Abstract

A study of uranium in groundwater in northeastern Washington was conducted to make a preliminary assessment 

of naturally occurring uranium in groundwater relying on existing information and limited reconnaissance sampling. 

Naturally occurring uranium is associated with granitic and metasedimentary rocks, as well as younger sedimentary 

deposits, that occur in this region. The occurrence and distribution of uranium in groundwater is poorly understood. 

U.S. Environmental Protection Agency (EPA) regulates uranium in Group A community water systems at a maximum 

contaminant level (MCL) of 30 μg/L in order to reduce uranium exposure, protect from toxic kidney effects of 

uranium, and reduce the risk of cancer. However, most existing private wells in the study area, generally for single 

family use, have not been sampled for uranium. This document presents available uranium concentration data 

from throughout a multi-county region, identifies data gaps, and suggests further study aimed at understanding the 

occurrence of uranium in groundwater.

The study encompasses about 13,000 square miles (mi2) in the northeastern part of Washington with a 2010 

population of about 563,000. Other than the City of Spokane, most of the study area is rural with small towns 

interspersed throughout the region. The study area also includes three Indian Reservations with small towns and 

scattered population. The area has a history of uranium exploration and mining, with two inactive uranium mines on 

the Spokane Indian Reservation and one smaller inactive mine on the outskirts of Spokane.

Historical (1977–2016) uranium in groundwater concentration data were used to describe and illustrate the general 

occurrence and distribution of uranium in groundwater, as well as to identify data deficiencies. Uranium concentrations were detected at greater than 1 microgram per liter (μg/L) in 60 percent of the 2,382 historical samples (from 

wells and springs). Uranium concentrations ranged from less than 1 to 88,600 μg/L, and the median concentration of 

uranium in groundwater for all sites was 1.4 μg/L. 

New (2017) uranium in groundwater concentration data were obtained by sampling 13 private domestic wells 

for uranium in areas without recent (2000s) water-quality data. Uranium was detected in all 13 wells sampled for 

this study; concentrations ranged from 1.03 to 1,180 μg/L with a median of 22 μg/L. Uranium concentrations of 

groundwater samples from 6 of the 13 wells exceeded the MCL for uranium. Uranium concentrations in water 

samples from two wells were 1,130 and 1,180 μg/L, respectively; nearly 40 times the MCL. 

Additional data collection and analysis are needed in rural areas where self-supplied groundwater withdrawals 

are the primary source of water for human consumption. Of the roughly 43,000 existing water wells in the study area, 

only 1,755 wells, as summarized in this document, have available uranium concentration data, and some of those data 

are decades old. Furthermore, analysis of area groundwater quality would benefit from a more extensive chemicalanalysis suite including general chemistry in order to better understand local geochemical conditions that largely 

govern the mobility of uranium. Although the focus of the present study is uranium, it also is important to recognize 

that there are other radionuclides of concern that may be present in area groundwater.

Figure 1. Location of study area and areal distribution of existing water wells included in the Washington State Department of Ecology well-log database (Washington State Department of Ecology, 2017), 

northeastern Washington.

Introduction

Groundwater monitoring in northeastern Washington has shown elevated concentrations of uranium in 

private wells and several community water systems. Naturally occurring uranium is associated with granitic and 

metasedimentary rocks, as well as younger sedimentary deposits, that occur in this region. The occurrence and 

distribution of uranium in groundwater, however, is poorly understood and warrants investigation in order to 

reduce human exposure to uranium, protect kidneys from toxic effects of uranium, and reduce the risk of cancer. 

Basic knowledge and a greater awareness of the occurrence and distribution of uranium in groundwater throughout 

northeastern Washington would aid homeowners and health officials in evaluating its potential presence and making 

informed decisions on further testing and treatment of drinking water supplies.

Purpose and Scope 

This document presents available uranium concentration data from throughout a multi-county region, identifies 

data gaps, and suggests further study aimed at understanding the occurrence of uranium in groundwater. It also 

conveys the issue and presents available information to local health agencies and the general public in order to 

reduce exposure of humans to potentially harmful naturally occurring uranium in groundwater. Historical geologic, 

hydrogeologic, and uranium concentration data for groundwater for an area of northeastern Washington was compiled 

from multiple sources, tabulated, and mapped. Recent (2017) groundwater samples were collected by the U.S. 

Geological Survey (USGS) and analyzed for uranium concentrations from 13 wells in areas without recent waterquality data. The distribution of uranium concentrations in groundwater was evaluated with regard to the geology; the 

material within the water-bearing zone of the sampled water wells and the material mapped at land surface at the well 

and spring locations.

Description of Study Area

The study area includes all of Ferry, Stevens, and Pend Oreille Counties, most of Spokane County, and parts 

of Okanogan, Douglas, Grant, and Lincoln Counties, and encompasses about 13,000 mi2 in the northeastern part of 

Washington (fig. 1). Based on the 2010 Census, the population of the study area is about 563,000; the largest city is 

Spokane, Washington, with a population of about 209,000 (Washington State Office of Financial Management, 2017). 

With the exception of Spokane, most of the study area is rural with small towns interspersed throughout the region. 

