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Finding the best test Tom Cairney looks at the problems of selecting a laboratory testing regime appropriate to identifying actual risks in contaminated land investigations

When the Environment Act (1995) comes into force this summer, contaminated land assessments will have to be justified on the 'source-pathway-target' basis. This is likely to exacerbate an already obvious weakness in current contaminated land investigation practice: selecting an appropriate testing regime to identify what risks actually exist.

Today, contaminated land investigations are far better than was the case even a few years ago. However, the improvements are largely those which constitute the 'pathway' element. When it comes to establishing the particular risks from soil and water contamination, improvements are much less apparent.

In many reports it can be difficult to understand why a particular analysis was included, what benefits had been expected from the chosen chemical analytical suite and indeed - despite the provision of page after page of expensive chemical results - what contamination risks actually exist in a site. Since appropriate identification of contaminant types and concentrations is essential to establish the significance of a 'source', current industry standards appear to be inadequate to satisfy the new assessment regime.

Choice of analytical testing suites

Faced with the choice of contaminant testing, too many investigators continue to fall back on the 1987 ICRCL listing. This includes the commoner heavy metals, a few metals which can reduce plant growth, and the organics and sulphates found in gasworks. ICRCL was, and still is, an excellent basis for assessing the risks to human health and plants posed by coal carbonisation.

However, for other types of site - dockyards and power stations (asbestos), garages and light engineering works (various oils and fuels), vehicle and furniture works (a range of solvents), former military airfields and workshops (radioactivity from luminescent dial paints) - the ICRCL listing is patently deficient. The more worrying contaminants, indicated in the brackets, do not even feature in the 1987 listing. Thus, important risks can be overlooked.

The ICRCL guidance also includes analyses of very doubtful use. For example, the toluene extractable matter (TEM) test was a cheap indicator of the presence of coal tars at a time when more indicative analyses were not widely available. Because the TEM test strips out a vast range of organic matter (humus, sawdust, coal dust, peat etc), and since no standard test methodology exists - so laboratories each use their own unique approach - its employment today cannot be recommended.

Other aspects of the use of the ICRCL testing regime could be criticised. For example, a total free sulphur determination was included because free elemental sulphur can occur on gasworks and be a severe risk to human health. But it was never intended to imply a measurement of the total bound-up sulphur (ie the sum of the sulphur in already analysed sulphates and sulphides). The ICRCL testing regime is entirely inadequate to address the range of contaminants risks which brownfield sites can pose.

Type of determinations wanted

ICRCL advocated the measurement of 'total' metal concentrations. Obviously, this will be useful if the concern is that people could inhale or ingest metal-rich dusts. However, if other risks - for example, to water or plants - seem more likely, it is logical to ask for water solubility and plant available testing of the metallic constituents, and not for 'total' determinations.

Again, the point has to be that only appropriate testing is ever justified and worth its costs.

Risks for land contamination

When former industrial land is to be reused, a wide range of risks might arise. Some would be breaches of statute law and expose a land developer and his investigator to court appearances. These include the risk of polluting surface waters, polluting groundwater, creating area-wide air pollution, and of causing off-site contaminant migration.

Others, such as the risk of gases and vapours entering dwellings, building materials being attacked, plant growth being affected and adverse effects on human health, could harm the interests of future inhabitants or users of reclaimed land.

Given this range, and the certainty that different contaminant assemblages and different measurements of contaminant mobility and availability areimportant for each of these risks, it is obvious that the appropriate choice of chemical tests will become crucial when the Environment Act regime is fully in force.

Many investigators whose chemical knowledge is not strong could see this as adding to their problems. This need not be so. Laboratories are staffed by trained chemists who, given an explanation of a particular site's likely risks, are able to offer helpful expertise.

Tom Cairney is a consultant to WA Fairhurst & Partners

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