Sustainability focus needed in land clean-up

The UK has a depth of remediation expertise, but a DEFRA-commissioned study has concluded that a greater focus on sustainability is required.

The UK land remediation industry needs to raise its game on sustainability considerations, a report from industry body, Contaminated Land: Applications in Real Environments (CLAIRE) has found.

Commissioned by the environment department (DEFRA), the report aimed to summarise current understanding and use of remediation techniques, identify the factors influencing their selection and assess their economic, environmental and social costs and benefits. A survey of technology vendors and environmental consultants supplemented desk-based research.

The report profiles 21 treatments, focused on technologies classified into: in situ techniques (those taking place without excavation of soil or groundwater); ex situ (applied to excavated soils, abstracted groundwater or gaseous emissions); and civil engineering-based techniques (disposal to landfill).

Each technique is described alongside an assessment of its effectiveness in tackling contaminants, and when circumstances may or may not make them suitable.

While the profiles present little that is new, they do offer a timely overview of current remediation techniques in the UK. 

The study also assessed their environmental, social and economic impacts and benefits. Together, these describe each technique’s sustainability. The framework developed by the Sustainable Remediation Forum UK (surf) provided a basis for assessment (ENDS Report 423, p 23).

Surf’s 18 sustainability indicators were evaluated to see which are appropriate at the technology-specific level. Ten were found suitable as sustainability yardsticks to aid technique selection. Twelve in situ techniques and seven ex situ techniques were evaluated against them and the results presented in tabulated form.  

The report finds the industry deficient in how it measures the sustainability of remediation techniques. Indeed, practitioners had a mixed interpretation of ‘sustainability’. Some had measurement systems in place or in development, while others did not. CLAIRE concludes: “From the responses received, it is clear that each organisation is at a different stage of development in terms of measuring sustainability.”

The report also sought to assess the costs of remediation techniques. But even after drawing on sources from the past 10 years, a literature search identified a lack of generic information. This was attributed to costs being highly site-specific and subject to varied remediation goals and geological, hydrogeological and chemical factors.

The survey sought data on costs, for small and large sites, handling less than and more than 5,000m3 of material, respectively.

But it found “remediation costs are not something which can generically be provided with any degree of certainty or reliability” and that they “should be costed on a site-by-site basis”.

Moreover, no broad conclusions could be drawn on the relative costs of in situ and ex situ techniques, or which have more variable costs. But it found average costs declined as larger volumes of contaminated material were handled.

This was particularly apparent for permeable reactive barriers (ENDS Report 425, pp 23-24), ex situ thermal desorption and soil washing; technologies that have high mobilisation and initialisation costs that make them more cost- effective with larger soil volumes.

Choice and frequency

Data on the current and historic use of each remediation technique was also collated. Respondents were asked to report on the choice and frequency of the techniques they used during 2008 and 2009.

Most technology vendors had experience in most in situ techniques. Consultants had also offered a wide range of remediation methods.

To compare the historic use of different techniques with the 2008-09 data, comparisons with information with that gathered by CLAIRE in 2005 were undertaken.

The main trend identified was the growing use of in situ methods and a decline in ex situ techniques. The downturn in large-scale land development projects, which typically favour ex situ methods, was a likely contributory factor.

The rising use of in situ techniques is expected to continue. Two in five respondents expressed a strong view this would occur. Particular mention was made of thermal treatment, chemical oxidation and enhanced bioremediation processes.

The survey also identified drivers for technique selection. From a list of 13, technology vendors and environmental consultants cited the four most important drivers: operational constraints, effectiveness in cutting risk, cost of implementation and applicability to contaminants and media.

Finally, the status of emerging and potential remediation techniques was considered, in order to identify areas for research and development and those that may attract investment.

However, the report concludes that while a number of research projects are ongoing, they are yet to disseminate their results. This makes it difficult to assess the benefits that they may bring to the UK remediation industry.

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