U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 00-4273

Prepared in cooperation with the U.S. Environmental Protection Agency,

Office of Ground Water and Drinking Water

Occurrence of Selected 

Radionuclides in Ground Water Used 

for Drinking Water in the United States: 

A Reconnaissance Survey, 1998 
i

Occurrence of Selected Radionuclides in

Ground Water Used for Drinking Water in the

United States: A Reconnaissance Survey, 1998

By Michael J. Focazio, Zoltan Szabo, Thomas F. Kraemer, Ann H. Mullin,

Thomas H. Barringer, and Vincent T. dePaul

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 00-4273

Prepared in cooperation with the

U.S. Environmental Protection Agency,

Office of Ground Water and Drinking Water

science for a changing world

USGS
ii

U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement

by the U.S. Government.

Reston, Virginia 2001

For additional information write to:

U.S. Geological Survey

Office of Ground Water

Mail Stop 411

12201 Sunrise Valley Drive

Reston, VA 20192

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286, Mail Stop 417

Denver Federal Center

Denver, CO 80225-0286
iii

CONTENTS

ABSTRACT .............................................................................................................................................................. 1

INTRODUCTION ..................................................................................................................................................... 1

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

 Acknowledgments ............................................................................................................................................. 2

 General Background on Radionuclide Chemistry ............................................................................................. 2

 Existing Sources of Information for Radionuclide Data .................................................................................. 3

 Radium in Water Resources of the United States ...................................................................................... 5

 Occurrence of Radium-224 ....................................................................................................................... 5

 Occurrence of Radium-226 ....................................................................................................................... 5

 Occurrence of Radium-228 ....................................................................................................................... 5

 Other Naturally Occurring Alpha-Particle Emitting Radionuclides .......................................................... 6

 Limitations of Data Sources ...................................................................................................................... 6

DATA COLLECTION AND LABORATORY ANALYTICAL METHODS ............................................................ 7

 Well Selection .................................................................................................................................................... 7

 Sample-Collection Methodology...................................................................................................................... 7

 Analytical Methodology .................................................................................................................................... 7

 Reporting of Analytical Results and Statistical Calculations with Raw-Data Values ....................................... 9

OCCURRENCE OF SELECTED RADIONUCLIDES IN GROUND WATER USED

AS DRINKING WATER ..........................................................................................................................................11

 Radium-224 ......................................................................................................................................................11

 Radium-226 and Radium-228 ......................................................................................................................... 12

 Radium Isotope Ratios and Correlations ......................................................................................................... 13

 Polonium-210 and Lead-210 ........................................................................................................................... 14

LIMITATIONS AND PERSPECTIVE ON THE RECONNAISSANCE SURVEY............................................... 14

 Analysis of Quality-Control Data .................................................................................................................... 14

 The Effects of a Targeted Sampling Design on

 Interpretations of Results of the Survey ........................................................................................................ 14

 Cancer Risk Estimates for Radium Isotopes in Drinking Water ..................................................................... 17

 Interpretations of Polonium-210 and Lead-210 Data ...................................................................................... 18

IMPLICATIONS FOR COMPLIANCE MONITORING ...................................................................................... 19

 Compliance Monitoring Procedures for Regulated Radionuclides Used by Public

 Water-Supply Systems and Results of Previous Studies ............................................................................... 19

 Limitations in the Current Monitoring Procedures for Alpha-Particle Emitting

 Radionuclides and the Combined Radium Standard .................................................................................... 20

CONCLUSIONS ..................................................................................................................................................... 21

REFERENCES CITED ........................................................................................................................................... 22

GLOSSARY ............................................................................................................................................................ 24

APPENDIX Radionuclide Data and Ancillary Information ................................................................................... 27
iv

FIGURES

1. Schematic diagram showing theuranium-238 and thorium-232 radioactive decay series................................... 4

2. Map showing the locations of wells sampled and physiographic provinces ....................................................... 8

3. Reported concentrations, concentrations plus and minus

the combined standard uncertainty (CSU), and the minimum detectable

concentration (MDC) for Ra-224 (A), Ra-226 (B), and Ra-228 (C), for all

samples including duplicates ............................................................................................................................. 12

4–7. Graphs showing relations between:

4. Radium-224 to radium-228 (A), radium-224 to radium-226 (B), and

radium-226 to radium-228 (C) ................................................................................................................. 13

5. Environmental sample and duplicate environmental sample

concentrations for radium-224 (A), radium-226 (B), and radium-228 (C) .............................................. 15

6. Duplicate environmental samples for radium-224 analyzed by alpha

spectrometry and gamma spectrometry (A), and radium-226 analyzed by

alpha spectrometry and gamma spectrometry (B), and radium-228

analyzed by beta counting and gamma spectrometry (C) ........................................................................ 15

7. Cumulative frequency distributions for radium-226 in the 1998

U.S. Geological Survey reconnaissance survey (A; targeted survey design) and in

the National Inorganics and Radionuclide Survey (B; random survey design) ....................................... 16

8. Cumulative frequency distributions for radium-228 in the 1998

U.S. Geological Survey reconnaissance survey (A; targeted survey

design) and radium-228 in the National Inorganics and Radionuclide Survey

(B; random survey design) ....................................................................................................................... 16

9. Cumulative frequency distribution for radium-224 in the 1998

U.S. Geological Survey Reconnaissance survey (targeted sampling design) .......................................... 16

10. Schematic diagram showing the compliance monitoring scheme for

radionuclides in public-drinking-water supplies........................................................................................... 19

11. Graph showing relation between radium-226 and combined radium

(radium-226 + radium-228) concentrations.................................................................................................. 21

TABLES

1. Radionuclides analyzed in the U.S. Geological Survey reconnaisance survey,

associated analytical method, and number of samples (including

environmental and quality control samples) analyzed by each method ......................................................... 9

2. Estimations of the population served by the public water-supply

systems that were sampled............................................................................................................................ 10

3. Percentage of samples with reported concentrations that are greater or

less than the minimum detectable concentration (MDC) plus or minus

the combined standard uncertainty (CSU) for all radium isotopes analyzed ............................................... 11

4. Summary statistics of concentrations of radionuclides analyzed in the survey................................................. 13

5. Percent of samples reported to exceed specified concentrations ....................................................................... 13

6. Spearman correlation coefficients (significant at the 0.05 confidence level)

for radium isotope concentrations ................................................................................................................ 13

7. U.S. Environmental Protection Agency cancer risk estimates for radium

isotopes in drinking water ............................................................................................................................. 17
v

 Multiply By To Obtain

 Volume

 gallon (gal) 3.785 liter (L)

 3785 milliliter (mL)

Physical and Chemical Water-Quality Units and Common Abbreviations

Temperature: Water and air temperature are given in degrees Celsius (o

C), which can be converted to degrees

Fahrenheit (o

F) by use of the following equation:

o

F = 1.8(oC) + 32

Milligrams per liter (mg/L) or micrograms per liter (μg/L): Milligrams per liter is a unit expressing the

concentration of chemical constituents in solution as weight (milligrams of solute per unit volume (liter)) of water.

One thousand micrograms per liter is equivalent to one milligram per liter. For concentrations less than 7,000 mg/

L, the numerical value is the same as for concentrations in parts per million.

Picocuries per liter (pCi/L): Picocuries per liter is a unit expressing the concentration (or activity) of radionuclides in solution as particles emitted per unit volume (liter) of water. By definition, one gram of radium has one

curie of activity. A picocurie is a millionth of a millionth of a curie. In practical terms, one picocurie per liter

equals 2.2 radioactive disintegrations per minute per unit volume (liter) of water.

CSU, Combined Standard Uncertainty

MCL, Maximum Contaminant Level

MDC, Minimum Detectable Concentration

MRL, Minimum Reporting Level

NIRS, National Inorganics and Radionuclide Survey of the USEPA

USEPA, United States Environmental Protection Agency

CONVERSION FACTORS, WATER-QUALITY UNITS, AND ABBREVIATIONS
1

Occurrence of Selected Radionuclides in Ground Water

Used for Drinking Water in the United States:

A Targeted Reconnaissance Survey, 1998

By Michael J. Focazio, Zoltan Szabo, Thomas F. Kraemer, Ann H. Mullin, Thomas H. Barringer,

and Vincent T. dePaul

 ABSTRACT

The U.S. Geological Survey, in collaboration with the

U.S. Environmental Protection Agency, the American Water

Works Association, and the American Water Works Service

Company, completed a targeted national reconnaissance survey of selected radionuclides in public ground-water supplies. Radionuclides analyzed included radium-224 (Ra224), radium-226 (Ra-226), radium-228 (Ra-228),

polonium-210 (Po-210) and lead-210 (Pb-210).

This U.S. Geological Survey reconnaissance survey focused intentionally on areas with known or suspected elevated concentrations of radium in ground water to determine if Ra-224 was also present in the areas where other

isotopes of radium had previously been detected and to determine the co-occurrence characteristics of the three radium

isotopes (Ra-224, Ra-226, and Ra-228) in those areas.

Ninety-nine raw-water samples (before water treatment)

were collected once over a 6-month period in 1998 and 1999

from wells (94 of which are used for public drinking water)

in 27 States and 8 physiographic provinces. Twenty-one of

the 99 samples exceeded the current U.S. Environmental Protection Agency drinking-water maximum contaminant level

of 5 picocuries per liter (pCi/L) for combined radium (Ra226 + Ra-228). Concentrations of Ra-224 were reported to

exceed 1 pCi/L in 30 percent of the samples collected, with a

maximum concentration of 73.6 pCi/L measured in water

from a nontransient, noncommunity, public-supply well in

Maryland. Radium-224 concentrations generally were higher

than those of the other isotopes of radium. About 5 percent

of the samples contained concentrations of Ra-224 greater

than 10 pCi/L, whereas only 2 percent exceeded 10 pCi/L for

either Ra-226 or Ra-228. Concentrations of Ra-226 greater

than 1 pCi/L were reported in 33 percent of the samples, with

a maximum concentration of 16.9 pCi/L measured in water

from a public-supply well in Iowa. Concentrations of Ra-228

greater than 1 pCi/L were reported in 22 samples, with a

maximum concentration of 72.3 pCi/L measured in water

from a non-transient, noncommunity, public-supply well in

Maryland.

Radium-224, which is a decay product of Ra-228 in the

Th-232 decay series, was significantly correlated with Ra-228

(Spearman’s rank correlation coefficient “r” equals 0.82) and

to a lesser degree with Ra-226 (r equals 0.69), which is an isotope in the U-238 decay series. The rank correlation coefficient between Ra-226 and Ra-228 was 0.63. The high correlation between Ra-224 and Ra-228 concentrations and the

corresponding isotopic ratios of the two (about 1:1 in 90 percent of the samples) indicates that the two radionuclides occur

in approximately equal concentrations in most ground water

sampled. Thus, Ra-228 can be considered as a reasonable

proxy indicator for the occurrence of Ra-224 in ground water.

The maximum concentration of Po-210 was 4.85 pCi/L

and exceeded 1 pCi/L in only two samples. The maximum

concentration of Pb-210 was 4.14 pCi/L, and about 10 percent of the samples exceeded 1 pCi/L. Areas with known, or

suspected, elevated concentrations of polonium and lead

were not targeted in this survey.

Three major implications are drawn for future radionuclide monitoring on the basis of this information: (1) grossalpha particle analyses of ground water should be done

within about 48–72 hours after collection to determine the

presence of the short-lived, alpha-particle emitting isotopes,

such as Ra-224, which was detected in elevated concentrations in many of the samples collected for this survey; (2) the

isotope ratios of Ra-224 to Ra-228 in ground water are variable on a national scale, but the two radioisotopes generally

occur in ratios near 1:1, therefore, the more commonly measured Ra-228 can be used as an indicator of Ra-224 occurrence for some general purposes other than compliance; and

(3) the isotopic ratios of Ra-226 to Ra-228 were less than 3:2

in many samples. These ratios corroborate results of previous

studies that have shown the presence of Ra-228 (a beta-particle emitter) can cause a flaw in conventional radium compliance monitoring when the gross-alpha particle screen indicates no need for further analysis (the gross alpha particle

activity is less than 5 pCi/L) even though the ratio of Ra-226

to Ra-228 is less than 3:2.

INTRODUCTION

The Drinking Water Initiative of the U.S. Geological

Survey (USGS) provides scientific information for regulatory agencies and other water-resource planners and managers who must balance water-supply protection with the wise

use of public funds (Patterson, 1997). In fulfilling the goals

of the USGS Drinking Water Initiative, and to provide information on the occurrence of selected radionuclides in ground

water, the USGS in collaboration with the U.S. Environmental Protection Agency (USEPA) performed a reconnaissance

survey of selected radionuclides in ground water that is used

as a source of drinking water in the United States.

Drinking-water standards for radionuclides have been

in place since 1976 (U.S. Environmental Protection Agency,

1976). Revisions to the drinking water standards for radionuclides were proposed by the USEPA in 1991 but never en-
2

acted into law. The USEPA is currently (2000) taking action

under a court agreement (Order on Stipulated Motion for Relief from Judgment or Order, and Motion to Dismiss All Consolidated Cases, Joseph L. Miller v. Carol M. Browner, Civ.

Nos 89-6328 et al (D. Ore, 1996)) on the 1991 proposed revisions. This action includes establishment of a Maximum Contaminant Level (MCL) for uranium and either promulgating

or stating the reasons for not promulgating any other elements

of the proposal. As part of these actions, the USEPA published a Notice of Data Availability (NODA) in the Federal

Register on April 21, 2000 (U.S. Environmental Protection

Agency, 2000) to update the public and the regulated community on issues regarding radionuclides since the publication of

the proposed radionuclides rule in 1991. The NODA summarizes the available information on the occurrence of radionuclides, among other things, and includes data from the 1998–

99 reconnaissance survey reported in this report. Much of the

data on occurrence of radionuclides in ground water summarized in the NODA were from previous occurrence surveys

(Longtin, 1988); however, insufficient information on the occurrence of Ra-224 in water resources was available (Hess

and others, 1985) until recently (Szabo and others, 2000).

The reconnaissance survey was designed to provide

data and interpretative information on the potential national

scope of the occurrence of the short-lived Ra-224 and its associated contribution to gross alpha-particle radiation in

drinking-water supplies where it was presumed to exist in elevated concentration. In addition, the survey was designed to

provide data and information on the co-occurrence characteristics of the three radium isotopes; Ra-224, Ra-226, and Ra228. The survey focused on areas that have ground water

with known, or suspected elevated concentrations of radium224 (Ra-224; half life, 3.64 days), as inferred by previously

published data and information on the occurrence of radium,

geochemical models, geologic maps, and other geochemical

or water-quality considerations.

Raw-water samples were collected once over a 6-month

period in 1998 from 99 wells in 27 States and 8 physiographic provinces across the United States. Of these wells,

94 were used for public drinking-water supply, one was used

for domestic supply; four research wells are not used for

drinking-water supply. The samples, which were collected as

close to the wellhead as possible, represent the raw (untreated) water that is used for drinking-water purposes. The

public water-supply systems surveyed serve a broad range of

population sizes, including several serving less than 500

people and one serving more than 1,000,000 people. The

number of people that consume water from each well

sampled is unknown.

Purpose and Scope

The purpose of this report is to provide information and

data that describe concentration distributions of Ra-224 in

drinking water from selected ground-water sources nationwide. Radiochemical analyses of raw, untreated ground water

from public water-supply systems provide the source of the

data. The USGS is providing these data to USEPA to augment existing sources of information to assess the potential

national impacts of revisions to drinking-water standards

(MCLs) and compliance monitoring for the targeted radionuclides. Results of this survey can also provide information

needed to design a more complete survey of radium occurrence (particularly Ra-224) and co-occurrence (particularly

of Ra-224, Ra-226, and Ra-228) in the Nation’s ground-water resources.

Acknowledgments

The authors thank the public water-supply system personnel who voluntarily collected and shipped water samples

to the respective laboratories. Daniel Pedersen, formerly of

the American Water Works Association, and Daniel Schecter

of the American Water Works Service Company provided

crucial liaison support with the volunteers and helped select

the sampling sites. David McCurdy, Ashok Banavli, and Jeffrey Raimondi of Duke Engineering and Services, and John

Griggs and David Kappelman of USEPA, are among those

who performed and helped coordinate the laboratory analyses. Lowell Ralston and Neal Nelson of USEPA and Patty

Toccalino of the Oregon Graduate Institute provided guidance and review for the presentation of the human health

risks of radium in drinking water. David Huber, William

Labiosa, James Taft, and other members of the USEPA radionuclide rule assessment team, were instrumental in providing

support, discussion, and suggestions for many aspects of the

project from conception to completion. Alison Gordon,

USGS, assisted in contacting volunteers and coordinating the

sample collection. Glenn Patterson, USGS, helped in many

aspects of the project from proposal development to reviews

of parts of the manuscript. Robert Hirsch, USGS, provided

useful comments on an early version of the manuscript. Colleague reviews were provided by Robert Kay, Lisa Senior,

and David McCurdy.

General Background on Radionuclide Chemistry

There are about 2,000 known radionuclides, which are

species of atoms that emit radiation as they undergo radioactive decay through emission of alpha particles, beta particles,

or gamma rays. Naturally occuring radionuclides are ubiquitous trace elements found in rocks and soils and, in general,

radionuclides can be categorized in three ways:

• by type of radioactive decay (alpha, beta, or gamma

emission),

• by radioactive decay series,

• as naturally occurring or manmade,

Some of the naturally occurring and manmade radionuclides are directly regulated by the current drinking-water

standards. The natural radionuclides include the primordial

elements that were incorporated into the earth’s crust during

its formation, the radioactive decay products (or progeny) of

these primordial elements, and radionuclides that are formed

in the atmosphere by cosmic ray interactions. Manmade radionuclides are produced through the use of nuclear fuels,

radiopharmaceuticals, and other activities of the nuclear industry and have been released into the atmosphere as the re-
3

sult of atmospheric testing of nuclear weapons and, in rare

cases, accidents at nuclear-fuel stations, and discharge of

radiopharmaceuticals. Further discussion on manmade radionuclides is beyond the scope of this report.

The two types of isotopes with radioactive decay that

carry the most health risk due to ingestion of water are alpha-particle emitters and beta/photon-particle emitters

(Lappenbusch and Cothern, 1985). Many radionuclides are

mixed emitters with either an alpha or beta emission coupled

with gamma (photon) emission, or in some cases, all three.

Each radionuclide has a primary mode of disintegration. The

most common, heavy, naturally occurring radionuclides are

largely alpha-particle emitters, although their progeny often

emit beta particles. The alpha-particle emitting radionuclides

discussed in this report include two isotopes of radium (Ra224 and Ra-226) and polonium-210. Alpha radiation is composed of a particle, consisting of two protons and two neutrons, spontaneously emitted from the nucleus of a subset of

radioactive elements (mostly the heaviest elements) during

radioactive decay. Alpha radiation is ionizing radiation,

meaning that it strips electrons from adjacent atoms as it

passes. Alpha radiation cannot penetrate skin; thus, an alpha-particle emitting radionuclide must be ingested in order

to come into contact with internal tissue. Because of the

large size, alpha particles are likely to collide with cell tissue, causing tissue damage. An accumulation of tissue damage in the cell nucleus may lead to cell mutation and potential cancer.

The naturally occurring radionuclides derived from uranium-238, thorium-232, and uranium-235 are products of the

radioactive decay series known as the uranium, thorium and

actinium series, respectively. Each decay series follows a

known sequence of radioactive decay, producing various isotopes that also emit either an alpha or a beta particle as they

decay (fig. 1). Each series terminates with a stable isotope of

lead. The crustal abundance of U-235 is very low in comparison with the other decay series (U-238 to U-235 mass ratio is

on the order of 140 to 1). Thus, the actinium series is not

considered an important source of radionuclides in drinking

water derived from ground water and is, therefore, not included in figure 1.

Radium in nature is composed of four isotopes: Ra223, Ra-224, Ra-226, and Ra-228. Radium-223 is a member

of the U-235 decay series and, therefore, rarely occurs in the

environment in high concentrations. Radium-224 is the fifth

member of the Th-232 decay series, has a half-life of 3.64

days, and decays by alpha-particle emission. Radium-226 is

the fifth member of the U-238 decay series, has a half-life of

about 1,602 years, and decays by alpha-particle emission.

Radium-226 is the most abundant radium isotope in the environment in terms of actual mass because of its long halflife. Radium-228 is the second member of the Th-232 decay

series, has a half life of 5.75 years, and decays by beta-particle emission.

The occurrence of radionuclides in ground water depends first on the presence and solubility of the parent element. Each radioactive decay product has unique chemical

characteristics common to the element but differing slightly

by isotope. For the general purposes of most occurrence

analyses, the different isotopes of radium are chemically indistinguishable. The occurrence of a parent radionuclide in

solution does not necessarily indicate the presence of its decay products. For example, U-238 (parent product of Ra226) tends to be the least mobile in oxygen-poor ground water, and tends to be strongly adsorbed onto humic substances.

Conversely, radium tends to be most mobile in oxygen-poor

ground water that is chloride-rich with high concentrations

of total dissolved solids (Kraemer and Reid, 1984; Zapecza

and Szabo, 1987). Radium chemically reacts similarly to

other divalent alkaline-earth cations such as calcium, strontium, and barium. Therefore, in aquifers with limited sorption or ion-exchange sites, radium solubility can be enhanced

by the common-ion effect where competing cations are

present in abundance. Recently, high concentrations of radium were found to be associated with ground water that was

geochemically affected by land use (agricultural) practices in

recharge areas, presumably due to waters enriched with competing ions such as hydrogen, calcium, and magnesium

(Szabo and dePaul, 1998). Ra-228 was detected in about

equivalent concentrations as Ra-226 in an acidic aquifer in

New Jersey, where agricultural fertilizers were ruled out as a

source of radium (Szabo and dePaul, 1998).

When an alpha particle is ejected from the nucleus of a

radionuclide during decay, the newly created progeny radionuclide recoils in the opposite direction. This process is

known as the alpha-recoil process, and it enhances the solubility of alpha-particle emitting radionuclides. The energy associated with this recoil is 104

–106 times larger than typical

chemical-bond energies (Cothern and Rebers, 1990) and can

cause atoms on the surface of a grain to be recoiled directly

into the water in pore spaces.

