United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Las Vegas NV 89114
Research and Development
EPA-600/S4-83-038 Nov. 1983
Project Summary
Test Procedure for
Uranium in Drinking Water:
Interlaboratory Collaborative
Study
C. A. Phillips, C. T. Bishop, and E. L Whittaker
An interlaboratory collaborative
study was conducted for a test pro-
cedure to measure the concentration of
uranium in drinking water. The pur-
pose of the study was to estimate
the precision and accuracy for the
test procedure that can be expected
when the procedure is used by any
competent laboratory. The test pro-
cedure was published in the EPA
Manual, "Prescribed Procedures for
Measurement of Radioactivity in
Drinking Water" [EPA-600/4-80-
032. August 1980].
Drinking water samples containing
uranium alpha concentrations of 8.1,
17.4, and 75.3 pCi/l were analyzed
(in triplicate by most participants) by
19 collaborating laboratories using
the test procedure. Statistical analy-
sis of the test results, using pro-
cedures recommended by the ASTM
[E-691, E-177, E-178, ASTM Standard
Part 41, 1980] showed coefficients of
variation for repeatability (within-
laboratory precision) of 14.6, 8.1, and
8.3 percent respectively for the three
uranium concentrations for an average
repeatability precision of 10.3 percent.
The analysis also showed coefficients
of variation for reproducibility (com-
bined within- and between-laboratory
precision) of 15.3, 14.9, and 9.1 per-
cent for the respective sample uranium
concentrations for an average reproduc-
ibility precision of 13.1 percent.
A comparison of the grand average
test results with the known values
for the three samples demonstrated
accuracy indexes of 98.0, 102.6, and
101.9 percent respectively, for an
accuracy index of 100.8 percent in
the range of uranium alpha concen-
trations between 8 pCi/l and 75 pCi/l.
This Project Summary was devel-
oped by EPA's Environmental Mon-
itoring Systems Laboratory, Las
Vegas. NV, to announce key findings
of the research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
The National Interim Primary Drinking
Water Regulations (NIPDWR) state, in
Section 141.15, that the maximum con-
tainment level for gross alpha parti-
cle activity "... (including radium-226 but
excluding radon and uranium) ..." is 1 5
pCi/l. This statement implies that when-
ever a gross alpha measurement of a
drinking water sample exceeds 15 pic-
ocuries per liter (pCi/l), an analysis for
uranium should be done to determine
the uranium alpha contribution to the
gross alpha concentration. The method
listed in the NIPDWR for the measure-
ment of uranium in drinking water is a
fluorometric method which determines
uranium in mass units. It is now known
(subsequent to the promulgation of the
NIPDWR) that the ratio of uranium alpha
activity to uranium mass concentration
in ground waters can vary significantly
from that which is common to natural
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uranium ore deposits. Therefore, a test
procedure that will better relate total
uranium alpha activity to gross alpha
activity in drinking water samples is
needed to either complement or replace
the approved method.
The method of analysis used in this
study is a simplified version of a method
that measures the uranium isotopic con-
centrations in the sample by alpha spec-
trometry. This method measures total
uranium alpha activity, the measure-
ment needed for a gross alpha assess-
ment of a drinking water sample.
Conclusions
The estimated repeatability precision
(within-laboratory precision), reproduci-
bility precision (the combined within- and
between-laboratory precision), and the
accuracy have been determined for the
test procedure by a multilaboratory test
in this study and they are hereby set up
as criteria by which to evaluate an alter-
nate test procedure for equivalency.
The study showed accuracy indexes of
98.0, 102.6, and 101.9 percent for an
average of 100.8 percent for the test
procedure over the uranium alpha con-
centration range of 8 to 75 pCi/l, indi-
cating that accurate test results can be
obtained with the test procedure used
in this study.
The estimated coefficients of variation
for repeatability (repeatability index) for
the three uranium concentration levels
were calculated to be 14.6, 8.1, and 8.3
percent (respectively, for 8.1, 17.4 and
75.3 pCi/l) for an average repeatability
index of 10.3 percent.
The estimated coefficients of variation
for reproducibility (reproducibility index)
for the three uranium concentration lev-
els were calculated to be 15.3, 14.9,
and 9.1 (for 8.1, 17.4, and 75.3 pCi/l,
respectively) for an average reproduci-
bility index of 13.1 percent.
