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The U.S. Geological Survey (USGS) Chlorofluorocarbon (CFC) Laboratory in Reston, Va., has been measuring concentrations of CFCs in ground-water samples since 1989 to estimate the year that a water sample was recharged to a ground-water flow system. The water samples have been collected in flame-sealed borosilicate ampoules. Typically for each site, three samples were analyzed within days to a few months after collection, and additional samples were archived for extended periods of time (up to four years). The stability of CFC concentrations in the archived water samples from the USGS CFC Laboratory was investigated by analyzing the CFC concentrations in archived water samples and comparing them with the CFC concentrations that were obtained soon after the samples were collected. The archived samples selected for analysis were chosen from sites with a wide variety of hydrogeologic and geochemical conditions. For CFC-11 and CFC-12 concentrations, approximately 14% and 10.5%, respectively, of the archived samples were statistically different (both higher and lower) from the concentrations obtained from analyses conducted soon after the sample collection. Most of the extraneous values were attributed to natural variability of CFC concentrations originally in the water discharged from wells, rather than to microbial degradation within the ampoule on storage.
Abstract
Introduction
Purpose and Scope
Degradation of CFC Concentrations
Approach
Stability of CFCs in archived ground-water samples
Conclusions
Acknowledgments
References Cited
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For more information contact:
Branch of Regional Research, Eastern Region
U.S. Geological Survey
Attn: Dr. E. Busenberg
12201 Sunrise Valley Drive
MS 432
Reston, VA 20192
E-mail: ebusenbe@usgs.gov
Copies of this report can be purchased from:
U.S. Geological Survey
Information Services
Box 25286, Federal Center
Denver, CO 80225
e-mail: infoservices@usgs.gov
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