C A N A D A

MEX ICO

ATLANTIC

OCEAN

CANADA

PACIFIC

OCEAN

Gulf of 

Alaska

Gulf of Mexico

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Principal aquifer system

EXPLANATION

0 400 MILES

0 400 KILOMETERS

0 50 MILES

0 50 KILOMETERS

0 100 200 400 MILES

0 200 400 KILOMETERS

Well and radium concentration—

 In picocuries per liter

Greater than or equal to 5 

1 to 4.99

Less than 1

Western Foreland Tertiary/

 Cretaceous sandstone

Rio Grande and Basin and 

 Range basin fill

Pacific Coastal (Central Valley

 and Willamette Basins) 

 alluvium and fill

Basalt

Western alluvium and fill

Coastal Plain, Southeastern

Coastal Plain—Texas Upland, 

 Gulf lowland, Mississippi Embayment

Floridan and surficial

Mid-Continent and Ozark Plateau 

 Cambro-Ordovician

High Plains Tertiary alluvium and fill

Glacial sand and gravel

Crystalline rock New England/New York

Northern Atlantic Coastal Plain

Appalachian Piedmont Mesozoic Basins

Valley and Ridge and Mississippian limestone

Base modified from U.S. Geological Survey 1:2,000,000 digital data, 1972 300

Albers Equal-Area Conic projection, Standard parallels 29°30'N and 45°30'N 

Central meridian 96°00'W 

Figure 1.  Elevated radium concentrations occur most commonly in aquifers in the

eastern and central United States for the wells sampled in 15 principal aquifer systems

across the United States. Ninety-eight percent of the wells that exceeded the combined

radium (radium-226 plus radium-228) drinking-water standard of 5 picocuries per liter

established by the U.S. Environmental Protection Agency were in aquifers east of the

High Plains (modified from U.S. Geological Survey, 2003).

Principal Aquifers Can Contribute Radium to Sources of 

Drinking Water Under Certain Geochemical Conditions

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3113

January 2012

What are the most important factors affecting dissolved radium concentrations in principal aquifers used for drinking 

water in the United States? Study results reveal where radium was detected and how rock type and chemical processes 

control radium occurrence. Knowledge of the geochemical conditions may help water-resource managers anticipate 

where radium may be elevated in groundwater and minimize exposure to radium, which contributes to cancer risk.

Summary of Major Findings

• Concentrations of radium in principal

aquifers used for drinking water 

throughout the United States generally

were below 5 picocuries per liter 

(pCi/L), the U.S. Environmental 

Protection Agency (USEPA) maximum 

contaminant level (MCL) for combined 

radium—radium-226 (Ra-226) plus 

radium-228 (Ra-228)—in public water 

supplies. About 3 percent of sampled 

wells had combined radium concentrations greater than the MCL. 

• Elevated concentrations of combined 

radium were more common in groundwater in the eastern and central United 

States than in other regions of the 

Nation. About 98 percent of the wells 

that contained combined radium at 

concentrations greater than the MCL 

were east of the High Plains. 

• The highest concentrations of combined 

radium were in the Mid-Continent and 

Ozark Plateau Cambro-Ordovician aquifer

system and the Northern Atlantic Coastal 

Plain aquifer system. More than 20 percent

of sampled wells in these aquifers had 

combined radium concentrations that 

were greater than or equal to the MCL.

• Concentrations of Ra-226 correlated 

with those of Ra-228. Radium-226 and 

Ra-228 occur most frequently together 

in unconsolidated sand aquifers, and 

their presence is strongly linked to 

groundwater chemistry.

• Three common geochemical factors 

are associated with the highest radium 

concentrations in groundwater: 