Existing Sources of Information for Radionuclide Data

Results of the National Inorganics and Radionuclides

Survey (NIRS) (Longtin, 1988) were used to develop the

USEPA proposed radionuclide rule in 1991 (Federal Register

Vol. 56, No. 138). The objective of the NIRS was to characterize the occurrence of a variety of constituents present in

community ground-water supplies (finished water) in the

United States, its territories, and its possessions. The survey

included a random sample from 990 collection sites at wellheads and entry points to water-distribution systems that

were stratified into four population categories that represented about 2 percent of drinking-water supplies in each

category. Longtin (1988) summarized the NIRS data and

compared it with data from other studies completed at that

time, especially that of Hess and others (1985), who summarized existing data from national and State surveys to describe the occurrence of radioactivity in public water supplies in the United States. Zapecza and Szabo (1987)

summarized the occurrence data for uranium, radium, and

radon in ground water in the United States on the basis of

USGS, State regulator, and university research documents

and databases. A comparable national survey for radionu-
4

U-238

4.49x109

y

U-234

22.48x105

y

Th-230

8.0x104

y

Po-214

1.4x10-4s

Ra-226

1622 y

Rn-222

3.825 d

Po-218

3.05 m

Bi-214

19.7 m

Pb-214

26.8 m

Pb-210

22 y

Pb-206

(stable)

Po-210

138.4 d

Bi-210

5.0 d

Th-234

24.1 d

Pa-234

1.18 m

Th-232

1.41x1010y

Po-212

0.30x10-6s

Th-228

1.91 y

Ra-224

3.64 d

Ac-228

6.13 h

Rn-220

55 s

Po-216

0.16 s

Bi-212

60.5 m

TI-208

3.10 m

Pb-212

10.64 h

Pb-208

(stable)

Ra-228

5.75 y

Uranium

Protactinium

Thorium

Radium

Radon

Polonium

Bismuth

Lead

Thorium

Actinium

Radium

Radon

Polonium

Bismuth

Lead

Thallium

Uranium-238

EXPLANATION

Alpha decay

Beta decay

Thorium-232

EXPLANATION

Alpha decay

Beta decay

Figure 1. Diagram showing uranium-238 and thorium-232 radioactive decay series. (Radionuclides of

interset in this study are shaded). [Times shown are half-lives: y, years; d, days; h, hours; m, minutes;

s,seconds]. (From Hall and others, 1985.)
5

clides has not been done since the cited examples were completed in the late 1980’s.

Radium in Water Resources of the United States

As previously noted, natural radium is composed of

four isotopes, with three of the four (Ra-224, Ra-226, and

Ra-228) to be discussed in this report. To date, measured radium in surface waters has been traced to discharge from

ground water (Elsinger and Moore, 1983) or industrial waste

(Kraemer and Curwick, 1991); discussion in this report is

thus limited to ground water.

Occurrence of Radium-224

The NIRS (Longtin, 1988) did not include Ra-224.

Based on a limited number of analyses, however, Hess and

others (1985) report that the activity of Ra-224 can be equal

to or greater than the activity of Ra-228 in ground water;

they assume concentrations could reach as high as 30 to 40

pCi/L. Hess and others (1985) conclude that Ra-224 activity

is likely unsupported because activities of its parent, Th-228,

are usually less than 0.01 pCi/L. Ra-224 can enter ground

water by alpha recoil during the decay of Th-228 adsorbed

on the surface of aquifer solids. Elsinger and Moore (1983)

used radium to trace ground-water discharge in the South

Carolina Coastal Plain and documented the occurrence of

Ra-224 in the local ground-water resource.

Occurrence of Radium-226

Ra-226 is a progeny of U-238, and U-238 is commonly

found in ground water. The relatively high solubility of U238 as compared to thorium is a cause of its widespread distribution, and, thus, the widespread distribution of its daughter products such as Ra-226. The geochemical properties of

Ra-226 differ from those of U-238, however, and co-occurrence is not common (Szabo and Zapecza, 1991) because the

degree and chemical conditions of mobilization of the parent

U-238 and product Ra-226 are different. Uranium forms

soluble complexes particularly with carbonates under oxygen-rich conditions, and precipitates from ground water under oxygen-poor conditions (Zapecza and Szabo, 1987;

Cothern and Rebers, 1990). The concentration of uranium in

water and rock can thus be expected to range widely with

different geochemical environments. Szabo and Zapecza

(1991) detail the differences in the occurrence of uranium

and Ra-226 in oxygen-rich and oxygen-poor waters of hard

rock aquifers.

The most extensive region in the Nation where Ra-226

occurs in elevated concentrations in ground water is in the

north-central states, including southern Minnesota, Wisconsin, northern Illinois, Iowa, and Missouri (Zapecza and

Szabo, 1987; Gilkeson and others, 1983; Kay, 1999). In these

States, the drinking-water wells tap deep aquifers of Cambrian and Ordovician sandstones and dolomites and Cretaceous sandstones. These aquifers tend to have limited sorption sites, and radium solubility is enhanced by the

common-ion effect wherever the concentration of total dissolved solids are high (Gilkeson and others, 1983). In some

areas, such as northern Illinois, reduction of sulfate decreases

coprecipitation of Ra-226 with barium sulfate, another

mechanism which, if present, tends to limit dissolved Ra-226

(Gilkeson, and others, 1983).

Ra-226 is also found in high concentrations in water

derived from aquifers that straddle the Fall Line of the southeastern States from Georgia to New Jersey (King and others,

1982; Zapecza and Szabo, 1987; Szabo and dePaul, 1988).

These aquifers are composed of unconsolidated sands that

contain fragments of uranium-bearing minerals derived from

the crystalline rocks of the Blue Ridge and Piedmont provinces. Sands of the Coastal Plain where uranium and radium

concentrations tend to be the highest (Zapecza and Szabo,

1986) were directly derived from these crystalline rocks as

fluvial deposits. Furthermore, in areas with saltwater intrusion or brackish water, the common-ion effect again is likely

the cause for high concentrations of dissolved Ra-226

(Kraemer and Reid, 1984; Miller and Sutcliffe, 1985).

Of the sites surveyed for NIRS, activities of Ra-226

equaled or exceeded the MRL of 0.18 pCi/L in 40.2 percent

of the samples (Longtin, 1988). The national median activity

(of the samples with concentrations greater than 0.18 pCi/L)

was 0.39 pCi/L and the maximum was 15.1 pCi/L. About 1

percent of the samples had concentrations greater than 5 pCi/

L, the value that would place the drinking-water supply system out of compliance with the MCL for radium, even in the

absence of Ra-228.

Occurrence of Radium-228

Although Ra-228 is chemically similar to Ra-226, its

distribution in ground water can be different for several reasons. The relatively short half-life of Ra-228 limits the potential for unsupported transport (transport without the presence

of the parent product in solution) relative to that of the longer

lived Ra-226 isotope. Consequently, because of the relatively

slow movement of ground water in most aquifers, Ra-228

cannot migrate far from its source before it decays into its

progeny. Thorium-232, the parent of Ra-228, is extremely insoluble (Cothern and Rebers, 1990) and is not subject to mobilization in most ground-water environments. The insolubility of thorium (unlike the moderate solubility of uranium)

thus limits the distribution of Ra-228 in ground water to

some degree.

Michel and Cothern (1986) developed a national model

to depict the occurrence of Ra-228, based primarily on the

thorium content of the rock or sediment material that composed the aquifer. Data from NIRS showed that Ra-228 activities tend to be the highest in arkosic sand and sandstone

aquifers, indicating the model is representative of the distribution of Ra-228. Generally, the areas that are associated

with the highest potential for Ra-228 include the Coastal

Plain aquifers that straddle the Fall Line from Georgia to

New Jersey and Pennsylvania. Ground-water data from this

region confirms the presence of dissolved Ra-228 in Coastal

Plain and Paleozoic quartzite (metamorphosed arkosic sandstone) aquifers (Szabo and dePaul, 1998; King and others,

1982; Senior and Vogel, 1995). Large areas of northern Illinois, Iowa, Minnesota, and Wisconsin were also ranked as
6

having a high potential for the occurrence of Ra-228 as a result of the presence of sandstone aquifers with high total dissolved solids; actual occurrence data verifies this distribution

(Gilkenson and others, 1983). In contrast, aquifers that were

mostly composed of alluvial or glacial sand and gravel deposits were rated as having low potential for Ra-228 occurrence in those same states.

The High Plains aquifers and feldspathic sandstone

aquifers were also considered to have some potential for

Ra-228 occurrence. Granitic rocks that have the prerequisite

geochemical characteristics for Ra-228 occurrence underlie

other parts of the country such as local areas in Colorado,

Montana, and California. Aquifers in these rock types do not

yield much water and are not used extensively for large public water supplies. Localized alluvial valley sandstone aquifers in these same areas may also contain dissolved Ra-228.

These are areas that require additional testing in the future.

The concentration of Ra-228 was greater than 1 pCi/L

at about 12 percent of the sites sampled for NIRS (Longtin,

1988). The median activity of Ra-228 for samples with concentrations greater than 1 pCi/L (the MRL) was 1.47 pCi/L,

and the maximum was 12.1 pCi/L. About 18 percent of the

samples had concentrations that exceeded 2 pCi/L, the concentration that would put a system out of compliance if it had

a Ra-226 concentration of 3 pCi/L (the concentration of

Ra-226 that triggers analysis for Ra-228). Four percent of the

samples had concentrations that exceeded 5 pCi/L, the value

that would place the drinking-water-supply system out of

compliance with the MCL for radium even in the absence of

Ra-228.

Other Naturally Occurring Alpha-Particle Emitting

Radionuclides

Generally, the alpha-particle emitting radionuclides of

concern for drinking-water standards include those with halflives that are considered long enough to travel through drinking-water distributions systems and be ingested. Radionuclides having a half-life of 1 hour or less were not considered

in the group proposed for regulation in the 1991 proposed rule

(U.S. Environmental Protection Agency, 1991) because most

are likely to decay before the drinking water is consumed. The

widespread occurrence of Ra-224 in New Jersey (Szabo and

others, 1998a) increased concerns regarding the occurrence of

radionuclides with half-lives on the order of 1 day or a few

days in drinking-water supplies. Alpha-particle emitting radionuclides with a half-life longer than 1 hour include:

Decay

series

Alpha-particle emitting 

radionuclides with half-life 

longer than 1 hour

Uranium U-238, U-234, Th-230, Ra-226, Rn-222, Po-210

Actimium U-235, Po-231, Th-227, Ra-223

Thorium Th-232, Th-228, Ra-224, Pb-212

Long-lived (half-life greater than 1 day) beta-particle

emitting radionuclides, other than Ra-228 and Pb-210 are, in

large part, found in water resources affected by manmade

sources of radiation. The naturally occurring Ra-228 and

Pb-210 are the only beta-particle emitting radionuclides analyzed in this study. Other radionuclides, such as the thorium

isotopes, were analyzed in this study for quality-control purposes only.

Hess and others (1985) summarized the limited data on

Po-210 concentrations in ground water. Po-210 is particle reactive and is not expected to be found in high concentrations

in most natural waters. Po-210 was found at an unusually

high concentration (290 to 607 pCi/L) in a well used for

drinking water in Louisiana (Mullin, 1982) and was above

2 pCi/L in some wells in the Grants Mineral Belt of New

Mexico (Kaufmann and others, 1976). The source of Po-210

in the well in Louisiana is unknown. Uranium ore of mineable grade was presumed to be the source of Po-210 in the

wells in New Mexico. It is not known if changes in water

quality as a result of mining increased the mobility of the

Po-210. Po-210 has also been found in a shallow aquifer in

west-central Florida (Harada and others, 1989). Uranium-enriched phosphatic strata that contains sulfidic acidic water

high in Rn-222 characterize the aquifer. Water of this

geochemical type is rare in the environment and not typical of

water used for drinking-water supplies.

The geochemistry and occurrence of Rn-222 and all

other radionuclides not specifically mentioned above are not

within the scope of this study. A separate drinking-water standard for Rn-222 has been proposed by USEPA (1999b).

Limitations of Data Sources

The analytes quantified by NIRS included Ra-226,

Ra-228, Rn-222, uranium (mass analysis), and gross alphaparticle and gross beta-particle activities. The gross alphaand gross beta-particle activities were surveyed, in part, due

to recognition of the potential combined contribution to radioactivity in drinking water from the many other naturally

occurring and manmade radioisotopes. The gross alpha- and

beta-particle activities were determined after variable holding

times and, therefore, do not give complete information about

the contribution of short-lived radionuclides. Radium-224

was not analyzed in NIRS or any other national survey, and

since the completion of NIRS, no national-scale survey to

characterize radium in drinking water has been done.

Recent investigations to determine more accurately the

distribution of radioactivity in selected aquifers in New Jersey led to the finding that gross alpha-particle activity varies

considerably based on the amount of time that passed between sample collection and sample analysis (Szabo and others, 1998a; Parsa, 1998). Ongoing scientific study has shown

that this phenomenon is the result of the presence of shortlived radionuclides that previously were not believed to be

present in large concentrations in ground water. Modifications

and improvements to analytical techniques led to recognition

that large amounts of short-lived Ra-224 were widespread in

the water of the targeted aquifer (Szabo and others, 1998b).
7

The New Jersey study illustrates that targeted, national-scale

radionuclide data from drinking-water sources is incomplete

and insufficient for assessing the occurrence of short-lived

radionuclides, such as Ra-224, and their contribution to

gross-alpha particle activity.

DATA COLLECTION AND LABORATORY ANALYTICAL

METHODS

Samples were collected from wells selected for the purposes of assessing the occurrence of radium-224 in areas

known, or inferred to be associated with, high concentrations

of radium in drinking water supplies. Targeted sampling

makes use of knowledge about the likely controlling factors

on water quality in particular areas and can be useful in identifying water-quality problems that would be missed or underrated by typical random survey designs (Alley, 1993). In

addition, targeted sampling designs provides data to test specific hypotheses. For example, hypotheses regarding the relation of the occurrence of radium with geologic and other factors, the ratios of isotopes of radium in water, and factors

controlling the presence of the short-lived Ra-224 can be

tested with these data. Finally, this approach provided a way

to maximize limited resources in order to quickly assess the

potential scope of the occurrence of elevated concentrations

of these radionuclides in drinking-water sources on a national

scale and determine whether further study is warranted.

One well was sampled once from each public watersupply system (except those used for quality control where

sequential split samples were taken). Consequently, not accounted for are variability in concentrations of radionuclides

as a result of long-term and seasonal changes or other factors

associated with well construction and the operations of the

public water-supply systems (Alley, 1993; Alley and Cohen,

1991; Reilly and others, 1989). A single sample thus may not

necessarily represent the water quality of the groundwater resource used by the public water-supply system over

a long period of time. An individual sample is representative

of the quality of the local ground-water flow that contributes

water to the targeted well for the time at which it was

sampled. This sample may not represent the overall water

quality of the associated ground-water resource used by the

public water-supply system or ultimately delivered to their

customers, particularly where waters from various wells or

sources are mixed. Individual samples, which provide a snapshot of water quality at the time of sampling, can provide

reasonable depictions of the general water quality of an aquifer, however, particularly where slow movement of ground

water limits rapid fluctuations in water chemistry.

Well Selection

Areas in 27 States were targeted for sampling. These

selections were based on availability of previous occurrence

data and models, geologic maps, and known or inferred

geochemical properties of aquifers (Hess and others, 1985;

Michel and Cothern, 1986; Zapecza and Szabo, 1987;

Longtin, 1988). The well selections were narrowed to targeted areas with known, or suspected, high concentrations of

radium in the ground water within the same physiographic

province. Wells from public water-supply systems in these areas were randomly selected for sampling by personnel from

the American Water Works Association (AWWA) and American Water Works Service Company (AWWSC) (fig. 2). At

least one sample was collected from eight of the major physiographic provinces in the United States.

The water purveyors selected to participate were each

asked to complete a questionnaire to provide information on

well age and construction, local geology, and the population

served by their system (Appendix 1). Data on the population

served by the surveyed public water-supply systems represent

both quantified and estimated numbers. Estimates made by the

water purveyors typically represent the maximum population

that their system serves.

Sample-Collection Methodology

Unfiltered, raw-water samples were collected as close to

the wellhead as possible after the pump had been running a

minimum of one-half hour. Latex gloves were worn during

sample collection to avoid sample-handling contamination.

Samples were shipped overnight to the laboratory. Chemical

separation and analysis was begun within 48 hours for Ra-224,

Ra-226, and Po-210, and as soon as possible after that for Ra228 and Pb-210. The samples were acidified to pH 2 with reagent-grade nitric acid (HNO3

) and filtered with a 0.45-micrometer plate filter. Analysis for concentrations of Th-232,

Th-230, and Th-228 were conducted if the Ra-224 concentration was 4 pCi/L or greater. Concentrations of alpha-particle

emitting Ra-223 were determined for a randomly chosen subset of samples. Results from various analytical methods were

compared and extensive evaluation of quality-assurance

samples was completed .

Analytical Methodology

Measurement of radioactivity determines the amount of

radioactivity in a given volume of water. For water, the amount

of radioactivity generally is expressed in units of picocuries

per liter. A picocurie per liter equals 2.22 radioactive disintegrations per minute per liter of water. Many techniques are

available for measuring radioactivity; the specific technique

chosen depends on the radionuclide whose concentration is being determined. Alpha spectrometry, gamma spectrometry, and

low-background gas-proportional beta counting were the general techniques used in this study (table 1); the specific details

of each analysis are detailed.

Alpha spectrometry specifies the amount of alpha radiation emitted at specified energy levels, thus allowing

quantitation of individual radionuclide concentrations. Solidstate detectors, such as germanium or passivated ion-implanted

planar silicon (pips) detectors, are very sensitive and the most

commonly used sensors. Gamma spectrometry specifies the

amount of gamma radiation emitted at specified energy levels,

thus allowing quantitation of individual radionuclide concentrations. Beta-particle activity is counted in a low-background,

gas proportional counter. Detection efficiency is highest for

beta particles emitted with the highest energy.
8

Alpha spectrometry was the primary method used to

determine the concentration of alpha-particle emitting radionuclides of radium (Ra-224 and Ra-226). Improvements in

separation and purification chemistry (Sill and Williams,

1981) have allowed the alpha spectrometry measurement

technique to become available as a rapid, accurate, low-cost

analytical method for the alpha-particle emitting radionuclides of radium. The counting time required for alpha spectrometric determination of the radium concentrations is

shorter, and the instrumentation is not as bulky as that required for gamma-spectrometric determination; thus, many

analyses could be performed quickly to obtain timely results

for this large-scale survey.

The alpha-spectrometry method used and briefly described here is not yet approved by either USEPA or the

American Society for Testing Materials (ASTM) but is only

slightly modified from the widely used method of Sill and

others (1979). After acidification and filtration, a radioactive

barium (Ba) radionuclide (Ba-133) was added as a yield

tracer. Cation exchange chromatography (Bio-Rad AG 50WX8 cation exchange resin) was used to separate and purify

the Ra and Ba. The eluent from the exchange resin was removed with 8 molar HNO3

, and the Ra and Ba were co-precipitated with barite (BaSO4

) in a cold-water bath using a

seeding suspension (Sill and Williams, 1981). The seeding

suspension is needed to ensure the formation of uniform

fine-grained crystals of the BaSO4 that were then mounted

directly on filter paper, which was counted for 100 minutes

using alpha spectrometry with adjusted instrument operating

conditions that minimize background contamination (Sill and

Olsen, 1970). The count time was chosen to ensure a contractual minimum detectable concentration (defined in following section) of 1 pCi/L or less for most samples. Yield

was determined by gamma-spectrometric analysis of the concentration of the radioactive Ba-133 yield tracer.

The concentration of the beta-particle-emitting Ra-228

radionuclide was determined on a separate aliquot using the

USEPA-approved low-background beta count of the actinium228 progeny (Krieger and Whittaker, 1980) because the concentration of this radionuclide could not be determined using

alpha spectrometry. The beta-counting technique provided a

contractual minimum detectable concentration (defined in following section) of about 1 pCi/L for Ra-228.

Radium concentrations in about one-third of the

92

150 300 MILES

0 150 300 KILOMETERS

0

3

4

5

6

7

8

9

10

11

13 15

16

17 18

19

20 21

22

24

25

26

27

28

29 30

31

32

33

34

35

36

37

38

39

40

42

45

46 47 48

49

50

51

52

53

54

55 56 57 58

59

60

61 63 62

64

65

66 67

72

7374

75

76

77

78

79

80

81

82 83 84

85 86

87

88

89

90

91

93

95

96

9798

99

400 MILES

0 400 KILOMETERS

0

1

2

23

94

6869

2

7071

1

41

43

44

14

Figure 2. Major physiographic provinces of the United States and locations of wells with completed radium-224

analysis, 1998.
9

samples were also determined using gamma spectrometry as

part of the quality-assurance program. Analysis of the concentration of the beta-particle emitting Ra-228 isotope can be

performed on the same sub-sample aliquot as the alpha-particle-emitting Ra-226 and Ra-224 isotopes.

Several approaches to gamma-spectrometric measurement of Ra-224 concentrations have been compared and

found to give consistent results (Szabo and others, 1998b);

the gamma-spectrometric analytical technique used and

briefly described here is not yet approved by either USEPA

or the ASTM and is only slightly modified from the original

method of Elsinger and others (1982). After acidification

and filtration, Ra was coprecipitated with BaSO4

 and

mounted directly on filter paper. The Ra-224 activity was

counted using the 238.6 KeV energy emission of the Pb-212

progeny for 1,000 minutes 52 hours after coprecipitation

using a lead-shielded high-efficiency (about 40 percent)

gamma spectrometer with a well-type germanium-lithium

detector. The radium-bearing BaSO4 was recounted for 1,000

minutes about 28 days later to determine the concentration of

Ra-226 and Ra-228. The count time was chosen to ensure a

contractual minimum detectable concentration of 1.0 pCi/L

for each radionuclide. The barium yield was determined

gravimetrically.

The concentration of the alpha-particle-emitting Po-210

radionuclide was determined using alpha-spectrometry. The

sample bottle was soaked for 1 hour in concentrated HNO3 to

remove adsorbed Po-210 from the container walls. The Po210 was deposited from a concentrated hydrochloric acid

(HCl) solution onto a polished copper disk. Sample counting

time by alpha spectrometry was 100 minutes to ensure a contractual minimum detectable concentration of about 1 pCi/L.

Special care was taken to minimize counter contamination

for the volatile polonium radionuclides using the techniques

outlined by Sill and Olsen (1970). The concentration of a

Po-208 radioactive isotope tracer added to the sample was determined to compute yield.

The concentration of the beta-particle-emitting Pb-210

radionuclide was determined using the USEPA-approved lowbackground beta count of the bismuth-210 progeny after 10-

day ingrowth. The Pb-210 was preconcentrated and purified

using cation exchange chromatography (I-Chrome Pb-specific

cation exchange resin). Sample counting time was 300 minutes

to ensure a contractual minimum detectable concentration of

about 1 pCi/L.

The concentration of the alpha-particle-emitting radionuclides of thorium (Th-232, Th-230, and Th-228) were determined using alpha-spectrometry on a selected number of

samples. The concentration of the beta-particle-emitting

Th-234 isotope, a member of the U-238 decay series, cannot be

determined using this technique. Because Ra-224 is a direct

progeny of Th-228 originating in a different decay series (the

Th-232 decay series) than Th-234, the measurement of Th-234

concentrations was not necessary. The isotopes of thorium

were preconcentrated and purified using cation-anion exchange

chromatography (Bio-Rad AG 1-X8 anion exchange resin)

from which the Th isotopes were eluted with dilute HCl, then

electroplated at 1 ampere for 60 minutes onto a stainless-steel

disk. Sample counting time by alpha spectrometry was 100

minutes to ensure a contractual minimum detectable concentration of about 1 pCi/L.

