Radionuclide Rule Compliance - American Water Works Association

Transcription

1
Radionuclide Rule Compliance:
Utility Guidance on Analytical Methods
Dr. Andrew Eaton and Mr. Robert Shannon
Copyright ©2015 American Water Works Association
Acknowledgements
This guidance was developed and prepared using a collaborative workshop process to elicit the
expertise and experience of utility, laboratory, and state/federal agency professionals. This
guidance builds on analytical examinations and utility compliance observations associated with
the application of the radionuclide methods.
Dr. Andrew Eaton, Eurofins Eaton Analytical
Robert Shannon, Quality Radioanalytical Support, LLC
Dr. Kevin M. Morley, American Water Works Association
Joe Drago, Kennedy Jenks
Kevin Dixon, CH2M
Michella Karapondo, USEPA
Dan Hauptman, USEPA
Bernie Lucey, New Hampshire Department of Health (Retired)
Dr. Bob Read, Tennessee Department of Health
Robert Rosson, Georgia Tech Research Institute
Glynda Smith, USEPA
Carol Storms, Aqua New Jersey
Zoltan Szabo, USGS
Steve Wendelken, USEPA
Larry Umbaugh, CSC
Project Funding
This project was funded by the American Water Works Association (AWWA), utilizing the Water
Industry Technical Action Fund (WITAF), Project # 327.
3
Contents
Executive Summary....................................................................................................................................... 4
Acronyms, Abbreviations and Units.............................................................................................................. 6
Radionuclide Methods and Compliance Challenges ..................................................................................... 8
Obtaining Reliable Data for Decision Making about SDWA Compliance .................................................... 15
Utility guidance to Enhance Data Reliability ............................................................................................... 16
Method Proficiency Testing ........................................................................................................................ 22
Recommendations for review and action based on analytical results ....................................................... 29
Appendix A: Discussion of ERA Proficiency Testing (PT) Data .................................................................... 32
Appendix B: Calculations Used to Assess Method Performance ................................................................ 42
Appendix C: How Does Measurement Uncertainty Impact Compliance Decisions? .................................. 43
References .................................................................................................................................................. 47
4
Executive Summary
Utilities in many parts of the country are challenged by compliance issues associated with the
Radionuclide Rule, in large part due to the performance limitations associated with the existing
approved analytical methods for radionuclides such as gross alpha activity, radium-226 (226Ra),
and radium-228 (228Ra). When utilities are supplying water that is low in radium and/or gross
alpha, the method limitations do not typically affect compliance. However, when source waters
contain these analytes near decision levels (e.g. 5 pCi/L as a trigger for 226Ra or 15 pCi/L for
adjusted gross alpha (alpha activity minus uranium and radon, but including radium) or 5 pCi/L
for 226Ra, 228Ra or combined radium), selection of appropriate analytical methods and ensuring
that laboratories are performing those methods in a manner to minimize uncertainty is critical.
This guidance document is limited to 226Ra and 228Ra, with discussion of gross alpha as it
relates to 226Ra, but also points out the general issues with the current gross alpha analytical
methods. It provides background on the relevant radionuclide methods that are commonly
used for compliance monitoring for these constituents. It provides criteria by which utilities can
a) evaluate performance of laboratories as pre-qualifications for bids when maximum accuracy
is important; b) set requirements for bid documents to ensure that labs understand the
requirements; and c) let utilities evaluate the data upon receipt to ensure that the laboratory met
the requirements.
The document does not suggest options for utilities which have high adjusted gross alpha
results that cannot be explained by either 226Ra alone or uranium. The document assumes that
uranium measurements are not as problematic as the gross alpha and radium methods. The
guidance document also provides recommendations for selection of the most appropriate
methods and sample handling techniques for compliance monitoring, to assist utilities in
specifying methods that are most likely to provide higher quality results.

To ensure maximum accuracy for gross alpha measurements, in situations where 224Ra
is not a consideration, the document recommends that utilities hold samples for 2-3
weeks before submittal to the laboratory to allow short lived radionuclides such as 224Ra
to decay, and then have the lab count gross alpha immediately (ideally within 24-48
hours) after sample preparation to minimize ingrowth.

For selection of methods, EPA is currently revising Method 900.0, but as it is currently
written it does not result in the most accurate measurements, in part due to the
requirement that samples be held for at least 72 hours after preparation and before
counting.

Specifically, this guidance document recommends that gross alpha measurements be
conducted using the Standard Methods 7110 B protocol with counting immediately after
preparation to minimize ingrowth of radium.

The co-precipitation method (7110 C) is recommended for samples with high dissolved
solids.
5

