Prepared for:
                     Office of Ground Water and Drinking Water
                       U.S. Environmental Protection Agency
                               401 M. Street, SW
                             Washington, DC 20460
       Prepared by •
                                ICF Consulting
                               9300 Lee Highway
                               Fairfax, VA 22031
                          EPA Contract No. 68-C7-0005
                             Work Assignment 1-03

                                 August 6,1999

This document was prepared for the Office of Ground Water and Drmking Water
(OGWDW) of the Umted States Environmental Protection Agency with substantial input from other
EPA offices. The authors of the document express their thanks to Peter Lassovszky, Ben Smith and
Andrew Schulmann of OGWDW, and Timothy Barry of the Office of Policy, Planmng and
Evaluation, EPA, for the advice and comments. Professor H. Christopher Frey of North Carolma
State Umversity, Department of Civil Engineering and Zoltan Szabo of the United States geologic
Survey served as peer reviewers. William Labiosa of OGWDW was the principal author of Chapter 2
of this document.
The authors also express their thanks to the Association of State Drinking Water
Administrators (ASDWA) for their Assistence in identifying and gathermg data related to radon
occurrence, the Radon Techmcal Work Group of the American Water Works Association (AWWA)
for constructive comments on early drafts, and to all the individuals and orgamzations noted in this
document who provided data for the analysis.
Methods, Occurrence and Monitoring Document for Radon

11 Purpose of This Document 1-I
1.2 Statutory Requirements 1-1
2 1 Introduction 21
2.1 Inventory of Methods 2-2
2.1.1 Liquid Scintillation Counting 2-2
2.1.2 The Lucas Cell Techmque 2-4
2.2 Major Analytical Methods 2-4
2.2.1 Liquid Scintillation Counting and Lucas Cell Methods 2-4
2.2.2 Standard Method 7500: Radon Liquid Scintillation Counting 2-6
2.3 Other Radon Measurement Techniques 2-8
2 3.1 Delay-Coincidence Liquid Scintillation Counting System 2-8
2.3.2 Activated Charcoal Passive Radon Collector 2-9
2 3.3 Degassing Lucas Cell 2-11
2.3 4 Electret Ionization Chamber System . .. 2-12
2 4 Performance Capabilities of the Methods 2-14
2.5 Skill Requirements 2-15
2.6 Practical Availability of Methods 2-16
2.7 Anticipated Unit Costs 2-19
2 8 Practical Performance and Analytical Uncertainties 2-20
2.9 Degree To Which Each Method Meets EPA’s Regulatory Needs 2-22
2.10 References 2-22
3 1 Natural Sources of Radon Groundwater Contamination 3-1
3.1.1 Release and Transport Properties of Radon and Radium 3-2
3.1.2 Factors Affecting Distribution of Radon in Groundwater 3-2
3.1 3 Large-Scale Geographic Patterns of Radon Occurrence in Groundwater . 3-3
3.2 Anthropogenic Sources of Radon Contammation in Groundwater 3-4
3.3 Distribution System Sources 34
3.3.1 Radon Sources in Distribution Systems . . . 3-4
3.3.2 Radon Sources in Households 3.4
3.4 Non-Water Supply Sources of Radon Exposures 3-5
3 5 References 3-5
Methods, Occurrence, and Monitoring Document for Radon 11

4.1 Physical and Chemical Properties of Radon and Progeny 4-1
4 2 Relationship of Fate and Transport Properties to Human Exposures and Intake
4 3. Exposures to Radon in Indoor Air After Release Durmg Domestic Water Use
4.4 Relationship of Fate and Transport Properties to Radon Behavior m Treatment
and Distribution Systems .. . . 4-2
4.4.1 Aeration Technologies 4-3
4.4.2 Granular Activated Carbon Treatment 4-3
4.4.3 Radon Release from Pipe Scale . . . 4-3
4.5 References 4-5
5.1 Data Availability and Quality 5-1
5.1.1 Previous EPA Data Gathering Efforts Related to Radon Occurrence in
Groundwater Supplies 5-1
5.1.2 Data Gathermg Efforts m Support of the Revised Occurrence
Analysis 5-7
5.1.3 Results of the Data Gathering Effort 5-7
5.2 Methods Used in the Data Analysis .. .. 5-13
5.2.1 Statistical Analysis of Radon Distributions 5-13
5 2.2 Distribution Fitting and Goodness-of-Fit Testing ... 5-18
5.2.3 Hypothesis Testing for Differences in Radon Activity Levels
and Distributions 5-20
5.2.5 Computing Methods 5-22
5.3 Analysis of Radon Occurrence Data Approach to Stratification 5-22
5.3 1 Stratification by System Size ... 5-23
5 3 2 Alternative Stratification Vanables ... 5-23
5 4 Distribution of Radon Level in the MRS Database. 5-24
5.4.1 Distribution of Radon m Nationally Aggregated NIRS Data 5-25
5.4.2 Distributions of Radon in Regionally Stratified MRS Data 5-28
5.4.3 Goodness of Fit Testing of Lognormal and Alternative Distributions of
NIRS Data 5-30
5.5 The Distribution of Radon in the Supplementary Data Sets . 5-32
5.5.1 Distributions of Radon in Supplemental Data Sets 5-35
5.5.2 Radon Summary Statistics from Supplementary Data Sets 5-37
5.6 Comparison of NIRS and Supplemental Data Sets ... 5-42
5.6.1 Comparison of Log Mean Radon Levels Between NIRS and Supplemental
Data Sets . . . . . . . 5-43
5.6.2 Comparison of Log Standard Deviations . 5-45
5.7 Sources and Magnitude of Variability in Groundwater Radon Levels 5-46
5 7.1 Identification of Sources of Variability in Radon Levels 5-47
Methods, Occurrence, and Monitoring Document for Radon iii.

5.7.2 Estimating Contributions to Variability . 5-47
5.7.3 Magnitude of Contributions to Radon Variability 5-48
5.8 Estimates of Numbers of Groundwater Systems Exceedmg Potential Regulatory
5.8.1 Characterizing Radon Distributions for States and Regions 5-49
5 8.3 Numbers of Community Water Systems in the U.S 5-59
5.8.4 Numbers of Community Water Systems Exceeding Potential Regulatory
Levels 5-60
5.8.5 Comparison of Predicted Exceedences For States and Regions 5-62
5.8.6 Estimates of Non-Transient Non-Community Systems Exceedmg Potential
Regulatory Levels 5-63
5.8.7 Sensitivity Analysis of Estimates of Systems Exceeding Radon Levels . 5-65
5 9 Comparison of Current Estimates of Radon Exceedences to Previous EPA
Occurrence Analyses 5-70
5 10. References 5-72
6.1 Data Sources 6-1
6.2 Populations Above Regulatory Levels 6-1
6.3 Special Populations 6-2
7.1 Data Sources 71
7.2 Co-Occurrence of Radon With Other Contammants 7-1
7.2 Implications of Co-Occurrence .... . 7-2
7.3 References
8.1 Background 8-1
8.2 Objectives of Monitoring Program 8-1
8 3 Description of Proposed Monitoring Requirements 8-2
8.4 Costs and Effectiveness of the Proposed Monitoring Requirements 8-8
8 4.1 Incremental Skills/Equipment Requirements and Cost of
Radon Monitoring 8-8
8.5 References 8-8
A. I Data Management and Manipulation A-i
A.2 Supplemental Data Sets A-6
Methods, Occurrence, and Monitoring Document for Radon iv

B.1 MLE Approach to Estimating Summary Statistics for Radon Data Sets. . . B-i
B.2 Calculation of Proportions of Systems Above Radon Levels and Confidence Limits on
Proportions (Distributional Approach) .. B-3
B 3 Estimation of Confidence Intervals (Distribution-Free Method) B-6
C. 1 A Variance Apportionment (ANOVA) Model For Evaluating Radon
Data Sets . . . . C-i
C.i.l Identification of Sources of Radon Variance C-2
C. 1.2 Estimating Contributions to Variance C-3
C.2. Analytical Variance C-4
C.3 Combined Sampling and Analytical Variance C-6
C.4 Combined Sampling, Analytical and Temporal Variance .. . C-8
C.5 Combined Sampling, Analytical, and Between-Well Variance C-i 1
C.6 Combined Sampling, Analytical, Temporal, and Intra-System Variance ... C-12
C 7 Vanance from All Sources C-13
C.8 Estimates of Vanance Contributions C-15
C 9 References C- 17
AND SIZE . . D-1
D 1. Proportions of Systems Exceeding Potential Radon Regulatory Levels in
the Eight NIRS regions . . D-2
D 2 Proportions of Systems Exceeding Potential Radon Regulatory Levels in
Seven States With Supplemental Data D- 12
E I Number of Non-Transient Non-Community Systems in the U.S ... ... E-1
E 2. Distribution of Radon Levels in Non-Community Non-Transient Systems E- 1
E.3 Estimation of Radon Distributions in Non-Transient Non-Community Systems of
Different Sizes E-4
E 4. Estimated Numbers and Proportions of Non-Transient Non-Community Systems
Exceeding Potential Regulatory Levels E-6
Methods, Occurrence, and Monitoring Document for Radon v

1.1 Purpose of This Document
This Methods, Occurrence, and Monitoring (MOM) Document has been developed by
EPA in support of the rulemaking process for radon in drinking water The Agency is proposmg a
Maximum Contammant Level Goal (MCLG) and National Primary Drinking Water Regulations
(NPDWR) for radon-222 in public water supplies (EPA, 1 999a). The purposes of this document
• Identification of available analytical methods for monitoring radon in groundwater sources
and in drinking water,
• Discussion of the patterns of occurrence of radon in groundwater and drinking water, and
• Explanation of alternative monitoring schemes for assuring compliance with the proposed
1.2 Statutory Requirements
The 1996 Amendments to the Safe Drmlung Water Act (PL 104-182) establish a new
charter for public water systems, states, tnbes, and EPA to protect the safety of drinking water
supplies. Among other mandates, Congress amended Section 1412 to direct EPA to take the
following actions regarding radon in drmkmg water.
Withdraw the 1991 Proposed Regulation for Radon
Congress specified that EPA should withdraw the drinking water standards proposed for
radon in 1991.
Arrange for a National Academy of Sciences Risk Assessment.
The amendments in § 1412(b)(13)(B) require EPA to arrange for the National Academy
of Sciences (NAS) to conduct an independent risk assessment for radon in drinking water and an
assessment of the health nsk reduction benefits from various mitigation measures to reduce radon
in indoor air.
Set an MCLG, MCL, and BA Tfor Radon-222
Congress specified in § 1412 (b)(3)(C) that EPA should propose a new MCLG and
NPDWR (an MCL, BAT, and monitoring, reporting, and public notification requirements) for
radon-222 by August, 1999. EPA is also required to finalize the regulation by August, 2000. As
a preliminary step, EPA was required to publish a radon health risk reduction and cost analysis
Methods, Occurrence and Monitoring Document for Radon 1-1

