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Contaminated land risk assessment is the overarching process used to ensure a site or development will not present unacceptable risk to those occupying, using or otherwise affected by it. With the degree of risk being closely related to the proposed use, rather than the mere existence of contamination alone, this is known as 'the suitable for use approach'.
There is no shortage of case study material relating to sites where risk assessment was not applied properly or was not yet the norm, with the subsequent discovery that the land is not "suitable for use", for example as residential gardens. This unfortunate situation is usually an artefact of our industrial past, and can ultimately lead to determination as contaminated land under Part 2A of the Environmental Protection Act (1990).
Based on the specifics of the site or development proposals, we work with clients to develop a targeted risk assessment approach based on a realistic conceptual site model, in line with government statutory guidance and CLR11.
We undertake both qualitative and quantitative risk assessments as necessary to meet the demands of regulators such as local authority planning (as required by the NPPF) and building control, the Environment Agency, or the requirements of stakeholders such as warranty providers or lenders.
A risk based approach is often employed in identifying and/or prioritising sites for development, disposal or acquisition. Local authorities also utilise risk assessment to in their role as regulators under 'Part 2A', which allows them to issue a remediation notice and bring further enforcement action where unacceptable risk is identified.
Any credible and compliant contaminated land assessment will always be founded on information gained from a desk study and phase 1 preliminary risk assessment, especially if regulator acceptance is required.
Equally importantly, it is often possible to exit the risk-assessment process at this stage without advancing to costly intrusive phase 2 investigation works on site; this typically occurs where the desk study review of records on historical land-use, such as historical mapping, aerial photography, trade directories and anecdotal knowledge indicate significant contamination is unlikely and the overall risk is acceptably low. Similarly, qualitative assessment of the above factors together with available environmental data such as local geology, controlled waters, abstractions, protected sites and proposed site use may lead to the conclusion that a significant pollutant or contaminant linkage is unlikely to affect the development or wider environment.
Whether you require risk assessment for a single plot development, an oil refinery, or anything in between, Adeptus has the capabilities and experience to devise the optimum solution for your project.
Where the preliminary (phase 1) risk assessment has identified a risk of significant contamination at a site, phase 2 investigation is undertaken to obtain chemical data on subsurface conditions at the site. Equally, the information obtained during phase 1 may be sufficient for the parties to decide against further investigation.
Phase 2 involves the collection of physical samples, which are then subjected to laboratory analysis for relevant contaminants identified during the desktop study.
Soil samples may be retrieved from hand-dug trial pits or with the use of machinery such as a mechanical excavator, and in some cases from boreholes formed with a drilling rig or window sampling rig. In some cases, groundwater samples may be retrieved from trial pits but more commonly, groundwater sampling (if required) is undertaken via dedicated monitoring wells installed to greater depths. These intrusive site works are generally referred to as site investigation.
Data on soil, groundwater, or surface water conditions obtained from the above intrusive sampling and lab analysis are then compared with applicable thresholds to establish whether or not they exceed these standards. This quantitative assessment provides an indication of the degree of risk to receptors such as sensitive site users or the wider environment, and may be applied in one or more of the scenarios below.
Human health risk assessments are undertaken by comparing the concentrations of contaminants in media to which humans might be exposed, such as soils in proposed gardens, to standards developed by authorities such as the Environment Agency and Defra.
Initial 'risk screening' may be carried out using broadly applicable published criteria designed to provide an efficient means for identifying low-risk sites on which no further assessment is required - this step is known as generic quantitative risk assessment (GQRA).
Where applicable generic assessment criteria are exceeded, more detailed site specific risk assessment may be warranted, in order to determine whether the generic criteria are in fact overprotective based on the numerous factors that may differ from the generic exposure scenario. The use of site specific assessment criteria is known as detailed quantitative risk assessment (DQRA).
Human health risk assessments for contaminated land in the UK commonly utilise the contaminated land exposure assessment (CLEA) software tool developed by the Environment Agency.
Controlled waters include all surface waters and groundwaters. Risks to controlled waters are assessed by comparison of sample data with published criteria such as drinking water standards, or environmental quality standards (EQSs).
In some cases, the subject water body may be sampled directly to give an indication of current chemical status, such as when groundwater is encountered in a borehole and a monitoring well may be installed, or when dealing with a surface water body. However, in many cases it is more appropriate to undertake surface water and groundwater risk assessments on a predictive basis due logistical, time and cost issues.
Modelling provides a quantitative indication of the potential for contaminants identified of anticipated in one environmental compartment or location to migrate to and significantly impact another. For instance, the leachable fraction of contaminants in soil may have the potential to affect underlying groundwater quality, or there may be a risk of impacted shallow groundwaters migrating into a sensitive aquifer. Only by identifying significant risks can effective mitigation or control measures be devised.
Although based on a similar process as human health risk assessment, ecological risk assessments are likely to consider effects on more than one species. Ecological risk assessments are usually undertaken where there is potential for soil or water (ground or surface waters) contamination to affect ecosystems defined as receptors for the purposes of Part 2A of the EPA 1990.
Relevant ecological receptors include (but are not limited to) all designated: Sites of Special Scientific Interest (SSSI); Special Protections Areas (SPA); Special Areas of Conservation (SAC); National Nature Reserves; and RAMSAR sites. The potential for impacts to such receptors is often increased significantly by construction and/or remediation works as contaminants are often mobilised and new pathways created for contaminants to reach receptors. Ecological systems can clearly be impacted by hazardous substances, but may also be affected by increased levels of non-hazardous pollutants, and in some cases, even nutrients.
Ground gases are produced naturally by the decomposition of organic matter. In the presence of a source of buried organic matter, significant volumes of gas may accumulate such that a pressure gradient is produced, driving migration via the path of least resistance (known as a preferential pathway).
Although in certain circumstances a hazard can emanate from natural ground gas sources such as peat bogs, man made sources tend to present the greatest risk in terms of gas concentration and pressure. These include abandoned mine workings and informal, older and often unlined landfills, where large quantities of decomposing organic matter may produce large quantities of gas. Other substances such as hydrocarbon vapours and the radioactive gas radon can also require consideration.
However, the risk from many of the potential sources characteristic of previously developed land is often significantly lower than perceived, and mitigated by a range of factors that should be accounted for in the ground gas risk assessment.
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