A population of about 438,000 in the study area is served by public water systems, and 22 percent, or a population of 

about 125,000, is served by private domestic wells (Washington State Department of Health, 2017; Washington State 

Office of Financial Management, 2017). The distribution of the roughly 43,000 existing water wells in the study area 

is shown in figure 1.

Uranium in the Environment

Uranium is a radioactive element, or radionuclide, that occurs naturally, generally in low concentrations, in 

rock, soil, surface water and groundwater (Argonne National Laboratory, 2007). Unlike many water pollutants, all 

radionuclides dissolved in water are colorless, odorless, and tasteless and, therefore, cannot be detected by our senses 

(Zapecza, and Szabo, 1988). Uranium can be highly concentrated in intrusive igneous rocks, primarily granitic rocks, 

and also is found in sedimentary rocks such as black shales, soils above limestone, and phosphate rocks (Ayotte and 

others, 2007, 2011).

Uranium-238 is the most common of several natural isotopes and accounts for 99 percent of the mass of natural 

samples. Uranium decays slowly by emitting alpha particles and has multiple daughter products and decay paths (fig. 

2). Radiation, in the form of alpha and beta particles, is matter and energy that is released from the unstable nuclei 

of uranium and its daughter products. Figure 2 shows the important daughter products in the U-238 decay series, 

indicates whether the primary decay mode is through alpha or beta emission, and gives the half-life (length of time 

required for half of the atoms of a radioactive isotope to decay). For example, through the decay series of U-238, 

alpha and beta particles are emitted and radium and radon are formed as interim radiogenic daughter products. These, 

in turn, ultimately decay to a stable form of lead.

Federal Regulation

EPA’s Final Rule for Radionuclides in Drinking Water took effect in 2003, regulating uranium at a maximum 

contaminant level (MCL) of 30 μg/L (U.S. Environmental Protection Agency, 2000). The rule also regulates radium, 

and alpha and beta particles due to their radiological toxicity. Group A community water systems, which serve at least 

15 service connections or 25 residents regularly year round, are required to meet the final MCLs in order to reduce 

uranium exposure, protect from toxic kidney effects of uranium, and reduce the risk of cancer (U.S. Environmental 

Protection Agency, 2001). 

Geologic Setting and Uranium Exploration

The geology of northeastern Washington is complex and is composed of various types of bedrock (for 

example, shale, slate, dolomite, quartzite, and granite) overlain in many places with varying types and thicknesses 

of unconsolidated sediment such as silt, sand, gravel, and clay (fig. 3). Bedrock units in the area record a complex 

structural history involving repeated periods of folding, faulting, and igneous intrusion (Lasmanis, 1991).

Uranium ore was discovered in Washington in the 1950s, and was mined at several locations including the 

Midnite and Sherwood Mines on the Spokane Reservation in Stevens County, and the smaller Daybreak Mine on the 

western side of Mount Spokane in Spokane County (fig. 3). Uranium assays (prospects) also occur throughout the 

region (fig. 3). Extraction of uranium ore at these mines largely ended by the early 1980s (Dahlkamp, 2011).

The uranium ore at the Midnite Mine was located in a contact zone between a granitic intrusion and surrounding 

metasedimentary rocks. At the Sherwood Mine, the uranium ore was located in conglomerate overlying granite where 

the mineralization was associated with carbonaceous matter within the conglomerate matrix (Dahlkamp, 2011). 

At the Daybreak Mine, uranium minerals were concentrated along shear zones and within pegmatite dikes within 

granitic rocks, including museum-quality autunite (hydrated calcium uranyl phosphate) crystals (Dahlkamp, 2011). 

Weathering of uranium-bearing units such as the granites resulted in occurrence of uranium in younger sedimentary 

deposits, including a small peat bog near Colville (Johnson and others, 1987). Due to the presence of uranium-rich 

granitic rocks, as well as the general mobility of uranium in circulating groundwater, the regions that are likely 

susceptible to occurrences of uranium in groundwater include Pend Oreille, Stevens, and Ferry Counties, as well as 

eastern Okanogan, northern Spokane, and northernmost Lincoln Counties (fig. 3).

Historical Data Sources

Although much of the study area is remote and sparsely populated, the bedrock aquifers in northeastern 

Washington are increasingly being developed for drinking-water supply. In most situations, private wells are only 

tested at the well owner’s discretion or when they are newly constructed. In order to inform owners of private and 

unregulated wells, two fact sheets were developed to encourage private well owners to test the water from their wells 

for uranium and their indoor air for radon gas (Northeast Tri-County Health District and Washington State Department 

of Health, 2006; Washington State Department of Health, 2011). Historical (1977–2016) uranium concentration 

data were obtained from various local and national sources to describe and illustrate the general occurrence and 

distribution of uranium in groundwater in northeastern Washington.

