Stabilisation solidification technology provides new approach to dealing with contaminated land

An innovative solution to tackling contaminated land and hazardous waste is on line to being introduced into the UK later this year. Changing UK contaminated land policy, dwindling landfill capacity and new EU legislation on landfill means that the process of using cement could become one of the most effective means of remediating contaminated land, according to a leading innovator in the field. Geo-environmental specialist Mike Southall, of Castle Cement, says that the UK is now on the verge of change in the way it dealt with contaminated sites.

Stabilisation solidification technology – or “s/s techniques” in the experts’ parlance – could be set to become one of the most ideal means of remediating contaminated land in answer to UK policy, environmental needs and the new EU landfill directive, in the view of Castle Cement’s Mike Southall. He believes that the UK is on the verge of change in the way it deals with contaminated sites.

“The UK needs an alternative technique which is effective and appropriate to UK conditions often typified by physically difficult ground containing a cocktail of different contaminants arising from more than one contaminative source,” he adds.

The use of cementitious-based stabilisation is flexible, cost-effective, and a realistic alternative to landfill.

“As well as dealing with contamination, the technique also has the added value of being able to improve the physical engineering properties of the ground which offers a very cost effective way of dealing with brownfield sites/marginal land in a single process,” Mr Southall continues.

“The opportunity for this technology in the UK is very significant. There is increasing acknowledgement of its benefits and growing willingness to consider it as a realistic solution. Most significant are the implications of the new EU landfill regulations which will introduce massive change to the practice of landfill in the UK. Cementitious remediation will inevitably become more widely used as an alternative to landfill and as a means of pre-treating wastes prior to disposal,” he adds.

New technique researched

Dr Colin Hills, Senior Research Fellow at the University of Greenwich, who has headed a two year investigation into stabilisation solidification technology, says that the new method is a “more obvious choice” to deal with certain types of contamination.

He is currently finalising a draft report on the new technique which is due to go before the Environment Agency in the Summer.

Four monitoring cells were constructed to receive different s/s soil mixes at the Astra pyrotechnics site at the University of Greenwich in Kent as part of field trials.

“This technology method has a place in the remedial technologies that are available to treat contaminated land and hazardous waste. When used properly it is very effective. The technology is relatively simple, is proven and also cost effective. The method is well established outside Britain and definitely has a place in the UK,” says Dr Hills.

As well as treating hazardous waste on site there is a potential to re-use the treated product in a wide variety of engineering uses, which makes it cost effective, he adds.

Wide range of applications

Mike Southall, a remediation specialist, explains that the solidification stabilisation procedure can effectively manage a wide range of contaminants including organic and inorganic matter.

It involves mixing cement and other hydraulic binders into contaminated waste to physically solidify and chemically stabilise it. The cement mixture modifies the physical properties of contaminants whilst triggering a chemical reaction, rendering them chemically stable and immobile.

During solidification, cement mixed into soil reacts with water forming a physical bond which immobilises contaminants. Solidification lowers the permeability of treated material, inhibiting water movement and preventing leaching.

During stabilisation, hazardous constituents are chemically changed. Cement, when added to contaminated soil, forms less soluble and more stable hydration products with the contaminants.

“Each contaminated site is different and therefore the remedial solution is bespoke. The solution is designed to take into account site conditions and characteristics of the contamination, using a combination of laboratory tests, field trials and on going monitoring works as the remediation works are implemented,” says Mr Southall., a chartered engineer specialising in remediating contaminated land.

Benefits of using s/s techniques

In recent a Paper on The role of cement in land remediation, Mike Southall spells out the benefits of cementitious remediation, which he says are “considerable when compared with more conventional and widely used remediation techniques, particularly ‘dig and dump’.”

He lists the following points:

  • the technique is based on well understood science and works well with other techniques
  • the technique manages a wide range of different contaminants
  • the technique has a proven track record, albeit outside the UK, and should be considered as a technique that extends the existing ‘comfort zone’, rather than removing it, by introducing unquantified uncertainties as to its efficacy and success.
  • the technique provides solutions which have a defined cost profile and programme implications
  • the technique works particularly well when applied ex-situ and, as such, lends itself particularly well to remediation requirements in the UK
  • the technique can provide an improvement to the physical characteristics of the ground in addition to managing the contamination issues

Mr Southall also states in his Paper: “Notwithstanding the technical issues, the greatest benefit from cementitious remediation is its contribution to sustainable construction.

“S/s materials can avoid disposal of contaminated materials to landfill, a finite and diminishing resource, and provides collateral benefits (eg reduced environmental impact from traffic movements, less noise and less dust).”

In other cases, he points out, this technique can reduce the volume of material to be landfilled with the material being placed being rendered more inert and presenting less of a long term environmental risk.

Future applications

Castle Cement sees the new technology as in line with Government policy of minimising the threat of contaminated land by encouraging appropriate action to deal with unacceptable risks to public health and the environment. The Government is actively encouraging reclamation and recycling of brownfield land.

In Europe the move is towards stricter controls on landfill sites aimed at reducing the amount of waste being disposed.

The new EU landfill directive, requires that waste should be treated before landfilling.“It is anticipated that following implementation of the Landfill Directive, the number of hazardous waste landfills will be limited and disposal costs for hazardous wastes will rise due to a number of factors, including increased costs for transporting wastes greater distances,” said Jill Leather, of the Environment Agency.

In America, cement based solidification stabilisation was first used in the 1950’s to treat radioactive waste from weapons development and manufacture and nuclear power generators. Now an established treatment technology, it is used at a quarter of contaminated sites in the US and is considered to be the best available technology for more than 50 different types of hazardous wastes.

Alternative technique

“With its track record in other countries, there is no reason why the UK should not adopt it as a mainstream remedial technique which offers a realistic alternative to landfill,” states Mike Southall.

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