(HRRCA) for possible radon MCLs for public comment by February, 1999. This analysis must
consider seven topics: (1) health risk reduction benefits that come directly from controllmg radon;
(2) health risk reduction benefits likely to come from reductions in contaminants that occur with
radon; (3) costs, (4) incremental costs and benefits associated with each MCL considered; (5)
effects on the general population and on groups within the general population likely to be at
greater risk; (6) any increased health risk that may occur as the result of compliance; and (7) other
relevant factors, including the quality and extent of the information, the uncertainties in the
analysis, and factors with respect to the degree and nature of the risk.
Set an Alternative MCL (AMCL) and Develop Multimedia Mitigation (MMM)
Program Guidelines
The amendments in § 14l2(b)(13)(F) introduce two new elements into the radon in
drrnkmg water ruleS (1) an Alternative Maximum Contaminant Level (AMCL) and (2) radon
multimedia mitigation (MIvIM) programs. If the MCL established for radon m dnnking water is
more stringent than necessary to reduce the contribution to radon in indoor air from drinking
water to a concentration that is equivalent to the national average concentration of radon in
outdoor air, EPA is required to simultaneously establish an AMCL. The AMCL would be the
standard that would result in a contribution of radon from drinking water to radon levels in
indoor air equivalent to the national average concentration of radon in outdoor air. If an AMCL
is established, EPA is to publish guidelines for state multimedia mitigation (MMM) programs to
reduce radon levels in mdoor air. Section V describes what a state or public water system must
have m their multimedia mitigation program
Evaluate Multimedia Mitigation Programs Every Five Years
Once the MMM programs are established, EPA must re-evaluate them no less than every
five years. [ 141 2(b)( 13)] EPA may withdraw approval of programs that are not expected to
meet the requirement of achieving equal or greater nsk reduction.
DevelopMonitoring Requirements and Characterize Containin ant Occurrence
Under every SDWA rule, EPA is required to develop monitoring requirements to assure
compliance with the rule. Water systems are responsible for conducting monitoring of drinking
water to ensure that it meets all drinking water standards. To do this, water systems and states
use analytical methods developed by government agencies, umversities, and other organizations.
EPA is responsible for evaluating analytical methods developed for drinking water and
approves those methods that it determines meet Agency requirements Laboratories analyzing
drinking water compliance samples must be certified by the EPA or the state. Chapter 2 of this
document reviews the available analytical methods for radon in drinking water and their
performance and costs.
Methods, Occurrence and Monitoring Document for Radon 1-2

EPA must also characterize the sources of drinking water contaminants, their fate and
transport properties, and how they relate to potential exposures. Available data related to the
occurrence of contammants must be evaluated, and the patterns of occurrence across different
regions of the country, different types of water systems (community and non-community) and m
water systems of different sizes, must also be evaluated m order to develop a national picture of
the distribution of contaminants. The degree to which the occurrence of the contaminant is
correlated with that of other contaminants must also be evaluated. Chapters 3 through 7 of this
document address these issues.
Whether addressing a regulated or unregulated contaminants, EPA establishes
requirements as to how often water systems must momtor for the presence of the subject
contammant Water systems servmg larger populations generally must conduct more momtormg
(temporally and spatially) because there is a greater potential human health impact of any
violation, and because of the physical extent of larger water systems (e.g., miles of pipeline
carrying water). Small water systems can receive variances or exemptions from momtormg in
limited circumstances. In addition, under certain conditions, a state may have the option to
modify monitoring requirements on an interim or a permanent basis for regulated contammants,
with a few exceptions. Chapter 8 of this document discusses monitoring strategies for
determining compliance with the proposed nile.
Methods, Occurrence and Monitoring Document for Radon 1-3

2.1 Introduction
This chapter addresses the analytical methods that may be applicable to the measurement
of radon m drinking water samples. It does not recommend a specific method for radon analyses,
but rather, identifies possible candidate techmques and evaluates the extent to which the
performance of those techniques has been demonstrated
As part of its overall responsibility for regulating the nation’s drinking water supplies, in
1991 EPA proposed regulations on various radionuclides under 40 CFR Parts 141 and 142 (July
18, 1991, FR 56 [ 138]: 33050-33 127). Although eventually withdrawn, part of that proposal
addressed the regulation of radon ( 222 Rn or radon-222). Among other topics, the proposal
discussed methods for the analysis of radon m drinking water.
As EPA prepares to propose new regulations for radon in drinking water, the Agency has
reviewed and updated the information on the analytical techniques that appeared in the 1991
proposal (EPA 1991). Specifically, in 1998, at EPA’s direction, SAIC reviewed the mformation in
the 1991 proposal and also conducted an electronic literature search to identify additional
analytical techniques that might be used to measure the concentration of radon m drmkrng water
The focus of the 1998 effort was to determme if new momtoring techmques had become available
since the 1991 proposal. The techniques identified by that search were further evaluated to
determine their performance capabilities and possible costs. The remamder of this chapter
addresses the followmg aspects of the techniques:
• Inventory of methods
• Performance capabilities of the methods
• Skill requirements
• Practical availability of methods
• Anticipated unit costs
• Practical performance and analytical uncertainties
• Degree to which each method meets EPA ’s regulatory needs
This last section summarizes the results of the review of the analytical techniques relative to
EPA’s need for a method for a nationwide compliance monitoring program. The focus of this
section is on techniques for the analysis of radon in drmkmg water, and as such, does not attempt
to review information relevant to the analysis of other environmental matrices
Methods, Occurrence, and Monitoring Document for Radon 2-1

2.1 Inventory of Methods
The 1991 EPA proposal focused on two techniques for the analysis of radon in drinking
water. liquid scintillation counting and the Lucas cell. The 1991 discussion of these techniques is
summarized m Sections 2.1.1 and 2.1.2, below.
Five newer techniques, or combinations of techniques, were identified in an electromc
search of the open literature. Because EPA had reviewed older analytical techniques prior to
proposing the radionuclides rule in 1991, the search was constrained to identify publications that
have appeared since 1990, m an effort to identify newer techniques that may not have been
considered in conjunction with the 1991 proposed rule on radionuclides. The discussion of the
five newer techniques is presented in Sections 2.3.1 to 2.3 5.
2.1.1 Liquid Scintillation Counting
Radon is an alpha-emitting radionuclide and is just one of 14 radionuclides in what is
known as the “uranium series,” the term used to describe the chain of 15 elements that begins with
238w and ends with 206 Pb, a stable (non-radioactive) element 222 Rri is the seventh element in the
series, created as a decay product of 226 Ra. Radon undergoes radioactive decay itself, formmg
218 Po through the loss of an alpha particle. Polonium decays through the emission of a beta
particle to form 214 Pb. The portion of the decay series from radon onward is illustrated in the
Exhibit 2-1, and includes the manner of the decay (alpha or beta particle) and the half-life of each
Exhibit 2-1. Radon Decay Series
Decay Emission
222 pm
3.8 days
218 Po
3 minutes
214 pb
27 minutes
2 14 Bi
20 minutes
214 Po
1.6 xlO seconds
2 °Pb
22.3 years
210 B i
5 days
210 Po
138 days
206 pb
Methods, Occurrence, and Monitoring Document for Radon 2-2

Radon’s alpha particle emissions can be used as the basis for measuring radon m a variety
of environmental media The principal technique for radon analysis considered by EPA m the
1991 proposal was liquid scintillation counting.
Scintillation counting refers to the measurement of the light emitted when an alpha particle
from the sample strikes some form of scmtillating material. The two most common forms of
scintillators are the scintillation disk, with is a planchet or metal disk coated with zinc sulfide, and
a liquid scintillation fluid or an organic phosphor. The light emitted from the scintillator strikes
the surface of a photomultiplier tube that is placed next to the sample m a light-proof container,
releasing electrons from the photocathode in the tube at levels proportional to the intensity of the
emitted light. The electrical pulses that result are counted to determine the number of
disintegrations per minute (dpm) that occur, which can be related to the concentration of a given
In liquid scintillation counting, a volume of sample is mixed with the organic phosphor
contained in a mineral oil solution or “cocktail” in a glass container which is then placed in the
instrument, where it is held against the photomultiplier for counting.
As noted in the 1991 proposal, radon can be measured through a direct, low-volume liquid
scintillation technique m which approximately 10 ml of water is added to a vial with the
scintillation cocktail, mixed, and placed in a liquid scintillation counter. The sample can be left in
the counter for periods ranging from several minutes to several hours, depending on the level of
radon m the sample.
The energy of the alpha particles released by radioactive decay is characteristic of the
radionuclide. In the case of liquid scintillation counting techniques, the counting apparatus can be
configured to measure the scintillations is narrow energy ranges across the emission spectrum In
the case of radon analyses the counter can set to look in the portion of the energy spectrum that
represents the alpha particles emitted by 222 Rn and as well as 2 i$p 0 and 2 14 Po, the next two alpha-
emitting daughters in the series. Given the short half-lives of these two daughters, their alpha
particle emissions can be measured along with that of the radon itself in less than an hour of
counting time. From a practical standpoint, the emissions of three alpha particles can be
measured and related back to one radon atom, thereby amplifying the signal from that smgle
radon atom’s decay.
It is important to distinguish between an analytical technique and a specific analytical
method. Liquid scintillation counting is a technique EPA’s 1991 proposal stated that the Agency
planned to establish a specific analytical method, EPA Method 913, based on the liquid
scintillation technique.
Methods, Occurrence, and Monitoring Document for Radon 2-3

2.1.2 The Lucas Cell Technique
The second technique that EPA considered m the 1991 proposal mvolved the Lucas cell, a
specially constructed 100- to 125-mi metal cup coated on the inside with zinc sulfide (a
scintillator) and fitted with a transparent window The Lucas cell replaces the scintillation disk or
planchet in the counting instrument. The analysis of radon in a water sample is accomplished by
purging a volume of the sample with radon-free helium or “aged” air (air in which the radon has
already decayed). The purge gas removes the dissolved radon from the sample and carries it into
a Lucas cell that has been evacuated of any air. After an equilibration period of three to four
hours, the Lucas cell is placed m the counter and the scintillations resulting from the alpha
particles striking the zinc sulfide are counted through the transparent window.
The Lucas cell technique is a modification of other scmtillation counting techniques and
was considered by EPA because it can permit the measurement of lower levels of radon than m
the liquid scintillation techmque. However, the Agency noted that the method is more difficult to
use than the liquid scintillation method, in particular, requiring specialized glassware and greater
skill on the part of the analyst It was the Agency’s intent to include procedures for the Lucas cell
technique in Method 913, as an adjunct to the liquid scintillation procedures.
2.2 Major Analytical Methods
2.2.1 Liquid Scintillation Counting and Lucas Cell Methods
Subsequent to the 1991 proposal, EPA published a report on its method validation efforts
in fiscal year 1992 (Pia and Hahn 1992). That report described the results of collaborative
studies for the analysis of radon m drmkmg water and provided performance data on both the
direct low-volume liquid scintillation technique and the Lucas cell technique that the Agency
planned to incorporate into Method 913
The 1992 study evaluated both the liquid scintillation technique and the Lucas cell
technique for the analysis of performance evaluation samples spiked with radon at levels of 111
and 153 picoCuries per liter (pCifL).’ The 1992 study also investigated two means of spikmg the
samples. The first sample was spiked with radium ( 226 Ra), which produces radon as a decay
product. The second sample was produced using a “radon generator” in which 226 Ra was bound
to a strong cation exchange resin. The decay of the radium released radon into the water, while
the remaining radium was still bound to the resin and therefore not present in dissolved form in
The Curie is a measure of a quantity of radioactive matenal. Specifically, a Curie is
defined as the quantity of a radioactive nuclide which produces 3.7 x iO’° atomic disintegrations
per second. The prefix “pico” stands for one trillionth (1Q 12), thus, a picoCurie would be 3.7xl0 2
atomic disintegrations per second.
Methods, Occurrence, and Monitoring Document for Radon 2-4

