study of the Spokane River and the Spokane Valley/Rathdrum

Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 2000-01........................................ 10

2. Trace elements detected in ground-water field blank samples, 2000-01......................................................... 13

3. Trace elements with relative percent differences greater than 20 percent or with differences greater

than 1 microgram per liter in ground-water replicate sample pairs, 2000-01 ............................................ 14

4. Monthly mean streamflow, calculated losses, and water temperature of the Spokane River between

Post Falls, Idaho, and Spokane, Washington, water years 2000-01........................................................... 16

5. Median specific conductance, pH, and major-ion concentrations of the Spokane River and ground

water from monitoring wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001............... 26

6. Summary of selected trace element data collected from the Spokane River and ground water from

monitoring wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001 ................................. 31

7. Total-recoverable and dissolved cadmium, lead, and zinc concentrations of ground-water samples

from monitoring wells within the Spokane Valley/Rathdrum Prairie aquifer, 2000-01.................................. 36

8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water

from monitoring wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001.............................. 55
viii Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley-Rathdrum Prairie Aquifer, Idaho and Washington

CONVERSION FACTORS, DATUM, ABBREVIATED WATER-QUALITY UNITS, AND ACRONYMS

Temperature can be converted from degrees Celsius (°C) to degrees Fahrenheit (°F) by using the following equation:

F = 9/5(°C)+32

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83), unless otherwise noted. Vertical coordinate 

information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Abbreviated water-quality units and related terms used in this report:

Acronyms used in this report:

Multiply By To obtain

Length

inch 2.54 centimeter

foot 0.3048 meter

mile 1.609 kilometer

Area

acre 4,047 square meter

Mass

pound 0.454 kilogram

Flow

cubic feet per second (ft3/s) 0.02832 cubic meter per second

gallon per minute 0.06309 liter per second

Hydraulic conductivity

foot per day 0.3048 meter per day

Transmissivity

foot squared per day 0.0929 meter squared per day

δ delta

μm micrometer

μS/cm microsiemens per centimeter at 25 degrees Celsius

μg/g micrograms per gram

μg/L micrograms per liter

mg/L milligrams per liter

‰ per mil, parts per thousand

δ D deuterium/hydrogen ratio, referenced to Vienna Standard Mean Ocean Water

δ 18O oxygen-18/oxygen-16 ratio, referenced to Vienna Standard Mean Ocean Water

AL U.S. Environmental Protection Agency Action Level

GPS Global Positioning System

LHA U.S. Environmental Protection Agency Lifetime Health Advisory

LRL Laboratory Reporting Level

MCL Maximum Contaminant Level

MRL Minimum Reporting Level

NAWQA National Water-Quality Assessment

NROK Northern Rockies Intermontane Basins

PVC Polyvinyl Chloride

RPD Relative Percent Difference

SDWR U.S. Environmental Protection Agency Secondary Drinking-Water Regulation

SVRP Spokane Valley/Rathdrum Prairie

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VSMOW Vienna Standard Mean Ocean Water
INTRODUCTION 1

Surface-Water/Ground-Water Interaction of the Spokane 

River and the Spokane Valley/Rathdrum Prairie Aquifer, 

Idaho and Washington

By Rodney R. Caldwell and Craig L. Bowers

ABSTRACT

Historical mining in the Coeur d’Alene River 

Basin of northern Idaho has resulted in elevated concentrations of some trace metals (particularly cadmium, lead, and zinc) in water and sediment of Coeur 

d’Alene Lake and downstream in the Spokane River in 

Idaho and Washington. These elevated trace-metal 

concentrations in the Spokane River have raised concerns about potential contamination of ground water in 

the underlying Spokane Valley/Rathdrum Prairie 

aquifer, the primary source of drinking water for the 

city of Spokane and surrounding areas. A study conducted as part of the U.S. Geological Survey’s National 

Water-Quality Assessment Program examined the 

interaction of the river and aquifer using hydrologic 

and chemical data along a losing reach of the Spokane 

River. The river and ground water were extensively 

monitored over a range of hydrologic conditions at a 

streamflow-gaging station and 25 monitoring wells situated from 40 to 3,500 feet from the river. River stage, 

ground-water levels, water temperature, and specific 

conductance were measured hourly to biweekly. Water 

samples were collected on nearly a monthly basis 

between 1999 and 2001 from the Spokane River and 

were collected up to nine times between June 2000 and 

August 2001 from the monitoring wells. 

Hydrologic and chemical data indicate that 

the Spokane River recharges the Spokane Valley/

Rathdrum Prairie aquifer along a 17-mile reach 

between Post Falls, Idaho, and Spokane, Washington. 

Ground-water levels in the near-river aquifer (less than 

300 feet from the river) indicate variably saturated 

conditions below the river and a ground-water flow 

gradient away from the losing reach of the river. Calculated monthly mean losses, during water years 2000 

and 2001 along a nearly 7-mile reach between two 

gages, ranged from near 69 to 810 cubic feet per 

second. Losses generally increased with increased 

streamflow. However, late summer warm water 

temperatures also appear to be a factor as losses 

increased due to lower viscosity as water temperatures 

increased. Chemical data indicated that river recharge 

may influence ground-water chemistry as far as 

3,000 feet from the river, but ground water within a few 

hundred feet of the river is most affected. Major-ion 

concentrations, stable isotopes, and temperature of the 

river and ground water from near-river wells were similar and exhibited similar temporal trends, whereas 

ground water from wells located farther from the river 

generally had higher major-ion concentrations and 

more stable temperatures and chemistry.

Although trace-element concentrations sometimes exceeded aquatic-life criteria in the water of the 

Spokane River and were elevated above national 

median values in the bed sediment, trace-element concentrations of all river and ground-water samples were 

at levels less than U.S. Environmental Protection 

Agency drinking-water standards. The Spokane River 

appears to be a source of cadmium, copper, zinc, and 

possibly lead in the near-river ground water. Dissolved 

cadmium, copper, and lead concentrations generally 

were less than 1 microgram per liter (μg/L) in the river 

water and ground water. During water year 2001, dissolved zinc concentrations were similar in water from 

near-river wells (17-71 μg/L) and the river water (22-

66 μg/L), but were less than detection levels in wells 

farther from the river. Arsenic, found to be elevated in 

ground water in parts of the aquifer, does not appear to 

have a river source. Although the river does influence 

the ground-water chemistry in proximity to the river, it 

does not appear to adversely affect the ground-water 

quality to a level of human-health concern.

INTRODUCTION

Historical mining activities within the South 

Fork Coeur d’Alene River Basin (fig. 1) of northern 

Idaho resulted in large quantities of trace-metal 

enriched tailings that were placed directly in or along 
2 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

streams during ore processing (Long, 1998). These 

tailings have resulted in elevated trace-metal concentrations in water and sediment within the South Fork 

Coeur d’Alene River Basin and downstream along 

and within the Coeur d’Alene River (Spruill, 1993; 

Bookstrom and others, 2001), the lakebed of Coeur 

d’Alene Lake (Horowitz and others, 1995; Woods and 

Beckwith, 1997), and the Spokane River (Maret and 

Skinner, 2000; Grosbois and others, 2001; Woods, 

2001; Beckwith, 2002, 2003; Box and Wallis, 2002) 

(fig. 1). Maret and Skinner (2000) and Beckwith 

(2002) reported elevated concentrations of arsenic, 

cadmium, copper, lead, mercury, and zinc in Spokane 

River bed sediment. Grosbois and others (2001) 

reported that streambed sediment (less than the 

63-micrometer (μm) fraction) was enriched in some 

trace elements relative to local background levels, with 

the maximum enrichment in the upper Spokane River 

near Coeur d’Alene Lake. Some of the elevated concentrations were high enough to present potential 

aquatic and human-health problems.

The Spokane Valley/Rathdrum Prairie (SVRP) 

aquifer is the primary source of drinking water for the 

rapidly growing population of Spokane, Washington, 

and nearby communities (fig. 2). The Spokane River 

recharges the SVRP aquifer in places, and ground water 

discharges to the river in other places (Drost and Seitz, 

1978; Bolke and Vaccaro, 1981; and Gearhart and 

Buchanan, 2000). Although gaining and losing reaches 

of the Spokane River have been delineated and gains 

and losses have been calculated, there are still uncertainties including the quantification of the gains to or 

losses from the river, temporal variations of gains and 

losses due to changes in streamflow and (or) groundwater levels, and the conditions (saturated or unsaturated) beneath losing reaches of the river. An increased 

understanding of the surface-water/ground-water interaction along the Spokane River is needed to address the 

overall significance of the Spokane River in the water 

budget and water quality of the SVRP aquifer. 

There is concern that the trace elements in the 

water and sediment of the Spokane River could contaminate the SVRP aquifer. Temporal variations in 

ground-water chemistry in response to changes in river 

chemistry and streamflow also are of concern. Zheng 

(1995) examined water quality of the area and noted 

that trace-metal concentrations in ground water generally were very low, but also reported consistently high 

zinc concentrations in the river. Marti and Garrigues 

(2001) provided baseline data of the physical and 

chemical influences of the Spokane River on part of the 

SVRP aquifer in Washington. Cadmium, lead, and zinc 

were found to be elevated in the near-river ground 

water, but all concentrations were less than drinkingwater standards. Both Zheng (1995) and Marti and 

Garrigues (2001) recommended that further study be 

conducted to better define the interactions between the 

river and aquifer.

A study of the interaction between the Spokane 

River and the SVRP aquifer in Idaho and Washington 

was conducted as part of the Northern Rockies Intermontane Basins (NROK) Study Unit of the U.S. 

Geological Survey’s (USGS) National Water-Quality 

Assessment (NAWQA) Program (figs. 1 and 2). Specific objectives of this study were to: (1) increase 

the understanding of the dynamics of the surfacewater/ground-water interaction along the Spokane 

River; (2) quantify the occurrence, distribution (vertical and areal), and source of trace elements in ground 

water adjacent to the Spokane River; and 

(3) investigate temporal variations in ground-water 

quality in response to fluctuating streamflow and 

chemistry of the Spokane River. This study was conducted on two general scales: (1) a detailed study of a 

17-mile reach of the Spokane River between Post Falls, 

Idaho, and Spokane, Washington, and the surrounding 

SVRP aquifer up to 3 miles from the river (fig. 3), and 

(2) a reconnaissance study of the entire SVRP aquifer 

(fig. 2) using primarily existing data to provide a 

hydrogeologic framework to better understand the 

detailed study area. A small area of basin-fill aquifer 

extends beyond the established southern boundary of 

the SVRP aquifer within the detailed study area (fig. 2). 

For brevity, this area is hereinafter included within the 

SVRP aquifer in the text and figures regarding the 

detailed study area. 

The NROK Study Unit is located in western 

Montana, northern Idaho, and northeastern Washington 

(fig. 1) and is one of more than 50 study units selected 

for assessment under the NAWQA Program. The 

major goals of the NAWQA Program are to assess the 

status and trends of our Nation’s water quality, and the 

natural and human factors that can affect these 

resources (Gilliom and others, 1995). NAWQA 

ground-water investigations have focused on waterquality conditions in major aquifers, with an emphasis 

on recently recharged ground water associated with 

present and recent human activities (Gilliom and 

others, 1995). Study activities in the NROK Study Unit 

began in late 1996. The study area for this report is 

nested within a regional ground-water quality assessment area (fig. 2) conducted as part of the NAWQA 

Program (Bowers and others, 2003).
INTRODUCTION 3

Figure 1. Location of the Northern Rockies Intermontane Basins Study Unit, Montana, Idaho, and Washington.

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

 AND SURROUNDING BASIN-FILL AQUIFERS

Black

Pend

Oreille

River

River

Priest

Priest

Lake

Lightning

Creek

Pend

Oreille

Lake

Little Spokane

River

Spokane River

Coeur

d'Alene

Lake River

d'Alene

North

Fork

South Frk

St. Joe River

Fork

Clark

North

Fork

Fork

Middle

Hungry

Horse

Reservoir

Flathead

Lake

South

Fork

Flathead

River

Blackfoot River

Clark

Fork

River

Rock

Creek

Flint

Creek

Little foot

Warm Springs

Cr Silver Bow Cr

Bitterroot

Coeur

River

Lake

Spokane

Hangman

Cr

Creek Nevada

Fork

Clark

Bull

River

Rock

Cr

Spokane

Kellogg

Kalispell

Butte

Missoula

Clark

Fork

Enaville

Pinehurst

Harrison

Calder

Mullan

St. Regis Perma

Bonner

Clinton

Anaconda

Galen

West

Glacier

Columbia Falls

Helmville

Noxon

Priest

River

0 10 30 20 40 50 MILES

0 10 30 20 40 50 KILOMETERS

GLACIER

NATIONAL

PARK

SPOKANE

INDIAN

RES.

COEUR d'ALENE

INDIAN

RESERVATION

KALISPEL

INDIAN

RESERVATION

49o

48o

47o

46o

117o

116o

115o

114o

118o 113o

DIVIDE

CONTINENTAL

FLATHEAD

INDIAN

RESERVATION

WASHINGTON

IDAHO

IDAHO

MONTANA

CANADA CANADA

UNITED STATES UNITED

STATES

Base modified from U.S. Geological Survey digital 

data. Hydrologic unit maps, 1:100,000, 1994; rivers 

and streams, 1:250,000, 1994; Albers Equal-Area 

Projection. Standard parallels 46o00', 48o30', and 

115o00', 45o00'. No false easting or false northing.

North American Datum of 1927 (NAD 27)

Inset shown on

figures 2, 4, 13

Coeur d'Alene

EXPLANATION

WASHINGTON

OREGON

MONTANA

IDAHO

Study

 unit

Columbia

River

Northern Rocky

Mtns

BRITISH COLUMBIA ALBERTA SASKATCHEWAN

CONTINENTAL

DIVIDE
4 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 2. Location of Spokane Valley/Rathdrum Prairie aquifer and detailed study area of northern Idaho and eastern Washington.

Post

Falls

Hayden

Coeur d'Alene

Athol

Deer

Park Bayview

Sandpoint

Newport

Spokane

Lake

Pend Oreille

Coeur

d'Alene

Lake

Hayden

Lake

Little

Spokane

River

River

River

Priest

Pend

Oreille

Spokane

River 7-mile

Bridge

T.57N.

T.56N.

T.55N.

T.54N.

T.53N.

T.52N.

T.51N.

T.50N.

T.49N.

T.48N.

T.32N.

T.31N.

T.30N.

T.29N.

T.28N.

T.27N.

T.26N.

T.25N.

T.24N.

T.33N.

B O N N E R C O

K O O T E N A I

C O

S H O S H O N E C O

S P O K A N E C O

S T E V E N S C O

P E N D

O R E I L LE

C O

WASHINGTON

IDAHO

Detailed study area

inset shown in 

figures 3, 7, 15, 18, 19

R.42E. R.43E. R.44E. R.45E. R.5W. R.4W. R.3W. R.2W. R.1W. R.1E. R.46E. R.6W. R.2E.

R.40E.

R.41E.

SPOKANE

INDIAN

RESERVATION

EXPLANATION

GENERAL EXTENT OF BASIN-FILL AQUIFERS. REGIONAL

 GROUND-WATER QUALITY ASSESSMENT AREA OF

 BOWERS AND OTHERS (2003)

APPROXIMATE BOUNDARY OF SPOKANE VALLEY/

 RATHDRUM PRAIRIE AQUIFER

WEATHER STATION AND NAME Spokane WSO

0 5 10 15 KILOMETERS

0 5 10 15 MILES Extent of basin-fill aquifers modified from Stoffel

and others (1991) and Tuck and others (1996)

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)

117o30' 116o45'

48o

47o45'

Spokane WSO
INTRODUCTION 5

Figure 3. Location of monitoring wells and gaging stations in the detailed study area utilized in the surface-water/ground-water 

interaction study of the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington. WASHINGTON IDAHO

EXPLANATION

MONITORING WELL AND NUMBER

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

90

90

Post Falls

Spokane

Highway 290

Seltice Way

Harvard Road

Barker Road

Sullivan Road

Spokane

River

Liberty

Lake

12419000

12419500

12420500

1,2

3

4,5

25

24

20

23

21 22 17

16

18 19

15 10

8,9

6

7

14 13

11,12

24

U.S. GEOLOGICAL SURVEY STREAMFLOW-GAGING

 STATION AND SITE IDENTIFICATION NUMBER

MILES

KILOMETERS

0

0

6

1 3 2 45 6

135 2 4

T.51N.

T.50N.

T.26N.

T.25N.

R.44E. R.45E. R.6W. R.46E. R.5W.

117o10' 117o00'

47o42'30"

47o40'

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)

12419000

Purpose and Scope

The purpose of this report is to describe the magnitude and extent of influence of the Spokane River on 

ground-water flow and chemistry of the SVRP aquifer 

in Idaho and Washington (fig. 2). The surfacewater/ground-water interactions are described using a 

variety of hydrologic information including calculated 

streamflow losses from the Spokane River, groundwater levels measured in a network of observation 

wells, and water-temperature and water-chemistry data 

from surface and ground water. This report presents 

results of hydrologic and chemical measurements and 

sampling conducted between March 1999 and August 

2001.

Acknowledgments

The authors gratefully acknowledge the local 

well owners for access to their wells for data collection. 

The study would not have been possible without the 

support of David and Nancy Traner, Inland Empire 

Paper Company, Liberty Lake Sewer and Water 

District, University of Idaho Research Park, Consolidated Irrigation District, Washington State Parks and 

Recreation Commission, and the Washington Department of Transportation for allowing us to drill wells 

on their property. Stan Miller, Reanette Boese, and 

Beatrice Lackaff of the Spokane County Public Works 

Department, and John Roland and John Covert of the 

Washington Department of Ecology were helpful with 
6 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

local support and knowledge of the area. Jerry Simms 

and Jim McLefresh of the Spokane County Public 

Works Department were extremely gracious with their 

time and equipment to assist in surveying altitudes of 

several area wells. Thanks to USGS personnel Fred A. 

Bailey, Rick L. Backsen, C. Lee Chambers, Angela 

Frandsen, Karen L. Payne, and Galen J. Schuster for 

help in the field on this project. A special thanks goes 

to USGS hydrologic technician Keith L. Hein, who 

spent many days in the field on every aspect of this 

study.

DESCRIPTION OF STUDY AREA

The study area is included within eastern Washington and northern Idaho (fig. 2). The most extensive 

data collection occurred along a 17-mile reach of the 

Spokane River between Post Falls, Idaho, and Spokane, 

Washington, and the surrounding SVRP aquifer up to 

3 miles from the river (fig. 3). The primary drinkingwater resource in the area is the SVRP aquifer, which 

supplies water to over 400,000 people (Idaho Department of Environmental Quality, 2000). The U.S. 

