Remediation: It’s a question of technique

For all those with a vested interest in the swift and successful remediation of contaminated land, the news that the Environment Agency is investigating available and emerging techniques for the characterisation of land contamination will come as a welcome revelation. The whole subject of contaminated land has been synonymous in recent times with problems of various types, and the issue bady needs, and would certainly benefit from, some constructive attention.

The project itself, which is being carried out by the Agency’s National Groundwater and Contaminated Land Centre in Olton, Birmingham, is focusing on field techniques. These are tools and techniques (chemical, biological or physical) which may be used in the field, either in-situ or in field labs, to provide real-time analysis and testing of environmental parameters and contaminated media.

These tools may be used as part of a site characterisation strategy or for monitoring both the performance of a remediation treatment and the longer term status of the site.

The aims of the project are:

• to identify a range of current and future technologies and techniques which can characterise areas of land contamination and be used as monitoring tools during remediation and long term monitoring programmes;

• to detail how relevant these techniques are to different contaminants and media and what role such tools may have in a site characterisation or remediation monitoring programme;

• to develop an understanding of how the data from the tools and techniques may be interpreted within a site characterisation or remediation programme.

Field techniques

Examples of the field techniques the Groundwater and Contaminated Land Centre will consider include direct-push tools such as Rapid Optical Screen Tool (ROST). This is a laser-induced fluorescence sensor deployed by Cone Penetration Testing (CPT) equipment that characterises stratigraphy and petroleum hydrocarbons in soils. This process is accomplished continuously, in real-time and without collecting samples.

ROST uses a state-of-the-art laser to produce light that is pulsed down a fibre optic cable to a sapphire window on the side of the CPT probe. The pulsed light causes petroleum hydrocarbons in the soil to emit fluorescence. The emitted fluorescence travels through a second cable to a detection system within the CPT work area. Relative concentration and a special product fingerprint are presented continuously in real-time. Since fluorescence intensity is proportional to petroleum hydrocarbon concentration, ROST can effectively delineate the extent of affected soils.

Another technique that will be considered is chemical sensors (eg: multi-variate sensor arrays). Sensor array systems are analytical instruments that can characterize an odour without reference to its chemical composition. A variety of sensor technologies have been used in sensor array systems, the most common of which are metal oxide sensors, conducting polymers, surface acoustic wave devices, and quartz crystal microbalances.

Biosensors will also be considered by the Centre. Biosensors are devices that use living organisms, such as enzymes, tissues, microbes and antibodies, to produce reactions, which are then analyzed to detect the presence of a chemical or chemical reaction. An example of this is an immunosensor, which acts on the principle that the immune response of certain biological species (usually bacteria) to contaminants will produce antibodies, which in turn can be measured.

Other field techniques that the Groundwater and Contaminated Land Centre will consider include bioassays / toxicity tests, chemical and immunoassay colourimetric tests, and other field laboratory analysis.

According to the Environment Agency, the use of field techniques within a structured risk management framework has a number of potential benefits, including:

• They can be used as a preliminary screening tool to provide a focus for more targeted sampling and analysis. For instance, circumstances permitting, equipment such as portable flame-ionisation detectors or photo-ionisation detectors can be used to identify hot-spots of solvent contamination by rapidly testing for the presence of volatile organic compounds in soil vapour. Off-site laboratory analysis of soil, porewater, free-product and / or groundwater could then be used to characterise the extent of the contamination.

• Time and money can be saved through the use of in-situ and on-site analytical tools to assess land contamination and remediation treatments. Using these technologies can enable larger sample sizes to be assessed for a given budget. This can reduce data uncertainty arising from the heterogeniety of soil and groundwater and contaminant distribution within it.

Existing barriers

It is also recognised that a number of barriers exist to the effective and widespread use of field techniques. These include a lack of understanding of how to use and interpret the data generated by new field technologies and techniques within site characterisation strategies and monitoring plans during remediation. Also, there is a paucity of published data detailing the application (successful or not) of field techniques within a range of environmental settings and for different contaminant types.

The Environment Agency aims to address these issues by understanding the application and limitations of many of these established field techniques and the more innovative tools.

The project is being run under contract by the Envirocentre in Glasgow and is due to be finalised and published in July 2003. The initial part of the project involves the gathering of information on available techniques from technology developers, vendors and users.