Reporting of Analytical Results and Statistical

Calculations with Raw-Data Values

Raw, unrounded values for all radionuclide concentrations were reported directly by the laboratory, along with the

minimum detectable concentration (MDC), and a combined

standard uncertainty (CSU) or a counting error. An explanation

Methods

Radionuclide Alpha

spectrometry

Number of

samples

Number of

samples

Number of

samples

Number of

samples

Split with 

both methods

Split with 

both methods

in duplicate

Number of

samples

Split with 

both methods

Split with 

both methods

in duplicate

Gamma

spectrometry

Beta

counting

Alpha and

gamma 

spectrometry

Beta counting

and gamma 

spectrometry 

Ra-224 X 90 X 12 X 15

36

15

36 Ra-226 X

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

90 X 12 X

Ra-228 X 12 X 90 X 15

36

Pb-210 X 109

Po-210 X 113

Thorium X 33

Table 1. Radionuclides analyzed in the United States Geological Survey reconnaissance survey, associated analytical 

method, and the number of samples (including environmental and quality-control samples) analyzed by each method 

[—, not applicable]
10

of these terms is provided in this section.

The decay of any radionuclide occurs at a given rate

over a specific period of time. In any instant of time, however, the rate of radiation is random, resulting in a degree of

uncertainty in the measurement known as the counting uncertainty term (also called the counting error). Thus, any

measurement of radioactivity has a counting uncertainty independent of, and in addition to, laboratory sources of analytical uncertainty. Increasing the time of the count can decrease the counting uncertainty term. The greater the degree

of uncertainty, the more difficult it is to quantify small

amounts of radiation. Quantifying small amounts of radiation

is further complicated because the analytical instruments

contain background radiation that varies with every measurement. The radiation from the radionuclide being quantified

must be clearly distinguishable above the ambient background radiation. A contractual minimum detectable concentration (American Society of Testing Materials, 1999) is contractually determined with the laboratory before a project

begins and is generally based on the scope of the project and

available resources. The contractual (also called the a priori)

MDC was targeted for 1 pCi/L for all radionuclides analyzed

in this study. The sample-specific MDC is computed individually for each radionuclide analysis on the basis of instrument operating conditions at the time of measurement and

reported by the laboratory for each analysis. For purposes of

this paper, the sample-specific (or a posteriori) MDC will be

referred to simply as the MDC unless otherwise noted.

Uncertainty can be reported in a variety of ways; the

most common include (1) the sum of the laboratory and

counting uncertainty, known as the combined standard uncertainty (CSU, also called the total propagated uncertainty),

and (2) a counting uncertainty only. There is a 67-percent or

95-percent probability (based on one or two standard deviations, respectively) that the true value of the radionuclide

concentration is within the measured value plus or minus the

uncertainty. The uncertainty terms are generally smaller than

the measured value except when the measured values are low

concentrations (near the MDC). The uncertainties associated

with the various radionuclides in this report are provided directly by the individual laboratories as:

 • One standard deviation of the CSU: Ra-224 and Ra-226

 by alpha spectrometry.

 • Two standard deviations of the CSU: Ra-228 and Pb-210

 by beta counting, Po-210 by alpha spectrometry.

 • One standard deviation of the CSU: Ra-224, Ra-226,

 and Ra-228 by gamma spectrometry.

The raw analytical result is interpreted in the context of

the CSU and the MDC. The raw result specifies the instrumental reading after the count is completed, even if it is a

negative value. A negative value is a result from a radiation

measurement (count) of a sample over a fixed interval of

time where the measured radioactivity from the sample is

less than the long-term average background radiation determined routinely by the instrument. A negative result simply

indicates that it is unlikely the radionuclide is present in a

quantifiable amount.

Raw, unrounded values of concentrations reported directly by the laboratories were used to compute standard distributional statistics and correlation coefficients for all radionuclides. Correlations were calculated using the Spearman

correlation coefficient. The Spearman correlation coefficient

(correlation of the ranks of the data, not the actual values) is

a measure of the degree to which the two data sets increase

(or decrease) together. Negative values were set to zero for

computational, but not reporting, purposes. No other manipulation or screening of the raw-data values was attempted unless otherwise stated in order to avoid biases due to omitting

the low but detectable concentrations. Consequently, some

calculations were performed with raw data that were at or below the MDC and (or) the CSU in a limited number of cases.

This approach is a simple way to deal with the various possible combinations of raw values and associated CSU and

MDC. This approach is not expected to affect the majority of

data above 1 pCi/L, the contractual (a priori) MDC targeted

by the laboratories. For example, ratios of radionuclide concentrations were determined using raw values; it is understood, however, that ratios may have bias when concentrations are below the MDC and (or) the CSU.

Statistical, or other calculations that omit data reported

below the MDC and CSU are also biased, however, because

some of the values omitted may actually be detectable radioactivity. Further, the omitted data still represent measurements of environmental radioactivity at levels that cannot be

quantified; their omission biases the overall population distribution. Alternative approaches to calculating summary, and

other statistics on water-quality data with concentrations near

or below quantitation or reporting levels were discussed by

Helsel (1990) and, although not used in this report, provide

additional insights. These approaches are typically designed

for concentrations that are reported as “less than” a minimum

value, usually a minimum reporting level (MRL), whereas

the raw unrounded data values were reported by the laboratories for the present study. For example, one such approach

provides that a numeric value one half the MRL concentraRange of estimated number 

of people served Number of public water-supply

systems sampled

0–500

501–1,000

1,001–3,300

3,301–10,000

10,001–100,000

100,001–1,000,000

> 1,000,000

8

7

21

29

22

5

1

Table 2. Number of public water-supply systems sampled, 

by range of estimated number of people served

[ >, greater than]

Note: Two public water-supply systems did not provide information, 

and four wells surveyed were not affiliated with public water supplies.

∑ 93 wells
11

tion be substituted for the sample result before summary

statistics are calculated. The latter approach has been shown

to be a more appropriate representation of the entire distribution of data below and above the MRL than simply ignoring the samples with concentrations below the MRL. The

lack of a documented comparison of alternative approaches

for radionuclide data preclude arbitrary use of such simple

solutions that accurately portray the entire distribution of

data for this study. Consequently, the correlations and other

calculations that were performed with all data regardless of

the associated MDC or CSU contain an unknown, but small,

amount of uncertainty and potential bias, mostly limited to

concentrations less than about 1 pCi/L (the contractual

MDC). Attempts to quantify this uncertainty were beyond

the scope of this report.

OCCURRENCE OF SELECTED RADIONUCLIDES IN

GROUND WATER USED FOR DRINKING WATER

A total of 94 wells from public water supplies were

sampled, as were 1 domestic well and 4 research wells (fig.

2). The populations served by the public water-supply systems that participated in the reconnaissance survey range

from less than 500 to more than 1,000,000 (table 2). The

public water-supply systems selected for the survey incorporate most areas depicted by Michel and Cothern (1986) as

those where a medium to high relative probability of elevated concentrations of Ra-228 were expected to occur in

ground water. Some of the areas in the western United

States ranked with medium-to-high probability of containing elevated dissolved Ra-228 in ground water by Michel

and Cothern (1986) were not included in this survey because large populations rarely rely on public ground-water

sources in those areas. Because of the limited resources

available to the study, small systems relying on ground water in the western United States were generally not sampled.

We note this is an issue that needs to be resolved in future

sampling work. The estimates of populations served are provided here for a general perspective on the distribution of

public water-supply systems surveyed; the number of

people that consume water from each well sampled is unPercentage of sample (including duplicate)

results with

Radionuclide

The reported 

concentration greater 

than the MDC and the 

concentration minus the 

CSU greater than the MDC

The reported

concentration greater 

than the MDC and the

concentration minus the

CSU less than the MDC

The reported

concentration less 

than the MDC and the

concentration plus the

CSU greater than the MDC

The reported

concentration less 

than the MDC and the

concentration plus the

CSU less than the MDC

Ra-224 41 13 27 19

Ra-226 81 7 10 2

Ra-228 28 12 25 35

Table 3. Percentage of samples with reported concentrations that are greater or less than the minimum detectable 

concentration (MDC) plus or minus the combined standard uncertainty (CSU) for all radium isotopes analyses

(MDC< minimum detectable concentration; CSU, combined standard uncertainty)

known. Accordingly, no attempt was made to analyze or

associate the occurrence data on the basis of population

served by public water-supply systems.

Twenty-one of the 99 samples exceeded the current

combined radium standard. The reported concentrations of

each radionuclide and the reported concentrations plus or

minus the CSU were compared to the MDC (table 3). The

lesser amount of uncertainty that is associated with the Ra226 analyses than with the Ra-224 or Ra-228 analyses results in a higher percentage of samples with concentrations

and CSUs that are greater than the MDC in the Ra-226

samples than in the other isotopes. Fifty-four percent of the

reported Ra-224 concentrations were greater than the

MDC; 88 percent of the Ra-226 concentrations were

greater than the MDC, and 40 percent of the Ra-228 concentrations were greater than the MDC. This relative difference in analytical uncertainty is further illustrated by comparing the cumulative frequency of the reported

concentrations, the concentrations plus and minus the

CSU, and the MDC for each isotope (fig. 3). Table 3 and

figure 3 provide insight and perspective on the reported

concentrations and the associate uncertainties in the data

base. Additional analyses of the relative uncertainties is beyond the scope of this report. Forty-five percent of the Po210 concentrations were greater than the MDC and 36 percent of the Pb-210 concentrations were greater than the

MDC. The distributions of the concentrations of all radionuclides analyzed are summarized in tables 4 and 5, and

radium isotope co-occurrence is statistically summarized

by analysis of correlation in table 6. Other radionuclides

analyzed, such as thorium isotopes and Ra-223, are strictly

part of the quality-assurance analysis and to test the experimental methods and are not within the scope of this discussion. The data for all radionuclides analyzed, however, are

presented in Appendix 1.

Radium-224

Concentrations of Ra-224 in samples analyzed for

the survey ranged from less than the MDC to 73.6 pCi/L

(table 4). The Ra-224 concentration of 73.6 pCi/L is the
12

A.

B.

C.

0

–10

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120

0 20 40 60 80 100 120

0 0

–5

10

5

20

15

0

10

20

30

40

50

60

70

80

90

100

–10

0 20 40 60 80 100

EXPLANATION

X Minimum detectable concentration (MDC)

Combined standard uncertainty (CSU)

Reported concentration

Combined standard uncertainty

EXPLANATION

X Minimum detectable concentration (MDC)

Combined standard uncertainty (CSU)

Reported concentration

Combined standard uncertainty

EXPLANATION

X Minimum detectable doncentration (MDC)

Combined standard uncertainty (CSU)

Reported concentration

Combined standard sncertainty

Sample number

Sample number

Sample number

Radium-228, in picocuries per liter Radium-226, in picocuries per liter Radium-224, in picocuries per liter

Figure 3. Graph showing reported concentrations,

concentrations plus and minus the combined standard

uncertainty (CSU), and the minimum detectable

concentration (MDC) for Ra-224 (A), Ra-226 (B), and

Ra-228 (C), for all samples including duplicates.

highest concentration of all radionuclides in this survey and

was from a well completed in a Coastal Plain aquifer in

Maryland. Most of the samples (70 percent) contained less

than the contractual MDC of 1 pCi/L of Ra-224, with half

the concentrations reported less than 0.3 pCi/L (table 4).

About 5 percent of the samples exceeded 10 pCi/L (table 5).

The ranked concentrations of Ra-224 were significantly correlated with those of Ra-228 and Ra-226 (table 6).

The concentrations of Ra-224 plotted against those of the

corresponding Ra-228 concentrations group closely about

the 1:1 line (fig. 4A), particularly in the ranges above

1 pCi/L. Comparisons of values less than about 1 pCi/L tend

to be at or near the sample-specific MDC and are below the

contractual MDC; comparison may be affected by analytical

uncertainty; difference in the quality of analytical results obtained at the low concentration levels with the different analytical techniques used, and artifacts. Scatter in relative

terms is, therefore, much greater about the 1:1 line for concentration values below 1 pCi/L than above this value. One

of the plotted values that deviate substantially from the 1:1

ratio for activity of Ra-224 when compared to Ra-228 when

concentrations were above 1 pCi/L include the samples

from research wells not used for drinking water in the

Coastal Plain Physiographic Province in South Carolina.

The Ra-224-rich water samples from South Carolina are

highly acidic (pH < 4) and may not be typical of community

drinking water supplies throughout the Nation. Ancillary

water-quality information was not available for the sample

from the State of Missouri that is also an exception to the

1:1 trend for the activity ratios.

The concentration of Ra-224 plotted against those of

the corresponding Ra-226 concentrations group do not plot

closely about the 1:1 line (fig. 4B). Much more scatter

around the 1:1 line relative to Ra-226 is apparent than is the

case relative to Ra-228 (fig. 4A and 4B) for concentration

ranges both above and below 1 pCi/L; this consistency indicates that the result is not an analytical artifact. Although the

ranked concentrations of Ra-224 correlate significantly with

those of Ra-226, it is possible to have large quantities of either one and not the other in ground water.

Radium-226 and Radium-228

Most of the concentrations of Ra-228 in samples analyzed for the reconnaissance survey are less than the contractual MDC of 1 pCi/L, and half are below 0.5 pCi/L (table 4).

The maximum concentration of Ra-228 (72.3 pCi/L) was

found in the same Coastal Plain well in Maryland with the

maximum Ra-224 concentration. The maximum concentration of Ra-226 was 16.9 pCi/L from a well in Iowa. Most of

the concentrations of Ra-226 were less than the contractual

MDC of 1 pCi/L, with a median concentration of 0.4 pCi/L.

The Spearman correlation coefficient of Ra-226 and

Ra-228 indicates that the ranked concentrations of the two

isotopes are significantly correlated (table 6). The general

weak nature of co-occurrence of Ra-226 with Ra-228 is illustrated in fig. 4C where it can be seen that many samples

do not plot near the 1:1 line.
13

Radium Isotope Ratios and Correlations

Concentrations of Ra-228 were correlated with those of

Ra-224. Radium isotopic ratios may be biased because attempts to account for uncertainty in analytical methodologies

was beyond the scope of this report. However, there is a

physical basis to the high degree of correlation because both

isotopes originate from the same decay series (that of thorium-232), and Ra-224 is indirectly derived from decay of

Ra-228 through Th-228. Parsa (1998) reports that the Ra224:Ra-228 ratios ranged from 1.2 to 2.0 in initial results

from the Coastal Plain of New Jersey. The Ra-224:Ra-228

ratios ranged from 1.2 to 2.0 in South Carolina ground water

and from 0.8 to 1.7 in Connecticut according to values reported from the literature (Hess and others, 1985). The

strong correlations found in the reconnaissance survey corroborate the previous studies and indicate a typical ratio of

Ra-224 to Ra-228 of near 1. Thus, the conclusion that Ra224 and Ra-228 co-occur in nearly equal concentrations is

based on many samples collected from a variety of geohydroRa-224 Ra-226 Ra-228

Ra-224

Ra-226

Ra-228

1.0

—

—

0.69

1.0

—

0.82

0.63

1.0

0.01 0.1 1 10 100

0.01

0.1

10

100

0.01 0.1 1 10 100

0.01

0.1

10

1

1

100

0.01 0.1 1 10 100

0.01

0.1

1

10

100

Radium-224, in picocuries per liter Radium-224, in picocuries per liter Radium-228, in picocuries per liter

Radium-228, in picocuries per liter

Radium-226, in picocuries per liter

Radium-226, in picocuries per liter

Line of equal 

relation (1:1)

Line of equal 

relation (1:1)

Line of equal 

relation (1:1)

A.

B.

C.

Note: Values of radium isotopes less than 1pCi/L tend to be equal to or near 

(above or below) the minimum detectable concentration and may not be 

reasonable for comparison because of the difference in quality of analytical 

results abtained at low concentrations.

Figure 4. Relations of radium-224 to radium-228 (A),

radium-224 to radium-226 (B), and radium-226 to radium228 (C).

Table 4. Summary of radionuclide concentrations in the

United States Geological Survey reconnaissance survey

Table 5. Percent of samples reported to exceed specified

radionuclide concentrations

Concentration, in picocuries per liter

Radionuclide Mean Median Standard

deviation Maximum Number of

samples 

Ra-224 3.2 0.3 10.1 73.6 99

Ra-226 1.6 0.4 2.8 16.9 99

Ra-228 2.1 0.5 7.9 72.3 99

Pb-210 0.6 0.5 0.5 4.1 96

Po-210 0.1 0.01 0.5 4.9 96

Radionuclide

Total number

 of samples

Percent of samples that 

exceed specified concentrations, 

in picocuries per liter

Ra-224 99 30 26 20 15 9 5

1235 7 10

Ra-226 99 33 22 17 10 5 2

Ra-228 99 26 18 14 9 2 2

Po-210 95 3 1 1 1 0 0

Pb-210 96 10 311 0 0

Table 6. Spearman correlation coefficient matrix (significant at 0.05 level) for radium isotope concentrations
14

logic settings across the Nation. The water samples in this reconnaissance survey were collected from a multitude of aquifers and geochemical environments from most of the major

physiographic provinces of the United States. It is thus reasonable for screening purposes to use Ra-228 as a proxy indicator

for the much shorter lived and infrequently sampled Ra-224.

For example, indications of high concentrations of Ra-228 in

water from a particular aquifer or region could help provide an

“early warning” to public water-supply systems that analysis

for the concentration of Ra-224 and determination of gross alpha-particle activity within 48-to-72 hours after sample collection should be considered. The USEPA suggests that regions

suspected of containing Ra-224 in ground water should use the

short holding time of 48-to-72 hours for analysis of gross alpha

particle activity (USEPA, 2000). Furthermore, a more rigorous

analysis of the occurrence and distribution of Ra-228 concentrations in ground water across the Nation could aid in the design of a more complete national survey targeted for Ra-224

than this initial effort was able to provide.

 The ranked concentrations of Ra-226 and Ra-228 also

correlate significantly (table 6); many samples, however, deviate from the 1:1 ratio (fig. 4C). The Ra-228 and Ra-226 concentration data in this study thus are consistent with numerous

other studies, which all indicate that Ra-228 and Ra-226 are

not uniformly present in a nearly 1:1 ratio in ground water

(Hess and others, 1985; Blanchard and others, 1985; Szabo,

1990). Ra-226 is not a good proxy indicator of concentrations

of Ra-228 or Ra-224 in ground water, although where Ra-226

is present, Ra-228 and Ra-224 also are likely to be present.

Polonium-210 and Lead-210

The maximum concentration of Po-210 was 4.9 pCi/L

(table 4) in a sample collected from a well in the Coastal Plain

of Virginia. Only one other sample, which had a Po-210 concentration of 1.4 pCi/L, exceeded the contractual MDC of

1 pCi/L. The water chemistry from the well with the highest

Po-210 concentration does not provide any information to indicate why Po-210 is likely to be present in elevated concentrations (David Nelms, USGS, Virginia District, written

comm. 1999). The radium isotope and Pb-210 concentrations

were all less than one (except for the maximum). The pH was

7.5 (near neutral, not acidic), the specific conductance was

259 microsiemens/cm2 (not unusual for ground water in this

Coastal Plain aquifer), the turbidity was 0.53 NTU (below

drinking water secondary standards), the alkalinity was 119

mg/L as CaCO3 (buffered), and there was measurable dissolved oxygen [dissolved oxygen should be 0 in sulfidic waters, the type of waters reported by Harada and others, (1989)

to contain Po-210].

The maximum concentration of Pb-210 was 4.1 pCi/L in

a sample collected from the Appalachian Province in Connecticut (table 4). Approximately 10 percent of the samples

exceeded a Pb-210 concentration of 1 pCi/L (the contractual

MDC; table 5), but only one sample exceeded 3 pCi/L. The

greatest frequency of detection was for samples from the Appalachian Physiographic Province, especially those from the

northeastern United States.

LIMITATIONS AND PERSPECTIVE ON THE U.S.

GEOLOGICAL SURVEY RECONNAISSANCE SURVEY

The reconnaissance survey was designed to target areas

of known, or suspected, high concentrations of Ra-224 as inferred by associated radium-occurrence data, geologic maps,

and other geochemical considerations. Thus, the reconnaissance survey is likely biased toward the high end of the frequency of occurrence distribution for Ra-224 and the co-occurring natural contaminant, Ra-228. Targeted sampling and

modeling provides an important evaluation of distribution

trends, even in cases where a contaminant is not randomly

distributed (Michel and Cothern, 1986). In addition, targeted

sampling can be useful in identifying water-quality problems

that would be missed or underrated by typical random survey

sampling designs and can provide enhanced detail on spatial

distributions and variability (Alley, 1993). The results obtained even in this limited targeted sampling thus provide crucial information that could be used to design a comprehensive

national analysis of the contributing factors (geologic, hydrologic, geochemical) that control the occurrence distributions

of Ra isotopes in various parts of the Nation. The results also

fill the data gap in documenting the widespread occurrence of

Ra-224 documented to date only in southern New Jersey

(Szabo and others, 2000) and add insight to the geologic occurrence of elevated concentrations of Ra-224 in ground water

and associated ratios of radium isotopes in various geochemical environments.

Analysis of Quality-Control Data

Sequential duplicate samples were collected at about 20

percent of the sampling sites, and preliminary qualitative

comparisons were made. The duplicates of the environmental

samples analyzed for all radium isotopes with the same techniques indicated reasonable concurrence of results (fig. 5).

This result indicates a nearly linear relation among the results

of duplicate analyses; the analytical techniques were of suitable quality to provide reproducible results. Although a few

pairs of duplicate samples substantially deviate from a 1:1

correspondence for the concentrations of Ra-224 (fig. 5A),

the overall fit across the concentration range observed is

closely constrained around a 1:1 line. The concentrations of

samples analyzed for Ra-224 and Ra-226 by gamma spectrometry are similar to those analyzed by alpha spectrometry

(fig. 6A and B). Similarly, the concentrations of Ra-228 analyzed by gamma spectrometry are similar to those analyzed

by beta counting (fig. 6C). A more thorough analysis of the

quality assurance data is beyond the scope of this report;

however, these preliminary results indicate that laboratory

methodologies and sample collection are not a significant

source of error.

The Effects of the Targeted Sampling Design on

Interpretations of the Results of the U.S. Geological

Survey Reconnaissance Survey

The effects on the apparent distribution of radium concentrations due to the targeted sampling design and raw-water

sampling can be seen by comparing the results with those of
15

the National Inorganics and Radionuclide Survey (NIRS)

(Longtin, 1988) . The NIRS employed a random sampling

design stratified by the size (population served) of the individual public water-supply systems and finished-water sampling (although most samples came from systems that were

not treating their water). In this way, data collected in this

USGS reconnaissance survey from areas of the Nation with

known, or presumed, high concentrations of radium in raw

ground water are compared with data collected at random

across the Nation from raw and finished ground water

(NIRS).

The NIRS data were collected in the public water-supply distribution system and may thus represent effects of the

distribution system on water chemistry, as well as effects of

water treatment. It is not possible with the data at hand to

quantitatively distinguish differences in the USGS reconnaissance and NIRS data due to sampling design and other facDuplicate Sample (radium-224, in picocuries per liter) Duplicate Sample (radium-226, in picocuries per liter) Duplicate Sample (radium-228, in picocuries per liter)

Environmental sample (radium-224, in picocuries per liter)

Environmental sample (radium-226, in picocuries per liter)

Environmental sample (radium-228, in picocuries per liter)

Line of equal 

relation (1:1)

A.

B.

C.

0 10 20 30 40 50 60 70 80

0

10

20

30

40

50

60

70

80

0 5 10 15

0

5

10

15

0 10 20 30 40 50 60 70 80 0

10

20

30

40

50

60

70

80

Line of equal 

relation (1:1)

Line of equal 

relation (1:1)

Figure 5. Environmental sample and duplicate environmental sample concentrations for radium-224 (A),

radium-226 (B), and radium-228 (C).

