Hello Charlotte, and thank you for your response, which is most thought-provoking. The point that I was trying to make is that, under the present system, are we actually able to distinguish between the two scenarios? We can use models (conceptual and computerised) for many determinands, but if we do not know what "significant" means, how can the final "decision" step have a reliable basis?
This may run and run, I suspect.
With best regards
Anthony
Dr. Anthony Luke
Principal Officer (Contaminated Land)
TEC Services
The Highland Council
38 Harbour Road
Inverness IV1 1UF
01463-228703
07766-298104
The opinions expressed herein are my own and do not necessarily reflect those of the council
-----Original Message-----
From: Charlotte Wheatley [mailto:[log in to unmask]]
Sent: 20 October 2011 15:34
To: Anthony Luke; [log in to unmask]
Subject: Detail v Judgement
Anthony/all
I was having this conversation yesterday infact, particularly with consideration of the predicament in the Westcountry with respect to natural arsenic concentrations. The situation is a little better now because we can take into consideration bioaccessibility, but the SSAC still end up fairly low relative to the natural levels. And yet it seems (and I suppose this could be debatable!!) the population of Devon and Cornwall - aside from those actually digging and processing ore - appears to have been hearty and healthy for thousands of years.
We have a site where we are exporting and importing soil for tiny pristine gardens, and there is an allotment site next door...which has been there for ages supporting some very healthy locals!
Occasionally I lift my head away from the intricacies of QRA and am torn between - 'quantitative risk assessment has to start and finish somewhere, and in many scenarios for many determinands our system is probably a reasonable guide', and 'where did common sense go/are we being overzealous and unsustainable?'. Makes for an interesting job...
Miss Charlotte Wheatley BSc MSc DIC FGS
Principal Geo-Environmental Consultant
Hyder Consulting (UK) Ltd
Telephone: 01392 374606 / 07767617885
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Anthony Luke
Sent: 20 October 2011 13:20
To: [log in to unmask]
Subject: Re: GACs ? which to use
Good afternoon everyone.
Here's a thought: if the actual chronic health risk posed by substances in soil is "unknowable", how can we ever know that we are in the correct risk protective ballpark?
What does risk protective ballpark actually mean, anyway?
The forum regularly features detailed consideration of values of GACs / SSVs / HGVs (whatever in Sam Hill we are calling them at the moment) but the more central, deep philosophical points about what we do are rarely, if at all, the subject of discussion.
What does "significant" mean? If it means (in accordance with DEFRA's incredibly helpful guide to the legal definition) "whatever the local authority feels to be significant", then does this not make the final step in the long, detailed risk assessment process a "stab in the dark"?
I will admit to finding this more troubling all the time. I may be alone, but I suspect that I am not!
With all best regards
Anthony
Dr. Anthony Luke
Principal Officer (Contaminated Land)
Transport, Environmental and Community Services
The Highland Council
Environmental Health and Trading Standards
38 Harbour Road
Inverness IV1 1UF
telephone 01463 228703
mobile 07766 298104
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Dainton
Sent: 20 October 2011 12:13
To: [log in to unmask]
Subject: Re: GACs ? which to use
Hello Paul
I'm still a bit confused by the comments in your two posts.
The original post was about differences between LQM GAC numbers and Atkins SSV numbers for residential & commercial use.
Both Atkins and LQM have used the Agency CLEA model and have adopted the SR3 conceptual exposure scenarios models for residential use and commercial use (correct me if I'm wrong on that for Atkins).
So the primary issue being discussed (in my mind anyway) has nothing do do with choice of 'exposure assessment tool' or 'conceptual site model' or 'parameterisation' of these elements as they should be the same for both Atkins/LQM (perhaps that could be clarified by users of the Atkins numbers).
The differences (I'm assuming) are likely to be down to differences in Atkins/LQMs approach to HCV selection, phys-chemical parameters, chemical specific veg uptake parameters and dealing with saturation limits.
So, if this is the case, then I would agree with the main thrust of Clive's post that its probably not appropriate to consider either LQM or Atkins as being more accurate than the other as they are just representations of differing (and hopefully both equally valid and robust!) experienced risk assessor opinions about parameter selection.
Now as to your more general point about accuracy being vital in human health risks assessment.
There is an interesting debate to be had around the question: 'Can contaminated land human health risk assessment ever be accurate?'.
That's a whole different can of worms and perhaps best saved for a separate thread..... which I might come back to next week as I'm away for a few days.
But I'll start it off with a few comments that the List could think about:
Do human heath risk assessors delude themselves via:
1. The illusion of accuracy through precision
2. The illusion of accuracy through complexity
To me it is more vital to have confidence that we are at least in the right risk protective ballpark and to appreciate how inaccurate human health risk assessment outputs are likely to be compared with the actual (and unknowable) chronic health risk posed by substances in soil.
And lastly, I also do not think that GACs should necessarily, by default, be considered as the low bar to determine whether soil concentrations are 'fine' (to use your words and continue your analogy). Common sense needs to prevail: for example, I would not advocate the residential GAC/SGV levels of the heavier end TPH fractions, some of the 16 PAHs and the TEX compounds as being acceptable/fine thresholds in surface soils in gardens.
Kind regards
Chris Dainton
Peak Environmental Solutions Limited
http://peakenvironmentalsolutions.com/
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