Local Sources

The presence of naturally occurring uranium in local groundwater became evident in the early 2000s following 

selected testing of new or existing water sources, many near Colville in Stevens County, Washington (Northeast 

Tri-County Health District (NETCHD) and Washington State Department of Health (WDOH), 2006; Schneider, 

2016). Due to increasing concerns about the possible presence of uranium in area groundwater, the NETCHD added 

uranium to their water-quality testing recommendations in 2012 in the three counties it serves—Ferry, Stevens, and 

Pend Oreille (M. Schanz, NETCHD, written commun., 2013). By November 2016, samples from 411 private wells 

had been collected in the Tri-County area. In 2017, the NETCHD Board of Health added initial testing of uranium for 

Group B public water-supply systems (which generally serve 3 to 14 connections or fewer than 25 people per day) in 

Ferry, Stevens, and Pend Oreille Counties based on the criteria that uranium is a contaminant of concern in the area 

(M. Schanz, written commun., February 2017). Adding the testing of Group B systems expands the understanding of 

the occurrence of uranium in most public water-supply systems in the Tri-County area. However, the testing does not 

address the existing private, generally single-family use, wells which are the most common sources of drinking water 

in the rural areas.

In 2012, the Spokane Tribe of Indians began a sampling program of all private wells on the Spokane Reservation 

in southern Stevens County (fig. 1). In addition, the Tribe conducted follow-up testing for gross alpha concentrations 

in wells where uranium concentrations exceeded 4 μg/L and samples from numerous wells with adjusted gross alpha 

concentrations exceeded the MCL of 15 picocuries per liter (pCi/L). Similar to the building requirements in Stevens 

County, Indian Health Services now requires sampling for uranium of all newly drilled wells on the reservation (B. 

Crossley, Spokane Tribe Department of Natural Resources, written commun., 2013). As of 2016, the Spokane Tribe 

had sampled 237 wells for uranium. 

WDOH requires testing of Group A systems in Washington State according to EPA’s Final Radionuclide Rule 

and maintains analytical results in an on-line database (https://fortress.wa.gov/doh/eh/portal/odw/si/Intro.aspx). There 

are several systems that are currently (2014) addressing water-quality issues associated with elevated radionuclides 

(uranium or radium) in Okanogan, Spokane, and Stevens Counties (B. Stasney, Washington State Department of 

Health, written commun., January 2014). As of November 2016, uranium concentration data for 48 Group A systems 

in the study area were available from the WDOH database (table 1).

Table 1. Historical uranium concentrations in groundwater samples, northeastern Washington, 1977–2016.

Table 1 is a Microsoft® Excel file that is available for download at https://doi.org/10.3133/sim3401.

U.S. Geological Survey Data Sources

A nationwide program of uranium exploration, the National Uranium Resource Evaluation (NURE) program, 

was operated from 1973 to 1983 with the intention of identifying areas favorable for uranium exploration throughout 

the United States (Smith, 1997). The program included geologic and geophysical mapping, as well as selected 

geochemical analyses of water (wells, springs, and streams) and stream sediment. NURE data for 980 wells and 639 

springs were obtained for the area of study in northeastern Washington (U.S. Geological Survey, 2004) and used in 

this study (table 1).

Uranium concentration data for 67 wells in the study area also were obtained from the USGS National Water 

Information System (NWIS) database (table 1). The values obtained are for the most recent sample from a mix of 

monitoring, domestic, and public supply wells sampled by the USGS for various studies from 1980 to 2016. The 

highest concentrations (nine that are greater than 8,000 μg/L) are associated with monitoring wells near Midnite Mine.

Uranium (U)

Protactinium (Pa)

Thorium (Th)

Radium (Ra)

Radon (Rn)

Polonium (Po)

Bismuth (Bi)

Lead (Pb)

U-238

4.5×109 y

U-234

22.5×104 y

Th-234

24.1 d

Pa-234

1.2 m

Th-230

8.0×104 y

Ra-226

16×102 y

Rn-222

3.8 d

Po-218

3.1 m

Pb-214

26.8 m

Bi-214

19.7 m

Pb-206

(stable)

Po-210

138 d

Bi-210

5.0 d

Po-214

1.4×10-4 s

Pb-210

22 y

α

α

α

α α α

β

β

β

β

α α

β

β y=year

d=day

m=minute

s=second

Figure 2. Uranium-238 radioactive decay series (from Ayotte and others, 2007).

Uranium Concentrations in Groundwater

Historical (1977–2016) uranium concentration data were compiled from NETCHD, the Spokane Tribe, USGS 

(NWIS and NURE), and WDOH and were used to describe and illustrate the general occurrence and distribution 

of uranium in groundwater in northeastern Washington. The data are from a total of 2,382 sites (wells and springs) 

and are listed in table 1, summarized in table 2, and shown in figure 4 by ranges of uranium concentrations. 

Uranium concentrations were detected at greater than 1 μg/L in 60 percent of the 2,382 historical samples. Uranium 

concentrations ranged from less than 1 to 88,600 μg/L, and the median concentration of uranium in groundwater for 

all sites was 1.4 μg/L. A total of 84 sites sampled (4 percent) exceeded EPA’s MCL of 30 μg/L uranium (table 2, fig. 

4). Uranium concentrations ranged from less than 1 to 965 μg/L, not including the results for the monitoring wells 

near Midnite Mine.