Radium-224, in picocuries per liter

(gamma spectroscopy)

Radium-226, in picocuries per liter

(gamma spectroscopy)

Radium-228, in picocuries per liter

(gamma spectroscopy)

Radium-224, in picocuries per liter (alpha spectroscopy)

Radium-226, in picocuries per liter (alpha spectroscopy)

A.

B.

C.

Line of equal 

relation (1:1)

Line of equal 

relation (1:1)

Line of equal 

relation (1:1)

0 5 10 15

0

10

20

30

40

50

60

70

15

0 10 20 30 40 50 60 70 80

0

10

20

30

40

50

60

70

80

Radium-228, in picocuries per liter (beta counting)

0 10 20 30 40 50 60 70 80

0

10

20

30

40

50

60

70

80

Figure 6. Duplicate environmental samples for radium224 analyzed by alpha spectrometry and gamma spectrometry (A), and radium-226 analyzed by alpha spectrometry and gamma spectrometry (B), and radium-228

analyzed by beta counting and gamma spectrometry (C).
16

tors, such as water treatment and distribution-system effects.

Several types of water-treatment practices can remove at

least some percentage of radium from water, including lime

softening, ion exchange, iron removal, and filtration. A preliminary analysis of the NIRS data revealed that the distribution of concentrations of radium in water samples collected

from public water-supply systems with no treatment (the majority of samples in NIRS) were not different than samples collected from systems with treatment (William Labiosa, U.S. Environmental Protection Agency, Office of Ground Water and

Drinking Water, written commun., 1999). The treatment technologies associated with the treated water samples in NIRS

were not necessarily targeting radium removal. Based on the

preliminary analysis, water treatment is not expected to bias

comparisons of raw (USGS reconnaissance survey) and finished (NIRS) waters, not because potential treatment techniques are ineffective, but because treatment techniques for

many sites surveyed in the NIRS were not used for the purpose

of Ra removal. The major differences in interpretations of the

distribution of radium concentrations in the two databases are

thus most likely due to differences in survey design.

Graphical comparisons of the cumulative frequency distributions of Ra-226 and Ra-228 are illustrated in figs. 7 and 8

respectively (Ra-224 was not analyzed in NIRS). The occurrence of concentrations of Ra-226 above 1, 3, 5, 7, and 10 pCi/

L is more frequent in the targeted sample design of the present

USGS reconnaissance survey (fig. 7A) than in the random

NIRS design (fig. 7B). A dashed line indicates the

5 pCi/L concentration level, the level at which the combined

radium (Ra-226 + Ra-228) MCL is exceeded. Results from the

NIRS random design show that the combined radium MCL is

Cumulative frequencyCumulative frequency

Radium-228, in picocuries per liter Radium-228, in picocuries per liter

A. USGS B. NIRS

EXPLANATION

MCL—Combined radium standard

(Ra–226 + Ra–228 = 5 pCi/L)

Note: Data in (B) are censored by 

the laboratory at 

1.0 picocuries per liter

0.01 0.1 1 10 100

0

0.2

0.4

0.6

0.8

1

0.1 1 10 100

0

0.2

0.4

0.6

0.8

1

Maximum

contaminant

level for

combined

radium

Maximum

contaminant

level for

combined

radium

Figure 8. Cumulative frequency distributions for radium-228 in the 1998 U.S. Geological Survey (USGS) reconnaissance

survey (A; targeted survey design) and radium-228 in the National Inorganics and Radionuclide Survey (NIRS) (B; random

survey design). (MCL, maximum contaminant level.) Cumulative frequency

Radium-224, in picocuries per liter

0.1 1 10 100

0

0.2

0.4

0.6

0.8

1

Maximum 

contaminant 

level for grossalpha particle 

activity

Figure 9. Cumulative frequency distribution for

radium-224 in the 1998 U.S. Geological Survey

Reconnaissance survey (targeted sampling design).

0.01 0.1 1 10 100

0

0.2

0.4

0.6

0.8

1

0.1 1 10 100

0

0.2

0.4

0.6

0.8

1

Cumulative frequencyCumulative frequency

Radium-226, in picocuries per liter Radium-226, in picocuries per liter

Maximum

contaminant

level for

combined

radium

Maximum

contaminant

level for 

combined

radium

EXPLANATION

MCL—Combined radium standard

(Ra–226 + Ra–228 = 5 pCi/L)

Note: Data in (B) are censored by 

the laboratory at 

0.18 picocuries per liter

A. USGS B. NIRS

Figure 7. Cumulative frequency distributions for radium-226 in the 1998 U.S. Geological Survey (USGS) reconnaissance survey (A; targeted survey design) and in the National Inorganics and Radionuclide Survey (NIRS) (B; random

survey design). (MCL, maximum contaminatnt level.)
17

exceeded by Ra-226 alone in less than 1 percent of the

samples in the entire United States (fig. 7B). On the other

hand, the targeted sampling design (fig. 7A) shows that about

10 percent of the samples exceed the MCL in areas of the

country that were presumed to have the types of geology and

geochemical environments conducive to uranium and radium

in source material and high degrees of radium mobility, thus

resulting in high concentrations of Ra-226 in ground water.

Comparison of the cumulative frequency distributions of

Ra-228 between the random sampling design of NIRS and

the targeted sampling design of the USGS reconnaissance

survey indicates a similar bias in the data from the targeted

sampling. Less than 1 percent exceed 5 pCi/L in the NIRS

data (fig. 8B) and about 9 percent exceed 5 pCi/L in the targeted survey data (fig. 8A). The cumulative frequency distribution of Ra-224 from the targeted sampling design (fig. 9)

is included for completeness; about 15 percent (table 5) of

the samples in the targeted survey exceed a value of 5 pCi/L

for Ra-224, and nearly 5 percent of the samples exceed

15 pCi/L, the MCL for gross alpha-particle activity.

The targeted sampling design of the USGS reconnaissance survey clearly results in a data distribution with a

greater frequency of concentrations above any given value

than in the case of the random sampling (NIRS). For the targeted regions, then, the rate of compliance clearly is lower

than for the Nation as a whole and represent the regions

where future investigations need to be focused to define the

scope of the exposure problem. For the targeted regions, the

rate of compliance with the MCL will be a function of the

sampling design and will depend on the variability of the Ra

distribution within the affected aquifers.

Cancer Risk Estimates for Radium Isotopes in Drinking

Water

The tables, statistics, and graphics presented in this report summarize the concentrations of the targeted radionuclides. The concentration data, although useful for the many

purposes as previously stated, can also be associated with

human-health risk information to provide the reader with an

additional perspective in interpreting the importance of the

results in terms of human-health risk.

In evaluating exposure to radionuclides in drinking

 water, the USEPA considers only carcinogenic risk for all

radionuclides, except uranium (N. Nelson and L. Ralston,

U.S. Environmental Protection Agency, Office of Radiation

and Indoor Air, written commun., 1999). Uranium is the only

element for which chemical toxicity (as a kidney toxin) has

been identified to be comparable to or greater than the radiotoxicity, and for which a reference dose has therefore

been established to evaluate chemical toxicity. Thus, for radioisotopes of uranium, both chemical toxicity and radiogenic cancer risks are evaluated. Other types of detrimental

health effects are also associated with exposure to ionizing

radiation, including mutagenic, teratogenic, and acute toxicity effects. These effects are generally less significant for

doses associated with environmental exposures. Therefore,

the USEPA considers carcinogenic risk to be a sufficient basis for assessing radiation-related human-health risks for

drinking water (N. Nelson and L. Ralston, U.S. Environmental Protection Agency, Office of Radiation and Indoor Air,

written commun., 1999). For the majority of radionuclides,

the risks from any chemical toxicity are much smaller than

the radiation-related risk (radiotoxicity), so that only radiological risks normally need to be evaluated (U.S. Environmental Protection Agency, 1999a).

The USEPA estimates of excess fatal (mortality) and

total (morbidity) cancer risks for lifetime intakes of Ra-224,

Ra-226, and Ra-228 in drinking water (table 7) are obtained

from Federal Guidance Report No. 13 (U.S. Environmental

Protection Agency, 1999a). The first set of values (columns 2

and 3) in table 7 are the unit concentration risks; that is, the

estimated excess fatal and total cancer cases per million perEstimated number of excess fatal and total cancers per million persons

The Unit Concentration† (1 pCi/L)

Assuming a lifetime (70 year) intake of 

2 liters of drinking water per day at:

Assuming a lifetime (70 year) intake of 

2 liters of drinking water per day at:

The Current MCL‡

Radionuclide

Isotope

Fatal (mortality) Total (morbidity) Fatal (mortality) Total (morbidity)

Ra-224 5 9 na na

Ra-226 14 20 70 100

Ra-228 38 53 190 265

Table 7. U.S. Environmental Protection Agency’s cancer risk estimates for radium isotopes in drinking water

[MCL, maximum contaminant level; na, not applicable; pCi/L, picocuries per liter]

† The risk from 1 pCi/L. From Federal Guidance Report No.13 (U.S. Environmental Protection Agency, 1999), assuming a lifetime intake of 51,100 liters. See text for details.

‡ Assumes that each isotope is ingested alone at the following concentrations in 
18

sons per pCi per liter of water ingested (pCi/L)-1, assuming

lifetime intake. These values are conversions of USEPA’s

tap-water mortality and morbidity risk coefficients and

USEPA’s assumptions for lifetime intake (2 liters of water

per day, 365 days per year, for a lifetime of 70 years, equivalent to a total of 51,100 L of water consumed over a lifetime). The unit concentration risk is defined by USEPA

(1999a) as:

UCRF/T = RCF/T * 0.037 * 51,100

where

UCR is the unit concentration risk (pCi/L)-1 for 70-year

 lifetime for fatal (UCRF

) or total (UCRT) cancer cases

RC is the radionuclide-specific tap water risk coefficient

 in SI units (units of risk per becquerel; Bq-1) for fatal

 (RCF) and total (RCT),

F/T is fatal (mortality) or total (morbidity),

0.037 is a conversion factor (for converting Bq-1 to pCi-1), and

51,100 is the assumed lifetime intake of drinking water (L).

 For example, the fatal UCRF for Ra-226, given

RCF = 7.17E-09 Bq-1 (USEPA, 1999a) is found by converting

to the desired units and using USEPA’s assumption of lifetime intake: 7.17E-09 x 0.037 x 51,100 = 1.36E-05 or about

14 fatalities per million (table 7). The fatal RCF for Ra-224

and Ra-228 are 2.74E-09 Bq-1 and 2.00E-08 Bq-1, respectively (USEPA, 1999a). The total RCT for Ra-224, Ra-226,

and Ra-228 are 4.50E-09 Bq-1, 1.04E-08 Bq-1, and

2.81E-08 Bq-1, respectively.

The second set of values (columns 4 and 5) in table 7

are the estimated excess fatal and total cancer cases per million persons assuming lifetime intake of each radionuclide

alone at its current associated maximum contaminant level.

The risks associated with the current MCLs are:

MCLRF/T = UCR F/T * MCL

where

MCLR is the lifetime excess risk at the MCL for fatal

 (MCLRF) or total (MCLRT) cancer cases, and

MCL is the current maximum contaminant level

 (pCi/L).

For example, given the UCRF

 of 14 (per 106) for Ra-226 and an

MCL of 5 pCi/L, the MCLRF

 for Ra-226 is 70 fatalities per

million people.

In this way, the unit concentration risk (USEPA, 1999a)

of any of the three radium isotopes listed in table 7 can be

used to provide some preliminary perspective on the humanhealth risk associated with consuming 2 L of drinking water

every day for a lifetime within the ranges of concentration of

radium found in the USGS reconnaissance survey (tables 4

and 5). Each raw-water sample was collected near the wellhead from only one well in each targeted public water-supply

system, and each well was sampled only once. Consequently,

variability in concentrations of radionuclides due to longterm and seasonal changes over time and other factors are

not determined, and an individual sample is representative of

the water quality of the local ground-water-flow system contributing water to the targeted well for the time at which it

was sampled. The data presented in this report, therefore,

may not be appropriate for estimates of “reasonable maximum exposure” used in risk assessments. This discussion is

intended only to provide perspective beyond the presentation

of concentration values so that the associated human-health

risk of drinking water with the concentrations of radium

found in the USGS reconnaissance survey can more easily be

understood.

The cancer-risk estimates (table 7) may be interpreted

in two ways: either as the age-averaged, lifetime excess

probability of cancer induction within a population of individuals of all ages and genders, or as the individual lifetime

excess probability of cancer induction for an average or representative member of a given population (N. Nelson and L.

Ralston, U.S. Environmental Protection Agency, Office of

Radiation and Indoor Air, written commun., 1999). For example, the value of 100 total cancers per million persons, estimated for the lifetime intake of Ra-226 at its current MCL,

can also be interpreted as an individual risk of 1 in 10,000

(that is, 100 per 106

 = 1 per 104). Federal Guidance Report

No. 13 (USEPA, 1999a) details uncertainties, assumptions,

and limitations associated with the cancer-risk estimates.

Interpretations of Polonium-210 and Lead-210 Data

Polonium-210 and Pb-210 are derived from the U-238

decay series; the same decay series that produces Ra-226.

Because the USGS reconnaissance survey was primarily designed to assess the distribution of Ra-224, some areas in the

United States that contain high uranium concentrations in

aquifer materials without accompanying high thorium concentrations are likely not represented or are under-represented by the sampling. Such regions may include areas of

phosphate rock from Florida or the western United States, or

uraniferous sandstones from the Colorado Plateau region.

The presence of high concentrations of Po-210 or Pb-210 in

ground waters is possible even in the absence of the presence

of high concentrations of Ra-224. Results for the dissolved

concentration distributions of these radionuclides are possibly biased low, as opposed to the concentration distributions

of Ra-224 that are likely biased high. Within these constraints, nevertheless, the Po-210 and Pb-210 concentration

data collected as part of the reconnaissance survey can be

used to begin to fill the gap in information on the occurrence

of these isotopes. These isotopes (Po-210, Pb-210) have recently been proposed for inclusion on the list of contaminants under the Unregulated Contaminant Monitoring Rule

(U.S. Environmental Protection Agency, 1999c).

Polonium-210 was found in concentrations exceeding

1 pCi/L in only two wells. The two observations could not be

associated with unique geochemical environments as was the

case in a previous study from Florida (Harada and others,

1989). With only two results greater than 1 pCi/L, further investigations would be necessary to infer anything more about

the national distribution and occurrence of Po-210.

Ten percent of the samples exceeded a Pb-210 concentration of 1 pCi/L; only one sample, however, contained a

concentration greater than 3 pCi/L. The greatest frequency of

detection was in the Appalachian Physiographic Province of
19

the northeastern United States, especially in the States of

Connecticut and Pennsylvania. The geochemical mechanism

that controls Pb-210 dissolution is not established and needs

further study. It is known that lead is more difficult to extract

from sediment material than radium, and adsorbs more

quickly onto aquifer solids (Krishnaswami and others, 1982).

One possible explanation for the frequent detection of Pb210 in concentrations greater than 1 pCi/L in the Appalachian region may be the high concentrations of radon-222 in

ground water in this region (Zapecza and Szabo, 1987). As

the radon in solution decays through a series of very short

half-lived products to Pb-210, a small fraction of the Pb-210

may not be immediately sorbed onto the aquifer matrix, or

may be only weakly sorbed, or may be re-ejected to the water

through alpha recoil after weak adsorption of the radioactive

parent product, Po-214. If the latter is true, the higher the initial Rn-222 concentration, the more likely it is that measurable amounts of Pb-210 are detected in the ground water. Regions where Pb-210 concentrations need to be characterized

could be identified by elevated Rn-222 and U-238 concentrations in ground water. This hypothesis could not be tested in

this initial USGS reconnaissance survey, however, because

the Rn-222 concentrations were not analyzed.

IMPLICATIONS FOR COMPLIANCE MONITORING

The occurrence of the various radionuclides and the ratios of the three radium isotopes analyzed in the USGS reconnaissance survey indicate that conventional compliance monitoring for gross alpha-particle activities and combined radium

may be inadequate in some parts of the United States. This

section first describes the commonly used compliance monitoring procedures and then shows their limitations in light of the

results of the USGS reconnaissance survey.

Compliance Monitoring Procedures for Regulated

Radionuclides Used by Public Water-Supply Systems

and Results of Previous Studies

Lappenbusch and Cothern (1985) discuss the regulations

for radioactivity in drinking water at that time and present a

flow chart for compliance monitoring (fig. 10) that is still in

conventional use today. The amount of alpha-particle emitting

radionuclides are initially determined by analyses of the gross

alpha-particle activity of a given water sample. Depending on

the gross alpha-particle activity, subsequent analyses may be

required. The gross alpha-particle activity screen is viewed as a

cost-effective way to determine when additional analyses

could be required to quantify the most important alpha-particle

Measure Gross

Alpha-Particle Activity

Is Alpha-Particle Activity

>5 pCi/L?

Is Ra-226 + Ra-228

>5 pCi/L?

Is Ra-226

>3 pCi/L?

Measure Ra-226

Measure Ra-228

Noncompliance

Compliance

Is Alpha-Particle Activity

>15 pCi/L?

Is Gross Alpha-Particle Activity

Minus

Activity due to Radon and Uranium

>15 pCi/L?

Measure Radon

and Uranium

NO

NO

NO

NO

NO

YES

YES YES

YES

YES

Figure 10. Schematic diagram showing the compliance monitoring scheme for radionuclides in publicdrinking-water supplies. Shaded boxes emphasize where this, and other, studies have shown potential for

errors in combined radium and short-term gross alpha-particle compliane monitoring. [Modified from

Lappenbusch and Cothern (1985).]
20

emitting radionuclides in a public water-supply system. A

combined radium (Ra-226 and Ra-228) standard was associated with this process to avoid the additional costs involved

with separate Ra-228 analyses for many public water-supply

systems. By use of the gross-alpha particle screening process, a gross alpha-particle activity that does not exceed 5

pCi/L is taken to imply a combined radium concentration

that does not exceed 5 pCi/L; similarly, a Ra-226 concentration that does not exceed 3 pCi/L is taken to imply that the

Ra-228 concentration does not exceed 2 pCi/L (Blanchard

and others, 1985). Hess and others (1985) explain that this

scheme, in the absence of actual data, was based on the assumption that Ra-226 was the dominant radioactive component of drinking water and that the Ra-226: Ra-228 ratio was

3:2 or greater.

Data collected from State surveys conducted by the

USGS, State Regulators, and university research staff

showed a range in the Ra-226: Ra-228 ratio of more than 14

to less than 0.07 (King and others, 1982; Hess and others,

1985; Szabo, 1990; Senior and Vogel, 1995; Kay, 1999). A

high degree of correlation between Ra-228 and Ra-226 concentration was not consistently found in most samples, nor

were there specific trends in the distribution or ratios of concentrations of these two isotopes by either aquifer, depth, or

extent of aquifer when examining large-scale regional or national-scale concentration data (Hess and others, 1985).

Blanchard and others (1985) concluded that although the

schedule to screen for gross alpha-particle activity has been

useful in identifying many initial problem areas, screening

has limitations. For example, the screening would miss situations when the gross alpha-particle activity is less than 5

pCi/L, Ra-226 is less than 3 pCi/L, and Ra-228 concentrations are greater than 2 pCi/L; in these instances the presence of elevated concentrations of Ra-228 would go unrecognized. Consequently, where the ratio of Ra-226: Ra-228 is

less than 3:2, the gross alpha-particle activity determination

is not suitable for combined radium compliance monitoring.

Blanchard and others (1985), even with the limited

amount of information available, note that occasionally Th232, Po-210, or Ra-224 contribute to the alpha-particle activity. The short-lived Ra-224 requires measurements for

gross-alpha particle activity to be made within the short time

frame before it decays (Parsa, 1998; Szabo and others,

1998a). Regulatory guidelines do not, however, exist to address the limited time required for gross-alpha-particle

analyses. Therefore, gross-alpha-particle activity data collected to date for national data bases could be biased low if

analyses were not completed before short-lived isotopes decay. Consequently, more public water-supply systems may

be out of compliance with the gross alpha-particle activity

MCL, and potentially the radium MCL, than has been realized. Szabo and others (1998a) showed that alpha-particle

radioactivity in drinking-water supplies from the KirkwoodCohansey aquifer system in New Jersey was larger than previously determined in all 12 community water supplies that

were re-evaluated with strict adherence to the 48-hour holding time for analysis. The gross alpha-particle activity MCL

of 15 pCi/L was exceeded in all 12 community water supplies when analyzed within 48 hours of collection, whereas

for 10 of these wells that were previously sampled for gross

alpha-particle activity but analysis was completed at a random time frame after sampling, only 1 was out of compliance. Parsa (1998) outlined the potential effects that shortlived radionuclides such as Ra-224 may have on the

monitoring schemes for radionuclides proposed within the

Safe Drinking Water Act.

Limitations in the Current Monitoring Procedures for

Alpha-Particle Emitting Radionuclides and the

Combined Radium Standard

The effectiveness of the national drinking water MCL

for gross alpha-particle activity and use of this result as a

compliance-monitoring screen for combined radium have

been shown to be dependent on the holding time between

collection and analysis (Parsa, 1998; Szabo and others,

1998a), and the ratios of Ra-226:Ra-228 and Ra-224:Ra 226.

The gross alpha-particle activity must be analyzed within

about 48-to-72 hours in order to account for the presence of

the short-lived alpha-particle-emitting isotopes such as Ra224. A concurrent study of ground-water supplies by the

USGS in cooperation with the State of New Jersey (Szabo

and others, 2000) is providing more insight into the role of

the distribution of Ra-224 and progeny in determining the

distribution of dissolved gross alpha-particle activities. In

that study in New Jersey, gross alpha-particle emissions were

measured before decay of Ra-224 and after sufficient time

had elapsed for nearly complete decay (about 20-to-22 days).

The difference between the initial gross-alpha measurement

and the final measurement is indicative of the contribution of

Ra-224 and all other alpha-particle emitting isotopes that

would decay within this time frame. The results indicate that

the contribution of Ra-224 and short-lived products is consistent with the theoretical prediction of Parsa (1998) and is

approximately three times the concentration of Ra-224. Although this analysis was developed with a small data set in a

restricted geographic range, it is based on a physical process.

Thus, the result has important implications for USEPA or

other regulatory agencies to allow them to project Ra-224

occurrence in association with gross alpha-particle activities

and Ra-228 concentrations that are already determined for

many public water-supply systems nationwide. The results

from New Jersey, allowing for at least an initial estimate of

the Ra-224 concentration, are also important in light of both

the costliness and difficulty in scheduling the Ra-224 analysis. The results also make clear that in regions where radium

is present in ground water, gross alpha-particle activity determined more than 72 hours after sample collection can significantly under represent the actual gross alpha-particle activity of the water.

