A new airtight sampling method for sulfur hexafluoride (SF6) in groundwater

In the past 20 years, sulfur hexafluoride (SF₆) has been considered a highly reliable tracer for assessing modern water (< 65 yrs old) in groundwater. However, modern-air contamination may introduce complications in interpreting data obtained using current sampling methods. A new airtight methodology isolates the sample from modern ambient air; thus, returning more reproducible and reliable results when compared to two traditional (air-sensitive and non-airtight) methods. The new airtight method returned results within 0.03-0.05 fmol/L SF₆ of expected SF₆ concentration for pre-modern waters (0.02-0.09±0.01 fmol/L). In contrast, the air-sensitive and non-airtight traditional methods returned results within 0.00-0.90 fmol/L and 0.02-1.21 fmol/L of the expected value, respectively. It is suspected that transformers in proximity to wells leak SF₆ which subsequently partitions into the samples obtained using traditional air-sensitive and non-airtight methods, thus creating erratic SF₆ results.•Comparative analyses of a new airtight method with traditional methods were performed and returned lower SF₆ concentrations with the new 2022 airtight method.•The new airtight method shows reproducible low-level detection of SF₆ concentrations and may reduce sampling error in production wells in urban areas that are co-located with transformers which are SF₆-emitting sources.