Science or art?

A crucial step in restoring contaminated land and water happens before clean-up begins. Technical Director Simon Cole makes the case for a strategic approach to risk assessment in reducing the impact and duration of a remediation project.

Understanding the type, amount and possible effects of contamination requires a scientific approach. However, for a risk assessment to be truly effective, judgement and skill are needed to interpret risk model data — this is where the ‘art’ of risk assessment comes in, and helps ensure clean-up activities are appropriate for each site.

Traditional site risk assessment feeds data into a standard software model, for example using industry standard toxicity figures from respected bodies such as the World Health Organisation (WHO), as well as data from desk studies and site investigations. In turn, the result of the assessment governs the type and amount of remediation that is needed, but there can be limitations.

Each site is different, and the fit between reality and standardised computer models is rarely exact. Like any computer system, the quality of output depends on the quality of input. Incorrect information about a site could lead to an inappropriate solution.

A holistic approach

What if you could reduce potential exposure of contamination to human health and the wider environment by treating just a proportion of it and leaving the rest to degrade naturally? This could also make clean-up quicker and more cost-effective.

Rather than identifying contaminants and cleaning them up to standardised concentrations, a risk-based approach to remediation evaluates the health and ecological risks of specific contaminants at each particular site, and then implements solutions to mitigate these risks. As well as potentially reducing clean-up costs, clients can benefit from shorter remediation timescales, meaning site sales or redevelopment dates could be brought forward, potentially bringing the site back into use for the community’s benefit much sooner.

Real-world data

Risk assessment needs to feed into all parts of remediation to get a clearer understanding of the contaminants at work on each site and the steps required to remove them. AECOM’s team use mathematical models that incorporate ‘real-world’ data wherever possible. If data is limited at the start of the project, our models evolve as more information comes to light.

Sustainability is another potential benefit. Less remediation means a smaller carbon footprint and lower resource use. As well as benefiting the environment, this may help clients achieve regulatory approval. Of course, the scientific and technical justifications for doing less remediation need to be rock-solid. Regulators, remediators and communities need to be absolutely sure that potential contamination hazards are minimised with risks reduced to acceptable levels, and that those paying for the clean-up aren’t just passing costs onto other stakeholders or future generations.

Experience and judgement

In this situation, getting a risk assessment right becomes incredibly important. In fact, the data it provides becomes a foundation of the whole remediation process. That’s why, unlike traditional approaches, our teams carry out risk assessments at the beginning of a project. We ensure we understand the objectives of the remediation and the type of data we need, using only the best modelling software and real-world site data.

Most important of all, we use our experience and judgement to assess the data generated from our risk assessment models dispassionately. This is critical because models — however good — rarely provide a single, ‘right’ answer. We use modelling to support decision-making, not replace it. Our risk assessments are iterative processes, with several run‑throughs to refine the results. Only then can we design a remediation solution that’s right for a site.

Realising the benefits

For those clients familiar with risk-based approaches in their corporate policies, this may be pushing at an open door. They will understand that, while this may add some extra time and cost at the start of their project, this is usually more than paid back in the longer term. However, not everyone is convinced. Commercial pressures may drive a quick clean‑up. So, for example, if a site is due to be sold for redevelopment, the attitude may be one of ‘just get it done’. Remediators have to mobilise quickly to dig or pump out contaminated material as soon as possible.

In these situations, emphasising the benefits of a risk-based approach — reducing the amount of heavy remediation they need to do, cutting the cost of the project and bringing the end date forward — is critical.

Global perspective

Regulators, too, vary in their thinking. The sophisticated risk-based regimes in the UK and US are in stark contrast to that in Germany, which sets out a prescribed list of chemicals to test for and a threshold number that must be met, regardless of the site context. Interestingly, China’s rapidly developing regulatory regime seems to be adopting a risk-based approach, with an emphasis on supporting the efficiency of remediation efforts rather than bureaucratic box ticking. AECOM is involved in collaborative initiatives and discussions at various levels as China seeks to establish an appropriate regulatory management system.

So, is risk assessment science or art? It has to be both. The best, most accurate models, populated with the most cost-effective data you can get, combined with the expert judgement and analysis gained from years delivering remediation projects in the field. Data plus judgement. Science plus art — the best of both worlds.

Off the shelf or on the ground?

Technical Director Richard Knott explains how a judicious analysis of risk assessment data helped significantly reduce the cost of cleaning up a former chemical production site.

The WHO considers mercury one of the top 10 chemicals of major public health concern — but how toxic it is to humans and the wider environment depends on factors such as the type, duration and level of exposure.

Through site investigations, we identified mercury contamination in soils in several areas of a former chemical works site in Baglan, south Wales, UK. As lead technical support on the project, AECOM was responsible for clearing the site of mercury leftover from previous clean-ups, in preparation for the construction of a new gas-fired power station.

Our initial risk assessment identified how likely it was that the mercury from the soil would seep into nearby groundwater, so tough clean-up targets were initially put in place and as the project gained momentum, we gathered more real-world data from the site.

Our first round of investigations and risk assessment combined site data with Environment Agency figures detailing the rate at which mercury dissolves into groundwater. However, our team noticed that the real-world data was showing a lot less mercury in the groundwater than our model initially predicted — something wasn’t right. We re-ran the risk assessment using the new site investigation data. The results showed a much smaller risk of groundwater contamination, enabling us to agree revised clean-up targets.

In addition, the new data showed that, instead of being spread evenly around the site, the mercury contamination tended to be concentrated in certain areas. Using this information we concluded that that removing soil only from those areas would remove 80 per cent of the mercury. The rest could stay on site because it was within the new agreed levels of contaminant. This approach won praise from the regulator in terms of sustainability, as we reduced the amount of materials that needed to be transported on the local road network (reducing the carbon footprint) as well as reduced landfill.

In all, our risk management based approach led to substantial savings for the client.