Contaminated Land Inspection Strategy 2019-2024
2.0 Contaminant linkages and risk assessment
2.1 Contaminant Linkage
For any land to be identified as contaminated land at least one contaminant linkage needs to be established.
A contaminant linkage consists of three main elements:
- A "contaminant" is a substance which is in, on or under the land and which has the potential to cause significant harm to a relevant receptor, or to cause significant pollution of controlled waters
- A "pathway" is a route by which a receptor is or might be affected by a contaminant
- A "receptor" is something that could be adversely affected by a contaminant, for example a person, an organism, an ecosystem, property, or controlled waters
- The term "contaminant linkage" means the relationship between a contaminant, a pathway and a receptor. All three elements of a contaminant linkage must exist in relation to particular land before the land can be considered potentially to be contaminated land, including evidence of the actual presence of contaminants.
The term "significant contaminant linkage" means a contaminant linkage which gives rise to a level of risk sufficient to justify a piece of land being determined as contaminated land under Part 2A of the Environmental Protection Act 1990.
The term "significant contaminant" means the contaminant which forms part of a significant contaminant linkage.
Determining what constitutes a significant contaminant linkage can be an extremely complex process. Stockton Borough Council will make its decision based on the best available evidence at the time of the investigation and on an individual site basis.
2.2 "Normal" Levels of Contaminants
The Statutory Guidance states that the Part 2A regime should not apply to land with levels of contaminants in soil that are common place and widespread throughout England and for which in the majority of cases there is no reason to consider that there is an unacceptable risk.
Normal levels of contaminants should not be considered to cause land to qualify as contaminated land, unless there is a particular reason to consider otherwise. Normal levels of contaminants in soil may be the result of the natural presence of contaminants or the presence of contaminants caused by low level diffuse pollution, and common human activities other than past industrial uses.
In October 2012 DEFRA published a report and Technical Guidance Sheets on Normal Background Levels of Contaminants in English Soils. This work was undertaken by the British Geological Survey (BGS) on behalf of Defra and was commissioned to support the revised Statutory Guidance.
Normal levels of contaminants are considered to be those levels which are not significantly different to those likely to be typical or widespread within the authority's area or other areas of England, e.g. resulting from soil formations or geology and have not been shown to pose an unacceptable risk to health or the environment, or, resulting from human activity such as the historic use of unleaded petrol or the spreading of domestic ash in gardens at levels that might reasonably be considered typical.
2.3 Risk
The Statutory Guidance states that "risk" means the combination of:
- the likelihood that harm, or pollution of water, will occur as a result of contaminants in, on or under the land; and
- the scale and seriousness of such harm or pollution if it did occur
Risk assessments should be based on information which is:
- scientifically based
- authoritative
- relevant to the assessment of risks arising from the presence of contaminants in soil; and
- appropriate to inform regulatory decisions in accordance with Part 2A and the revised Statutory Guidance
2.4 The Process of Risk Assessment
Identification of the contaminant linkage and whether it is significant is ascertained by following a staged process of risk assessment. This is to gain an understanding of the risks presented by the land and any associated uncertainties. The risks are then communicated in what is known as a site conceptual model which can either be presented in writing or diagrammatic format.
The staged process commences with a strategic preliminary inspection which is informed by the collection of desk-based information and a site walkover, possibly with limited soil and / or water sampling. Where this strategic preliminary risk assessment suggests that further understanding of the risks is required, a more detailed site inspection is then carried out.
Detailed site inspection commences with a generic quantitative risk assessment whereby detailed information on the ground conditions is collected to further develop the site conceptual model through gaining a more thorough understanding of the risks and uncertainties involved.
Depending on the findings of the generic quantitative risk assessment it may become necessary to carry out various further stages of more detailed risk assessment to support a decision as to whether or not a site meets the definition of contaminated land under Part 2A.