The gross alpha-particle activity screen, when used to

determine compliance with the combined radium (Ra-226 +

Ra-228) standard of 5 pCi/L, could produce false negative

results for Ra-228. The concentration of Ra-228 is greater

than that of Ra-226 in many samples analyzed in this study
21

over the entire range of concentrations of both radium isotopes (fig. 3). The gross alpha-particle activity screen currently in place for combined radium compliance (Hess and

others, 1985) relies on Ra-226 concentrations being present

in higher concentrations than Ra-228. About 6 percent of the

USGS reconnaissance samples contained combined radium

concentrations (Ra-226 + Ra-228) greater than 5 pCi/L when

Ra-226 was less than 3 pCi/L (fig. 11); these samples would

not have been tested for Ra-228 if current traditional compliance monitoring were used (fig. 10).

CONCLUSIONS

The USGS reconnaissance survey targeted ground-water supplies of known, or suspected, high concentrations of

radium to determine the concentrations of Ra-224 where

other isotopes of radium had previously been detected and to

determine the co-occurrence characteristics of the three radium isotopes (Ra-224, Ra-226, and Ra-228). About 30, 33,

and 26 percent of the samples collected were reported above

1 pCi/L (the contractual minimum detectable concentration)

in concentration for Ra-224, Ra-226, and Ra-228, respectively, in the USGS radionuclide reconnaissance survey.

About 5 percent of the samples exceeded 10 pCi/L of Ra-224.

Several of the samples from the eastern United States

(Coastal Plain Physiographic Province) were reported to have

pH less than 4.0 and contained detectable concentrations of

thorium isotopes, including Th-228, indicating that the analytical result for Ra-224 may be biased high in these areas.

Twenty one of the samples exceeded the MCL for combined

radium. Six percent of the samples contained combined radium concentrations (Ra-226 and Ra-228) greater than 5 pCi/

L when Ra-226 was less than 3 pCi/L (the ratio of Ra226:Ra-228 was less than 3:2). Concentrations of Pb-210

were greater than 1 pCi/L in about 10 percent of the samples

analyzed; for Po-210, about 3 percent exceeded 1 pCi/L.

Although the number of data points in the USGS reconnaissance survey was limited, it provides new insight into the

nationwide occurrence of Ra-224 and the co-occurrence with

Ra-226 and Ra-228. The presence of Ra-224 has an effect on

compliance with the present drinking-water MCLs for gross

alpha-particle emissions and the associated procedures for

compliance monitoring for an unquantified number of community drinking water systems across the Nation. Conventional monitoring procedures, which do not require analysis

of gross-alpha-particle activities in time to account for the

contribution of short-lived isotopes such as Ra-224, could

lead to false indications of compliance. The documented correlation in occurrence and the small variation in the isotopic

ratio of Ra-224 and Ra-228 in this study which encompasses

several physiographic provinces, indicates that the more frequently monitored Ra-228 is a reasonable proxy to indicate

the potential for Ra-224 occurrence. The isotopic ratios of

Ra-226 to Ra-228 were below 3:2 in many samples, corroborating previous studies that indicated that the gross-alphaparticle screen commonly used as a first step to determine

combined radium (Ra-226 + Ra-228) compliance could be

inadequate in some unquantified number of community water systems. Finally, concentrations of Pb-210 and Po-210

were detectable in a small number of well-water samples, although uranium-rich strata were not targeted in the survey.

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24

GLOSSARY

Activity: The amount of radioactivity in a given volume of

such material as water or air. For water, activity is generally

expressed in units of picocuries per liter.

Alpha radiation: Alpha radiation is composed of a particle,

consisting of two protons and two neutrons, spontaneously

emitted from the nucleus of a subset of radioactive elements

(mostly the heaviest elements) during radioactive decay. Alpha radiation is ionizing radiation, meaning that it strips electrons from adjacent atoms as it passes. Alpha radiation cannot penetrate skin; thus, an alpha-particle emitting

radionuclide must be ingested in order to come into contact

with internal tissue. Because of the large size, alpha particles

are likely to collide with cell tissue, causing tissue damage.

An accumulation of tissue damage in the cell nucleus may

lead to cell mutation and potential cancer formation.

Alpha radioactivity, gross: A laboratory measurement of total alpha radioactivity emitted by a sample. This measurement includes radioactivity emitted by Ra-226, Ra-224, Ra223, Po-210, and numerous other naturally occurring

alpha-particle-emitting radioactive isotopes. SHORT-TERM

measurement, conducted within 3 days after sample collection, provides information with regard to the amount of alpha

radiation present from unsupported, short-lived radionuclides, such as Ra-224. LONG-TERM measurement, usually

conducted 20- to-30 days after sample collection, measures

only the amount of alpha radiation present from long-lived

radionuclides, such as Ra-226 (half-life, 1,602 years).

Alpha spectrometry: An analytical technique that specifies

the amount of alpha radiation emitted at specified energy

levels, thus allowing determination of individual radionuclide concentrations (from known energy levels of alpha particles unique to each radionuclide). The gridded-pulse-ionization chamber is the most sensitive and most commonly

used instrument.

Beta radioactivity: Beta radiation is composed of a particle,

consisting of an electron, spontaneously emitted from the

nucleus of a subset of radioactive elements during radioactive decay. Beta radiation, like alpha radiation, is ionizing radiation—it strips electrons from adjacent atoms as it passes.

Beta radiation can only penetrate the surface layer of skin;

thus, a beta-particle emitting radionuclide must be ingested

in order to come into contact with internal organs or tissues.

An accumulation of tissue damage in the cell nucleus may

lead to cell mutation and potential cancer formation.

Beta radioactivity, gross: A laboratory measurement of total

beta radioactivity emitted by a sample. This measurement includes radioactivity emitted by Ra-228 and Pb-210, and numerous other naturally occurring beta-particle-emitting radioactive isotopes. As with gross alpha-particle

measurements, both SHORT-TERM and LONG-TERM measurement are possible, providing information regarding the

amount of beta radiation present from unsupported shortlived radionuclides and from long-lived radionuclides, such

as Ra-228 (half-life, 5.75 yrs).

Beta radioactivity count: An analytical technique that

specifies total beta radioactivity emitted by a chemically purified sample that contains only one radionuclide of interest.

The beta-particle activity is counted in a low-background gas

proportional counter. Because detection efficiency is highest

for beta particles emitted with the highest energy, the betaparticle activity of a short-lived product of the radionuclide

of interest is typically determined. Thus, the concentrations

of Ra-228 and Pb-210 are determined by counting the products Ac-228 (actinium-228) and Bi-210 (bismuth-210), respectively.

Contaminant: As defined in the Safe Drinking Water Act,

any physical, chemical, biological, or radiological substance

or matter in water.

Decay product of radiation: The isotope remaining after a

radioactive decay event.

Gamma radioactivity: Gamma radiation is composed of a

packet of energy, also known as a photon or photon particle,

spontaneously emitted from the nucleus of most radioactive

elements during radioactive decay. Gamma radiation is ionizing radiation, meaning that it strips electrons from adjacent

atoms as it passes. Gamma radiation can penetrate through

skin into internal tissues as opposed to alpha and beta radiation, which cannot. An accumulation of tissue damage in the

cell nucleus from gamma radiation may lead to cell mutation

and potential cancer formation.

Gamma spectrometry: An analytical technique that specifies the amount of gamma radiation emitted at specified energy levels, thus allowing determination of individual radionuclide concentrations (from known energy levels of emitted

gamma radiation unique to each radionuclide). A high-efficiency hyper-pure germanium or germanium-lithium detector is typically used for laboratory work requiring low

MRLs; the latter was used in the USGS Ra-224

Reconaissance Survey.

Isotope: Various forms of a single element differing in the

number of neutrons in the nucleus. Unstable isotopes of an

element decay through the emission of a form of radioactivity.

Maximum contaminant level (MCL): The maximum permissible level of a contaminant in water that is delivered to

the free-flowing outlet of the ultimate user of a public watersupply system (except in the case of turbidity). The MCL for

Ra-226, Ra-228, and gross alpha-particle activity in community water systems is:

(a) Combined Ra-226 and Ra-228: 5 pCi/L;

(b) Gross alpha-particle activity (including Ra-226 but excluding radon and uranium): 15 pCi/L.

Minimum detectable concentration or activity (MDC):

The minimum quantity of a specific radionuclide detected by

the counting instrument for any sample for a given analysis.

It is defined by the requirement that the counted radioactivity

must differ from the background count by three times the

standard deviation of the background count. This value is

computed individually for each radionuclide analysis based
25

on instrument operating conditions at the time. A contractual

minimum detectable concentration (ASTM, 1999) is contractually determined with the laboratory before the project begins and is generally based on the scope of the project and

available resources. The contractual (also called the a priori)

MDC was targeted for 1 pCi/L for all radionuclides analyzed

in this study. For purposes of this paper, the sample-specific

(also called a posteriori) MDC will be referred to simply as

the MDC unless otherwise noted. This value is computed individually for each radionuclide analysis based on instrument

operating conditions at the time of measurement and reported

by the laboratory for each analysis.

National contaminant occurrence database (NCOD): The

Safe Drinking Water Act as amended in 1996 requires

USEPA to develop and maintain a national data base that

could be used for regulatory determinations by the Administrator. The first release of the NCOD was in August 1999.

The NCOD contains ambient water-quality data obtained by

a retrieval from the USGS National Water Information System and data from USEPA’s Safe Drinking Water Information System (including compliance data and data collected in

anticipation of the Unregulated Contaminant Monitoring

Rule). The radionuclide data collected for the USGS Radionuclide Reconnaissance Survey will likely reside in the

NCOD. Public access to NCOD is provided by USEPA

through the website: www.epa.gov

Notice of data availablity (NODA): One of the outlets used

by USEPA for public comment and interaction is through a

NODA. The NODA for radionclides that USEPA plans to issue will contain all of the existing information that USEPA

has on occurrence, health effects, treatment technology, and

other pertinent information, including results from the USGS

study reported here.

Negative result: A result from a radiation measurement

(count) of a sample over a fixed interval of time where the

measured radioactivity from the sample is less than the longterm average background radiation reported routinely by the

instrument.

Picocurie per liter: The unit expressing the amount of radioactivity in water. One picocurie per liter equals 2.2 radioactive disintegrations per minute per liter of water.

Radionuclide: An isotope of an element that emits radiation.

Uncertainty: A calculated measure of uncertainty of the

laboratory analysis. Because radioactive elements decay randomly at any given instant of time, any measurement of radioactivity has an associated uncertainty (also called “counting error”) independent of, and in addition to, laboratory

sources of analytical uncertainty. Uncertainty can be reported

in a variety of ways; the most common include (1) the sum

of the laboratory and counting uncertainty, known as “combined standard uncertainty (CSU)” (or the “total propagated

uncertainty”), and (2) a counting uncertainty only. There is a

67-percent or 95-percent probability (based on one or two

standard deviations, respectively) that the true value of the

radionuclide concentration is within the measured value plus

or minus the uncertainty. The uncertainty terms are generally

smaller than the measured value except when the measured

values are low concentrations (near the MDC). The uncertainties associated with the various radionuclides in this report are (excluding EPA quality control lab):

• One standard deviation of the CSU: Ra-224 and Ra-226 by

alpha spectrometry

• Two standard deviation of the CSU: Ra-228 and Pb-210 by

beta counting, Po-210 by alpha spectrometry

• One standard deviation of the CSU: Ra-224, Ra-226, and

Ra-228 by gamma spectrometry

Unit concentration risk: Expression of the health risk of developing or dying from cancer per unit concentration of a

harmful substance entering the body (exposure). The current

estimate listed in USEPA (Federal Guidance Report No. 13)

is that 1 picocurie per liter of Ra-226 is associated with an

excess fatal cancer rate of 14 people per million if ingested at

a rate of 2 liters per day over a 70-year lifetime. The excess

fatal cancers from consuming a unit concentration of Ra-224

is approximately 5 people per million, whereas it is 38

people per million from Ra-228.
26
27

APPENDIX
28

. 44322 1 AK 2 68.85 147.84 2 3 45 85 45000

. 44323 2 AK . 68.85 147.84 2 3 . 

. 44320 2 AK . 68.85 147.85 2 3 16 97 10000

. 44321 1 AK 1 68.85 147.85 2 3 .

.

.

.

.

. 

. 43372 0 AR 3 36.30 91.52 4 5 26 4200

5914D 45344 0 AZ 4 33.52 111.90 2 1 26 1430 10000

5910Z-1 45345 1 CA 5 34.06 118.08 2 1 75 378 40000

5910Z-2 . 2 CA . 34.06 118.08 2 1 . 

6040F 45429 0 CA 6 36.59 121.88 2 1 10 481 110000

. 44087 1 CA 7 33.94 117.39 2 1 53 415 245000

. 44088 2 CA . 33.94 117.39 2 1 .

.

.

.

.

. 44179 0 CA 8 34.10 117.29 2 1 27 1104 55000

. 44319 0 CO 9 40.63 103.22 5 1 14 82 11000

. 44328 0 CO 10 40.26 103.62 4 1 6 128 5000

. 99904 0 CT 11 41.18 73.19 3 3 33 60 14400

5796R 45219 0 CT 12 41.00 73.67 3 3 15 52 2340

. 99909 0 CT 13 41.69 73.23 3 4 . 560 150

. 99906 0 CT 14 41.46 72.15 3 4 . 106 5

. 99907 0 CT 15 41.46 72.15 3 4 . 190 5

5798U 45222 0 CT 16 41.32 71.90 3 4 8 750 100

. 43553 0 FL 17 27.90 82.78 1 5 38 314 400000

. 43468 0 FL 18 28.04 81.96 2 5 16 210 151322

. 99908 0 FL 19 27.33 82.54 1 5 5 600 65000

5621T 45066 0 GA 20 32.44 81.77 1 5 22 384 24000

. 45426 2 GA . 33.10 81.99 1 1 . 5700

6038M 45425 1 GA 21 33.10 81.99 1 1 . 

5620R 45065 0 GA 22 31.49 82.84 1 5 6 705 3000

5659H 45085 0 GA 23 31.60 81.88 1 5 9 890 9000

. 45083 2 GA . 34.77 84.93 3 5 . 21761

5661B 45084 1 GA 24 34.77 84.93 3 5 . .

.

. .

.

.

. 43473 0 IA 25 43.26 91.47 4 2 83 890 4020

. 47128 1 IA 26 41.82 90.63 4 3 4 260 620

. 47129 2 IA . 41.82 90.63 4 3 . 

. 44325 0 IA 27 40.91 91.39 4 2 38 1850 1900

. 43368 0 IA 28 41.14 91.65 4 2 8 1910 900

. 43475 0 IA 29 42.07 90.83 4 5 15 190 137

. 43407 0 IA 30 42.25 90.43 4 2 51 1500 2400

. 43831 1 IA 31 43.32 91.79 4 3 20 70 8063

. 99913 2 IA . 43.32 91.79 4 3 . . 

. 43951 1 IL 32 41.75 88.29 4 2 40 1719 117000

. 43968 2 IL . 41.75 88.29 4 2 . .

. 44181 2 IL . 41.84 88.30 4 2 20 1400 6000

. 44182 1 IL 33 41.84 88.30 4 2 . 

. 43845 2 IL 34 41.71 88.33 4 2 41 1340 4600

. 43846 1 IL . 41.71 88.33 4 2 .

. .

. .

.

. 44329 1 IL 35 41.84 89.48 4 5 41 1700 6000

. 44330 2 IL . 41.84 89.48 4 5 .

6036K 99914 0 IL 36 40.75 89.60 4 3 59 120 113504

. 44316 0 IL 37 41.76 89.69 4 3 8 130 9700

5671D 45125 0 IN 38 39.74 86.77 4 3 5 134 700

. 44324 0 KS 39 37.97 100.86 5 1 33 377 30000

. 44967 2 KS 40 37.04 100.93 5 1 2 600 16500

5477D 44968 1 KS . 37.04 100.93 5 1 .

. 45424 2 MD . 38.99 76.56 1 1 . . 450

6025G 45423 1 MD 41 38.99 76.56 1 1 . .

.

. .

.

.

.

.

. 

. 45422 2 MD . 38.99 76.56 1 1 1 100 5

6026H 45421 1 MD 42 38.99 76.56 1 1 .

. 99905 0 MD 43 39.15 76.61 1 1 51 115 42000

5911A 45343 0 MD 44 39.53 76.35 3 4 3 500 2000

6299H 45648 0 MI 45 47.24 88.45 4 3 31 100 9228

. 43409 0 MI 46 42.73 84.47 4 . . . 51000

. 43369 0 MI 47 42.70 84.55 4 2 28 330 100000

. 43408 0 MI 48 42.46 84.17 4 . . . 1200

. 43544 0 MN 49 45.08 93.25 4 2 38 840 29000

5547A 99911 1 MN 50 44.45 95.78 4 3 . . 12000

5547A . 2 MN . 44.45 95.78 4 3 . . . 

. 43370 0 MN 51 43.62 95.60 4 3 10 106 10000

Maximum

population

served

Region Geology Well age

(years) 

Well 

depth

(feet) 

State Map

key

Latitude

(Degrees

North) 

Longitude

(Degrees

West) 

EPA

serial

number 

USGS

serial

number 

Duplicate

. 44177 1 MN 52 46.01 92.89 4 2 1 390 1200
29

. 44178 2 MN . 46.01 92.89 4 2 

. 99912 2 MN .

.

.

.

.

.

46.01 92.89 4 2 .

 . 

 

. 99910 0 MN 53 44.45 93.16 4 2 21 388 10500

6160N 45603 0 MO 54 39.16 91.87 4 5 14 1500 14000

. 43949 2 MO . 37.55 94.51 4 5 25 825 690

. 43950 1 MO 55 37.55 94.51 4 5 . . 

. 43833 0 MO 56 37.71 91.12 4 5 20 680 748

. 43546 0 MO 57 37.16 94.31 4 2 7 1500 11000

. 43552 0 MO 58 37.14 94.47 4 5 86 1015 1875

6037L 45428 0 MO 59 38.76 93.72 4 2 . . 7500

. 43824 0 MO 60 36.96 93.72 4 5 10 1300 6500

. 43467 0 MO 61 37.60 93.41 4 5 46 1055 8370

. 47127 0 MO 62 37.92 90.54 4 5 10 700 4000

. 43472 0 MO 63 37.84 94.35 4 5 14 1200 10000

. 99903 0 NC 64 35.17 78.98 1 1 18 90 8000

. 44084 0 NE 65 42.11 102.88 5 1 4 405 9800

. 44180 0 NE 66 42.67 103.40 5 1 2 102 1200

. 44085 2 NE . 42.82 103.00 5 1 29 265 6000

. 44086 1 NE 67 42.82 103.00 5 1 . . . 

5662C-1 45087 1 NJ 68 39.44 75.22 1 1 33 120 18000

5662C-2 45088 2 NJ . 39.44 75.22 1 1 . . . 

5660A-1 45089 1 NJ 69 39.48 75.00 1 1 65 158 32000

5660A-2 45090 2 NJ . 39.48 75.00 1 1 . . 

. 46849 1 NJ 70 40.34 74.44 1 1 45 120 5605

. 46850 2 NJ . 40.34 74.44 1 1 . . 

. 43554 0 NJ 71 39.92 74.20 1 1 2 280 8000

. 43622 2 NJ . 39.81 74.24 1 1 9 248 1950

. 43623 1 NJ 72 39.81 74.24 1 1 . . . 

5800U 45224 0 NJ 73 40.71 75.03 3 2 . . 4977

5797T 45223 0 NJ 74 40.71 74.36 3 2 . . 19757

5924F-1 45352 1 NM 75 34.41 103.22 5 1 60 368 30000

5924F-2 . 2 NM . 34.41 103.22 5 1 . . . 

5478E-1 44966 1 OK 76 36.69 101.47 5 1 33 360 7800

5478E-2 . 2 OK . 36.69 101.47 5 1 . . . 

. 43832 0 PA 77 40.20 75.09 3 2 . . 35000

. 44176 0 PA 78 41.05 76.24 3 5 39 87 16000

. 44239 0 PA 79 40.78 76.23 3 2 . . 4700

5479F-A 44969 1 SC 80 33.32 81.43 1 1 . . 0

5479F-B 44970 2 SC . 33.32 81.43 1 1 . . 

5490A-A 44971 2 SC . 33.32 81.43 1 1 . . 0

5490A-B 44972 2 SC . 33.32 81.43 1 1 . . 

5799V 45220 1 SC 81 33.12 81.31 1 1 . . 0

. 45221 2 SC . 33.12 81.31 1 1 . . 

. 99902 0 SC 82 33.73 81.10 1 1 . . 500

5517U 45002 0 SC 83 34.28 81.61 3 4 25 110 600

. 45052 2 SC . 34.21 81.53 3 4 21 465 600

5546Z 45051 1 SC 84 34.21 81.53 3 4 . . . 

. 43948 1 SD 85 43.43 103.48 5 1 47 26 1800

5663D 45086 2 SD . 43.43 103.48 5 1 . 21 2500

. 44175 0 SD 86 43.37 99.85 5 1 17 230 5000

. 99901 0 TX 87 29.70 95.46 2 1 29 1630 2209174

5912B 45348 1 TX 88 29.78 95.18 1 1 17 1020 3500

. 45349 2 TX . 29.78 95.18 1 1 . . . 

5913C 45351 1 TX 89 29.78 95.18 1 1 24 1242 2850

. 45350 2 TX . 29.78 95.18 1 1 . . . 

. 43411 2 TX . 30.74 99.22 5 1 27 437 2043

. 44080 1 TX 90 30.74 99.22 5 1 . . 2043

. 44078 0 TX 91 30.74 99.22 5 1 15 340 2043

. 43428 2 TX 92 30.74 99.22 5 1 . . 2000

. 44079 1 TX . 30.74 99.22 5 1 2 355 2043

. 43477 1 TX 93 31.16 98.73 5 5 3 120 2626

. 43493 2 TX . 31.16 98.73 5 5 . . . 

. 43969 0 VA 94 37.77 77.32 1 1 5 487 400

. 43914 1 VA 95 36.93 77.44 1 1 10 88 100

. 43915 2 VA . 36.93 77.44 1 1 . . . 

. 43410 0 WI 96 43.94 88.09 4 5 75 981 3500

. 43371 0 WI 97 43.48 89.74 4 2 37 387 11000

. 43545 0 WI 98 43.29 89.74 4 2 . . 2380 . 43474 0 WI 99 43.26 89.74 4 2 7 565 1430

Maximum

population

served

Region Geology Well age

(years) 

Well 

depth

(feet) 

State Map

key

Latitude

(Degrees

North) 

Longitude

(Degrees

West) 

EPA

serial

number 

USGS

serial

number 

Duplicate
30

44322 2 -1.20E-02 1.40E-01 2.50E-01

44323

. . . ... ... . . . . ... ...

. . . . ... ... . . . ... ...

. . . ... ...

...

... .. . . . . . . . . . ... ... ... . . . . ... ... . . . ... ...

. . . ... ...

. . . ... ... . . . ... ... . . . .. . . . ... ...

. . . ... ...

. . . ... ... . . . ..

. . . ... ...

. . . ... ... . . . ... ... ... . . . . ... ...

...

. . . .. . . . . ... ... . . . ..

. . . ... ...

2.10E-01 9.50E-02 . ... ... . . . . ... ... . . . ... ...

. . . ... ...

. . . ... ...

. . . ... ...

. . . ... ... . . . . . . . ... ... ... ... . ... ...

. . . . ... ... ... ... . . . ... ... . ... ... ... ... . . . . ... ... . . . . . . .. . . . ... ...

...

. . . ... ...