the sample. The data from the 1992 study are summarized Exhibit 2-2, for both techniques, both
radon concentrations, and both sources of radon.
Exhibit 2-2. Summary of EPA 1992 Collaborative Study Data
Mean Conc.
Recovery (%)
within Lab
% Bias
I LSC Ra = Liquid scintillation counting of samples spiked with 226 Ra
LSC Rn Liquid scintillation counting of samples spiked with radon generator
LC Ra = Lucas cell counting of samples spiked with 226 Ra
LC Rn = Lucas cell counting of samples spiked with radon generator
Another important aspect of the EPA 1992 collaborative study were the fmdings with
regard to sampling, sample containers, and sample handling EPA conducted smgle-laboratory
studies that were designed to evaluate factors related to sampling methods for proficiency testing
of radon laboratories. Such performance evaluation (PE) samples have been used as an important
aspect of EPA’s certification program for laboratories performing analyses under the Safe
Drinking Water Act monitormg programs. The 1992 report describes studies of four sample
collection techniques (displacement, immersion, catch, and grab sampling) EPA also evaluated
the effectiveness of two types of scintillation vial cap materials (polypropylene and PTFE-hned
caps) at maintaining the integrity of the samples. The effects of headspace or bubbles in the
sample containers were also evaluated.
The analysis of sampling techniques found that the four techniques were statistically
equivalent, in that no systematic error was introduced into the results by any of the four
techniques. The report stated that displacement sampling and immersion sampling were the most
conservative sampling approaches, requiring only that the flow of water from which the sample is
collected not be aerated or turbulent.
With regard to the vial cap materials, EPA found that as much as 10-15% of the radon in
the sample may be lost by its sorption into the polypropylene cap itself. The loss appeared to
Methods, Occurrence, and Monitoring Document for Radon 2-5

occur within the first four hours after the sample was collected. Caps equipped with PTFE liners
did not show this loss of radon over time.
As with volatile organic constituents, radon in water samples may be lost into the
headspace of the sample container. Although careful sampling techniques should result in the
sample container being filled to the top and sealed with no headspace, changes in sample
temperature will affect the solubility of all gases dissolved in the sample, including air and radon.
As the temperature of the sample in the sealed container increases, the solubility of all gases will
decrease and they may come out of solution, formmg bubbles at the top of the container. It is not
uncommon to observe air bubbles in a container that form as a result of such a temperature
increase. Given the typical levels of radon in water, it is highly unlikely that a visible bubble of
pure radon would form However, the concentration of air is much higher and if radon is present
in the sample, then the radon can partition into the headspace created by a bubble of air and the
radon in the headspace would be lost from the sample when the container is opened.
EPA compared the radon concentrations measured m samples containing six air bubble
volumes ranging from 0 - 5 ml in 63-mi sample bottles. The results of this study indicate that for
bubbles up to 0.25 ml in volume, there was no significant loss of radon from solution. At a bubble
volume of 0.5 ml, the loss of radon was 12%, with even larger losses for larger bubbles. Based
on the soiubihty of air at 20°C and 24°C, EPA concluded that the headspace resulting from the
formation of air bubbles as the sample warmed did not present a problem with respect to the loss
of radon from the sample.
In the 1992 report, Pia and Hahn noted that there was a relatively large positive bias for
the Lucas cell technique when using the radon generator approach (13 7 and 14.5% for the 111
pCiIL and 153 pCilL sample, respectively) They attributed this bias to a problems with
transferrmg the radon standard supplied by EPA and calibration of the instrument in the Lucas cell
procedure. They indicated that the systematic error could be addressed by standardizing the
technique used to transfer the sample and the radon standard, and that this issue would be
addressed in EPA Method 913.
2.2.2 Standard Method 7500: Radon Liquid Scintillation Counting
This method is published in Standard Methods for the Examination of Waler and
Wastewater, (APHA 1996). The method is specific for 222 Rn in drinking water supplies from
groundwater and surface water sources. This method grew out of EPA efforts in connection
with the 1991 radionuclides proposal. In that proposed rule, EPA discussed the development of
EPA Method 913, a liquid scintillation technique for radon analysis. Subsequent to the 1991
radionuclides proposal, EPA submitted the draft procedure to APHA and it was published in
Standard Methods as SM 7500-Rn. Having been published by a consensus organization (APHA),
there was no need for EPA to pursue the promulgation of a separate EPA method.
Methods, Occurrence, and Monitoring Document for Radon 2-6

In Standard Method 7500-Rn, the radon is partitioned selectively mto a mineral-oil
scintillation cocktail that is immiscible with the water sample. The sample is held in the dark for
three hours. This “dark adaptation” serves two purposes. First, exposure to light can cause the
cocktail to scintillate and this period m the dark allows this light-induced scintillation to dissipate
before sample analysis, thereby reducing the background count. Secondly, the decay of the radon
creates a number of short-lived daughter products. Compared to the half-lives of its daughter
products, the half-life of radon is relatively long, 3 8 days (see the table in Section 2.1). Thus,
durmg this equilibration period, the alpha emissions due to the daughter products 218 Po and 214 Po
become equal to that of the radon itself and the signal from the radon is essentially amplified by a
factor of three. After the equilibration penod, the alpha particle emissions from the sample are
counted in a liquid scmtillation counter using a region or window of the energy spectrum optimal
for the alpha particles from the three radionuclides. The results are reported in units of pCifL.
The diffusion of radon is affected by temperature and pressure. Therefore, it is important to
allow the samples to equilibrate to room temperature before processing
The precision of the method is affected by the background signal in the counting window
used for analysis A procedure is provided for selection of the analytical wmdow to minimize the
background contribution to the measurement. An important aspect of SM 7500-Rn is that it does
not include any mention of the Lucas cell technique that EPA had planned to include in EPA
Method 913.
The performance data in SM 7500-Rn shown in Exhibit 2-3 were incorporated from the
1992 EPA collaborative study cited earlier, which mcluded 36 participants. However, the EPA
1992 study data were incorporated without differentiation between the liquid scintillation
counting and Lucas cell techniques, even though, as previously noted, SM 7500-Rn does not ever
mention the use of the Lucas cell.
Exhibit 2-3. Standard Method 7500-Rn Performance Data
Sample Cone.
The significance of the inclusion of the Lucas cell data is probably not great As can be
seen by comparing the data above with that in Exhibit 2-2, the accuracy data reported by EPA
differ only by one percent between the two techniques. At each sample concentration, the
reported precision within a laboratory (repeatability in the table above) is the same for both
techniques and differs by only 1 pCiJL between the two radon activity levels. The most notable
differences are in the reproducibility figures, where the lower value in the 16 - 18 pCilL range,
and the higher value in the 2.3 - 3 4% bias range both come from the Lucas cell techrnque.
Methods, Occurrence, and Monitoring Document for Radon 2-7

SM 7500-Rn incorporates other important mformation from the EPA studies as well. For
example, the method specifies the use of glass sample containers or glass scintillation vials with
PTFE- or foil-lined caps, avoiding the problems associated with the loss of radon into the polymer
caps. The method describes the sample collection and employs the immersion procedure,
although the method does not use that term by name.
2.3 Other Radon Measurement Techniques
As noted in Section 2.1, EPA’s literature search identified several other recently
developed radon measurement techniques, which are discussed in turn m the followmg sections
2.3.1 Delay-Coincidence Liquid Scintillation Counting System
The literature search performed in 1998 identified a report of an automated liquid
scmtillation counting system for determination of 222 Rn in ground water (Theordorsson 1996).
The focus of the report was on the use of radon activity levels for earthquake prediction m
Iceland. The report describes an automated radon detection system intended for mostly
unattended operation
The technique involves a two-part system which includes a prototype assembly for
transferring radon ( 222 Rn) from water to toluene and a single phototube liquid scintillation
counter. The radon in the toluene is detected by liquid scintillation counting, using a method
known as delayed coincidence counting. Delayed coincidence countmg takes advantage of the
fact that the next four daughter products of radon all have short half-lives. As shown in Exhibit
2-1, the half-lives of 2 8 Po, 214 Po, and 214 Bi are all under 30 minutes, and the half-life of 214 Po is
only 0 16 milliseconds. The delayed coincidence counter is programmed to respond to the beta
particle decay of an atom of 214 Bi Upon detecting that beta particle from 214 Bi, the system waits
about 5 microseconds and then opens an electronic “gate” to the detector channel that
corresponds to the energy of the alpha particle decay of 214 Po and holds that gate open for about 1
millisecond. The result is that the background count measured by the detector is greatly reduced
because the detector is only looking for 2 14 Po scmtillations in the very narrow time interval
immediately after the beta particle decay of 214 Bi The detection efficiency for the delayed
coincidence counting of 214 Po is about 95%.
Most of the other aspects of the technique are modifications of those used in liquid
scintillation counting and the Lucas cell techniques. For example, the transfer of the radon from
the water sample by purging is employed in the Lucas cell, though in this case, the final reservoir
is an organic liquid not unlike that used in liquid scintillation counting.
This techmque is designed to permit the use of a much larger water sample than any of the
previously described techniques. The use of a larger sample compensates for the fact that the
percentage of radon transferred from the water to the toluene is only about 40%. In addition,
delayed coincidence counting essentially ignores the alpha decay of the parent radon and 218 Po,
Methods, Occurrence, and Monitoring Document for Radon 2-8

