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THE VALUE OF SOIL

GEOENVIRONMENTAL ENGINEERING

The role of Soil Guideline Values and DEFRA proposals for a Way Forward

The Cabinet Office set up an SGV task force in 2004 to examine the production, use and practicality of SGVs, in response to stakeholders' concerns.

One of these concerns related to the nature and extent of contamination and the potential impact that SGVs could have on the need for, and scope of, remediation. This unease was relevant to sites determined as contaminated land under Part IIA of the Environmental Protection Act and also to brownfi eld sites being redeveloped under the planning regime.

Last summer the Association of Geotechnical and Geoenvironmental Specialists (AGS) was asked to prepare a short paper illustrating these particular matters for presentation to the task force. The paper aimed to provide a background to several other presentations describing DEFRA's proposals for a Way Forward.

The AGS paper drew on contributions from several members, but also benefi ed from input from the British Geological Survey, the National House Building Council (NHBC), several local authority contaminated land offi cers and from Judith Lowe, acting as a specialist consultant to DEFRA.

DEFRA published the Way Forward document in November 2006.

It is now generally recognised that the UK's Industrial Revolution has resulted in a legacy of contamination that is not just confined to the country's industrial heartlands.

Also, the relationship between particular contaminative land uses and the types of contamination present in the ground is highly complex and highly variable.

Published guidance relating these two aspects - such as the old Department of the Environment Industry Profi les, R&D 66 and CLR8 - provide advice. But inevitably, these documents generalise both the nature of those industrial activities and the chemical determinands associated with them.

In addition to this man made pollution, there are several sources of contamination naturally present in soils and rocks or associated with natural geochemical processes.

These include elevated concentrations of arsenic present in several soil and rock types. Radon is also associated with several strata and elevated concentrations of methane can be found derived from biodegradation processes in alluvium and peat.

The publication of SGVs for a number of determinands raised concerns from many quarters that the concentrations supposedly set to indicate significant contamination were close to, at, or even below, concentrations prevalent in the general environment (concentrations that could be considered representative of background conditions). These concerns were supported by data published by the British Geological Survey (BGS) which indicated that a relatively high proportion of soils in both rural and urban settings exceed the published SGVs.

Illustration of this was provided by one urban local authority that had conducted a survey of topsoils in public open space and gardens across the borough. Concentrations of both lead and arsenic were commonly recorded at elevated concentrations with, for example, more than 60% of the samples exceeding the SGV for arsenic.

For many sites, this problem of concentrations exceeding guideline values is most commonly encountered with benzo(a)pyrene (B(a)P).

This substance is a known carcinogen and is commonly associated with products of incomplete combustion, such as ash and clinker.

It is not surprising that in the gardens of many older residential properties (as well as industrial settings), concentrations of B(a)P are present from the practice of digging ash from coal fi res into garden soils as a soil improver. The disposal of ash from coal fi red boilers has produced the same effect on brownfield development sites.

The scale of the fi nancial cost of dealing with land contaminated by such substances with concentrations marginally above SGVs is diffi cult to estimate. But it can be illustrated by considering the possible impact on housing development sites over the coming decade. A simple capping solution, if required on all such sites, could give rise to costs of around £135M to £450M per year.

Using the Communities and Local Government Department's forecasts for the construction of new homes on brownfi eld sites, this would mean several billion pounds in the period between 2001 and 2016. Of course, this is a considerable simplification.

Not all such brownfi eld sites require remediation due solely to marginally exceeding SGVs for these particular contaminants.

But there is no doubt that a substantial proportion of development sites do fall into this category. There is also the possibility that some such sites will be formally determined as contaminated land, followed by a formal requirement for remediation with associated costs.

A continuation of current practice will, therefore, be expensive for the UK economy and there is little confi dence within the contaminated land community, that such costs will realise proportionate or appropriate benefi ts.

DEFRA's Way Forward paper presents proposals for addressing these and other related issues. This paper is out for consultation until 25 February. It is most important that practitioners in the contaminated land area review and comment upon these proposals either via their industry bodies - such as the AGS or EIC - or individually by emailing DEFRA at landqualityenquiries @defra. gsi. gov. uk

Hugh Mallett leads the geoenvironmental activities within the Buro Happold ground engineering team.

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