For radium isotopes, the document strongly recommends the use of the gamma
counting methods developed by Georgia Tech, as they demonstrate better precision and
accuracy in proficiency testing (PT) studies.
The document provides flow charts and tables that should assist utilities in obtaining the best
quality data, given limitations of existing methods, when radionuclide activity is near various
compliance points.
Note that actual compliance with the Safe Drinking Water Act (SDWA) adjusted gross alpha
Maximum Contaminant Level (MCL) is based on a running quarterly annual average, but
individual gross alpha measurements may be highly inaccurate and impact this compliance
decision, whereas the major focus of this document is on the radium measurements and the
gross alpha measurement itself. A utility should keep both issues in mind when evaluating
data.
Appendices to the document provide information on the performance of various methods in PT
studies, examples of relevant calculations for accuracy and precision, and a demonstration of
the issues involved in compliance determinations due to method uncertainty.
6
Acronyms, Abbreviations and Units
%RSD .............. relative standard deviation
133
Ba ................. barium-133
210
Po ................. polonium-210
212
Po ................. polonium-212
214
Bi .................. polonium-216
214
Pb ................. polonium-212
216
Po ................. polonium-216
220
Rn ................ radon-222
222
Rn ................ radon-222
223
Ra ................ radium-223
224
Ra ................ radium-224
226
Ra ................ radium-226
228
Ra ................ radium-228
228
Th ................. thorium-228
228
Ac ................. actinium-228
230
Th ................. thorium-230
235
U .................. uranium-235
AAL .................. analytical action level
Cert Manual .... Manual for the Certification of Laboratories Analyzing Drinking Water
Criteria and Procedures Quality Assurance (5th Edition, 2005) USEPA
CFR ................. Code of Federal Regulations
DL .................... Safe Drinking Water Act Detection Limit
EPA.................. Environmental Protection Agency
ERA ................. Environmental Resource Associates
GA Tech ........... Georgia Tech
GPC ................. gas-flow proportional counting
HPGe ............... high purity germanium
ID ..................... identifier
L ....................... liter
LCS .................. laboratory control sample
LFB .................. laboratory fortified blank
max .................. maximum
min. .................. minimum
MCL ................. Maximum Contaminant Level
mg .................... milligram
mg/L ................. milligram per liter
MS ................... matrix spike
MSD ................. matrix spike duplicate
NJ .................... New Jersey
pCi/L ................ picocurie per liter
ppm .................. part per million (mg/L)
PT .................... proficiency testing
QC ................... quality control
Ra .................... radium
RB .................... reagent blank
RDL .................. required detection limit (RDL)
RER ................. replicate error ratio
RPD ................. relative percent difference
σ ...................... sigma (standard deviation)
7
SDWA .............. Safe Drinking Water Act
SM ................... Standard Methods (for the Examination of Water and Wastewater)
Stnd. Dev. ....... standard deviation
TDS.................. total dissolved solids
USEPA. ............ United States Environmental Protection Agency
USDHS. ........... United States Department of Homeland Security
8
Radionuclide Methods and Compliance Challenges
Utility Challenges
The current Radionuclide Rule, coupled with the precision and accuracy of existing approved
radioanalytical methods, and inherent variability in the way individual laboratories perform the
testing, present potential compliance challenges to utilities. This is particularly true for utilities
which have 226Ra and/or 228Ra present in their source waters. The method variability noted above
impacts the reported gross alpha activity, possibly more even than it does the test results for 226Ra
or 228Ra. Examples of this variability are shown below. The purpose of this guidance document
is to assist utilities in maintaining compliance with the Radionuclide Rule by minimizing method
inaccuracies and imprecision and selecting labs based on performance capabilities that support
these concepts.
Some of the variability seen by utilities is attributable to a lack of specific guidance to laboratories
that would help them navigate the complexity and options available when performing commonly
used approved methods. This would range from the selection of methods, and the size of samples
being processed, to decisions about the timing of sample counts. This all ultimately impacts the
uncertainty in radioanalytical measurement results. Failure to minimize uncertainty can
significantly increase the rate of incorrect decisions about whether drinking water is determined
to be compliant with Safe Drinking Water Act (SDWA) regulations. Decision errors about
compliance can have quite significant consequences. They may result in potential public health
issues associated with failing to identify water with levels of radionuclides that are above
compliance limits. Alternatively, incorrectly deciding that a water system is out of compliance may
result in costly treatment. Either example can result in a concern that is nearly as serious, loss of
public confidence in the water supply.
Background Information about SDWA Approved Methods
Some background about the methods follows that should help put the challenges into perspective.
These observations focus on the most commonly performed methods based on the relative
numbers of proficiency testing results submitted as a laboratory certification / accreditation
requirement.
Gross Alpha – Relevant Background Information and Testing Concerns
Under the SDWA, the primary concern for alpha emitters is long-lived 226Ra, with a half-life of
1600 years, (and to a lesser extent other medium-lived, non-uranium alpha emitters such as 210Po,
with a half-life of 138 days). Gross alpha is a non-specific screening method for alpha emitters. It
is relatively inexpensive but the non-specific nature of the analytical determination can lead to
down-stream compliance risks and costs.
Gross alpha methods should be designed to reliably identify waters that could contain 226Ra in
excess of an amount that would be compliant with the SDWA maximum contaminant level (MCL)
for combined radium (226Ra + 228Ra). The SDWA allows gross alpha results to be substituted for
226
Ra to demonstrate compliance with the combined radium MCL if the sum of the gross alpha
and 228Ra is less than or equal to 5 pCi/L. When the sum of the gross alpha and 228Ra exceeds
the combined radium MCL, a utility is not automatically out of compliance. Rather a radionuclidespecific method for 226Ra is run that presumably will not overestimate the 226Ra activity (see further
discussion of 226Ra methods below). The results of this analysis are then used to determine
compliance with the combined radium MCL. These results may be used to determine compliance
with the combined radium MCL and may increase the frequency of required testing. Both cases
will result in higher overall costs for radioanalytical testing.
9
EPA has also established an MCL for alpha particle emitters (including 226Ra but excluding radon
and uranium), referred to as adjusted gross alpha. When the gross alpha result (“adjusted” by
subtracting the uranium activity) exceeds the MCL of 15 pCi/L, the drinking water is determined
to be out of compliance. This can have consequences that range from additional testing to
implementation of treatment.
Approved methods for gross alpha involve concentrating the sample by evaporation or coprecipitation, followed by analysis of alpha emissions from the test source in a low-background
gas flow proportional counter. Although turn-around times as rapid as 1-3 days are possible,
depending on regulatory requirements, as will be discussed later, the most accurate screening
results for 226Ra will be obtained by delaying preparation of the sample for 2-3 weeks after
collection.
Water utilities should be careful in their interpretation of gross alpha results. It is crucial to keep
in mind that this method is a screen and that it is not specific for 226Ra. It also assumes that the
utility has measured the uranium level, which is also a source of alpha, but is subtracted in
determining the adjusted gross alpha. If alpha emitters other than 226Ra are present, the result
protectively overestimates the activity of 226Ra present. In addition to the presence of alpha
emitters not related to 226Ra, other uncontrolled factors associated with approved methods can
artificially increase the bias and uncertainty associated with measurements of alpha activity.
When 226Ra is present in a sample, the length of time between the preparation and the counting
will dramatically impact the sample result. Radium-226 decays into a noble gas familiar to many
as a radionuclide of concern for indoor air, radon-222 (222Rn), with a half-life of 3.8 days. Since
the evaporation used to prepare samples drives off any dissolved gases, including 222Rn, the
concentration of radon (and its decay progeny) upon completion of sample preparation, will
essentially be zero. The sample at this point has been converted by the preparation process to a
thin layer of solid salts on a 2-inch planchet. From this point, 226Ra continues to decay forming
new atoms of 222Rn. The newly generated radon has limited capability to escape from the solid
salt matrix, which allows it to build up over time. As 222Rn and its short-lived alpha-emitting decay
products, polonium-218 and polonium-214, build up in the sample, the alpha activity in the sample
actually increases. The activity doubles in the first three to four days after preparation and
continues to increase until it reaches a maximum of four times the initial concentration of 226Ra
(See Figure 1) after about four weeks. For example, if a sample containing 4 pCi/L of 226Ra (as
the sole contaminant) is counted immediately after evaporation, the alpha activity will be
approximately 4 pCi/L (less than 1/3 the gross alpha MCL), whereas if the sample count occurs
three weeks after evaporation, the activity could be as high as 16 pCi/L which would be out of
compliance with the MCL for adjusted gross alpha. However, bear in mind that compliance is
determined by the running average of quarterly samples, so even under these circumstances, a
sampling point may or may not be out of compliance based on an individual result.
10
Figure 1: Four-fold Increase in Alpha Activity after Sample Preparation due to 226Ra
Decay Products
Alphas Emitted per Decay of 226Ra
4
3.5
3
Total Alpha Activity
2.5
Ra-226 Activity
2
1.5
1
0.5
0
0.0
3.8
7.6
11.4
15.2
19.0
22.8
Days Elapsed Since Evaporation
26.6
SDWA-approved gross alpha methods have different requirements regarding the minimum time
that must elapse between the preparation and counting of samples. One of the major sources of
interlaboratory variability is associated with labs counting samples containing short-lived
radionuclides at different points after sample collection. For example, the most commonly used
method, EPA Method 900.0, requires delay of the sample count for 72 hours after evaporation
whereas SM 7110B or SM 7110C allow the sample to be counted immediately following
preparation. Depending on the choices made about when the sample is counted, a Method
900.0 result could arbitrarily be 2-4 times that of a Method 7110B or 7110C result. It should be
noted that there are no method restrictions that require samples to be counted more quickly
than is needed to meet holding time restrictions1.
In contrast to 226Ra, 224Ra has a very short half-life of 3.7 days. Although 224Ra is produced through
decay of its parent, thorium-228 (228Th), the solubility of thorium in water is extremely low and
228
Th is rarely present in drinking water. Lacking a radioactive parent, 224Ra begins to decay as
soon as the sample is collected. Following preparation, the alpha emitters in the decay chain
below 224Ra (220Rn, 216Po and 212Po) very quickly reach equilibrium (minutes to hours). After this
point these radionuclides decay as a group over the next several weeks following the half-life
characteristic of 224Ra (see Figure 2).
1
A regulatory hold-time restriction for gross alpha of 180 days from collection to analysis is the upper limit for
delay of the count of a sample. Note that this hold-time is not protective when medium-lived radionuclides such as
210
Po with its 138 day half-life, since it could allow considerable decay of these radionuclides prior to analysis. The
State of New Jersey has implemented much more stringent requirements than the EPA and has prescribed specific
methods gross alpha and radium. Two counts of each sample are required, one quickly (within 24 hours if possible)
to capture the activity of short-lived 224Ra plus unsupported 212Po from unsupported 212Pb (in addition to 226Ra),
and one after 48 hours to protectively capture the activity of short-lived 224Ra plus supported 212Po while accepting
that this will introduce a positive bias in the screening estimate is 226Ra is present in the sample. If the gross alpha
activity exceeds 5 pCi/L, specific 226Ra analysis is required.
11
AlphasEmitted per Decay of 224Ra
Figure 2: Rapid Decay after Sample Collection of Alpha Activity from
Progeny
224
Ra and Decay
3.5
3
2.5
Total Alpha Activity
2
Ra-224 Activity
1.5
1
0.5
0
0
3.7
7.4 11.1 14.8 18.5 22.2 25.9 29.6 33.3 37
Days Elapsed Since Sample Collection
Analogous to 226Ra, when 224Ra is present in a sample, the timing of the count will have a
substantial impact on gross alpha results. Since radium is not lost during preparation of the
sample (as was radon with 226Ra), it is the length of time between sample collection and the count
that matters. Inspection of Figure 2 shows that, in contrast to 226Ra, the sooner the sample is
counted, the higher the result will be. The ingrowth of progeny from 224Ra detectable by the gross
alpha test takes place on the order of minutes, hence the very sharp increase in gross alpha
immediately after sample collection.
If 224Ra is of regulatory concern, such as is the case in New Jersey, the sample must be counted
as quickly following collection as possible, but not longer than 72 hours. In NJ, on the basis of the
prevalence of 224Ra in major aquifers, gross alpha is used as a conservative test to capture
elevated levels of 224Ra that are considered to be of regulatory concern. If 224Ra is not of regulatory
concern, however, the presence of this short-lived radionuclide will be detected by the gross alpha
measurement and increase the risk of non-compliance. In such cases, delaying the count of the
sample will minimize the likelihood that the gross alpha MCL will be exceeded.
Another limitation of all approved gross alpha evaporation methods2 relates to interference from
sample solids. High sample solids is a recognized interference to evaporation methods. Most
methods require that laboratories limit the size of sample that can be measured to that which will
produce less than one-hundred milligrams of dried solids. As sample solids concentrations
increase, the size of the sample that can be counted decreases and the uncertainty of results
increases. If solids concentrations are too high, it may not be possible for a laboratory to meet the
SDWA Required Detection Limits (RDL) for gross alpha of 3 pCi/L. While there is no formally
enforced limit, Standard Methods and EPA methods recommend using a co-precipitation method
instead of the evaporation method for samples containing more than 500 mg/L of total dissolved
solids.3
Although laboratories must adhere to the 100 mg limit on solids, and some laboratories extend
counting times to meet Required Detection Limits, these measures may not always produce
results that are compliant with SDWA requirements for sensitivity. It may be difficult or impossible
for data users (or even laboratories) to identify non-compliant data unless the laboratory
2
3
All methods except SM 7110C and EPA 00-02 rely on evaporation of the sample to prepare the test source.
SDWA-approved methods, SM 7110C and EPA 00-02, use the principle of co-precipitation to chemically isolate
alpha emitters from sample solids which can usually produce SDWA compliant results for samples containing
elevated solids above 500 mg/L.
12
calculates and reports the actual (a posteriori) SDWA Detection Limit achieved for each sample
result using information specifically associated with that sample. This sample-specific information
allows utilities to more readily identify non-compliant results that are not of sufficient quality to be
used to make compliance decisions.4
Another source of interlaboratory variability for the evaporation methods results from counting
sample planchets with unevenly distributed solids residues. While this is in part an intrinsic
weakness of a method that requires evaporation of a wide variety of types of waters, weak
laboratory technique can exacerbate the issue. Finally, an EPA Method 900.0 requirement
specifies that laboratories calibrate the instrument using solid residues obtained by evaporating
their tap water. This may result in calibration standards that are both poorly intercomparable with
other laboratories and poorly representative of samples being analyzed5, and thus introduce
varying degrees of bias into gross alpha measurements. The impact of these two issues on the
utilities’ results are best controlled by ensuring that results for internal quality control (QC) data
(laboratory control samples (LCS) and matrix spikes (MS)), and for proficiency testing (PT) show
results that are consistent with minimum requirements presented later in this document (i.e., Table
4).
Radium 226 (226Ra) - Relevant Background Information and Testing Concerns
Three general analytical approaches are used by SDWA-approved methods for 226Ra
determinations: gas-flow proportional counting (GPC)6, radon emanation methods, and gamma
spectrometry. The cost and reliability of these methods varies. In general, higher cost tends to
be positively correlated with better performance and reliability.
Precipitation and Gas Flow Proportional Counting Methods
Most 226Ra methods rely on the measurement of alpha emissions. The least costly of the methods
tend to be precipitation methods of which EPA Method 903.0 and SM 7500-Ra B7 are the most
widely used. Although the methods are generally described as screening techniques for 226Ra,
they can be run in a manner that eliminates interference from 224Ra producing results that will
provide accurate measurements of the true 226Ra concentration in the sample.
These approaches all combine chemical complexation with co-precipitation to produce a test
source of purified radium in a barium sulfate precipitate. Alpha emissions from the test source are
analyzed using low-background gas flow proportional counting 8 with corrections applied for
detection efficiency, ingrowth, and in the case of SM 7110 B (but not EPA 903.0), chemical yield.
The turn-around time for this method can be as quick as 24 hours, although, as will be discussed
below, higher quality results can be obtained by delaying the counting of the sample after
preparation for up to three weeks.
These methods measure alpha-emitting isotopes of radium and are commonly given the
misleading name of “Total Radium” or “Total Alpha-Emitting Radium Isotopes”. Since isotopes of
a given element cannot be chemically separated from one another, the test source will contain
any radium isotopes present in the sample, including 228Ra, 226Ra, 224Ra, and 223Ra. While 228Ra
4
See the Generic SDWA Detection Limit Calculation in Appendix B.
since the chemical composition of dissolved solids in the calibration matrix differ from than that of samples being
analyzed
6
Alpha scintillation of the evaporated test source is permissible but is only infrequently performed. Alpha spectral