thereby reducing the techmque’s sensitivity by a factor of three. Theodorsson anticipates this
concern, arguing that although the ability to count multiple pulses for each disintegration of a
radon atom is generally considered to increase the sensitivity and accuracy of measurements, that
assumption is in error because the pulses are “not statistically independent.” He states that the
delayed coincidence counting
“hardly effects [ sic] the resulting accuracy and sensitivity, compared to counting
in a broad alpha-beta window, although the latter may give a pulse rate almost
five times higher.”
Unfortunately, Theodorsson does not present any performance data to substantiate this statement.
At the time of the report, the author had only constructed a prototype system that was
designed for primarily unattended operation m the field This technique may be attractive for
vanous types of low-level environmental radon measurements since it is relatively simple, very
sensitive, and well protected from disturbances However, no multiple laboratory data describing
such performance characteristics as sensitivity are provided in the article. Thus, it is not possible
to evaluate this technique more fully.
2.3.2 Activated Charcoal Passive Radon Collector
A technique that measures 222 Rsi in nver water using an activated charcoal passive radon
collector has been descnbed by Yoneda, et a! (1994). Unlike other radon methods that require
the collection of a discrete water sample, the passive radon collector is immersed in the river by
means of a string.
The radon collector used in this study consists of a sealed polyethylene bag containing a
thin layer of activated charcoal. As water passes through the collector, the radon is adsorbed
onto the charcoal and retained there After a suitable period of immersion in the water of interest,
the bag is removed and sealed in an air-tight plastic contamer and allowed to stand overnight until
secular equilibrium among the decay products was achieved. The radon on the charcoal is
determined by gamma-ray spectral analysis of its 214 Pb and 214 Bi daughter products.
The author describes experiments that evaluated the performance of the passive collector,
including an evaluation of bag thickness, amount of charcoal used in the collector, immersion time
and, most importantly, the use of dry and wet charcoal. This method claims to have the
advantage of simplicity, low cost, and the ability to measure the average radon activity in flowing
water over a specified period of time.
The author reported that
• The mean amount of 222 Rn adsorbed by the collector was about reached a maximum
when the quantity of charcoal reached 20 grams. and that the quantity of radon did not
Methods, Occurrence, and Monitoring Document for Radon 2-9

appear to be proportional to the amount of charcoal in the collector. Also, the
charcoal should be fully spread out in a single layer within the bag.
The thickness of the polyethylene bag did have an impact on the final results (a thin
film collects more 222 Rii), but it was noted that when wet charcoal was used, the
effectiveness of the polyethylene film decreases. The general recommendation was
that a relatively thick polyethylene film, 0.005 cm, be used because it is stronger and
less likely to tear.
• Collectors containing dry charcoal collected more 222 Rn than those containing wet
charcoal. However, given the difficulty in keepmg the charcoal dry during the
immersion phase, it was concluded that, in order for efficient quantitative measurement
of radon, wet charcoal should be used in the collectors. A revised radon absorption
equation was developed to indicate the amount of 222 Rn collected m the wet charcoal
The principal advantage of this method is that a discrete sample is not required, as the
passive collector is immersed directly in the body of water This method does not measure radon
directly, rather itmeasures the decay of the daughter ions. An equation is given that allows the
user to quantify the total 222 R ri absorbed by fully wet-activated charcoal sealed in a polyethylene
bag in water
The study report includes data for a variety of tests of the collection device. While some
tests were conducted at lower radon levels, the majority of the performance data were generated
from waters containing greater than 100 Bq/L of 222 Rn (>2700 pCiIL) Thus, it is not clear how
well the method would perform at the levels of interest to EPA. The available performance data
described in the article are limited to a single laboratory.
Because of the way that the monitoring is conducted, e.g., immersing the collector in the
water body and monitoring the average radon concentration over a long time period (6-10 days),
it may not be a particularly useful technique for monitoring compliance with a Maximum
Contaminant Level (MCL). Low radon levels over a portion of the monitoring period could mask
higher levels that would violate the MCL. However, if performance data were available for radon
levels near the likely MCL (300 pCiJL), this technique might be useful as a screening method. If
used as a screening method, long-term sample results that averaged over the MCL could be
expected to violate the MCL if a grab sample were analyzed using a method such as Standard
Method 7500-Rn, so no additional testing would be needed. In contrast, long-term sample results
below the MCL would still require confirmation using another technique on a grab sample.
However, such screening might not be cost-effective.
In addition, the need to leave the collector in a container of running water for 6-10 days
imposes some practical limitations in comparison to other methods that employ some a sample
Methods, Occurrence, and Monitoring Document for Radon 2-10

collected over a short period (e.g, a few mmutes). The adsorption coefficient of radon from
water onto the charcoal can be defmed as:
Bq radon per gram of charcoal
adsorption coefficient (k) = _____________________________
Bq radon per mL of water
where Bq, the Becquerel, is the SI unit of radioactivity corresponding to 1 disintegration per
second (approximately 27 picoCuries). It may be possible that the adsorption coefficient reaches
a constant during the exposure period of the collector. However, the study does not provide
sufficient data to determine if that is the case If the adsorption coefficient is not found to
constant, it would be necessary to determine the total volume of water passing over the collector
during that 6-10 day period. In some monitoring situations, such measurements would likely be
more difficult than the measurement of the radon itself.
No collaborative data were available for this method.
2.3.3 Degassing Lucas Cell
A paper by Mullin and Wanty (1991) compares the use of a “degassmg Lucas cell” (DLC)
technique with liquid scintillation counting This paper describes the degassmg Lucas cell
technique in general terms, noting that a paper by Reimer in the same volume of the USGS
Bulletin provides greater detail. The paper by Reimer was not reviewed directly, as the
comparisons conducted by Mullin and Wanty provided more useful information.
As noted in Section 2.2 , the Lucas cell techrnque is a well-established method for the
analysis of radionuclides in water, including radon. In the degassing Lucas cell technique, a water
sample is agitated in a closed vessel to extract the radon. The air in the headspace of the vessel is
sampled with a gas-tight syrmge and injected into a Lucas cell for counting. The principal
advantage of this technique is that the results can be obtained m the field, at each site, which was
the apparent reason for developing the techmque.
The primary disadvantage of this method is that unless the sample is analyzed immediately,
the radon level can be biased low by radon diffusmg out of the syringe contaimng the air sample.
Increased lag time from sampling to analysis via the DLC leads to greater uncertainty and usually
lower radon measurements, both of which were attributed to loss of radon from the syrmges in
which the samples were stored The loss of radon through radioactive decay during the lag time
between sample collection and measurement was accounted for by using an exponential formula
that corrects for the decay of the radon in the sample. However, that correction factor does
account for the diffusion losses of radon from the syringe.
In addition, as written, this method does not expressly include the three-hour equilibrium
penod, in an effort to speed the use of the technique for field measurements. The lack of the
Methods, Occurrence, and Monitoring Document for Radon 2-11

equilibration period presents concerns as well. In particular, 2 18 Po, one of the short-lived progeny
of 2 Rn, closely approaches secular equilibrium with 222 about 10 minutes, and may not be
accounted for adequately in the calibration scheme. Finally, because the DLC analyses is
performed at a time when the net alpha activity of 2 18 Po is rapidly building, large errors in
apparent radon levels may result.
The authors of the study concluded that the liquid scmtillat ion techmque was more
accurate than the degassmg Lucas cell techmque, but that the degassing Lucas cell may have
utility for reconnaissance sampling, where the results can be used to design samplmg schemes for
use of the more accurate liquid scintillation techmque However, field measurements may not be
an important factor relative to SDWA compliance monitormg for radon.
2.3.4 Electret Ionization Chamber System
Several articles were found that discuss the use of an electret system for the measurement
of radon (Tai-Pow 1992, Sabol et al. 1995) Additional information was provided to EPA by the
US manufacturer of the electret device, Rad Elec Inc., of Frederick, MD
An electret is a device which has been treated to hold a stable electrostatic-field potential
(imtially 700 to 750 volts) In the case of these two studies, the electret is made of a wafer of
Teflon that is housed in a chamber made of electrically-conducting plastic The device is called an
electret passive environment radon momtor (E-PERM) by the manufacturer of the device.
The decay products from the radon gas enter the chamber through the filtered inlet at the
top and the alpha particles striking the electret discharge the static charge on the electret. The
surface charge of the electret is measured before and after exposure by using a specially designed
voltage reader This electric field sensor can detect small changes on the electret. The electret is
designed to handle exposures of two to seven days at levels of 0.04 to 1.85 Bq/L (ito 50 pCi/L)
of radon in air.
Electret ionization chambers are simple, portable, and easy to use. They are also well-
suited for field measurements, since more than one measurement can be made from the same
electret. Drawbacks to this simple and relatively inexpensive method mclude poor reproducibility
at lower radon levels, uncertainty in the use of manufacturer-suggested gamma correction factors,
and limited reusability. The electret device lacks specificity for radon. The surface charge of the
electret will change with exposure to gamma radiation from within the sample chamber or from an
external gamma source. It will also change in response to the alpha decay of other volatile
radionuclides that enter the chamber headspace from the water.
When measuring radon concentrations in air, the gamma radiation can be subtracted
through the use of voltage-dependent correction factors, resulting in improved accuracy. In the
studies cited above, the end results showed that a higher concentration of radon in water may
result in elevated airborne radon concentration in the surrounding areas, including increased radon
Methods, Occurrence, and Monitoring Document for Radon 2-12

activity in buildings served by a hot spring water. For routine waterborne radon monitoring,
including use in field conditions, the technique based on electret ion chamber technology may
sometimes be a suitable choice.
In a 1990, a survey of laboratories conductmg radon analyses in drinking water was
performed by Wade Miller Associates, under contract to EPA. The goals of that study were to
identify the types of certification programs that exist for radon analyses m drinking water, to
identif ’ laboratories capable of performing the analyses, and to determine the daily analysis
capacity of each identified laboratory. Of 45 commercial and state laboratones contacted in 1990,
only one listed the electret method.
Recent information provided by the US manufacturer included cited three additional
studies that were not directly reviewed by SAIC. These include the following papers and
• Kotrappa, P and Jester, W A.,”Electret Ion Chamber Radon Monitors Measure
Dissolved 222 pm in Water,” Health Physics, 64. 397-405 (1993)
• Colle, R. Kotrappa, P., and Hutchmson, J.M.R., “Calibration of Electret-Based
Integral Radon Momtors Using NTST Polyethylene-Encapsulated 226 RaP 22 Rri
Emanation (PERE) Standards,” Journal of Research of National Institute of
Standards and Technology, 100: 629-639 (1995).
• Budd, G, and Bentley, C, “Operational Evaluation of the EIC Method for
Determining Radon In Water Concentrations,” 1993 International Radon Conference,
Hosted by AARST
Those studies provide precision and bias data on the electret technique over a wide range of
concentrations. According to the manufacturer, the electret techmque has recently been certified
by the States of Maine and New Hampshire for monitormg radon in water.
As summarized by the manufacturer, the precision of the electret technique ranged from 4
to 10% across all three of the studies. The bias of the technique was estimated by the
manufacturer to be from -17% to +1% in these three studies, following the application of a
correction factor of 1.15 to the initial sample results. Prior to the use of this correction factor, the
bias ranged from -27% to -9% across these three studies. SAIC contacted the manufacturer and
obtained information on the ranges of radon concentrations that were used in these studies.
Accordmg to the manufacturer, the Kotrappa and Jester study examined five radon
activity levels, rangmg from a low of about 220 pCifL to a high of 73,200 pCiIL, and found no
significant change in precision and bias across the range. The Colle et al. study examined only
one radon level of 10 Bq/g, which equates to approximately 270,000 pCifL. The Budd and
Bentley study examined a vanety of activity levels, ranging from about 350 pCifL to 46,000
Methods, Occurrence, and Monitoring Document for Radon 2-13