(1) oxygen-poor water, (2) acidic 

conditions (low pH), and (3) high 

concentrations of dissolved solids.
2

Study Design

The U.S. Geological Survey (USGS), 

with participation from the USEPA, 

conducted a study characterizing the 

occurrence of radium in groundwater 

in major aquifers of the United States 

as part of the National Water-Quality 

Assessment (NAWQA) Program (Szabo 

and others, 2012). As part of this study, 

1,270 wells were sampled over 15 years 

(during 1990–2005) and analyzed for 

Ra-226, Ra-228 and other water-quality 

parameters. A subset of 645 water 

samples were analyzed for the shortlived radium radionuclide, radium-224 

(Ra-224). All samples were analyzed for 

major ions and trace elements, and field 

parameters, such as dissolved oxygen 

and pH were measured. Wells generally 

were sampled once, and raw-water 

samples were collected and filtered 

(0.45 micron) as close to the wellhead 

as possible and before any treatment. Of 

the sampled wells, 48 percent were used 

for domestic supply, 14 percent were 

used for public drinking-water supply, 

and 34 percent were observation wells 

for sampling recently recharged water 

in drinking-water-supply aquifers. Type 

or use was unknown for 4 percent of the 

sampled wells. All of the water samples 

were analyzed for at least one or the 

other longer-lived radium radionuclides, 

Ra-226 or Ra-228. A minimum of 

30 samples were collected and analyzed 

for at least Ra-226 or Ra-228 from each 

principal aquifer. More details on the 

sampling and analyses can be obtained 

in Szabo and others (2012). 

This assessment is the first to characterize 

occurrence of the three major radionuclides of radium throughout much 

of the United States, specifically in 

15 principal aquifer systems in 45 States

(fig. 1). The principal aquifer systems 

used in the study by Szabo and others 

(2012) are grouped slightly different from 

the classification of Lapham and others 

(2005) and the classification of DeSimone 

and others (2009). This study also 

relates radium occurrence with extensive 

geologic, geochemical, and hydrologic 

information and data previously lacking 

on this scale, particularly in the westcentral and western United States. In 

addition, the study extends work from 

previous national surveys by Longtin 

(1988) and Focazio and others (2001). 

What is Radium? 

Radium is a naturally occurring radioactive element (or radionuclide) and 

known carcinogen that generally is 

present at low levels in all soil, water, 

and rocks. It is derived from the common 

long-lived radioactive elements, uranium 

and thorium, which decay slowly to 

produce other radioactive elements, such 

as radium. Three commonly occurring 

radionuclides of radium are Ra-224, 

Ra-226, and Ra-228, each of which 

varies in abundance because each decays 

to a daughter product at a different rate 

(known as “half-life”). Radium-226 is 

the most abundant radium isotope in 

the environment in terms of its mass, 

primarily because of its long half-life. 

Ra-226 and Ra-228 have half-lives 

measurable in terms of years and, there-

fore, once dissolved can be mobile for 

considerable periods of time in groundwater. Radium-224 has a shorter half-life, 

measured in days; however, all radium 

radionuclides can contribute to the 

total amount of radioactivity in a water 

sample. This total level of radioactivity, 

measured as gross alpha-particle or 

beta-particle activity, often is used as a 

cost-effective screening tool to determine 

the general presence of radionuclides in 

water samples.

How Does Radium Get From 

Rocks Into Groundwater?

Radium is derived from the radioactive 

decay of naturally occurring uranium and

thorium in rocks and sediment. Most 

rocks and sediment contain some 

uranium and thorium and, thereby, 

contain radium as well, but usually in 

small quantities. Uranium and thorium 

are most common in granitic and 

metamorphic crystalline rocks and 

in associated weathered sedimentary 

deposits in the central United States and 

mountainous regions of the East and 

West (Grauch, 1976; Duval and Riggle, 

1999; Ayotte and others, 2007). Groundwater flows slowly through pores or 

cracks in underground rocks and aquifer 

sediments and dissolves radium-bearing 

minerals as it moves. Chemical processes 

in groundwater and on rock surfaces, 

such as mineral dissolution, desorption, 

and ion-exchange reactions, control the 

release of radium from aquifer solids. 

Radium can also be physically pushed 

into pore water during isotope decay.

What Human Health Concerns 

Are Related to Radium?

Exposure to radium over long periods 

of time can increase the risk of cancer. 

Radium can enter the body in drinking 

water, food, or inhaled dust particles 

that contain radium. Radium in the 

body behaves similarly to calcium 

and can replace calcium in tissues, 

particularly bone. Long-term exposure to 

radium increases the risk of developing 

diseases such as bone and sinus cancer, 

lymphoma, and leukemia (Mays and others, 1985; U.S. Environmental Protection 

Agency, 1999). Radium in drinking water 

is a serious concern because the uptake 

What is an MCL?