methods are available but not approved.
7
SM 7500-Ra D may optionally incorporate the precipitation approach used in SM 7500-Ra B.
8
Other alpha detection methods may be used but this is rare. The alpha spectral method is more sensitive but
requires more detailed wet chemistry preparation.
5
13
is of regulatory concern, it is a low-energy beta emitter and will not be detected using these
methods that are sensitive only to alpha emitters9. The other three radium isotopes are all alpha
emitters that will be detected if they are present in the test source at the time of the count. 226Ra
is the analyte of concern. 224Ra is an interference to the determination of the methods meant to
screen for 226Ra.10 While 224Ra is often present in freshly collected samples at levels similar to
228
Ra, it decays away in the first 2-3 weeks after sample collection (see discussion and Figure 2
above). 223Ra is a member of the naturally-occurring 235U decay chain that may be present in
samples at the time of collection at approximately five percent the concentration of 226Ra so it
does not contribute very significantly to the overall activity.
This precipitation / GPC method is generally described as a screening technique for 226Ra. The
largest weakness of this method regards interference from 224Ra. Similar to the approach
discussed for gross alpha above, delaying the sample count until at least 2-3 weeks after
collection allows time for 224Ra to decay away (see Figure 2). During this time, 222Rn and its
progeny continue to ingrow (see Figure 1) and effectively amplify the signal from 226Ra. This
further overwhelms any interference remaining from 224Ra to the point where its impact is
equivalent to less than about 2% of its original activity.
One difference between the two most commonly used approaches is that EPA 903.0 does not
apply a chemical yield correction, whereas SM 7110 B does. Radiochemical methods routinely
correct results for losses occurring during chemical separation based on the recovery of
carriers/tracers that are added to the sample prior to processing. Failure to account for such
losses could result in significantly low results and failure to properly identify water as being out of
compliance with SDWA requirements.
Interlaboratory proficiency testing data for 226Ra precipitation / gas flow proportional counting
methods (Appendix A) show positive bias and high relative uncertainties. The skew toward high
results may be evidence that at least some laboratories are counting ERA Proficiency Testing
samples (PTs) that contain ingrown 224Ra promptly after separation. EPA 903.0 shows a mean
recovery of 107% and a relative standard deviation (%RSD) of 44% with the average recovery
and %RSD rising to 120% and 70%, respectively, at concentrations in the 3-10 pCi/L range where
compliance decisions are made. A high %RSD for proficiency testing results, especially when
there are data from large numbers of laboratories, usually indicates that a method is inherently
variable. SM 7500-Ra B shows a mean recovery of 100% with a %RSD of 16%. Although there
is no change in average recovery, the %RSD rises to 20% at concentrations in the 3 -10 pCi/L
range where compliance decisions are made. While the reason for the difference in performance
of the two similar methods cannot be determined with certainty, the extended discussion in
Method SM 7500-Ra B of the impact of 224Ra on measurements may prompt laboratories to delay
counting of sample to address the interference.
Radon-Emanation Methods
In contrast to the precipitation methods above, which are often described as screening methods,
radon emanation methods are generally considered to be definitive or confirmatory methods
capable of very accurate and precise measurements. The cost for these methods tends to be
higher than the precipitation GPC approach.
Radium in the sample is first chemically separated using the complexation approach common to
the precipitation methods above. The precipitate is dissolved and the liquid transferred to a
bubbler apparatus, purged of radon, and sealed and stored for a period of time to allow 222Rn to
9
See below for further discussion of 228Ra methods.
Except in New Jersey.
10
14
ingrow (see Figure 1). The radon gas is then carefully flushed into an alpha scintillation cell for
counting on a photomultiplier tube device.
This is an old, but tried -and-true method. When run reliably, it can deliver accurate and precise
measurements. In practice, however, it is very time intensive and technique dependent. It requires
complex glassware and a skilled analyst. The most commonly run method, EPA Method 903.1,
does not correct results for losses during processing (chemical yield). Unknown losses of radon
can also occur during the transfer of radon gas. While in the hands of a capable analyst, these
losses are generally, on average, minimal, but more significant issues may occur with individual
samples and the problem will never be detected. Frequent analysis of standards can help identify
recurring leakage and weak technique, but the additional quality control is time consuming and
costly. Turn-around times for this method vary from 1 - 4 weeks depending on the length of the
ingrowth period used by the laboratory, with 3-4 weeks being typical to achieve the best sensitivity
levels.
Interlaboratory proficiency testing data for EPA Method 903.1 (Appendix A) show an average
recovery of 97% with a %RSD of 18%.
Gamma Spectrometry Methods
With gamma spectrometry methods, radium in the sample is co-precipitated with barium sulfate.
The crystalline precipitate, which does not allow ingrowing radon to escape, is stored for a period
of time (generally 2-4 weeks) to allow 222Rn and its decay progeny, 214Bi and 214Pb, to come to
radioactive equilibrium. During this time, 228Ac, the decay product of 228Ra also comes to
equilibrium with 228Ra. The precipitate is then measured on an HPGe gamma ray spectrometer
and the activity of 226Ra and 228Ra calculated from ingrown progeny activity.
This is a newer option for drinking water analysis. High Purity Germanium (HPGe) gamma-ray
spectrometry, however, has been used for at least two decades to produce highly accurate and
precise determinations of 226Ra and 228Ra in water samples. While the sensitivity of this approach
may not quite match that of the precipitation or de-emanation approaches, this is more than
compensated for by the reliability and specificity possible using gamma-ray spectrometry, and the
relative ease and robustness of sample preparation and analysis. While the cost of this method
tends to be somewhat higher than for the precipitation and de-emanation methods (due to the
high cost of the detection system), it does allow both 226Ra and 228Ra to be determined in a single
measurement. To increase the sensitivity at low levels, however, large sample sizes (e.g., 3-4
liters) and / or a considerable increase in counting time is needed.
Given that this is a method has only been more recently approved for use with SDWA, the
interlaboratory proficiency testing data (Appendix A) are sparse; however results are generally
tighter than for the other types of methods. The most frequently performed method is the Georgia
Tech (GA Tech) method. Average recovery for 226Ra is 99% with a %RSD of 12%.
Radium 228 (228Ra) - Relevant Background Information and Testing Concerns
Two general analytical approaches, gas-flow proportional counting (GPC) of beta emissions and
gamma spectrometry, are used by SDWA-approved methods for 228Ra determinations. Both of
these involve measurement of 228Ac, the short-lived decay progeny of 228Ra. The cost and
reliability of these methods varies. In general, higher cost tends to be positively correlated with
better performance and reliability.
Chemical Separation of 228Ac Followed by Gas Flow Proportional Counting
Most 228Ra methods, including EPA Methods 904.0, Ra-05, SM 7500 Ra-D and several older EPA
methods, rely on the measurement of the beta emissions from purified actinium-228 (228Ac)
15
progeny in a low-background gas-flow proportional counter. The 228Ac measurement follows
extended and complex chemical separation schemes involving complexation, coprecipitation/precipitation, and in some cases, liquid-liquid extractions. Calculation of the final
result involves applying correction factors to the count results. These correction factors include
instrument response (efficiency), decay and ingrowth of the radionuclides, and chemical yield,
each of which can introduce significant uncertainty and bias into the final result. For these
methods, however, the combined uncertainty associated with the correction factors can be
significant. Because SDWA specifications for uncertainty currently only consider counting
statistics (“count uncertainty”), the uncertainty reported in association with results is likely to
significantly underestimate overall uncertainty.
Interlaboratory proficiency testing data (Appendix A) for approved 228Ra methods that employ gas
flow proportional counting show average recoveries ranging from 97-108% (overall average
100%), with %RSDs ranging from 20-26% (overall 24%). It is noted that the acceptance range
for PT samples containing 228Ra at the 5 pCi/L MCL is 41% to 153% and for PT samples
containing 228Ra at 15 pCi/L where counting uncertainty is lower, would be 53% - 135%. EPA’s
Drinking Water Certification Manual specifies that recoveries for control samples (LCS/LFB) which
can be spiked at the higher activity, should fall in the range of 100 ± 20% (1σ = 8.3%).
Gamma Spectrometry Methods
The general gamma spectrometry method was described previously in the 226Ra discussion and
is not repeated here. Given that this is a newer method, the interlaboratory proficiency testing
data (Appendix A) is sparse. The most frequently performed method is the Georgia Tech (GA
Tech) method. Average recovery for 228Ra is 102% with a %RSD of 16%, significantly more
precise than the other methods.
Obtaining Reliable Data for Decision Making about SDWA Compliance
At present, there are insufficient criteria in the existing methods to ensure that utilities will
consistently get reliable results from multiple labs, even while the labs are following approved
methods. The purpose of this section is to provide a framework for utilities to use in contracting
with laboratories that, if followed, will allow them to improve the precision and accuracy of
measurements. Ultimately, EPA needs to update the SDWA radionuclide methods, but that is
not a short term solution. In the meantime utilities need to know that before they invest significant
capital on treatment systems, that they truly have verified a compliance problem.
PT acceptance ranges are established based on a statistical evaluation of historical PT results.
These acceptance criteria reflect actual laboratory performance, using available approved
methods, as written, as opposed to being driven by an evaluation of the quality of results needed
to maintain decision errors about compliance at low and tolerable levels.
At the low end of the PT acceptance range, counting uncertainty is by far the largest contributor
to overall uncertainty of the result. This error-source identification is positive since counting
uncertainty is generally the most predictable and easily managed component of uncertainty. The
effect on the results can be minimized by processing larger amounts of sample and by extending
sample count times. Neither of these measures requires that methods be modified so they can
be done within the bounds of approved methods. As larger sample sizes are processed and count
times are extended and measurement uncertainties approach a minimum, the uncertainty is
controlled by uncertainties associated with the core efficacy/reliability of the analytical approach
itself, factors such as the uncertainty associated with yield determinations and detector
calibrations.
16
For this reason, EPA’s Drinking Water Certification Manual specifies that the recovery for control
samples (LCS/LFB), which can be spiked at higher activities, should fall within the range of 100
± 20%. This ensures that relative uncertainties be maintained at approximately 8.3% (1σ) and
forces laboratories to ensure that they have control of core analytical process (as opposed to
relying on counting uncertainty to explain anomalous results).
Once laboratories have control over the core integrity of their analytical method, they and the
utility are in a position to obtain data optimized to make reliable decisions. By using performance
data such as QC and PT sample results, water utilities can identify reliable and well qualified
laboratories to perform analysis. They can make ongoing decisions that balance the need for
high precision, accuracy and reliability against cost based on what they do (or do not) know about
water samples. For example, if they expect results to be close to key decision points (e.g., MCLs
or levels that impact the frequency of required testing) or if they just do not know what levels of
contaminant may be in a sample, they can instruct the laboratory to minimize result uncertainty
by implementing more costly measures. Such measures might include using the most reliable,
accurate and precise methods, processing larger samples, and/or extending count times. In
contrast, when results are expected to be well below key decision points and the need for
precision is lower, they can allow the laboratory to use less costly analytical approaches. This
requires extensive communication with the laboratory that should be considered as part of the
original contracting process between the lab and the utility.
Utility guidance to Enhance Data Reliability
Flow Charts to Assist Utilities in Lab Evaluation and Contracting
Default analytical methods will not necessarily produce results that ensure reliable decisions
about whether water samples actually comply with SDWA requirements. These two sets of flow
charts (Figures 3 and 4), along with Tables 1 through 3, will help utilities select the analytical
methods and contractual terms that will help them maximize the likelihood of correct compliance
decisions by selecting reliable and capable laboratories, and using more optimal methods and
analytical parameters. The recommendations also consider some key characteristics of samples
and should result in minimizing uncertainty and bias and producing data that will help minimize
the risk of costly incorrect compliance decisions. These are presented in two steps.
The first flow chart addresses the process that can be used to identify laboratories that are
qualified and capable of meeting and exceeding minimum requirements specified in EPA’s
Manual for the Certification of Laboratories Analyzing Drinking Water Criteria and Procedures
Quality Assurance (5th Edition, 2005).
Seek another
lab for this
parameter
No
Consider whether lab can
function as back-up for
parameters for which they
are certified.
No
Is
lab in good
standing
(certification/
accreditation)
for all
parameters?
Evaluate qualifications
from each lab
Request qualifications
from each potential lab
Consult list of
approved labs for
required parameters
Yes
Yes
No
Yes
Acceptance
ranges for batch
QCs for each
parameter per
Cert Manual
specifications
(see Tables
1-3)
Yes
Review internal QC result
information
Review PT results and corrective
actions for each parameter
Is
historical PT
performance
satisfactory
for each
parameter?
No
Seek another
lab for this
parameter
Yes
Write request for bid Including
requirements to implement
recommendations of this
report.
Evaluate bids and confirm
capabilities and award to
one or more of the best
qualified labs.
Send compliance samples for
analysis.
Ensure on an ongoing basis that reported results are
adequate to support compliance decisions.
Verify RDL has been met, that uncertainties were
optimally managed using aliquot size, count duration, and
timing of the count relative to collection and preparation.
17
Figure 3: Procurement of Radiological Laboratory Services for Reliable Drinking Water
Compliance Measurements
Use State of New
Jersey approved lab
and methods.
(48-hour hold-time for
2 counts)
Yes
Is 224Ra a
concern for
compliance
(State of NJ)
?
No
No
Will
samples
contain
>500
mg/L
solids?
Yes
Any EPA-approved
gross alpha method
may be used
Flow chart for selection of method and optimal
analytical parameters for gross alpha
Analyze using
default method
parameters to meet
RDL
Use approved
evaporation or
coprecipitation
method
Use a
coprecipitation
method
(e.g., SM 7110C or
EPA 00-02)
No
Yes
Gross
alpha
> ½ MCL
(7.5
pCi/L)
Take measures to minimize uncertainty
(i.e., use more reliable/sensitive method,
increase aliquot, increase count duration, adjust
timing of preparation and count to address
decay progeny
Yes
Is
combined
radium
>2 pCi/L
Yes
Past
radiological
testing
results
available?
No
No
Take measures to minimize uncertainty until
the true alpha activity of the water is known
(i.e., increase aliquot and count duration, delay
preparation until 2-3 weeks after collection,
and specify method that allows count of
prepared sample within 24 hours of prep) and
require prompt counting after preparation.
18
The second flow chart addresses selection of methods and analytical parameters for required
parameters. This flow chart assumes that the laboratory selected to do the work has been chosen
using a process similar to that proposed in the first flow chart.
Figure 4: Election of Optimal Methods and Analytical Parameters for Reliable Drinking
Water Compliance Measurements for gross alpha.
19
Sample Scope of Work – Background and Rationale
The EPA has indicated that it intends to make improvements in approved EPA methods or to
push for changes in methods from other organizations such as Standard Methods (as well as
potentially withdrawing methods that do not meet performance or expectations for QC, etc.). Until
changes for compliance monitoring are made and codified through rulemaking and other
processes, there are limits to what utilities can do to improve data quality. We suggest that utilities
who may have potential radionuclide concerns consider incorporating this scope of work into
requests for pricing and laboratory contracts. An explanation of the rationale for each step is
shown. Note that some states may have requirements that supersede this guidance, in which
case the state requirements must be satisfied.
Some of the recommendations go beyond literal requirements of the SDWA program – but
following these requirements will improve the accuracy and precision of results and can
minimize the rate of decision errors about compliance with SDWA requirements.
Gross alpha analysis
 Gross alpha is meant to screen for longer-lived radionuclides, principally 226Ra and uranium,
and for medium-lived nuclides such as 210Po. In cases where short-lived nuclides such as
224
Ra or other short-lived nuclides are not of regulatory concern11, delaying analysis of the
sample will minimize interference of short-lived radionuclides and produce results that most
accurately estimate of the activity of longer-lived radionuclides in the sample. Interference
from 224Ra can best be minimized by holding samples for several weeks after collection before
submittal to the laboratory (or by having the laboratory delay initiating analysis of samples for
the same time). This ensures that by the time the sample is counted, short half-lived nuclides
such as 224Ra have decayed.12 This consistency in hold time will also minimize interlaboratory
variability associated with labs counting samples containing short-lived radionuclides at
different points after sample collection. It is important, however, to minimize the time period
before analysis to ensure that moderately-lived nuclides that can be of concern (e.g. 210Po,
with a half-life of 138 days) will still be reliably detected. Since alpha activity from 210Po is of
regulatory concern, holding the sample for the maximum permissible time of 180 days is
neither protective nor advisable because more than half the 210Po will have decayed during
the holding time.

