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Techniques and Methods 5–B6

Prepared by the U.S. Geological Survey Office of Water Quality, National Water Quality Laboratory

Interpreting and Reporting Radiological Water-Quality Data

By David E. McCurdy, John R. Garbarino, and Ann H. Mullin

Book 5, Laboratory Analysis
Section B, Methods of the National Water Quality Laboratory
Chapter 6


Thumbnail of and link to PDF (3 MB)This document provides information to U.S. Geological Survey (USGS) Water Science Centers on interpreting and reporting radiological results for samples of environmental matrices, most notably water. The information provided is intended to be broadly useful throughout the United States, but it is recommended that scientists who work at sites containing radioactive hazardous wastes need to consult additional sources for more detailed information. The document is largely based on recognized national standards and guidance documents for radioanalytical sample processing, most notably the Multi-Agency Radiological Laboratory Analytical Protocols Manual (MARLAP), and on documents published by the U.S. Environmental Protection Agency and the American National Standards Institute. It does not include discussion of standard USGS practices including field quality-control sample analysis, interpretive report policies, and related issues, all of which shall always be included in any effort by the Water Science Centers. The use of “shall” in this report signifies a policy requirement of the USGS Office of Water Quality.

Version 1.0

Posted September 2008

Suggested citation:

McCurdy, D.E., Garbarino, J.R., and Mullin, A.H., 2008, Interpreting and reporting radiological water-quality data: U.S. Geological Survey Techniques and Methods, book 5, chap. B6, 33 p.




1. Analytical Information Reported by the Contract Laboratory

2. Definitions of Important Analytical Parameters

2.1 Combined Standard Uncertainty

2.2 Sample-Specific Critical Level (ssLC)

2.3 Minimum Detectable Concentration

2.3.1 a priori Minimum Detectable Concentration (a priori MDC)

2.3.2 Sample-Specific Minimum Detectable Concentration (ssMDC)

2.4 Comparison of Radiological, Inorganic, and Organic Detection Levels

3. National Water Quality Laboratory Evaluations of Contract Laboratory Results

3.1 Initial Evaluation Criteria

3.2 Rounding Results

3.3 Review of Negative Results

3.4 Assigning Remark and Value-Qualifier Codes

3.5 Information Sent to the National Water Information System (NWIS) Database

3.6 Information in Detailed Data Packages

4. Water Science Center Reviews of National Water Information System (NWIS) Database Results

5. Publishing Results

5.1 Technical Reports

5.2 Nontechnical Reports

6. Interpretation and Reporting of Results from an Aggregated Dataset


References Cited


Appendix: Typical Equations for Calculating Radiological Parameters

A1. Calculating the Concentration

A2. Calculating the Combined Standard Uncertainty

A3. Calculating the Critical Level

A3.1 General Principles

A3.2 Calculating the Sample-Specific Critical Level (ssLC)

A3.3 Practical Approach for Verifying the Reported Sample-Specific Critical Level

A4. Calculating the Minimum Detectable Concentration

A4.1 General Principles

A4.2 Calculating the Sample-Specific Minimum Detectable Concentration (ssMDC)

A4.3 Practical Approach for Verifying the Reported Sample-Specific Minimum Detectable Concentration

A4.4 The Effect of Sample Size and Counting Time on the Reported Sample-Specific Minimum Detectable Concentration (ssMDC)

A4.5 The Relation between the Combined Standard Uncertainty and the Calculated Activity in a Sample for Two Radioanalytical Measurement Techniques


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