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Your focus on contaminated sites in July's issue accurately reflected the considerable pressure coming from central government for more 'brownfield' sites to be developed.

There are, however, a number of potentially expensive and environmentally unsound hurdles to be overcome by some of the more conventional method of remediation described. This is particularly so in the removal of the material from site (a particularly anti-social activity in heavily built up areas where many of the contaminated sites are) and disposal of this material into landfill sites. The government is actively discouraging this latter activity and, as an industry, we need to be ever aware that landfill sites are a diminishing resource.

The Envirotreat process, developed by our company and environmental consultant Envirotreat, in co-operation with Birmingham University, addresses both of these issues, and offers another choice for developers looking to build on 'brownfield' sites in urban locations.

The technique is an in situ method of treating contaminated land, which uses modified clays to absorb and bond contaminants. Essentially, it is a chemical fixation process, which has the benefit of working on soils contaminated with both organic and inorganic pollutants.

The modified clay technology is the basis of two types of treatment application: non-pillared clays (for mass treatment applications) and pillared clays which allow the passage of contaminated water and bring soluble pollutants into contact with appropriate reagents. The clays are generally combined with cementitious material to solidify the soil thereby physically encapsulating pollutants such as heavy metals.

This opens the way for two types of treatment: a stabilisation/solidification process and active containment whereby establishing a barrier wall and treating the soil within it or funnelling the pollutants out of the containment area through a reactive 'gate'.

Stabilisation and solidification processes have been applied to the treatment of contaminated soils and hazardous wastes for several years. The United States Environmental Protection Agency (USEPA) regards stabilisation/solidification as an established treatment technology. The USEPA Superfund Programme Records of Decision show that 29% of remediation projects carried out during the period 1982-1994 incorporated stabilisation/solidification as part of the selected treatment process, making stabilisation/solidification the most frequently selected technology.

The application of stabilisation/solidification technologies is a developing market in the UK and Eire with significant potential both in the remediation of contaminated land and in the treatment of hazardous wastes, particularly as a pre-treatment process prior in landfill.

Active containment systems have been used in the UK before. May Gurney Envirotreat used one in conjunction with the stabilisation/solidification on a site in West Drayton, London last year (GE December 1997). These systems essentially consist of a permeable barrier of reactive clays that allow groundwater to flow through but remove contamination.

But if either method is used, no material needs to be removed from site and the contaminated land can be made suitable for building, even for housing, highly cost effective, environmentally sensitively and with the minimum of disturbance.

Mike Teale, Special projects manager, May Gurney (Technical Services), Norwich NR14 8SZ

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