For all samples:
o Ensure that the laboratory meets all requirements defined in 40 CFR 141 and that the
laboratory uses a validated method that satisfies the batch quality control requirements
summarized in Table 4 below. Many laboratories do not currently adhere to the
specifications for batch quality controls presented in EPA’s Laboratory
Certification Manual. Although it is considered to be guidance in some states,
EPA requires that state primacy laboratories meet the requirements.
Incorporating its requirements into scopes of work will help minimize the
11
New Jersey regulates 224Ra. NJ’s required methods require initial and second counting of the sample within 48
hours of collection which will help ensure that samples containing significantly elevated levels of 224Ra will be
reliably identified. If the gross alpha at that point is elevated above 5 pCi/L, testing for 226Ra directly is indicated.
This approach conservatively presumes uniform strong association among the Ra radionuclide occurrences,
which is true for many (but not all) aquifers. The additional alpha count of the sample approximately three
weeks after preparation with amplifed signal from 226Ra, is not required although it is advisable. Exceeding the
15 pCi/L MCL for Combined Gross Alpha after the counts are completed within 48 hours necessitates action by
the utility on the basis of the prevalence of 224Ra in aquifers of the State of New Jersey.
12
For example, only 7% and 2%, respectively, of the amount of 224Ra initially present will remain 14 and 21 days
after sample collection (Figure 2).
20
uncertainty of results and improve the reliability of decisions about SDWA
compliance.
13
o
Count gross alpha samples as soon as possible after evaporation or co-precipitation.
226
Ra decay progeny ingrow over time and the longer one waits after preparation
the higher the apparent gross alpha may become. Even 96 hours may increase
the gross alpha due to 226Ra by up to two times, but method 900.0 currently
requires a minimum 72-hour holding time after evaporation.
 If using EPA Method 900.0, count the sample as soon as possible after the
required 72-hour holding time between preparation and the count.
 If using a method such as SM 7110 B, EPA 00-02, or SM 7110 C, there is no
hold-time, so the sample may be counted as soon as possible after
preparation.
o
Ensure that the SDWA Required Detection Limit (RDL) of 3 pCi/L has been met for
each sample by optimizing the sample aliquot and count time.
 Optimize the volume of sample taken for analysis – There are multiple
sources of uncertainty in the gross alpha analysis, but the dominant
source in low-activity samples is the counting uncertainty, which is
inversely proportional to the square root of the number of counts.
Processing larger sample aliquots will provide higher signal-to-noise and
decrease the counting uncertainty. Beyond practical limitations
(available equipment, bounds of validated methods), the maximum size
of sample that can be processed is limited by methods to that which will
produce ≤ 100 mg of solid residue in a 2” planchet.
 If sample TDS concentration is known, process enough sample to
ensure that the RDL will be met in the count time planned for samples.
Gross alpha counting efficiency is highly impacted by the solids
present in the sample. Lower counting efficiencies result in lower
count rates and much greater uncertainty.
 If solids concentrations in samples are unknown, estimate the TDS
(using conductivity of an unpreserved portion of multiplied by 0.6).
Alternatively a small portion of sample may be evaporated and used to
estimate the solids in the sample. Once an estimate of the solid content
is obtained, this can be used to calculate the amount of sample needed
to produce residues that approach but do not exceed 100 mg in a 2”
diameter planchet
 If the TDS concentration is known to exceed 500 ppm, analyze the
sample using a coprecipitation method (e.g., SM 7110 C) rather than
an evaporation method (e.g., EPA 900.0 or 7110 B).
 Clearly, there is a practical limit to how long a sample can be counted.
Count samples to meet a SDWA detection limit of 3 pCi/L, or to result
in a relative counting uncertainty of less than or equal to 16% (1.96σ)
assuming 15 pCi/L is present in each sample, whichever is longer.
 The laboratory should calculate the actual SDWA DL13 achieved for
each sample and QC sample analyzed and verify that they have at least
met the RDL of 3 pCi/L for gross alpha. Require that the laboratory
report, for each result, the DL achieved in the laboratory report to the
utility and to regulators (see Appendix B for a generic calculation). If the
A generic calculation for the SDWA Detection limit is presented in Appendix B. Note that the SDWA DL is specific
to the SDWA and should not be confused with other detection concepts such as: LLD, MDA, MDC, RL, or Lc. The
SDWA DL should be calculated and reported for each sample result.
21
detection limit is not met, consider reprocessing the sample using more
optimal conditions to obtain the required sensitivity.