pCiIL. The first and third studies included at least some activities near the levels of interest to
The correction factor recommended by the manufacturer is intended to relate the electret
results to those expected by the liquid scintillation counting method, although the manufacturer
points out that the liquid scmtillation method may not be “accurate with traceability to NIST”
As is the case for the activated charcoal collector method described m Section 2.3.2, the
electret method requires a long exposure of the detector to the sample. The range of exposure
times in the papers reviewed by SAIC is 2-7 days. However, unlike the charcoal collector
technique, the electret is exposed to a discrete sample container in a sealed vessel. Thus, although
the measurement may take up to 7 days to complete, the results represent the concentration of
radon in the discrete water sample.
Although the manufacturer’s literature indicates that electret techmque performed well m a
1994 US Department of Energy (DOE) “intercomparison” study, those data appear to be for the
measurement of radon in air. No collaborative data for water samples have been identified.
2.4 Performance Capabilities of the Methods
The performance capabilities of these methods for the analysis of radon were difficult to
evaluate in a consistent manner, in part, because many of the methods were developed m
umversity settings for purposes other than those envisioned by EPA, i.e, not for compliance
monitonng Wherever possible, SAIC has reviewed the information on the sensitivity (detection
limit) and precision of these methods. The selectivity of the procedures for 222 Rn is generally
excellent and consistent across most of the methods. This is because most of the methods
measure the alpha particle decay of 222 Rn and/or its daughter products, and these particles are
released at discrete alpha energies. In the case of 222 Rn, the energy of the alpha particle is 5.49
MeV The exception is the electret method described by Tai-Pow eta!., which measures the
change in the electrical potential of the circuit containmg the electret. This technique is less
selective for radon than the other techniques, in that it will respond to both gamma radiation and
other volatile radionuclides m the water sample.
As noted earlier, most of the methods lack data from collaborative studies. The two
exceptions are the liquid scintillation method (SM 7500-Rn) and the Lucas Cell method. Both of
these method were evaluated as part of the 1992 EPA collaborative study. The accuracy,
reproducibility, repeatability, and bias data for Standard Method 7500-Rn and for the Lucas Cell
method are shown in Section 2 3, above.
As noted above, the performance capabilities of some of the other techniques have not
been demonstrated for relatively low activities of 222 Rn. Several of the techniques were described
as having poorer performance as low radon activities. A number of the papers did not present
data on the sensitivity of the techniques, and in those cases no attempts were made to estimate the
Methods, Occurrence, and Monitoring Document for Radon 2-14

sensitivities. Rather, the radon levels at which performance was demonstrated were noted in the
Based on the information provided by the manufacturer, the performance of the electret
method has also been relatively well-characteristics. While the summary information suggests that
the bias is greater than that reported for Standard Method 7500-Rn, even the -17% figure is not
so severe as to rule out this procedure, smce methods for some orgamc analytes can be shown to
have similar bias. However, as noted earlier, no collaborative study data on water samples were
2.5 Skill Requirements
The two major techmques employed m most of these methods are liquid scintillation and
Lucas cell countmg. Neither of these techrnques is techmcally difficult. Liquid scintillation
counting has been used in medical laboratones arid environmental research laboratories for over
30 years. The skills required are primarily the ability to remove an aliquot of the sample from the
original vial and adding an aliquot of the scintillation cocktail, sealing the vial, and placmg it into
the counter The counting process is highly automated and the equipment runs unattended for
days, if needed.
The Lucas cell methods described in the papers considered for this report requires
somewhat more manual skill. As noted in the 1991 proposed rule, EPA expects that this
technique would require greater efforts to train technicians than the liquid scintillation technique
The Lucas cell technique requires that the counting cell be evacuated to about 10 mTorr pressure.
Then, a series of stopcocks or valves must be manipulated to transfer the radon that is purged
from the sample into the counting cell. Potential problems with the analysis, such as a high
background level of radon that can develop over the course of the day, or aspirating water into
the counting cell, can be minimized by a well-trained analyst. However, as EPA concluded in
1991, the Lucas cell techrnque is not expected to form the sole basis of a compliance momtoring
program for radon in drinking water.
The electret method is relatively simple to perform The water sample (
reproducible fashion. As noted in Section 7.0, the ability to generate useful analytical results for
radon is dependent in an important way on the sample collection process. The 1992 EPA
collaborative study evaluated four sample collection techniques and found them all equally good
at providing equivalent results. The State of California has developed a sampling protocol for
radon in water that employs one of the four techniques evaluated by EPA, namely the immersion
technique. SAIC has reviewed a copy of that protocol that was provided to EPA (Jensen, 1997)
As described in the Califorma protocol, the well is purged for 15 minutes to ensure that a
representative sample is collected Purging simply means that the water is withdrawn from the
well for this period of time After purgmg, a length of flexible plastic tubing is attached to the
spigot, tap, or other connection, and the free end of the tubing is placed at the bottom of a small
bucket. The water is allowed to fill the bucket, slowly, until the bucket overflows. The bucket is
emptied and refilled at least once.
Once the bucket has refilled, a glass sample container of an appropriate size is opened and
slowly immersed into the bucket in an upright position. Once the bottle has been placed on the
bottom of the bucket, the tubing is placed into the bottle to ensure that the bottle is flushed with
fresh water. After the bottle has been flushed, the tubing is removed while the bottle is still on the
bottom of the bucket. The cap is placed back on the bottle while the bottle is still in the bucket,
and the bottle is tightly sealed. As noted in the California protocol, the choice of the sample
container is dependent on the laboratory that will perform the analysis, and will be a function of
the liquid scintillation counter that is employed. If bottles are supplied by the laboratory, there is
no question of what container to employ.
Once the sealed sample bottle is removed from the bucket, it is inverted and checked for
bubbles that would indicate headspace. If there are no bubbles, the outside of the sealed bottle is
wiped dry and cap is sealed in place with electrical tape, wrapped clockwise. After the sample
bottle is sealed, a second (duplicate) sample is collected in the same fashion from the same bucket.
The date and time of the sample collection is recorded for each sample
As described above, the sample collection procedures are not particularly labor-mtensive.
Most of the time is spent allowing the water to overflow the bucket. Likewise, there are no
significant manual skills required. Personnel who can manage to slowly fill a 1-liter glass bottle to
collect a sample for analysis of semivolatile organics, or fill a 40-mL VOA vial without headspace,
can certainly collect samples for radon, using the method described above.
2.6 Practical Availability of the Methods
In order to determine the practical availability of the methods, SAIC considered two major
factors First, the availability of the major instrumentation was reviewed. Secondly, several
laboratories performing drinking water analyses were contacted to determine their capabilities to
perform radon analyses.
Methods, Occurrence, and Monitoring Document for Radon 2-16

The major instrumentation required for Standard Method 7500-Rn is a liquid scintillation
counter. Automated counters capable of what that method terms “automatic spectral analysis”
are available from at least a dozen suppliers. The Lucas cell apparatus is the same as has been
used for radium analyses for many years. The electret system is used for the measurement of
radon in air as well as m water Information provided by the manufacturer of the electret system
suggests that there are more than 600 users in the US, of whom, the manufacturer estimates, 10%
measure radon in water
In order to evaluate the availability of laboratory capacity to perform radon analyses, in
early 1998 SAIC contacted the drinking water certification authorities in the states of California,
Maryland, and Pennsylvania These states were chosen based on SAIC’s knowledge of radon
problems associated with the “Readmg Prong” that stretches through parts of Pennsylvania and
Maryland, and the overall status of California’s laboratory certification program. A total of eight
commercial laboratories were contacted during this imtial survey Each laboratory was advised
that SAIC was simply collecting information on the availability and relative costs of radon
analyses for drinking water. SAIC was limited in its ability to perform a broader survey, since an
upper limit of mne was placed on the survey, m order to abide by the Federal information
collection regulations.
Six of the eight laboratories that were contacted in the initial survey perform radon
analyses. All the laboratories were certified in one or more states to perform radiochemical
analyses, though it was unclear if the certifications were specifically for radon or the more general
radiochemical analysis category.
When asked what specific methods were used, the laboratories responded with either the
techmque (liquid scintillation counting) or a specific method citation EPA Method 913 was cited
by two of the six laboratories. As noted earlier, this method is the precursor to the current
Standard Method 7500-Rn. EPA Method “EERF Appendix B” was cited by another laboratory
The remaining three laboratories indicated that they performed liquid scintillation analyses and
could accommodate requests for methods employing that technique.
When asked about capacity, the laboratories indicated that they perform between 100 and
12,000 analyses per year. The latter figure came from a laboratory that is currently involved m a
large ground water monitoring project m the western US. The next largest estimate was 300
samples per year. However, SAIC expects that like any other type of environmental analysis,
given a regulatory driver to perform the analysis, the laboratory capacity would develop quickly.
The 1992 EPA collaborative study on radon analysis (Pia and Hahn, 1992) included 51
laboratones with the capability to perform liquid scintillation analyses. This suggests that there
already exists a substantial capacity for these analyses. Further, the liquid scintillation apparatus is
used for other radiochemical analyses, including tritium. Information from EPA regarding the
performance evaluation program for tritium analyses suggests that there are approximately 100-
200 laboratories with the necessary equipment. Much of the capacity for tntium analyses could
also be used for radon (EPA 1997) . As of September 1997, 136 of 171 participating laboratories
Methods, Occurrence, and Monitoring Document for Radon 2-17

achieved acceptable results for tritium. Both the total number of participants and the number
achieving acceptable results vary from study to study, but these data indicate that there is already
a substantial capability for liquid scintillation analysis nationwide
Recent information provided by the manufacturer of the electret indicate that the States of
Maine and New Hampshire are certifying laboratories for drinking water analysis using the
electret method. Several months after the initial laboratory survey, based on information from the
manufacturer, SAIC contacted a laboratory in New Hampshire that uses the electret method and
obtained information on the analysis price for water samples. The laboratory charges $30 per
sample for drinking water analyses. They have been certified for drmking water analyses using
the electret method in New Hampshire for at least three years and in Maine for one year They
have a current capacity of at least 40 samples per week (2000 per year), and indicated that they
could easily increase that capacity to meet demand
The availability of laboratories is also dependent on laboratory certification efforts in the
individual states with regulatory authority for their drinking water programs A major component
of many of these certification programs is continued participation by the laboratory in the current
EPA Water Supply (WS) performance evaluation (PE) program Efforts are underway at EPA
that will lead to the privatization of all of EPA’s PE programs, including the WS studies. Those
efforts will affect laboratory certifications for all analytes regulated under the SDWA, including
radiochemicals such as radon. Any delays in implementing a private PE program will affect not
only radon, but the certification status of laboratories for all regulated analytes.
Because of the issue involved with safe handling of radiochemical standards, there will
likely be fewer laboratories seeking certification for radon than for other non-radiochemical
parameters. However, there is no fundamental regulatory reason that a radon laboratory in one
state cannot receive certification m another state Even for more commonly performed analyses,
there are numerous commercial laboratories that are certified in multiple states Given the
regulatory requirement for radon analyses, one can expect that those laboratories with the
capability for radon analysis will pursue certifications in as many states as practical.
The National Environmental Laboratory Accreditation Conference (NELAC) is also
evaluating the issues surrounding privatization of the SDWA PE program through its proficiency
testing committee NELAC serves as a national standard-setting body for environmental
laboratory accreditation, and includes members from both state and Federal regulatory and non-
regulatory programs.
The short holding time for radon, 4 days in Method 7500-Rn, presents a concern relative
to the practical availability as well. The 4-day holding time was also the focus of a number of
comments that EPA received in response to the 1991 proposed rule. Many commenters stated
that if a local laboratory is not available, the only alternative would be to send the samples by
overnight delivery to a laboratory elsewhere. Again, this situation is not unique to the analysis of
radon. Several large commercial laboratories already account for a sizable share of the market for
Methods, Occurrence, and Monitoring Document for Radon 2-18

