Measurement of Gross Alpha: Application, Interpretation and New Method Options

Collaborative Efforts to Improve Environmental Monitoring - Session 2
Oral Presentation

Prepared by G. Smith
U.S. EPA, 26 West Martin Luther King Drive, Mail Stop 140, Cincinnati, Ohio, 45268, United States

Contact Information: [email protected]; 513-569-7652


Gross alpha is a non-specific screening method for determining the level of alpha emitters in drinking water. The maximum contaminant level (MCL) specified in the drinking water regulations at 40 CFR 141.66(c) is 15 pCi/L, including activity contributed by radium-226, but excluding radon and uranium activities. It is a relatively simple and inexpensive analytical procedure, but the non-specific nature of the gross determination can lead to inconsistent results when samples are improperly processed by laboratories. Bias and uncertainty in gross alpha determinations depend appreciably on the radionuclide used as the calibration reference, the level of dissolved solids in the sample, the time between sample collection and sample preparation, and the time between sample preparation and counting.

The presentation will describe the sources of variability associated with gross alpha determination and how to control and minimize the impact of these factors. In addition, newer method options for drinking water gross alpha compliance monitoring will be discussed.