Groundwater Sampling – Are we doing it right?

The Future of Contaminated Land Risk Assessment

(Geological Society, Janet Watson Meeting, November 6th-7th, 2017) – Photo: Workshop in the Geological Society Council Chamber

I was recently invited to lead a groundwater sampling workshop at the Janet Watson meeting of the Geological Society on November 7th, 2017.
This was a fascinating 2-day conference covering everything from conceptual models and risk assessment to treatment technologies, guidance and regulation. It also addressed the need for us all to rationalize and explain risk in a coherent and understandable way to a non-technical and risk-averse society. Amongst the eclectic mix of speakers and topics, I was excited to find I’d been allocated the Geological Society Council Chamber to deliver a one-hour workshop on groundwater sampling and to pose the question “Are we doing (groundwater sampling) right?”

Amongst the Icons.
Delivering a workshop underneath the gaze of some of the giants of British geology, and being in the splendidly grand Victorian Council Chamber for the first time, was a rare honour – and a little unnerving.
The chamber is curiously dominated by a painting recording a distinguished group of scientists examining the skull of Piltdown Man . The “discovery” of the skull in 1912 was hailed as the missing link between man and ape and used to demonstrate Britain (Sussex to be precise) as the undisputed birthplace of mankind. It was over 40 years later in 1953 that a forensic re-examination revealed the fossil as a fraudulent construction of a 500-year-old skull combined with the jaw of an Orang-utan! The lead perpetrator of the fraud, whilst strongly suspected, has never been conclusively identified. The whole shameful episode is a sobering reminder of the need for scientific rigour and the importance of maintaining high ethical standards in our day jobs.

A Noisy Workshop
Given the technical audience, and limited time, I decided not to do much talking and asked everyone to work in pairs to design a sampling strategy for a monitoring borehole at a contaminated site. The resulting noise in the packed-out room was tremendous, and I’m thankful for the enthusiasm with which everyone engaged. There was some good discussion and insightful exchanges as we shared and discussed together the best way to obtain a “representative” sample.
I’m not sure I changed anyone’s views on whether they or their organisation’s sampling processes were right or wrong, but here’s a few pointers I picked up from the session.

  • Most organizations have their own standard operating procedures for groundwater sampling, but few were aware which, if any, guidance underpinned these.
  • Low Flow purge and sampling was the preferred methodology chosen by most of those in the room. However, it was clear that most do not fully appreciate the
    limitations of the Low Flow method, or the need to assess uncertainties (and fundamentally, the need for critical and considered interpretation of the resulting analytical results).
  • Many seemed surprised that the simple concept of a well volume was significantly different in different guidance documents.
  • There seemed some lack of awareness that if product layers are present (LNAPL or DNAPL) then the safest sampling strategy (in the absence of a pre-planned special procedure) is to not sample at all rather than mix product into groundwater (which would produce a very unrepresentative dissolved groundwater sample).
  • And we ran out of time!

Are we Doing it Right?
Analytical data generated from groundwater samples underpins all our risk assessment models. It is critically important to not only collect the best possible “representative” sample but to also understand its provenance. Our conceptual models depend on this for validation, to define the extent of contaminant distribution and to quantify the risk to water receptors. A considered interpretation of groundwater sampling results is even more critical where complex remediation strategies are being proposed.
The way we sample and the way we interpret data from groundwater sampling programmes from contaminated sites is not often questioned or subject to critical scrutiny. I worry that we have collectively fallen into the trap of ignoring the sometimes-inconvenient science underpinning the sampling methods we use in the interests of “getting the job done”.
It is tempting in the historic surroundings of the Council Chamber to draw a little from our history. It is exactly a consequence of others not questioning and looking more carefully at the scientific evidence, why the well respected and influential perpetrator of the Piltdown Man fraud was successful, and why it took 40 years for their claims to be disproved.

 

 

For more on groundwater sampling see earlier blogs: 

Links to In-Situ sampling equipment 

Peter.Dumble@pdhydrogeology.com 

©Peter Dumble 2017
November 25th, 2017 

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