SDWA analyses for non-radon parameters, including organics, for which the holdmg times are
often 7 days Given that a day would be required for shipping the samples, only three days would
remam for the laboratory to perform the radon analysis (the day on which the sample is collected
being “day zero”). Some commenters argued that for a large commercial laboratory servmg the
water utilities, this short holding time will make it difficult if not impossible to perform the
necessary analyses within the holding time However, through common-sense scheduling efforts
between the utility and the laboratory, such as not collectmg samples on Thursdays and Fridays,
the holding time issue should be able to be accommodated with relative ease. At worst, some
laboratories may choose to offer analytical services over the weekend, perhaps at an increased
For the vast majority of other analytes for which EPA has established formal holding times
m its various regulatory programs, the holdmg times are specified in “days.” This is typically
understood to mean “calendar days” with the day of sample collection being “day zero.” Because
of the relatively short half-life of radon, the holding time is expected to be proposed as 4 days,
beginning at the time of collection SAIC strongly urges EPA to publish this holding time as “96
hours” instead of just “4 days,” in an effort to reinforce how the holdmg time is to be calculated
2.7 Anticipated Unit Costs
As part of its 1991 proposal, EPA conducted a limited survey of laboratories providing
radon analyses. Four laboratories provided price information to EPA regardmg the analysis of a
single SDWA compliance monitoring sample, employing liquid scintillation countmg as the
analytical techmque. The data from the 1991 survey are in Exhibit 2-4.
As part of the 1998 review of analytical methods for radon, SAIC contacted nine laboratories that
perform radiochemical analyses. Of those nine, seven perform radon analyses. The prices from
the those seven laboratories are shown m Exhibit 2-5. None of the laboratories contacted were
among those contacted by EPA in 1991, but to avoid any confusion, the arbitrary numbers
assigned to each laboratory begin where the 1991 numbers left off.
There was no clear correlation between the estimated price and the method cited by the
laboratory. One of the laboratories that provided an estimate of $40 per sample is certified by the
States of Maine and New Hampshire to perform radon analyses of drinking water usmg the E-
PERM electret device. The other laboratory that quoted a price of $40 employs liquid
scintillation counting The 1998 range of prices brackets those collected by EPA in 1991.
Exhibit 2-4. 1991 Radon Cost Survey Data
Arbitrary Lab Number
Cost Estimate
I $49.80
Methods, Occurrence, and Monitoring Document/or Radon 2-19

$47 00
4 $75 Range $45
Minimum $30
Maximum $75
Exhibit 2-5. 1998 Radon Cost Survey Data
Arbitrary Lab Number
Cost Estimate
As noted above, one possible response to concerns about the effect of the short holding
time on laboratory capacity would be for some laboratories to offer analyses over the weekend.
The increased cost of such services would likely be due to mcreased labor costs, particularly if
overtime were paid to the analysts. Assuming a 1.5 multiplier for overtime (e g., “time and a
half’), the unit cost might rise to the range of $60 to S 112 per sample, but only for those utilities
that could not arrange to sample at more convenient times.
2.8 Practical Performance and Analytical Uncertainties
The available information on the performance of the various methods is greatest for the
liquid scintillation procedure, SM 7500-Rn, and the Lucas Cell technique The data from the
1992 EPA collaborative study cited earlier indicate excellent precision and accuracy for liquid
scintillation. The Lucas Cell technique yielded slightly less accurate and less precise results, but
still within the realm of performance that EPA has accepted for the measurement of other
contaminants. Performance data for the electret method are incomplete, with no clear evidence
of a collaborative study in drinking water.
As with many environmental measurements, an overall evaluation of the effectiveness of a
monitoring method must also consider the practical aspects of collecting a representative sample.
The analysis of radon presents two specific challenges. First, like many organic contaminants,
Methods, Occurrence, and Monitoring Document for Radon 2-20

radon is volatile, and some radon will come out of solution in a sample if exposed to the
atmosphere for long periods. Secondly, being a radioisotope, 222 Pii undergoes radioactive decay.
The volatility of radon can be addressed m a fashion similar to that for the orgamc
chemicals, namely careful sample collection techniques that minimize the disturbance of the
sample, and the use of containers that can be sealed tightly
The conclusions of the 1992 collaborative study indicate that while all four sample
collection techniques examined m that study (displacement, immersion, catch, and grab sampling)
can provide equivalent results, displacement and immersion sampling are the preferred
approaches. Both can be accomplished with little or no specific expertise. Displacement
sampling involves attaching a filling tube attached to the water source, insertmg the other end into
the sample contamer, and allowmg the water to fill the contamer with no aeration until the
container overflows. The filling tube is withdrawn while still running, so that water constantly
overflows the container. The container is then quickly sealed with an appropnate cap (e.g.,
Immersion sampling is somewhat similar, m that a sample contamer is placed m the bottom
of a large container The filling tube is then inserted mto the sample container which is then filled
to overflowing with the water to be sampled. The sample container is removed from the larger
container with forceps and sealed. The use of immersion sampling further reduces the chances of
leaving headspace in the sample container, by allowing the filling tube to be withdrawn while the
sample container is still submerged m the larger container. However, as noted in the 1992 study
report, there was little difference between the results from both sampling techniques. The
sampling procedure developed by California that was described earlier in this document is an
immersion technique. The losses of radon due to sorption on cap liners and m air bubbles that
occur dunng transportation and storage appear to be minimal for this techmque.
The radioactive decay of 222 Rn presents some concerns because the half-life of this isotope
is approximately 3.82 days. However, even with this relatively short half life, it is both possible
and practical to calculate the concentration of 222 Rn at the time of sampling with a high degree of
accuracy. Depending on the regulatory action level (MCL or other level) that is specified, the
sensitivity of the liquid scintillation method should be sufficient to be used for compliance
monitoring even if the sample is held for several days. Method 7500-Rn currently specifies a 4-
day holding time. For this analyte, sampling documentation must include the time of sample
collection, as well as the date. However, this documentation requirement does not present any
practical difficulty for this technique.
2.9 Degree To Which Each Method Meets EPA’s Regulatory Needs
Of the six techniques for the measurement of radon that were evaluated in this report, only
two appear to meet all of EPA ’s needs relative to compliance monitoring. SM 7500-Rn and the
Methods, Occurrence, and Monitoring Document for Radon 2-21

Lucas Cell technique can achieve reasonable standards for precision and accuracy, are readily
available, and have been subjected to collaborative testing.
The four other techniques lack collaborative testing data, which is a significant problem m
establishing methods for a nationwide compliance monitoring program such as the SDWA Of
those four other techniques, the electret technique shows greatest promise, and should
collaborative data indicating acceptable performance in water matrices become available in the
future, EPA may wish to consider this technique at a later date.
The other three techniques, the delayed coincidence liquid scintillation counting system,
the activated charcoal passive collector techmque, and the degassing Lucas cell technique may
have some utility in screening samples or in field measurements The activated charcoal
procedure requires a lengthy exposure to running water and provides an average radon
concentration over the entire sampling period. The extent to which such time-averaged
measurements might be employed in SDWA compliance monitoring is a policy decision that goes
beyond the scope of this evaluation.
In summary, the results of this most recent review of possible analytical techniques for
radon in drmkmg water has reached the same conclusions as that of the 1991 EPA proposal. The
liquid scintillation counting technique (SM 7500-Rn) is most able to support a SDWA compliance
momtoring program, supported by the possible use of the Lucas cell technique.
2.10 References
Banks, T, WMA, Feb. 21, 1990 Memorandum to G Helms USEPA-OW on Laboratories
Conducting Analysis of Radon in Drinking Water.
Banks, T, WMA, Nov. 14, 1989, Memorandum to G. Helms, USEPA-OW regarding The Lucas
Cell Method of Testing for Radon in Water
Budd, G, and Bentley, C, “Operational Evaluation of the EIC Method for Determining Radon In
Water Concentrations,” 1993 International Radon Conference, Hosted by AARST.
Che Yang, I. “Sampling and Analysis of Dissolved 222 Rn m Water by the De-emanation Method,”
US Geological Survey Bulletin, 1991, pp. 227-230.
Colle, R. Kotrappa, P., and Hutchinson, J.M.R., “Calibration of Electret-Based Integral Radon
Monitors Using NIST Polyethylene-Encapsulated 226 RaP 22 Rn Emanation (PERE) Standards,”
Journal of Research of National Institute of Standards and Technology, 100: 629-639 (1995).
Deloatch, I., Mar. 27, 1991 Memorandum to G. Helms, regarding estimated cost of analyses for
Methods, Occurrence, and Monitoring Document for Radon 2-22

Jensen, Jane T, 1997 California Department of Health Services Environmental Laboratory
Accreditation Program (ELAP) September 3 letter to William Labiosa, EPA-OGWDW.
Jensen, Jane T, California Department of Health Services Environmental Laboratory
Accreditation Program (ELAP) Attachment to the September 3, 1997 letter to William Labiosa of
Kitto, M.E. et al. “Direct Comparison of Three Methods for the Detection of Radon in Well
Water”. Health Physics. Vol. 70, No. 3, pp. 358 —362. 1996.
Kotrappa, P. and Jester, W.A.,”Electret Ion Chamber Radon Monitors Measure Dissolved 222 Pm
in Water,” Health Physics, 64 397-405 (1993).
Mullan, A. and Wanty, RB (“A Comparison of Two Techniques for 222 Rn Measurement in Water
Samples,” US Geological Survey Bulletin, 1991, pp. 231-235).
Pia, S H and P B. Hahn, 1992, “Radiation Research and Methods Validation Annual Report,”
Sabol J, et a!, “Monitonng of 222 Rn m Taiwanese Hot Sprmgs Spa Waters Using a Modified
Electret Ion Chamber Method,” Health Physics, Vol. 68, No. 1, 1995, pp. 100-104).
Standard Method 7500-Rn, Standard Methods Examination of Water and Wastewater .
19 th Edition Supplement. Clesceri, L., A. Eaton, A Greenberg, and M. Franson, eds. American
Public Health Association, Amencan Water Works Association, and Water Environment
Federation. Washington, DC. 1996.
Tai-Pow J, et al., “The Determination of Dissolved Radon in Water Supplies by the E-PERM
System (Electret Ionization Chamber),” International Journal of Radiation Applications and
Instrumentation, Part A, Vol. 43,No. 1-2, 1992, p 95-101.
Theodorsson, “A New Method for Automatic Measurement of Low-Level Radon in Water”
Journal of Applied Radiation Isotopes”. Vol. 47, No. 9/10, pp. 885 — 895. 1996
USEPA ,“Tritium in Water Performance Evaluation Study, A Statistical Evaluation of the August
8, 1997 Data,” EPAI600IR-97/097, September 1997.
USEPA. “Radiation Research and Methods Validation: Annual Report 1992”. EPA 600/X-
93/030. April 1993. (incorrectly cited as “Pia and Hahn 1992” - should be “USEPA 1993”)
Yoneda, M., eta! (“Quantitative Measurement of 222 Rri in Water by the Activated Charcoal
Passive Collector Method: 1. The Effect of Water in a Collector,” Journal of Hydrology, Vol.
155, No. 1-2, 1994, pp. 199-223).
Methods, Occurrence, and Monitoring Document for Radon 2-23

