Overview: Context, Calculating Risk and Using Consultants

PETER J. YOUNG, SIMON POLLARD AND PHILLIP CROWCROFT

1 Introduction

Historical Perspectives

The presence of land contamination is an inevitable legacy of an industrial past. At least since the time of Roman lead mining, the UK has seen human activities leave naturally present contamination concentrated, or altered in its chemical form. Since the industrial revolution of the late 18th century, an increasing range of new compounds have been manufactured and added to the list of contaminants, and the affected area of land has increased dramatically. Current estimates suggest between 100 000 and 220 000 ha of land is contaminated, representing between 0.4 and 0.8% of the total UK land area. Table 1 sets out the principal types of contamination and its typical severity for major industrial land uses, based on results from more than 500 site-based studies.

Much uncertainty over the presence of contaminated land is derived from the lack of a consistent definition. Other designations of land such as vacant, derelict, industrial or damaged can be confused with evidence for contamination. Contaminated land is not the same as derelict land; nor is the term contaminated land applied in the strict scientific sense of indicating the presence of an introduced substance which is harmful. If the substance is harmful, it is a 'pollutant'.

The Department of the Environment (DoE) has described contaminated land as 'land which represents an actual or potential hazard to health or the environment as a result of current or previous use'. Contrast this with derelict land which is 'land so damaged by past activities that it is incapable of beneficial use without treatment'. Clearly the two are independent. A worked-out limestone quarry may be derelict but will not be contaminated. In contrast, many established chemical factories will be contaminated but not derelict. Contaminated land poses a potential threat to the environment, but derelict land is a threat to future development, although it may be aesthetically unattractive as well.

Against this complex background of definition, the public, and financial markets, became alerted to land contamination by a sequence of well publicized incidents in the 1980s and early 1990s (Figure 1). At this time, investigation for soil and groundwater contamination was merely costed for in the purchase of land for redevelopment, and prior investigation was frequently patchy or non-existent. Three events which were influential in focusing concern about contaminated land are summarized in Table 2.

These and other sites were described to the House of Commons Environment Committee in 1989 and their report, published in 1990, called for registers of contaminated land to be established. This greatly influenced DOE thinking on the Environmental Protection Act, which was at the final drafting stage. The DOE had previously aimed to provide guidance to developers through advisory limits for concentrations of contaminants through publications from the Interdepartmental Committee on the Redevelopment of Contaminated Land (ICRCL). The idea of registering known or potentially contaminated land was more interventionist and, if not handled extremely carefully, could blight urban areas where redevelopment and investment is most needed.

In 1990, the DOE published the Government's response to the Environment Committee. Linked to this were three actions which injected momentum into the field of contaminated land assessment:

1. A provision (section 143) was made in the Environment Protection Act 1990 for regulations requiring local authorities to compile registers of potentially contaminated land.

2. The DOE initiated a process of consultation on registers and contaminated land policy.

3. The DOE began to expand its research programme to provide broader guidance on contaminated land.

Once a proposal for registers of potentially contaminated land was incorporated in legislation, a lengthy and active debate was triggered. The Government sought to focus and inform this debate by a series of consultation papers as new policy was developed. The DOE also informed itself through international liaison where alternative approaches have been offered, many of these coming under national criticism over expense or quality of environmental protection. An interpretation of the key points emerging during this debate is offered in Table 3. In understanding the current legislative position on contaminated land it is important to have regard to this recent period of debate and uncertainty, with the emergence of a true risk-based approach founded on firm scientific and toxicological principles. Further detail on the current regulatory framework and its foundation on risk assessment is given in Section 3.

Current Consequences

The current position with contaminated land is largely attributable to the response from Government, and more widely to the concerns highlighted at the beginning of this decade. These have led to a radical and rapid change in the technical approach to evaluating and remediating contaminated land. The routine introduction of risk assessment, a phased and chemically orientated approach to site investigation, and the selection of remediation strategies from more technologies than simple cap and cover systems are all rapidly developing areas described below in Sections 3–5. Underpinning these developments have been the changes in the legislative position, the growth in research based guidance, particularly from DOE, and the availability of specialist expertise from environmental consultants (see Section 6).

From a technical viewpoint, recent developments have been extremely beneficial. The complexity of evaluating contamination has been thoroughly exposed, and the risk associated with facile and inadequate approaches prevailing in the market place has been much reduced. The prospect of new guidance values for key contaminants which take account of the availability, toxicity, pathway and impact of the contaminant will be a significant improvement over existing ICRCL guidance. However, the draft guideline values only address human health. Separate and additional assessment techniques are required for ecological, phytotoxic and physical damage potential. The link has also been made between the soil and water environments, so that contaminated land assessment and remediation should succeed in addressing all potential impacts in one overall risk-based approach. Such an integrated approach places new demands on the quality of the advice available on contaminated land. Awareness of the rapidly developing...