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 su bmitted to the TSC Alternate Test Procedure (ATP) Coordinator for evaluation as an alternate test method t o EPA Method
908.0 for the analysis of uranium in drinking water. An earlier version of t he method (ASTM D 6239

- 02)

was previously submitted for cons ideration as a new meth od but it was rejected due to a poorly organized data package and inadequate quality control in the method.

Evaluation s

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 maxi mize 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 e xtraction efficiency as a function of pH. Solutions of natural uraniu m 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 alpha

emitters such as Th

- 230, Po

- 210, Pu

- 238, Am

- 241, and Ra

- 226. On av erage 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 + 3.8Element 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 (Ca 2+

, Fe 2+ , SO 4 2

- , H 2 PO 4 - , HC 2 O 4 - ) . 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 a pproved
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 radioche mistry 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, t he 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 critic al 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 re ference 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 radionuclide s 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.