2.5 Generic Assessment Criteria and other Technical Tools
Stockton Borough Council's Environmental Protection Team will use generic assessment criteria for assessing risks to human health, controlled waters and ecological systems. Generic assessment criteria and other technical tools are used as screening tools to help assessors decide when land can be excluded from the need for further detailed inspection and assessment, or when further work may be warranted.
The criteria are derived using generic assumptions about the characteristics and behaviour of contaminants, pathways and receptors. These assumptions can be used to simplify the assessment of human health risks arising from long-term and on-site exposure to chemical contamination in soil, in a defined range of conditions.
For human health, the findings of detailed inspections of soil will be compared against generic and site-specific assessment criteria, generated using the most up to date version of CLEA UK (Contaminated Land Exposure Assessment) in order to interpret and risk assess the data and make an informed decision under Part 2A. In terms of ecological assessment, the most up to date guidance on the use of soil screening values in ecological risk assessment will be used, such as soil screening values proposed by the Environment Agency (2020) Derivation and use of soil screening values for assessing ecological risks.
Contaminants in ground water and surface water, will be assessed for their risk to human health, by comparing to the UK Drinking Water Standards (DWS) or World Health Organisation (WHO).
Generic assessment criteria for assessing the risks to controlled waters and ecological systems include the River Basin Standards or the Environment Agencies hydrogeological risk assessment guidance tools to protect the aquatic environment (LCRM 2020).
Other criteria may also be used Stockton Borough Council must however, understand how they were derived and how they can be used appropriately to assess risks in accordance with Part 2A and the revised Statutory Guidance.
2.6 Risk Categories
The Statutory Guidance (Defra 2012) introduced 4 risk assessment categories for sites investigated under Part 2A of the Environmental Protection Act 1990. Stockton Borough Council will use the categories detailed in Paragraphs 4.19 to 4.29 of The Statutory Guidance to characterise its sites inspected under this legislation.
Table 1. Summary of the 4 Risk Assessment Categories
Categories | Human Health | Controlled Waters |
|---|---|---|
1 | There is an unacceptably high probability supported by robust evidence of the significant possibility of significant harm occurring if no action is taken to stop it. Significant harm may have already been caused and could occur again if no action is taken to stop it. | There is a strong and compelling case that a significant possibility of significant pollution of controlled waters exists. This would include cases where there is robust science-based evidence for considering that it is likely that high impact pollution would occur if nothing were done to stop it |
2 | There is a strong case for considering that the risks from the land are of sufficient concern, that the land poses a significant possibility of significant harm, however, there is little or no direct evidence that similar land, situations or levels of exposure have caused harm before, but available evidence suggests that there is a strong case for taking action under Part 2A on a precautionary basis. | The strength of evidence to put the land into Category 1 does not exist. There is however, sufficient concern that the land should be considered to pose a significant possibility of significant pollution of controlled waters on a precautionary basis. This may include land where there is a relatively low likelihood that the most serious types of significant pollution might occur. |
3 | There is not a strong case that land is capable of being determined as contaminated land on the grounds of significant possibility of significant harm and therefore the positive legal test cannot be met and it is not clear that net benefit is achievable. Although intervention under Part 2A is not in the opinion of Stockton Borough Council warranted, risks are not low and owners or occupiers of the land may take action to reduce risks outside of the Part 2A regime if they choose. | The risks are such that the tests in Categories 1 and 2 are not met and therefore regulatory intervention under Part 2A is not warranted. This includes land where it is very unlikely that serious pollution would occur; or where there is a low likelihood that less serious types of significant pollution might occur. |
4 | There is no risk, or the level of risk posed is low because for example, no relevant contaminant linkages have been established, there are only normal levels of contaminants in soil, there are no exceedances of generic assessment criteria or estimated levels of exposure to contaminants in soil are likely to form only a small proportion of what a receptor might be exposed to anyway through other sources of environmental exposure. | There is no risk, or the level of risk posed is low because for example, no contaminant linkage has been established, the possibility only relates to types of pollution that should not be considered to be significant, or the water pollution is similar to that which might be caused by background contamination. |
2.7 Stockton Borough Council's Approach to Categorising Sites
Following strategic preliminary inspections which will involve undertaking desk study research, site walkovers and on occasion ground and water sampling, Stockton Borough Council may be able to place some sites within Category 4 where no relevant contaminant linkage exists. Further risk assessment may be necessary for other sites to place them into Categories 1-3.
