This paper really illustrates the wider issue of what are "Normal Background Levels" and do they have any relevance in Land Contamination assessment? To my mind "background" should be representative of natural undisturbed ground and reflect natural mineralisation only - as they do in Australia (yawn!).
The Australian regulators fought long and hard with industry to confine "background" adjustments to the natural mineralisation of soils (reflecting the vast reserves of iron, copper, tin, uranium, and other heavy metal rich soils, asbestos!) and even managed to exempt manmade acidification and liberation of heavy metals from acid sulphate soils. Uranium rich mineral sands which are naturally present in southwest Australia, presented a particularly challenging campaign, but it was finally agreed that radiation derived from washed and graded waste sands no longer represented a natural state and therefore did not represent background levels. Now "background" is clearly defined in statute as the levels found in naturally occurring, undisturbed ground.
As background levels are ridiculously hard to establish (let alone justify), most practitioners don't even bother to try. They find their resources are much better spent focussing on assessing and mitigating public health risk, rather that attempting to avoid liability by arguing the unarguable!
Best wishes to all
David E Jackson
|