Environmental Protection Agency (USEPA) designated 

the aquifer as a Sole Source Aquifer as defined under 

section 1424(e) of the Safe Drinking Water Act of 1974 

(U.S. Environmental Protection Agency, 2000). The 

USEPA defines such an aquifer as one that supplies at 

least 50 percent of the drinking water consumed in the 

area overlying the aquifer (U.S. Environmental 

Protection Agency, 2000). People depending on a Sole 

Source Aquifer generally do not have a viable alternative drinking-water source.

Physiography, Land Use, and Climate

The SVRP aquifer underlies a relatively flat, 

alluvium-covered valley. Land-surface altitudes in the 

valley range from about 1,900 to nearly 2,400 feet 

above the National Geodetic Vertical Datum of 1929 

(NGVD 29). The valley is surrounded by bedrock 

highlands. Several lakes are located along the margins 

of the aquifer, the largest of which are Coeur d’Alene 

Lake and Lake Pend Oreille in Idaho. The valley 

generally is void of perennial streams other than the 

Spokane and Little Spokane Rivers.

Ground-water use in the area is primarily public 

supply, irrigation, commercial, industrial, and domestic 

(U.S. Geological Survey, 2001). Primary land-cover 

types overlying the aquifer in the area include agriculture and urban (Nakagaki, Hitt, and McNamara, U.S. 

Geological Survey, written commun., 2001). The 

uplands surrounding the aquifer area primarily are 

covered with coniferous forests and residential 

housing. Agricultural land use consists predominantly 

of hay, wheat, grass seed, barley, oats, and pasture. 

Cities in the area include parts of the Spokane metropolitan area in Washington and Coeur d’Alene and Post 

Falls in Idaho. Residential and commercial development is rapidly increasing in the area as evidenced 

between the 1990 and 2000 censuses, with a 16-percent 

population increase in Spokane County, Washington, 

and nearly a 56-percent increase in Kootenai County, 

Idaho (U.S. Census Bureau, 2002).

The climate throughout the study area varies 

from subhumid to semiarid with warm, dry summers 

and cool, moist winters (Molenaar, 1988). Mean 

annual (1961-1990) precipitation was 16.5 inches per 

year at the Spokane WSO Airport (Western Regional 

Climate Center, 1998) (fig. 2). Most of the precipitation falls as snow during the 5-month period from 

November through March (Molenaar, 1988).

Hydrogeologic Setting

The Spokane River is the only surficial outflow 

of Coeur d’Alene Lake. The river flows out of the 

northern end of Coeur d’Alene Lake and then westward 

into the alluvium-covered valley and through the city of 

Spokane, Washington. Between the lake and the IdahoWashington State line, the river flows adjacent to bedrock uplands to the south or through narrow bedrock 

channels in places. Near the Idaho-Washington State 

line and westward, the river flows through a relatively 

narrow valley incised within the alluvium. Flow from 

Coeur d’Alene Lake into the Spokane River is regulated by a set of dams at Post Falls; therefore, streamflow below the dams does not always represent the 

concurrent inflows to the lake. During normal years, 

the dam gates are usually open between December and 

June, and streamflow rises during the spring snowmelt 

and subsides in June. During most of the summer, the 

dam gates are set to maintain specific water levels in 

Coeur d’Alene Lake. Because of below-average precipitation and reduced inflow to the lake during water 

year 2001 (October 1, 2000, through September 30, 

2001), the gates were closed earlier than usual to 

maintain lake levels. From late September through 

December, the gates typically are incrementally opened 
STUDY DESIGN AND METHODS 7

to lower the lake to its natural level (Box and Wallis, 

2002). The Spokane River at Post Falls has been gaged 

by the USGS since 1913.

The SVRP aquifer (fig. 4) is composed of unconsolidated coarse-grained sand, gravel, cobbles, and 

boulders primarily deposited by a series of catastrophic 

glacial outburst floods during the Pleistocene Epoch 

(Molenaar, 1988). The sediment deposited in this highenergy depositional environment is coarser grained 

than is typical for most basin-fill deposits, resulting in 

one of the most productive aquifers in the United States 

(Molenaar, 1988). Although much of the area includes 

the coarse-grained flood deposits of high permeability, 

fine-grained sedimentary material of lower permeability is present locally. The aquifer is underlain and 

laterally bounded by relatively impermeable metamorphic, igneous, sedimentary, and metasedimentary bedrock of Precambrian to Tertiary age, which is exposed 

as highlands at several locations (fig. 4). Although 

some water-supply wells are completed in the bedrock, 

these units are not considered to be major aquifers.

The saturated thickness of the SVRP aquifer is 

not well defined, but is reported to range from less than 

50 feet in places along the aquifer margin and northwest of Spokane to more than 400 feet in the central 

part of the aquifer near the Idaho-Washington State line 

east of Spokane, Washington (Bolke and Vaccaro, 

1981; Gerstel and Palmer, 1994). Depth to water ranges 

from less than 50 feet along the Spokane River near 

Spokane to more than 400 feet below land surface near 

Athol, Idaho (Bolke and Vaccaro, 1979; Berenbrock 

and others, 1995; Briar and others, 1996; and Stone and 

others, 1996). The slope of the water table generally 

reflects the local surface topography, resulting in a general southward direction of ground-water flow from the 

area near the southern end of Lake Pend Oreille, 

towards the city of Coeur d’Alene, and then westward 

towards the city of Spokane (Drost and Seitz, 1978; 

Molenaar, 1988). Most of this ground water either discharges to the Spokane and Little Spokane Rivers or is 

withdrawn by wells (Drost and Seitz, 1978; Molenaar, 

1988). Generalized ground-water flow directions in the 

SVRP aquifer are illustrated in figure 4. Recharge to 

the aquifer occurs by infiltration of precipitation, irrigation water and septic tank effluent, subsurface inflow 

from adjoining highlands and tributary valleys, and 

leakage from adjacent and overlying surface-water 

sources (Molenaar, 1988). 

Wells completed in the saturated coarse-grained 

deposits rarely extend more than 100 feet into the saturated zone, but can yield several thousand gallons per 

minute (Bolke and Vaccaro, 1979; Stone and others, 

1996). Estimated transmissivity values range from 

several thousand to several million feet squared per 

day, with estimated ground-water velocities exceeding 

60 feet per day in some areas (Drost and Seitz, 

1978). 

Several investigations reported that water from 

the Spokane River recharges the SVRP aquifer in 

places. Piper and La Rocque (1944) noted that the 

stage in the upper reach of Spokane River to a point 

4 miles west of the Idaho-Washington State line (near 

Spokane) appeared to be higher than the regional 

water table. More recently, Gearhart and Buchanan 

(2000) examined the hydraulic connection between 

the Spokane River and the aquifer. They concluded 

that the river had a losing reach between Post Falls and 

near Spokane (the Barker Road bridge, fig. 3) with 

unsaturated flow conditions between the river and 

aquifer. From the Barker Road bridge downstream to 

the Sullivan Road bridge (fig. 3), the river was transitional as it varied from losing to gaining based on 

periodic measurements of ground-water levels and 

river stage.

STUDY DESIGN AND METHODS

The primary focus of the study described in this 

report was to examine the influence of surface water 

on ground water in the SVRP aquifer in areas where 

the Spokane River loses streamflow. The first step in 

the study was to use historical gaging-station and 

ground-water level data to determine which reaches of 

the Spokane River likely lose water to the groundwater system. These reaches were identified from 

information collected during an inventory of existing 

wells and from streamflow-gaging records. Once the 

losing reaches were identified, the following methods 

were used in a detailed study of the near-river area to 

examine and quantify the surface-water/ground-water 

interaction. Monitoring wells were installed in areas 

with no existing wells, particularly in areas near the 

Spokane River. River stage, ground-water levels, 

specific conductance, and water temperature were 

monitored. Water-chemistry samples were collected 

over a range of streamflow conditions. USGS datacollection and processing procedures were followed 

for quality control/quality assurance.
8 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 4. Generalized geology and ground-water flow directions of the Spokane Valley/Rathdrum Prairie aquifer and surrounding basinfill aquifers.

Lake

Pend

Oreille

Coeur

d'Alene

Lake

Hayden

Lake

Spokane

River

N

Regional

flow

117o30' 116o45'

48o

47o45' ground-water

Base modified from U.S. Geological Survey digital data

Public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995; and

rivers, 1:100,000, 1985; hillshade from EROS Data Center, 1992. 

North American Datum of 1927 (NAD 27)

Geology modified from Stoffel and others, 1991 and Tuck and others, 1996

Ground-water flow directions from information in Drost and Seitz, 1978;

Molenaar, 1988; EMCON, 1992; Briar and others, 1996

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

ALLUVIAL AND GLACIAL OUTBURST FLOOD DEPOSITS 

 (of Holocene and Pleistocene age)—Unconsolidated

 boulders, cobbles, gravel, sand, silt, and clay

GLACIAL DEPOSITS (Pleistocene age)—Unconsolidated 

 gravel, sand, silt, and clay

BEDROCK, UNDIFFERENTIATED (of Tertiary through 

 Precambrian age)—Igneous, metamorphic, metasedimentary, 

 and sedimentary rocks

APPROXIMATE BOUNDARY OF SPOKANE VALLEY/

 RATHDRUM PRAIRIE AQUIFER

GENERALIZED DIRECTION OF GROUND-WATER FLOW
STUDY DESIGN AND METHODS 9

Well Inventory

One spring and 111 existing domestic, irrigation, 

public supply, and monitoring wells were inventoried 

between August 1999 and January 2001 (Bowers and 

others, 2003). Locations were determined using global 

positioning system (GPS). Most land-surface altitudes 

of the wells (especially wells near the Spokane River) 

were determined using standard differential leveling 

procedures or with GPS equipment with accuracies of 

less than 1 foot. Land-surface altitudes of some wells 

farther from the river were interpreted from USGS 7.5-

minute topographic maps with accuracies generally less 

than 10 feet. Synoptic measurements of water levels 

and specific conductance for the inventoried wells and 

spring were made to help determine the local groundwater flow regime and to further refine the extent of the 

losing reaches of the Spokane River. Water levels were 

measured to an accuracy of 0.01 foot. Specific conductance was measured in samples collected as near as 

possible to the well head.

Monitoring Wells

Twenty-five monitoring wells were utilized for 

this study (table 1), 18 of which (wells 1, 2, 4-19) were 

installed between June and September 2000. The 

newly installed wells filled spatial and vertical gaps in 

the existing well network, especially close to the river 

(fig. 3). Pre-existing wells (wells 3, 20-25) were drilled 

between 1996 and 1998. Newly installed wells were 

located at various distances from the river in five general locations where the Spokane River was suspected 

of recharging the aquifer. These wells were installed at 

various depths below the water table. Four sets of 

nested well pairs (wells 1 and 2, 4 and 5, 8 and 9, 11 and 

12) were completed at different depths to examine the 

vertical distribution of water levels and water chemistry 

(fig. 3). All wells consisted of 2-inch diameter polyvinyl chloride (PVC) casing, with PVC screen lengths 

of 5 to 10 feet (wells drilled for this study) or 30 to 

40 feet (pre-existing wells) set at the bottom of the 

wells. Wells installed for this study were drilled with an 

air rotary drill rig and had 6-inch diameter steel casing 

driven to temporarily keep the hole open. Silica sand 

was placed from the bottom of the borehole to about 

5 feet above the top of the screen. About 1 foot of bentonite pellets were placed immediately on top of the 

sand, and the remainder of the annulus was filled with 

bentonite grout. The temporary steel casing was 

incrementally pulled out as the sand and bentonite 

material was placed in the annulus between the PVC 

and steel casing.

Streamflow and Calculated Losses

Differences in streamflow between USGS 

streamflow-gaging stations on the Spokane River 

were used to determine the amount of leakage in the 

river reach between Post Falls, Idaho, and the eastern 

city limits of Spokane, Washington (fig. 3). This section of the river potentially loses water to the underlying aquifer at all times because the water-table 

altitude in the area is lower than the river surface. 

Measurement errors in streamflow for the Post 

Falls, Idaho (station 12419000), and Otis Orchards, 

Washington (station 12419500) gages determined 

from the stage-discharge relation for each station are 

estimated to be within ±5 percent. Measurements at 

the Greenacres, Washington gage (station 12420500) 

have an estimated error of up to ±10 percent based 

on hydrologic conditions (Galen Schuster, U.S. 

Geological Survey, oral commun., 2002).

Water-Level, River-Stage, WaterTemperature, and Specific Conductance 

Monitoring

Ground-water level, water temperature, and 

specific conductance were measured hourly to 

biweekly in the 25 monitoring wells (fig. 3). Water 

level, specific conductance, and temperature were 

manually measured biweekly at all wells. Water 

levels were measured to an accuracy of 0.01 foot with 

an electric or steel tape. Temperature and specific 

conductance were measured downhole or during 

sample collection in a flow-through cell. Pressure 

transducers were installed in 10 monitoring wells to 

record water levels hourly. Sixteen monitoring wells 

were instrumented to record water temperatures 

hourly. Specific conductance, temperature, and river 

stage (gage height) of the Spokane River near the Post 

Falls (station 12419000, fig. 3) gage were recorded 

hourly during water year 2001. 
10 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Table 1. Selected site information for monitoring wells utilized in the surface-water/ground-water interaction detailed study of the 

Spokane River and the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 2000-01

[All wells are screened within Quaternary-age alluvium glacial-outburst flood deposits and constructed of 2-inch diameter polyvinyl chloride casing. 

Remarks: W, instrumented with digital water-level recorder; T, instrumented with digital temperature recorder; NR, no recorder installed]

Well

number

(fig. 3)

Location

number1

Site

identification

number

Latitude2 Longitude2

Altitude of

land surface

(feet above

NGVD 29) (degrees, minutes, seconds)

1 50N05W07DABC01 474134117002201 474134.3 1170022.4 2,069.46

2 50N05W07DABC02 474134117002202 474134.6 1170022.3 2,070.32

3 26N46E31CBBC01 474226117024801 474225.6 1170248.1 2,090.20

4 25N45E01ABDD01 474151117031101 474150.7 1170310.8 2,035.41

5 25N45E01ABDD02 474151117031102 474150.7 1170310.8 2,035.27

6 25N45E01ABDD03 474149117031101 474149.4 1170311.5 2,034.90

7 25N45E01ACAD01 474144117031401 474144.2 1170314.1 2,045.75

8 25N45E01CBBD02 474130117035902 474130.1 1170358.8 2,025.02

9 25N45E01CBBD01 474130117035901 474130.1 1170358.8 2,024.89

10 25N45E01CBBC01 474131117040401 474130.9 1170403.5 2,031.22

11 25N45E10BAAA01 474106117060501 474106.3 1170605.0 2,030.62

12 25N45E10BAAA03 474107117060502 474106.6 1170605.2 2,031.47

13 25N45E10BAAA02 474107117060501 474107.3 1170604.9 2,036.51

14 25N45E03CDDD01 474110117060601 474109.6 1170605.8 2,033.10

15 25N45E03CDDA01 474115117060301 474115.1 1170603.1 2,040.18

16 25N45E03BDDA01 474140117060401 474140.2 1170604.3 2,052.57

17 25N45E10CBDA01 474033117062501 474033.5 1170625.2 2,037.95

18 25N45E09ADAD01 474050117064201 474050.4 1170641.7 2,023.05

19 25N45E09ADAB01 474053117064701 474053.5 1170646.6 2,021.28

20 25N45E17BBAA05 474016117085601 474015.5 1170855.8 2,035.60

21 25N45E08CBBC02 474037117091301 474037.2 1170913.1 2,018.00

22 25N45E08CBBC01 474038117091201 474038.2 1170912.0 2,017.50

23 25N45E07ADDD01 474046117091501 474045.5 1170914.9 2,001.50

24 25N45E07AAAA04 474109117091701 474109.3 1170917.1 2,021.70

25 25N44E11DDAC01 474026117115301 474025.6 1171153.2 1,965.90

1

Described in the appendix.

2

Referenced to North American Datum of 1983 (NAD 83).
STUDY DESIGN AND METHODS 11

Depth of

well

(feet below 

land surface)

Top of

casing

(feet above 

land surface)

Screened interval Approximate

distance from

Spokane River

(feet)

Top County State Remarks

(feet below 

land surface)

Bottom

(feet below 

land surface)

79.3 2.6 69.0 79.0 100 Kootenai Idaho W, T

45.8 2.8 35.4 45.4 100 Kootenai Idaho W, T

151 1.7 112 147 2,700 Spokane Washington NR

74.3 2.3 63.9 73.9 40 Spokane Washington W, T

60.7 2.8 55.3 60.3 40 Spokane Washington NR

77.8 2.7 67.4 77.4 130 Spokane Washington T

86.9 2.8 76.4 86.4 700 Spokane Washington T

32.9 2.7 22.6 32.6 80 Spokane Washington W, T

76.1 2.7 65.8 75.8 80 Spokane Washington W, T

71.0 2.9 60.6 70.6 400 Spokane Washington T

71.6 2.6 61.2 71.2 100 Spokane Washington W, T

136.7 2.8 126.3 136.3 100 Spokane Washington W, T

75.5 2.7 65.1 75.1 200 Spokane Washington T

88.8 .0 78.4 88.4 475 Spokane Washington W, T

97.5 .2 87.1 97.1 900 Spokane Washington T

117.3 2.7 107.0 117.0 3,500 Spokane Washington W, T

97.1 2.6 86.8 96.8 2,600 Spokane Washington NR

77.4 2.9 67.0 77.0 640 Spokane Washington T

70.9 2.7 60.5 70.5 80 Spokane Washington W, T

113 2.2 82.5 112.5 2,500 Spokane Washington NR

98 1.6 61 96 200 Spokane Washington NR

97 2.2 62 97 100 Spokane Washington NR

80 .0 40 80 100 Spokane Washington NR

100 1.7 70 100 2,500 Spokane Washington NR

67 1.3 26 66 100 Spokane Washington NR
12 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Water-Quality Sample Collection and Analysis

Periodic water-quality samples were collected 

from 25 monitoring wells and the Spokane River at 

Post Falls to investigate temporal and spatial variations 

in water chemistry with stream-stage fluctuation 

(fig. 5). Monitoring wells were sampled as many as 

eight times between June 2000 and August 2001 

(fig. 5). All samples were collected using documented 

NAWQA sampling procedures (Shelton, 1994; Koterba 

and others, 1995). Prior to sampling each well, the 

water level was measured to the nearest 0.01 foot with 

an electric or steel measuring tape. Samples were 

collected after a minimum of three well-bore volumes 

were purged and after field measurements of pH, dissolved oxygen, temperature, turbidity, and specific 

conductance had stabilized. Samples were collected 

from the monitoring wells using a 1.75-inch diameter 

stainless-steel submersible pump with Teflon impellers, tubing, and valves and stainless-steel connections. 