Figure 3. Geology, locations of uranium assay sites or mines, and locations of wells and springs with historical uranium concentrations in groundwater of greater than or equal to 10 micrograms per liter (μg/L), northeastern Washington, 1977–2016.

Recent (2017) Uranium Concentration Data

The USGS collected groundwater samples from 13 private domestic wells for uranium analysis in July 2017 in 

areas without recent (2000s) water-quality data but within areas where granite or shale was the predominant geology, 

mostly in northern Lincoln and Spokane Counties (fig. 6, table 4). The new data collected as part of this study was 

done in accordance with the USGS Washington Water Science Center water-quality assurance plan (Conn and others, 

2017). Groundwater samples from the selected wells and associated quality-assurance samples were analyzed for 

uranium at the USGS National Water Quality Laboratory in Denver, Colorado, following inductively coupled plasmamass spectrometry techniques described in Garbarino and others (2005). All data associated with these sample sites 

are stored in the USGS NWIS; site identifiers and results are included in table 4.

Uranium was detected in all 13 wells sampled for this study; concentrations ranged from 1.03 to 1,180 μg/L 

(tables 1 and 4) with a median of 22 μg/L. Uranium concentrations of groundwater samples from 6 of the 13 wells 

exceeded the MCL for uranium. Uranium concentrations in water samples from two wells (USGS02 and USGS11) 

were 1,130 and 1,180 μg/L, respectively; nearly 40 times the MCL.

The geographic distribution of the wells sampled shown by ranges of uranium concentrations are shown in 

figure 6. Only one (USGS07) of the three wells sampled in northern Lincoln County exceeded the MCL for uranium 

(table 4) and neither of the wells (USGS12 and USGS13) sampled in Stevens and Pend Oreille Counties exceeded the 

MCL for uranium (table 4). In northern Spokane County, however, five (USGS02, USGS04, USGS06, USGS09, and 

USGS11) of the eight wells sampled greatly exceeded the MCL for uranium with concentrations ranging from 152 to 

1,180 μg/L.

Figure 4. Magnitude and distribution of historical uranium concentrations in groundwater samples, 

northeastern Washington, 1977–2016.

Considerations for Future Data-Collection Efforts

During the course of this investigation, several data needs were identified that, if filled, would provide a 

more complete understanding of the occurrence and distribution of uranium and other radionuclides of concern 

in northeastern Washington. Completion of these tasks could aid homeowners and health officials in evaluating 

the potential presence of harmful constituents and making informed decisions on further testing and treatment of 

drinking-water supplies. Potentially beneficial data-collection efforts identified during this study are listed below, in 

no particular order of importance.

• Much of the study area is under-represented in terms of available uranium concentration data for drinkingwater sources. Additional data collection and analysis are needed in rural areas where self-supplied 

groundwater withdrawals are the primary source of water for human consumption. Most existing private 

wells in the study area have not been sampled for uranium. Of the roughly 43,000 existing water wells in the 

study area (fig. 1), only 1,755 wells, as summarized in this document, have available uranium concentration 

data, and some of those data are decades old.

• Although the focus of the present study is uranium, it is important to recognize that there are other 

radionuclides of concern that may be present in area groundwater. Based on limited data from regulated 

public supply systems and the Spokane Tribe, uranium concentrations in some wells were less than the 

standard, but radium and or alpha particle concentrations were greater than levels of concern (B. Stasney, 

WDOH, written commun., January 2014; B. Crossley, Spokane Tribe, written commun., June 2017). 

Expanded testing of radionuclides in groundwater would provide area residents and local health agencies a 

Study 

Area

WASHINGTON

Table 2. Summary of historical uranium concentrations in groundwater including number of sites in each dataset, range of sample collection dates, and range of values, northeastern Washington, 1977–2016.

[Source of data: DOH, Washington State Department of Health; NURE, National Uranium Resources Evaluation program; NWIS, U.S. Geological Survey National Water Information System; NETCHD, Northeast Tri County Health District; Spokane Tribe, Spokane Tribe of Indians. Uranium 

concentration: Reported in micrograms per liter (μg/L) [minimum value, median value, maximum value, <less than]. Number of sites ≥30 μg/L: Number of sites with uranium concentrations greater than or equal to 30 micrograms per liter]

Source of data Area sampled

(or County)

Number of sites

Range of sample 

collection dates

Uranium concentration

[min; median; max]

(μg/L)

Number of sites 

≥30 μg/L 

(percent)

Notes

Wells Springs

DOH All of study area 47 1 1994–2016 [<1; 8.29; 49.6] 8 (17) Most recent untreated unblended sample when available (3 samples from well fields when samples from individual wells not available).

NURE (USGS) All of study area 980 639 1977–1979 [<1; 1.17; 165] 22 (1) One-time sample during national uranium exploration.

NWIS (USGS) All of study area 67 0 1980–2016 [<1; 2.18; 88,600] 15 (22) Most recent sample; sites are a mix of monitoring, domestic, and public supply wells. Highest values are associated with monitoring wells 

near Midnite Mine.

