There was a time when the rehabilitation of land ravaged and abandoned by industry was the preserve of green radicals. Their methods were eccentric and the technologies unproven.
Developers shunned brownfield sites in favour of less troublesome agricultural land far from decaying city centres.
On the rare occasions when brownfield land is commercially redeveloped the clients usually demand massively expensive dig and dump operations which remove all suspect material from the site.
Now, however, the Government is putting the screws on the developers. Planning permission for greenfield sites is much harder to get, especially for superstore complexes and the like. Last week the Government's Urban Task Force suggested a number of financial carrots to persuade developers to look again at the 50,000-200,000ha of derelict land that could be rehabilitated - much of it in urban areas. The long term ambition is to get all brownfield land back into use within 30 years.
But the big question, as far as investors and clients are concerned at least, is whether the technology exists to allow these sites to be developed safely and economically.
Many sites, of course, are 'contaminated' by no more than building rubble and a little boiler ash. Even when contamination is present, it is rarely spread uniformly across the site. Development could be planned to fit end use to contamination levels. An office or carpark will effectively cap a contaminated area, sealing off the nasties from the users. It is only in conventional housing developments, with small children playing in gardens, that contamination levels need to be seriously low.
Currently it costs around £100/m3 to remove contaminated land from a city centre site and dispose of it in a registered landfill. Then comes the cost of replacing the contaminated material with approved fill. The very act of excavating the contaminated material carries risk - dust can blow onto adjoining properties, adjacent watercourses could be poisoned.
It would seem obvious that methods which remediate or encapsulate suspect material insitu would be preferable - but there are problems of credibility.
A popular alternative method at the moment is to cap contaminated land with a permeable barrier of clean material. But future construction, particularly trenching work, can lead to inadvertent mixing of the clean and the dirty. There is a problem of saleability as well, with developers unconvinced that housebuyers would flock to properties where chemicals are known to lurk below the surface.
The nascent geo-environmental engineering industry is already offering a bewildering variety of biological and chemical rehabilitation options. But all the techniques tend to share some key characteristics - they are expensive and largely unproven.
However, the situation is beginning to change. Projects like Pride Park in Derby, where everything from old landfill and the residues of gasworks and heavy industry to nuclear waste was dealt with entirely within a site bounded by an unpollutable river, show what can be done (NCE 4 December 1997).
A few developers are beginning to realise that the potential demand for housing in urban areas, especially for the young, single and childless, shows signs of explosive growth. This type of high density housing is ideally suited to brownfield sites.
So the challenge for engineers is twofold. First, they must develop, promote and test new technologies for dealing with sites which may be contaminated, often by a complex cocktail of organic and inorganic pollutants.
Developers, tenants and homeowners alike must be convinced that sites can be made safe enough, cheaply enough.
Secondly, developers and clients have to be made to accept the implication of modern risk management techniques. No site will ever be totally safe for ever and no developer will ever be totally free of risk.
Engineers are capable of coming up with technical solutions that reduce long-term risk to low, even very low levels. But developers have to realise one fundamental law of the universe - total safety could only be achieved by the application of infinite resources.
Or in other words, you get what you pay for. And trying to transfer liability to the consultants (employed by competitive tender) is a medium term recipe for stagnation.
One survey by the Royal Institute of Chartered Surveyors revealed that 58% of developers would 'never' touch brownfield land.
The government wants 60% of new homes to be built on brownfield sites. Presumably the Government believes that engineers are capable of coming up with effective and economic solutions to any contaminated land problems.
Unless the developers find similar faith in the profession, or can be financially induced to take the risk, the numbers look irreconcilable.