If sample gross alpha concentrations are unknown, may be variable, or are known or are
expected to be within 5 pCi/L of the 15 pCi/L MCL, proceed as follows, and as price permits:
o Use the most reliable method for analysis. Based on PT data analyzed in this paper,
we would recommend that SM 7110 C be used (regardless of solids content) since it
allows use of a significantly larger aliquot while producing a much more reproducible
test source;
o Follow recommendations from above regarding delay of processing samples until 2-3
weeks after collection;
o Minimize the time between the preparation and counting;
o Maximize the sample aliquot. If possible process up to 1 L of sample to minimize
uncertainty;
o Increase the counting time to target 1σ counting uncertainties of 5-8% (or better);
o Ensure that requirements for batch QC samples summarized in Table 4 are met or
exceeded.
o Review all results to ensure that only results that are compliant with SDWA
requirements are used to make compliance decisions.
228
14
Ra analysis
 Ensure that the laboratory meets all requirements defined in 40 CFR 141 and that the
laboratory uses a validated method that satisfies the batch quality control requirements
summarized in Table 6 below.
o Preferably specify the use of the GA-Tech method in lieu of EPA Method 904.0.
The specificity of the spectrometric method and the ability to more easily
process much larger samples produces more precise and accurate results.
Interlaboratory study results indicate that the GA Tech method yields results
with a relative standard deviation of 16% (1σ), as compared to 26% for EPA
Method 904.0 (see discussion above and data in Appendix A)
o If using Methods 904.0 or 7500 Ra-D which require determination of yield using
gravimetric methods, the laboratory’s LCS and MS recoveries should be inspected.
These methods have numerous chemical separation steps and
measurement of the barium and yttrium yield can be inaccurate. This can be
exacerbated if samples contain more than a few mg of barium to begin with.
(In theory elevated levels of barium should not occur in finished drinking
waters, as the barium MCL is 2 mg/L but some source waters may contain
high levels.)
 If mean/median values significantly less than 100% are observed, we
recommend that yield measurements be confirmed by monitoring barium
with either ICP-AES or ICP-MS analysis or by using 133Ba as a tracer. If
gravimetric yield and confirmation method differ by more than 10%
absolute, repeat sample preparation with a fresh aliquot as the nongravimetric techniques are not currently allowed for compliance
measurements until new versions of the methods are approved (Consider
whether re-precipitation (i.e., repeating BaSO4, or Y2(C2O4)3 precipitation
steps) may be used to purify precipitates)14. Alternatively, use a more
reliable method (e.g., GA Tech).
This may require involving the regulator to obtain concurrence on the approach to be used.
22

