Contamination made clearer than CLEA

Atkins Environment has developed a set of benchmarks aimed at streamlining the assessment process of potentially contaminated brownfield sites

Current government policy often makes brownfield sites the only viable option for much needed new commercial and industrial developments. However, the already hard-hit industrial sector in the UK can be faced with the additional obstacle of assessing suspected land contamination before remediation can occur and new developments can be built. The issues involved in such remediation are often difficult - even the decision on whether any land contamination will actually result in a risk to human health is complex.

Yet decisions of this sort are required at many stages of a development project, and getting it right is crucial. When land is transferred between an industrial problem-holder and a potential investor, both sides may well require their own contamination assessment. The buyer will need to estimate the likely cost of any remediation which will influence their judgement of market value. The seller will wish to establish a realistic price for their site. Potential funders may want reassurance that the site is worth the money lent. Later regulators will need to be sure that the site is suitable for use post-redevelopment and that it does not present an unacceptable risk to either human health or the environment. What all parties want the most is a simple set of numbers for concentrations of contaminants in soil to use as a benchmark for assessing land contamination.

It all becomes CLEA

In the past the primary benchmarks used were the ICRCL trigger values, sometimes supplemented by guideline values from other countries such as the Netherlands. More detailed 'site-specific' risk assessment was then sometimes used by consultants for complex sites, or to establish that the contamination would not present a risk to specified receptors, given the actual site conditions. The ICRCL values were withdrawn in December 2002 by Defra, because they were not consistent with a transparent framework, as required under Part IIA of Environmental Protection Act 1990. Although Part IIA applies to current rather than future use, the Office of the Deputy Prime Minister has made it clear that this approach also applies to redevelopment. In March 2002 Defra and the Environment Agency (EA) launched the Contaminated Land Exposure Assessment (CLEA) model, together with a suite of Soil Guideline Values (SGVs) intended to replace ICRCL for human health receptors.

Costly risk assessment

Problems arise because so far only seven SGVs have been produced, leaving significant gaps, particularly for organic contaminants such as benzene, toluene, ethylbenzene, xylenes [BTEX] and polycyclic aromatic hydrocarbons [PAHs], which arise from a range of industrial activities. This situation is a source of frustration to contaminated land professionals, developers and regulators alike because where there are no available values for pollutants found on a site, the option recommended by the EA CLEA helpline is to undertake an expensive Detailed Quantitative Risk Assessment (DQRA). The alternative of using other countries' numbers, for instance the Dutch Intervention Values, is not encouraged by the EA because different policy decisions on matters such as whether contamination from air, food and drinking water is accounted for, and how genotoxic carcinogens are treated may produce radically different numbers. This could create the situation where future SGVs may be much lower and recently developed land could then have to be re-assessed under Part IIA.

The requirement to undertake a DQRA also has implications for the timeframe of any land transfer or development. This is because DQRAs not only take time for consultants to produce but reviewing and agreeing them is an additional workload for hard-pushed regulators. The situation is exacerbated because the version of the CLEA model that will be used by the Environment Agency and Defra to produce future SGVs is not available to consultants. The currently available version is not adaptable for site conditions. Moreover it contains an approach to estimating how much contaminated air people are exposed to in buildings which the EA intends to update because of its conservatism. Undertaking a DQRA usually involves consultants in the adaptation of foreign models for UK conditions and policy-decisions, and regulators in checking that this has been done correctly. If the routine performance of this costly step could be removed, industrial clients would save not only considerable sums of money, but also valuable time.

So with no viable alternative to the limited number of SGVs, a large number of sites have to undergo costly DQRAs because there are no benchmark values, despite often having only small traces of the pollutants.

Soil screening values

Atkins Environment has invested significantly in producing a set of benchmarking values, in a manner consistent with UK policy, in order to streamline the process of contaminated land assessment for their many industrial clients. The values are known internally as Soil Screening Values or SSVs "Our client base includes at least one major problem-holder and it simply did not represent good value for money to undertake DQRAs for a large portfolio of sites, when essentially only a factual report was required," said Naomi Earl, principal human health risk assessor for Atkins Environment. "Of course where sites are more complex and don't fit the conceptual model used in deriving our SSVs, our risk assessment team would undertake a DQRA." The SSVs have been developed for commercial-industrial and residential land uses, with conceptual models consistent with those within the CLEA SGVs.

Cautious approach

The SSVs represent many months of concerted effort by the Atkins human health risk assessment team. A well-established model incorporating the EA's favoured approach to modelling vapours in buildings was adapted to UK conditions, policy context and approach to toxicology. Where CLEA uses a range of values to represent some parameters, single inputs values had to be chosen. A deliberate decision was made to err on the side of caution when describing how humans behave. This was so that sites which 'passed' using the SSVs would likely be accepted by the regulator. On the other hand if sites do fail they are not necessarily unacceptably contaminated and would be examined in more detail.

The process was laborious - calculations were checked internally, members of the risk assessment team agreed the parameters before hand and the calculations were run on two PCs to remove the chance of input error. Full documentation was assembled so that when reports go to regulators, all steps of the process are transparent. The SSVs were launched internally across Atkins' UK offices in November and December 2003, and the risk assessment team are now involved in reviewing reports to ensure they are used appropriately.

The SSVs are currently available for BTEX, a range of PAHs, phenol and cyanide and though not intended for widescale publication, Atkins may seek to make them available selectively to local authority regulators and key brownfield stakeholders. The SSVs are already extensively used on behalf of industrial clients, for local authority clients as a preliminary step when considering land under Part IIA, and for internal benchmarking when deciding whether the cost of further DQRA is likely to provide returns to clients. Further work is already underway to add values for widely-used chlorinated solvents left over from common land uses like scrap yards and workshops.

Industry figures may not need to know the ins and outs of risk assessment modelling but the bottom line is that if they can reduce budgets and timescales for reinvesting in 'safe' brownfield sites by removing a layer of the preparatory work, the SSVs could provide a very welcome boost.



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