Spokane River samples were collected approximately monthly between March 1999 and August 2001 

(fig. 5) using depth and width-integrated sampling 

techniques. Sampling procedures are described in 

more detail by Bowers and others (2003). 

Samples were analyzed for physical properties 

and major ions, trace elements, and stable isotopes. 

Physical properties measured onsite included water 

temperature, dissolved oxygen, pH, specific conductance, and turbidity. Samples for analysis of alkalinity 

and dissolved major ions and trace elements were filtered onsite through a 0.45-μm pore-size capsule filter. 

Both filtered and total-recoverable (whole-water, unfiltered) samples were collected at some sites to examine 

the potential of colloidal transport of trace elements to 

and through the aquifer. All samples were processed in 

the field within 1 hour of sample collection. Alkalinity, 

major-ion, and trace-element samples were analyzed at 

the USGS National Water-Quality Laboratory (Denver, 

Colo.) by various methods (Fishman and Friedman, 

1989; Faires, 1993; Fishman, 1993; McLain, 1993; 

Hoffman and others, 1996; Garbarino and Struzeski, 

1998; Garbarino, 1999; Jones and Garbarino, 1999). 

Alkalinity of selected samples also was determined in 

the field using the incremental titration method (Wilde 

and Radtke, 1998). 

Figure 5. Ground-water and Spokane River sample-collection dates and streamflow of the Spokane River at 

Post Falls, Idaho, 1999-2001. STREAMFLOW, IN CUBIC FEET PER SECOND

0

5,000

10,000

15,000

20,000

25,000

30,000

Spokane River at Post Falls, Idaho (station 12419000)

Ground water

1999 2000 2001

SAMPLE-COLLECTION DATE

STREAMFLOW, SPOKANE RIVER AT POST FALLS, IDAHO

 (STATION 12419000)

EXPLANATION
STUDY DESIGN AND METHODS 13

Selected samples were analyzed for the isotopic 

ratios of 2

H/H and 18O/16O to investigate the use of the 

relatively conservative tracers to distinguish between 

ground water with a Spokane River source and ground 

water from the regional ground-water flow system. 

Values are reported as delta (δ) D (deuterium, 2

H) 

and δ18O in comparison to the standard reference 

composition of Vienna Standard Mean Ocean Water 

(VSMOW), where δ is expressed in units of per mil (‰, 

parts per thousand). The δD analyses were performed 

using a hydrogen equilibrium technique (Coplen and 

others, 1991), and the δ18O analyses were performed 

using a carbon dioxide equilibrium technique (Epstein 

and Mayeda, 1953) at the USGS Isotope Laboratory 

(Reston, Va.). Water-quality and isotopic data for all 

water samples are listed in Bowers and others (2003).

Quality Assurance/Quality Control

Quality-assurance/quality-control procedures 

consisted of collection and analysis of field blanks and 

replicates to evaluate the accuracy and precision of the 

analytical results. Procedures used for collecting 

quality-assurance samples are described in Koterba and 

others (1995) and Mueller and others (1997). Qualityassurance samples comprised about 10 percent of the 

samples and were collected, preserved, and analyzed 

using the same equipment, procedures, and analytical 

methods as the environmental samples. In addition, 

internal quality-assurance practices are performed 

systematically at the USGS National Water Quality 

Laboratory (Pritt and Raese, 1995). Quality-assurance 

data collected for this study are included in Bowers and 

others (2003).

Field blanks were analyzed for trace elements 

and used to evaluate potential contamination from the 

cleaning of equipment, sampling procedures, and/or 

laboratory analysis. Trace elements were detected 

infrequently in blanks, and when detected, concentrations generally were very low, indicating that field and 

laboratory procedures generally did not introduce contamination into the environmental samples. Trace-element concentrations in a field blank from the Spokane 

River at Post Falls during water year 2001 were all less 

than reporting levels. A summary of trace elements 

detected in ground-water blank samples (at concentrations greater than estimated values) are listed in table 2. 

Replicate ground-water samples were analyzed 

for major ions and trace elements to assess variability 

in results caused by sample-collection procedures and 

laboratory analysis. Results of the replicate samples 

indicate good agreement, with the greatest relative percent differences (RPDs) generally occurring when 

sample concentrations were low. The RPDs for major 

ions were less than 10 percent. Trace element RPDs 

generally were less than 20 percent and/or concentrations were less than 1 microgram per liter (μg/L) different between replicate pairs. Exceptions included 

some analyses of dissolved aluminum and boron, and 

total-recoverable iron, manganese, and zinc (table 3). 

In general, the replicate data indicate an acceptable 

level of precision for most analyses. No replicate samples were collected from the Spokane River near Post 

Falls for this study.

Table 2. Trace elements detected in ground-water field blank samples, 2000-01

[μg/L, micrograms per liter; μm, micrometer; MRL, minimum reporting level; LRL, laboratory reporting level; e, estimated value, <, less than]

Constituent

Number

of

blanks

Number of 

blanks with 

detectable 

concentrations

MRL or LRL of 

environmental

samples

(μg/L)

Highest blank 

concentration

(μg/L)

Range of

concentrations in 

ground-water 

samples

(μg/L)

Boron - 0.45-μm filtration 8 2 2.0 to 13 2.5 <2.0 to 25

Cobalt - 0.45-μm filtration 8 1 0.02 to 1.0 .03 e0.01 to 0.18

Copper - 0.45-μm filtration 8 2 0.20 to 1.0 .35 <0.20 to 7.4

Nickel - 0.45-μm filtration 8 1 0.06 to 1.0 .21 <0.06 to 9.8

Zinc - 0.45-μm filtration 8 1 1 2.0 <1.0 to 71

Zinc - whole water 1 1 1 1.1 <1.0 to 74
14 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Table 3. Trace elements with relative percent differences greater than 20 percent or with differences greater than 1 microgram per liter in 

ground-water replicate sample pairs, 2000-01

[RPD, relative percent difference; μg/L, micrograms per liter; <, less than; >, greater than; --, not applicable]

Aluminum,

dissolved

Boron,

dissolved

Iron, total 

recoverable

Manganese, 

total

recoverable

Zinc, total 

recoverable

Number of replicate samples 10 10 3 3 3

Number of RPDs1 exceeding 20 percent

or differences between replicate pairs

of greater than 1 μg/L

3 2 1 1 1

Environmental sample (μg/L) 5.0 11 133 9.3 43

Replicate sample (μg/L) < 1.0 < 7.0 78 5.6 32

RPD1 > 133 > 44 52 50 29

Environmental sample (μg/L) 3.9 < 7.0 -- -- --

Replicate sample (μg/L) < 1.0 9.8 -- -- --

RPD1 > 118 > 33 -- -- --

Environmental sample (μg/L) <1.0 -- -- -- --

Replicate sample (μg/L) 4.6 -- -- -- --

RPD1 > 129 -- -- -- --

1

Relative percent difference equals the difference between concentrations of environmental and replicate samples divided by the average of concentrations 

of the environmental and replicate samples. Concentrations less than reporting levels were set equal to reporting levels for RPD calculation.

SURFACE-WATER/GROUND-WATER 

INTERACTION

The conceptual model of the interaction of the 

Spokane River and SVRP aquifer and the results from 

this study are presented in this section. The conceptual 

model describes the basic dynamics of the relation 

between surface water and ground water in an unconfined-aquifer setting. Calculated streamflow losses, 

water-table mapping, ground-water hydraulic gradients, ground-water level and river-stage fluctuations, 

and water-temperature data are discussed to improve 

the understanding of the surface-water/ground-water 

interaction of the study area. Results of the waterquality monitoring are discussed with regard to the 

effect, area of influence, and temporal variability of 

water leaking from the Spokane River on the water 

quality of the SVRP aquifer.

Conceptual Model

The conceptual model for the losing section of 

the Spokane River between Post Falls and Spokane is 

either that the river is separated from the ground-water 

system by an unsaturated zone or that the zone beneath 

the river is saturated and the hydraulic gradient from the 

river to the aquifer is steep. The streambed of the 

Spokane River along this reach is composed primarily 

of cobbles and boulders (Box and Wallis, 2002). Below 

the surface of the streambed, the coarse material contains interstitial fine silt and clay (Box and Wallis, 

2002). The fine-grained material, some of which may 

have been transported with the leaking water from the 

river, likely reduces the permeability of the streambed 

and underlying substrate. This zone of reduced permeability acts as a leaky layer between the river and the 

underlying aquifer. 
SURFACE-WATER/GROUND-WATER INTERACTION 15

When the altitude of the river stage is higher than 

altitudes of ground-water levels in the nearby area, 

water flows from the river to the aquifer (a losing 

reach). Conversely, when the altitudes of ground-water 

levels are higher than the altitude of the river stage, 

water flows from the aquifer to the river (a gaining 

reach). The rate at which water flows between the river 

and the aquifer is dependent upon several factors 

including the hydraulic properties of the streambed and 

adjoining aquifer, the depth of penetration of the river 

into the aquifer, and the hydraulic gradient between the 

river and aquifer. Leakage to or from a river is computed using principles of Darcy’s Law as follows (from 

Prudic, 1989):

(1)

where

Q = leakage to or from the aquifer through the 

streambed (length3

/time);

Hs = hydraulic head in the stream (length);

Ha = hydraulic head in the aquifer side of the 

streambed (length); and

CSTR = conductance of the streambed (length2/time), 

which is the hydraulic conductivity (K) of 

the streambed (length/time) multiplied by 

the product of the width of the stream and 

its length divided by the thickness of the 

streambed.

When the water table is below the streambed, 

unsaturated conditions exist below the river, and 

leakage from the river is unaffected by the hydraulic 

head in the aquifer. In other words, the amount of 

leakage from the river remains the same regardless of 

how far the water table is below the river bottom. 

Therefore, if unsaturated conditions exist beneath the 

river, Ha is equal to the altitude of the river bottom in 

equation 1. Also, increased streamflow corresponds to 

a greater area of submerged streambed, resulting in 

increased streambed conductance (CSTR) and leakage. 

The occurrence and magnitude of fluctuations in 

ground-water levels in response to changes in river 

stage are indicators of the relation between the ground 

water and the river. Ground-water level fluctuations 

indicate varying rates of recharge and discharge 

(change in storage); a rise in ground-water levels indicates at least a temporary rate of recharge that exceeds 

the rate of discharge. A ground-water level rise in 

response to an increase in river stage is consistent with 

increased recharge to the aquifer from river leakage. 

Therefore, water-level fluctuations in the near-river 

Q CSTR Hs Ha = ( ) –

aquifer in response to changes of river stage are 

expected if the river is a local source of recharge to the 

aquifer.

Conceptually, as a river loses water to an 

aquifer, the physical and chemical properties of the 

river may affect those of the ground water. Depending 

on the occurrence of geochemical processes such as 

sorption and precipitation, surface water leaking to an 

aquifer may transport dissolved or possibly particulate 

constituents to the ground water. Depending on the 

relative chemistry, this may cause a decrease or 

increase in constituent concentrations in the ground 

water. Similarly, water temperature may be a useful 

tracer of river water recharging the aquifer. Surfacewater temperatures are generally more temporally 

variable than ground-water temperatures. Therefore, 

the temperature of ground water affected by local 

recharge from a river is likely to be more variable than 

the temperature of ground water of a more regional 

system. In addition, temporal changes in leakage 

could influence the distance that river water and its 

physical and chemical properties are transmitted into 

the aquifer. During high streamflow and resulting 

high leakage conditions, the river water may travel 

farther laterally out into the aquifer than during low 

streamflow.

Spokane River Streamflow Losses

The mean annual flow of the Spokane River 

near Post Falls over the period of record (1913 through 

2001) is about 6,200 cubic feet per second (ft3

/s). 

Annual mean flow during water year 2001 (October 1, 

2000, through September 30, 2001) was about 

2,700 ft3/s, or 44 percent of normal. Monthly mean 

losses for water years 2000 and 2001 based on the differences in streamflow between the gage at Post Falls 

and two downstream gages at Otis Orchards and 

Greenacres, Washington, are included in table 4. Calculations based on the streamflow values between the 

Post Falls and Otis Orchards gages consistently indicated losses, whereas gains were calculated in a few 

cases using data from the Greenacres gage. Because 

ground-water levels along the reach of river between 

the Post Falls and Greenacres gages are below the 

river, streamflow gains along this reach are not possible. Also, because of the greater confidence in the 

accuracy of measurements at the Otis Orchards gage 

relative to the Greenacres gage, there is a greater confidence in the calculated losses for data from the Post 

Falls and Otis Orchards gages. 
16 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Table 4. Monthly mean streamflow, calculated losses, and water temperature of the Spokane River between Post Falls, Idaho, and 

Spokane, Washington, water years 2000-01

[ft3/s, cubic feet per second; --, missing data; negative loss indicates a gain]

Date

Monthly mean streamflow (ft3/s) Calculated monthly mean

streamflow loss (ft3/s) Loss of

streamflow

between

stations 

12419000 and 

12419500

(percent)

Monthly1

mean water

temperature

at station 

12419000 

(degrees

Celsius)

Spokane River 

near Post Falls, 

Idaho

(station 

12419000)

Spokane River 

above Liberty 

Bridge near 

Otis Orchards, 

Washington

(station 

12419500)

Spokane River 

at Greenacres, 

Washington

(station 

12420500)

Between

stations 

12419000 and 

12419500

Between

stations 

12419000 and 

12420500

10/1999 1,952 1,705 1,628 247 324 12.7 --

11/1999 3,042 2,765 2,616 277 426 9.1 --

12/1999 7,489 6,913 6,738 576 751 7.7 --

01/2000 4,423 4,138 4,100 285 323 6.4 --

02/2000 6,602 6,171 6,068 431 534 6.5 --

03/2000 10,260 9,725 9,558 535 702 5.2 --

04/2000 20,750 20,210 20,030 540 720 2.6 --

05/2000 16,920 16,110 16,150 810 770 4.8 --

06/2000 7,231 6,716 6,646 515 585 7.1 --

07/2000 1,850 1,647 1,632 203 218 11.0 --

08/2000 522 391 432 131 90 25.1 23.2

09/2000 1,338 1,148 1,158 190 180 14.2 17.8

10/2000 2,383 2,199 2,159 184 224 7.7 12.7

11/2000 2,147 1,978 1,994 169 153 7.9 7.1

12/2000 1,666 1,514 1,591 152 75 9.1 3.7

01/2001 903 834 945 69 -42 7.6 2.8

02/2001 1,116 1,010 1,118 106 -2 9.5 2.6

03/2001 2,206 2,028 2,075 178 131 8.1 4.4

04/2001 4,938 4,678 4,593 260 345 5.3 5.9

05/2001 11,190 10,850 10,830 340 360 3.0 11.1

06/2001 3,395 3,145 3,124 250 271 7.4 16.3

07/2001 1,039 717 780 322 259 31.0 22

08/2001 366 149 150 217 216 59.3 22.6

09/2001 800 516 494 284 306 35.5 19.5

Minimum 366 149 150 69 -42 2.6 2.6

Maximum 20,750 20,210 20,030 810 770 59.3 23.2

Median 2,295 2,114 2,117 255 288 7.8 11.9

1

Hourly temperature data were recorded July 31, 2000, through September 30, 2001.
SURFACE-WATER/GROUND-WATER INTERACTION 17

Daily mean Spokane River streamflow values 

(water years 2000 and 2001) from the Post Falls and the 

Otis Orchards gages (Kimbrough and others, 2001, 

2002) indicated that daily losses ranged from 10 to 

900 ft3/s, with a median of 240 ft3/s, although some 

daily losses were within the estimated 5-percent range 

of measurement error. Some daily loss estimates may 

be affected by the time of travel between Post Falls and 

Otis Orchards because streamflow changes rapidly on 

some days due to releases at the dam at Post Falls. 

Therefore, streamflow losses based on daily values 

may be underestimated or overestimated during 

periods of rapidly fluctuating streamflow. Calculating 

losses using monthly mean streamflow values reduces 

the effect of traveltime between the two gages. 

Monthly mean losses between the Post Falls and Otis 

Orchards gages during water years 2000 and 2001 

ranged from 69 to 810 ft3

/s, with a median of 255 ft3/s 

(table 4). Estimates of monthly mean streamflow loss 

over the 6.8-mile reach between the two gages ranged 

from about 10 to 119 ft3

/s per river mile. Losses determined from this study are somewhat similar to those 

calculated by Gearhart and Buchanan (2000), who used 

streambed areas and Darcy’s Law for the reach 

between the Idaho-Washington State line and the 

Sullivan Road bridge (losses of 104 ft3/s during low 

flow conditions to 571 ft3/s during high flow conditions).

The greatest losses during water years 2000 and 

2001 occurred when streamflow was greatest, consistent with increased leakage as a result of increased 

streambed area and streambed conductance. However, 

losses during relatively low late-summer flows were 

greater than during some other parts of the year with 

similar or greater streamflow (fig. 6). For example, the 

mean streamflow for July 2001 was 1,039 ft3

/s with a 

calculated loss of 322 ft3/s between Post Falls and Otis 

Orchards. The mean streamflow for February 2001 

was higher (1,116 ft3/s), but the calculated loss was 

lower (106 ft3

/s). With the exception of October 1999, 

the greatest relative percentage of streamflow loss 

occurred during the summer months (July, August, 

and September) with the warmest water temperatures 

(table 4). The change of water viscosity with 

Figure 6. Spokane River streamflow and water temperature at Post Falls, Idaho, and calculated streamflow losses between 

Post Falls, Idaho (station 12419000), and Otis Orchards, Washington (station 12419500), water year 2001. STREAMFLOW AND CALCULATED LOSSES, IN CUBIC FEET PER SECOND

0

5

10

15

20

25

STREAMFLOW—Spokane River at Post Falls, Idaho (station 12419000)

CALCULATED LOSS BETWEEN STATIONS 12419000 AND 12419500

WATER TEMPERATURE—Spokane River at Post Falls, Idaho (station 12419000)

Decreasing streamflow, nearly

 stable losses, and elevated 

 water temperature - evidence

 of temperature influence on

 water viscosity and losses.

10,000

1,000

100,000

10

1

100

WATER TEMPERATURE, IN

DEGREES CELSIUS

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

2000 2001

EXPLANATION

WATER YEAR 2001
18 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

temperature may explain why summer low flows have 

a relatively high percentage of streamflow loss. The 

hydraulic conductivity of a porous material (including 

streambed material) is influenced by water temperature; as water temperature increases, the viscosity of 

water decreases. Constanz and Murphy (1991) 

reported that an increase of water temperature from 0 to 

25 degrees Celsius (°C) results in a doubling of 

ponded-infiltration rates through streambeds. 