Optimize the sample aliquot and count samples to meet a SDWA detection limit of 1 pCi/L,
or to result in a relative counting uncertainty of 16% (1.96σ) assuming 5 pCi/L is present
in each sample, whichever is more restrictive.
o The laboratory should calculate the actual SDWA DL achieved for each sample
and QC sample analyzed (see Appendix B for a generic DL calculation) and verify
that they have at least met the RDL of 1 pCi/L for 228Ra. Require that the laboratory
report, for each result, the DL achieved in the laboratory report to the utility and to
regulators (if the regulatory reporting system allows that). If the detection limit is
not met, consider whether reprocessing the sample using more optimal conditions
will result in meeting the required sensitivity.
Method Proficiency Testing
Method-Specific PT studies support these recommendations
Appendix A contains a detailed summary and analysis of proficiency testing results by analyte
and method that indicate performance for different methods for all drinking water laboratories.
The data also show differences between methods as shown in the following proficiency testing
data review.
Overall Performance of Approved Gross Alpha Methods Based on Proficiency Testing
Results
Laboratory performance for proficiency testing samples run as an ongoing requirement for
laboratory certification / accreditation for gross alpha is summarized in Table 1. 15
Table 1:
Summary of Gross Alpha Proficiency Testing Results from ERA PT
Studies 55-99
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 900.0
1537
95%
24%
27%
52%
93%
148%
246%
EPA 00-02
223
91%
20%
40%
49%
93%
130%
195%
SM 7110 C
198
92%
16%
7.5%
62%
92%
124%
133%
SM 7110 B
162
97%
22%
7.2%
54%
98%
137%
174%
2119
94%
23%
7.2%
52%
93%
143%
246%
Method
Gross
Alpha
All Methods
Interlaboratory proficiency testing samples contained activities ranging from 7 pCi/L to 70 pCi/L.
The NELAC FOPT table acceptance ranges for Gross Alpha (230Th) PT samples at 7 pCi/L, 15
pCi/L (the MCL for Corrected Gross Alpha), and 25 pCi/L are 10%-204%, 25%-167%, and 38%154%, respectively.
The result that ranges for recovery converge towards 100% with increasing activity is consistent
with findings of other such tabulations. Although the distribution of results is largely normal, long
tails reflect intermittent extreme results. It is not clear whether this reflects method performance
or the fact that data contain results from more and less reliable laboratories.
PT results for gross alpha evaporation methods showed an average recovery of 95% and a %RSD
of 23% (1σ). At concentrations close to the MCL of 15 pCi/L where compliance decisions are
made, the %RSD for Method 900.0 was somewhat higher at 29% (1σ) with SM 7110 B largely
15
See Appendix A for detailed analysis of drinking water laboratory proficiency testing results.
23
unchanged at 22% (1σ). PT results for Gross Alpha co-precipitation methods showed an average
recovery of 92% with an %RSD of 18% (1σ). For method SM 7110 C, at concentrations close to
the MCL of 15 pCi/L, where compliance decisions are made, the average recovery was 91% with
a %RSD of 15% (1σ). At concentrations around the MCL, EPA co-precipitation Method 00-02
showed average recovery of 96% and %RSD of 26% (1σ).
For the four approved methods for which there were a significant number of results provided,
there were notable differences in the quality of results. While the range of average recoveries
among the methods was relatively small (91%-97%), the most commonly used method, EPA
900.0, showed the poorest precision with a standard deviation of 24% (1σ). In contrast, coprecipitation method SM 7110 C, showed a relative standard deviation of 16% (1σ) which is 2033% lower than the other methods, likely a result of the nearly uniform planchet matrix and mass
generated by the technique. For 7110 C, 95% of reported results fell between 62% and 124%, a
range that, although slightly skewed low, is close to the ideal range targeted for internal quality
control sample results (LCS/LFB) in the Drinking Water Certification Manual. As such, SM 7110 C
would appear to be the best method available for samples with unknown activities, or samples
with true activities close to a trigger point.
It is important to note that the alpha emitter in gross alpha PT samples is 230Th, which does not
exhibit the time-sensitive changes in activity discussed for 226Ra and 224Ra. Thus, PT statistics
provide a false sense of security about the quality of results that will be obtained when
analyzing real samples. As described above, and depending on individual laboratory practices,
time-sensitive effects may introduce additional bias and uncertainty into actual test results in
excess of 400% of the activity of radium isotopes present. Especially as the sample activity
approaches the MCLs, the uncertainty apparent in the PT results will combine with uncertainty
associated with the timing of the count and significantly increase the risk that measurement
conditions may result in arbitrary compliance decisions.
If gross alpha were used only as a screening technique for radium, and if exceedances were
always followed by confirmation using more reliable testing methods (such as is the case for 226Ra
or beta emitters), elevated uncertainties might be tolerable. This is not the case for adjusted gross
alpha, however, where the result obtained is compared directly to the gross alpha MCL to make
a final compliance decision. Thus, uncontrolled uncertainty (and bias) in the gross alpha
measurement can have quite a large and arbitrary effect on compliance decisions. Further
discussion of the impact of measurement uncertainty and measures that might be taken to
minimize its negative impact on compliance decisions follows below.
24
Overall Performance for 226Ra Methods Based on Proficiency Testing Results
laboratory certification / accreditation for 228Ra is summarized in Table 2.16
Table 2:
Summary of 226Ra Proficiency Testing Results from ERA PT Studies 55-99
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 903.0
534
107%
44%
16%
80%
103%
321%
619%
EPA 903.1
SM
7500-Ra-B
Ga. Tech
312
97%
18%
23%
61%
97%
125%
223%
150
100%
16%
55%
70%
99%
133%
171%
33
99%
12%
77%
85%
99%
125%
143%
1029
103%
34%
16%
68%
99%
146%
619%
Method
Radium
226
All Methods
Interlaboratory proficiency testing samples contained with activities ranging from 3 pCi/L to 20
pCi/L. PT acceptance ranges for samples containing 226Ra at 5 pCi/L (Ra MCL) and 15 pCi/L are
65%-133% and 64% - 125%, respectively. Convergence in the ranges of recovery is not as
noticeable with increasing concentration as it is for increasing gross alpha activity because the
specific isotope analyses for 226Ra uses more elaborate preparation techniques and
instrumentation that produce results considerably more accurate and precise than the gross alpha
measurement (the exception being use of GPC for Method 903.0).
Among the four approved methods for which there were a significant number of results provided,
there were notable differences in the quality of results. While the difference in average recoveries
among the methods was relatively small (99-107%), the most commonly used method, EPA
903.0, demonstrably showed the poorest precision with a standard deviation of 44% (1σ). In
contrast, the least commonly used method, the gamma spectrometry method from Georgia Tech,
showed a standard deviation of 12% (1σ) which was 25-73% better than the other methods.
Consistent with this observation, 95% of reported results for the Georgia Tech method fell
between 85% and 125%, a range that is very close to the ideal range 80%-120% targeted in the
Drinking Water Certification Manual for internal quality control sample results (LCS/LFB). As
such, the Georgia Tech gamma spectrometry method would appear to be the best method
available for samples with unknown activities, or samples with true activities close to a trigger
point.17
Overall Performance for 228Ra Methods Based on Proficiency Testing Results
laboratory certification / accreditation for 228Ra is summarized in Table 3.18
16
17
It is noted that the number of data points available for the GA Tech method was small, but the statistics are
consistent with method performance that would be expected using much more modern spectrometric
instrumentation. There is a possibility of inadvertent sample compilation bias with regards to this method – if
only experienced labs offering high level of sample care from expert analytical staff use it. Investigation may be
warranted to further characterize the performance of this method as more data become available. The authors
do note gradual movement at laboratories away from de-emanation while gamma spectrometry appears to be
25
Table 3:
Summary of 228Ra Proficiency Testing Results from ERA PT Studies 55-99
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 904.0
689
99%
26%
10%
58%
97%
161%
295%
EPA Ra-05
SM
7500 Ra-D
Brooks &
Blanchard
Ga Tech
334
102%
24%
26%
63%
99%
150%
274%
74
97%
20%
49%
79%
106%
158%
216%
45
108%
22%
35%
79%
106%
158%
178%
40
102%
16%
70%
72%
101%
137%
155%
1182
100%
24%
10%
59%
98%
154%
295%
Method
Radium
228
All Methods
The PT samples contained activities that range from 3 pCi/L to 20 pCi/L. PT acceptance ranges
for samples containing 228Ra at 5 pCi/L (Ra MCL) and 15 pCi/L are 41% - 153% and 53% - 135%,
respectively.
Among the five approved methods for which there were a significant number of results provided,
there were notable differences in the quality of results. While the difference in average recoveries
among the methods was relatively small, the most commonly used method, EPA 904.0, showed
the poorest precision with a standard deviation of 26% (1σ). In contrast, the least commonly used
method, the gamma spectrometry method from Georgia Tech, showed a standard deviation of
16% (1σ) which was 20-40% lower than the other methods. Consistent with this observation, 95%
of reported results for the Georgia Tech method fell between 72% and 137%, a range that is close
to the ideal range targeted in the Drinking Water Certification Manual for internal quality control
sample results (LCS/LFB). As such, the Georgia Tech gamma spectrometry method would
appear to be the best method available for samples with unknown activities, or samples with true
activities close to a trigger point.19 There are no comparable approaches that provide better
sensitivity of even comparable accuracy and precision as was the case for the de-emanation
method for 226Ra.
Key performance characteristics that can help in lab selection
Ultimately it is incumbent upon the utility to do an adequate job of reviewing a laboratory’s
capabilities to achieve reliable data on an ongoing basis. It is NOT sufficient to assume that
because a laboratory is EPA or state certified, that you can expect data of sufficient quality for
appropriate decision making, in the same way that having a driver’s license does not automatically
make one a good driver.
Listed here are some lab performance characteristics that should help in evaluation of a lab’s
ability to meet requirements.
gaining in popularity. While the de-emanation method offers similar (and better performance at the lowest
detection levels (i.e., <<0.5 pCi/L where detection capability of the gamma spectral method diminishes). As far as
228
Ra is concerned, the absolute sensitivity of the gamma measurement is not as good as for 226Ra, but in relative
terms, it is at least comparable to that provided by GPC with significantly better performance as far as bias,
precision, specificity, and robustness and reliability are concerned.
18
19
It is noted that the number of data points available for the GA Tech method was small, but the statistics are very
consistent with method performance that would be expected using much more modern spectrometric
instrumentation. See footnote 15.
26
Gross alpha/beta
 Method selection
o Commitment and ability to use a method that does not delay the count of samples
for 72-hours after preparation as documented by an SOP that states that samples
shall be counted as quickly as possible but which establishes a holding time
between sample preparation and counting of 48 hours (and preferably sooner). At
present this would eliminate Method 900.0 as an option, but it is expected that
EPA’s newer version of 900.0 will eliminate the 72-hour delay (in upcoming
revisions).
o Commitment and ability to use co-precipitation for any samples with TDS >500
ppm, and for samples that are deemed to require higher precision results (i.e.,
results that are very close to decision or trigger points).

Maximum RDL of 3 pCi/L
o The laboratory determines compliance with SDWA on a sample-by-sample basis
and re-prepares any samples for which sensitivity requirements are not met.

LCS spikes are high enough to minimize counting uncertainty. Current LCS control charts
are provided to demonstrate that the QC limits for LCS fall within the range of 100 ± 20%
(3σ), and that the laboratory is consistently able to meet these requirements.

Matrix spikes (MS) are at approximately 10 times the lab’s default detection limit (or 10
times the expected sample activity, whichever is higher), which under the SDWA must be
at or below 3 pCi/L for alpha, so ~30 pCi/L. Current MS control charts are provided to
demonstrate that the QC limits for MS fall within the range of 100 ± 30% (3σ), and that the
laboratory is consistently able to meet these requirements.

PT results indicate good performance with the method at the laboratory
o The laboratory runs PT samples using the same method and approach as it uses
for samples. If the laboratory uses more than one approach, it submits PT results
accordingly. If it extends count times, it may submit PT samples at the lower and
upper range of count times it plans to use.
o Four out of the five most recent PT rounds show results for gross alpha that meet
acceptance limits.
o Any results at or above 15 pCi/L should fall within ± 25% of assigned value (unless
there was a problem with the study documented by the PT provider).
o If results fail to meet these requirements, prompt corrective action is performed,
and documented to show that the root cause was identified and the problem
eliminated.

Agreement to follow the requirements of the Lab Certification Manual for radiochemistry
and the batch QC requirements presented in Table 4.

Ability to report elapsed time between prep and counting and the SDWA detection limit
achieved for each sample.
Radium 226 (226Ra)
 Method selection –
o Preferred labs would use the Georgia Tech method (gamma spectrometry) or
equivalent.
o If the laboratory uses EPA 903.0 or SM 7500-Ra B, it is able to and commits to
prepare sample promptly when received, and to hold the sample for 2-3 weeks
prior to counting to minimize positive bias and uncertainty.
27

Maximum DL of 1 pCi/L
and reprepares any samples for which sensitivity requirements are not met..

LCS spikes are high enough to minimize counting uncertainty (e.g., 15 pCi/L)
o Current LCS control charts are provided to demonstrate that the QC limits for LCS
fall within the range of 100 ± 10% (3σ), and that the laboratory is consistently able
to meet these requirements.

Matrix spikes are at approximately 10 times the lab’s default detection limit (which must
be at or below 1 pCi/L under the SDWA), or 10 times the sample activity, whichever is
higher); so ~10 pCi/L, depending on sample activity.
o Current MS control charts are provided to demonstrate that the QC limits for MS

o Four out of the five most recent PT rounds show results for 226Ra that meet
acceptance limits.
eliminated.


Ability to report elapsed time between prep and counting and the SDWA achieved for each
sample.
Radium 228 (228Ra)
 Method selection –
o Preferred labs would use the Georgia Tech method (gamma spectrometry) or
equivalent.
o Commitment and ability to process larger sample sizes (e.g., 4 L) for any samples
that are deemed to require higher precision results (i.e., results that are very close
to decision or trigger points)

Maximum DL of 1 pCi/L
and reprepares any samples for which sensitivity requirements are not met.

LCS spikes are high enough to minimize counting uncertainty (e.g., 15 pCi/L)
o Current LCS control charts are provided to demonstrate that the QC limits for LCS
28

Matrix spikes are at approximately 10 times the lab’s default detection limit (which must
be at or below 1 pCi/L under the SDWA), or 10 times the sample activity, whichever is
higher); so ~10 pCi/L, depending on sample activity.
o Current MS control charts are provided to demonstrate that the QC limits for MS

o Four of the five most recent PT rounds show results for 228Ra that meet acceptance
limits.
eliminated.