. . . ... ... . ...

. ... ...

. ... ...

. . . ... ... ...

. . . ..

. . . ... ...

. . . ... ...

. . . ... ...

. . . ... ... ... .. . . . . . . . . . . . . ... ...

.72E-01 1.50E-01 2.40E-01

44320 -2.00E-01 2.80E-01 5.10E-01

44321 1 3.20E-02 1.86E-01 3.20E-01

43372 3 3.64E-02 1.30E-01 2.30E-01

45344 4 3.30E-01 3.20E-01 4.90E-01 2.05E-01 1.50E-01 3.20E-02 4.10E-01 5.50E-01 2.80E-01

45345 5 2.00E-03 1.78E-01 3.20E-01 1.70E-01 1.70E-01 4.30E-02 3.93E-01 6.10E-01 3.00E-01

6.90E-02 9.80E-02 2.80E-02

45429 6 9.30E-01 3.20E-01 3.50E-01 1.67E-01 1.30E-01 3.20E-02 8.81E-01 7.10E-01 3.00E-01

44087 7 1.90E-01 2.20E-01 3.70E-01 3.80E-01 8.00E-02 .

44088 3.34E-01 1.86E-01 2.60E-01

44179 8 1.50E-01 2.40E-01 3.90E-01

44319 9 2.80E+00 2.00E+00 3.10E+00

44328 10 4.84E-01 1.94E-01 2.40E-01

99904 11 8.00E-02 1.60E-01

45219 12 2.00E-02 2.00E-01 3.70E-01 1.52E-01 1.50E-01 3.90E-02 1.10E+00

99909 13 1.44E+00 1.50E-01

99906 14 -1.60E-01 1.90E-01

99907 15 -7.00E-02 7.00E-02

45222 16 1.23E-01 1.94E-01 3.20E-01 8.60E-02 1.30E-01 3.70E-02 9.20E-01

43553 17 1.50E-01 5.00E-01 8.40E-01

43468 18 -5.55E-02 2.80E-01 5.10E-01

99908 19 4.60E-01 1.20E-01

45066 20 2.70E-01 4.00E-01 6.70E-01 -5.36E-03 7.60E-02 3.10E-02 5.00E-01 5.80E-01 3.00E-01

45426 .53E-01 1.88E-01 2.50E-01

45425 21 4.70E-01 2.60E-01 3.20E-01 6.60E-01 1.10E-01 3.95E-01 1.70E-01 2.60E-02 8.18E-01 6.50E-01 3.50E-01

45065 22 2.90E-01 2.20E-01 3.10E-01 3.38E-01 1.80E-01 3.30E-02 5.67E-01 6.60E-01 3.20E-01

45085 23 1.13E-01 1.58E-01 2.60E-01 2.20E-02 9.00E-02 3.00E-02 1.20E+00

45083 -1.80E-01 2.40E-01 4.60E-01

45084 24 4.70E-02 1.52E-01 2.70E-01 4.30E-02 1.10E-01 3.40E-02 8.30E-01

43473 25 1.09E-01 1.34E-01 2.00E-01

47128 26 2.20E-02 9.40E-02 1.60E-01

47129 2.80E-02 8.40E-02 1.40E-01

44325 27 1.11E+00 6.60E-01 8.40E-01

43368 28 9.64E-01 8.20E-01 1.20E+0

43475 29 1.52E-01 5.80E-01 1.00E+00

43407 30 2.15E+00 6.20E-01 4.60E-01

43831 31 2.02E-01 1.46E-01 2.20E-01

99913

43951 32 8.30E+00 1.28E+00 4.50E-01 6.44E+00 5.90E-01

43968 8.20E+00 1.26E+00 3.60E-01 6.76E+00 5.10E-01

44181 5.54E+00 9.00E-01 4.90E-01

44182 33 5.13E+00 7.60E-01 3.60E-01 5.43E+00 4.10E-01

43845 34 4.76E+00 9.40E-01 6.80E-01

43846 3.96E+00 8.00E-01 6.00E-01 4.38E+00 4.00E-01

44329 35 5.34E+00 7.60E-01 3.50E-01 4.36E+00 3.40E-01

44330 4.93E+00 6.80E-01 2.70E-01

99914 36 8.80E-02 9.00E-02 1.80E-02 8.50E-01

44316 37 5.80E-01 6.00E-01 9.00E-01

45125 38 3.50E-01 2.40E-01 3.40E-01 3.34E-01 1.80E-01 2.80E-02 6.17E-01 6.10E-01 2.50E-01

44324 39 4.40E-01 2.20E-01 3.10E-01

44967 40 4.90E-01 2.80E-01 3.90E-01

44968 4.49E-01 1.60E-01 2.00E-01 2.33E-01 1.20E-01 2.20E-02 7.46E-01 4.60E-01 2.30E-01

45424 4.62E+01 6.40E+00 8.30E-01 4.09E+01 3.52E+00

45423 41 4.96E+01 7.60E+00 1.10E+00 4.70E+01 3.49E-01 4.56E+01 4.20E+00 2.00E-02 4.82E+01 3.10E+00 1.50E+00

45422 6.37E+01 9.20E+00 9.70E-01 6.36E+01 4.73E-01

45421 42 7.36E+01 1.06E+01 1.00E+00 7.13E+01 5.40E+00 6.61E+01 5.40E+00 2.70E-02 7.54E+01 4.60E+00 2.40E+00

99905 43 6.57E+00 5.70E-01

45343 44 8.00E-02 2.20E-01 3.90E-01 -3.36E-02 1.60E-01 6.50E-02 5.57E-01 6.80E-01 3.30E-01

45648 45 1.31E-01 1.16E-01 1.80E-01 1.60E-02 8.80E-02 3.10E-02 9.60E-01

43409 46 2.02E+00 6.00E-02 4.60E-01

43369 47 2.62E+00 7.00E-01 6.30E-01

43408 48 9.54E-01 4.20E-01 5.50E-01

43544 49 7.05E+00 1.16E+00 4.70E-01

99911 50 6.60E-01 8.00E-02 3.74E-01 3.30E-01 8.10E-02 9.71E-01 1.20E+00 6.20E-01

1.32E+00 9.60E-01 4.90E-01

43370 51 1.17E+00 3.40E-01 3.30E-01

alpha spectroscopy alpha spectroscopy gamma spectroscopy

result CSU1 MDC result CSU1 na result CSU2 MDC result CSU2 MDC

USGS

serial

number 

Map

key

Ra224 (pCi/L) - USGS Ra224 (pCi/L) - EPA (quality-control lab)

gamma spectroscopy

1

One standard deviation

2

Two standard deviations based on counting error only
31

44177 52 2.79E+00 5.20E-01 5.60E-01 5.36E+00 4.20E-01

44178 3.34E+00 5.80E-01 3.50E-01

99912 5.90E+00 4.50E-01

99910 53 1.19E+00 1.00E-01

45603 54 4.70E-01 3.00E-01 4.20E-01 6.11E-01 3.30E-01 5.50E-02 7.06E-01 7.00E-01 4.50E+00

43949 3.15E-01 2.20E-01 2.80E-01

43950 55 4.06E-01 3.00E-01 4.00E-01

43833 56 7.61E+00 1.66E+00 1.30E+00

43546 57 5.43E-01 4.80E-01 6.80E-01

43552 58 5.80E-01 3.00E-01 3.70E-01

45428 59 1.10E-01 4.40E-01 7.70E-01 7.67E-01 3.10E-01 5.10E-02 5.27E-01 7.60E-01 4.00E-01

43824 60 -2.00E-02 2.80E-01 5.20E-01

43467 61 1.79E-01 1.60E-01 2.30E-01

47127 62 6.04E+00 1.28E+00 1.10E+00

43472 63 1.41E+00 5.40E-01 6.30E-01

99903 64 5.95E+00 4.70E-01

44084 65 8.00E-02 3.00E-01 5.00E-01

44180 66 4.50E-02 1.54E-01 2.60E-01

44085 4.60E-02 1.72E-01 3.00E-01

44086 67 1.28E-01 1.48E-01 2.40E-01 3.40E-01 7.00E-02

45087 68 5.72E+00 1.00E+00 5.50E-01 5.91E+00 4.90E-01 5.89E+00 8.10E-01 2.40E-02 7.08E+00 9.20E-01 4.40E-01

45088 5.93E+00 9.00E-01 5.80E-01

45089 69 3.39E+00 6.20E-01 4.70E-01 3.52E+00 3.40E-01 3.20E+00 5.00E-01 2.50E-02 3.72E+00 8.60E-01 4.10E-01

45090 3.03E+00 8.80E-01 7.90E-01

46849 70 4.58E+00 8.00E-01 3.90E-01 4.57E+00 3.75E-01

46850 4.95E+00 9.00E-01 4.20E-01

43554 71 1.83E-01 1.16E+00 2.90E-01

43622 3.53E-01 2.80E-01 4.00E-01

43623 72 3.07E-01 1.58E-01 2.10E-01

45224 73 1.23E+00 5.20E-01 6.10E-01 6.30E-01 2.50E-01 3.20E-02 1.08E+00 6.30E-01 3.10E-01

45223 74 3.00E-01 2.20E-01 3.30E-01 2.03E-01 1.50E-01 3.30E-02 9.26E-01 7.60E-01 3.70E-01

45352 75 5.00E-02 1.94E-01 3.40E-01 0.00E+00 9.00E-02 3.60E-02 2.30E+00

1.60E+00

44966 76 2.15E-01 1.72E-01 2.70E-01 1.04E-01 1.60E-01 4.70E-02 1.00E+00

1.57E-01 1.10E-01 2.20E-02

43832 77 1.63E-01 9.60E-02 1.40E-01

44176 78 3.38E-01 1.56E-01 2.10E-01

44239 79 1.50E-01 2.20E-01 3.70E-01

44969 80 5.10E+01 8.40E+00 4.10E+00 3.33E+01 2.50E+00 2.98E+01 5.30E+00 1.30E-01 2.07E+01 2.00E+00 9.90E-01

44970 5.32E+01 9.80E+00 2.30E+00 1.85E+01 1.80E+00 9.00E-01

44971 4.86E+01 8.00E+00 2.80E+00 1.65E+01 1.20E-00 3.09E+01 7.80E+00 2.60E-01 2.25E+01 2.00E+00 1.00E+00

44972 4.58E+01 8.00E+00 3.80E+00 2.29E+01 1.80E+00 9.10E-01

45220 81 5.50E+00 4.40E+00 6.80E+00 6.38E+00 5.00E-01 5.16E+00 9.40E-01 5.80E-02 7.46E+00 8.60E-01 4.20E-01

45221 1.18E+01 2.60E+00 1.60E+00

99902 82 3.90E-01 8.00E-02

45002 83 -6.40E-02 1.96E-01 3.60E-01 1.56E-01 1.30E-01 3.00E-02 7.80E-01

45052 2.03E-01 1.20E-01 1.70E-01

45051 84 1.65E-01 1.12E-01 1.70E-01 2.24E-01 1.70E-01 3.70E-02 9.10E-01

43948 85 9.00E-01 2.40E+00 4.10E+00

45086 8.20E-01 1.00E+00 1.60E+00 2.15E-01 1.50E-01 3.20E-02 7.10E-01

44175 86 2.47E-01 1.94E-01 2.60E-01

99901 87 8.00E-01 8.00E-02

45348 88 5.13E-01 1.96E-01 2.30E-01 4.72E-01 1.40E-01 1.80E-02 8.29E-01 7.50E-01 3.70E-01

45349 7.10E-01 2.80E-01 3.20E-01

45351 89 4.70E-01 2.00E-01 2.90E-01 7.40E-01 2.20E-01 2.92E-01 2.40E-01 5.10E-02 1.34E+00 8.80E-01 4.40E-01

45350 4.85E-01 1.94E-01 2.30E-01

43411 3.25E+00 7.00E-01 2.50E-01

44080 90 8.31E+00 1.50E+00 5.60E-01

44078 91 1.06E+01 1.76E+00 6.50E-01

43428 92 1.85E+01 2.40E+00 3.40E-01

44079 1.02E+01 1.68E+00 5.00E-01

43477 93 3.80E-01 2.80E-01 4.20E-01

43493 2.10E-01 3.00E-01 4.60E-01

43969 94 6.08E-02 1.26E-01 2.10E-01

43914 95 3.22E-01 1.90E-01 2.40E-01

43915 4.69E-01 2.00E-01 2.50E-01

43410 96 1.46E-01 1.90E-01 3.10E-01

43371 97 2.12E+00 4.60E-01 3.30E-01

43545 98 6.11E+00 1.32E+00 6.30E-01

43474 99 4.11E+00 6.20E-01 3.20E-01

alpha spectroscopy alpha spectroscopy gamma spectroscopy

result CSU1 MDC result CSU1 na result CSU2 MDC result CSU2 MDC

USGS

serial

number 

Map

key

Ra224 (pCi/L) - USGS Ra224 (pCi/L) - EPA (quality-control lab)

gamma spectroscopy

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. . . . ... ... ... ... . . . . ... ... . . . ... ... . . . . ... ... . . . ... ...

...

... . . . . .. .. . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . ... ...

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.

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1

One standard deviation

2

Two standard deviations based on counting error only
32

result CSU1 MDC result CSU1 na result CSU2 MDC result CSU2 MDC

44322 2 1.30E-01 4.00E-02 3.40E-02 . . . . . . . . .

44323 . 1.31E-01 4.20E-02 3.90E-02 . . . . . . . . .

44320 . 1.09E-01 5.20E-02 6.80E-02 . . . . . . . . .

44321 1 1.59E-01 5.20E-02 5.10E-02 . . . . . . . . .

43372 3 4.92E-02 3.80E-02 5.10E-02 . . . . . . . . .

45344 4 8.60E-02 1.00E-01 1.50E-01 . . . 1.02E-01 7.40E-02 1.80E-02 4.18E-01 2.40E-01 2.80E-01

45345 5 1.64E-01 6.00E-02 5.30E-02 . . . 1.40E-01 1.00E-01 2.50E-02 . . 7.40E-01

. . . . . . . . 9.20E-02 7.40E-02 2.10E-02 . . .

45429 6 2.87E+00 4.80E-01 7.90E-02 . . . 1.22E+00 2.50E-01 1.50E-02 1.67E+00 3.40E-01 4.30E-01

44087 7 3.00E-01 9.00E-02 7.60E-02 2.00E-01 3.00E-02 . . . . . .

44088 . 2.72E-01 7.80E-02 4.80E-02 . . . . . . . . .

44179 8 2.55E-01 1.28E-01 1.20E-01 . . . . . . . . .

44319 9 1.60E-01 4.00E-01 7.10E-01 . . . . . . . . .

44328 10 2.13E-01 6.80E-02 5.70E-02 . . . . . . . . .

99904 11 . . . 9.00E-02 3.00E-02 . . . . . .

45219 12 1.21E-01 4.40E-02 3.90E-02 . . . 3.07E-01 1.40E-01 2.20E-02 5.25E-01 3.20E-01 6.90E-01

99909 13 . . . 2.84E+00 2.90E-01 . . . . . .

99906 14 . . . 1.00E+00 1.00E-01 . . . . . .

99907 15 . . . 2.27E+00 1.70E-01 . . . . . .

45222 16 1.61E-01 5.20E-01 3.80E-02 . . . 2.27E-01 1.10E-01 1.60E-02 6.47E-01 2.90E-01 6.50E-01

43553 17 1.54E+00 3.20E-01 1.20E-01 . . . . . . . . .

43468 18 5.17E-01 1.40E-01 1.10E-01 . . . . . . . . .

99908 19 . . . 6.21E+00 4.60E-01 . . . . . .

45066 20 6.30E-01 2.20E-01 1.70E-01 . . . 5.72E-01 1.70E-01 1.70E-02 3.95E-01 3.20E-01 6.40E-01

45426 . 3.61E-01 9.80E-02 5.50E-02 . . . . . . . . .

45425 21 4.85E-01 1.40E-01 7.70E-02 3.70E-01 5.00E-02 3.11E-01 1.30E-01 1.70E-02 . . 6.90E-01

45065 22 2.49E+00 3.60E-01 7.30E-02 . . . 2.73E+00 4.40E-01 1.80E-02 1.97E+00 3.50E-01 4.20E-01

45085 23 2.93E-01 8.00E-02 5.60E-02 . . . 3.28E-01 1.40E-01 1.60E-02 . . 6.60E-01

45083 . 1.09E-01 6.20E-02 7.20E-02 . . . . . . . . .

45084 24 5.70E-02 4.40E-02 6.30E-02 . . . 1.38E-01 8.20E-02 1.60E-02 . . 6.60E-01

43473 25 1.88E-01 5.40E-02 3.30E-02 . . . . . . . . .

47128 26 3.66E-01 6.80E-02 2.40E-02 6.20E-01 6.00E-02 . . . . . . .

47129 . 3.23E-01 6.00E-02 2.10E-02 . . . . . . . . .

44325 27 1.62E+01 2.40E+00 1.90E-01 . . . . . . . . .

43368 28 1.23E+01 1.98E+00 1.80E-01 . . . . . . . . .

43475 29 3.13E-02 1.12E-01 2.20E-01 . . . . . . . . .

43407 30 3.48E+00 6.40E-01 8.90E-02 . . . . . . . . .

43831 31 4.48E-01 9.60E-02 6.10E-02 . . . . . . . . .

99913 . . . . . . . . . . . . .

43951 32 5.16E+00 7.60E-01 8.10E-02 4.59E+00 3.50E-01 . . . . . .

43968 . 5.18E+00 7.60E-01 8.10E-02 4.70E+00 3.80E-01 . . . . . .

44181 . 8.22E+00 1.18E+00 4.50E-02 . . . . . . . . .

44182 33 6.90E+00 9.20E-01 4.20E-02 6.62E+00 5.20E-01 . . . . . .

43845 34 6.39E+00 9.80E-01 5.50E-02 . . . . . . . . .

43846 . 5.88E+00 8.80E-01 6.00E-02 5.23E+00 4.30E-01 . . . . . .

44329 35 4.06E+00 5.20E-01 4.70E-02 3.34E+00 2.80E-01 . . . . . .

44330 . 3.72E+00 4.80E-01 3.60E-02 . . . . . . . . .

99914 36 . . . . . . 3.50E-02 4.00E-02 1.20E-02 . . 7.00E-01

44316 37 4.70E-01 2.80E-01 2.60E-01 . . . . . . . . .

45125 38 7.86E-01 1.56E-01 4.30E-02 . . . 7.28E-01 1.80E-01 1.50E-02 5.96E-01 3.00E-01 3.60E-01

44324 39 1.37E-01 6.00E-02 7.10E-02 . . . . . . . . .

44967 40 4.08E-01 1.26E-01 1.20E-01 . . . . . .

44968 . 3.16E-01 7.80E-02 6.00E-02 . . . 2.82E-01 1.00E-01 1.20E-02 1.58E+00 3.30E-01 4.00E-01

45424 . 8.48E+00 1.20E+00 7.80E-02 9.04E+00 7.30E-01 . . . . . .

45423 41 9.31E+00 1.46E+00 8.50E-02 8.63E+00 6.70E-01 7.64E+00 8.60E-01 1.30E-02 6.89E+00 5.90E-01 6.90E-01

45422 . 1.14E+01 1.66E+00 4.70E-02 1.14E+01 8.90E-01 . . . . . .

45421 42 1.30E+01 1.92E+00 4.30E-02 1.32E+01 1.00E+00 1.19E+01 1.10E+00 1.30E-02 1.06E+01 7.20E-01 7.80E-01

99905 43 . . . 2.45E+00 1.90E-01 . . . . . .

45343 44 5.70E-02 5.60E-02 8.40E-02 . . . 1.71E-01 1.30E-01 3.40E-02 3.84E-01 3.40E-01 5.20E-01

45648 45 2.50E-02 2.60E-02 3.90E-02 . . . 0.00E+00 3.60E-02 2.20E-02 . . 7.60E-01

43409 46 3.29E+00 6.40E-01 1.10E-01 . . . . . . . . .

43369 47 3.02E+00 5.40E-01 1.40E-01 . . . . . . . . .

43408 48 3.68E-01 9.20E-02 5.80E-02 . . . . . . . . .

43544 49 5.80E+00 8.40E-01 7.60E-02 . . . . . . . . .

99911 50 . . . 2.10E-01 4.00E-02 5.58E-01 2.80E-01 4.40E-02 . . 1.30E+00

. . . . . . . . . . . 1.09E+00 6.30E-01 1.10E+00

43370 51 3.71E-01 1.02E-01 6.60E-02 . . . . . . . . .

44177 52 4.01E+00 5.40E-01 6.50E-02 5.55E+00 8.30E-01 . . . . . .

USGS

serial

number 

Map

key

Ra226 (pCi/L) - USGS Ra226 (pCi/L) - EPA (quality-control lab)

alpha spectroscopy gamma spectroscopy alpha spectroscopy gamma spectroscopy

1

One standard deviation

2

Two standard deviations based on counting error only
33

44178 . 3.54E+00 5.20E-01 4.60E-02 . . . . . . . . .

99912 . . . . 6.38E+00 5.00E-01 . . . . . .

99910 53 . . . 1.09E+00 2.20E-01 . . . . . .

45603 54 2.34E+00 3.66E-01 5.80E-02 . . . 2.98E+00 5.00E-01 2.50E-02 1.36E+00 5.10E-01 6.20E-01

43949 . 2.23E+00 3.80E-01 7.10E-02 . . . . . . . . .

43950 55 2.91E+00 5.00E-01 1.10E-01 . . . . . . . . .

43833 56 8.75E-01 1.60E-01 6.80E-02 . . . . . . . . .

43546 57 1.12E+00 2.60E-01 8.30E-02 . . . . . . . . .

43552 58 6.33E-01 1.66E-01 9.80E-02 . . . . . . . . .

45428 59 1.76E+00 3.20E-01 8.50E-02 . . . 1.53E+00 3.50E-01 2.40E-02 1.63E+00 3.80E-01 4.70E-01

43824 60 6.56E-01 1.22E-01 5.70E-02 . . . . . . . . .

43467 61 5.33E-01 1.00E-01 3.50E-02 . . . . . . . . .

47127 62 3.50E+00 4.40E-01 2.50E-02 . . . . . . . . .

43472 63 8.96E+00 1.30E+00 8.20E-02 . . . . . . . . .

99903 64 . . . 2.29E+00 1.80E-01 . . . . . .

44084 65 6.20E-02 6.80E-02 1.10E-01 . . . . . . . . .

44180 66 2.13E-01 5.80E-02 4.10E-02 . . . . . . . . .

44085 . 3.40E-02 4.20E-02 6.70E-02 . . . . . . . . .

44086 67 4.10E-02 3.20E-02 4.70E-02 6.00E-02 2.00E-01 . . . . . .

45087 68 4.39E+00 6.80E-01 4.60E-02 5.40E+00 8.10E-01 4.81E+00 6.30E-01 7.60E-03 4.53E+00 4.40E-01 5.20E-01

45088 . 5.10E+00 6.40E-01 3.10E-02 . . . . . . . . .

45089 69 3.24E+00 4.40E-01 5.10E-02 3.43E+00 5.40E-01 3.05E+00 4.20E-01 1.40E-02 2.72E+00 3.70E-01 4.60E-01

45090 . 3.78E+00 6.80E-01 1.20E-01 . . . . . . . . .