Ground-Water Levels and Flow Directions

Water levels in monitoring wells and inventoried 

wells ranged from about 12 feet to more than 200 feet 

below land surface (Bowers and others, 2003). Water 

levels in about 70 alluvial wells measured primarily 

during August and September 2000 were used to construct the water-table map of the area between Post 

Falls and Spokane (fig. 7). Based on the generalized 

Figure 7. Generalized water table of the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, 

Washington.

WASHINGTON

IDAHO

EXPLANATION

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

AREA OF GROUND-WATER MOUND OR STEEP SLOPE

 OF WATER TABLE—Water-table altitudes range from

 1,970 to 2,040 feet above NGVD 29

90

90

?

Post Falls

Spokane

Highway 290

Seltice Way

Harvard Road

Barker Road

Sullivan Road

Spokane

River

Liberty

Lake

1,990

1,970

1,980

1,960

1,950

1,940

1,970

1,990

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

1,970

WELL—Water level measured August-September, 2000

APPROXIMATE DIRECTION OF GROUND-WATER FLOW

WELL—Water level measured March, 2000

WATER TABLE CONTOUR—Shows altitude of water

 table, 2000. Dashed where approximately located.

 Contour interval 10 feet. Queried where uncertain.

 Vertical datum is NGVD 29

MILES

KILOMETERS

0

0

6

1 3 2 45 6

135 2 4

T.51N.

T.50N.

T.26N.

T.25N.

R.44E. R.45E. R.6W. R.46E. R.5W.

117o10' 117o00'

47o42'30"

47o40'

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)
GROUND-WATER LEVELS AND FLOW DIRECTIONS 19

water-table contours (fig. 7), the hydraulic gradient for 

the regional flow system in the central part of the valley 

is about 0.001 (5.4 feet per mile), which is consistent 

with the reported high transmissivity for the aquifer. 

However, the hydraulic gradient determined using data 

for the monitoring wells near the losing reach of the 

river is more than an order of magnitude larger (0.08 or 

422 feet per mile). This large hydraulic gradient results 

from localized recharge from the river and possibly 

less-permeable, near-river aquifer material. A possible 

cause of the lower permeability in the near-river part of 

the aquifer (near-river aquifer) is a larger proportion of 

fine-grained material, which had been transported into 

the interstitial spaces of the aquifer by leakage from the 

river.

Figure 8 displays generalized hydrogeologic sections of the SVRP aquifer showing selected monitoring 

wells. Water levels in nearly all of the wells were below 

that of the river, and the slope of the water table was 

away from the river (fig. 8), which indicates that water 

was flowing from the river into the aquifer. These findings are consistent with a study by Gearhart and 

Buchanan (2000), who concluded that the river lost 

streamflow between Post Falls and the Barker Road 

bridge near Spokane (fig. 3) with unsaturated conditions between the river and aquifer. Downstream near 

well 25 (fig. 3), Gearhart and Buchanan (2000) determined that the river was transitional as it varied from 

losing to gaining as the water table and river stage fluctuated.

Because water levels in most wells were tens of 

feet below the river, previous investigations concluded 

that unsaturated conditions exist between the river and 

the water table along most of the upper Spokane River. 

However, previous studies did not have wells located as 

close to the river as this study did. Water levels in nearriver wells indicate that saturated conditions may exist 

below some parts of the losing reach of the Spokane 

River. Conditions appear saturated below the river in 

the vicinity of wells 1 and 2, as the water-level altitude 

in the shallow well (2) is similar to the altitude of the 

bottom of the river channel (fig. 8a). Saturated conditions also may exist at locations shown in figures 8b, 

8c, and 8d. The water table would intercept the river at 

those locations if the water table measured in the nearriver wells were extended towards the river along a similar gradient. Farther downstream (figs. 8e and 8f), the 

slope of the water table is relatively flat and well below 

the river, especially for the August 2001 data, and likely 

indicates unsaturated conditions in that area. 

Conditions beneath the river may not only vary 

from saturated to unsaturated spatially, but also with 

time and river stage. There is considerable variability 

in the observed hydraulic gradients in the near-river 

aquifer indicating that leakage, streambed conductance, and/or aquifer properties may vary along the 

losing reach of the river. Hydraulic gradients at the 

more downstream wells (figs. 8e and 8f) were nearly 

flat (less than 0.01) during low streamflow in August 

2001, indicating that less water is leaking from the 

river within those areas or that the near-river aquifer is 

more permeable as compared to upstream. However, 

during May 2001 when streamflow was large and 

leakage increased, the water table would intercept the 

river based on the water-table gradient at wells 18 and 

19 (fig. 8e). Unsaturated conditions beneath the river 

still appeared to exist at the downstream wells (fig. 8f) 

during May 2001.

Downward components of flow are large where 

water enters the ground as recharge, as would be 

expected along a losing reach of the Spokane River. 

Water levels in pairs of shallow and deep near-river 

wells (wells 1 and 2, 4 and 5, 8 and 9, and 11 and 12) 

indicate a large downward component of flow in the 

near-river aquifer. Water-level altitudes were lower in 

the deep near-river wells and higher in the shallow 

wells. A downward component of flow is smaller in 

wells completed at different depths farther from the 

river, indicating dominant horizontal flow representative of the regional flow system. 

Hydrographs for water year 2001 for the monitoring wells are presented in figure 25 in the appendix. 

Temporal water levels for individual monitoring wells 

(based on hourly to biweekly measurements) varied 

from 4.7 to 18.4 feet during water year 2001. The 

water-level variations primarily represent the response 

to changes in recharge, pumping, and river stage. 

Water levels in most of the wells (3, 4, 6, 7, 12, 14, 15, 

16, 17, 18, 20, 21, 22, 23, 24, and 25) followed the 

same general trend, whereas water levels in the 

shallow near-river wells (1, 2, 5, 8, 9, 10, 11, 13, and 

19) often deviated from that trend (fig. 25). 

Figure 9 illustrates river stage of the Spokane 

River at Post Falls, calculated streamflow losses, and 

water levels in a representative shallow near-river well 

(11) and a representative regional ground-water 

system well (14). The river stage is used as a relative 

measure of streamflow, with higher stages corresponding to greater streamflows. 
20 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 8. Generalized hydrogeologic sections of the Spokane River channel and Spokane Valley/Rathdrum Prairie 

aquifer showing selected monitoring wells including water levels and inferred water table. Well locations are 

shown in figure 3. ALTITUDE, IN FEET ABOVE NGVD 29

0 100 200 300 400

1,950

2,000

2,050

2,100

2,150

2 1

S N

DISTANCE, IN FEET

Spokane River

sand and gravel

silt and sand

A. Wells 1 and 2

1,900

1,950

2,000

2,050

2,100

7

?

S N

6 4 5

DISTANCE, IN FEET

100 200 300 400 500 600 700 800 900 1,000

Spokane River

0

Water table

Sand and gravel

B. Wells 4, 5, 6, and 7

1,900

1,950

2,000

2,050

2,100

W E

10 8 9

?

DISTANCE, IN FEET

Water table

Spokane River

Sand and gravel

0 100 200 300 400 500 600 700

C. Wells 8, 9, and 10

Water level 8-23-01

Water level 8-14-01

Water level 8-23-01

VERTICAL EXAGGERATION 1.5X

VERTICAL EXAGGERATION 1.5X

VERTICAL EXAGGERATION 1.5X
GROUND-WATER LEVELS AND FLOW DIRECTIONS 21

Figure 8. Generalized hydrogeologic sections of the Spokane River channel and Spokane Valley/Rathdrum Prairie 

aquifer showing selected monitoring wells including water levels and inferred water table. Well locations are 

shown in figure 3 (Continued). ALTITUDE, IN FEET ABOVE NGVD 29

0 100 200 300 400 500 600 700 800

1,900

1,950

2,000

2,050

2,100

18 19

SE NW

1,900

1,950

2,000

2,050

2,100

S N

?

?

?

?

DISTANCE, IN FEET

Spokane River

E. Wells 18 and 19

Water table

Water table

0 1,000 2,000 3,000 4,000 5,000

20

21 22

23

24

Spokane

 River

Sand and gravel

DISTANCE, IN FEET

F. Wells 20 through 24

Water table

Water table

Water level 5-02-01 through 5-03-01

Water level 8-14-01 through 8-15-01

Water level 5-01-01

Water level 8-23-01

Water table

Water table

1,875

1,925

1,975

2,025

2,075

11 12 13

S N

15

?

DISTANCE, IN FEET

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

14

Sand and gravel

16

Spokane

 River

Water table

D. Wells 11 through 16

Water level 8-13-01 through 8-15-01

VERTICAL EXAGGERATION 6X

VERTICAL EXAGGERATION 1.5X

VERTICAL EXAGGERATION 7.5X
22 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 9. Spokane River stage, water levels in representative wells, and calculated streamflow loss, water year 2001.

200

400

600

800

2,010

2,000

2,020

1,980

1,970

1,990

STREAMFLOW LOSS,

IN CUBIC FEET PER SECOND

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

2000 2001

EXPLANATION

1,950

1,960

0

RIVER STAGE—Spokane River at Post Falls, Idaho (station 12419000)

RIVER STAGE AND GROUND-WATER

ALTITUDE, IN FEET ABOVE NGVD 29

DAILY MEAN STREAMFLOW LOSS—Calculated between Post Falls,

 Idaho (station 12419000), and Otis Orchards, Washington

 (station 12419500)

WELL 14—475 feet from river

WELL 11—100 feet from river (shallow)

WATER YEAR 2001

Water levels in all wells increased coincident 

with the high streamflow events in April and May 2001 

(example wells 11 and 14, fig. 9). These ground-water 

level rises are consistent with increased recharge to the 

aquifer from river leakage, but also may be consistent 

with increased regional recharge to the aquifer from 

precipitation and snowmelt during those months. More 

conclusive evidence of direct river influence on groundwater levels is the rise in water levels in all monitored 

wells in response to a distinct and abrupt change in river 

stage as flow was increased at the Post Falls dam during 

September 2001 (fig. 9). Piper and La Rocque (1944) 

observed this phenomenon during one of the initial 

investigations of the aquifer. They noted that groundwater level fluctuations were similar to fluctuations of 

stage in the river and primarily were a backwater effect 

of fluctuating river stage. Water moves between a river 

and a hydraulically connected aquifer depending on the 

head gradient. As the stage rises to a level higher than 

the water level in the adjacent hydraulically connected 

aquifer, water flows from the river to the aquifer and 

water levels in the near-river aquifer increase. The 

combination of increased stage (where hydraulically 

connected) and increased recharge along the losing 

reach of the river are both contributors to the rise in the 

water table that is propagated throughout the study 

area. 

Although river stage and streamflow loss are 

strongly associated, water levels in most near-river 

wells continued to rise or remain stable coincident with 

declining river stage during the summer (example 

well 11, fig. 9). This rise of the near-river water table 

during the summer apparently resulted from increased 

recharge from the river due to the decrease in water viscosity as the water temperatures increased. In contrast, 

the summer water levels in deeper wells and in wells 

farther from the river appeared to follow the downward 

trend representative of the regional ground-water 

system (example well 14, fig. 9). Conceptually, ground 

water in the shallow near-river aquifer has a steep gradient away from the river or is a mound of the water 

table underlying the river that exists only because of 
WATER TEMPERATURE 23

recharge from the river. Therefore, water levels in the 

near-river aquifer are controlled by hydraulic properties of the aquifer material and the amount of local 

recharge from the river, in combination with waterlevel fluctuations of the regional system.

Water levels in near-river wells 2, 4, 8, 9, 11, and 

at times well 19 responded very rapidly to changes in 

river stage and/or streamflow loss (fig. 25; well 11, 

fig. 9). The rapid response to changes in stage in the 

near-river wells is consistent with saturated conditions 

or a thin unsaturated zone between the river and the 

underlying aquifer at those locations. The difference in 

the magnitude of the response to river-stage fluctuations among the near-river wells may result from differing hydraulic properties in the near-river aquifer and 

streambed material, and the resulting amount of 

leakage from the river. 

Water levels in near-river wells downstream indicate unsaturated or transitional conditions between the 

river and underlying aquifer. Water levels in well 19 

varied from obvious responses to changes in river stage 

during the spring high-flow conditions to more subtle 

or delayed responses at other times (fig. 25). The variation in response to river stage and the temporal change 

in the hydraulic gradient (discussed previously) indicate that conditions may vary from saturated to unsaturated below the river at that location. Ground-water 

levels obtained during this study and continuous data 

from Gearhart and Buchanan (2000) showed only 

small-scale or delayed responses to fluctuations in river 

stage at the downstream wells (wells 21-23, fig. 8f), 

indicative of unsaturated conditions or less leakage 

from the river at that location. 

Water Temperature

Water temperature appears to be a useful tracer 

of the ground-water recharge from the Spokane River. 

Measured water temperatures for each of the 25 monitoring wells are included in figure 25. Temperatures 

varied about 22°C from near 2 to 24°C in the river at 

Post Falls during water year 2001 (fig. 6). Groundwater temperature variations for individual wells 

ranged from 0.1°C (well 16) to 23.4°C (well 9) during 

the year. More stable ground-water temperatures characterized the regional system, whereas water temperatures in near-river wells were more variable, indicative 

of local recharge. 

Temperature ranges observed in the river and 

wells along a generalized hydrologic section are illustrated in figure 10, and temporal variations are shown 

in figure 11. The greatest range of temperatures 

occurred in the Spokane River, and in wells 11 through 

14 (fig. 10). Temperatures in wells farther from the 

river (wells 15 and 16) were relatively constant. The 

temperature variations in the river and wells 11 through 

Figure 10. Generalized hydrologic section showing temperature range of the Spokane River measured at Post Falls, 

Idaho, and ground water from wells 11 through 16, water year 2001.

RANGE IN WATER TEMPERATURE,

 IN DEGREES CELSIUS

20.6

EXPLANATION

11 WELL NUMBER

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

ALTITUDE,

IN FEET ABOVE NGVD 29

1,875

1,925

1,975

2,025

2,075

22.7

Water table

S N

20.6 0.4 0.1

Spokane River?

21.7 20.5 18.7 14

11 12 13 15

16

DISTANCE, IN FEET

Water level 8-13-01 through 8-15-01

VERTICAL EXAGGERATION 6X
24 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

14 are similar (fig. 11), indicating that water recharging 

the aquifer from the river travels quickly. The sharp 

contrast in temperature variation between well 14 

(about 475 feet from the river) and well 15 (about 

900 feet from the river) (fig. 11) indicates that recharge 

water from the river is constrained within a relatively 

narrow zone (less than 900 feet from the river) at that 

location. 

Water temperature in several wells (2, 4, 5, 6, 8, 

9, 10, 11, 12, 13, 14, and 23) responded rapidly to temperature changes in the river and also followed the 

same general temperature variation (fig. 25). The rapid 

response in these wells indicates that river water is 

flowing to these wells quickly. Water-temperature 

variations in wells 1, 19, 21, and 22 also appear to be 

affected by river recharge, but the temperature variations did not coincide with the river temperature, and 

the magnitude of the temperature variations were not as 

great (fig. 12). These wells include a component of 

river recharge, but represent water with longer traveltimes from the river to these wells, the effects of water 

traveling through an unsaturated zone, possibly a mixture of water of different origins, or some combination 

of these three processes. Temperatures in other wells 

(3, 7, 15, 16, 17, 18, 20, 24, and 25) varied by only a 

few degrees during the study (fig. 25), indicative of 

more regional ground water that is unaffected by local 

river recharge. 

Water Chemistry

The surface water and ground water sampled for 

this study was of good quality and generally acceptable 

for most purposes. All constituents analyzed were at 

Figure 11. Temperature record of the Spokane River measured at Post Falls, Idaho, and ground water from 

wells 11 through 16, water year 2001.

0

5

10

15

20

25

30

SPOKANE RIVER AT POST FALLS, 

 IDAHO (station 12419000)

WELL 11

WELL 12 

WELL 13 

WELL 14 

WELL 15 

WELL 16 

Missing data

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

WATER TEMPERATURE, IN DEGREES CELSIUS

2000 2001

WATER YEAR 2001

EXPLANATION
WATER CHEMISTRY 25

concentrations less than USEPA drinking-water standards (U.S. Environmental Protection Agency, 2002a). 

Physical properties and water chemistry data for the 

Spokane River and ground water sampled as part of this 

study are included in Bowers and others (2003). 

Median concentrations of selected physical 

properties and major ions of the Spokane River and 

monitoring wells are listed in table 5. The sampled 

waters were generally of low ionic concentrations with 

median dissolved-solids concentrations less than 

200 milligrams per liter (mg/L) at all sites. Median 

dissolved-solids concentrations were 34 mg/L in the 

river at Post Falls and ranged from 37 to 196 mg/L in 

the ground-water samples. Field values of pH ranged 

from 6.4 to 8.2 (Bowers and others, 2003), with only 

one sample (well 23, pH of 6.4) outside the acceptable 

USEPA Secondary Drinking Water Regulation 

(SDWR) range of 6.5 to 8.5 (U.S. Environmental 

Protection Agency, 2002a). 

Specific Conductance

Specific-conductance data (an indication of dissolved solids) from this study and others (Bolke and 

Vaccaro, 1979; Parliman and others, 1980; Stone and 

others, 1996) shows that ground water adjacent to the 

losing reach of the Spokane River has a lower ionic 

strength than regional ground water (fig. 13). The river 

had the lowest measured specific conductance values 

(median of 50 microsiemens per centimeter). The 

lower specific conductance in near-river wells is further 

evidence of river water recharging the aquifer. 

Major Ions

In samples from the Spokane River and the 25 

monitoring wells, bicarbonate generally had the 

highest concentrations of the major ions, followed by 

calcium, sulfate, sodium, magnesium, chloride, and 

potassium (table 5). Fluoride and bromide concentrations were less than 0.2 mg/L in all samples (Bowers 

and others, 2003). The relative proportions of major 

ions in ground water and the Spokane River generally 

were similar (fig. 14)—all calcium magnesium bicarbonate type waters. River source, transitional, and 

regional ground water shown in figure 14 are defined in 

the following discussion of dissolved solids.

Figure 12. Temperature record of the Spokane River measured at Post Falls, Idaho, and ground water from 

wells 1, 19, 21, and 22, water year 2001.

