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Local authorities face a dilemma when designating contaminated land using guidance values, says Phil Studds.

Gaps in government guidance are hampering local authority attempts to determine what is 'contaminated land' under Part IIA of the Environmental Protection Act.

This is particularly noticeable where contamination levels in domestic gardens exceed soil guideline values (SGVs).

Local authorities say it is unlikely they will be able to designate residential properties as contaminated, because of recent guidance issued by the Department for Environment, Food and Rural Affairs (Defra), CLAN02/05. Defra itself admits this guidance does not help with the key criteria.

Local authorities are in a difficult situation. They will be pressured by residents to decide whether or not land is contaminated, but lack the guidance with which to do it.

Defra has been reported as considering a new series of guidance values, which are anticipated to be higher than the current SGVs - possibly ten times greater. And there is a school of thought that considers the proposed values emerging from the guidance should be sufficient to decide whether land is contaminated.

While such values will be useful in working out remediation strategies for proposed developments, it is questionable whether they are suitable for existing ones.

Designating existing residential property as contaminated raises considerable socio-economic issues including blight, property value, health concerns and the time taken to resolve uncertainty.

This can lead to a reluctance to designate land as contaminated if it is a residential property rather than a proposed development, particularly under the current state of the guidance.

Use of guideline values poses the question as to whether the definition of contaminated land should be based on contaminant concentrations or risks to human health and the environment.

The defiition of contaminated land cannot solely be based on the guidance value. Contaminated land assessment embodies the concept of risk assessment based on sitespecific criteria, whereas guidance values are based on generic criteria that may be similar but not identical to the site in question.

For a risk of pollution or environmental harm to occur as a result of ground contamination, a 'significant' source-pathway-receptor pollutant linkage must be established.

To designate land as 'contaminated' under Part IIA (when considering human health) the assessor must demonstrate 'significant' harm or 'significant' possibility of 'signifint' harm. 'Significant' needs some form of qualification and assessment; therefore the de'nition of contaminated land embodies the concept of risk assessment.

The UK framework for assessing significant environmental risk follows three key stages (as given in CLR 11, Model procedures for the management of contaminated land):

1 Preliminary risk assessment - developing an initial conceptual site model and establishing potentially unacceptable risks (pollutant linkage);

2 Generic quantitative risk assessment - comparison of contaminant concentrations to generic screening values, eg SGVs; and

3 Detailed quantitative risk assessment - using site-specific data in a simple, commercially available analytical model to evaluate the significance of the pollutant linkage

A final stage of 'assessor judgement' is required to complete the risk assessment. The competency of the assessor advising the local authority therefore becomes crucial at this stage. Practitioners routinely use the protocol of:

ºdefing the conceptual site model;

ºstatistical analysis of the contaminant concentrations;

ºevaluating the results of a detailed quantitative risk assessment of the source-pathway-receptor pollutant linkage; and

ºassessor judgement, to assess previously developed land as contaminated.

Based on the results of this assessment, practitioners provide suitable remedial solutions to allow the development of the land to a standard that is suitable for a specific end use.

Assessment of contaminated land should not be based solely on comparison of individual laboratory test results with a table of generically derived values, however attractive, because it is an unsound basis for sustainable land use decisions.

Rather, assessment should be based on a careful evaluation of the risks to human health and the environment and not be solely reliant on contaminant concentrations.

Protocols to assess the risks associated with contaminated land allow determination but ultimately rely heavily on the competency of the assessor.

Indiscriminate use of generic guidance values may still lead to inaccurate assessment of land as contaminated. Further guidance is required on acceptable practice for risk assessment.

Phil Studds heads the QRA skills group at White Young Green Environmental.

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