46849 70 1.97E+00 3.00E-01 3.30E-02 5.60E+00 1.60E-01 . . . . . .

46850 . 1.90E+00 3.20E-02 3.70E-03 . . . . . . . . .

43554 71 1.82E-01 7.60E-02 5.60E-02 . . . . . . . . .

43622 . 1.68E-01 8.60E-02 6.80E-02 . . . . . . . . .

43623 72 1.57E-01 5.40E-02 4.30E-02 . . . . . . . . .

45224 73 2.88E-01 8.20E-02 5.70E-02 . . . 3.59E-01 1.60E-01 2.50E-02 . . 8.30E-01

45223 74 1.79E-01 5.40E-02 4.30E-02 . . . 2.51E-01 1.10E-01 1.70E-02 8.43E-01 3.60E-01 7.40E-01

45352 75 1.04E-01 3.60E-02 3.60E-02 . . . 6.00E-02 6.40E-02 2.00E-02 . . 1.50E+00

. . . . . . . . . . . . . 1.20E+00

44966 76 1.46E-01 5.60E-02 5.20E-02 . . . 5.25E-01 1.90E-01 2.20E-02 3.40E-01 3.30E-01 4.80E-01

. . . . . . . . 2.52E-01 1.00E-01 6.80E-03 . . .

43832 77 3.06E-01 6.80E-02 3.70E-02 . . . . . . . . .

44176 78 2.34E-01 6.00E-02 4.40E-02 . . . . . . . . .

44239 79 5.10E-02 5.60E-02 8.90E-02 . . . . . . . . .

44969 80 8.50E-01 6.40E-01 9.90E-01 7.00E-02 5.00E-02 3.41E-01 2.70E-01 6.80E-02 1.43E+00 4.50E-01 5.20E-01

44970 . 4.40E-01 3.60E-01 5.20E-01 . . . . . . 7.35E-01 5.60E-01 6.90E-01

44971 . 3.40E-01 2.80E-01 3.90E-01 1.40E-01 4.00E-02 1.14E-01 2.60E-01 1.20E-01 1.33E+00 6.20E-01 1.40E+00

44972 . 2.00E-01 3.80E-01 6.70E-01 . . . . . . 1.62E+00 4.40E-01 1.30E+00

45220 81 1.63E+00 5.00E-01 3.80E-01 8.20E-01 1.30E-01 1.98E+00 4.40E-01 3.30E-02 6.67E-01 2.90E-01 3.60E-01

45221 . 1.06E+00 3.00E-01 2.10E-01 . . . . . . . . .

99902 82 . . . 4.40E-01 1.40E-01 . . . . . .

45002 83 4.10E-02 3.40E-02 5.00E-02 . . . 1.96E-01 1.10E-01 9.50E-03 3.25E-01 2.10E-01 6.30E-01

45052 . 1.49E-01 5.00E-02 5.20E-02 . . . . . . . . .

45051 84 1.72E-01 4.60E-02 3.50E-02 . . . 8.60E-02 7.40E-02 2.00E-02 3.35E-01 4.10E-01 7.60E-01

43948 85 5.40E-01 2.40E-01 2.50E-01 . . . . . . . . .

45086 . 3.50E-01 2.60E-01 3.40E-01 . . . 2.45E-01 1.20E-01 1.70E-02 6.01E-01 3.10E-01 3.80E-01

44175 86 7.50E-02 6.00E-02 6.90E-02 . . . . . . . . .

99901 87 . . . 9.80E-01 8.00E-02 . . . . . .

45348 88 4.55E-01 9.80E-02 5.40E-02 . . . 3.77E-01 9.80E-02 7.60E-03 . . 7.10E-01

45349 . 6.51E-01 1.40E-01 5.80E-02 . . . . . . . . .

45351 89 1.43E+00 2.20E-01 2.80E-02 1.62E+00 1.30E-01 1.32E+00 3.80E-01 4.10E-02 1.44E+00 3.90E-01 4.80E-01

45350 . 1.82E+00 2.80E-01 4.30E-02 . . . . . . . .

43411 . 1.94E+00 4.00E-01 8.10E-02 . . . . . . . . .

44080 90 1.63E+00 3.80E-01 1.30E-01 . . . . . . . . .

44078 91 1.73E+00 3.80E-01 1.30E-01 . . . . . . . . .

43428 92 2.89E+00 4.20E-01 4.30E-02 . . . . . . . . .

44079 . 1.86E+00 3.80E-01 1.20E-01 . . . . . . . . .

43477 93 9.57E+00 1.34E+00 6.40E-02 . . . . . . . . .

43493 . 1.01E+01 1.44E+00 5.50E-02 . . . . . . . . .

43969 94 9.06E-02 4.20E-02 5.10E-02 . . . . . . . . .

43914 95 4.30E-01 1.34E-01 7.40E-02 . . . . . . . . .

43915 . 4.53E-01 1.28E-01 7.40E-02 . . . . . . . . .

43410 96 9.99E-02 5.20E-02 6.80E-02 . . . . . . . . .

43371 97 8.79E-01 1.70E-01 5.60E-02 . . . . . . . . .

43545 98 1.61E+00 4.00E-01 1.30E-01 . . . . . . . . .

43474 99 1.66E+00 2.40E-01 4.60E-02 . . . . . . . . .

result CSU1 MDC result CSU1 na result CSU2 MDC result CSU2 MDC

USGS

serial

number 

Map

key

Ra226 (pCi/L) - USGS Ra226 (pCi/L) - EPA (quality-control lab)

alpha spectroscopy gamma spectroscopy alpha spectroscopy gamma spectroscopy

1

One standard deviation

2

Two standard deviations based on counting error only
34

result CSU3 MDC result CSU1 na result CSU2 MDC

44322 2 5.12E-02 2.90E-01 7.49E-01 . . . . . .

44323 . . . . . . . . . .

44320 . . . . . . . . . .

44321 1 1.75E-01 2.60E-01 6.72E-01 . . . . . .

43372 3 3.37E-01 3.10E-01 7.39E-01 . . . . . .

45344 4 4.35E-01 3.00E-01 5.81E-01 . . . 1.83E-01 2.50E-01 9.70E-01

45345 5 3.92E-01 3.60E-01 8.72E-01 . . . . . 1.30E+00

.. . . . . . . . . .

45429 6 8.11E-01 4.10E-01 7.93E-01 . . . 6.48E-01 7.50E-01 3.40E-01

44087 7 5.32E-01 3.50E-01 7.31E-01 2.90E-01 8.00E-02 . . .

44088 . 2.52E-01 2.90E-01 7.29E-01 . . . . . .

44179 8 5.46E-01 3.30E-01 5.91E-01 . . . . . .

44319 9 7.22E-01 3.90E-01 7.68E-01 . . . . . .

44328 10 3.12E-01 2.90E-01 6.96E-01 . . . . . .

99904 11 . . . 9.00E-02 9.00E-02 . . .

45219 12 2.36E-02 2.70E-01 7.68E-01 . . . . . 1.00E+00

99909 13 . . . 1.28E+00 1.60E-01 . . .

99906 14 . . . 9.00E-02 1.50E-01 . . .

99907 15 . . . 7.00E-02 7.00E-02 . . .

45222 16 2.71E-01 3.30E-01 8.18E-01 . . . . . 1.10E+00

43553 17 2.06E-01 2.30E-01 5.23E-01 . . . . . .

43468 18 8.14E-01 3.60E-01 5.31E-01 . . . . . .

99908 19 . . . 2.30E-01 1.10E-01 . . .

45066 20 8.58E-02 3.00E-01 8.21E-01 . . . . . 1.10E+00

45426 . 5.37E-01 3.40E-01 7.29E-01 . . . . . .

45425 21 3.92E-01 3.60E-01 8.72E-01 6.70E-01 9.00E-02 9.39E-01 7.20E-01 1.20E+00

45065 22 1.77E-01 3.10E-01 8.15E-01 . . . 1.66E-01 2.60E-01 1.40E+00

45085 23 1.66E-01 2.40E-01 5.63E-01 . . . . . 1.30E+00

45083 . 1.56E-01 2.60E-01 6.17E-01 . . . . . .

45084 24 2.94E-01 2.80E-01 5.88E-01 . . . 6.59E-01 7.20E-01 1.10E+00

43473 25 4.69E-01 3.30E-01 7.36E-01 . . . . . .

47128 26 2.14E-01 3.50E-01 8.98E-01 7.60E-01 1.10E-01 . . . .

47129 . . . . . . . . . .

44325 27 1.09E+00 4.15E-01 4.97E-01 . . . . . .

43368 28 1.28E+00 4.30E-01 4.28E-01 . . . . . .

43475 29 1.97E-01 2.70E-01 6.87E-01 . . . . . .

43407 30 2.45E+00 7.40E-01 7.95E-01 . . . . . .

43831 31 7.47E-01 4.50E-01 9.33E-01 . . . . . .

99913 . 4.33E-01 3.70E-01 8.70E-01 . . . . . .

43951 32 6.60E+00 1.60E+00 8.26E-01 6.40E+00 5.00E-01 . . .

43968 . . . . 6.61E+00 6.10E-01 . . .

44181 . . . . . . . . . .

44182 33 5.20E+00 1.30E+00 4.91E-01 5.08E+00 5.60E-01 . . .

43845 34 . . . . . . . . .

43846 . 3.89E+00 1.10E+00 9.85E-01 4.11E+00 3.80E-01 . . .

44329 35 3.64E+00 9.65E-01 7.43E-01 3.84E+00 4.30E-01 . . .

44330 . 3.36E+00 8.90E-01 6.94E-01 . . . . . .

99914 36 2.28E-01 2.90E-01 7.40E-01 . . . . . 1.50E+00

44316 37 3.12E-01 3.10E-01 7.16E-01 . . . . . .

45125 38 8.33E-01 4.60E-01 8.90E-01 . . . . . 9.70E-01

44324 39 4.60E-01 3.50E-01 7.17E-01 . . . . . .

44967 40 . . . . . . . . .

44968 . 2.52E-01 3.40E-01 8.25E-01 . . . 3.26E-01 2.40E-01 2.40E-01

45424 . . . . 4.19E+01 3.20E+00 . . .

45423 41 3.64E+01 7.90E+00 9.04E-01 3.90E+01 2.94E+00 3.47E+01 2.30E+00 4.50E-01

45422 . . . . 6.89E+01 5.17E+00 . . .

45421 42 7.23E+01 1.50E+01 8.78E-01 7.89E+01 5.98E+00 6.79E+01 4.10E+00 4.80E-01

99905 43 . . . 4.81E+00 5.60E-01 . . .

45343 44 1.99E-01 3.20E-01 8.47E-01 . . . . . 1.10E+00

45648 45 1.42E-01 3.10E-01 8.37E-01 . . . . . 1.50E+00

43409 46 2.15E+00 7.00E-01 8.94E-01 . . . . . .

43369 47 2.50E+00 7.30E-01 5.12E-01 . . . . . .

43408 48 6.04E-01 3.90E-01 8.15E-01 . . . . . .

43544 49 6.03E+00 1.50E+00 5.20E-01 . . . . . .

99911 50 5.00E-01 3.60E-01 8.13E-01 5.00E-01 1.10E-01 4.84E-01 7.30E-01 7.30E-01

. . . . . . . . . . 2.30E+00

43370 51 1.11E+00 4.70E-01 7.88E-01 . . . . . .

44177 52 5.77E+00 1.40E+00 7.98E-01 5.57E+00 5.20E-01 . . .

44178 . . . . . . . . . .

USGS

serial

number 

Map

key

Ra228 (pCi/L) - USGS Ra228 (pCi/L) - EPA (quality-control lab)

beta counting gamma spectroscopy gamma spectroscopy

1

One standard deviation

2

Two standard deviations based on counting error only

3

Two standard deviations 
35

result CSU3 MDC result CSU1 na result CSU2 MDC

USGS

serial

number 

Map

key

Ra228 (pCi/L) - USGS Ra228 (pCi/L) - EPA (quality-control lab)

beta counting gamma spectroscopy gamma spectroscopy

99912 . . . . 6.66E+00 6.40E-01 . . .

99910 53 . . . 9.70E-01 1.30E-01 . . .

45603 54 6.84E-01 3.70E-01 7.40E-01 . . . . . 2.10E+00

43949 . . . . . . . . . .

43950 55 6.35E-01 4.80E-01 1.04E+00 . . . . . .

43833 56 4.40E-01 3.80E-01 8.80E-01 . . . . . .

43546 57 5.05E-01 3.10E-01 6.54E-01 . . . . . .

43552 58 3.70E-01 2.60E-01 5.13E-01 . . . . . .

45428 59 3.86E-01 3.40E-01 8.06E-01 . . . . . 1,5

43824 60 2.62E-01 2.90E-01 6.37E-01 . . . . . .

43467 61 7.12E-01 3.40E-01 6.08E-01 . . . . . .

47127 62 3.43E+00 9.50E-01 8.40E-01 . . . . . .

43472 63 1.57E+00 5.20E-01 6.70E-01 . . . . . .

99903 64 . . . 4.13E+00 2.30E-01 . . .

44084 65 2.60E-01 3.10E-01 7.18E-01 . . . . . .

44180 66 5.23E-01 3.10E-01 5.51E-01 . . . . . .

44085 . . . . . . . . . .

44086 67 3.37E-01 3.20E-01 7.22E-01 1.40E-01 4.00E-02 . . .

45087 68 3.87E+00 1.04E+00 5.94E-01 4.68E+00 4.70E-01 3.40E+00 6.60E-01 2.80E-01

45088 . . . . . . . . . .

45089 69 1.77E+00 5.40E-01 4.74E-01 2.59E+00 3.60E-01 2.19E+00 5.80E-01 4.10E-01

45090 . . . . . . . . . .

46849 70 4.67E+00 1.20E+00 8.48E-01 5.60E+00 4.30E-01 . . .

46850 . . . . . . . . . .

43554 71 7.75E-01 3.60E-01 6.47E-01 . . . . . .

43622 . . . . . . . . . .

43623 72 6.31E-01 3.10E-01 4.77E-01 . . . . . .

45224 73 1.69E+00 5.70E-01 5.65E-01 . . . . . 1.10E+00

45223 74 8.11E-01 4.40E-01 8.73E-01 . . . . . 1.10E+00

45352 75 4.63E-01 3.60E-01 8.45E-01 . . . . . 2.60E+00

. . . . . . . . 1.95E+00 1.50E+00 2.10E+00

44966 76 4.74E-01 3.30E-01 7.38E-01 . . . . . 1.20E+00

.. . . . . . . . . .

43832 77 4.07E-01 4.00E-01 9.15E-01 . . . . . .

44176 78 4.38E-01 3.00E-01 5.65E-01 . . . . . .

44239 79 4.32E-01 2.70E-01 4.92E-01 . . . . . .

44969 80 9.39E-01 5.30E-01 1.04E+00 7.60E-01 1.10E-01 . 5.80E-01 1.80E+00

44970 . . . . . . . . 6.60E-01 2.00E+00

44971 . 1.05E+00 4.90E-01 8.78E-01 6.60E-01 9.00E-02 5.00E-01 . 7.40E-01 2.30E+00

44972 . . . . . . . 1.75E+00 1.50E+00 1.80E+00

45220 81 1.70E+00 5.70E-01 7.61E-01 1.48E+00 3.20E-01 5.00E-01 1.02E+00 5.70E-01 2.70E-01

45221 . . . . . . . . . .

99902 82 . . . 4.30E-01 1.10E-01 5.00E-01 . . .

45002 83 2.40E-01 2.90E-01 7.28E-01 . . . . . 1.20E+00

45052 . . . . . . . . . .

45051 84 1.65E-01 3.10E-01 8.26E-01 . . . . . 1.30E+00

43948 85 4.64E-01 3.20E-01 6.29E-01 . . . . . .

45086 . . . . . . . . . 8.70E-01

44175 86 5.02E-01 3.60E-01 8.05E-01 . . . . . .

99901 87 . . . 7.50E-01 1.50E-01 . . .

45348 88 8.16E-01 3.80E-01 5.88E-01 . . . . . 1.40E+00

45349 . 9.43E-01 4.20E-01 7.42E-01 . . . . . .

45351 89 8.35E-01 4.20E-01 7.88E-01 4.00E-01 1.20E-01 . . 1.70E+00

45350 . . . . . . . . . .

43411 . 4.34E+00 1.10E+00 7.69E-01 . . . . . .

44080 90 5.02E+00 1.30E+00 5.31E-01 . . . . . .

44078 91 6.60E+00 1.70E+00 6.88E-01 . . . . . .

43428 92 . . . . . . . . .

44079 . 5.90E+00 1.50E+00 7.18E-01 . . . . . .

43477 93 3.40E-01 2.80E-01 5.71E-01 . . . . . .

43493 . . . . . . . . . .

43969 94 2.34E-01 2.70E-01 6.76E-01 . . . . . .

43914 95 5.96E-01 3.50E-01 7.28E-01 . . . . . .

43915 . . . . . . . . . .

43410 96 3.53E-01 2.80E-01 5.63E-01 . . . . . .

43371 97 1.18E+00 4.80E-01 7.89E-01 . . . . . .

43545 98 2.41E+00 7.10E-01 5.76E-01 . . . . . .

43474 99 2.99E+00 8.50E-01 6.26E-01 . . . . . .

1

One standard deviation

2

Two standard deviations based on counting error only

3

Two standard deviations 
36

44320 . . . . . . . . . . . . . . . .

44321 1 . . . . . . . . . . . . . . .

43372 3 . . . . . . . . . . . . . . .

45344 4 . . . . . . . . . . . . . . .

45345 5 . . . . . . . . . . . . . . .

.. . . . . . . . . . . . . . . .

45429 6 . . . . . . . . . . . . . . .

44087 7 . . . . . . . . . . . . . . .

44088 . . . . . . . . . . . . . . . .

44179 8 . . . . . . . . . . . . . . .

44319 9 . . . . . . . . . . . . . . .

44328 10 . . . . . . . . . . . . . . .

99904 11 . . . . . . . . . . . . . . .

45219 12 . . . . . . . . . . . . . . .

99909 13 . . . . . . . . . . . . . . .

99906 14 . . . . . . . . . . . . . . .

99907 15 . . . . . . . . . . . . . . .

45222 16 . . . . . . . . . . . . . . .

43553 17 . . . . . . . . . . . . . . .

43468 18 . . . . . . . . . . . . . . .

99908 19 . . . . . . . . . . . . . . .

45066 20 . . . . . . . . . . . . . . .

45426 . . . . . . . . . . . . . . . .

45425 21 . . . . . . . . . . . . . . .

45065 22 . . . . . . . . . . . . . . .

45085 23 . . . . . . . . . . . . . . .

45083 . . . . . . . . . . . . . . . .

45084 24 . . . . . . . . . . . . . . .

43473 25 . . . . . . . . . . . . . . .

47128 26 . . . . . . . . . . . . . . .

47129 . . . . . . . . . . . . . . . .

44325 27 . . . . . . . . . . . . . . .

43368 28 . . . . . . . . . . . . . . .

43475 29 . . . . . . . . . . . . . . .

43407 30 . . . . . . . . . . . . . . .

43831 31 . . . . . . . . . . . . . . .

99913 . . . . . . . . . . . . . . . .

43951 32 . . . 9.70E-01 1.60E-01 4.30E-01 . . . 1.80E-01 1.40E-01 4.50E-01 . . .

43968 . . . . 3.60E-01 1.20E-01 4.30E-01 . . . -3.80E-01 1.60E-01 8.60E-01 . . .

44181 . . . . 3.40E-01 1.40E-01 4.40E-01 . . . -3.80E-01 1.60E-01 6.00E-01 . . .

44182 33 . . . 7.00E-01 1.40E-01 3.40E-01 . . . -3.10E-01 1.50E-01 5.60E-01 . . .

43845 34 . . . 2.10E-01 1.30E-01 4.60E-01 . . . -7.00E-02 1.60E-01 7.60E-01 . . .

43846 . . . . . . . . . . . . . . . .

44329 35 . . . 1.30E-01 1.10E-01 3.80E-01 . . . 3.00E-01 1.70E-01 5.30E-01 . . .

44330 . . . . 2.80E-01 1.90E-01 6.50E-01 . . . -4.60E-01 1.70E-01 9.40E-01 . . .

99914 36 . . . . . . . . . . . . . . .

44316 37 . . . . . . . . . . . . . . .

45125 38 . . . . . . . . . . . . . . .

44324 39 . . . . . . . . . . . . . . .

44967 40 . . . . . . . . . . . . . . .

44968 . . . . . . . . . . . . . . . .

45424 . . . . 1.83E+00 2.10E-01 4.70E-01 . . . 2.90E-01 1.60E-01 5.10E-01 . . .

45423 41 3.88E-01 1.10E-01 6.60E-02 9.20E-01 2.80E-01 8.90E-01 3.87E+00 2.80E-01 4.60E-02 5.10E-01 2.10E-01 8.90E-01 6.41E-02 3.20E-02 2.00E-02

45422 . . . . 3.36E+00 2.70E-01 4.00E-01 . . . 1.20E-01 1.70E-01 5.50E-01 . . .

45421 42 7.00E-01 1.40E-01 4.30E-02 3.82E+00 3.00E-01 4.80E-01 5.18E+00 3.20E-01 4.10E-02 -3.00E-02 1.60E-01 5.40E-01 6.25E-02 2.80E-02 9.40E-03

99905 43 . . . . . . . . . . . . . . .

45343 44 . . . . . . . . . . . . . . .

45648 45 . . . . . . . . . . . . . . .

43409 46 . . . . . . . . . . . . . . .

43369 47 . . . . . . . . . . . . . . .

43408 48 . . . . . . . . . . . . . . .

43544 49 . . . 2.30E-01 2.30E-01 8.10E-01 . . . 3.50E-01 2.00E-01 8.50E-01 . . .

99911 50 . . . . . . . . . . . . . . .

.. . . . . . . . . . . . . . . .

43370 51 . . . . . . . . . . . . . . .

44177 52 . . . . . . . . . . . . . . .

44178 . . . . . . . . . . . . . . . .

99912 . . . . . . . . . . . . . . . .

result MDC result MDC result MDC result MDC result MDC

Th230 (pCi/L) - USGS Th230 (pCi/L) - EPA

alpha spectroscopy alpha spectroscopy

Th228 (pCi/L) - USGS Th228 (pCi/L) - EPA

alpha spectroscopy alpha spectroscopy

USGS

serial

number 

Map

key

Th227 (pCi/L) - EPA

alpha spectroscopy

CSU2 CSU1 CSU2 CSU1 CSU2

1

One standard deviation

2

Two standard deviations based on counting error only
37

99910 53 . . . . . . . . . . . . . . .

45603 54 . . . . . . . . . . . . . . .

43949 . . . . . . . . . . . . . . . .

43950 55 . . . . . . . . . . . . . . .

43833 56 . . . 2.10E-01 2.90E-01 1.00E+00 . . . -1.50E-01 2.10E-01 1.00E+00 . . .

43546 57 . . . . . . . . . . . . . . .

43552 58 . . . . . . . . . . . . . . .

45428 59 . . . . . . . . . . . . . . .

43824 60 . . . . . . . . . . . . . . .

43467 61 . . . . . . . . . . . . . . .