NETCHD Ferry 12 0 2012–2016 [<1; 2.5; 965] 28 (7) Owner-collected sample as part of building permit requirement or recommendation of Health Department (331 wells have driller’s log).

Pend Oreille 73 0 2012–2016

Stevens 326 0 2008–2016

Spokane Tribe Spokane Reservation, Stevens 237 0 2012–2016 [<1; 1.99; 203] 11 (5) Initial sampling of all wells on the Reservation.

All sources All of study area 2,382 1977–2016 [<1; 1.4; 88,600] 84 (4) Compilation of all data sources.

Agency for Toxic Substances and Disease Registry, 2008, Health Consultation, Mission Creek Water System, Evaluation of 

uranium and alpha particles in drinking water serving Mt. Hall School and surrounding areas, Boundary County, Idaho: U.S. 

Department of Health and Human Services, Atlanta, Georgia, 25 p.

Argonne National Laboratory, 2007, Radiological and chemical fact sheets to support health risk analyses for contaminated areas; 

133 p., accessed November 26, 2013, at http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf.

Ayotte, J.D., Flanagan, S.M., and Morrow, W.S., 2007, Occurrence of uranium and 222radon in glacial and bedrock aquifers in 

the northern United States, 1993–2003: U.S. Geological Survey Scientific Investigations Report 2007-5037, 84 p., https://pubs.

usgs.gov/sir/2007/5037/.

Ayotte, J.D., Gronberg, J.M., and Apodaca, L.E., 2011, Trace elements and radon in groundwater across the United States, 1992–

2003: U.S. Geological Survey Scientific Investigations Report 2011–5059, 115 p., https://pubs.usgs.gov/sir/2011/5059.

Caldwell, R.R., Nimick, D.A., and DeVaney, R.M., 2013, Occurrence and hydrogeochemistry of radiochemical constituents in 

groundwater of Jefferson County and surrounding areas, southwestern Montana, 2007 through 2010: U.S. Geological Survey 

Scientific Investigations Report 2013-5235, 61 p., https://pubs.usgs.gov/sir/2013/5235/.

Conn, K.E., Huffman, R.L., and Barton, Cynthia, 2017, Quality-assurance plan for water-quality activities in the U.S. Geological 

Survey Washington Water Science Center: U.S. Geological Survey Open-File Report 2017–1044, 66 p., https://doi.org/10.3133/

ofr20171044.

Table 4. Uranium concentrations measured in groundwater samples with well depth and type, northeastern Washington, 

July 2017.

[PROJ ID, project identifier. Uranium concentration: Concentration of uranium in groundwater reported in micrograms per liter (μg/L). Well 

depth, in feet below land surface. Wells with uranium concentrations greater than 30 μg/L are highlighted]

PROJ ID USGS site 

identifier

Uranium 

concentration

(μg/L)

Geologic material of 

open interval

Well depth 

(ft) County

USGS01 474248117191301 1.38 Granite 320 Spokane

USGS02 474607117114601 1,130 Granite 600 Spokane

USGS03 474719117070701 9.97 Granite 483 Spokane

USGS04 474906117105501 152 Granite 473 Spokane

USGS05 474950117254101 5.3 Sand and gravel 64 Spokane

USGS06 474953117255601 160 Granite 517 Spokane

USGS07 475234118134401 35 Granite 498 Lincoln

USGS08 475253118095101 10.2 Granite 497 Lincoln

USGS09 475312117123501 210 Granite 298 Spokane

USGS10 475325118100401 10.6 Granite 598 Lincoln

USGS11 475545117135201 1,180 Granite 550 Spokane

USGS12 483432117485201 22 Shale 500 Stevens

USGS13 485224117202601 1.03 Shale 400 Pend Oreille

Figure 5. Locations of wells with associated uranium concentrations showing generalized geologic material of open interval, Ferry, Pend Oreille, and Stevens 

Counties, Washington. Wells with groundwater samples with uranium concentrations greater than or equal to 30 micrograms per liter are labeled.

Figure 6. Magnitude and distribution of uranium concentrations in groundwater samples collected 

from wells by the U.S. Geological Survey, northeastern Washington, July 2017.

Table 3. Summary of historical uranium concentrations in groundwater samples by geologic material of open interval for 

332 wells with available drillers logs, northeastern Washington. 

[Median depth of well, in feet below land surface. Number of sites ≥30 μg/L: Number of sites with uranium concentrations greater than or equal 

to 30 micrograms per liter. Uranium concentration: Reported in micrograms per liter (μg/L) [minimum value, median value, maximum value, 

<less than]

Geologic material of open interval

[unit abbreviation]

Median depth 

of well

(ft)

Number of sites 

≥ 30 μg/L

(percent)

Total 

number of 

sites

Uranium concentration

[min; median; max]

(μg/L)

Basalt and associated interbeds [BT] 154 0 (0) 18 [<1; <1; 2.50]

Gneiss [GN] 240 0 (0) 1 [16]

Granite [GR] 300 17 (18) 96 [<1; 4.68; 119]

Limestone [LM] 300 0 (0) 26 [<1; 1.86; 26.0]

Multiple units [M] 116 1 (12) 8 [1.11; 11.3; 76.5]

