Managing risks from land contamination

Managing contamination issues can amount to a significant cost on brownfield redevelopment projects. The Olympics is a case in point where the cost of enabling works (demolition and remediation) is expected to be around 6 percent of the total planned build cost of £6bn. Variations in the cost of the remediation can therefore have a significant impact on the overall financial viability of a development. In today’s economic downturn these costs have become all the more important. This article discusses newly released guidance on the assessment of risks from contamination and the likely impact that this has on remediation.

The requirement for remediation is driven by risk. A developer must demonstrate to the planning authority that sufficient steps will be taken to manage the risks from contamination to enable safe development of the site. Risk assessment is a necessary part of this process and is used to determine the need for remediation. Risk assessment can be a highly complex activity and the models and assumptions used by practitioners can have a strong bearing on the interpreted need and extent of remediation. Best practice guidance helps to ensure that a consistent approach is adopted and provides comfort to the developer, local authority and eventual property purchaser that the risks from contamination are not of concern.

UK based best practice guidance on the assessment of risks to groundwater and surface water from land contamination has been around since the 1990s and is now well established. Guidance on the assessment of risks to human health was introduced by DEFRA and the Environment Agency in 2002 but has been fraught with difficulties ever since. This non-statutory guidance was produced to support Part IIA of the Environmental Protection Act 1990 (introduced in 2000) which tasks local authorities to identify land that poses unacceptable risks from contamination. Part IIA applies indirectly to development sites through Planning Policy Statement PPS23 which effectively states that, as a minimum, sufficient remediation (or risk mitigation) should be undertaken to prevent the site from being determined as contaminated land under Part IIA following development.

One of the major points of contention with the non-statutory package of guidance was the Soil Guideline Values (SGVs). SGVs were intended as a screening tool to facilitate the assessment of risks to human health from soil contamination. Provided that the soil concentrations at a site fell below the relevant SGVs (and that sufficient care had been exercised to ensure the SGVs were applicable) the risks to human health from soil contamination were deemed to be acceptable. If the soil concentrations at the site were greater than the SGVs then further work would be required, such as more detailed risk assessment or remediation. 

There were several difficulties with the SGVs and the related guidance. Firstly, SGVs were only published for a limited range of contaminants and so were of limited use. Secondly, SGVs were misinterpreted by some as remediation trigger values, i.e. if soil concentrations at a site exceeded the SGV then remediation would be required. This misinterpretation undoubtedly led to unnecessary remediation at some sites where further risk assessment would have shown that the risks were in fact acceptable. Thirdly, it became apparent that for some contaminants the SGVs would be below typical background concentrations. This could result in vast swathes of the country requiring detailed risk assessment and this would likely show that remediation would be required. Benzo(a)pyrene provides a good example. This is a common contaminant associated with ash and is widespread throughout urban areas. Soil concentrations of 5 mg/kg are not uncommon in residential areas, yet risk assessments were showing that remediation would be required with greater than 1 or 2 mg/kg. These problems, and the confusion that ensued, created a barrier for brownfield remediation, lengthening the time required to gain regulatory approvals for development work and sometimes resulting in unnecessary and costly remediation.

Pressure from the Environmental Industries Commission (EIC) and other stakeholder groups forced the Government to set up a Cabinet Office task force for better regulation to resolve these issues. This culminated in DEFRA producing its “Way Forward” document in November 2006. This proposed a series of improvements to the non-statutory guidance for assessing risks to human health. Many of the proposed improvements were aimed at reducing conservatism in human health risk assessment and were designed to ensure that risks were managed in a sustainable and proportionate manner. In other words, improved guidance would be given to avoid further unnecessary remediation of sites where risks were not of concern. 

A key aspect of the Way Forward was the distinction between the upper bound of an acceptable risk and the lower bound of an unacceptable risk. Uncertainty in risk assessment, especially with regards to the toxicity of contaminants, means that there is a grey area between these two bounds. The required condition for a site to be determined as “contaminated land” under the Part IIA regime is that there are unacceptable risks.  However, SGVs represented the upper bound of acceptable risk and so could not be used to determine a site as contaminated land or to demonstrate that remediation was warranted.

Finally, after one and half years of deliberation, the promised improved package of guidance is beginning to appear. The Environment Agency has published two key pieces of guidance. The first, the SR2 document, describes the protocol for deriving health criterion values – the toxicological criteria that represent acceptable or minimal risk. The second, the SR3 document, describes the exposure modelling methodology (the CLEA model) that is used in conjunction with the health criterion values to derive generic or site specific soil assessment criteria. This is supported by the freely available CLEA model software and DEFRA’s legal definition of contaminated land that clarifies the role of the SGVs and the health criterion values.  Earlier this year, CIEH and CL:AIRE published a guidance document on the statistical procedures for assessing risks. Together, this package of guidance offers a clear and robust methodology for practitioners to determine whether the risks on a site are acceptable. 

What remains unclear is what level of risk should be regarded as unacceptable and when remediation is warranted. As before, exceedence of an SGV or site specific assessment criteria does not necessarily mean that the risks will be unacceptable and that remediation is required. DEFRA’s legal definition offers no further guidance on what should be regarded as an unacceptable risk (i.e. a “significant possibility of significant harm” – SPOSH). DEFRA state that the decision of what should 
be regarded as SPOSH lies firmly with the local authority and involves socio-economic factors as well as the science of risk assessment.

PPS23 implies that a more precautious approach to risks should be adopted for development sites than existing sites being considered under the Part IIA regime. This makes sense because remediation on development sites is normally a less costly and disruptive activity than remediation of an existing site where people require re-housing and where working in and around existing properties presents additional constraints. However, it is still unclear whether site specific assessment criteria derived using the health criterion values should be used as remediation criteria for development sites. This will likely be the default position adopted by many local authorities but may not always be the case. For example, it would not make economic sense to remediate a site to below background concentration if this does not result in a significant reduction in risk.

EIC will continue to press DEFRA and work with industry and regulators to clarify these issues and develop the necessary tools and guidance to ensure that risks are managed in a sustainable and proportionate manner.