PONDERING A DECADE OF TOTAL DISSOLVED GAS PRESSURE MEASUREMENTS IN GROUNDWATER (OR LACK THEREOF)

The total dissolved gas pressure (P_TDG) probe was introduced formally to the groundwater community by Manning et al. (Ground Water v.41(4), 2003) just over a decade ago. A variety of potential uses of P_TDG probes for groundwater investigations have been put forward by Manning et al. and others since, including: i) performing excess air calculations; ii) identifying air contaminated wells; iii) showing the presence of a gas phase; iv) supporting gas concentration calculations (e.g. with passive gas samplers); v) informing groundwater sampling from wells; and vi) continuous (or not) in situ monitoring for dissolved gas changes related to biogeochemical reactions and/or water-gas phase transport. Here, we consider the reported use of P_TDG probes in the scientific hydrogeology literature over the past decade, and some of our recent unpublished work of field and lab studies. We identify the successes that have been achieved to date and opportunities not yet taken, with a focus on in situ monitoring. We also discuss some potential short-comings and issues with P_TDG measurements in groundwater, and possible directions for future research.