Office of Ground Water and Drinking Water

January 20, 2012

MEMORANDUM

SUBJECT: Basis for Expedited Approval of ASTM Method D 6239-09

FROM: Glynda Smith and Steve Wendelken

Standards and Risk Management Division, Technical Support Center

TO: The Record

Background

Uranium is toxic as both a metal and as an alpha-emitting radionuclide. The maximum contaminant 

level (MCL) for uranium is defined at 40 CFR 141.66(e) as 30 μg/L based on metal toxicity. This level can 

be converted to an activity of 20.1 pCi/L assuming that it is naturally-occurring uranium. ASTM Method 

D 6239-09 (“Uranium in Drinking Water by High-Resolution Alpha Liquid Scintillation Spectrometry”) is 

capable of determining uranium activity in drinking water at 1.0 pCi/L and was submitted to the TSC 

Alternate Test Procedure (ATP) Coordinator for evaluation as an alternate test method to EPA Method 

908.0 for the analysis of uranium in drinking water. An earlier version of the method (ASTM D 6239-02) 

was previously submitted for consideration as a new method but it was rejected due to a poorly 

organized data package and inadequate quality control in the method.

Evaluations

Research supporting the development of ASTM Method D 6239 was published in the Journal of 

Radioanalytical and Nuclear Chemistry (Duffey, J., et.al. Journal of Radioanalytical and Nuclear 

Chemistry, 1997, Vol. 221, pp. 115-122. Development of a rapid procedure for the measurement of 

uranium in drinking water by PERALS® spectrometry). The author coordinated the ASTM Method 

D 6239 round robin test evaluations, and the paper details the parameters that were evaluated during 

method development including:

• Determination of optimal equilibration time with the extractive scintillator to maximize 

extraction efficiency. This entailed triplicate analyses over times ranging from 15 seconds to 6 

minutes. Extractions were found to be complete within 60 seconds.

• Evaluation of extraction efficiency as a function of pH. Solutions of natural uranium were 

prepared at pH values of 1.0, 2.0, 3.0, 4.0 and 5.0 and extracted. The table below shows 

excellent recovery for uranium with minimal recovery of other potentially interfering alphaemitters such as Th-230, Po-210, Pu-238, Am-241, and Ra-226. On average less that 0.5% of Am, 

Po, Pu, Ra and Th were extracted when the solution pH was 3.0.

Element Equilibrium pH Number of 

Replicates

%Recovery

Uranium 1.0 +0.1 9 99.4 + 5.7

2.0 +0.1 3 103.7 + 3.8
Element Equilibrium pH Number of 

Replicates

%Recovery

3.0 +0.1 3 102.7 + 3.8

4.0 +0.1 5 98.0 + 5.9

5.0 +0.1 1 99.8 + 5.3

Thorium 2.0 +0.1 4 1.80 + 0.16

2.5 +0.1 3 1.17 + 0.16

3.0 +0.1 4 0.28 + 0.07

3.5 +0.1 2 0.19 + 0.11

Polonium 2.0 +0.1 4 0.14 + 0.08

2.5 +0.1 3 0.65 + 0.16

3.0 +0.1 6 0.34 + 0.03

Plutonium 2.0 +0.1 4 1.91 + 0.25

3.0 +0.1 4 0.38 + 0.11

Americium 2.5 +0.1 1 0.55 + 0.23

3.0 +0.1 3 0.05 + 0.03

Radium 3.0 +0.1 4 0.22 + 0.08

• Evaluation of extraction efficiency as a function of the aqueous phase volume. The percentage 

of uranium extracted into the extractive scintillator was determined as a function of aqueous 

phase volume over the range of 4.0 to 200.0 mL. In all cases, uranium recovery was 

quantitative.

• Evaluation of the influence of potential chemical interferences on uranium extraction efficiency 

(Ca2+, Fe2+, SO4

2-

, H2PO4

-

, HC2O4

-

). Calcium concentrations ranged from 0.01 to 1.0M, iron 

concentrations ranged from 0.0004 to 0.06M, and sulfate, phosphate and oxalate 

concentrations ranged from 0.01 to 1.0M. Uranium extractions were quantitative.

• Comparison with EPA Method 908.0. EPA Method 908.0 is approved for the analysis of uranium 

in drinking water as cited at 40 CFR 141.25(a). The alpha liquid scintillation methodology with 

pulse shape discrimination (ASTM Method D 6239) was evaluated alongside the approved 

method which relies on precipitative extraction followed by separation on an ion exchange 

column. The comparison involved the analysis of seven drinking water samples and an EPA 

performance evaluation (PE) sample. In the data shown in the following table, the proposed 

ASTM method yielded results that were comparable, and under certain conditions, or better 

than those obtained with the approved method. Two of the samples (95-464 and 95-465) 

contained total dissolved solids > 2000 mg/L. Under such conditions, EPA Method 908.0 loses 

some of the uranium in the anion exchange separation step due to column breakthrough.
Sample ID Total U in pCi/L, 

EPA 908.0

Total U in pCi/L,

ASTM D 6239

95-06254 35.9 + 2.4 38.7 + 3.0

95-464 19.5 + 1.6 28.2 + 2.6

95-465 71.8 + 3.8 89.2 + 4.5

95-461 10.3 + 1.0 10.2 + 1.6

95-466 13.4 + 3.2 13.8 + 1.8

95-635639 9.6 + 1.0 8.8 + 1.4

95-372 8.2 + 1.4 9.1 + 1.5

PE Sample, 15.2 

pCi/L 15.1 + 1.4 15.8 + 1.9

A reorganized data package for ASTM Method 6239 was provided by ASTM. The package contained the 

results of two different interlaboratory studies – an initial test comparing multiple single operators and 

then the ASTM-supported round robin. Seven radiochemistry laboratories across the country 

participated in the round robin and each laboratory was instructed to use their own laboratory tap 

water to prepare blanks and dilutions, thus demonstrating the ruggedness and reliability of the method. 

Precision and bias obtained from the round robin study are provided in the ASTM-approved final 

method.

Finally, in addressing the earlier concerns regarding inadequate quality control, the quality control 

section in the ASTM Method D6239-09 has been expanded and includes the following:

• Section 11.2 discusses importance of the reagent blank

• Subsections 13.2 through 13.5 have been added to incorporate calculations associated with 

determination of standard uncertainties, determination of critical activity concentration, and 

minimum detectable uranium activity concentration

• Quality Control Section 15 addresses:

o Calibration/calibration verification

o Detector efficiency

o Initial Demonstration of Capability – precision and bias study

o Incorporation of a laboratory control sample in each batch of no more than 20 samples

o Incorporation of a method blank in each batch of no more than 20 samples

o Incorporation of sample duplicates in each batch of no more than 20 samples

o Quarterly evaluation of independent reference materials

Recommendation

The technique based on alpha liquid scintillation with pulse shape discrimination has been in use for 

nearly twenty years and it offers the capability of equaling, and sometimes bettering, detection limits 

for radionuclides such as uranium relative to alpha spectrometric methods. Based on the performance 

characteristics of ASTM Method 6239-09 relative to EPA Method 908.0, ASTM Method 6239-09 is 

considered equally as effective as the approved method for determining uranium in drinking water.