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/
|