0

5

10

15

20

25

30

SPOKANE RIVER AT POST FALLS, 

 IDAHO (station 12419000)

WATER TEMPERATURE,

IN DEGREES CELSIUS

2000 2001

WATER YEAR 2001

EXPLANATION

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

WELL 1

WELL 19 

WELL 21

WELL 22
26 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Table 5. Median specific conductance, pH, and major-ion concentrations of the Spokane River and ground water from monitoring wells 

within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L milligrams per liter]

Site1/well 

number2

Number 

of

samples

collected

Specific 

conductance, 

field

(μS/cm)

pH,

field 

(standard 

units)

Calcium, 

dissolved

(mg/L as 

Ca)

Magnesium,

dissolved

(mg/L as 

Mg)

Sodium, 

dissolved

(mg/L as 

Na)

Potassium,

dissolved

(mg/L as 

K)

Bicarbonate, 

dissolved

(mg/L as 

HCO3)

Sulfate, 

dissolved

(mg/L as 

SO4)

Chloride,

dissolved

(mg/L as 

Cl)

Dissolved 

solids,

calculated

(mg/L)

Spokane River 28 50 7.4 5.4 1.6 1.7 0.71 22 4.2 0.90 34

1 7 74 6.7 9.2 2.5 2.5 .82 39 5.0 1.3 54

2 8 54 7.1 5.8 1.8 1.8 .66 24 5.0 .92 38

3 5 284 8.0 32 15 2.9 2.2 156 12 2.4 156

4 8 52 7.0 5.8 1.7 1.9 .78 26 4.6 1.0 38

5 7 54 6.8 5.8 1.7 2.0 .77 26 4.8 .98 38

6 7 54 6.9 5.8 1.7 1.9 .76 26 4.7 .93 37

7 7 87 7.2 11 2.8 2.0 .95 46 4.9 1.2 57

8 9 54 7.0 5.7 1.7 1.8 .73 26 4.8 .98 37

9 8 54 7.0 5.8 1.7 1.8 .72 26 4.8 1.1 38

10 7 54 7.0 5.7 1.7 1.8 .74 26 4.8 1.0 37

11 7 52 7.0 5.7 1.7 1.8 .69 24 4.5 1.0 38

12 6 52 7.0 6.0 1.8 1.9 .70 26 4.8 1.0 38

13 7 53 7.0 6.1 1.8 1.9 .65 26 4.9 1.1 38

14 6 56 7.2 6.6 1.8 2.0 .68 28 4.9 1.0 40

15 7 307 7.8 35 17 2.8 2.2 181 15 1.8 174

16 6 323 7.7 37 18 3.0 2.0 191 16 1.6 182

17 7 91 7.8 12 2.7 1.8 .94 49 4.5 1.0 57

18 7 58 7.0 7.2 1.8 1.8 .81 30 4.2 1.1 42

19 7 53 6.9 5.9 1.6 1.9 .79 26 4.6 .88 39

20 6 134 7.4 16 5.4 2.2 1.2 71 6.5 1.6 80

21 6 52 6.8 6.0 1.6 1.8 .69 26 5.0 1.0 38

22 6 53 6.8 5.8 1.7 1.8 .74 26 4.7 1.0 38

23 6 58 6.8 6.4 1.8 1.9 .74 26 4.9 1.3 40

24 6 346 7.7 42 18 3.1 2.1 208 16 1.4 196

25 6 259 7.9 30 13 2.8 1.7 150 12 1.7 147

1Spokane River sampled at Post Falls, Idaho (station 12419000).

2Number corresponds to wells listed in table 1 and shown in figure 3.
WATER CHEMISTRY 27

Figure 13. Specific conductance of ground-water samples from the Spokane Valley/Rathdrum Prairie aquifer, Idaho and Washington.

Post

Falls

Hayden

Coeur d'Alene

Athol

Deer

Park Bayview

Sandpoint

Newport

Spokane

Lake

Pend Oreille

Coeur

d'Alene

Lake

Hayden

Lake

Little

Spokane

River

River

River

Priest

Pend

Oreille

Spokane

River

T.57N.

T.56N.

T.55N.

T.54N.

T.53N.

T.52N.

T.51N.

T.50N.

T.49N.

T.48N.

T.32N.

T.31N.

T.30N.

T.29N.

T.28N.

T.27N.

T.26N.

T.25N.

T.24N.

T.33N.

B O N N E R C O

K O O T E N A I

C O

S H O S H O N E C O

S P O K A N E C O

S T E V E N S C O

P E N D

O R E I L LE

C O

WASHINGTON

IDAHO

R.42E. R.43E. R.44E. R.45E. R.5W. R.46E. R.6W. R.4W. R.3W. R.2W. R.1W. R.1E. R.2E.

R.40E.

R.41E.

SPOKANE

INDIAN

RESERVATION

EXPLANATION

GENERAL EXTENT OF BASIN-FILL AQUIFERS.

 REGIONAL GROUND-WATER QUALITY

 ASSESSMENT AREA (BOWERS

 AND OTHERS, 2003)

APPROXIMATE BOUNDARY OF SPOKANE VALLEY/

 RATHDRUM PRAIRIE AQUIFER

0 5 10 15 KILOMETERS

0 5 10 15 MILES Extent of basin-fill aquifers modified from Stoffel

and others (1991) and Tuck and others (1996)

117o30' 116o45'

48o

47o45'

0 to less than 100

100 to less than 200

200 to less than 300

Greater than or equal to 300

SPECIFIC CONDUCTANCE, IN MICROSIEMENS

 PER CENTIMETER AT 25 DEGREES CELSIUS

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)
28 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 14. Trilinear diagram showing major-ion composition of the Spokane River at Post Falls, Idaho, and ground water 

from 25 monitoring wells from the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, 

Washington.

SPOKANE RIVER AT POST FALLS,

 IDAHO (station 12419000)

GROUND WATER

River source

Transitional

Regional

EXPLANATION

PERCENTAGE OF TOTAL MILLIEQUIVALENTS PER LITER

CALCIUM ANIONS CHLORIDE ANIONS

100

80

60

40

20

0

100

80

60

40

20

0

0

20

40

60

80

100

BICARBONATE

SULFATE

0

100

100

80

60

40

20

0

100

80

60

40

20

0

MAGNESIUM

SODIUM PLUS POTASSIUM

20

40

60

80

CALCIUM PLUS MAGNESIUM

80

100

60

40

20

0

80

100

60

40

20

0

SULFATE PLUS CHLORIDE

Dissolved-solids concentrations varied with 

location, with the river having the lowest concentrations and ground water farthest away from the river or 

in the area where ground water discharges to the river 

having the highest concentrations (fig. 15). The similarity in major-ion concentrations between samples 

from the river and several of the near-river monitoring 

wells indicates that river water with low major-ion concentrations recharges the aquifer along the upper 

reaches of the Spokane River from Post Falls to near 

Spokane. 

Ground-water wells were categorized into three 

groups (figs. 14 and 15) based on median dissolvedsolids concentrations: (1) river-source wells, in areas 

where ground water primarily originated from the 

Spokane River; (2) regional wells, in areas where 

ground water did not include water recently recharged 

from the river; and (3) transitional wells, in areas where 

ground water was possibly a composite of recharge 

from the river and water from the regional system. The 

river-source wells had water with median dissolvedsolids concentrations similar to those of the river (less 
WATER CHEMISTRY 29

than 50 mg/L), were within 650 feet of the river, and 

had water-level data indicative of local flow (recharge) 

from the river. The regional wells had water with 

dissolved-solids concentrations of greater than 

100 mg/L, ranged from 100 feet (well 25, which is 

located in an area of ground-water discharge to the 

river) to 3,500 feet from the river, and were in areas 

with relatively flat hydraulic gradients. The transitional wells had water with moderate dissolved-solids 

concentrations between 50 and 100 mg/L, ranged from 

500 to 2,600 feet from the river, and possibly 

represented a mixture of the river-source and regional 

ground water. Although the relative proportions of 

major ions in the river and ground-water samples generally were similar, ground water categorized as transitional or regional generally had slightly greater relative 

proportions of calcium, magnesium, and bicarbonate 

than the river and river-source ground water (fig. 14). 

Dissolved-solids concentrations of all the samples collected from the river and the three well categories are 

illustrated in the boxplots in figure 16. 

Figure 15. Median dissolved-solids concentrations of samples collected from the Spokane River at Post Falls, Idaho, and 

ground water classified as river-source, transitional, or regional ground water in the Spokane Valley/Rathdrum Prairie 

aquifer, Idaho and Washington, 1999-2001.

WASHINGTON

IDAHO

EXPLANATION

90

90

Post Falls

Spokane

Highway 290

Seltice Way

Harvard Road

Barker Road

Sullivan Road

Spokane

River

Liberty

Lake

4,5

23

21 22

18 19

3

25

24

16

15 10

8,9

6

14 13

11,12

2

12419000

12419000

1

20

17

7

1

3

2

MEDIAN DISSOLVED-SOLIDS CONCENTRATION,

 WELL CLASSIFICATION, AND WELL NUMBER 

Less than 50 milligrams per liter - River-source ground water 

50 to 100 milligrams per liter - Transitional ground water 

Greater than 100 milligrams per liter - Regional ground water 

U.S. GEOLOGICAL SURVEY STREAMFLOW-GAGING

 STATION AND NUMBER—Median dissolved-solids

 concentration less than 50 milligrams per liter

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

MILES

KILOMETERS

0

0

6

1 3 2 45 6

135 2 4

T.51N.

T.50N.

T.26N.

T.25N.

R.44E. R.45E. R.6W. R.46E. R.5W.

117o10' 117o00'

47o42'30"

47o40'

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)
30 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 16. Boxplots summarizing dissolved-solids concentrations of samples collected from the Spokane River at 

Post Falls, Idaho (station 12419000, water years 1999 through 2001), and ground water identified as river source, 

transitional, or regional (June 2000 through August 2001) from the Spokane Valley/Rathdrum Prairie aquifer between 

Post Falls, Idaho, and Spokane, Washington.

0

50

100

150

200

250

Spokane

River

Ground

water, river

source 

Ground

water,

 transitional

Ground

water,

regional 

28 27 112 30

EXPLANATION

Number of samples

Outliers

90th percentile

75th percentile

Median

25th percentile

10th percentile

Outliers

30

CONCENTRATION, IN MILLIGRAMS PER LITER

Trace Elements

A summary of trace-element concentrations for 

the Spokane River and ground-water samples and 

drinking-water standards are listed in table 6. All concentrations in surface-water and ground-water samples 

were less than USEPA drinking-water standards 

(table 6). However, trace-element concentrations in 

river samples did exceed freshwater aquatic-life criteria 

(U.S. Environmental Protection Agency, 2002b). 

Beckwith (2003) reported that zinc concentrations 

exceeded aquatic-life criteria in 22 of the 26 samples 

collected at Post Falls. Other metals in the river, 

including cadmium, copper, and lead, exceeded 

aquatic-life criteria for the reported hardness levels 

(Bowers and others, 2003). Dissolved (0.45-μm filtration) and total-recoverable concentrations of trace elements of particular interest (arsenic, cadmium, lead, 

and zinc) in the river and ground water are listed in 

table 8 in the appendix. 

Based on 1999 and 2000 data, Clark (2003) calculated that 4,600 pounds per year (lb/yr) cadmium, 

44,000 lb/yr lead, and 980,000 lb/yr zinc was discharged from Coeur d’Alene Lake and was transported 

to the Spokane River (at Post Falls, Idaho). Clark 

(2003) estimated losses of 900 lb/yr of cadmium and 

80,000 lb/yr of zinc from the Spokane River in the 

reach between Post Falls and about 39 miles downstream at 7-mile Bridge near Spokane (fig. 2). It was 

speculated that river leakage to the aquifer may account 

for most of the decreased loads along that reach of the 

Spokane River.

Boxplots of trace-element concentrations for 

water year 2001 data (a period of consistently low analytical reporting levels) indicate that the Spokane River 

is a likely source of cadmium, copper, zinc, and possibly lead in the near-river aquifer (fig. 17). Zinc had 

the highest concentrations (up to 71 μg/L in ground 

water) compared to the other trace elements (figs. 17 

and 18). Median dissolved concentrations of cadmium, 

copper, and zinc were the highest in the river and in the 

near-river wells adjacent to the losing reach of the river. 

Median dissolved lead concentrations were highest in 

the river with sporadic occurrences higher than 

reporting levels in the river-source and transitional 

ground water (fig. 17), which could be related to a river 

source. 
WATER CHEMISTRY 31

Table 6. Summary of selected trace element data collected from the Spokane River and ground water from monitoring wells within the Spokane V1999-2001[Due to changing analytical reporting levels, some maximum values are less than the median values. The Maximum Contaminant Level (MCL) is a regulated level thgenerally must meet. The Lifetime Health advisory (LHA) is a nonenforceable guideline for non-carcinogens determined based on a 70-kilogram adult consuming 2 lifetime. The Action Levels (ALs) for lead and copper are regulated according to Treatment Types, which may be considered analogous to an MCL for these element

(CMC) is an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed briefly without resulting in an unacce

Concentration (CCC) is an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed indefinitely without res

micrograms per liter; e, estimated; <, less than; --, no data]

Trace

elements

Spokane River at Post Falls, Idaho (station 12419000) Ground water

Drinking-water

standard1

(μg/L)

 Median

dissolved

(μg/L)

Maximum

dissolved

(μg/L)

Median total

recoverable

(μg/L)

Maximum total 

recoverable

(μg/L)

Median

dissolved

(μg/L)

Maximum

dissolved

(μg/L)

Antimony <1.0 <1.0 <1.0 <1.0 0.35 0.94 6 (MCL) Arsenic <.90 0.59 <2.6 1.6 .35 4.6 10 (MCL) Barium 11 14 12 14 14 32 2,000 (MCL) Beryllium <1.0 <1.0 <5.0 <5.0 <.06 .04 4 (MCL) Boron <12 e8.2 -- -- 5.8 25 3600 (LHA) Cadmium <1.0 .22 .21 .44 <.04 .68 5 (MCL) Chromium <.80 e.40 <1.0 e.58 .54 11 100 (MCL) Copper <1.0 1.5 <12 e14 .56 7.4 1,300 (AL) Lead <1.0 1.6 1.0 7.8 <.08 1.6 15 (AL) Mercury -- -- <.30 <.30 -- -- 2 (MCL) Molybdenum <1.0 <1.0 <1.0 1.8 .11 2.0 40 (LHA) Nickel <1.0 <1.0 <1.8 <1.8 .35 9.8 100 (LHA) Selenium <.70 e1.5 <2.6 <2.6 <.33 e .43 50 (MCL) Strontium 17 21 16 21 20 137 4,000 (LHA) Thallium <.90 <.90 -- -- <0.04 .18 2 (MCL) Uranium <1.0 <1.0 -- -- < 0.02 3.9 30 (MCL) Zinc 54 90 63 96 12 71 2,000 (LHA) 1U.S. Environmental Protection Agency (2002a) drinking-water or health advisory.2U.S. Environmental Protection Agency (2002b) National Recommended Water Quality Criteria: 2002. Values are expressed as dissolved concentrations.3Under review.4Value based on median hardness (20 mg/L as CaCO3) of the Spokane River at Post Falls, Idaho (Bowers and others, 2003).5Chromium III criteria.
32 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 17. Boxplots summarizing dissolved concentrations of selected trace elements in samples collected from the Spokane River at 

Post Falls, Idaho (station 12419000), and ground water identified as river source, transitional, or regional from the Spokane Valley/

Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, water year 2001.

EXPLANATION

Number of samples

Outliers

90th percentile

75th percentile

Median

25th percentile

10th percentile

Outliers

30

Spokane

River

Ground

water, riversource 

Ground

water,

transitional

Ground

water,

regional 

Spokane

River

Ground

water, riversource 

Ground

water,

transitional

Ground

water,

regional 

9 92 22 28

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

9 92 22 28

5

4

3

2

1

0

CONCENTRATION, IN MICROGRAMS PER LITER

9 92 22 28

100

10

1

0.1

0.01

9 92 22 28

2.0

1.5

1.0

0.5

0

9 22 92 28

80

70

60

50

40

30

20

10

0

Reporting level

Note: Values less than reporting levels are plotted

 as one-half the reporting levels

CONCENTRATION, IN MICROGRAMS PER LITER

ARSENIC

COPPER

ZINC

CADMIUM

LEAD

Median=0.6
WATER CHEMISTRY 33

Figure 18. Median dissolved zinc concentrations of samples collected from the Spokane River at Post Falls, Idaho, and ground 

water from the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, water year 2001. WASHINGTON IDAHO

EXPLANATION

90

90

Post Falls

Spokane

Highway 290

Seltice Way

Harvard Road

Barker Road

Sullivan Road

Spokane

River

Liberty

Lake

4,5

23

21 22

19

10

8,9

6

13

11,12

2

2

12419000

12419000

1

1

20

17

7

3

24

16

18

15 14

25

MEDIAN DISSOLVED ZINC CONCENTRATION, IN

 MICROGRAMS PER LITER, AND WELL NUMBER

Less than 1.0 

Equal to or greater than 1.0 

U.S. GEOLOGICAL SURVEY STREAMFLOW-GAGING

 STATION AND NUMBER—Median dissolved zinc

 concentration equal to or greater than 1.0 microgram

 per liter

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

MILES

KILOMETERS

0

0

6

1 3 2 45 6

135 2 4

T.51N.

T.50N.

T.26N.

T.25N.

R.44E. R.45E. R.6W. R.46E. R.5W.

117o10' 117o00'

47o42'30"

47o40'

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985

North American Datum of 1927 (NAD 27)

Arsenic in ground water does not appear to have 

originated from the Spokane River and probably is 

derived through the natural interaction of water with 

rocks and soils. Arsenic concentrations were consistently highest in regional wells (up to 4.5 μg/L) with 

concentrations in the river and the river-influenced 

wells all less than 1.0 μg/L (figs. 17 and 19). Data collected during a regional ground-water assessment as 

part of the NROK NAWQA in 1999 corroborate these 

findings (Bowers and others, 2003). Water samples 

from three wells along the losing reach of the river had 

arsenic concentrations of less than 1.0 μg/L. Water 

samples from three wells in the aquifer from the 

regional study exceeded the USEPA Maximum Contaminant Level of 10 μg/L (Bowers and others, 2003). 

The river also does not appear to be a significant source 

of lithium, molybdenum, strontium, and uranium 

because concentrations of these trace elements were 

elevated in the regional ground water as compared to 

the river or the river-source wells (Bowers and others, 

2003).

Although the trace-element concentrations are 

relatively low in the surface and ground water, concentrations in streambed sediment collected in the Spokane River are elevated (Beckwith, 2002). Elements 

of particular environmental concern include arsenic, 
34 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

cadmium, chromium, copper, lead, mercury, nickel, 

selenium, and zinc because of toxicity to aquatic and 

terrestrial biota. Concentrations of these trace elements 

(excluding selenium) in the bed sediment from the river 

at Post Falls exceeded the national median value of 

samples collected between 1992 and 1996 as part of the 

NAWQA Program (Beckwith, 2002). Of particular 

interest were high concentrations of lead (1,620 micrograms per gram (μg/g)) and zinc (3,210 μg/g). Because 

the bed sediment has elevated concentrations of trace 

elements, the potential exists for transport of dissolved 

and particulate trace elements from the river to the 

aquifer. 

