Environmental geophysics Evolution not revolution over the past 25 years Welcome readers to this issue’s column on geophysics applied to the environment. I was having some trouble thinking of a topic this month then my wife (a geochemist at the University of Adelaide) got me thinking about how the science/art of geophysics applied to the environment has changed over the last 25 years. She then (being the master of net searches) found a 1994 article by Robert Whitely in Exploration Geophysics titled“Environmental Geophysics: Challenges and Perspectives” (Whiteley 1994). She followed up by finding a second, short 1994 abstract/ article by Phillip Romig in the SEG conference archives titled“Environmental Geophysics – Fad or Future”(Romig 1994). These articles were written 25 years ago, and seemed to me to be good starting points for thinking about how environmental geophysics has changed over that time, and where it might be going. They also reminded me about some things that we might usefully revisit from way back then. One article has a more Australian viewpoint, the other has a more American viewpoint. Let’s start with the Romig abstract – while short, it makes several very good points (some that overlap with Bob’s article as well). Romig comes at the topic from the viewpoint of a geophysicist contemplating a move from the oil industry to environmental geophysics during one of the oil industry downturns. He starts by reviewing predictions for the environmental geophysics“industry” – with some observers at the time stating that environmental geophysics could quite soon be bigger than the oil industry; others, of course, claiming that it was nothing more than a fad. In my opinion it still feels as if environmental geophysics is in its infancy (25 years later!), and has a way to go before it becomes a routinely used tool in a geo- hydrologist’s toolbox. More on that later. Romig also points out that site characterisation (I am thinking of this as“the final product”) differs between oil exploration and the environmental industry. Exploration is driven by a“risk- taking, revenue-generation psychology” whereas the environmental industry is more about cost-control and risk minimisation. His final point is on the source and quantity of available money for this type of work in these respective industries. Oil exploration is directly funded by the oil companies – their success at finding oil, at a lower cost than producing the oil, is sufficient justification for using geophysics (in my possibly oversimplified view). As Romig says:“No such simple cause-and-effect relationships exist in the environmental business”. The economic issues that Romig highlights are, for me, a big part of the problem. In exploration even a slight improvement in drilling success based on geophysical information can be worth the investment in geophysics. My feeling when talking to professionals in the environmental industry is that geophysics is seen as too expensive and not worth the effort – possibly given the (occasionally?, frequently?) ambiguous results. I think that this attitude is starting to change, but we will need to keep improving our outputs to close the gap between perception and reality. Bob Whiteley’s article gives two examples of environmental problems that were current 25 years ago – at least in the Australian setting. The first is still a huge issue over here: dryland salinity. His main point (that I got anyway) is that as environmental geophysicists we cannot just make maps that show the locations of reflectors, or conductive features, etc. We need to produce maps that show parameters that actually mean something to a hydrologist or engineer. He describes the painstaking process of converting conductivity data collected using a typical earth conductivity meter into actual soil conductivity by regressing the geophysical data against lab-measured soil parameters so that, for example, the total volume of salt stored in the top 5 m of soil could be estimated over a project area. The original conductivity map is likely to look similar to this final product, but actual salt content will not be“correct” without understanding local conditions, specifically clay distribution in the soils. The second example given by Whiteley is also still a major issue: contaminant leakage (specifically LNAPLs and DNAPLs) into groundwater. Direct detection of these contaminants is very difficult, even though electrical contrasts between the contaminant and the host can be large. In my limited experience, which is only two or three surveys in the last 25 years, it is the urban setting that is the problem. Surveys can run over, for example, concrete pads reinforced with metal rebar that can make most electrical data nearly useless. There are often power lines and other noise sources that also make the use of electrical techniques in these settings difficult. Seismic techniques, in turn, are affected by, for example, local traffic that introduces vibrational noise into those data sets. Unfortunately we have not yet worked out how to see past such urban noise. So what is different (better?) about environmental geophysics these days?To me there isn’t any development that has been truly revolutionary, with most only evolutionary. But we are getting there. One of the most important improvements is the incorporation of GPS information into most data sets, so that we really do know exactly where we are over most survey areas. Our ability to get down to centimetre accuracy with only moderate effort has also made a big difference. In addition, our ability to make the data“real” has improved – here I am thinking of the nearly routine inversion of most of the data that we collect, as well as the improvement in inversion quality. I think that this is a major step toward making our data sets more accessible to others who need to use this information but are not geophysicists. Along with these developments I think that we are finally starting to make progress removing some of the inherent Mike Hatch Associate Editor for Environmental geophysics michael.hatch@adelaide.edu.au 24 PREVIEW Environmental geophysics FEBRUARY 2019