The Statutory Guidance states that where all factors are taken into account, if the local authority, therefore Stockton Borough Council, cannot decide whether or not a significant possibility of significant harm exists, it should conclude that the legal test has not been met and the land shall be placed in Category 3.
2.8 The Investigation Procedure
Stockton Borough Council will investigate its sites under Part 2A of the Environmental Protection Act 1990 in accordance with the procedure outlined in Figure 2.
2.9 Written Statement
The revised Statutory Guidance has introduced Written Statements for that land which is likely to be inspected by local authorities and then considered not to be contaminated under Part 2A.
In implementing Part 2A of the Environmental Protection Act 1990, Stockton Borough Council is likely to inspect land that it then considers is not contaminated land. For example, this will be the case where the Council has ceased its inspection and assessment of land on grounds that there is little or no evidence to suggest that it is contaminated land. In such cases, the Council will issue a Written Statement to that effect (rather than coming to no formal conclusion) to minimise unwarranted blight. The Written Statement will make clear that on the basis of the assessment, the Council has concluded that the land does not meet the definition of contaminated land under Part 2A.
Stockton Borough Council will therefore inform the owners of the land of its conclusion and give them a copy of the Written Statement and keep a record of all Written Statements itself. The Council will consider making Written Statements available to other interested parties proactively and will always provide Written Statements on request.
2.10 Risk Summaries
The revised Statutory Guidance has introduced Risk Summaries for any land where, on the basis of its assessment, the local authority considers it is likely that the land in question may be determined as contaminated land.
Stockton Borough Council will produce a Risk Summary for any land within the borough which it considers likely to be determined as contaminated land under Part 2A of the Environmental Protection Act 1990.
The Risk Summaries will explain Stockton Borough Council's understanding of the risks and any other relevant factors. They will be prepared in advance of any formal determinations of land as contaminated land under Part 2A. The risk summaries shall be targeted towards the landowners and members of the public who may be affected by the decision.
Risk summaries are not required for:
- land which will not be determined as contaminated land (that land in Categories 3 and 4).
- land which has been prioritised for detailed inspection but which has not yet been subject to risk assessment.
- land determined as contaminated land before the revised Statutory Guidance (April 2012) came into force.
- land where there are only normal levels of contaminants in soil.
2.11 Determining Land as Contaminated Land under Part 2A of the Environmental Protection Act 1990
Following completion of the detailed site investigation and risk assessment, the site conceptual model will be updated to show whether one or more significant contaminant linkages exist or otherwise. Where one or more significant contaminant linkages exist between any sources of contamination and relevant receptors under Part 2A, the Environmental Protection Team will follow the procedure for determining that land as contaminated land, as set out in Section 78A (2) of the Environmental Protection Act 1990 and the revised Statutory Guidance and the land will be placed in either Category 1 or Category 2.
Stockton Borough Council may decide to defer the determination of contaminated land after informing interested parties because the landowner or other interested person may choose to undertake the remediation on a voluntary basis, and to an appropriate standard and timescale, agreed with the Environmental Protection Team.
The determination may also be postponed should one or more significant contaminant linkages only exist if the circumstances of the land were to change in the future within the bounds of the current use of the land.
Stockton Borough Council may reconsider a determination if new information comes to light, which is significant enough to alter the original decision. In such cases, Stockton Borough Council will decide whether to retain, vary or revoke the determination.
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