Recently I came across a possible misinterpretation in a drill hole log. This involved a feature that might possibly be a buried alluvial channel of Pleistocene age, but which had been logged as weathered rock. The setting is a valley located in an area where buried channels are possible, due to former lower sea levels and subsequent infill by alluvium and colluvium when sea levels rose. The uncertainty is partly due to the fact that the portion of the drill hole in question was wash bored. Without going into the details, the potential consequences are significant.
So, what can you do when logging to reduce the possibility of such misinterpretations and their consequences? I suggest that, wherever possible, you:
1) Find out what the project is for, where the site is located and what the geo-team (Brunsden, 2001) consider to be the project’s key areas of interest, uncertainty and risk.
2) Familiarise yourself with the local geological setting before you log. What are the expected materials, geomorphological setting, structure, geological history and processes?
3) Go to site often during the drilling. This allows you to see the setting, see the materials come out of the ground, speak to the drillers and generally develop a much better understanding of the geological setting.
4) Consider any drilling anomalies such as loss of flush carefully. To further develop the current example, if a section of a drill hole has been wash bored ask yourself why this is the case – better still – ask the drillers.
5) Make sure that you clearly communicate any important features and uncertainties (such as tens of metres of wash boring) to the other members of the geo-team. This can be done in several ways, including on the logs, in the report text, on figures, in uncertainty and risk registers and of course – face to face or over the phone (although make sure you document these issues as well).
6) Make every effort to achieve good communication – be proactive and reach out to other members of the geo-team. Do not assume that others will recognise the important features and problems – no one else will have as good a ‘feel’ for the ground as you, the person who has logged it.
7) Seek out experienced mentors to train and advise you and check your work.
All of the above seems elementary, but it is rarely the case that all aspects are satisfactorily carried out. In my experience items 1, 2, 5 and 6 are generally not carried out well, which can be frustrating as these issues could be easily resolved.
As always, I would be interested to hear what others think – do you agree or disagree? What do you think could be done to improve logging?