Particulate transport of trace elements in ground 

water was examined by collecting total-recoverable 

(whole-water, unfiltered) samples and filtered 

(0.45 μm) samples from selected wells. Total-recoverable zinc concentrations were consistently equal to or 

greater than the filtered concentrations in all samples 

with measurable (greater than the reporting limit) zinc 

concentrations (table 7). Measurable cadmium concentrations were low (less than 1.0 μg/L), and the totalrecoverable concentrations were equal to or greater 

than filtered concentrations, with only one exception 

(table 7). Total-recoverable lead was detected in five 

samples from the shallow, near-river wells (2, 5, 8, and 

11) at concentrations ranging from 1.3 to 4.2 μg/L and 

Figure 19. Median dissolved arsenic concentrations of samples collected from the Spokane River at Post Falls, Idaho, and ground water 

from the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, water year 2001. WASHINGTON IDAHO

EXPLANATION

90

90

Post Falls

Spokane

Highway 290

Seltice Way

Harvard Road

Barker Road

Sullivan Road

Spokane

River

Liberty

Lake

25

24

20

16

15

3

3

12419000

12419000

1

1,2

4,5

23

21 22

17

18 19

10

8,9

6

14 13 7

11,12

MEDIAN DISSOLVED ARSENIC CONCENTRATION, IN

 MICROGRAMS PER LITER, AND WELL NUMBER 

Less than 1.0 

Equal to or greater than 1.0 

U.S. GEOLOGICAL SURVEY STREAMFLOW-GAGING

 STATION AND NUMBER—Median dissolved zinc

 concentration less than 1.0 microgram per liter

SPOKANE VALLEY/RATHDRUM PRAIRIE AQUIFER

MILES

KILOMETERS

0

0

6

1 3 2 45 6

135 2 4

T.51N.

T.50N.

T.26N.

T.25N.

R.44E. R.45E. R.6W. R.46E. R.5W.

117o10' 117o00'

47o42'30"

47o40'

Base modified from U.S. Geological Survey digital data

City boundaries, 1:24,000, various years (1961 through 1986);

public land survey, 1:100,000, 1985; lakes, 1:100,000, 1995;

and rivers, 1:100,000, 1985.

North American Datum of 1927 (NAD 27)
WATER CHEMISTRY 35

with associated dissolved lead concentrations of less 

than 0.08 μg/L (table 7). Lead may be transported at 

times in the ground water in the particulate phase. The 

data indicate that zinc and cadmium are transported primarily in the dissolved (less than 0.45 μm) phase, but a 

component may be transported in the near-river ground 

water in the particulate phase.

The chemistries of the river and ground water 

identified as having a dominant river source were compared to determine if there was a net change in dissolved concentrations as water moved from the river to 

the aquifer. Although dissolved cadmium concentrations were less than 1.0 μg/L in all samples (fig. 20), 

several of the river-source wells had cadmium concentrations exceeding that of the river. Cadmium concentrations in ground water decreased to values less than 

reporting levels farther away from the river in the 

transitional and regional ground-water wells. Dissolved lead concentrations in the ground water generally were near or less than those in the river, except 

during December 2000 when the river concentration 

(0.14 μg/L) was exceeded in 3 of the 16 river-source 

wells (fig. 20). The cause for these anomalously high 

concentrations (up to 1.6 μg/L) in the ground water is 

unknown. Zinc concentrations in ground water were 

near or less than river concentrations in all but a few 

samples collected during extreme low-flow conditions 

in August 2001. Low leakage rates from the river 

during these conditions likely altered ground-water 

flow directions, thus complicating the comparison of 

the river and ground-water chemistries. 

Figure 20. Dissolved concentrations of cadmium, lead, and zinc in samples collected from the Spokane River at Post Falls, Idaho, and 

ground water identified as river source from the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, 

Washington, water year 2001.

O N D J F M A M J J A S

2000 2001

1.0

0.8

0.6

0.4

0.2

0

CONCENTRATION,

IN MICROGRAMS PER LITER

CADMIUM

O N D J F M A M J J A S

2000 2001

2.0

1.5

1.0

0.5

0

LEAD

O N D J F M A M J J A S

2000 2001

100

80

60

40

20

0

CONCENTRATION,

IN MICROGRAMS PER LITER

ZINC

SPOKANE RIVER AT POST FALLS, IDAHO

 (station 12419000)

GROUND WATER, RIVER SOURCE

Note: Values less than reporting levels are plotted as one-half

 the reporting levels

REPORTING LEVEL

EXPLANATION

WATER YEAR 2001

WATER YEAR 2001
36 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Table 7. Total-recoverable and dissolved cadmium, lead, and zinc concentrations of ground-water samples from monitoring wells within 

the Spokane Valley/Rathdrum Prairie aquifer, 2000-01

[μg/L, micrograms per liter; e, estimated; ND, could not be determined; <, less than; >, greater than; --, missing data]

Well

number1 Date

Cadmium (μg/L as Cd) Lead (μg/L as Pb) Zinc (μg/L as Zn)

Total

recoverableDissolved

Total

recoverable

minus

dissolved

 Total

recoverableDissolved

Total

recoverable

minus

dissolved

Total

recoverable Dissolved

Total

recoverable

minus

dissolved

1 08-14-01 <0.04 <0.04 ND <1.0 <0.08 ND 1.7 <1.0 >0.7

2 08-14-01 .70 .68 0.02 2.6 <.08 >2.52 74 66 8

4 08-07-00 <1.0 <1.0 ND <1.0 <1.0 ND 35 34 1

4 08-13-01 .45 .42 .03 <1.0 <.08 ND 46 42 4

5 08-07-00 <1.0 <1.0 ND <1.0 <1.0 ND 22 21 1

5 08-13-01 .33 .28 .05 1.5 <.08 >1.52 36 29 7

6 08-13-01 .38 .34 .04 <1.0 <.08 ND 41 32 9

8 07-12-00 <1.0 <1.0 ND <1.0 <1.0 ND 31 26 5

8 08-09-00 <1.0 <1.0 ND <1.0 <1.0 ND 34 32 2

8 05-02-01 .24 .21 .03 1.3 e.06 1.24 62 56 6

8 08-13-01 .22 .20 .02 <1.0 <.08 ND 35 32 3

8 08-14-01 .22 .19 .03 <1.0 <.08 ND 43 31 12

9 08-09-00 <1.0 <1.0 ND <1.0 <1.0 ND 22 22 0

9 08-13-01 .16 .15 .01 <1.0 <.08 ND 26 24 2

9 08-14-01 .16 .13 .03 <1.0 <.08 ND 24 23 1

10 08-13-01 .16 .10 .06 <1.0 <.08 ND 23 16 7

11 08-09-00 <1.0 <1.0 ND <1.0 <1.0 ND 27 23 4

11 05-01-01 .31 .27 .04 2.1 <.08 >2.02 51 43 8

11 08-16-01 .34 .27 .07 4.2 <.08 >4.12 42 27 15

12 05-01-01 .10 .10 .00 <1.0 <.08 ND 18 18 0

12 08-16-01 .11 .08 .03 <1.0 <.08 ND 12 8.4 3.6

13 08-09-00 <1.0 <1.0 ND <1.0 <1.0 ND 14 12 2

13 05-01-01 .15 .15 .00 <1.0 <.08 ND 23 23 0

13 08-16-01 .16 .15 .01 <1.0 <.08 ND 15 14 1

14 05-02-01 <.04 <.04 ND <1.0 <.08 ND 1.1 <1.0 >.1

14 08-15-01 <.04 <.04 ND <1.0 <.08 ND 1.5 <1.0 >.5

15 05-02-01 <.04 <.04 ND <1.0 <.08 ND <1.0 <1.0 ND

15 08-13-01 .04 e.02 .02 <1.0 <.08 ND 1.1 <1.0 >.1

16 08-10-00 <1.0 <1.0 ND <1.0 <1.0 ND <1.0 <1.0 ND

19 08-15-01 .17 .16 .01 <1.0 <.08 ND 20 20 0

21 08-15-01 .06 .05 .01 <1.0 <.08 ND 12 9.8 2.2

22 08-15-01 .15 .12 .03 <1.0 <.08 ND 18 17 1

23 08-15-01 .50 .52 -.02 <1.0 <.08 ND 44 44 0

25 08-14-01 <.04 <.04 ND <1.0 <.08 ND <1.0 <1.0 ND

1Number corresponds to wells listed in table 1 and shown in figure 3.
WATER CHEMISTRY 37

In general, it does not appear that concentrations 

of cadmium, lead, and zinc increase dramatically as 

river water is transmitted through the streambed. Slight 

increases in concentrations that may be attributed to the 

bed sediment appear to be localized and of small scale. 

It is possible that some colloidal trace elements (particularly cadmium) may be transported into the near-river 

aquifer from the river.

Major ion, temperature, and specific conductance data provide fairly conclusive evidence of the 

influence of river recharge on the adjacent alluvial 

aquifer. However, the trace-element chemistry reveals 

that cadmium, lead, and zinc are not transported as far 

out into the aquifer as the other river-source indicators. 

Zinc concentrations were highest in the river and in the 

shallowest of the near-river wells (well 11) (fig. 21). 

Zinc concentrations decreased with depth in the nearriver wells and with distance away from the river. 

However, the major-ion chemistry and dissolved-solids 

concentrations at depth and distance remained consistent and similar to the river farther out in the aquifer 

(example well 14, fig. 21). The decrease in zinc concentration with depth and distance does not appear to 

result from mixing of zinc-free regional waters and 

may be attributed to sorption or precipitation processes 

that would result in the lowering of zinc concentrations. 

Sorption reactions of zinc are strongly dependent on 

pH; as pH increases zinc becomes more strongly 

sorbed. For example, the sorption of zinc onto hydrous 

ferric oxide rises from near 0 to almost 100 percent 

between pH values of 5 and about 7.5 (Stumm and 

Morgan, 1996, p. 542-543). The neutral pH conditions 

of the sampled waters (pH values between 6.4 and 8.2) 

are consistent with the sorption of zinc. Similarly, 

cadmium also may react with materials in the aquifer.

Figure 21. Median dissolved-solids and dissolved zinc concentrations of the Spokane River measured at Post Falls, 

Idaho, and ground water from wells 11 through 16, water year 2001.

DISSOLVED-SOLIDS CONCENTRATION,

 IN MILLIGRAMS PER LITER

DISSOLVED ZINC CONCENTRATION,

 IN MILLIGRAMS PER LITER

37

EXPLANATION

11 WELL NUMBER

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

ALTITUDE, IN FEET ABOVE NGVD 29

Spokane River

DISTANCE, IN FEET

Water level 8-13-01 through 8-15-01

1,925

1,975

2,025

2,075

2,125

Water table

S N

Sand and gravel

1,875

14

11 12 13 15

16

60

38

14

38

14 40 174

182

<1

38

42

37

<1 <1

60

VERTICAL EXAGGERATION 6X
38 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Stable Isotopes 

The isotopic composition of precipitation generally follows a trend parallel to the global meteoric 

water line of Craig (1961) with a δD/δ18O slope of 

about 8 (Coplen and others, 1999). Evaporation of 

water results in the enrichment of D and 18O in the 

residual water resulting in a δD/δ18O slope usually 

between 3 and 6 (Coplen and others, 1999). Because 

Coeur d’Alene Lake and the Spokane River undergo 

various degrees of evaporation, ground water derived 

all or in part from these surface-water sources should 

have an isotopic signature that is consistent with evaporation. Stable isotope values from samples of the 

Spokane River and ground water collected from the 25 

monitoring wells had a slope of near 5.5 (fig. 22), consistent with evaporation. The stable isotopes support 

the hypothesis that ground water from the central part 

of the Spokane Valley/Rathdrum Prairie aquifer contains a component of water originating from the 

Spokane River and/or Coeur d’Alene Lake. However, 

ground water identified as transitional or regional 

based on major-ion chemistry data (fig. 15) generally 

was isotopically similar to the river and ground water 

determined to be of a river source (fig. 22).

Although individual isotopic values may not be 

distinct among the ground-water samples, the temporal 

variability of the river and river-influenced ground 

water does appear to be distinct. Variations of nearly 

1 ‰ δ18O and 4 ‰ δD were observed in samples collected from the Spokane River between 1999 and 2001 

(Bowers and others, 2003). Ground water previously 

identified as having a river source closely approximated the δ18O trend observed in the river (fig. 23). 

Regional ground water had isotopic values within the 

range observed in the river, but lacked the temporal 

variation observed in the river and near-river wells 

(fig. 23). The temporal isotopic data generally indicate 

that the near-river ground water includes at least a component of recharge from the river, and the recharged 

water moves quickly from the river to the wells.

Figure 22. Relation between δD and δ18O in water from the Spokane River and ground water from the Spokane 

Valley/Rathdrum Prairie aquifer of Idaho and Washington classified as river source, transitional, and regional 

based on concentrations of dissolved solids, 1999-2001.

-16.5 -16.0 -15.5 -15.0

-125

-130

-120

-115

-110

-105

-100

-95

-90

Trend - river and ground water from this study

δD = 5.5 δ18O - 30.1 per mil, r2 = 0.60, P <0.0001

-14.5 -14.0 -13.5

δD, IN PER MIL (‰)

δ18O, IN PER MIL (‰)

Global Meteoric Water Line (Craig, 1961), δD = 8 δ18O + 10 per mil

Spokane River

Ground water

River source

Transitional

Regional
WATER CHEMISTRY 39

Figure 23. δ18O of samples from the Spokane River at Post Falls, Idaho, ground water influenced by recharge from 

the Spokane River, and regional ground water of the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001.

-15.5

-15.0

-14.5

-14.0

GROUND WATER, RIVER SOURCE (wells 2,4,8,10,11,12,14,18,19)

GROUND WATER, REGIONAL (well 24)

GROUND WATER, REGIONAL (well 3) 

SPOKANE RIVER AT POST FALLS, IDAHO (station 12419000)

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

1999 2000 2001

EXPLANATION

δ18O, IN PER MIL (‰)

Temporal Variability in Water Chemistry

Temporal water-chemistry variations in the 

ground water near the river appear to be associated with 

variability in the river. Dissolved-solids concentrations 

of the Spokane River ranged from 29 to 39 mg/L during 

1999-2001. Dissolved-solids concentrations in samples from shallow wells adjacent to the losing reach of 

the river consistently followed the trend of the river, 

with concentrations near or slightly greater than the 

river (example well 11, fig. 24). Dissolved-solids concentrations in samples from the transitional and 

regional wells were elevated as compared to the river 

and were relatively unaffected by changes in the river. 

Zinc concentrations in the river were quite variable, 

ranging from 22 to 90 μg/L between 1999 and 2001. 

Zinc concentrations in samples from wells close to the 

losing reach of the river followed the same pattern as 

the river, but at concentrations generally less than those 

of the river (example well 11, fig. 24). Zinc concentrations in samples from most transitional and regional 

wells (example wells 15 and 17, fig. 24) commonly 

were less than reporting levels.

Changes in ground-water chemistry in response 

to streamflow conditions were most apparent in samples from well 25, which is located near the river in an 

area where ground water usually discharges to the river 

(fig. 3). The water chemistry in samples from well 25 

was indicative of water from the regional flow system. 

However, during high streamflow in May 2001, the 

dissolved-solids concentrations in samples from well 

25 decreased to a value of near that of the river, and 

zinc concentrations increased to values greater than the 

reporting level. This is evidence that this reach of the 

river changed from gaining to losing during the high 

streamflow event. Anomalies such as the one-time 

occurrence of detectable zinc in a sample from well 7 

(fig. 3) during May 2001 high streamflow and the 39 to 

90 mg/L range in dissolved-solids concentrations in 

samples from well 1 (fig. 3) also probably result from 

changes in river stage and recharge. Overall, it appears 

that periods of high streamflow had limited temporal 

effect on the ground-water chemistry in samples from 

individual wells and limited spatial effect in terms of 

the distance that recharged river water traveled laterally 

into the aquifer. It should be reiterated that during this 

study, ground water was sampled during relatively low 

flow conditions (about 44 percent of normal) for the 

Spokane River and that conditions in the near-river 

aquifer may be different during normal or above 

average flow conditions.
40 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 24. Dissolved-solids and zinc concentrations of the Spokane River at Post Falls, Idaho, and ground water from 

selected monitoring wells within the Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, 

Washington, 1999-2001.

0

20

40

60

80

100

120

140

160

180

200

0

5,000

10,000

15,000

20,000

25,000

30,000

0.1

1

10

100

1,000

J F M A MJ J A S O N D J F M A MJ J A S O N D J F M A MJ J A S O N D

1999 2000 2001

CONCENTRATION,

IN MICROGRAMS PER LITER

CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED SOLIDS

DISSOLVED ZINC

0

5,000

10,000

15,000

20,000

25,000

30,000

STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

STREAMFLOW—Spokane River at Post Falls, Idaho 

 (station 12419000)

MINIMUM REPORTING LEVEL

DISSOLVED-SOLIDS OR ZINC CONCENTRATION—

 Zinc values reported as less than 1.0 microgram

 per liter are plotted as 0.5 microgram per liter

Ground water, river source (well 11)

Ground water, transitional (well 17)

Ground water, regional (well 15)

Spokane River at Post Falls, Idaho (station 12419000)
SUMMARY 41

SUMMARY

This report describes a study conducted as part of 

the U.S. Geological Survey’s National Water-Quality 

Assessment Program to examine the interaction of 

the Spokane River and underlying Spokane Valley/

Rathdrum Prairie aquifer, the primary source of 

drinking water for Spokane and surrounding communities in Idaho and Washington. Elevated concentrations 

of trace elements (particularly cadmium, lead, and zinc) 

in the bed sediment and water of the Spokane River 

have raised concerns about potential contamination of 

this ground-water resource. The river and ground water 

were monitored over a range of hydrologic conditions 

at one streamflow-gaging station and at 25 monitoring 

wells situated from 40 to 3,500 feet from the river. The 

river stage, ground-water levels, water temperature, and 

specific conductance were measured hourly to 

biweekly. Water samples were collected about monthly 

from 1999 through 2001 from the Spokane River, and 

up to nine times between June 2000 and August 2001 

from the monitoring wells. 

Ground-water levels and streamflow data indicate that the Spokane River loses water to the underlying aquifer along a 17-mile reach from Post Falls, 

Idaho, downstream to Spokane, Washington. Nested 

wells located near the river indicated a large downward 

component of flow in the aquifer. Although water 

levels in the near-river wells typically were several feet 

below the bottom of the river channel, the hydraulic 

gradient indicates that conditions near the river may 

change from saturated to unsaturated based on spatial 

and temporal variations. Ground-water levels in the 

study area responded to river stage fluctuations, but 

water levels near the river responded more quickly than 

those farther away from the river and were much more 

sensitive to small scale fluctuations in river stage. 

