Contamination Remediation – Analyse, Attenuate or Intervene?
The current Governments policy is to maximise benefits arising from operation of free enterprise and control any adverse effects by regulation of industries. Hence the burden of remediating contaminated land falls largely on land owners and developers.
The key legislative driver is Part 2a of the Environmental Protection Act 1990, introduced in 2000. This requires Local Authorities to determine land within their constituency that may pose a contamination related risk to either site users or the environment and subsequently serve notices for investigation/action as appropriate to the site owner. It is however, becoming increasingly common that these issues are requiring resolution as part of the planning process for any new development.
Due to the fragile nature of development programming, dealing with unexpected delays that were not budgeted for during project design can be frustrating and sometimes expensive. The Environment Agency, as main regulator, is keen to promote remediation of sites even when they are within an industrial environment with heavy and extensive contamination elsewhere.
We are pleased to announce the formation of our specialist ground remediation team. Headed up by Giles Sommerwill and Matthew Eynon, we have taken on board the specialist expertise of Professor Paul Bardos. Paul literally ‘wrote the book’ on remediation in the UK and he is the co-author of EPP Contaminated Land Management Ready Reference, one of the best handbooks to help make sense of the environmental and statutory challenges confronting any one dealing with brown field sites.
Although the detail may be complicated, the process of managing land contamination falls into three clearly defined elements.
- Establish whether there are unacceptable risks.
- Appraise remediation options and identify the most appropriate strategy.
- Implement remediation plan and validate its effectiveness.
We do not promote any single technique but will select the best method for the specific problems encountered at your site. Our practices conform with the most recent EA guidance as published in CLR11 (The Model Procedures) and we adopt a logically phased approach to ensure that your specific site needs are satisfied at minimum cost and risks. At appropriate stages in the scheme we liaise with the regulators to reduce response timescales following submission.
Guidelines for Action
Initially, the risk assessment is completed using conservative assumptions and generic models approved by the EA. Even if the results indicate problems, it may be possible to reduce assessed risks by analysing the situation in greater detail using modelling calculations tailored to the specific site conditions. A Detailed Quantitative Risk Assessment (DQRA) is performed whereby Site Specific Target Levels (SSTL’s) are derived for relevant contaminants. Common models that are used to assist in a DQRA are:
- CLEA, SNIFFER – Long term health risks only (UK Models);
- RD20, CONSIM – Controlled water risks only (UK Models);
- RBCA – Both health and controlled water risks (US Model).
Your site may benefit from further analysis if it has the following characteristics:
- Moderate to high contamination in solid form;
- Low to moderate leachibility;
- Potential for dilution, dispersion and attenuation before contaminants reach receptor.
If unacceptable risks are confirmed, we can sometimes take advantage of the self cleansing properties of nature. Natural Attenuation can be suitable for many sites, provided there is sufficient time and the contamination is stable – rather than caused by ongoing pollution. Where relatively nominal testing proves that Natural Attenuation is adequately protective, low-intensity long term monitoring is then introduced to confirm that the system is behaving equal to or better than that predicted, resulting in the remedial strategy Monitored Natural Attenuation (MNA). MNA can be an economical solution for sites where dilution, dispersion and attenuation are proven and there is sufficient time in the development program to implement the strategy.
Intervening to remediate may involve removal of contaminated soil (becoming less common), low impact remediation of organic contamination or more aggressive techniques suitable for a range of industrial contaminants. When intervention is required, the selection of an appropriate remedial technique should be driven by the Conceptual Model and the need to modify the existing pollutant linkages in order to reduce or eliminate the risk to identified receptors. Some general examples are provided below:
- Biological Processes: Requires the use of living organisms to break down contaminants;
- Chemical Processes: Destroy, fix or concentrate toxic compounds by using one or more types of chemical reaction;
- Physical Processes: Separate contaminants from the soil matrix by exploiting physical differences between the soil and contaminant (e.g. volatility) or between contaminated and uncontaminated soil particles (e.g. density);
- Solidification and Stabilisation Processes: Immobilise contaminants through physical and chemical processes;
- Thermal Processes: Exploit physical and chemical processes occurring at elevated temperatures.