Methods, Occurrence, and Monitoring Document for Radon 2-24

3.1 Natural Sources of Radon Groundwater Contamination
Radon is produced in rock, soil and water by the decay of naturally occurnng radioactive
elements in minerals This process transfers radon into air- or water-filled soil pore spaces by
alpha recoil or diffusion. Radon is then transported by air or water until it decays to its progeny
or reaches the atmosphere
Radon is a member of the “uranmm series”of radionuclides all the members of which are
derived from the decay of uraruum-238 Each radioactive isotope spontaneously decays to emit a
radioactive particle, radiant energy, and forms “progeny” isotopes This process continues until a
stable isotope of lead is formed. Radon has three naturally-occurring isotopes, radon-222 (Rn-
222), radon-220 and radon-2 19 Of the three radon isotopes, Rn-222 is the only one of
environmental concern, because the other isotopes have much shorter half lives which limit their
potential for causing human radiation exposure. Radon-222 decays into Polonium-3 18 with a
half-life of approximately 3.82 days by alpha emission. The uranium decay series is shown in
Exhibit 3-1.
EXHIBIT 3-1 Uranium Decay Series (Including Rn-222)
Uranium 238 - Thallium 234 + a
4 46 X iO years
Thallium 234 -3 Palladium 234 + 3
24 1 days
Palladium 234 -+ Uranium 234 +
117 minutes
Uranium 234 -$ Thorium 230 + a
2 45 x i0 5 years
Thorium 230 -9 Radium 226 + a
7 5 x i0 years
Radium 226 -4 Radon 222 + a
1622 years
Radon 222 -4 Polonium 218 + a
3.825 days
Polonium 218 -4 Lead2l4+a
311 minutes
Lead2l4 -4 Bismuth214+
Bismuth 214 -3 Polonium 214 + a
199 minutes
Polonium 214 -4 Lead 210 +
1 6 x IO minutes
Lead2lO 4 Bismuth210+
Bismuth 210 -4 Polonium 210 +
5 01 days
Polonium 210 -4 Lead 206 + a
1384 days
Lead 206
Methods, Occurrence, and Monitoring Document for Radon 3-1

3.1.1 Release and Transport Properties of Radon and Radium
On a microscopic scale, the release of radon mto groundwater water is directly related
both to the concentration of radium in the host soil or rock, which determines the amount of
radon generated, and to the emissivity of the mineral (which determines the fraction or the
generated radon that is released from the particle in which it is generated) The physical condition
of the rock (particle size, pore structure) plays a large role in determining emissivity. Because of
the importance of these physical factors in determimng radon release, there is often no strong
correlation between radium levels in rocks or soils and radon levels in adjacent groundwater. The
dominant radon route of release into interstitial water is diffusion
along microcrystalline fractures m the rock. However, in most cases (i e., cases in which the
percolation velocity is greater than lQ cmlsec), the mass transport of radon in groundwater
water is governed more by advection than this diffusion (Hess,et al. 1985).
Radium-226 is the immediate radiologic precursor of radon-222 Radium can be released
to groundwater by three routes: the dissolution of aquifer solids; by direct recoil across the liquid-
solid boundary during its formation by radioactive decay of its parent, and by desorbtion. In
contrast to radon, radium has very low solubility in water and very low mobility m groundwater.
Also, radium does not exist as a gas, and vapor phase transport is therefore not important. Thus,
as discussed below the transport patterns of radium generally do not greatly affect the transport of
radon and radium concentrations in groundwater can be a poor predictor of radon levels.
3.1.2 Factors Affecting Distribution of Radon in Groundwater
The levels of radon in groundwater in specific areas or types of systems are affected by a
number of factors. Geologic regime and geological parameters are strongly associated with radon
levels in groundwater. A number of studies have examined the correlations among radon levels in
groundwater and the occurrence of other elements, aquifer lithology, and the depth to the
groundwater Analysis has suggested, that for a defined geographic area, relative radon levels can
be inferred from the dominant aquifer lithology and implied activity levels of the parent isotopes
Loomis (1985) has identified six geologic and hydrologic vanables that together can be used to
predict radon activity m groundwater at a regional level. Each vanable, except meteorology,
tends to be strongly correlated with lithology type.
• Uranium-radium geochemistry. As noted above aquifer minerals with high uranium or
radium content may exhibit a relatively high rate of radon release.
• Physical properties of source rocks. The escape of radon from rocks into water varies
accordmg to the rock’s grain size, degree of weathering, microfractures, and the
distribution of radon’s parent nuclides within the rock’s mineral grains. Generally, the
smaller the grain size and more pervasive the fracturing and weathering, the greater the
amount of radon that escapes.
Methods, Occurrence, and Monitoring Document for Radon 3-2

• Dissolved radium. The relationship between dissolved radium in the water and radon in
water is inconclusive; several studies mdicate there is little to no correlation in the co-
occurrence of these two nuclides.
• Aquifer properties. The transfer of radon from rocks to the aquifer is largely determined
by the flow characteristics of water through the aquifer. The transfer of radon from rocks
to water is enhanced when the rocks are relatively permeable, weathered, and fractured
and flow rates are relatively high Given radon’s relatively short half-life, groundwater
flow must be relatively rapid for radon to reach water supply wells before it decays
• Meteorologic factors. Some studies have indicated that radon levels co-vary positively
with precipitation Moreover, there is some evidence that radon emanation from the rocks
and soils is related to barometric pressure. Several studies that have looked for a
relationship between radon in water and meteorologic factors have found none
• Well and water system design and use. Several studies have reported that radon levels in
water are mversely proportional to a groundwater system’s number of customers and
yield. Reasons for tius consistently-seen relationship are not clear, although it may be that
wells servmg smaller numbers of customers may draw from less productive gramtic
aquifers with higher levels of radon precursor elements.
The aquifers with the highest radon concentration have a lithology profile that is
dominated by granite and granite alluvia. These rocks tend to have higher levels of uranium and a
physical structure that facilitates the release of radon into adjacent water Radon levels are also
often elevated near volcamc ash layers Lower radon levels are found in basalts and sand aquifers.
This relationship between lithology and radon concentration is illustrated by the regional
differences in radon levels in groundwater between the southern Mississippi valley (a
predominance of basalts and sand results in low radon levels) and Appalachian uplands (a
predominance of granite results in high radon levels).
3.1.3 Large-Scale Geographic Patterns of Radon Occurrence in Groundwater
As noted above, groundwater radon levels in the United States have been found to be the
highest in New England and the Appalachian uplands of the middle Atlantic and southeastern
states. There are also isolated areas in the Rocky Mountains, California, Texas, and the upper
Midwest where radon levels in groundwater tend to be higher than the U.S. average. The lowest
groundwater radon levels tend to be found in the Mississippi valley, lower Midwest, and plains
states However, even in areas with generally very high or low levels of radon in groundwater,
local differences in geology strongly affect observed radon levels (e g., not all groundwater radon
levels in New England are high; not all radon levels in the Gulf Coast region are low) For
example, the presence of faults and shear zones in a geographic area charactenzed by low radon
levels can produce localized areas of high radon levels (Gunderson, et a!. 1992). It was found
that radon levels in groundwater were correlated with measured radioactivity of rocks and soils in
Methods, Occurrence, and Monitoring Document for Radon 3-3

the area, the prevalence of rock types know to produce radon in the area, and the area’s soil
permeability. The general pattern of groundwater radon occurrence across the US is shown in
Exhibit 3-2. Data related to geographical patterns or radon occurrence are discussed in more
detail in Chapter 5. The potential for radon to co-occur with other pollutants is discussed m
Chapter 7.
3.2 Anthropogenic Sources of Radon Contamination in Groundwater
Radon in the environment is derived primanly from natural sources. Because of its short
half life, there are relatively few anthropogemc sources of groundwater radon contamination. The
most common manmade sources of radon groundwater contamination are wastes from phosphate
or uramum mining or milling operations and from thorium or radium processmg These sources
can results in high groundwater levels in very limited areas if, for instance, homes are located on
soil contaminated with such wastes or tailings, or if a contaminated aquifer is used as a source of
potable water (EPA l999a). Otherwise, significant groundwater transport of radon is limited by
its short half-life.
3.3 Distribution System Sources
3.3.1 Radon Sources in Distribution Systems
Radon levels in distribution systems are usually lower m distnbution systems than in
source water because radioactive decay and water treatments involving storage, aeration, or
carbon filtration act to reduce radon levels. As will be discussed in more detail in Section 5.2, this
is not always the case, however. In a number of systems in Iowa, for example, radon levels in
finished water samples were found to be substantially higher than those from the wells supplying
the systems. Detailed studies have shown elevated levels of radium in pipe scale in these systems.
The decay of the radium increases radon levels over and above those already present in the
influent water The greater the length of old, scaled pipe through which the water passes, the
greater the radon levels. The extent to which this is a general phenomenon is not known, but it
suggests that care should be taken in estimating radon exposures on the basis of welihead or
point-entry-samples where iron-manganese scaling is likely to be a problem.
3.3.2 Radon Sources in Households
Except to the extent that pipe scale in residences sequesters radium, there are no radon
sources that increase the levels of radon after water enters the household. Radon is released to
indoor air during domestic water use, however, as discussed in Section 4.3.
Methods, Occurrence, and Monitoring Document for Radon 3-4

3.4 Non-Water Supply Sources of Radon Exposures
It has been estimated that only between 1 to 3% of the total residential radon exposures
results from radon in public water supplies (NRC 1998). The most important source of radon
exposure (accounting for approximately 95 percent of exposures) is indoor air contaminated by
radon released from rocks and soils and infiltrating into basements and living spaces. Other
sources of radon exposures include ambient (outdoor) air, fuel gas, and construction matenal
(primarily gypsum board).
3.5 References Cited
EPA (1 999a), Criteria Document for Radon in Drinking Water, Office of Research and
Development, Office of Science and Technology
Gundersen, L.C.S , et al. (1992) “Geology of Radon in the United States. Geological Society of
America” Special Paper 271.
Hess, Ct. al (1985), “The Occurrence of Radioactivity in Public Water Supplies in the United
States. Health Physics” Volume 48, Number 5. (pp. 5 53-586), May.
Loomis, Dana, (1987) “Radon-222 Concentration and Aquifer Lithology in North Carolina.
Ground Water Monitoring Review.” Volume 7, Number 2, (pp. 3 3-39).
National Academy of Sciences, (1998) Risk Assessment of Radon in Drinking Water, National
Research Council, Committee on Risk Assessment for Radon in Drmking Water, September 14
Methods, Occurrence, and Monitoring Document for Radon 3-5