Ability to report elapsed time between prep and counting and the SDWA achieved for each
sample. Control chart of gravimetric barium yield available.
29
Recommendations for review and action based on analytical results
The recommendations in these tables could also be incorporated into a scope of work. Note that
these are only CRITICAL for utilities that have radionuclide levels near compliance limits.
Table 4:
QC
Parameter
Recommended QC Sample Requirements for Gross Alpha Analyses
Frequency
Required
Detection
Limit
each
compliance
sample
Reagent
Blank
(RB)
one per
preparation
batch of up
to twenty
samples&
Matrix
Spike
Sample
(MS)
one per
preparation
batch of up
to twenty
samples&
Matrix
Spike
Duplicate
(MSD)
exception
Laboratory
Control
Sample
(LCS)++
one per
preparation
batch of up
to twenty
samples&
Sample
Duplicate
(SD)
or MSD
one per
preparation
batch of up
to twenty
samples&
and
at least one
per ten
samples&
Acceptance Criteria and
Considerations
The sample specific DL for each
compliance sample must be less
than or equal to the RDL for gross
alpha of 3 pCi/L. The DL will vary by
sample since solids determine the
maximum sample size and the
count is often adjusted to meet the
RDL.
The RB activity must be less than
the 1.96σ counting uncertainty.@
The reagent blank must be counted
at least as long as the longest
sample in the batch. Duplicates are
counted the same duration.
MS recovery must fall within the
range of historical MS results (mean
± 3 sd) where this range must fall
within the range of 70-130%.#
The certification manual allows
MSDs to be run in lieu of sample
duplicates when results are
frequently below the DL.
LCS recovery must fall within the
range of historical MS results (mean
± 3 sd) but the acceptance range
may not extend outside 80-120%.
If the mean activity of the duplicate
pair is greater than 5 × RDL, the
Relative Percent Difference (RPD)
must be ≤20%.
If the RPD >20% and the mean
activity of the duplicate pair is ≤5 ×
DL, the Replicate Error Ratio (RER)
must be ≤ 2.
Action / Comment
If the SDWA RDL is not met, 1) recount affected
samples longer or on lower background detectors to
achieve RDLs**, 2) If a recount cannot meet the
RDL, where possible re-prepare samples using a
larger aliquot (to improve sensitivity), or 3) analyze
samples using a more sensitive method (e.g., coprecipitation).
If RB result is unacceptable; 1) check for errors –
samples may be recounted once ** 2) If recounting
fails to produce acceptable results, re-prepare all
samples in preparation batch to obtain QC results
that satisfy all requirements and produce unqualified
results
Spike MS at ~30 pCi/L (~10×RDL) or 10 times the
expected sample activity; If MS recovery is
unacceptable, 1) check for errors – samples may be
recounted once. 2) If recounting fails to produce
acceptable results, re-prepare all samples in
preparation batch to obtain QC results that satisfy
requirements (i.e., unqualified results)
MSDs must be evaluated both as matrix spikes (i.e.,
recovery) and as duplicates (RPD/RER).
Spike LCS at a minimum of 30 pCi/L (~10×RDL); If
LCS recovery is unacceptable, 1) check for errors –
samples may be recounted once. 2) If recounting
that satisfy requirements (i.e., unqualified results)
If RPD is unacceptable, 1) check for errors –
If RER is unacceptable 1) check for errors –
@ Sample size varies within the batch depending on the solids content of samples. Requiring that the count duration of the
blank is at least as long as that of the longest sample improves the probability that the blank will detect contamination
that could impact samples.
# The Drinking Water Certification Manual permits acceptance limits as wide as low as 70% - 130% but wider limits allow
larger uncertainties and increase the risk of incorrect compliance decisions.
& Ten and twenty sample limits do not include quality control samples.
** Within limits, extending the duration of a sample count can lower uncertainty. Sample counts, however, should not be
extended beyond the duration of the routine background subtraction counts since the laboratory cannot demonstrate
statistical control over longer counts.
++ The LCS is also referred to as the Laboratory Fortified Blank (LFB).
30
Table 5:
QC
Parameter
Recommended QC Sample Requirements for 226Ra Analyses
Frequency
Considerations
compliance sample and QC sample
must be ≤ 1 pCi/L (i.e., ≤ RDL for
226Ra).
Note: Batch QC samples should be
prepared and processed using the
same sample size and count
durations as samples in the batch.
Required
Detection
Limit
each
compliance
sample
and QC
sample
Reagent
Blank
(RB)
one per
preparation
batch of up
to twenty
samples&
The activity and the 1.96σ counting
uncertainty must both be less than the
1 pCi/L (i.e., the RDL must be
satisfied and the activity for 226Ra less
than the 1.96σ counting uncertainty).
Matrix
Spike
Sample
(MS)
one per
preparation
batch of up
to twenty
samples&
MS recovery must fall within the range
of historical MS results (mean ± 3σ)
where this range may not fall outside
the range of 80-120%.
exception
The certification manual allows MSDs
to be run in lieu of sample duplicates
when results are frequently below the
DL.
Matrix
Spike
Duplicate
(MSD)
Laboratory
Control
Sample
(LCS)++
one per
preparation
batch of up
to twenty
samples&
Sample
Duplicate
(SD)
or MSD
one per
preparation
batch of up
to twenty
samples&
and
at least
one per ten
samples&
LCS recovery must fall within the
range of historical MS results (mean ±
3 sd) but the acceptance range
should not extend outside 90-110%
If the mean activity of the duplicate
pair is greater than 5 × RDL, the
Relative Percent Difference (RPD)
must be ≤20%.
If the RPD >20% and the mean
activity of the duplicate pair is ≤5 ×
DL, the Replicate Error Ratio (RER)
must be ≤ 2.
Action / Comment
If the SDWA RDL is not met, 1) recount
affected samples longer or on lower
background detectors to achieve RDLs**
2) re-prepare samples to obtain lower
uncertainty (e.g., using a larger aliquot, obtain
better yield), or 3) analyze samples using a
more sensitive method.
If RB result is unacceptable; 1) check for
errors – samples may be recounted once.** 2)
If recounting fails to produce acceptable
results, re-prepare all samples in preparation
batch to obtain QC results that satisfy all
requirements and produce unqualified results.
Spike the MS at a minimum of 10 pCi/L
(~10×RDL) or ~10 times expected sample
activity; If MS recovery is unacceptable,
1) check for errors – samples may be
recounted once.** 2) If recounting fails to
produce acceptable results, re-prepare all
samples in preparation batch to obtain QC
results that satisfy requirements (i.e.,
unqualified results).
MSDs must be evaluated both as matrix
spikes (i.e., recovery) and as duplicates
(RPD/RER).
Spike LCS at a minimum of 10 pCi/L
(~10×RDL); If LCS recovery is unacceptable,
1) check for errors – samples may be
recounted once.** 2) If recounting fails to
produce acceptable results, re-prepare all
unqualified results)
samples may be recounted once.** 2) If
recounting fails to produce acceptable results,
re-prepare all samples in prep batch to obtain
QC results that satisfy requirements (i.e.,
unqualified results)
re-prepare all samples in preparation batch to
obtain QC results that satisfy requirements
(i.e., unqualified results)
** Although extending the duration of a sample count can lower uncertainty, for methods that measure 222Rn following separation
from 226Ra, recounting must be conducted promptly to be a viable option due to the short half-life of the analyte. For methods
that measure gamma spectrometry methods, extending counts will help achieve lower uncertainty. Sample counts should not
be extended beyond the duration if the routine background subtraction count since the laboratory cannot demonstrate
statistical control over longer counts.
31
Table 6: Recommended QC Sample Requirements for 228Ra Analyses
QC
Parameter
Frequency
Considerations
compliance sample and QC sample must
be ≤ 1 pCi/L (≤ RDL for 228Ra).
Note: Batch QC samples should be
prepared and processed using the same
sample size and count durations as
samples in the batch.
Required
Detection
Limit
each
compliance
sample
and QC
sample
Reagent
Blank
(RB)
one per
preparation
batch of up
to twenty
samples&
The activity and the 1.96σ counting
uncertainty must both be less than the 1
pCi/L (i.e., the RDL must be satisfied and
the activity for 228Ra less than the 1.96σ
counting uncertainty).
Matrix
Spike
Sample
(MS)
one per
preparation
batch of up
to twenty
samples&
MS recovery must fall within the range of
historical MS results (mean ± 3σ) where
this range may not fall outside the range
of 70-130%.#
Matrix
Spike
Duplicate
(MSD)
exception
The certification manual allows MSDs to
be run in lieu of sample duplicates when
results are frequently below the DL.
Laboratory
Control
Sample
(LCS)++
one per
preparation
batch of up
to twenty
samples&
Sample
Duplicate
(SD)
or MSD
one per
preparation
batch of up
to twenty
samples&
and
at least
one per ten
samples&
LCS recovery must fall within the range
of historical MS results (mean ± 3 sd) but
the acceptance range should not extend
outside 80-120%
If the mean activity of the duplicate pair
is greater than 5 × RDL, the Relative
Percent Difference (RPD) must be
≤20%.
If the RPD >20% and the mean activity
of the duplicate pair is ≤5 × DL, the
Replicate Error Ratio (RER) must be ≤ 2.
Action / Comment
If the SDWA RDL is not met, 1) recount
affected samples longer or on lower
background detectors to achieve RDLs** 2) reprepare samples to obtain lower uncertainty
(e.g., using a larger aliquot, obtain better
yield), or 3) analyze samples using a more
sensitive method.
If RB result is unacceptable; 1) check for
errors – samples may be recounted once.** 2)
If recounting fails to produce acceptable
results, re-prepare all samples in preparation
batch to obtain QC results that satisfy all
requirements and produce unqualified results.
Spike the MS at ~10 pCi/L (~10×RDL) or ~10
times expected sample activity; If MS recovery
is unacceptable, 1) check for errors – samples
may be recounted once.** 2) If recounting fails
to produce acceptable results, re-prepare all
unqualified results).
MSDs must be evaluated both as matrix
spikes (i.e., recovery) and as duplicates
(RPD/RER).
Spike LCS at ~10 pCi/L (~10×RDL); If LCS
recovery is unacceptable, 1) check for errors –
# The Drinking Water Certification Manual permits acceptance limits as wide as 70% - 130% but wider limits allow larger
uncertainties and increase the risk of incorrect compliance decisions especially when the true activity of 226Ra or 228Ra may
be present above RDLs.
** Although extending the duration of a sample count can lower uncertainty, for methods that measure 228Ac following separation
from 228Ra the short half-life of the analyte eliminates recounting as a viable option. For gamma spectrometry methods,
extending the count will help achieve lower uncertainty but counts should not be extended beyond the duration for routine
background subtraction counts since the laboratory cannot demonstrate statistical control for longer counts.
32
Appendix A: Discussion of ERA Proficiency Testing (PT) Data
Over 7,000 data points for gross alpha, Gross Beta, 226Ra and 228Ra from studies Rad-55 – Rad
99 were obtained from ERA, the sole provider of radiochemistry proficiency testing for drinking
water. The information in Excel spreadsheet format included: study ID; analyte; laboratory
reported method IDs; laboratory reported result; ERA assigned true value. All laboratory identifiers
had been removed by ERA, which prevented an assessment of single laboratory versus overall
performance. It is also noted that measurement uncertainty and detection limits are not captured
by the PT data reporting program, and that ERA does not report uncertainties for its assigned
values. This prevents rapid assessment of whether individual results had been run with sufficient
precision to meet EPA assigned measurement quality objectives for SDWA.
Since ERA allows laboratories to manually enter method identifiers, a large number of variants of
methods were present in the data. The data had to be manually reviewed to eliminate records
where the laboratory supplied method identifier could not unambiguously be correlated to EPAapproved methods. The remaining data were then collated. Methods for which fewer than 30 data
points were reported were eliminated.
The percent recovery (the reported value divided by the true value times 100) was evaluated for
the three critical analytes (gross alpha, 226Ra, and 228Ra), and any method for which the minimum
of 30 data points was available. A normal probability plot was prepared for all methods and for
each of the methods to qualitatively assess the normality of results. The vast majority of results
appear to be normally distributed, and thus appear to be consistent with likely true output from
the method as opposed to spurious data points attributable to non-method-related occurrences in
the lab, such as data entry errors. Descriptive statistics were calculated on the remaining data
set, and again on smaller subsets of results close to the Maximum Contaminant Level.
For gross alpha methods, the distribution of recoveries generally conforms to a normal distribution
with a small number of apparent outlying data points. EPA Method 900.0 is the exception with a
positive skew and fat high tail. This implies that the standard deviation underestimates the number
of points in the high tail of the distribution.
For 226Ra, the analyte recovery distribution is largely normal. Methods EPA 903.0 and SM 7110
B show a heavier high-side tail than do the isotope specific methods. A high tail would be
consistent with results impacted by 224Ra present as an accumulated decay product of 228Ra in
the test samples20. While the distribution of results for the GA Tech method appears to conform
well to a normal distribution, the number of points available is too small to make firm conclusions.
Continued data collection is needed to develop a more robust characterization of the performance
of this method.
For 228Ra, methods EPA 904.0, and to a lesser extent EPA Ra-05, show a heavy high-side tail,
likely due to bias associated with yttrium yield correction. The distribution of analyte recovery for
methods SM 7500-Ra D and the Brooks and Blanchard Method appear to conform well to a
normal distribution. The distribution of results for the GA Tech method appears to conform to a
normal distribution, but the number of points available is too small to make any firm conclusions.
Similar to 226Ra, continued data collection is needed to develop a more robust characterization of
the performance of this method.
20
While some labs delay counting of the test source until 2-3 weeks after preparation to allow for 224Ra to decay,
other labs do not which would result in high bias for results counted more promptly after preparation.
33
Summary of Method Performance Data for ERA Gross Alpha PT Studies 55-99 Results
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 900.0
1537
95%
24%
27%
52%
93%
148%
246%
EPA 00-02
223
91%
20%
40%
49%
93%
130%
195%
SM 7110 C
198
92%
16%
7.5%
62%
92%
124%
133%
SM 7110 B
161
97%
22%
7.2%
54%
98%
137%
174%
2119
94%
23%
7.2%
52%
93%
143%
246%
Method
Gross
Alpha
All Methods
All Approved Gross Alpha Methods – Gross Alpha Recovery
Activity
pCi/L
number
average
Stnd.
dev.
minimum
2.5
percentile
Median
97.5
percentile
Maximum
All results
9-25
25-70
2119
451
1668
94%
98%
93%
23%
27%
21%
7.2%
35%
7.2%
52%
54%
51%
93%
95%
93%
143%
165%
138%
246%
246%
202%
All Methods
Gross Alpha Results < 25 pCi/L
130
120
110
100
90
80
70
60
50
40
30
20
10
0
y = 1.0178x - 0.6348
60
y = 0.8901x + 1.7477
Reported Value (pCi/L)
All Methods
All Gross Alpha Results
Alpha MCL
1:1 Line
50
Alpha MCL
40
30
1:1 Line
20
10
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Known Value (pCi/L)
0
5
10
15
Known Value (pCi/L)
20
25
30
34
EPA Method 900.0 – Gross Alpha Recovery
Activity
pCi/L
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All
results
9-25
25-70
1537
327
1210
95%
99%
93%
24%
29%
22%
27%
35%
27%
52%
54%
52%
93%
95%
92%
148%
167%
143%
246%
246%
202%
130
120
110
100
90
80
70
60
50
40
30
20
10
0
EPA Method 900.0
y = 0.8759x + 2.363
EPA Method 900.0
Alpha MCL
1:1 Line
0
5
y = 1.0419x - 0.8523
55
50
45
40
35
30
25
20
15
10
5
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Alpha MCL
1:1 Line
0
5
10
Known Value (pCi/L)
15
20
25
30
Known Value (pCi/L)
EPA Method 00-02 – Gross Alpha Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
9-25
25-70
223
46
177
91%
96%
90%
20%
26%
18%
40%
58%
40%
49%
59%
48%
93%
94%
93%
130%
146%
117%
195%
195%
144%
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
EPA 00-02
35
y = 0.8925x + 0.5624
y = 0.7199x + 3.7413
30
EPA 00-02
Alpha MCL
1:1 Line
Alpha MCL
25
20
15
1:1 Line
10
5
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
0
5
Known Value (pCi/L)
10
15
Known Value (pCi/L)
20
25
30
35
SM Method 7110 C – Gross Alpha Recovery
Activity
(pCi/L)
All
results
9-25
25-70
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
198
46
152
92%
91%
92%
16%
15%
17%
7.5%
39%
7.5%
62%
57%
63%
92%
92%
92%
124%
119%
125%
133%
124%
133%
SM Method 7110C
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
30
y = 1.0681x + 1.9004
SM Method 7110C
Alpha MCL
1:1 Line
y = 0.8066x + 1.5089
25
Alpha MCL
20
15
1:1 Line
10
5
0
0
5
10
15
20
25
30
35
40
45
50
55
0
60
5
10
15
20
25
30
Known Value (pCi/L)
Known Value (pCi/L)
EPA Method 7110 B – Gross Alpha Recovery
Activity
(pCi/L)
All
results
9-25
25-70
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
161
32
129
97%
93%
97%
22%
20%
22%
7.2%
48%
7.2%
54%
52%
54%
98%
97%
98%
137%
126%
137%
174%
128%
174%
SM Method 7110B
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
30
y = 0.9316x + 1.46
SM Method 7110B
Alpha MCL
1:1 Line
y = 0.9365x - 0.0211
25
Alpha MCL
20
15
1:1 Line
10
5
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Known Value (pCi/L)
0
5
10
15
Known Value (pCi/L)
20
25
30
36
Summary of Method Performance Data for ERA 226Ra PT Studies 55-99 Results
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 903.0
534
107%
44%
16%
80%
103%
321%
619%
EPA 903.1
SM
7500-Ra-B
Ga. Tech
312
97%
18%
23%
61%
97%
125%
223%
150
100%
16%
55%
70%
99%
133%
171%
33
99%
12%
77%
85%
99%
125%
143%
1029
103%
34%
16%
68%
99%
146%
619%
Method
Radium
226
All Methods
All Ra-226 Methods – Ra-226 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
3-10
10-20
1029
408
621
103%
110%
98%
34%
50%
16%
16%
44%
16%
68%
72%
67%
99%
101%
98%
146%
204%
128%
619%
619%
239%
Ra-226 - All Methods
3-10 pC/L
All Ra-226 Methods
y = 0.8983x + 1.2025
45
30
y = 0.8458x + 1.5511
35
30
5 pCi/L MCL
25
1:1 Line
20
15
10
5
25
20
5 pCi/L MCL
15
1:1 Line
10
5
0
0
0
5
10
15
0
20
1
2
3
4
5
6
7
8
9
10
Known Value (pCi/L)
Known Value (pCi/L)
Method 903.0 – Ra-226 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
3-10
10-20
534
186
348
107%
120%
100%
44%
70%
17%
16%
67%
16%
73%
80%
70%
101%
103%
99%
177%
321%
133%
619%
619%
239%
EPA Method 903.0
Ra-226 Results
40
EPA Method 903.0
Ra-226 Results from 3-10 pCi/L
30
y = 0.8835x + 1.782
30
35
40
5 pCi/L MCL
25
20
15
10
1:1 Line
5
0
y = 0.6663x + 3.4049
25
20
5 pCi/L MCL
15
1:1 Line
10
5
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Known Value (pCi/L)
0
1
2
3
4
5
6
Known Value (pCi/L)
7
8
9
10
37
Method 903.1 – Ra-226 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
312
97%
18%
23%
61%
97%
125%
223%
3-10
55
99%
15%
72%
75%
96%
124%
160%
10-20
257
96%
19%
23%
57%
97%
126%
223%
EPA Method 903.1
Ra-226 Results
20
y = 0.8645x + 0.9235
20
15
25
EPA Method 903.1
5 pCi/L MCL
10
1:1 Line
5
y = 0.9509x + 0.3089
15
5 pCi/L MCL
10
1:1 Line
5
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0
1
2
3
Known Value (pCi/L)
4
5
6
7
8
9
10
Known Value (pCi/L)
SM Method 7500-Ra B – Ra-226 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
150
100%
16%
55%
70%
99%
133%
171%
3-10
57
103%
20%
56%
63%
101%
152%
171%
10-20
93
99%
12%
55%
78%
99%
119%
120%
SM 7500 Ra-B
SM 7500 Ra-B
Ra-226 Results
15
y = 0.9479x + 0.5376
5 pCi/L MCL
15
10
y = 0.9552x + 0.4886
5 pCi/L MCL
20
25
1:1 Line
5
10
5
1:1 Line
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Known Value (pCi/L)
0
1
2
3
4
5
6
Known Value (pCi/L)
7
8
9
10
38
GA Tech Method – Ra-226 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All results
33
99%
12%
77%
85%
99%
125%
143%
3-10
10-20
10
23
98%
100%
13%
11%
77%
87%
79%
88%
98%
101%
119%
125%
120%
143%
GA Tech Method
All Ra-226 Results
40
35
30
y = 0.912x + 1.0185
5 pCi/L MCL
25
20
15
10
1:1 Line
5
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Known Value (pCi/L)
Summary of Method Performance Data for ERA 228Ra PT Studies 55-99 Results
Data
Points
Average
Stnd.
Dev.
Min.
2.5
percentile
Median
97.5
percentile
Max
EPA 904.0
689
99%
26%
10%
58%
97%
161%
295%
EPA Ra-05
SM
7500 Ra-D
Brooks &
Blanchard
Ga. Tech
334
102%
24%
26%
63%
99%
150%
274%
74
97%
20%
49%
79%
106%
158%
216%
45
108%
22%
35%
79%
106%
158%
178%
40
102%
16%
70%
72%
101%
137%
155%
1182
100%
24%
10%
59%
98%
154%
295%
Method
Radiu
m
228
All Methods
39
All Methods - Ra-228 Recovery
Activity
(pCi/L)
All
results
3-10
number
Averag
e
Stnd.
dev.
minimu
m
2.5
percentil
e
1182
588
100%
104%
24%
28%
10%
35%
595
96%
19%
10%
10-20
median
97.5
percentil
e
Maximu
m
59%
63%
98%
99%
154%
178%
295%
295%
57%
97%
137%
241%
All Ra-228 Methods
3-10 pCi/L
All Ra-228 Methods
50
y = 0.9215x + 0.6052
20
40
45
35
30
5 pCi/L MCL
25
20
1:1 Line
15
10
5
y = 0.9491x + 0.4696
5 pCi/L MCL
15
10
1:1 Line
5
0
0
0
5
10
15
0
20
1
2
3
4
5
6
7
8
9
10
Known Value (pCi/L)
Known Value (pCi/L)
EPA Method 904.0 - Ra-228 Recovery
Activity
number
Average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
maximum
All
results
689
99%
26%
10%
58%
97%
161%
295%
3-10
343
103%
29%
40%
65%
98%
180%
295%
10-20
346
94%
21%
10%
55%
96%
137%
241%
EPA Method 904.0
Ra-228 - 3-10 pCi/L
EPA Method 904.0
Ra-228 Results
40
20
y = 0.9019x + 0.6623
y = 0.9688x + 0.3317
30
35
5 pCi/L MCL
25
20
15
10
1:1 Line
15
5 pCi/L MCL
10
1:1 Line
5
5
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0
1
2
3
Known Value (pCi/L)
4
5
6
Known Value (pCi/L)
7
8
9
10
40
EPA Method Ra-05 - Ra-228 Recovery
Activity
(pCi/L)
number
average
Stnd.
dev.
Minimum
2.5
percentile
median
97.5
percentile
maximum
All
results
334
102%
24%
26%
63%
99%
150%
274%
3-10
161
106%
29%
42%
62%
103%
178%
274%
10-20
173
97%
16%
26%
67%
98%
131%
148%
EPA Method Ra-05
Ra-228 - 3-10 pCi/L
EPA Method Ra-05
Ra-228 Results
40
30
5 pCi/L MCL
25
20
15
10
y = 0.928x + 0.6882
30
y = 0.928x + 0.6882
35
1:1 Line
25
5 pCi/L MCL
20
15
1:1 Line
10
5
5
0
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1
2
3
Known Value (pCi/L)
4
5
6
7
8
9
10
Known Value (pCi/L)
SM 7500 Ra-D - Ra-228 Recovery
Activity
(pCi/L)
Number
average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
Maximum
All
results
74
97%
20%
49%
72%
97%
124%
216%
3-10
38
100%
25%
49%
75%
100%
148%
216%
10-20
36
94%
12%
71%
72%
94%
114%
119%
SM 7500-Ra D
SM 7500-Ra D
Ra-228 Results
40
15
y = 0.9196x + 0.4135
y = 0.9524x + 0.2732
30
35
5 pCi/L MCL
25
20
15
10
1:1 Line
10
5 pCi/L MCL
1:1 Line
5
5
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Known Value (pCi/L)
0
1
2
3
4
5
6
Known Value (pCi/L)
7
8
9
10
41
Brooks and Blanchard Method - Ra-228 Recovery
Activity
(pCi/L)
number
Average
Stnd.
dev.
minimum
2.5
percentile
median
97.5
percentile
maximum
All
results
45
108%
22%
35%
79%
106%
158%
178%
3-10
18
103%
22%
35%
54%
104%
132%
139%
10-20
27
111%
23%
86%
87%
109%
332%
178%
Brooks and Blanchard Method
Ra-228 - 3-10 pCi/L
Brooks and Blanchard Method
Ra-228 Results
40
35
5 pCi/L MCL
25
20
15
10
1:1 Line
30
25
20
5 pCi/L MCL
15
1:1 Line
10
5
5
0
0
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1
2
3
4
5
6
7
8
9
10
11
Known Value (pCi/L)
Known Value (pCi/L)
Ra-228 - GA Tech
Activity
(pCi/L)
All results
number Average
Stnd.
dev.
2.5
97.5
minimum percentile median percentile Maximum
40
102%
16%
70%
72%
101%
137%
155%
3-10
28
101%
16%
70%
71%
102%
136%
155%
10-20
12
104%
17%
85%
86%
97%
133%
136%
GA Tech
Ra-228 Results
40
y = 1.0039x + 0.1035
35
35
30
y = 1.298x - 1.6332
40
y = 1.1199x - 0.2974
30
5 pCi/L MCL
25
20
15
10
1:1 Line
5
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Known Value (pCi/L)
42
Appendix B: Calculations Used to Assess Method Performance
Replicate Error Ratio (RER)
The replicate error ratio, RER, assesses statistical agreement between duplicate results. The test
compares the magnitude of the difference between two results to the expected uncertainty of that
difference at the 95% confidence interval. To be acceptable, the EPA Laboratory Certification
Manual specifies that the RER ≤ 2. It is important to be sure that replicate error ratio (RER) is
properly calculated by the laboratory. RER is calculated as follows:
RER =
|A − B|
√sa2 + sb2
where;
A = Activity of the first measurement (in pCi/L)
B = Activity of the second measurement made from a different aliquot from the same
sample (in pCi/L)
sa = 1-sigma counting uncertainty of the first measurement (in pCi/L)
sb = 1-sigma counting uncertainty of the second measurement (in pCi/L)
Note that this formulation requires that the terms sa and sb be 1-sigma uncertainties. Inputting
1.96σ uncertainty, as has occurred at some laboratories, will result in the failure to properly identify
problematic precision for samples containing activity near the maximum contaminant level (MCL)
and can result in elevated rates of compliance decision errors for radium.
Generic SDWA Detection Limit Calculation
Note that this is a default calculation. The actual calculation should incorporate factors used
in the laboratory’s calculation of the sample activity
1.96 2
DL =