Quartz or quartzite [QT] 300 0 (0) 9 [<1; 2.57; 9.03]

Mostly sand and gravel; some silt and clay [SG] 98 1 (<1) 131 [<1; 2.44; 50.3]

Shale [SH] 280 6 (14) 43 [<1; 3.79; 965]

Comparison of Historical Uranium Concentrations with Geology

A surficial geologic map (fig. 3; U.S. Geological Survey, 2005) was used to examine if an association exists 

between the surface geology mapped at sample sites and elevated concentrations of uranium (greater than or equal 

to 10 μg/L) in the water samples collected at those sites. There is a general, but inconsistent, relation between the 

locations of the 352 historical sample sites (wells and springs) with elevated uranium concentrations and mapped 

surficial geologic units (fig. 3). The relation exists for 83 sites that plot where granite is mapped and for 16 sites that 

plot where shale is mapped. However, the relation does not exist for 147 additional sites with elevated uranium that 

are located where unconsolidated deposits are mapped at the surface. In the case where the sample sites are wells, 

these wells likely are open to and obtaining groundwater from deeper units, such as granite, than what is mapped at 

the land surface.

A better indicator for the potential occurrence of elevated uranium in groundwater produced from a well is the 

geologic material that supplies groundwater to the well. The lithologic description of the material that the wells were 

completed in (produced water from) was determined from the material described within the open intervals of the 

wells (locations of wells screens, perforations, or open bore holes) on the available driller’s logs for 332 NETCHD 

wells. Lithologic descriptions on each log were simplified into the major rock type described within the open 

interval of the well. These generalized lithologic descriptions (example, granite) were then compared to the uranium 

concentrations of the groundwater samples collected at those wells. Summary statistics are provided in table 3 and the 

locations of wells and well type (geologic material of open interval) are shown in figure 5. Uranium concentrations 

did not exceed the MCL (table 3) for wells completed in basalt (BT), limestone (LM), or quartzite (QT). However, 

uranium concentrations exceeded the MCL in 18 and 14 percent of wells completed in granite (GR) and shale (SH), 

respectively. Similarly, uranium concentrations exceeded the MCL in 12 percent of wells completed in multiple 

geologic units (M), but this was due to the wells being partially open to granite or shale. Uranium concentration was 

greater than the MCL in 1 of 130 wells completed in unconsolidated sediment, such as sand and gravel (SG). 

Most historical data were collected during the late 1970s as part of the NURE program to evaluate uranium 

resource potential rather than to assess groundwater quality. The NURE dataset does, however, provide the most 

widespread coverage of historical concentration data for uranium in groundwater. The remaining 763 historical sites 

were sampled specifically for water-quality purposes, and those data were from WDOH, USGS, NETCHD, and the 

Spokane Tribe (table 2). Stevens County, with data for 563 wells, had the greatest coverage compared to all counties 

in northeastern Washington due to the adoption of testing in 2012 through their building permit process, as well as the 

Spokane Tribe’s data collection that began at the same time.

more complete understanding of their potential presence. Further, with sufficient data, screening protocols 

also might be developed to help address which wells, based on location, geology, and possibly depth, should 

be sampled and for which constituents.

• Further analysis of area groundwater quality would benefit from a more extensive chemical-analysis suite 

including general chemistry—pH, dissolved oxygen, common ion and organic carbon concentrations, 

and reduction/oxidation potential—in order to better understand local geochemical conditions that largely 

govern the mobility of uranium. Uranium is most soluble in oxygen-rich (oxidizing) groundwater and can be 

fairly easily dissolved and transported by oxidizing groundwater; thus, it can be transported to areas far from 

its original emplacement (Zapecza and Szabo, 1988). Uranium is less mobile in oxygen-poor (reducing) 

groundwater, and it tends to be adsorbed strongly onto organic matter such as peat. By adding general 

chemistry to future sampling plans, a better understanding of local geochemical conditions and how they 

affect the movement of uranium could be gained.

• The occurrence of radionuclides in drinking water is not limited to Washington State but is rather a regional 

issue due to the occurrence of similar rock types in neighboring Idaho, Montana, and Canada. Recent studies 

in northern Idaho and western Montana document the presence of radionuclides at concentrations greater 

than health standards in area drinking water (Agency for Toxic Substances and Disease Registry, 2008; 

Caldwell and others, 2013). A region-wide assessment utilizing available data would help raise awareness 

about the possible presence of radionuclides in the region’s drinking water.

Dahlkamp, F.J., 2011, Uranium Deposits of the World: USA and Latin America: A Springer Live Reference. Springer-Verlag 

Berlin Heidelberg, accessed February 28, 2017, at http://www.springer.com/us/book/9783540785552?wt_mc=ThirdParty.

SpringerLink.3.EPR653.About_eBook.

Garbarino, J.R., Kanagy, L.K., and Cree, M.E., 2005, Determination of elements in natural-water, biota, sediment and soil samples 

using collision/reaction cell inductively coupled plasma-mass spectrometry: U.S. Geological Survey Techniques and Methods, 

book 5, chap. B1, 88 p., https://pubs.usgs.gov/tm/2006/tm5b1/.