A maximum contaminant level (MCL) is a legally enforceable USEPA drinkingwater standard. An MCL sets the maximum permissible level of a contaminant 

in water that is delivered to users of a public water system that provides water 

for human consumption through at least 15 service connections or regularly 

serves at least 25 individuals. The USEPA sets MCLs as close as feasible to the 

maximum contaminant level goal (MCLG), which is the maximum level of a 

contaminant in drinking water that has an adequate margin of safety and has 

not been shown or proved to cause adverse health effects. When establishing 

MCLs, the USEPA takes into account the best available analytical and treatment 

technologies and cost considerations. The MCL for combined radium applies to 

the finished drinking water provided by public water systems (after treatment 

and before distribution). In this study, radium concentrations in untreated source 

water for public-supply wells and private (domestic) wells were compared to the 

MCLs to provide an initial perspective on the potential significance of detected 

contaminants to human health. Concentrations measured in source water do not 

necessarily reflect the quality of finished water from public water systems. 
3

Western Foreland Tertiary/ Cretaceous sandstone

Rio Grande and Basin and Range basin fill

Pacific Coastal (Central Valley and 

Willamette Basins) alluvium and fill

Basalt

Western alluvium and fill

Coastal Plain, Southeastern

Coastal Plain—Texas Upland, Gulf lowland, Mississippi Embayment

Floridan and surficial

Mid-Continent and Ozark Plateau 

Cambro-Ordovician

High Plains Tertiary alluvium and fill

Glacial sand and gravel

Crystalline rock New England/New York

 Northern Atlantic Coastal Plain

Appalachian Piedmont Mesozoic Basins

Valley and Ridge and Mississippian limestone

30

41 60 90 61 87 30 271 32 62 30 58 42 39 55 35

EXPLANATION 

Number of values

Outlier

Outlier

75

90th percentile

10th percentile

th percentile

50th percentile

(median)

25th percentile

USEPA maximum contaminant level

10

1

0.1

100

Radium-226 plus radium-228,

in picocuries per liter

Principal aquifer system

Figure 2.  More than 20 percent of groundwater samples from the Mid-Continent and

Ozark Plateau Cambro-Ordovician aquifer system and the Northern Atlantic Coastal

Plain aquifer system had combined radium (radium-226 plus radium-228) concentrations

greater than or equal to the drinking-water maximum contaminant level of 5 picocuries

per liter. The next five listed principal aquifers have at least one sample that exceeded the

drinking-water standard for combined radium concentrations. Aquifers that exceeded the

drinking-water standard usually had geochemical conditions favorable for radium release

from aquifer solids, including oxygen-poor water or acidic (low pH) conditions, usually

with high concentrations of dissolved solids.

Aquifers of the Northern Atlantic Coastal Plain, primarily composed of quartz-rich

sand (above), had some of the highest concentrations of radium primarily because

of low pH conditions that release radium from the sediments.

by bone and other tissues is especially 

efficient for radium already dissolved in 

water. Because radium readily accumulates in the body, it is considered to pose 

a greater cancer risk than most other 

radioactive elements. Radiation exposure 

from radium received externally through 

washing, showering, or other uses of 

water is less of a concern since human 

skin tends to block exposure to alpha 

radiation and minimize penetration of 

beta radiation.

What Level of Radium 

in Drinking Water Is a 

Significant Health Risk? 

The MCL of 5 pCi/L, established by the 

USEPA, is for combined radium, defined 

as the sum of Ra-226 and Ra-228 (U.S. 

Environmental Protection Agency, 2000). 

Although not a requirement, the USEPA 

encourages public water-supply systems 

to perform sampling and analysis for 

Ra-224, because this radium radionuclide 

and its decay products can contribute 

substantially to gross alpha-particle 

activity (Focazio and others, 2001). 

How Do the Study Results 

Compare to the MCL?