Although there was no stable isotope
carrier to determine the uranium chemi-
cal recovery for each sample, separate
samples spiked with known uranium
radioactivity and analyzed by the test
procedure, along with the test samples,
showed good recoveries. The recoveries
for the 18 laboratories averaged 91 ±
15 percent.
The test procedure did not contain sig-
nificant systematic errors for the method
for uranium alpha concentrations up to
75 pCi/l in drinking water samples.
Recommendations
The test procedure in this study (de-
scribed in detail in Appendix B) of the
Project Report should be used to mon-
itor drinking water samples for uranium
alpha contribution to the gross alpha ac-
tivity when the gross alpha activity ex-
ceeds 15 pCi/l as specified in the
NIPDWR.
A change should be made in the pre-
paration of the separated uranium frac-
tion for counting the alpha activity. It is
also recommended that the change be
verified experimentally to demonstrate
the benefit to Method 908.0 [EPA-600/
4-80-032] before it is incorporated into
the test procedure. To make that change
in the preparation of the separated uran-
ium fraction for alpha counting, the fol-
lowing changes and additions to the
Test Procedure (Method 908.0) are pro-
posed. Replace existing steps 8.2.5
through 8.2.9 with the following 8.2.5
through 8.2.10 steps.
8.2.5 Elute the uranium with six
column volumes of 0.1 N HCI,
collecting the eluate in a 150-
ml beaker.
8.2.6 Evaporate the eluate to near
dryness, then add 1 ml 12^ HCI
(cone.), 10 ml of water, 0.2 ml
20% TiCI3, and 1 ml of lan-
thanum carrier solution, stir.
8.2.7 Add 0.5 ml HF (cone.), stir
well and allow to stand for 30
minutes.
8.2.8 Filter through 47 mm, 0.2
um pore membrane filter, col-
lecting the coprecipitated U/
LaF3.
8.2.9 Wash the U/LaF3with 10 ml
of water followed by 10 ml of
ethanol.
8.2.10 Air dry the filter for at least 1
hour before counting for alpha
activity.
Add the following item to the "Ap-
paratus" section of the procedure.
5.7 0.2 ^m pore, 47 mm diameter
membrane filter that with-
stands the acid treatment in
the Test Procedure and will lay
flat after drying (such as Gel-
man AN-200).
And add the following items to the
"Reagents" section of the procedure.
6.15 Lanthanum nitrate, (1.0 mg
La+3/ml). Dissolve 3.11 g
La(N03)s-6H20 in one liter
of 0.1N HN03.
6.16 Hydrofluoric acid, 25N : HF
(cone.) sp. gr. 1.18, 49%.
6.17 Titanium trichloride TiCh :
20%.
The term "column volume" in the test
procedure should be clarified. This can
be done by simply giving the milliliters
of the resin bed volume specified in the
procedure. A resin bed 1.3 cm in diam-
eter by 8.0 cm high will have a volume
of 10.6 ml. Then in Section 8.2.3 of the
procedure, after the expression "-- with
6 column volumes", put in parentheses
(6 x 10.6 ml = 63.6 ml, or 65. ml,
rounded to the nearest 5 ml).
Since no carrier or tracer is used in the
procedure to determine chemical recov-
ery, it is recommended that with each
set of samples to be analyzed by this
test procedure, a spiked sample (to de-
termine recovery) and a sample dupli-
cate (to verify precision) be analyzed.
This recommendation should be incor-
porated into the procedure.
Procedures
1. Analytical Test Procedure
The test procedure used in this study
is described in detail in Appendix B of
the Project Report. The water sample is
acidified by adding HCI and the sample
boiled to eliminate carbonate and bicar-
bonate ions. Uranium is coprecipitated
with ferric hydroxide and separated from
the sample. The uranium is then sepa-
rated from other radionuclides which
were carried down with the ferric hy-
droxide by dissolving the hydroxide pre-
cipitate in 8 N HCI, putting the solution
through an anion exchange column,
washing the column with 8 IS[ HCI, and
finally eluting the uranium with 0.1 N
HCI. The eluate (containing the uranium
from the sample) is evaporated and the
uranium chemical form is converted to
nitrate. The nitrate residue is transferred
to a stainless steel planchet, dried,
flamed, and counted for alpha particle
activity.