Health Canada, 2010, Water Talk Fact Sheet, Uranium in Drinking Water: Website, accessed August 7, 2017, at https://www.

canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/water-quality/water-talk-uraniumdrinking-water-2010-health-canada-brochure.html.

Johnson, S.Y., Otton, J.K., and Macke, D.L., 1987, Geology of the Holocene surficial uranium deposit of the north fork of Flodelle 

Creek, northeastern Washington: Geological Society of America Bulletin, v. 98, no. 1, p. 77-85.

Lasmanis, R., 1991, The Geology of Washington: Rocks and Minerals, v. 66, no. 4, July/August 1991, p. 262-277.

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northeast Washington drinking water wells: accessed November 3, 2017, at http://www.netchd.org/fileadmin/user_upload/

Environmental%20Health/Safe%20Drinking%20Water%20Protection/Uranium%20in%20Drinking%20Water/Radionuclides_

in_Private_Northeast_Washington_Drinking_Water_Wells.pdf.

Schneider, M., 2016, Uranium in the groundwater of three counties in northeast Washington State case study: University of Findlay 

Master of Science in Environmental, Safety, and Health Management, 47 p.

Smith, S.M., 1997, National geochemical database: Reformatted data from the National Uranium Resource Evaluation (NURE) 

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radionuclides.pdf.

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References

Base from U.S. Geological Survey digital data, 1:750,000

Lambert Conformal Conic projection: State Plane Washington North

£395

Wellpinit

Nespelem

Grand Coulee Dam

FERRY

STEVENS

OKANOGAN

LINCOLN

DOUGLAS

SPOKANE

PEND OREILLE

GRANT

Spokane River

Okanogan River

Kettle River

Pend Oreille River

Sanpoil River

Colville River

Columbia River

Hall Creek

Little Spokane River

Omak Creek

Toroda Creek

Dragoon Creek

Deep Creek

Myers Creek

Bonaparte Creek

Sherman Creek

Ninemile Creek

Nespelem

River

East Foster Creek

Salmon Creek

Tunk Creek

Coulee Creek

Wilson Creek

Goose Creek

Lynx Creek

Sinking Creek

Curlew Creek

DeerCreek

Deadman Creek

Mill Creek

Crab

Creek

Little Pend Oreille River

Sullivan Creek

Harvey Creek

Hawk Creek

Tacoma Creek

West Fork Sanpoil River

Lake Creek

West Foster Creek

Chamokane Creek

S ni lahekin Creek

Stepstone Creek

Lost Creek

Kalispell Creek

South Fork Boulder Creek

North Fork Chewelah Creek

Antoine Creek

Middle Foster Creek

North Fork Sanpoil River

Canniwai Creek

Hangman Creek

Lake

Roosevelt

Banks

Lake

Long

Lake

Omak

Lake

Osoyoos

Lake

Deer

Lake

Loon

Lake

Curlew

Lake

COLVILLE INDIAN RESERVATION

SPOKANE INDIAN RESERVATION

KALISPEL 

INDIAN

RESERVATION

CANADA

IDAHO

Omak

Spokane

Newport

Okanogan

Colville

Republic

Davenport Spokane

Valley

0 25 50 MILES

0 25 50 KILOMETERS

119° 118° 117°

49°

48°

EXPLANATION

Water well (Washington State 

Department of Ecology, 2017)

