The Reston Chlorofluorocarbon Laboratory

SF6 FAQ

  1. Where should I use SF6 dating?
    Some environments that appear to have given good results with SF6 include sandy aquifers (Atlantic and Gulf coastal plain), areas of rapid recharge and lack of mixing with old water (Blue Ridge Mountains of Virginia, some coastal aquifers), and some shallow, urban environments. For more details read the research section then contact the lab if you have further questions.
  2. How do I get sample bottles for SF6?
    See the SF6 Sampling page.
  3. How should the SF6 samples be stored after collection?
    They should be stored between collection temperature and room temperature. Warming can cause expansion of the water and breakage of the bottle. Avoid leaving samples in the sun or hot enclosed spaces (like field vehicles). Storage on ice is not recommended because the cooling causes contraction of the water and possibly, the formation of a bubble in the bottle. Some of the SF6 in the sample will be preferentially partitioned into the bubble headspace and will be lost when the bottle is opened for analysis. This can introduce a small old bias in the calculated SF6 age.
  4. How long can I keep the bottles before shipping?
    Although the samples are probably stable for several months, it is recommended that they be shipped to the CFC lab within one week of collection. They will be analyzed within approximately 2 months of receipt.
  5. How do I ship the bottles to the CFC lab without breaking?
    Wrap with bubble wrap, stand upright in coolers and ship via FedEx. Do not lay the bottles down stacked on top of each other. The stacking method has poor results with breakage.
  6. Can I get my bottles back after the samples are analyzed?
    Yes. They can be returned in your coolers after they are analyzed. They can be reused. Notify the lab with a note if you want the bottles returned.
  7. Can I pre-pay for analyses?
    Yes. Contact the lab.
  8. Should I leave a headspace in the bottle?
    No, never. See SF6 Sampling
  9. What if I see gas bubbles in the water during sampling?
    If gas bubbles are forming, some of the SF6 in the sample is likely being lost with the bubbles. The age can be biased old. Try to keep degassing to a minimum while sampling.