47127 62 . . . 5.30E-02 6.10E-02 2.10E-01 . . . -1.07E-01 7.70E-02 2.70E-01 . . .

43472 63 . . . . . . . . . . . . . . .

99903 64 . . . . . . . . . . . . . . .

44084 65 . . . . . . . . . . . . . . .

44180 66 . . . . . . . . . . . . . . .

44085 . . . . . . . . . . . . . . . .

44086 67 . . . . . . . . . . . . . . .

45087 68 5.58E-02 4.50E-02 5.40E-02 1.80E-01 1.60E-01 5.50E-01 1.12E-01 4.40E-02 3.80E-02 1.80E-01 1.80E-01 5.70E-01 2.90E-02 2.20E-02 2.00E-02

45088 . 9.92E-02 5.50E-02 5.90E-02 1.30E-01 2.30E-01 7.90E-01 1.32E-01 4.60E-02 4.60E-02 1.40E-01 2.30E-01 7.70E-01 . . .

45089 69 3.97E-03 2.30E-02 5.20E-02 . . . 1.38E-01 4.50E-02 3.90E-02 . . . 2.17E-02 1.60E-02 9.30E-03

45090 . 9.97E-03 2.60E-02 5.30E-02 . . . 1.10E-01 4.40E-02 4.80E-02 . . . 3.00E-02 2.00E-02 1.60E-02

46849 70 . . . 1.49E-01 5.40E-02 1.60E-01 . . . 6.00E-02 7.20E-02 2.30E-01 . . .

46850 . . . . -1.10E-02 6.70E-02 2.40E-01 . . . -5.90E-02 6.30E-02 2.20E-01 . . .

43554 71 . . . . . . . . . . . . . . .

43622 . . . . . . . . . . . . . . . .

43623 72 . . . . . . . . . . . . . . .

45224 73 . . . . . . . . . . . . . . .

45223 74 . . . . . . . . . . . . . . .

45352 75 . . . . . . . . . . . . . . .

.. . . . . . . . . . . . . . . .

44966 76 . . . . . . . . . . . . . . .

.. . . . . . . . . . . . . . . .

43832 77 . . . . . . . . . . . . . . .

44176 78 . . . . . . . . . . . . . . .

44239 79 . . . . . . . . . . . . . . .

44969 80 1.27E+00 4.10E-01 2.40E-01 2.10E+01 9.40E-01 8.40E-01 2.06E+01 1.40E+00 2.10E-01 1.50E+01 7.20E-01 7.90E-01 1.62E+01 1.20E+00 1.10E-01

44970 . . . . 2.20E+01 1.10E+00 8.80E-01 . . . 1.51E+01 8.20E-01 6.80E-01 . . .

44971 . 1.34E+00 4.40E-01 2.30E-01 2.10E+01 1.00E+00 9.40E-01 2.19E+01 1.50E+00 2.20E-01 1.69E+01 8.70E-01 6.90E-01 1.71E+01 1.20E+00 1.20E-01

44972 . . . . 2.07E+01 9.10E-01 7.10E-01 . . . 1.59E+01 7.30E-01 4.60E-01 . . .

45220 81 1.20E-01 2.50E-01 4.60E-01 1.49E+00 2.00E-01 4.90E-01 1.31E+00 3.40E-01 3.00E-01 7.40E-01 1.90E-01 5.20E-01 1.06E+00 2.80E-01 1.20E-01

45221 . . . . 1.61E+00 1.70E-01 3.40E-01 . . . 1.02E+00 1.90E-01 5.00E-01 . . .

99902 82 . . . . . . . . . . . . . . .

45002 83 . . . . . . . . . . . . . . .

45052 . . . . . . . . . . . . . . . .

45051 84 . . . . . . . . . . . . . . .

43948 85 . . . . . . . . . . . . . . .

45086 . . . . . . . . . . . . .

44175 86 . . . . . . . . . . . . . . .

99901 87 . . . . . . . . . . . . . . .

45348 88 . . . . . . . . . . . . . . .

45349 . . . . . . . . . . . . . . . .

45351 89 . . . . . . . . . . . . . . .

45350 . . . . . . . . . . . . . . . .

43411 . . . . . . . . . . . . . . . .

44080 90 . . . 7.70E-01 1.60E-01 4.20E-01 . . . 3.60E-01 2.00E-01 6.10E-01 . . .

44078 91 . . . 4.80E-01 1.30E-01 3.70E-01 . . . 2.10E-01 1.70E-01 5.30E-01 . . .

43428 92 . . . 1.15E+00 2.50E-01 7.40E-01 . . . -2.00E-01 1.80E-01 9.00E-01 . . .

44079 . . . . 7.20E-01 1.90E-01 5.70E-01 . . . -1.90E-01 1.50E-01 5.50E-01 . . .

43477 93 . . . . . . . . . . . . . . .

43493 . . . . . . . . . . . . . . . .

43969 94 . . . . . . . . . . . . . . .

43914 95 . . . . . . . . . . . . . . .

43915 . . . . . . . . . . . . . . . .

43410 96 . . . . . . . . . . . . . . .

43371 97 . . . . . . . . . . . . . . .

43545 98 . . . 1.00E-02 1.80E-01 6.70E-01 . . . -8.00E-02 1.80E-01 8.70E-01 . . .

43474 99 . . .

...

...

1.40E-01 2.10E-01 7.60E-01 . . . 0.00E+00 1.90E-01 9.20E-01 . . .

result CSU2 MDC result CSU1 MDC result CSU2 MDC result CSU1 MDC result CSU2 MDC

Th230 (pCi/L) - USGS Th230 (pCi/L) - EPA

alpha spectroscopy alpha spectroscopy

Th228 (pCi/L) - USGS Th228 (pCi/L) - EPA

alpha spectroscopy alpha spectroscopy

USGS

serial

number 

Map

key

Th227 (pCi/L) - EPA

alpha spectroscopy

44322 2 . . . . . . . . . . . .

44323 . . . . . . . . . . . . .

1

One standard deviation

2

Two standard deviations based on counting error only
38

result CSU1 MDC result CSU2 MDC result CSU3 MDC result CSU3 MDC

44322 2 . . . . . . 4.52E-03 9.40E-03 2.04E-02 1.13E+00 5.40E-01 9.04E-01

44323 . . . . . . . . . . . . .

44320 . . . . . . . . . . . . .

44321 1 . . . . . . 6.61E-03 1.33E-02 1.79E-02 4.16E-01 3.11E-01 5.90E-01

43372 3 . . . . . . -4.71E-03 5.50E-03 4.95E-02 1.98E-01 3.70E-01 8.03E-01

45344 4 . . . . . . 2.46E-03 1.30E-02 3.88E-02 4.26E-01 3.60E-01 6.90E-01

45345 5 . . . . . . 4.86E-03 1.20E-02 2.91E-02 5.59E-01 4.60E-01 9.09E-01

.. . . . . . . . . . . . .

45429 6 . . . . . . 3.84E-01 1.10E-01 3.13E-02 4.14E-01 3.60E-01 7.03E-01

44087 7 . . . . . . 2.23E-02 1.80E-02 1.91E-02 4.46E-01 3.00E-01 5.70E-01

44088 . . . . . . . 1.77E-02 1.80E-02 1.20E-02 2.91E-01 2.90E-01 5.84E-01

44179 8 . . . . . . 6.27E-03 1.10E-02 2.21E-02 5.86E-01 3.00E-01 5.31E-01

44319 9 . . . . . . 1.03E-02 1.90E-02 3.64E-02 -3.75E-01 4.50E-01 1.03E+00

44328 10 . . . . . . 1.84E-02 2.10E-02 1.66E-02 4.28E-01 3.30E-01 6.30E-01

99904 11 . . . . . . 6.26E-02 3.60E-02 2.34E-02 4.75E-01 4.50E-01 9.14E-01

45219 12 . . . . . . 2.34E-02 1.90E-02 1.06E-02 3.95E-01 3.60E-01 7.09E-01

99909 13 . . . . . . 1.24E+00 2.49E-01 1.79E-02 4.14E+00 9.60E-01 6.13E-01

99906 14 . . . . . . 5.75E-01 1.22E-01 2.06E-02 1.75E+00 5.10E-01 5.94E-01

99907 15 . . . . . . 9.55E-01 1.66E-01 1.04E-02 2.60E+00 6.78E-01 6.41E-01

45222 16 . . . . . . 1.27E-01 4.50E-02 2.21E-02 2.13E+00 6.10E-01 6.73E-01

43553 17 . . . . . . 1.75E-02 1.60E-02 1.77E-02 2.71E-01 3.00E-01 6.11E-01

43468 18 . . . . . . 1.01E-02 1.50E-02 2.65E-02 2.72E-02 4.30E-01 1.01E+00

99908 19 . . . . . . 1.33E-02 1.80E-02 2.88E-02 5.98E-01 4.40E-01 8.45E-01

45066 20 . . . . . . 3.92E-03 7.90E-03 1.06E-02 1.35E+00 4.70E-01 6.50E-01

45426 . . . . . . . -1.37E-03 2.80E-03 3.28E-02 -7.70E-01 1.10E+00 2.53E+00

45425 21 . . . . . . 4.86E-03 1.20E-02 2.91E-02 7.95E-01 7.30E-01 1.48E+00

45065 22 . . . . . . 1.42E-03 7.50E-03 2.25E-02 1.49E-01 3.20E-01 6.69E-01

45085 23 . . . . . . 0.00E+00 1.10E-02 9.90E-03 5.85E-01 3.40E-01 6.11E-01

45083 . . . . . . . -4.04E-03 4.70E-03 4.25E-02 1.94E+00 8.40E-02 1.34E+00

45084 24 . . . . . . -7.92E-04 1.60E-03 1.90E-02 8.23E-01 4.00E-01 6.76E-01

43473 25 . . . . . . 2.78E-02 2.60E-02 2.77E-02 1.50E-01 3.50E-01 7.86E-01

47128 26 . . . . . . 1.66E-02 1.50E-02 8.96E-03 3.00E-01 3.20E-01 6.71E-01

47129 . . . . . . . . . . . . .

44325 27 . . . . . . 2.17E-02 2.73E-02 3.71E-02 6.08E-01 3.70E-01 6.77E-01

43368 28 . . . . . . 1.49E-02 1.60E-02 1.87E-02 3.74E-01 4.00E-01 8.31E-01

43475 29 . . . . . . 7.36E-02 4.00E-02 1.42E-02 -5.95E-02 3.10E-01 7.34E-01

43407 30 . . . . . . 1.08E-02 1.30E-02 1.84E-02 3.99E-01 4.40E-01 9.11E-01

43831 31 . . . . . . 1.60E-02 1.40E-02 8.63E-03 5.77E-01 3.10E-01 5.45E-01

99913 . . . . . . . 2.73E-02 2.10E-02 2.03E-02 6.02E-01 3.29E-01 5.90E-01

43951 32 2.50E-02 2.20E-02 7.50E-02 . . . 4.69E-03 9.40E-03 1.27E-02 2.75E-01 2.60E-01 5.30E-01

43968 . 5.10E-02 3.00E-02 4.60E-02 . . . . . . . . .

44181 . 2.00E-02 2.80E-02 1.10E-01 . . . . . . . . .

44182 33 5.50E-02 4.10E-02 1.40E-01 . . . 6.59E-03 1.20E-02 2.33E-02 5.31E-01 3.20E-01 5.96E-01

43845 34 -1.10E-02 4.80E-02 2.10E-01 . . . . . . . . .

43846 . . . . . . . 6.90E-03 1.80E-02 4.13E-02 1.67E-01 2.70E-01 5.80E-01

44329 35 8.00E-03 3.00E-02 1.30E-01 . . . 0.00E+00 1.96E-02 1.76E-02 4.03E-01 3.38E-01 6.56E-01

44330 . 4.00E-02 2.80E-02 5.40E-02 . . . 2.00E-02 2.00E-02 1.35E-02 1.90E-01 4.40E-01 9.72E-01

99914 36 . . . . . . -1.51E-03 3.00E-03 3.61E-02 6.01E-01 5.40E-01 1.03E+00

44316 37 . . . . . . 1.40E-02 1.30E-02 7.58E-03 -2.85E-01 6.00E-01 1.41E+00

45125 38 . . . . . . 4.23E-03 1.10E-02 2.53E-02 6.55E-01 3.70E-01 6.60E-01

44324 39 . . . . . . 9.21E-03 1.31E-02 1.25E-02 6.27E-01 3.62E-01 6.49E-01

44967 40 . . . . . . . . . . . .

44968 . . . . . . . 0.00E+00 3.20E-02 2.69E-02 4.45E-01 4.10E-01 8.16E-01

45424 . 2.50E-02 1.80E-02 3.40E-02 . . . . . . . . .

45423 41 0.00E+00 . 4.90E-02 1.92E-02 1.70E-02 1.20E-02 1.23E-02 1.70E-02 1.66E-02 2.76E-01 4.00E-01 8.63E-01

45422 . -4.70E-02 3.90E-02 1.90E-01 . . . . . . . . .

45421 42 -1.60E-02 2.80E-02 1.40E-01 6.24E-03 8.80E-03 9.40E-03 3.39E-02 2.50E-02 2.08E-02 4.88E-01 3.70E-01 7.00E-01

99905 43 . . . . . . 1.33E-02 1.50E-02 1.20E-02 2.65E-01 4.10E-01 8.77E-01

45343 44 . . . . . . 0.00E+00 2.00E-02 1.79E-02 2.98E-01 3.20E-01 6.48E-01

45648 45 . . . . . . 1.31E-02 1.90E-02 1.77E-02 9.44E-01 4.10E-01 6.65E-01

43409 46 . . . . . . 3.98E-03 8.00E-03 1.08E-02 7.00E-01 4.90E-01 9.34E-01

43369 47 . . . . . . 1.28E-02 1.50E-02 1.16E-02 4.38E-01 4.50E-01 9.30E-01

43408 48 . . . . . . 1.73E-02 2.20E-02 2.96E-02 1.95E-01 3.50E-01 7.75E-01

43544 49 6.60E-02 3.30E-02 4.40E-02 . . . 4.75E-02 2.60E-02 9.18E-03 4.96E-01 3.50E-01 6.71E-01

99911 50 . . . . . . 0.00E+00 1.80E-02 1.65E-02 -6.90E-04 5.37E-01 8.30E-01

.. . . . . . . . . . . . .

43370 51 . . . . . . . . . 5.09E-01 4.20E-01 8.30E-01

44177 52 . . . . . . 9.30E-02 3.80E-02 1.73E-02 6.30E-01 3.00E-01 5.02E-01

44178 . . . . . . . . . . . . .

Po210 (pCi/L) Pb210 (pCi/L)

alpha spectroscopy alpha spectroscopy alpha spectroscopy beta filtered

USGS

serial

number

Map

key

Th232 (pCi/L) - USGS Th232 (pCi/L) - EPA

1

One standard deviation

2

Two standard deviations based on counting error only

3

Two standard deviations
39

99912 . . . . . . . 1.10E-01 4.50E-02 2.03E-02 1.07E+00 4.00E-01 5.90E-01

99910 53 . . . . . . 2.16E-01 7.00E-02 2.73E-02 1.10E+00 5.30E-01 8.81E-01

45603 54 . . . . . . 8.27E-03 1.50E-02 2.92E-02 . . .

43949 . . . . . . . . . . . . .

43950 55 . . . . . . 1.24E-02 1.80E-02 1.68E-02 2.76E-01 2.60E-01 5.15E-01

43833 56 2.50E-02 2.50E-02 6.80E-02 . . . 1.89E-02 2.10E-02 2.97E-02 7.59E-01 3.30E-01 5.25E-01

43546 57 . . . . . . 1.49E-02 1.90E-02 2.54E-02 4.42E-01 3.20E-01 6.12E-01

43552 58 . . . . . . 6.22E-03 8.80E-03 8.42E-03 5.74E-01 3.10E-01 5.41E-01

45428 59 . . . . . . 0.00E+00 2.00E-02 1.77E-02 4.18E-01 3.50E-01 6.83E-01

43824 60 . . . . . . 0.00E+00 1.00E-02 9.34E-03 4.28E-01 2.90E-01 5.49E-01

43467 61 . . . . . . 0.00E+00 1.40E-02 3.47E-02 2.10E-01 3.40E-01 7.37E-01

47127 62 1.10E-02 1.10E-02 2.90E-02 . . . 3.05E-02 2.20E-02 1.87E-02 7.57E-01 3.80E-01 6.28E-01

43472 63 . . . . . . 8.25E-03 1.50E-02 2.91E-02 5.44E-01 4.00E-01 7.80E-01

99903 64 . . . . . . 2.92E-02 1.90E-02 1.42E-02 7.99E-01 5.30E-01 1.01E+00

44084 65 . . . . . . 9.95E-03 1.40E-02 1.35E-02 9.20E-01 3.70E-01 5.50E-01

44180 66 . . . . . . 1.06E-02 1.30E-02 1.82E-02 8.68E-01 3.40E-01 5.19E-01

44085 . . . . . . . . . . . . .

44086 67 . . . . . . 4.40E-03 8.80E-03 1.19E-02 5.30E-01 3.10E-01 5.62E-01

45087 68 8.80E-02 3.60E-02 4.00E-02 0.00E+00 1.10E-02 1.10E-02 2.70E-03 9.35E-03 2.54E-02 1.29E+00 4.58E-01 6.52E-01

45088 . -5.70E-02 4.90E-02 2.80E-01 . . . . . . . . .

45089 69 . . . 6.18E-03 1.10E-02 2.10E-02 0.00E+00 1.80E-02 1.64E-02 4.97E-01 3.60E-01 6.87E-01

45090 . . . . 2.07E-03 6.50E-03 1.60E-02 . . . . . .

46849 70 7.00E-04 2.30E-03 1.90E-02 . . . 9.70E-03 1.10E-02 8.70E-03 1.21E-01 2.84E-01 6.32E-01

46850 . 1.90E-03 8.20E-03 4.20E-02 . . . . . . . .

43554 71 . . . . . . 2.23E-03 7.70E-03 2.10E-02 6.47E-01 3.20E-01 5.48E-01

43622 . . . . . . . . . . . . .

43623 72 . . . . . . 9.62E-03 1.30E-02 2.09E-02 2.91E-01 3.40E-01 7.18E-01

45224 73 . . . . . . 7.75E-03 1.60E-02 3.49E-02 1.16E+00 4.30E-01 6.25E-01

45223 74 . . . . . . 1.68E-02 2.00E-02 1.52E-02 7.97E-01 3.60E-01 5.97E-01

45352 75 . . . . . . 8.06E-03 1.50E-02 2.84E-02 2.10E-02 3.90E-01 9.05E-01

.. . . . . . . . . . . .

44966 76 . . . . . . -9.32E-04 1.90E-03 2.23E-02 4.90E-01 3.50E-01 6.70E-01

.. . . . . . . . . . . .

43832 77 . . . . . . 5.11E-02 3.40E-02 2.49E-02 1.03E+00 3.80E-01 5.61E-01

44176 78 . . . . . . 1.90E-02 1.90E-02 1.28E-02 4.79E-01 3.00E-01 5.65E-01

44239 79 . . . . . . 6.53E-02 3.70E-02 1.36E-02 7.29E-01 3.50E-01 5.94E-01

44969 80 . . . 1.62E+01 1.20E+00 4.70E-02 . . . . . .

44970 . 1.58E+01 8.20E-01 1.80E-01 . . . . . . . . .

44971 . 1.77E+01 8.80E-01 5.50E-02 1.51E+01 1.20E+00 5.10E-02 . . . . . .

44972 . 1.65E+01 7.40E-01 1.20E-01 . . . . . . . . .

45220 81 8.70E-01 1.20E-01 1.20E-01 1.08E+00 2.80E-01 1.10E-01 4.79E-02 3.40E-02 1.62E-02 5.43E-01 3.90E-01 7.45E-01

45221 . 1.16E+00 1.20E-01 1.10E-01 . . . . . . . . .

99902 82 . . . . . . 2.22E-02 1.80E-02 1.56E-02 5.00E-01 5.13E-01 9.70E-01

45002 83 . . . . . . 1.66E-02 1.60E-02 2.04E-02 5.60E-01 3.70E-01 6.94E-01

45052 . . . . . . . . . . . . .

45051 84 . . . . . . 4.99E-02 2.70E-02 9.64E-03 5.53E-01 3.70E-01 7.02E-01

43948 85 . . . . . . 3.07E-03 7.80E-03 1.84E-02 4.69E-01 3.00E-01 5.66E-01

45086 . . . . . . . . . . . . .

44175 86 . . . . . . 3.13E-03 6.30E-03 8.48E-03 2.74E-01 2.90E-01 6.01E-01

99901 87 . . . . . . 2.37E-02 1.90E-02 2.03E-02 8.13E-01 5.83E-01 5.80E-01

45348 88 . . . . . . 8.44E-03 1.20E-02 1.14E-02 7.84E-01 4.70E-01 8.61E-01

45349 . . . . . . . 3.60E-03 1.20E-02 3.39E-02 6.43E-01 3.70E-01 6.66E-01

45351 89 . . . . . . 1.59E-02 1.60E-02 1.08E-02 5.72E-01 4.00E-01 7.42E-01

45350 . . . . . . . . . . . . .

43411 . . . . . . . . . . 1.80E-01 4.00E-01 8.83E-01

44080 90 7.00E-03 3.00E-02 1.40E-01 . . . 6.38E-02 3.60E-02 2.21E-02 8.15E-01 3.40E-01 5.48E-01

44078 91 1.30E-02 3.80E-02 1.50E-01 . . . 5.03E-03 1.00E-02 1.36E-02 4.19E-01 3.00E-01 5.79E-01

43428 92 9.50E-02 4.30E-02 5.10E-02 . . . . . . . . .

44079 . 1.50E-02 1.50E-02 4.10E-02 . . . -1.84E-03 2.60E-03 2.60E-02 5.41E-01 2.90E-01 5.19E-01

43477 93 . . . . . . 9.57E-02 3.90E-02 1.71E-02 7.14E-01 4.20E-01 7.73E-01

43493 . . . . . . . . . . . . .

43969 94 . . . . . . 4.85E+00 6.10E-01 1.53E-02 2.39E-01 2.90E-01 6.10E-01

43914 95 . . . . . . 5.61E-03 8.00E-03 7.59E-03 4.33E-01 3.10E-01 6.03E-01

43915 . . . . . . . . . . . . .

43410 96 . . . . . . 1.96E-03 6.80E-03 1.85E-02 1.79E-01 3.80E-01 8.46E-01

43371 97 . . . . . . . . . 8.79E-01 4.50E-01 7.65E-01

43545 98 3.70E-02 2.60E-02 5.00E-02 . . . 2.78E-03 7.10E-03 1.66E-02 6.34E-01 3.00E-01 5.04E-01

43474 99 1.90E-02 1.90E-02 5.20E-02 . . . 1.33E-02 1.40E-02 1.68E-02 3.34E-01 3.70E-01 7.76E-01

result CSU1 MDC result CSU2 MDC result CSU3 MDC result CSU3 MDC

Po210 (pCi/L) Pb210 (pCi/L)

alpha spectroscopy alpha spectroscopy alpha spectroscopy beta filtered

USGS

serial

number

Map

key

Th232 (pCi/L) - USGS Th232 (pCi/L) - EPA

1

One standard deviation

2

Two standard deviations based on counting error only

3

Two standard deviations
40