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Reactive treatment zone

Stephan Jefferis opened the meeting at the ICE with an explanation of this remediation method. He defined a reactive treatment zone as a control surface or zone through which a contaminant or contaminated fluid (liquid or gas) can move; while doing so it is treated to improve its environmental acceptability. The zone is a method of cleaning a contaminant pathway and may not act to remove a source except in the long term. A cut-off wall may be used to contain the source contamination, directing its flow through the reactive treatment zone. The treatment zone acts as a permeable barrier, containing chemical components and allowing groundwater to flow through.

Jefferis outlined the basic chemical principles of the reactive treatment zone when treating chlorinated solvents. The zone contained zero valent iron, ie iron metal which produces a reducing environment once the iron had been allowed to rust. The reaction potential of the treatment zone was researched in the laboratory using a column test which demonstrated that a first order reduction by zero valent iron was taking place (Figure 1). The iron filings used in the reactor took off the chlorine to produce non-chlorinated hydrocarbons which were less toxic than chlorinated solvents. Column tests undertaken on groundwater in the laboratory showed that a 100% reduction of trichloroethene could be achieved, although a small intermediate concentration of 1,1 dichloroethene was produced during the degradation of trichloro- ethene (Figure 2). The rate at which this reaction can be achieved depends on the surface area of the iron used.

This remedial method's first application in the UK was for Northern Tele- com in Northern Ire- land, on a site contaminated with chlorinated solvents. The preliminary phase of the project was the installation of monitoring wells to determine the size and exact location of the contaminated ground- water plume, and the direction it was moving. The results were used to evaluate remedial options. Because of the site's geology, abstraction methods had high associated costs, an active treatment zone was considered technically feasible and a more cost effective solution.

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