Although radium radionuclides were 

present in raw water from sampled 

wells tapping every principal aquifer, 

the combined radium concentration 

generally was below the established 

MCL. Overall, few sampled wells (about 

3 percent, or 40 of 1,266 wells) contained 

individual concentrations or combined 

concentrations of Ra-226 and Ra-228 

greater than the MCL. No single isotope 

of radium was consistently responsible 

for the MCL being exceeded. Of the 

15 principal aquifers studied, 7 had 

combined radium concentrations that 

were greater than the MCL in at least one 

well (fig. 2). Two principal aquifers had 

detections of combined radium at levels 

above the MCL much more frequently 

than the other aquifers. These included 

the Mid-Continent and Ozark Plateau 

Cambro-Ordovician aquifer system 

and the Northern Atlantic Coastal Plain 

aquifer system. Both these aquifer are 

composed of materials low in the parent 

compounds uranium and thorium, which 

indicates that other factors, such as geochemistry, are important in determining 

concentrations of radium in the water.
4

0

1

2

3

4

5

6

7

8

9

10

11

12

Low oxygen boundary

0 1 2 3 4 5 6 7 8 9 10 11 12

Radium-226 plus radium-228, in picocuries per liter 

Dissolved oxygen, in milligrams per liter 

Principal aquifer system—Open symbol indicates 

 non-detects

Appalachian Piedmont Mesozoic Basins

Crystalline rock New England/New York

Mid-Continent and Ozark Plateau Cambro-Ordovician

Glacial sand and gravel 

USEPA maximum contaminant level

EXPLANATION

Figure 3.  Oxygen-poor groundwater

contains elevated concentrations

of combined radium (radium-226

plus radium-228) compared to

groundwater with higher dissolved

oxygen concentrations. Low-oxygen

conditions decrease the likelihood

that radium will adsorb to aquifer

materials and increases the mobility

of radium into groundwater. In

this study, low-oxygen conditions

were present in many aquifers,

but were generally found more

frequenty in the Appalachian

Piedmont Mesozoic Basins,

crystalline rock New England/

New York, Mid-Continent and

Ozark Plateau Cambro-Ordovician,

and parts of the glacial aquifer

systems in the eastern United States.

What Three Water Types Are 

Likely to Contain Radium?

Three water types were identified 

by Szabo and others (2012) as likely 

to have elevated concentrations of 

radium in groundwater, including 

(1) low-oxygen (dissolved oxygen less 

than [<] 1 milligram per liter [mg/L]) 

water with iron or manganese; 

(2) acidic (pH<6) water with high 

concentrations of nitrate or other acidic 

anions (sulfate, chloride) and calcium, 

strontium, or barium; and (3) water 

with high concentrations of dissolved 

solids containing one or more of the 

following in abundance: calcium, barium, 

magnesium, strontium, potassium, 

sulfate, or bicarbonate. These water 

types are indicative of conditions that 

may prevent radium from adsorbing 

onto aquifer sediments and increase the 

mobility of radium into surrounding 

water. High concentrations of combined 

radium and individual radionuclides 

Ra-226 and Ra-228 were found in water 

containing at least one of these chemical 

characteristics from the principal 

aquifers studied, because radium is most 

soluble and mobile in these geochemical 

conditions. Of these water types, 

low-oxygen conditions were the most 

abundant and explained the occurrence 

of the highest concentrations of radium 

in more principal aquifers than the other 

two water types (fig. 3). 

Which Principal Aquifers 

Are Most Vulnerable to 

Radium Contamination?

The greatest frequency of elevated radium 

in groundwater occurs primarily in the 

eastern and central United States (fig. 1). 

About 98 percent of the sampled wells 

that had combined radium concentrations 

greater than the MCL were located east 

of the High Plains. More than 20 percent 

of wells sampled in the Northern Atlantic 

Coastal Plain aquifer system and MidContinent and Ozark Plateau CambroOrdovician aquifer system had combined 

radium concentrations greater than or 

equal to the MCL. The single highest 

concentration of combined radium in 

this study (20.4 pCi/L) was detected in 

water from the Northern Atlantic Coastal 

Plain aquifer system (fig. 2). Among 

the remaining five principal aquifers 

with elevated radium concentrations, 

the Floridan aquifer system had the 

greatest frequency of sampled wells with 

combined radium concentrations greater 

than the MCL, followed by the granitic 

and metamorphic crystalline rocks of 

New England/New York, the Mesozoic 

sedimentary basins in or adjoining the 

Appalachian Piedmont, the Gulf Coast 

Coastal Plain aquifer systems, and the 

glacial deposits.

Results of a previous study have shown

that some parts of the Midwest have 

significantly higher than average combined

radium concentrations in groundwater 

(U.S. Environmental Protection Agency, 

2010); however, results of this current 

study indicate that radium occurrence is

not only related to source rock type but

also to aquifer geochemistry. Many aquifers

containing the highest concentrations of

combined radium in the eastern and central

United States had oxygen-poor water 

containing particularly high concentrations

of iron and manganese and, on occasion, 

high dissolved solids concentrations. 

These factors were found mostly in the

Mid-Continent and Ozark Plateau CambroOrdovician and Floridan aquifer systems 

(figs. 2, 3), but also in the Appalachian 

Piedmont Mesozoic Basins, Crystalline 

Rocks of New England/New York, and 

the Glacial sand and gravel aquifers. 

