Developing a Database of SF6, CFCs, and Dissolved Gases for the United States

Abstract:

Groundwater dating tracers have become a powerful tool for use in hydrologic studies. Over the past 30 years, hundreds of studies have been conducted using age tracers and dissolved gases. The data from these studies are often only available directly from the resulting publications, or via laborious re-interpretation of raw concentrations from databases like the U.S. Geological Survey (USGS) National Water Information System (NWIS). This decentralized nature of tracer and dissolved gas data presents challenges for the hydrologic community; for example, planning new investigations without knowledge of extant tracer data can result in duplicative efforts, and opportunities for synoptic, national scale, multi-aquifer studies are missed. Furthermore, there is a growing need for national-scale tracer data as input and validation for national-scale groundwater flow models.

To help alleviate these challenges, the USGS is creating a centralized, curated database of age tracers and dissolved gases. The USGS Groundwater Dating Laboratory has been in operation since 1992, and in that time has processed SF₆ samples for over 8,000 sites, CFC samples (CFC-11, CFC-12, and CFC-113) for over 10,000 sites, and dissolved gas samples (N₂, O₂, Ar, CO₂, and CH₄) for over 30,000 sites. We are combining these results to create a unified national database for the United States.

This curated database, created from laboratory records provides many opportunities. Apparent ages and dissolved gas pressure calculations can be updated using the most current methods, ensuring uniformity of results over time. Incorporating the metadata submitted with the samples allows tracer data comparisons with ancillary chemical data that are not available in other water quality databases or publications. Results can be directly cross referenced to instrument calibrations and quality assurance samples to obtain clear metrics of uncertainty. Additionally, laboratory performance over long time periods can be assessed. Our vision is to make this database publicly available on the USGS’s ScienceBase data portal, with synchronized non-interpretive data availability in NWIS, and to meet standards suggested for related international databases such as Isobank.