WASHINGTON

Study

Area

FERRY

STEVENS

OKANOGAN

LINCOLN

DOUGLAS

SPOKANE

PEND OREILLE

GRANT

CANADA

IDAHO

Base from U.S. Geological Survey digital data, 1:750,000

Lambert Conformal Conic projection: State Plane Washington North

0 25 50 MILES

0 25 50 KILOMETERS

119° 118° 117°

49°

48°

Uranium concentration in groundwater, 

in micrograms per liter, for wells

Uranium concentration in groundwater, 

in micrograms per liter, for springs

EXPLANATION

≤ 4.9

5.0 to 9.9

10.0 to 19.9

20.0 to 29.9

≥ 30.0

≤ 4.9

5.0 to 9.9

10.0 to 19.9

20.0 to 29.9

≥ 30.0

FERRY

STEVENS

OKANOGAN

LINCOLN

SPOKANE

PEND OREILLE

GRANT

CANADA

IDAHO

82

119

115

965

33.6

39.7

84.1

58.2

98.8

90.1

44.3

36.4

89.7

59.8

76.5

31.3

70.8

85.9

49.6

57.3

46.5

50.3

62.8

39.4

51.2

0 25 50 MILES

0 25 50 KILOMETERS

119° 118° 117°

49°

48°

EXPLANATION

Generalized geologic material at the open 

interval of the well—Number is uranium 

concentration labeled only when greater 

than or equal to 30 micrograms per liter

BT - basalt and interbeds

GN - gneiss

GR - granite

LM - limestone

M - multiple units

QT - quartz or quartzite

SG - sand and gravel; some silt and clay

SH - shale

Base from U.S. Geological Survey digital data, 1:750,000

Lambert Conformal Conic projection: State Plane Washington North

Spokane River

Okanogan River

Kettle River

Pend Oreille River

Sanpoil River

Colville River

Columbia River

Hall Creek

Little Spokane River

Omak Creek

Toroda Creek

Dragoon Creek

Deep Creek

Myers Creek

Bonaparte Creek

Sherman Creek

Ninemile Creek

Nespelem

River

East Foster Creek

Salmon Creek

Tunk Creek

Coulee Creek

Wilson Creek

Goose Creek

Lynx Creek

Sinking Creek

Curlew Creek

DeerCreek

Deadman Creek

Mill Creek

Crab

Creek

Little Pend Oreille River

Sullivan Creek

Harvey Creek

Hawk Creek

Tacoma Creek

West Fork Sanpoil River

Lake Creek

West Foster Creek

Chamokane Creek

Si n

al hekin Creek

Stepstone Creek

Lost Creek

Kalispell Creek

South Fork Boulder Creek

North Fork Chewelah Creek

Antoine Creek

Middle Foster Creek

North Fork Sanpoil River

Canniwai Creek

Hangman Creek

Lake

Roosevelt

Banks

Lake

Long

Lake

Omak

Lake

Osoyoos Lake

Deer

Lake

Loon

Lake

Curlew

Lake

Base from U.S. Geological Survey digital data, 1:750,000

Lambert Conformal Conic projection: State Plane Washington North

FERRY

STEVENS

OKANOGAN

LINCOLN

DOUGLAS

SPOKANE

PEND OREILLE

GRANT

COLVILLE INDIAN RESERVATION

SPOKANE INDIAN RESERVATION

KALISPEL

INDIAN

RESERVATION

Sherwood

Mine

Midnite

Mine

Daybreak

Mine

CANADA

IDAHO

Mt. 

Spokane

EXPLANATION

Uranium assay site or mine—From

Washington Division of Geology 

and Earth Resources (2015)

Well—Uranium concentrations in 

groundwater greater than or equal to 

10 micrograms per liter

Spring—Uranium concentrations in 

groundwater greater than or equal to 

10 micrograms per liter

!

Primary lithology (simplified from 

U.S. Geological Survey, 2005)

(83) Number of sites (wells and 

springs) located within area 

mapped as granite

Unconsolidated deposits

Stream, glacial, or wind-blown

sediment (147)

Sedimentary rocks

Arkose

Wacke (2)

Dolomite

Sandstone

Conglomerate (1)

Graywacke

Limestone (5)

Shale (16)

Volcanic rocks

Basalt (7)

Rhyodacite (3)

Latite

Andesite (2)

Intrusive igneous rocks

Quartz monzodiorite (1)

Quartz diorite

Granite (83)

Diorite

Granodiorite (6)

Syenite

Quartz monzonite

Gabbro

Metamorphic rocks

Schist

Quartzite

Greenstone

Phyllite (2)

Amphibolite

Serpentinite

Biotite gneiss

Metasedimentary rock (1)

Orthogneiss (3)

0 25 50 MILES

0 25 50 KILOMETERS

119° 118° 117°

49°

48°

STEVENS

SPOKANE

PEND OREILLE

Spokane River

Pend Oreille River

Colville River

Hall Creek

Little Spokane River

Dragoon Creek

Deep Creek

Sherman Creek

Coulee Creek

Lynx Creek

Deer Creek

Deadman Creek

Mill Creek

Crab Creek

Little Pend Oreille River

Sullivan Creek

Harvey Creek

Hawk Creek

Tacoma Creek

Lake Creek

Chamokane Creek

Kalispell Creek

South Fork Boulder Creek

North Fork Chewelah Creek

Hangman Creek

Lake

Roosevelt

Long

Lake

Deer

Lake

Loon

Lake

CANADA

IDAHO

Spokane

Colville

Davenport

Newport

Kettle

Falls

COLVILLE

INDIAN

RESERVATION

SPOKANE INDIAN RESERVATION

KALISPEL

INDIAN 

RESERVATION

USGS09 USGS08

USGS07 USGS06

USGS05

USGS04 USGS03

USGS01 USGS02

USGS13

USGS12

USGS11

USGS10

Mt. 

Spokane

0 10 20 MILES

0 10 20 KILOMETERS

118° 117°

49°

48°

Base from U.S. Geological Survey digital data, 1:750,000

Lambert Conformal Conic projection: State Plane Washington North

EXPLANATION

Uranium concentration 

in groundwater, in 

micrograms per liter, 

for wells sampled 

in July 2017—Number is 

U.S. Geological Survey 

(USGS) well No. 

(see table 4)

≤ 4.9

5.0 to 9.9

10.0 to 19.9

20.0 to 29.9

≥ 30.0

Uranium Concentrations in Groundwater, Northeastern Washington

By

Sue C. Kahle, Wendy B. Welch, Alison E. Tecca, and Devin M. Eliason

2018

Prepared in cooperation with the

Washington State Department of Health U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3401

ISSN 2329-132X (print)

ISSN 2329-1311 (online)

https://.doi.org/10.3133/sim3401