Downstream of the 17-mile reach between Post Falls 

and Spokane, ground water discharges to the river. 

Calculated monthly mean losses for a 7-mile 

reach of the river between the gages near Post Falls and 

Otis Orchards ranged from about 69 to 810 cubic feet 

per second during water years 2000-01. Losses generally increased with increased streamflow. However, 

water loss from the river appeared to increase during 

the late summer when the water temperature in the 

Spokane River was at its warmest. This increased water 

loss is probably a result of lower water viscosity and 

consequent increased infiltration capacity produced by 

the higher water temperature. 

Water temperature also appears to provide a 

useful tracer for ground-water recharge from the 

Spokane River. Water temperatures during water year 

2001 varied about 22 degrees Celsius (°C) in the river 

at Post Falls, and between 0.1 to 23.4°C in individual 

wells. Water temperature fluctuations in the near-river 

wells followed the same general pattern as the river, 

indicating local recharge from the river. The groundwater temperature in some near-river wells responded 

within hours to fluctuations in the water temperature 

in the river, indicating saturated conditions in those 

areas. Relatively stable water temperatures characterized regional ground water. 

Although water levels in the alluvial aquifer 

appeared to respond to river fluctuations over a large 

area, water-quality effects appeared to be restricted to 

an area of the aquifer near the losing reach of the river. 

Dissolved-solids concentrations in the Spokane River 

were low, with a median of 34 milligrams per liter 

(mg/L), in comparison to regional ground water, with 

concentrations greater than 100 mg/L. The effect of 

recharge from the river is evidenced by a reduction in 

the dissolved-solids concentration in the alluvial 

aquifer up to 3,000 feet from the river. Major-ion and 

stable-isotope chemistry in the river and in near-river 

ground water were similar and exhibited similar temporal trends. Ground water farther from the river had 

higher concentrations of dissolved solids and less variability in water chemistry.

Although the Spokane River loses water to the 

alluvial aquifer, the losses do not appear to have 

human health implications. Although concentrations 

of some trace elements in river water and bed sediment were elevated, concentrations in the river and in 

near-river ground water never exceeded U.S. Environmental Protection Agency drinking-water standards in 

the samples collected for this study. The Spokane 

River provides some cadmium, copper, zinc, and possibly lead to the near-river aquifer; however, concentrations of these trace elements do not increase 

substantially as river water is transmitted through the 

streambed. Dissolved cadmium, copper, and lead generally were less than 1 microgram per liter (μg/L) in 

the river and ground water. Dissolved zinc concentrations were similar in the river and the aquifer near the 

river, but were less than reporting levels in the aquifer 

farther from the river. Concentrations of arsenic were 

higher in ground water farther from the river, indicative of a more regional source.
42 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Changes in streamflow conditions had limited 

effect on the ground-water chemistry in the alluvial 

aquifer or in the distance that river water traveled from 

the river into the aquifer. However, water-chemistry 

data showed that a reach of the river near Spokane 

changed from gaining to losing during high streamflow 

in May 2001. During this study, ground water was 

sampled during relatively low flow conditions (about 

44 percent of normal) for the Spokane River. Water 

chemistry and effects of surface-water/ground-water 

interaction may be different during normal or above 

average flow conditions. 

Comparison of total-recoverable (whole-water, 

unfiltered) and dissolved (0.45-micrometer filtration) 

concentrations in water samples indicated that some 

trace elements may be transported from the river to the 

near-river ground water in the particulate phase. Zinc 

and cadmium appear to be transported from the 

Spokane River to the alluvial aquifer primarily in the 

dissolved phase, although some particulate transport 

was evident. Lead was detected in five whole-water 

samples from the near-river aquifer at concentrations 

up to 4.2 μg/L; however, the dissolved lead concentrations were less than 0.08 μg/L in the accompanying 

filtered samples.

Cadmium and zinc originating from the river 

water appear to be restricted to a narrow zone in the 

near-river aquifer. Cadmium and zinc concentrations 

generally were highest in the river and in the aquifer 

near the river, decreasing with depth and distance away 

from the river. In contrast to cadmium and zinc, other 

water-quality constituents such as major ions, water 

temperature, and stable isotopes reflected river water to 

a greater depth and distance from the river. The 

decrease in cadmium and zinc concentrations with 

depth and distance may reflect processes such as sorption and/or precipitation. The neutral pH of the aquifer 

water (pH values between 6.4 and 8.2) would promote 

these processes. These processes also may explain the 

apparent loss of cadmium and zinc load in the river 

downstream where ground water returns to the river.

REFERENCES CITED

Beckwith, M.A., 2002, Selected trace-element and 

synthetic-organic compound data for streambed 

sediment from the Clark Fork-Pend Oreille and 

Spokane River Basins, Montana, Idaho, and 

Washington, 1998: U.S. Geological Survey OpenFile Report 02-336, 26 p.

———2003, Summary of surface-water-quality data 

collected for the Northern Rockies Intermontane 

Basins National Water-Quality Assessment Program in the Clark Fork-Pend Oreille and Spokane 

River Basins, Montana, Idaho, and Washington, 

water years 1999-2001: U.S. Geological Survey 

Open-File Report 02-472, 47 p.

Berenbrock, Charles, Bassick, M.D., Rogers, T.L., and 

Garcia, S.P., 1995, Depth to water, 1991, in the 

Rathdrum Prairie, Idaho; Spokane River valley, 

Washington; Moscow-Lewiston-Grangeville area, 

Idaho; and selected intermontane valleys, eastcentral Idaho: U.S. Geological Survey WaterResources Investigations Report 94-4087, 

2 sheets.

Bolke, E.L., and Vaccaro, J.V., 1979, Selected hydrologic data for Spokane Valley, Spokane, Washington, 1977-78: U.S. Geological Survey Open-File 

Report 79-333, 98 p.

———1981, Digital-model simulation of the hydrologic flow system, with emphasis on ground water, 

in the Spokane Valley, Washington and Idaho: 

U.S. Geological Survey Open-File Report 80-

1300, 43 p.

Bookstrom, A.A., Box, S.E., Campbell, J.K., Foster, 

K.I., and Jackson, B.L., 2001, Lead-rich sediments, Coeur d’Alene River Valley, Idaho—area, 

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76 p.

Briar, D.W., Lawlor, S.M., Stone, M.A.J., Parliman, 

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Ground-water levels in the Intermontane Basins of 

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1:750,000.
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79 p.

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project 0622-001.02, 83 p. 

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Geological Survey Open-File Report 92-634, 28 p.

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U.S. Geological Survey National Water Quality 

Laboratory—Determination of inorganic and 

organic constituents in water and fluvial sediments: U.S. Geological Survey Open-File Report 

93-125, 217 p.

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determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, 

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U.S. Geological Survey National Water Quality 

Laboratory—Determination of dissolved arsenic, 

boron, lithium, selenium, strontium, thallium, and 

vanadium using inductively coupled plasma-mass 

spectrometry: U.S. Geological Survey Open-File 

Report 99-093, 31 p.

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of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—Determination of elements in whole-water digests using 

inductively coupled plasma-optical emission 

spectrometry and inductively coupled plasmamass spectrometry: U.S. Geological Survey 

Open-File Report 98-165, 101 p.

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hydraulic connection between the Spokane River 

and the Spokane-aquifer gaining and losing 

reaches of the Spokane River from State line, 

Idaho to Spokane, Washington: Cheney, 

Washington, prepared for the Spokane County 

Water Quality Management Program, 106 p.

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geophysical mapping of the Spokane aquifer—

Relevance to growth management: Washington 

Geology, v. 22, p. 18-24.

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Design of the National Water-Quality Assessment Program—Occurrence and distribution of 

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Survey Circular 1112, 33 p.

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Elrick, K.A., 2001, The effect of mining and 

related activities on the sediment-trace element 

geochemistry of Lake Coeur d’Alene, Idaho, 

USA, Part III, Downstream effects—the Spokane 

River Basin: Hydrological Processes, v. 15, 

p. 855-875.

Hoffman, G.L., Fishman, M.J., and Garbarino, J.R., 

1996, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Inbottle acid digestion of whole-water samples: 

U.S. Geological Survey Open-File Report 96-

225, 28 p.

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R.B., 1995, A summary of the effects of mining 

and related activities on the sediment-trace 

element geochemistry of Lake Coeur d’Alene, 

Idaho, USA: Journal of Geochemical Exploration, v. 52, p. 135-144.
44 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Idaho Department of Environmental Quality, 2000, The 

Spokane Valley-Rathdrum Prairie aquifer atlas: 

Idaho Department of Environmental Quality, 24 p.

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analysis by the U.S. Geological Survey National 

Water Quality Laboratory—Determination of 

arsenic and selenium in water and sediment by 

graphite furnace-atomic absorption spectrometry: 

U.S. Geological Survey Open-File Report 98-639, 

39 p.

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Smith, R.R., Knowles, S.M., and Renslow, V.F., 

2002, Water resources data, Washington, water 

year 2001: U.S. Geological Survey Water-Data 

Report WA-01-1, 576 p.

Kimbrough, R.A., Smith, R.R., Ruppert, G.P., Wiggins, 

W.D., Knowles, S.M., and Renslow, V.F., 2001, 

Water resources data, Washington, water year 

2000: U.S. Geological Survey Water-Data Report 

WA-00-1, 541 p.

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Ground-water data collection protocols and procedures for the National Water-Quality Assessment 

Program—Collection and documentation of 

water-quality samples and related data: U.S. Geological Survey Open-File Report 95-399, 113 p.

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of selected trace elements in fish tissue and 

streambed sediment in the Clark Fork-Pend Oreille 

and Spokane River Basins, Washington, Idaho, 

and Montana, 1998: U.S. Geological Survey 

Water-Resources Investigations Report 00-4159, 

26 p.

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Department of Ecology publication no. 01-03-024, 

40 p.

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Geological Survey National Water Quality Laboratory—Determination of chromium in water by 

graphite furnace atomic absorption spectrophotometry: U.S. Geological Survey Open-File 

Report 93-449, 16 p.

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water-quality characteristics: U.S. Geological 

Survey Water-Supply Paper 2265, 74 p.

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Quality-control design for surface-water sampling 

in the National Water-Quality Assessment 

Program: U.S. Geological Survey Open-File 

Report 97-223, 17 p.

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Ground-water quality in north Idaho: U.S. Geological Survey Open-File Report 80-596, 34 p.

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Survey Water-Supply Paper 889-B, p. 83-139. 

Pritt, J.W., and Raese, J.W., 1995, Quality assurance/quality control manual—National Water 

Quality Laboratory: U.S. Geological Survey 

Open-File Report 95-443, 35 p.

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modular, finite-difference, ground-water flow 

model: U.S. Geological Survey Open-File Report 

88-729, 113 p.

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Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 94-455, 42 p.

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County, Idaho: U.S. Geological Survey WaterResources Investigations Report 93-4091, 41 p.

Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, 

C.W., Korosec, M.A., and Bunning, B.B., 1991, 

Geologic map of Washington—northeast quadrant: Olympia, Washington Division of Geology 

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1:250,000, sheet 1.

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Selected geohydrologic data from a regional 

aquifer-system analysis of the northern Rocky 

Mountains intermontane basins in Idaho: U.S. 

Geological Survey Open-File Report 96-207, 30 p.

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chemistry—Chemical equilibria and rates in natural waters (3d ed.): New York, Wiley, 1,022 p.
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Tuck, L.K., Briar, D.W., and Clark, D.W., 1996, 

Geologic history and hydrogeologic units of Intermontane Basins of the northern Rocky Mountains, 

Montana and Idaho: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-738-A, scale 

1:750,000, sheet 1.

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http://quickfacts.census.gov/qfd/ 

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Source Aquifer Protection Program overview: 

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http://www.epa.gov/OGWDW/swp/ssa.html

———2002a, 2002 edition of the drinking water standards and health advisories: U.S. Environmental 

Protection Agency, EPA-822-R-02-038, 19 p.

———2002b, National recommended water quality 

criteria—2002: EPA-822-R-02-047, 33 p.

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in the United States in 1995: accessed August 6, 

2002, at URL 

http://water.usgs.gov/watuse/pdf1995/html

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1990 monthly normal: accessed January 26, 

2001, at URL http://www.wrcc.dri.edu/

Wilde, F.D., and Radtke, D.B., 1998, National field 

manual for the collection of water-quality 

data—Field measurements: U.S. Geological 

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water year within the Spokane River Basin, Idaho 

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trace-element enrichment of Coeur d’Alene Lake, 

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Paper 2485, 93 p.

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metals in groundwater of the Spokane aquifer, 

northeastern Washington—Water quality and 

river/aquifer interaction: Cheney, Eastern 

Washington University, unpublished M.S. thesis, 

123 p.
APPENDIX 47

APPENDIX
WELL-NUMBERING SYSTEM 49

Well-Numbering System

Wells are assigned well numbers (1-25; fig. 3; 

table 1) and location numbers that describe the geographic position within the rectangular grid system 

used for the subdivision of public lands. The locationnumbering system consists of 14 characters. The first 

three characters specify the township and its position 

north (N) of the Willamette Base Line in Washington, 

the Boise Base Line in Idaho, or the Baseline in 

Montana. The next three characters specify the range 

and its position west (W) or east (E) of the Willamette 

meridian in Washington, the Boise meridian in Idaho, 

or the Principal meridian in Montana. The next two 

numbers represent the section number. The next four 

characters sequentially designate the quarter (160-acre 

tract), quarter-quarter (40-acre tract), quarter-quarterquarter (10-acre tract), and the quarter-quarter-quarterquarter (2 1⁄2 -acre tract). The locations of quarter 

subdivisions within a section are designated A, B, C, D 

in a counterclockwise direction, beginning in the 

northeast quadrant. The final two characters are a 

sequence number assigned to differentiate multiple 

wells within a single quarter-quarter-quarter-quarter 

section; for example, a well location reported as 

26N43E31CBBC01 is the first well inventoried in the 

SW1/4NW1/4NW1/4SW1/4 section 31, township 26 

north, range 43 east.

Wells also are assigned 15-digit station-identification numbers (table 1). These numbers represent the 

approximate latitude and longitude of each well (first 

13 digits) plus the sequence number (last 2 digits). 

However, some station-identification numbers differ 

(table 1) from the latitude and longitude where wells 

were recently field checked and latitudes and longitudes were determined with greater accuracy.

5

6

4

3

2

1

7

8

9

10

11 12

13

14 15

16

17

18

19

22

21 20

28 27 26 25

24 23

29 30

34 35 36

32 33

1W 1E

2

4

3

5

57N

TOWNSHIP 26 NORT

R

H

ANGE 43 EAST

RANGE

TOWNSHIP

40E 41 42

43 44 45

46 6

56

55

54

53

52

51

50

49

48N

TOWNSHIP

24N

25

26

27

28

29

30

31

33N

32

IDAHO

WASHINGTON

Boise

Meridian

WASHINGTON

OREGON

MONTANA

IDAHO

Principal

Meridian

Base Line

Meridian Boise

Meridian

Willamette

Boise Base

Willamette

Location number 26N43E31CBBC01

(Well number 3)

A

A

A

A

A

B

D

C

B

B

B

B

C

C

C

C

D

D

D

D

SECTION 31

Line

Base Line
50 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 25. Ground-water altitude and water temperature measured in 25 monitoring wells within the 

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 

water year 2001.

1,995

2,000

2,005

2,010

2,015

0

5

10

15

20

25

30

Well number (1) 50N05W07DABC01

2,030

2,035

2,040

2,045

2,050

0

5

10

15

20

25

30

Well number (2) 50N05W07DABC02

1,965

1,970

1,975

1,980

1,985

0

5

10

15

20

25

30

Well number (3) 26N46E31CBBC01

1,960

1,965

1,970

1,975

1,980

0

5

10

15

20

25

30

Well number (4) 25N45E01ABDD01

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept 1,975

1,980

1,985

1,990

1,995

0

5

10

15

20

25

30

Well number (5) 25N45E01ABDD02

WATER YEAR 2001

WATER ALTITUDE, IN FEET ABOVE NGVD 29

TEMPERATURE, IN DEGREES CELSIUS

Recorded water temperature

Recorded water level

Recorded water temperature

Recorded water level

Measured water level

Measured water temperature

Recorded water level

Recorded water temperature

Measured water level

Measured water temperature
FIGURE 25 51

Figure 25. Ground-water altitude and water temperature measured in 25 monitoring wells within the 

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 

water year 2001 (Continued).

WATER YEAR 2001

WATER ALTITUDE, IN FEET ABOVE NGVD 29

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

TEMPERATURE, IN DEGREES CELSIUS

Recorded water level

Well Number (6) 25N45E01ABDD03

1,960

1,965

1,970

1,975

1,980

0

5

10

15

20

25

30

Well Number (7) 25N45E01ACAD01

1,960

1,965

1,970

1,975

1,980

0

5

10

15

20

25

30

Well Number (8) 25N45E01CBBD02

2,000

2,005

2,010

2,015

2,020

0

5

10

15

20

25

30

Well Number (9) 25N45E01CBBD01

1,980

1,985

1,990

1,995

2,000

0

5

10

15

20

25

30

Well Number (10) 25N45E01CBBC01

1,970

1,975

1,980

1,985

1,990

0

5

10

15

20

25

30

Recorded water temperature

Recorded water temperature

Recorded water temperature

Recorded water temperature

Measured water level

Measured water level

Recorded water level

Measured water level

Recorded water temperature
52 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 25. Ground-water altitude and water temperature measured in 25 monitoring wells within the 

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 

water year 2001 (Continued).

WATER YEAR 2001

WATER ALTITUDE, IN FEET ABOVE NGVD 29

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

TEMPERATURE, IN DEGREES CELSIUS

Recorded water temperature

Recorded water level

Well Number (11) 25N45E10BAAA01

1,970

1,975

1,980

1,985

1,990

0

5

10

15

20

25

30

Well Number (12) 25N45E10BAAA03

1,950

1,955

1,960

1,965

1,970

0

5

10

15

20

25

30

Recorded water level

Recorded water temperature

Well Number (13) 25N45E10BAAA02

1,970

1,975

1,980

1,985

1,990

0

5

10

15

20

25

30

Measured water level

Recorded water temperature

Well Number (14) 25N45E03CDDD01

1,950

1,955

1,960

1,965

1,970

0

5

10

15

20

25

30

Recorded water level

Recorded water temperature

Well Number (15) 25N45E03CDDA01

1,950

1,955

1,960

1,965

1,970

0

5

10

15

20

25

30

Measured water level

Recorded water temperature

Missing data
FIGURE 25 53

Figure 25. Ground-water altitude and water temperature measured in 25 monitoring wells within the 

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 

water year 2001 (Continued).

