The 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 the stuff can contain traces of anything from steel, concrete and brick to nappies and Coke cans – and that’s on a good day.
Ask anyone from the engineer taking samples at the coalface to the men in white coats analysing them, and you will find that there is no all-encompassing approach to deal with the ‘made ground’ conundrum. Nevertheless, with brownfield sites being universally hailed as the sustainable way forward, now, more than ever before, is the time to seriously evaluate the methods employed both on-site and in the laboratory and try to circumvent the insidious ‘no easy answer’ maxim.
Much of the confusion goes back to the introduction of the Environment Agency’s Monitoring Certification Scheme (MCERTS) for the chemical testing of soils. Any laboratory operating under this banner has to submit results that fulfil 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, inasmuch as it requires samples to conform to specific sample matrices in order for the results to become accredited. For relatively unadulterated soils, this has meant the creation of soil classification categories such as ‘loamy soil’, ‘sandy soil’ or ‘clay type soil’. It is worth noting that while some geotechnical engineers may see this as a tenuous oversimplification, it is widely regarded as the best available approach and has the full endorsement of the Environment Agency and UKAS – albeit based on economical drivers. Made ground’s inherent ambiguity throws a rather obtrusive spanner in the works when faced with these basic matrices and prompts all manner of interpretive stances and questions. Some good starters for ten: can you report made ground results as accredited? Is it possible to report them as ‘unaccredited’ to make it clear to the engineer that the sample does not fall into a clear defined matrix?
It isn’t just an issue of categorisation – the whole process, from preparation to final report, is divested of any consistency as laboratories adopt their own approach by asking questions such as do we dry the sample? Do we mill the sample to uniform particle size? Do we discard anything over 2mm? Do we ignore everything that is not soil? None of these methods will provide an inaccurate result per se, but each has the potential to give a misleading picture of the site.
If, in addition to that head-scratching list of questions, you consider the fact that the commercially driven nature of redevelopment schemes has turned laboratories into high-tech, scientific conveyor belts, the complexities of the problem becomes increasingly pronounced. It is a crossroads situation reliant on good judgement, experience and, above all, a decent sample. It is impossible to overstate the critical nature of the latter point: 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 a certain extent raised the standards in the laboratory, it missed an opportunity by not offering any guidance to the geotechnical engineer on the best available techniques (BAT) 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.
As throwing legislation at the problem is unlikely to be constructive, the best achievable course of action is to engender a milieu of interdisciplinary compatibility fuelled by open lines of communication, intellectual communality and the symbiotic sharing of knowledge. Geoscientists should learn how to adequately describe their sample, how to make the sample manageable for the laboratory and to understand the laboratory machinations of sample preparation, analysis and reporting. By the same token, chemists should acquire some field experience, learn about the conditions engineers face on-site and educate themselves on the processes that inform geotechnical sampling techniques.
If the question of how to produce consistently accurate results from made ground is reducible to a single answer, it can only be to ask 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 my acceptance criteria are calculated? Has the sample data been generated in ideal conditions using ideal standards which are unlikely to represent the conditions on my site? Add a soupçon of communication, wait for MCERTS to catch up and we’re well on our way.
Andrew Buck PhD, MSc, CSci, CChem, FRSC is the Technical Director of Envirolab (www.envlab.co.uk)