Contaminated Land Risk Assessment Tiers Explained

Risk assessments can be undertaken at three distinct levels of detail.  At each tier, the five key tasks, which have been listed below, are undertaken to provide information and data in order to make a risk management decision or to decide whether it is necessary to proceed to the next level of detail.

  • Problem Identification
  • Receptor Characterisation
  • Exposure Assessment
  • Toxicity Assessment
  • Risk Characterisation

Broadly, the degree of detail and quality of the data at each level can be described as:Contaminated Land Risk Assessment Tiers

  • Tier 1: Preliminary Risk Assessment
  • Tier 2: Generic Quantitative Risk Assessment
  • Tier 3: Detailed Quantitative Risk Assessment

This tiered approach provides a systematic way of determining what level of investigation is appropriate for the site of concern, minimising unnecessary investigations, and allowing more efficient use of resources. It has been selected as the most appropriate model for risk assessment in both the UK & Ireland.

Tier 1 Risk Assessment

The Tier 1 RA is intended to be a qualitative screening process. At this tier, the collation of information either through literature review or site investigation should be preliminary. The purpose of the Phase 1 Assessment is to determine two main points:

  • Whether there is a potentially complete pathway between the contaminant of concern and potential receptors.
  • Whether contaminant concentrations exceed benchmark or guideline values for relevant receptors or media of concern.

If the pathways are assessed as incomplete, or if contaminant concentrations do not exceed benchmark criteria for ecological or human health values, the RA process may be suspended without proceeding to Tier 2 assessment. A risk management decision may be made, based on the Risk Characterisation, to:

  • Carry out no further actions.
  • Perform an iteration.
  • Undertake a Tier 2 RA.
  • Undertake remedial work.

A Tier 1 Risk Assessment assesses contaminants of concern against published assessment criteria (guideline values or benchmark criteria).

These criteria’s have been developed to help companies like ourselves undertake risk assessments and incorporate in one step many of the factors involved in receptor identification, toxicity and exposure assessment.

In developing these criteria’s, specific receptors have been identified, certain contaminant pathways have been assessed, and specific contaminants of concern are identified. These criteria’s can be quite specific (e.g. maintenance worker exposure to benzene through inhalation).

In other cases, they can be quite general – for example, water quality guidelines for the protection of aquatic organisms provide protection to sensitive aquatic species, regardless of whether these receptors may actually be present in the receiving waters.

Tier 2 Risk Assessment

The Tier 2 RA is expected to be the most detailed level of RA undertaken for most sites. Tier 2 Land Contamination Risk Assessments may involve more detailed site investigations if required but is primarily intended to involve a more intensive literature search to modify the assumptions of the benchmark criteria used in Tier 1.

The intention of this stage is to undertake a preliminary customisation of criteria for each contaminant specific to the pathways, receptors, media, and environmental conditions found at the site, and to establish modified assessment criteria.

If the contaminant concentrations do not exceed the modified criteria, the RA process may be suspended without proceeding to Tier 3, and an ecological risk management decision would be made.

Tier 3 Risk Assessment

Few sites may be large or complex enough to justify the level of detail and investigation required for a Tier 3 RA. A Tier 3 RA will involve the development of complex models supported by further intensive site investigations of the contaminants of concern, pathways, and receptors characteristics.

The intention of this tier is to further customise the modified criteria values calculated in Phase 2 to achieve a more accurate representation of the risk posed by the contaminants to specific receptors.

The risk management decision may involve remediation or further iterations and will be made based on the Tier 3 Risk Characterisation of the site.

Currently seeking Contaminated Land Assessment?

We offer Contaminated Land Risk Assessments, in accordance with Part 2A of the Environmental Protection Act, to support planning applications for all types and scales of development throughout the UK and Ireland.  If you would like to receive a quotation an assessment today fill in our online enquiry form or call us directly on 028 3010 0121.

By |2018-10-29T14:19:52+00:00October 29th, 2018|Land Contamination, Remediation|