1 1
4t s2
 1  1 
 RB   
2
2t s 
1.96
 ts tB

2.22  ε  D  I  Y  A  V

 
 
DL
ts
ts
RB
2.22
= Safe Drinking Water Detection Limit
= sample count time
= background count time
= background count rate for subtraction
= conversion from dpm to pCi, (dpm/pCi)
ε
= calibrated efficiency (corrected for attenuation)
D
I
Y
A
V
= Factor to correct for sample decay
= Factor to correct for sample Ingrowth
= Factor to correct for chemical yield
= Factor to correct for abundance (decay particles/disintegration)
= volume of sample
43
Appendix C: How Does Measurement Uncertainty Impact Compliance
Decisions?
In evaluating data for radionuclides, particularly if results are very close to compliance points (e.g.
gross alpha substitution near the trigger level for 226Ra monitoring, 226Ra or 228Ra near the MCL,
gross alpha near the MCL), it is important to understand how the uncertainty of the measurement
may affect results. Even though uncertainty is not considered in most states as part of the
compliance decision (California is an exception, where gross alpha substitution for combined
radium compliance and adjusted gross alpha compliance is based on adding the error to the
measured value to be more conservative), minimizing measurement uncertainty is critical in
maximizing the likelihood of correct compliance decisions. This appendix demonstrates how
uncertainty of radionuclide measurements may influence those decisions.
For any measurement there is a finite possibility that results will generate a false positive or a
false negative. Figure 5 demonstrates that phenomenon.
Figure 5: Distribution of Possible Results for Samples Containing No Activity and Activity
at the MCL
Concentration Relative to Action Level
Measurement uncertainty is associated with and intrinsic to every measurement.
Measurement uncertainty will unavoidably lead to making incorrect decisions.
 The curve delineated by the dark red line shows the distribution of measurements
we would get if we were to measure a sample many, many times.
 Although each measurement would produce a slightly different result, those results
presumably group around the most likely result for analyte in the sample which is
the highest point in the curve.
 This distribution of measurements is bell-shaped, or Gaussian. Most results would
fall closer to the analytical action level with fewer and fewer as we move further
from the true value in the sample.
 A less precise measurement technique will produce wider distributions, and a more
precise technique, narrower ones.
In this example, the average measured concentration of analyte in the sample is equal to the
analytical action level. For SDWA analysis, the AAL might be the MCL (even though
compliance is based on the running annual average of quarterly samples, a utility would want
to be assured that no single measurement could drive it out of compliance.
44




Half of our measurement results will fall above the average and half below.
If we compare the results of each measurement directly to the action level, we will:
Incorrectly decide that the sample is in compliance (i.e., true value is less than
the action level) approximately 50% of the time (red shaded area).
Correctly decide that our sample is out of compliance (i.e., true value is equal to
or greater than the action level) approximately 50% of the time.
The blue curve emphasizes why it is so important to ensure that we control the uncertainty /
sensitivity of our measurements.
 The blue curve shows the distribution of measurements of a sample that contains
no analyte (i.e., a blank sample).
 In this case, the measurement uncertainty is large enough that a certain portion
of our measurements will produce results that are greater than the action level
such that we will incorrectly decide that there is activity above the AAL when
lower levels of activity are present (blue shaded area).
The next figure (Figure 6) shows a generic power curve, which relates the likelihood of
decision errors to the analyte concentration and allows one to assess the impact of incorrect
decisions. So how much uncertainty can we accept and achieve acceptable decision error
rates?



Decision makers use power curves to graphically show the rate of decision errors
relative to analyte concentration in the sample.
While we can minimize measurement uncertainty, this costs time and money.
Decision makers try to balance the cost of making incorrect decisions against the
cost of minimizing measurement uncertainty that make their decisions more
reliable.
The gray region is the area on either side of the action level.
 Its width is controlled by decision makers’ confidence about their tolerance to
making incorrect decisions.
 The rate of decision errors outside of the gray region is controlled at low rates
that are deemed to be acceptable by decision makers.
 Within the gray region, the concentration approaches the action limit and
measurement uncertainty will limit project planners’ ability to control decision
errors at the low rate possible outside the grey region.
 Ideally, the gray region should kept be as small as possible, but higher precision
measurements cost time and money.
45
Figure 6: The Gray Region - Activity near the Action Level 21
An example of how uncertainty impacts our gross alpha measurement is shown in Figure 7.
Figure 7: Comparison of distributions of results for a sample with a given activity.
True Sample Activity MCL
Distribution of
Measurements
of Sample
Activity
Upper 95th Percentile
of Sample
Measurements
(5% of measurements
fall above this value)
0
21
Distribution of
Measurements
at the MCL
Measurement
Results in
Shaded Area
Result in
Incorrect
Compliance
Decision
1
Figure 6 is from US EPA Office of Environmental Information, EPA-QA/G4 - Guidance on Systematic Planning
Using the Data Quality Objectives Process, EPA/240/B-06/001 February 2006, Washington, DC.
46
We want to determine whether a sample contains activity that is in compliance with the MCL
for gross alpha.
 The laboratory successfully follows the approved method and obtains an SDWA
DL of 3 pCi/L.
 The width of results distribution is a function of measurement uncertainty which
results when a measurement satisfies the SDWA required detection limit (RDL).
 About 5% of our distribution of measurements falls to the right of the action level.
Compare the measured result to the MCL for adjusted gross alpha to determine compliance
 Since 5% of our measurement results will fall above the MCL, one in twenty
measurements will incorrectly produce a result that indicates that the water is not
in compliance with SDWA regulations.
What can we do???
 Minimize the uncertainty of the measurement.
 The closer the true result is to the MCL, however, the less uncertainty can be
tolerated and the more expensive the measurement.
It is this guide’s goal to provide a relatively straightforward road map that will help water
utilities manage the analytical process and reasonably minimize the probability of making
incorrect compliance decisions by decreasing measurement uncertainty.
47
References
Georgia Tech (2004) The Determination of Radium-226 and Radium-228 in Drinking Water by
Gamma-ray Spectrometry Using HPGE or Ge(Li) Detectors, Revision 1.2. Georgia Institute of
Technology, Atlanta, GA.
Standard Methods (2012) Method 7110 B - Evaporation Method for Gross Alpha-Beta Standard
Methods for the Examination of Water and Wastewater, 22nd edition, 2012. American Public
Health Association, Washington, D.C.
Standard Methods (2012) Method 7110 C - Coprecipitation Method for Gross Alpha Radioactivity
in Drinking Water Standard Methods for the Examination of Water and Wastewater, 22nd edition,
2012. American Public Health Association, Washington, D.C.
Standard Methods (2012) Method 7500-Ra B - Precipitation Method Standard Methods for the
Examination of Water and Wastewater, 22nd edition, 2012. American Public Health Association,
Washington, D.C.
Standard Methods (2012) Method 7500-Ra D - Sequential Precipitation Method
Standard
Methods for the Examination of Water and Wastewater, 22nd edition, 2012. American Public
Health Association, Washington, D.C.
USEPA (1984) Method 00-02 – Radiochemical Determination of Gross Alpha Activity in Drinking
Water by Coprecipitation in: Radiochemistry Procedures Manual December 1984 EPA 520/5-84006 Washington, DC
USEPA (1980). Method 900.0 - Gross Alpha and Gross Beta Radioactivity in Drinking Water in:
Prescribed Procedures for Measurement of Radioactivity in Drinking Water, EPA 600/4- 80-032,
Cincinnati, OH
USEPA (1980) Method 903.0 - Alpha-Emitting Radium Isotopes in Drinking Water in: Prescribed
Procedures for Measurement of Radioactivity in Drinking Water, EPA 600/4-80-032 Cincinnati,
OH
USEPA (1980) Method 903.1 - Radium in Drinking Water, Radon Emanation Technique in:
Prescribed Procedures for Measurement of Radioactivity in Drinking Water, EPA 600/4-80-032
Cincinnati, OH
USEPA (1980) Method 904.0 - Radium-228 in Drinking Water in: Prescribed Procedures for
Measurement of Radioactivity in Drinking Water, EPA 600/4-80-032 Cincinnati, OH
USEPA (2005). Manual for the Certification of Laboratories Analyzing Drinking Water Criteria
and Procedures Quality Assurance (5th Edition) EPA 815-R-05-004 Cincinnati, OH
USEPA (2006) EPA-QA/G4 - Guidance on Systematic Planning Using the Data Quality Objectives
Process, EPA/240/B-06/001 February 2006, Washington, DC
USDHS (1990) Method Ra-05 - Radium-226 in Tap Water, Urine, and Feces Reference: EML
Procedures Manual, HASL-300, 27th Edition, Volume 1, 1990 New York, NY
Government Affairs Office
1300 Eye St. NW, Suite 701W
Washington, DC 20005
T: 202.628.8303
F: 202.628.2846

Radionuclide Rule Compliance - American Water Works Association

Transcription

Similar documents

Desktop Network PCI Card

Preparing for the Evolution: PCI DSS 3.0 and Beyond

The Olympian tribune - Murray State University

FROSTBURG STATE

MEERKAT

Aculab E1/T1 PCI card

Valentine`s Day Appeal 2016

Convention Re ections - Alpha Kappa Mu Honor Society

Radiochemistry Webinars Actinide Chemistry Series