WATER YEAR 2001

WATER ALTITUDE, IN FEET ABOVE NGVD 29

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

TEMPERATURE, IN DEGREES CELSIUS

Well Number (16) 25N45E03BDDA01

1,950

1,955

1,960

1,965

1,970

Well Number (17) 25N45E10CBDA01

1,950

1,955

1,960

1,965

1,970

Well Number (18) 25N45E09ADAD01

1,950

1,955

1,960

1,965

1,970

Well Number (19) 25N45E09ADAB01

1,958

1,962

1,966

1,970

1,974

1,978

Well Number (20) 25N45E17BBAA05

1,940

1,945

1,950

1,955

1,960

0

5

10

15

20

25

30

Recorded water level

Recorded water temperature

Measured water level

Measured water temperature

Measured water level

Measured water temperature

Recorded water temperature

Recorded water temperature

Recorded water level

Measured water level

0

5

10

15

20

25

30

0

5

10

15

20

25

30

0

5

10

15

20

25

30

0

5

10

15

20

25

30
54 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Figure 25. Ground-water altitude and water temperature measured in 25 monitoring wells within the 

Spokane Valley/Rathdrum Prairie aquifer between Post Falls, Idaho, and Spokane, Washington, 

water year 2001 (Continued).

WATER YEAR 2001

WATER ALTITUDE, IN FEET ABOVE NGVD 29

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

TEMPERATURE, IN DEGREES CELSIUS

Well Number (21) 25N45E08CBBC02

1,940

1,945

1,950

1,955

1,960

Well Number (22) 25N45E08CBBC01

1,940

1,945

1,950

1,955

1,960

Well Number (23) 25N45E07ADDD01

1,940

1,945

1,950

1,955

1,960

Well Number (24) 25N45E07AAAA04

1,940

1,945

1,950

1,955

1,960

Well Number (25) 25N44E11DDAC01

1,925

1,930

1,935

1,940

1,945

0

5

10

15

20

25

30

0

5

10

15

20

25

30

0

5

10

15

20

25

30

0

5

10

15

20

25

30

0

5

10

15

20

25

30

Measured water level

Measured water temperature

Measured water level

Measured water temperature

Measured water level

Measured water temperature

Measured water level

Measured water temperature

Measured water level

Measured water temperature
TABLE 8 55

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)

Spokane River 04-13-99 <1.0 <1.0 <1.0 <1.0 2.1 <1.0 82 90

05-19-99 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 <40 60

06-02-99 1.6 <1.0 <1.0 <1.0 7.7 <1.0 69 58

06-23-99 <1.0 <1.0 <1.0 <1.0 2.8 <1.0 63 46

07-27-99 <1.0 <1.0 <1.0 <1.0 1.1 <1.0 43 44

09-09-99 <1.0 <1.0 <1.0 <1.0 1.2 <1.0 36 31

10-20-99 <2.6 <2.0 .15 <1.0 <1.0 <1.0 37 43

01-12-00 <2.6 <2.0 .30 <1.0 e.59 <1.0 65 76

02-29-00 <2.6 <.90 .40 <1.0 1.4 <1.0 69 75

03-28-00 <2.6 <.90 .32 <1.0 e.74 <1.0 81 80

04-11-00 <2.6 <.90 .37 <1.0 2.1 <1.0 96 81

04-18-00 <2.6 <.90 .44 <1.0 5.6 <1.0 92 71

05-03-00 <2.6 <2.0 .29 <1.0 7.8 1.6 67 56

05-16-00 <2.6 <.90 .26 <1.0 3.6 <1.0 62 46

05-31-00 <2.6 <.90 .21 <1.0 2.1 <1.0 63 51

06-27-00 <2.6 <.90 .15 <1.0 1.1 <1.0 47 38

07-25-00 <2.6 <.90 .13 <1.0 1.1 <1.0 e29 38

08-30-00 <2.6 e.50 <.11 <1.0 1.3 <1.0 e26 22

11-08-00 <1.9 .44 .18 .14 <1.0 .13 46 45

12-21-00 <2.6 .47 .23 .20 <1.0 .17 68 66

01-22-01 <1.9 .53 .22 .19 <1.0 .15 60 66

03-13-01 <1.9 .45 .23 .18 <1.0 .16 66 65

04-09-01 <1.9 .40 .21 .18 <1.0 e.04 65 61

05-07-01 <1.9 .38 .29 .22 1.9 .41 71 60

06-11-01 <1.9 .39 .22 .16 1.5 .17 51 46

08-13-01 <1.9 .57 .11 .08 1.0 .12 30 28

08-14-01 <1.9 .59 .10 .10 1.1 .13 33 30

Well 1 08-08-00 -- <.90 -- <1.0 -- <1.0 -- <1.0

09-27-00 -- <.90 -- <1.0 -- <1.0 -- <1.0

12-15-00 -- e.17 -- <.04 -- <.08 -- 1.3

03-28-01 -- e.12 -- <.04 -- <.08 -- <1.0

05-03-01 -- e.09 -- <.04 -- <.08 -- <1.0

05-23-01 -- e.10 -- <.04 -- <.08 -- <1.0

08-14-01 <2.0 e.13 <.04 <.04 <1.0 <.08 1.7 <1.0
56 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Well 2 09-27-00 -- <0.90 -- <1.0 -- <1.0 -- 54

12-15-00 -- .36 -- .35 -- .12 -- 61

03-28-01 -- .31 -- .32 -- .09 -- 56

04-30-01 -- .32 -- .36 -- .09 -- 63

05-03-01 -- .27 -- .36 -- .11 -- 60

05-03-01 -- .30 -- .37 -- .12 -- 61

05-23-01 -- .38 -- .40 -- .12 -- 71

08-14-01 <2.0 .48 .70 .68 2.6 <.08 74 66

Well 3 10-04-00 -- 4.4 -- e.03 -- <.08 -- <1.0

12-20-00 -- 4.3 -- <.04 -- <.08 -- <1.0

05-01-01 -- 4.1 -- <.04 -- <.08 -- <1.0

05-23-01 -- 4.4 -- <.04 -- <.08 -- <1.0

08-14-01 -- 4.0 -- <.04 -- <.08 -- <1.0

Well 4 06-19-00 -- 1.3 -- <1.0 -- <1.0 -- 25

08-07-00 <2.6 e.52 <1.0 <1.0 <1.0 <1.0 35 34

09-25-00 -- <.90 -- <1.0 -- <1.0 -- 38

12-14-00 -- .28 -- .30 -- e.05 -- 43

03-26-01 -- .32 -- .33 -- <.08 -- 46

04-30-01 -- .42 -- .33 -- <.08 -- 49

05-22-01 -- .38 -- .35 -- <.08 -- 49

08-13-01 <2.0 .42 .45 .42 <1.0 <.08 46 42

Well 5 06-19-00 -- e.83 -- <1.0 -- <1.0 -- 25

08-07-00 <2.6 <.90 <1.0 <1.0 <1.0 <1.0 22 21

09-26-00 -- <.90 -- <1.0 -- <1.0 -- 24

03-26-01 -- .30 -- .26 -- <.08 -- 34

04-30-01 -- .37 -- .27 -- <.08 -- 36

05-22-01 -- .36 -- .31 -- <.08 -- 41

08-13-01 <2.0 .37 .33 .28 1.5 <.08 36 29

Well 6 08-07-00 -- e.48 -- <1.0 -- <1.0 -- 29

09-26-00 -- <.90 -- <1.0 -- <1.0 -- 29

12-14-00 -- .27 -- .33 -- <.08 -- 34

03-26-01 -- .21 -- .32 -- <.08 -- 35

04-30-01 -- .27 -- .29 -- <.08 -- 42

05-22-01 -- .33 -- .32 -- <.08 -- 38

08-13-01 <2.0 .37 .38 .34 <1.0 <.08 41 32

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001–Continued

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)
TABLE 8 57

Well 7 08-08-00 -- e0.52 -- <1.0 -- <1.0 -- <1.0

09-27-00 -- e.47 -- <1.0 -- <1.0 -- <1.0

12-14-00 -- .45 -- <.04 -- e.06 -- <1.0

03-26-01 -- .37 -- <.04 -- <.08 -- <1.0

04-30-01 -- .50 -- <.04 -- <.08 -- <1.0

05-22-01 -- .45 -- <.04 -- <.08 -- 6.8

08-14-01 -- .42 -- <.04 -- <.08 -- <1.0

Well 8 07-12-00 -- e.45 <1.0 <1.0 <1.0 <1.0 31 26

08-09-00 <2.6 <.90 <1.0 <1.0 <1.0 <1.0 34 32

09-26-00 -- <.90 -- <1.0 -- <1.0 -- 33

12-14-00 -- .46 -- .18 -- e.07 -- 53

03-28-01 -- .35 -- .21 -- .13 -- 54

05-02-01 <1.9 .30 .24 .21 1.3 e.06 62 56

05-23-01 -- .44 -- .24 -- e.06 -- 62

08-13-01 <2.0 .54 .22 .20 <1.0 <.08 35 32

08-14-01 <2.0 .52 .22 .19 <1.0 <.08 43 31

Well 9 08-09-00 <2.6 e.47 <1.0 <1.0 <1.0 <1.0 22 22

09-26-00 -- <.90 -- <1.0 -- <1.0 -- 23

12-14-00 -- .39 -- .16 -- e.07 -- 45

03-28-01 -- .30 -- .15 -- <.08 -- 41

05-02-01 -- .28 -- .17 -- e.07 -- 45

05-23-01 -- .38 -- .18 -- e.05 -- 48

08-13-01 <2.0 .51 .16 .15 <1.0 <.08 26 24

08-14-01 <2.0 .45 .16 .13 <1.0 <.08 24 23

Well 10 08-09-00 -- e.46 -- <1.0 -- <1.0 -- 14

09-26-00 -- <.90 -- <1.0 -- <1.0 -- 15

12-14-00 -- .30 -- .09 -- <.08 -- 19

03-28-01 -- .29 -- .09 -- <.08 -- 20

05-02-01 -- e.18 -- .24 -- <.08 -- 40

05-23-01 -- .33 -- .11 -- <.08 -- 25

08-13-01 <2.0 .39 .16 .10 <1.0 <.08 23 16

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001–Continued

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)
58 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Well 11 08-09-00 <2.6 e0.49 <1.0 <1.0 <1.0 <1.0 27 23

10-04-00 -- .35 -- .25 -- <.08 -- 28

12-19-00 -- .34 -- .22 -- e.06 -- 40

03-27-01 -- .32 -- .29 -- <.08 -- 45

05-01-01 <1.9 .39 .31 .27 2.1 <.08 51 43

05-23-01 -- .40 -- <.30 -- <.08 -- <48

08-16-01 <2.0 .51 .34 .27 4.2 <.08 42 27

Well 12 10-04-00 -- .51 -- .05 -- <.08 -- 4.0

12-19-00 -- .31 -- .07 -- e.06 -- 11

03-27-01 -- .27 -- .12 -- <.08 -- 18

05-01-01 <1.9 .28 .10 .10 <1.0 <.08 18 18

05-23-01 -- .34 -- .10 -- <.08 -- 18

08-16-01 <2.0 .43 .11 .08 <1.0 <.08 12 8.4

Well 13 08-09-00 <2.6 e.46 <1.0 <1.0 <1.0 <1.0 14 12

10-04-00 -- .39 -- .12 -- <.08 -- 13

12-19-00 -- .20 -- .08 -- 1.6 -- 12

03-27-01 -- e.17 -- .08 -- <.08 -- 10

05-01-01 <1.9 .23 .15 .15 <1.0 <.08 23 23

05-23-01 -- .30 -- .18 -- e.04 -- 25

08-16-01 <2.0 .47 .16 .15 <1.0 <.08 15 14

Well 14 10-03-00 -- .37 -- <.04 -- <.08 -- <1.0

12-19-00 -- .20 -- <.04 -- 1.1 -- <1.0

03-27-01 -- .21 -- <.04 -- <.08 -- <1.0

05-02-01 <1.9 e.17 <.04 <.04 <1.0 <.08 1.1 <1.0

05-24-01 -- .27 -- <.04 -- <.08 -- <1.0

08-15-01 <2.0 .47 <.04 <.04 <1.0 <.08 1.5 <1.0

Well 15 08-10-00 -- 4.6 -- <1.0 -- <1.0 -- <1.0

10-03-00 -- 4.5 -- .15 -- e.05 -- <1.0

12-19-00 -- 4.3 -- <.04 -- <.08 -- <1.0

03-28-01 -- 3.6 -- <.04 -- <.08 -- <1.0

05-02-01 4.8 4.0 <.04 <.04 <1.0 <.08 <1.0 <1.0

05-24-01 -- 4.2 -- <.04 -- <.08 -- <1.0

08-13-01 4.6 4.2 .04 e.02 <1.0 <.08 1.1 <1.0

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001–Continued

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)
TABLE 8 59

Well 16 08-10-00 3.0 3.1 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

10-04-00 -- 2.9 -- <.04 -- <.08 -- <1.0

12-19-00 -- 3.1 -- <.04 -- <.08 -- <1.0

05-01-01 -- 3.4 -- <.04 -- .10 -- <1.0

05-23-01 -- 3.0 -- <.04 -- <.08 -- <1.0

08-15-01 -- 2.9 -- <.04 -- e.08 -- 2.3

Well 17 08-08-00 -- <.90 -- <1.0 -- <1.0 -- <1.0

10-03-00 -- .32 -- <.04 -- <.08 -- <1.0

12-14-00 -- .28 -- <.04 -- <.08 -- 1.2

03-27-01 -- .29 -- <.04 -- <.08 -- <1.0

05-01-01 -- .32 -- <.04 -- <.08 -- <1.0

05-22-01 -- .30 -- <.04 -- <.08 -- <1.0

08-15-01 -- .28 -- <.04 -- 1.0 -- <1.0

Well 18 08-08-00 -- <.90 -- <1.0 -- <1.0 -- <1.0

10-03-00 -- .31 -- <.04 -- <.08 -- <1.0

12-19-00 -- .20 -- <.04 -- <.08 -- <1.0

03-27-01 -- e.17 -- <.04 -- <.08 -- <1.0

05-01-01 -- .24 -- <.04 -- <.08 -- <1.0

05-22-01 -- e.17 -- <.04 -- <.08 -- <1.0

08-15-01 -- .22 -- <.04 -- <.08 -- <1.0

Well 19 08-08-00 -- <.90 -- <1.0 -- <1.0 -- 8.9

10-03-00 -- .52 -- .09 -- <.08 -- 9.9

12-19-00 -- .25 -- .07 -- .34 -- 9.3

03-27-01 -- .23 -- .16 -- <.08 -- 19

05-01-01 -- .38 -- .06 -- e.04 -- 12

05-22-01 -- .26 -- .26 -- <.08 -- 26

08-15-01 <2.0 .35 .17 .16 <1.0 <.08 20 20

Well 20 10-05-00 -- .94 -- <.04 -- <.08 -- <1.0

12-20-00 -- 1.0 -- <.04 -- .23 -- <1.0

03-29-01 -- 1.0 -- <.04 -- <.08 -- <1.0

05-02-01 -- .98 -- <.04 -- <.08 -- <1.0

05-21-01 -- 1.0 -- <.04 -- <.08 -- 1.1

08-15-01 -- 1.1 -- <.04 -- <.08 -- <1.0

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001–Continued

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)
60 Surface-Water/Ground-Water Interaction of the Spokane River and the Spokane Valley/Rathdrum Prairie Aquifer, Idaho and Washington

Well 21 10-05-00 -- 0.27 -- 0.06 -- <0.08 -- 10

12-20-00 -- .29 -- <.04 -- .14 -- 1.6

03-29-01 -- .22 -- <.04 -- <.08 -- 3.7

05-03-01 -- .12 -- .15 -- <.08 -- 11

05-21-01 -- e.18 -- .04 -- <.08 -- 12

08-15-01 <2.0 .22 .06 .05 <1.0 <.08 12 9.8

Well 22 10-05-00 -- .33 -- .21 -- <.08 -- 27

12-20-00 -- .25 -- .13 -- <.08 -- 19

03-29-01 -- .22 -- .27 -- <.08 -- 43

05-03-01 -- .28 -- .08 -- <.08 -- 21

05-21-01 -- .21 -- .25 -- <.08 -- 42

08-15-01 <2.0 .20 .15 .12 <1.0 <.08 18 17

Well 23 10-05-00 -- .35 -- .41 -- <.08 -- 42

12-20-00 -- .22 -- .41 -- .09 -- 48

03-29-01 -- .24 -- .46 -- e.04 -- 60

05-03-01 -- .21 -- .42 -- e.05 -- 53

05-21-01 -- .33 -- .39 -- <.08 -- 49

08-15-01 <2.0 .49 .50 .52 <1.0 <.08 44 44

Well 24 10-05-00 -- 1.7 -- <.04 -- <.08 -- <1.0

12-20-00 -- 1.8 -- <.04 -- e.04 -- <1.0

03-29-01 -- 2.0 -- <.04 -- e.07 -- <1.0

05-03-01 -- 1.8 -- <.04 -- <.08 -- <1.0

05-21-01 -- 2.0 -- <.04 -- <.08 -- <1.0

08-15-01 -- 1.8 -- <.04 -- <.08 -- <1.0

Well 25 10-04-00 -- 2.4 -- <.04 -- <.08 -- <1.0

12-20-00 -- 2.0 -- <.04 -- <.08 -- <1.0

03-29-01 -- 2.6 -- <.04 -- e.07 -- 1.2

05-02-01 -- 3.2 -- <.04 -- e.05 -- 1.8

05-21-01 -- 2.6 -- <.04 -- <.08 -- <1.0

08-14-01 3.0 2.7 <.04 <.04 <1.0 <.08 <1.0 <1.0

1Spokane River sampled at Post Falls, Idaho (station 12419000).

2

Number corresponds to wells listed in table 1 and shown in figure 3.

Table 8. Selected trace-element concentrations of the Spokane River at Post Falls, Idaho, and ground water from monitoring 

wells within the Spokane Valley/Rathdrum Prairie aquifer, 1999-2001–Continued

[e, estimated; μg/L, micrograms per liter; <, less than; --, no data]

Site1/well

number2 Date

Arsenic

total

recoverable

(μg/L as 

As)

Arsenic,

dissolved

(μg/L as 

As)

Cadmium,

total

recoverable

(μg/L as 

Cd)

Cadmium,

dissolved

(μg/L as 

Cd)

Lead, total

recoverable

 (μg/L as 

Pb)

Lead,

dissolved

(μg/L as 

Pb)

Zinc, total 

recoverable

(μg/L as

Zn)

Zinc,

dissolved

(μg/L as

Zn)