Idom Merebrook Ltd
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Mr Simon Edwards
East Mill Bridgefoot
New CLEA proliferation?
Most interested observers will agree that there is still substantial work to be done in developing and agreeing contaminated land policy in the UK.We have come a long way in the last 10 years with a far more scientific approach having been followed than was historically the case but we are not quite there (wherever there is) yet.
The UK is in a position without parallel in the world when it comes to the need for assessment and remediation of contaminated land. We took a quick lead in the pollution stakes by inventing the Industrial Revolution and due to continued strong economic activity and other social pressures the demand for new land for housing remains strong. In order to preserve our undeveloped areas for the enjoyment of future generations we must recycle land, which has formerly been used for industrial purposes, for alternative usage which must include housing.
A decade ago many parties, both in the regulatory role and as advisors and practitioners, relied almost wholly upon threshold and action trigger values set out in a cross-departmental publication ICRCL 59/83. However, obvious deficiencies in this approach were apparent. These deficiencies included a limited range of contaminants addressed; blanks in the tables of trigger values; and a lack of transparency as to the scientific basis for the values provided. One may be excused for thinking that there was a complete lack of any scientific basis to the figures. Where ICRCL 59/83 and the figures it contained were possibly not so deficient, was in the guidance as to how the figures should be used.
Seeing that the system was in need of a radical overhaul, and to accompany the new powers under Part IIA of the Environmental Protection Act, Government commenced the programme of research which led to the development of the CLEA model and its release in 2000 together with published Soil Guideline Values (SGVs).
The CLEA model - detailed in its consideration of human exposure pathways and its modelling of UK exposure scenarios - was at first broadly welcomed by all parts of the contaminated land assessment community. It followed the well- accepted principles of assessing risk by constructing a theoretical exposure scenario and considering the means by which humans may be exposed to hazardous substances from the ground. The main feature of this approach is that it is scientific and can be used as a tool to forecast how much risk exists to people from the soil in or beneath their land. The SGVs were quickly adopted as a simple tool to assess contaminated land.
The fact is that when adopting such an approach to the assessment of risk, one must be prepared to deal with the ancillary issues inherent in any broad modelling approach. In addition another reality is that simple tools can, in insufficiently-trained hands, cause a lot of damage.
I feel that few of the practitioners referred to above would have any great concerns either with the general principles of CLEA or that SGVs may not be a useful concept.
Certain of the "problems" associated with ICRCL were not immediately solved by the introduction of CLEA. Most apparent of these was that few determinands were dealt with in respect of SGVs. It is a mark of the value that is placed upon the existence of simple figures, that voices were raised in calls for rapid extension of the determinands dealt with. However, the availability and transparency of the model meant that it was easy for anyone with suitable knowledge to input data and generate "SGV- like" output.
With a numerical model, what you get out depends on what you put in. It is therefore, all to easy to get out almost anything if you aren't too careful what you put in.
To consider the legal context surrounding these issues we must refer to Part IIA which contains a statutory definition of contaminated land. This definition includes land upon which "significant harm is being caused or there is a significant possibility of such harm being caused." From this we get that friendly-sounding acronym SPOSH (significant possibility of significant harm). Further guidance in Table B of Circular 2/2000 (and now Circular 1/2006) advises that, with respect to exposure to hazardous compounds, SPOSH is to be equated with the condition that "unacceptable intake" is occurring.
Now it is very easy to demonstrate using robust DEFRA/EA produced inputs that the SGV equivalent figure for certain compounds generated by CLEA are very low. That is that they are close to, and in some cases below the background levels in common and widely distributed natural soils.
Since 2000 this has led to many difficulties including pressure to remediate soils to below background levels; inability to find suitable import material for gardens; and possibly the determination of land by authorities as contaminated when that case is later found hard to sustain.
It seems to the writer that there was substantial mission creep between the original aims in 1995 that significant harm and significant possibility "...shall be determined in accordance with guidance issued for the purpose by the Secretary of State..." and the issue in 2000 of the SGV series of documents. It seems that official guidance was not clear enough to prevent users equating the two.
So by 2005 the scene was one of substantial confusion with some organisations "screaming" for more SGVs almost literally and others questioning the relevance or meaning of these. Some order has been restored with the work of the Cabinet Office SGV Task Force which has at least addressed some of these difficult questions head on. Although progress has been slow and some of the pragmatic decisions that industry has pressed for have not been taken forward yet. Further activity over this summer promises to take us to a more acceptable position with respect to guidance and regulation by, one hopes, early next year.
Glimpses of the direction that might be taken have been offered, and seem to include, a substantial revision of the modelling approach (something which was requested by Task Force members but not proceeded with); pragmatic decisions on health criteria input (similarly requested by sections of the Task Force); and further provision of new SGVs - SPOSHGVs if you like.
It must be accepted that "safe as houses" is an expression which must always be qualified. Science and statistics tell us that we can never say never, but we mustn't forget what many observers have postulated - that more ill health is generated by worry over minute amounts of ground contamination than by the contaminants themselves.
In summary the wholesale review of the nuts and bolts of the CLEA model and output is welcomed. Our hope for progress is that pragmatism should take some place in the deliberations. Science can only take us so far and imprecise definition of the input parameters can lead to solutions which are incompatible with our life choices.
The hard fact is that we can't all live on an organic farm in the middle of Dartmoor. Furthermore it is a truth of human nature that if we did we'd only be worrying about natural radioactivity anyway...
If you would like to discuss how Merebrook can assist with any of the issues raised above please contact the author: firstname.lastname@example.org
Simon Edwards - CPhys, MInstP, AMIOA, FRMetS.
Merebrook Science and Environment Ltd
For further information please email Merebrook Environmental Engineering Consultants