In the East, the shallow parts of the 

Northern Atlantic Coastal Plain aquifer 

system are unconfined and composed of 

unconsolidated quartz-rich sand with little 

acid-buffering capacity, which typically 

results in acidic (low pH) conditions that 

are optimal for dissolving or desorbing 

radium. The shallow part of this aquifer 

system is susceptible to the effects of 

urban and agricultural activities on the 

land surface, including septic-effluent 

disposal and fertilizer and lime applications, all of which can leach nitrate, 

phosphate, calcium, magnesium, and 

other dissolved solids into groundwater. 
5

Drinking-water sources in groundwater aquifers may be vulnerable to

contamination from radium, a known

carcinogen. Knowledge of the geochemical conditions in the Nation’s

aquifers helps water resource

managers understand where high

concentrations of radium may

occur in groundwater.

Possible Implications and 

Use of These Findings 

Understanding the factors controlling 

radium occurrence in groundwater can 

help managers anticipate conditions in 

which radium may be elevated, prioritize 

monitoring studies, improve decisions 

related to land-use planning, and assist 

well owners in determining suitable 

locations for new drinking-water supply 

wells. The findings help to identify 

how and why radium occurrence can 

vary in wells from different geographic 

regions, principal aquifers, and 

geochemical environments and may 

help target the appropriate level of 

assessment, testing, and protection 

to aquifers and geographic areas of 

most concern for elevated radium 

concentrations and, thus, human 

health concerns. Principal aquifers 

with relatively high drinking-water 

ingestion risks for radium identified in 

this study (fig. 2) were the same aquifers 

identified by Focazio and others (2001), 

despite different sampling approaches 

used (random and targeted, respectively). 

An example of the usefulness of 

the application of these findings is 

New Jersey’s Private Well Testing 

Act (New Jersey Register, 2002). 

Its regulations became effective in 

2002, requiring testing for gross alphaparticle activity in domestic wells of 

the Northern Atlantic Coastal Plain 

aquifer system in New Jersey, which is 

one of the most vulnerable regions in 

the United States to radium occurrence 

(Szabo and others, 2005). Also, the 

information can be particularly useful 

to private homeowners with domestic 

wells, because these water systems 

generally are not monitored regularly 

for radium, unlike public-supply wells 

that are monitored under the Safe 

Drinking Water Act (U.S. Environmental 

Protection Agency, 2000; Focazio and 

others, 2001). Improved information is 

needed on the number of people who 

rely on drinking water from domestic 

wells in specific regions that tap specific 

aquifers, and continued public education 

and testing of domestic wells is advised, 

particularly for naturally occurring 

inorganic chemicals (DeSimone and 

others, 2009).

Treatment Options for Radium in Drinking Water

A number of treatment options are available to public water suppliers and 

homeowners for removing radium from drinking water. Ion-exchange 

methods, also known as water softeners, can remove radium from water, 

in addition to calcium and magnesium, which cause hardness (Lucas, 

1987; Szabo and others, 2008). Sodium is used to replace (exchange) these 

constituents in water. For some people, such as for those on a low-salt 

diet, sodium can cause other health concerns. A major benefit, however, is 

that this type of treatment system can readily be used to treat water for the 

whole house. Reverse osmosis systems may provide an alternative means 

of treatment; however, this type of treatment system can produce only 

small volumes of treated water and cannot be used to treat water for the 

whole house. Also, green sands containing the mineral glauconite provide 

a natural treatment option for home owners and treatment facilities. 

Public water supplies have many other choices for treating the water to 

remove radium, including ion exchange, iron removal, and lime softening 

among others (Zapecza and Szabo, 1988). For more information on 

compliance options for the USEPA Radionuclides Rule, see http://water.

epa.gov/lawsregs/rulesregs/sdwa/radionuclides/compliancehelp.cfm.

Public water suppliers and private homeowners can contact the National 

Sanitation Foundation (www.nsf.org) and the Water Quality Association 

(www.wqa.org) for assistance in determining the best treatment options. 

In addition, the National Ground Water Association (www.ngwa.org) is 

dedicated to education efforts aimed at reducing contaminant risks to 

water supplies and provides a summary of treatment considerations and 

an overview of strategies for well owners (Treyens, 2009).

These chemical constituents can be 

involved in ion exchange and acidification 

reactions that are not readily buffered 

by quartz sand and thereby stimulate the 

release of radium from aquifer materials 

into the groundwater. 

