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Talking point: Alistair Kean considers how much of a reality on-site remediation is now.

Is on-site remediation any more popular in the new millennium than it was in the late 1980s? The answer must be yes, but why are nearly all remediation projects still completed by traditional civil engineering techniques?

A recent survey of landowners and developers showed that 94% of remediation is still achieved using civil engineering techniques.In the survey group, off-site disposal to landfill accounted for 76% of remediation projects.

So, why are newer soil and groundwater techniques not used more regularly and is there a need to encourage their use? There are several reasons why uptake of new techniques may be slow.

First, most large sites are remediated for immediate redevelopment.The regional development agencies no longer fund projects on a piecemeal basis and like to see the entire redevelopment take place at one time.Also, once funds and permissions are in place for a large project, speed is of the essence to maximise returns on investment.There is often too little time for using slower techniques on big sites.

Space limitations mean smaller sites often do not lend themselves to onsite remediation either.This is often the case for ex-situ remediation where space is required to lay out the soil for treatment.For smaller sites, the greatest uptake of the new techniques has been in petrol station clean-ups. Here the contamination is very often volatile, highly mobile and restricted to a limited area.Insitu techniques have done well in this market, especially where the site owners are multinational oil companies with more experience of remediation.

Sites with mixed wastes such as hydrocarbons and metals or oils blended with asbestos contamination are always going to be tricky for single solution techniques, further reducing opportunities for effective on-site remediation.

The good news is that some techniques have been used on many sites and their effectiveness is now accepted. Ex-situ bioremediation, insitu pump and treat, vacuum extraction and air sparging all now have a pedigree of successful projects.The watchword here is to stick to reputable contractors with a track record and a guarantee.

Another significant change is that quantitative risk assessment of contaminated land is becoming increasingly well understood and at long last is being employed in lieu of the outdated and much maligned ICRCL (International Committee for the Reclamation of Derelict Land) trigger levels.

The use of these assessment techniques is enshrined in the guidance documents for the Environmental Protection Act and is promoted by the Environment Agency and the Scottish Environment Protection Agency.

These mathematical modelling tools allow consultants to determine what risk to humans or environmental receptors may be presented by an area of soil or groundwater contamination.This has resulted in many contaminated soils that would once have been carted off to a landfill or remediated being left to disperse or for the contaminants to remain locked up in the soil.

In the US, where risk assessment has been widely practised for some years, 'trust in the tool'has led to a situation where many small insitu remediation businesses have had to diversify or risk folding.Experience of modelling hydrocarbon plumes in North America has also shown that in many geological settings the contamination does not migrate more than a few tens of metres.

In fact, the investigation, modelling and long-term monitoring of dispersing plumes may be one of the next growth areas.The process is termed monitored natural attenuation (MNA), and far from being a do-nothing approach, it is actually a sophisticated means of limiting spend on remediation while understanding scientifically what is happening to the dispersing pollution.

In the US, MNA has grown from a fledgling project in 1985 to more than 30 projects a year by 1997.Last year the Environment Agency published its own handbook to managing MNA projects in anticipation of an increase in this area.

So will landfill continue to be the method of choice for most remediation projects? Some changes are afoot, such as the new EC Directive on the landfilling of active waste.This states that all active wastes, such as contaminated soils, will need to be pre-treated before landfilling.The exact definition of pretreated has yet to be determined, but this directive could have a significant impact on the cost of landfilling waste soils.It may also reduce the number of hazardous waste landfills permitted to take this material.

As yet there has been no shortage of holes in the ground to put waste soils in and, for many contaminated sites, a properly engineered landfill may be the best solution for environmental protection.It remains to be seen whether the recently announced tax credit scheme for land clean-up or European legislation makes much of on an impact on the fate of contaminated sites or the fortunes of the UK's remediation industry.

For the time being it seems likely that on-site remediation will remain the preserve of a relatively small number of specialist contractors.

Alistair Kean is technical services manager at Shanks/Bio-Logic Remediation.

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