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MADE FOR EACH OTHER

LABORATORY TESTING - Analysing made ground is beset with problems, particularly when using Mcerts. A bit of interdisciplinary compatibility might help, says Andrew Buck.

Categorisation, analysis and reporting of made ground is a recurring nightmare for the modern laboratory. Traditionally a by-product of land reclamation schemes, a container of made ground can include traces of anything from steel, concrete and brick to nappies and household waste.

There is no all-encompassing approach to dealing with it. Nevertheless, with brown. eld sites universally hailed as the sustainable way forward, now is the time to seriously evaluate the methods used both onsite and in the laboratory.

Much of the confusion goes back to the introduction of the Environment Agency's Monitoring Certi. ation Scheme (Mcerts) for the chemical testing of soils (GE October 2004).

Any laboratory operating under this banner has to submit results that fulfill both the general requirements of ISO/IEC 17025 and the specific method validation and performance requirements of Mcerts.

The latter is problematic for laboratories dealing with made ground, as it requires samples to conform to specific sample matrices for results to be accredited. For relatively unadulterated soils, this has meant the creation of soil classification categories such as 'loamy soil', 'sandy soil' or 'clay type soil'.

And while some geotechnical engineers may see this as a tenuous oversimplification, the approach is widely regarded as the best available and has the full endorsement of the Environment Agency (EA) and the UK Accreditation Service (UKAS) - albeit based on economic drivers.

The inhomogeneous nature of made ground means all manner of inter etations and questions are raised when faced with these basic matrices. These include whether results can be reported as accredited or whether it is possible to report them as unaccredited to make it clear to the engineer that the sample does not fall into a clearly defined matrix.

This is not just an issue of categorisation - the whole process, from preparation to final report, is stripped of any consistency as laboratories adopt individual approaches by asking questions such as:

Should the sample be dried?

Should the sample be milled to uniform particle size?

Should everything over 2mm be discarded?

Should everything that is not soil be ignored?

None of these methods will provide an inaccurate result per se, but each has the potential to give a misleading picture of the site.

The problems become more complex when you consider that the commercially driven nature of redevelopment schemes has turned laboratories into high-tech, scientific conveyor belts. It is a situation reliant on good judgement, experience, and above all, a decent sample.

It is impossible to overstate the critical nature of the latter: without a comprehensive sample, the laboratory cannot do its job. In other words, it cannot capture the essence of a site's industrial legacy and act as a signpost to the appropriate action.

Though Mcerts has to some extent raised standards in the laboratory, it missed an opportunity by not offering any guidance to geo chnical engineers on the best techniques for sampling, storage and transportation; nor does it elaborate on the consequences of incorrect, inappropriate or inadequate sampling.

The reason the EA has put the onus on the laboratories is understandable - to allow continuity of testing pre- and post-Mcerts - but the resultant confusion and knowledge deficit, particularly with regards to sampling, is less than satisfactory.

Throwing legislation at the problem is unlikely to be constructive, so the best course of action is to create an environment of interdisciplinary compatibility fuelled by open lines of communication, intellectual communality and knowledge sharing.

Geoscientists should learn to adequately describe samples, to make samples manageable for the laboratory and to understand the laboratory processes of sample preparation, analysis and reporting.

By the same token, chemists should acquire some . eld experience, learn about the conditions engineers face onsite and educate themselves on the processes that inform geotechnical sampling techniques.

This could be achieved by sponsoring laboratory staff through geoscience degrees and encouraging transfers between teams.

Trying to answer the question of how to produce consistently accurate results from made ground just throws up more questions:

What are the limitations of the selected analytical method?

If there are limitations, do they matter in this case?

On what basis is the data reported?

Does it match the basis on which acceptance criteria are calculated?

Has the sample data been generated in ideal conditions using ideal standards which are unlikely to repre sent the conditions on site?

By answering these questions, improving communication and waiting for Mcerts to catch up, the categorisation, analysis and reporting of made ground can be changed for the better.

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