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Dig and dump has had its day

Sustainable solutions have significant economic and environmental benefits, says Mike Summersgill.

Most practitioners of ground engineering and soil science would like to think of themselves as working to benefit the environment and providing for future generations in tandem, if not always in harmony, with nature.

But research by CIRIA shows that UK construction accounts for 5 tonnes of quarried material per person per year, implying that industry is not really doing its bit for sustainability.

UK engineers still prefer to dig and dump (76% of all projects) and work with highway specifications that demand the use of virgin aggregate, rather than seriously considering recycled spoil.

But promoting the use of recovered material also means promoting the concept of planned maintenance for a reduced design life. Given the general public's difficulty in understanding the concept of risk (in the cases of BSE transmission or repeated flooding, for instance), this is not likely to be a particularly fruitful approach.

Or perhaps we should make it purely an economic argument, sustained by temporary tax exemptions.

But I believe we are making things too complicated.

Rather than presenting a technical argument, we should be using persuasion.

Consultants with an eye on their professional indemnity cover prefer to use tried and tested methods rather than to innovate. But what if there is a simple economic reason to back up the more unquantifiable 'savings' of future sustainability?

In industry, the argument is slowly being won in the field of waste minimisation.

Kent County Council recently published the results of its second research programme in this area. Among the cost savings in water use, chemicals and the landfilling of 'seconds' in industry, there is a summary of the Alfred McAlpine/Amec contract 330 on phase one of the Channel Tunnel Rail Link (Ground Engineering, June 2000).

About £450,000 was saved by sorting site-won soil for reuse in structural support, after mixing it with imported fill. The conditions of contract on this project undoubtedly assisted in such beneficial sustainability.

CLAIRE (Contaminated Land: Applications in Real Environments) reports a study into the clean-up at Basford gasworks in 1997 and 1998 (Ground Engineering, July 1998), where the client decided to spend money on trials and measurements of a 'new' technology, soil washing.

Eliminating 14,500 lorry movements saved 390,000 litres of diesel and air emissions were cut. Interestingly, soil washing used 30% less energy than digging and dumping, because of the relative energy consumptions of electric plant and diesel transport. Material recovery was therefore seen to be energy efficient and environmentally friendly.

If this generation does not act, the next one certainly will. I wonder what they will think of our half-hearted attempts at sustaining the planet's ecosystem. When my 14-yearold daughter asked me to explain where our nation's waste ended up. I pulled out my overhead slides from lecturing to Surrey MSc students, which were purloined for her to give her own lecture at school. A geography project followed swiftly; it was a subject I never took at O-level.

The same youthful enthusiasm and 'innocence' has been visible on the faces of visitors to VHE's recent soil washing project at Woolwich Arsenal in south-east London. A quarter of a million tonnes of soil was washed and 85% reused on site, which meant less clean aggregate had to be imported and lorry movements were reduced.

Even the contaminated fine material found a use as daily cover (replacing imported sand) at the landfill because of its consistency and workability when dried.

Why had such a simple, chiefly geotechnical, 'green' sorting operation not been done before? Put it down to economics and the lack of a brave client to be one of the first to try the process. In this case the driving forces were reduced lorry movements for the local planners, a completely 'clean' site for the developers and political kudos for English Partnerships.

As is often the case, some of our European partners are ahead of the game on these techniques. They have already set up processing centres to 'recirculate' construction spoil, using physical and biological methods. They legislate to ensure that soil and water resources are reused as a first choice, by restricting landfill and funding research.

The recent insitu remediation techniques conference in Utrecht was a case in point. The Dutch regard their soil as a resource to be treasured (and respected), which probably reflects their eternal battles with the sediments in the Low Countries. But what was even more evident was their love of the 'little creatures' in the soil and groundwater; they even ended the conference with a song to them!

Europe seems to be ahead of the UK in the consideration of using these creatures to clean up mankind's spills.

With a little help from oxygen and other introduced materials, the bugs convert our chemical spills into carbon dioxide and water. Total bioremediation, totally sustainable.

But wait a minute - what was that about climate change and gaseous emissions; will we not also need to control these bugs and their CO 2emissions? Better get them a bioremediation mobile plant licence first.

Sustainability will have to wait four months while the paperwork catches up.

Mike Summersgill, a soils and water engineer, is general manager of VHE Technology, and chairs the Service Providers Group of NICOLE, the European contaminated land network for industrial sites.

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