East of the High Plains, waters with high 

dissolved solids typically had low dissolved oxygen concentrations (< 1 mg/L) 

and generally did not contain enough 

sulfates to form insoluble barium-radium 

sulfate mineral. As a result, radium was 

mobile and detectable. Groundwater in the 

High Plains and to the west also contained 

high dissolved solids but was usually rich 

in oxygen and contained concentrations 

of sulfate high enough to form insoluble 

barium-radium sulfate mineral. High 

concentrations of dissolved oxygen and 

sulfate can limit radium concentrations in 

groundwater by increasing the likelihood 

that radium is adsorbed or precipitated. 
6

References

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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, 

85 p.; accessible online at http://pubs.

usgs.gov/sir/2007/5037/.

DeSimone, L.S., Hamilton, P.A., and 

Gilliom, R.J., 2009, Quality of ground 

water from private domestic wells: 

Water Well Journal, April 2009, 

p. 33–37.

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Profiles of gamma-ray and magnetic 

data from aerial surveys over the 

conterminous United States: U.S. 

Geological Survey Digital Data 

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Mullin, A.H., Barringer, T.H., and 

dePaul, V.T, 2001, Occurrence of 

selected radionuclides in ground water 

used for drinking water in the United

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accessible online at http://pubs.usgs.

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crystalline rocks of the eastern United 

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Programs 8, v. 8, no. 2, p. 184–185.

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Myers, D.N.,2005, National Water 

Quality Assessment Program Cycle 

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2005–3013, 4 p.; accessible online at 

http://pubs.usgs.gov/fs/2005/3013/.

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radium and uranium in groundwater: 

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a home water softener: Journal of 

Environmental Radioactivity, v. 5, 

p. 359–362.

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Stehney, A.F., 1985, Cancer risk 

from the lifetime intake of Ra and 

U isotopes: Health Physics, v. 48, 

p. 635–647.

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Administration, 2002, The Private 

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Rules, New Jersey Administrative 

Code, Title 7, Chapter 9E: New Jersey 

Register, v. 34, no. 18, p. 3236–3264.

Szabo, Z., dePaul, V.T., Fischer, J.M., 

Kraemer, T.F., and Jacobsen, E., 

2012, Occurrence and geochemistry 

of radium in water from principal 

drinking-water aquifers of the 

United States, Applied Geochemistry 

(2012), doi: 10.1016/j.apgeochem.

2011.11.002, 24 p.

Szabo, Z., dePaul, V.T., Kraemer, T.F., 

Parsa, B., 2005, Occurrence of 

radium-224 and comparison to that 

of radium-226 and radium-228 in 

water from the unconfined KirkwoodCohansey aquifer system, southern 

New Jersey: U.S. Geological Survey 

Scientific Investigations Report 

2004–5224, 92 p.; accessible online at 

http://pubs.usgs.gov/sir/2004/5224/.

Szabo, Z., Jacobsen, E., Kraemer, T.F., 

Parsa, B., 2008, Concentrations 

and environmental fate of Ra in 

cation-exchange regeneration brine 

waste disposed to septic tanks and 

accumulation in sludge, New Jersey 

Coastal Plain, U.S.A.: Journal of 

Environmental Radioactivity, v. 99, 

p. 947–965.

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Water Well Journal, April, p. 38–40.

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no. 13, cancer risk coefficients for 

environmental exposure to radionuclides: U.S. Environmental Protection 

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regulations; Radionuclides: Final 

rule, 40CFR parts 141 and 142; 

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radionuclides rule: http://water.

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radionuclides/basicinformation.cfm

(accessed September 28, 2010).

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aquifers of the 48 conterminous United 

States, Hawaii, Puerto Rico, and the 

U.S. Virgin Islands, accessible online 

at http://www.nationalatlas.gov/mld/

aquifrp.html.

Zapecza, O.S., and Szabo, Z., 1988, 

Natural radioactivity in ground 

water—A review, in Moody, D.W., 

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National Water Summary 1986—

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p. 50–57; accessible online at http://

pubs.usgs.gov/wsp/2325/report.pdf.

Authors and Additional Information

Zoltan Szabo

Research Hydrologist

(609) 771-3929

zszabo@usgs.gov

Jeffrey M. Fischer

Supervisory Hydrologist

(609) 771-3953

fischer@usgs.gov

Tracy Connell Hancock

USDA Forest Service

National Monitoring and 

Evaluation Coordinator

(202) 205-1724

tchancock@fs.fed.us

This fact sheet highlights the major 

findings and implications of the 

study and serves as a companion 

product to a journal article by Szabo 

and others (2012) that presents more 

detailed and technical information 

The URL to access the report online 

is http://water.usgs.gov/nawqa/

trace/radium/.

This publication is accessible 

online at http://pubs.usgs.gov/

fs/2010/3113/.