USGS Scientific Investigations Report 2008-5088

Prepared in cooperation with the U.S. Environmental Protection Agency
Measurement and Monitoring for the 21st Century Initiative

Userís Guide to the Collection and Analysis of Tree Cores to Assess the Distribution of Subsurface Volatile Organic Compounds

By Don A. Vroblesky

U.S. Geological Survey Scientific Investigations Report 2008-5088, 59 pages (Published online, July 2008)

This report is available online in PDF format: SIR 2008-5088 (Opens the PDF file in a new window. ) (2.6 MB)

Cover thumbnailAnalysis of the volatile organic compound content of tree cores is an inexpensive, rapid, simple approach to examining the distribution of subsurface volatile organic compound contaminants. The method has been shown to detect several volatile petroleum hydrocarbons and chlorinated aliphatic compounds associated with vapor intrusion and ground-water contamination. Tree cores, which are approximately 3 inches long, are obtained by using an increment borer. The cores are placed in vials and sealed. After a period of equilibration, the cores can be analyzed by headspace analysis gas chromatography. Because the roots are exposed to volatile organic compound contamination in the unsaturated zone or shallow ground water, the volatile organic compound concentrations in the tree cores are an indication of the presence of subsurface volatile organic compound contamination. Thus, tree coring can be used to detect and map subsurface volatile organic compound contamination. For comparison of tree-core data at a particular site, it is important to maintain consistent methods for all aspects of tree-core collection, handling, and analysis. Factors affecting the volatile organic compound concentrations in tree cores include the type of volatile organic compound, the tree species, the rooting depth, ground-water chemistry, the depth to the contaminated horizon, concentration differences around the trunk related to variations in the distribution of subsurface volatile organic compounds, concentration differences with depth of coring related to volatilization loss through the bark and possibly other unknown factors, dilution by rain, seasonal influences, sorption, vapor-exchange rates, and within-tree volatile organic compound degradation.

CONTENTS

Abstract

Introduction

Advantages of Tree Coring as a Tool to Examine Subsurface Volatile Organic Compound Concentrations

Limitations of Tree Coring as a Tool to Examine Subsurface Volatile Organic Compound Concentrations

Acknowledgments

Part 1. Methodology for Collection and Analysis of Tree Cores

Tree-Core Collection

Tree-Core Analysis

Quality Control and Assurance

Part 2. Historical Perspectives and Technical Considerations

Historical Perspectives

Technical Rationale for Methodology

Factors Influencing Volatile Organic Compound Concentrations in Tree Cores

Summary

References Cited

Appendix 1. Case Studies

Appendix 2. Air Sample Analysis for Volatile Organic Compounds

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Suggested citation: Vroblesky, D.A., 2008, Userís guide to the collection and analysis of tree cores to assess the distribution of subsurface volatile organic compounds: U.S. Geological Survey Scientific Investigations Report 2008Ė5088, 59 p. (available online at http://pubs.water.usgs.gov/sir2008-5088)

For more information, please contact Don A. Vroblesky.

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