4.1 Physical and Chemical Properties of Radon and Progeny
Radon, atomic number 86, is a “noble” and chemically inert gas. It does not react with
other elements in the environment. Radon is soluble in water, but also very volatile. It has a high
Henry’s Law Constant (>X10 3 m 3 /1), indicating a high potential to volatilize from water solution.
Its melting point is -71 °C and its boiling point is -61.8°C. It’s solubility in water is 230 cm 3 /liter
at 20°C Radon is adsorbed by activated carbon, and therefore presumably to some extent to
other orgamc matter, although radon partitioning to organic matter in the environment has not
been extensively studied.
As noted in Chapter 3, radon-222 has a half-life of 3.82 days Radon’s progeny
radionuclides (primanly isotopes of lead, polonium, and bismuth) unlike radon, are not gases, and
are less soluble in water than radon. When radon undergoes radioactive decay in water, the
resultant nuclides tend to precipitate out onto suspended particulates or other surfaces. Similarly,
radon progeny in air “plate out” onto airborne particles, and the bulk of radon-related radiation
exposures through the inhalation pathway are often due to the deposition of progeny-beanng
particulates in the respiratory tract.
4.2 Relationship of Fate and Transport Properties to Human Exposures and Intake
Radon’s chemical and physical properties, particularly its radioactive half-life and
volatility, greatly effect its behavior in the environment, and human exposures from domestic
water use.
Because of its short radioactive half-life, the distance over which radon can move in
groundwater is severely limited. In Just under four days, the activity of radon will be reduced
about 50 percent, and it will be reduced another 50 percent in the following four days, etc. In an
aquifer where typical horizontal flow velocities are on the order of 10-100 cm/day, this limits the
distance over which radon can be transported and still cause significant exposure to a few meters
or less. In bedrock aquifers, where water flow may be primarily through fractures, this distance
might be larger. As noted in Section 4.1, when radon decays in water, the resulting progeny are
much less soluble and mobile, and do not result in appreciable exposures.
Another consequence of radon’s short half-life is that radon levels are reduced when water
is stored for any appreciable time prior to use Thus, water systems which use storage devices
such as water towers, tanks or reservoirs, are already reducmg radon levels in water. The amount
of reduction achieved depends on the average residence time m the storage device, and whether
the storage vessel is open to the atmosphere (see below)
When radon is released to surface water, its high volatility results in rapid release to the
atmosphere. Radon levels in surface water bodies are almost always below measurable levels
Methods, Occurrence, and Monitoring Document 4-1

(NAS, 1998). Systems that store water in contact with the atmosphere therefore achieve radon
reduction both through radioactive decay and volatilization.
4.3. Exposures to Radon in Indoor Air After Release During Domestic Water Use
When water is heated or agitated during domestic use, radon is rapidly released to the air.
NAS (1998) estimates that between 80 and 100 percent of the radon in tap water remams in
solution to be ingested if the water is consumed immediately and is not heated. Between 60 and
80 percent of dissolved radon is released from water from showers, sinks, and washing machines.
If water is heated to boiling (e.g., during cooking), essentially all of the radon is driven off.
The radon level in indoor air resulting from domestic water use is often estimated using a
transfer factor (TF) approach. This transfer factor is defined as the average increase in long-term
radon in air @CifLa) due to a long-term increase of one pCi1L radon m water. The value of the
transfer factor depends on three factors:
o Patterns of household water use (amount, timing, duration, agitation, and
o Volume and air exchange rate of the room in which the water is being used; and
o Volume and air exchange rate of the entire house.
Measured Transfer factors in typical American houses generally fall between 1:1,000 and
1 100,000, with the mean being between 1:10,000 and 1: 15,000. That is, the domestic water
supply entering a house on average needs to have a radon level of approximately 10,000 pCiJl to
increase the average mdoor air level by 1.0 pC iIl This value is estimated based on modeling
studies, validated by some of the measurements described above.
More refined models are available for predicting radon levels as a function of water usage
and building design parameters (e.g, “the three-compartment model”). Generally, it has been
found that, while these models provide additional insights into short-term peak exposures in
specific areas of the home (for, example, in the shower), they provide little improvement in the
quality of long-term estimates of inhalation exposures compared to the simpler transfer factor
4.4 Relationship of Fate and Transport Properties to Radon Behavior in Treatment and
Distribution Systems
As noted above, radon undergoes spontaneous radioactive decay during storage and
residence in distribution systems Thus, radon levels in distribution systems and at the point of
use are usually lower than in the source water (but see below). In addition, radon’s chemical and
physical properties mean that some technologies that are used to remove other contaminants also
Methods, Occurrence, and Monitoring Document 4-2

result m reduced levels of radon These properties have also been used to design treatment
technologies specifically for removmg radon from domestic water. Because radon is an inert gas,
processes which involve chemical treatment of water (e.g , chlorination, ironlmanganese
sequestration, chemical coagulation) do not effect radon levels unless they cause it to volatilize or
be removed bound to solids.
4.4.1 Aeration Technologies
Aeration technologies make use of radon’s volatility to reduce radon levels in treated
water. In the Proposed Rule, (EPA 1999), high-performance aeration has been selected as the
Best Available Technology (BAT) for radon removal The specific technologies which have been
identified include packed-tower aeration, multi-stage bubble aeration, and shallow tray aeration.
In addition, there are other aeration technologies that can also cost-effectively achieve radon
reduction in commercial-scale use All the technologies identified above are capable, under
defined operating conditions, of achievmg at least 99.9 percent radon removal from influent
water. Capital and operating costs can be lower if lower removal efficiencies are required (EPA
1 999b).
A sigmficant proportion of commumty groundwater systems already employ aeration
technologies to remove odors or organic chemicals, or as an adjunct ironlmanganese removal.
EPA estimates (1999b) that between approximately 16 and 24 percent of groundwater systems
serving 1,000 or more customers currently employ some form of aeration treatment. A smaller
proportion of smaller systems also employ aeration technologies. EPA estimates that these
existing technologies are likely to achieve a 90 percent reduction m radon levels in the majority of
4.4.2 Granular Activated Carbon Treatment
As noted above, radon also can be adsorbed onto granular activated carbon (GAC). EPA
has indicated (1999b) that GAC technologies, while not BAT for most systems, may be
appropriate for some very small systems where the capital costs of aeration technologies are
prohibitive. Both point-of-entry (POE) and pomt-of-use (POU) GAC technologies can achieve
up to 99 percent radon removal under certain conditions. However, the amount of carbon and
contact time required to achieve high radon removal efficiencies are considerably greater than
those required to achieve efficient removal of organic chemicals. Thus, at a minimum, changes in
operating conditions would be required to adapt existmg GAC systems (which EPA estimates to
be present at about two percent of all small and very small systems) to address radon
4.4.3 Radon Release from Pipe Scale
As discussed in Section 3.3, there is evidence that radon can be released from pipe scale
pipes in distribution systems. The best information regarding this phenomenon comes from
Methods, Occurrence, and Monitoring Document 4-3

studies of radon distnbutions m groundwater systems from Iowa. Information was provided
concernmg raw and finished water radon analyses from 150 water systems across the state, from
systems of different sizes (Kelley and Mehrhoff, 1993). The geometric mean radon level m the
raw data samples was 284 pCill. As expected, the geometnc mean value of water radon levels
from the fimshed water was lower, at 176 pCi!!. However, the ratio of the radon levels in the
finished water to the raw water varied considerably In a substantial proportion of the cases
(Exhibit 4-1), the radon level in the fimshed water exceeded that from the raw water, by up to six-
Exhibit 4-1. Ratios of Finished/Raw Radon Levels in 150
Iowa Water Systems
Ratio Finished/Raw Radon
Number of Systems
Less than 1.0
1.0-1 5
Radon levels that were higher in finished water than in raw water occurred with varying
frequency across the types of geological formations. When water was drawn from alluvial
aquifers, finished water levels increased over the wellhead levels only five percent of the time
(3/60 systems). In contrast, this phenomenon was seen in 41 percent (9/22) of the wells finished
in Cambrianl Ordovician and 40 percent (2/5) of wells finished in Cambrian! Precambrian units.
Although no specific geochemical data were provided for the systems where the increases
in radon occurred after entry into the systems, the basis for this phenomenon has been previously
described m studies of several of the systems included in the Iowa data (Field et al. 1994, Fisher et
al 1998). The mcreases m radon m the distribution system appear to occur as a result of the
accumulation of iron pipe scale in the distribution systems. The scale sequesters radium, and the
resultant buildup of radium results in the releases of radon into the water as it passes through the
system. The ultimate outcome may be in-system radon levels that substantially exceed the levels
seen in the aquifers from which the water is drawn.
There is little evidence concerning the frequency or severity of this phenomenon outside of
Iowa, although there is no reason to think it would not occur wherever the geochemical
conditions are similar. There would a lower likelihood of scaling and radon buildup in systems
drawing from alluvial aquifers, and more potential for problems whenever iron levels are high and
eH levels low in the producmg aquifer. Systems treating water to reduce iron and manganese
might expect that radon levels would also be reduced m distribution systems.
Methods, Occurrence, and Monitoring Document

4.5 References
EPA (1999a) National Primary Drinking Water Regulations; Radon-222, Proposed Rule, —
Federal _______, (Date 9 )
EPA (1 999b), Regulatory Impact Analysis and Revised Health Risk Reduction and Cost Analysis
for Radon in Drinking Water, Office of Groundwater and Drinking Water, August.
Field, R.W., E L. Fisher, R.L Valentine, B.C. Kross, (1995), “Radium-Bearmg Pipe Scale
Deposits: Implications for National Waterborne Radon Sampling Methods”, American Journal of
Public Health, April, pp 5 67-570;
Fisher, E.L , L J. Fuortes, J Ledolter, D.J. Steck, R.W. Field, (1998), “Temporal and Spatial
Variation of Waterborne Point-of-Use radon in Three Water Distribution Systems”, Health
Physics, Vol. 74, No 2, February , pp. 242-248.
Kelley, R, and M. Mehrhoff , (1993), Radon-222 in the Source and Finished Water of Selected
Public Water Supplies in Iowa, Research Report Number 93-1, Umversity of Iowa Hygiemc
Laboratory, January 13.
National Academy of Sciences (1998), Risk Assessment for Radon in Drinking Water, Committee
on Risk Assessment for Exposure to Radon in Drinking Water, National Research Council,
Methods, Occurrence, and Monitoring Document 4-5