2. Collaborative Test Procedure
A total of 25 laboratories agreed tc
participate rn the collaborative study anc
19 laboratories submitted test results
Test results from 18 laboratories (result!
from 1 laboratory were rejected) wen
used for statistical analyses for estimates o
precision and accuracy.
Approximately 5 ml of an NBS standart
uranium solution was sent to each par
ticipating laboratory to determini
uranium recovery and uranium alph;
counter efficiency.
Three stock solutions, each containing
different concentration of uraniurr
were prepared from an NBS standard. >
20-ml portion of each of these solution
was provided to each participating labor?
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tory. The laboratories were requested to
prepare working solutions by diluting 5
ml aliquots of each solution to 1000 ml (1
liter) with drinking water. The resulting
concentrations of these working solutions
were8.1 ±.4pCi/l, 17.4± .9pCi/l, and
75.3 ± 3.9 pCi/l. Each laboratory was
requested to perform triplicate analyses
of the three whole volume working solu-
tion samples; to analyze a 1-1 sample of
their drinking water to determine a blank
value; and to submit completed data
sheets.
3. Data Processing Procedures
A statistical evaluation of the test re-
sults was done by the procedures de-
scribed in E-691, E-177, and E-178 of the
ASTM Standard Part 41, 1980, to deter-
mine the repeatability precision
(within-laboratory variation); the re-
producibility precision (combined within-
and between-laboratory variation); and
the accuracy of the test procedure. The
standard deviations and equations for
their calculations are listed below.
Standard deviation of replicate test
results within Lab i, for sample j, (Sj)
h=1
1/2
Eq.1
where: X^ = the result reported for the h
replicate of the j sample ma-
_ terial by Lab i
Xjj = the mean of the individual
results of sample j for Lab i
ny = the number of replicates of
sample j reported by Lab i.
Repeatability (within-laboratory) stan-
dard deviation for sample j, (Srj).
Since the number of replicates is the
same (3) for all participants for all three
samples, the equation can be given as
follows
(P \ 1/2
I/PS Sjj2) Eq.2
i=1 /
where: P = the number of participants in
the study.
Standard deviation of individual laboratory
average from grand average for the j sam-
ple material, (Sxj)
(XirXj)2/(P-1)
1/2
where: Xjj = the average of the test re-
sults for sample material j by
_ Lab i
Xj = the grand average for sample
material j.
Standard deviation of between-labora-
tories for the j sample material, (Sy).
/ 2 2 \ 1/2
SLj=\Sxj-Srj/n| Eq.4
Reproducibility (combined within- and
between-laboratory) standard deviation for
the j sample material, i
i v
1/2
Eq. 5
The coefficient of variation for repeatabil-
ity (within-laboratory precision) (also called
repeatability index) for sample j, (Vr:%)
Vrj%=100Srj/Xj Eq. 6
The coefficient of variation for between-
laboratory precision for sample j, (V(_:%)
VLj% = 100 S|_j/0
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Table 1. Summary of Collaborative Study Results - Precision and Accuracy
Uranium in Drinking Water Sample
Parameter a
Yj (pCi/l)
Xj (pCi/l)
Aj%
Sjf • (pCi/l)
Srj (pCi/l)
Si; (pd/li
1
SRj (pCi/l)
Vrj%
VL/%
VRi%
1
8.1 ±.4
7.9
98.0
0.76
1.15
0.37
1.21
14.6
4.7
15.3
2
17.4 ±.9
17.9
102.6
2.39
1.44
2.24
2.66
8.1
12.5
14.9
3
75.3 ±3.9
76.8
101.9
4.65
6.39
2.83
6.98
8.3
3.7
9.1
Average
100.8
10.3
7.0
13.1
a Terms are defined in the text.
C. A. Phillips and C. T. Bishop are with Monsanto Research Corporation,
Miamisburg, OH45342; the EPA author EarlL. Whittaker (also the EPA Project
Officer, see below) is with the Environmental Monitoring Systems Laboratory,
Las Vegas, NV 89114.
The complete report, entitled "Test Procedure for Uranium in Drinking Water:
Interlaboratory Collaborative Study," (Order No. PB 83-247 239; Cost: $8.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
•frUS GOVERNMENT PRINTING OFFICE 1983-659-017/7230
United States
Environmental Protection
Agency
Center for Environmental Research
Information
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Official Business
Penalty for Private Use $300
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