When it comes to remediation, it is rarely possible to restore a contaminated site to its pre-development conditions. Full restoration can be prohibitively expensive and is typically unnecessary for the safe use of a site. To determine appropriate clean-up goals, environmental consultants investigate the site for contamination and evaluate whether any potential contamination presents a risk to human or environmental health. Remediation solutions aim to mitigate identified risks.
A risk of adverse health effects can only be present if there is a link that connects a contaminant to a someone or something that may be affected by the contaminant (the receptor). That is, there needs to be a mechanism whereby the receptor could be exposed to elevated levels of contamination. Where there is no connection, there is no risk and no requirement for remediation.
A Tiered Approach
EPAs and other government entities set safe limits for contaminants in soil, water and air. These are called Tier 1 criteria and indicate site contamination that presents a low and acceptable risk. These criteria are generic and based on a number of conservative assumptions on how the receptor may be exposed. In general, if a contaminant exists at a concentration below Tier 1 criteria, the potential for a risk of adverse health effects is negligible.
Incorrect Use of Tier 1 Criteria
Tier 1 criteria are not clean up or response levels, though they are commonly and incorrectly used for this purpose. The use of Tier 1 criteria as default remediation criteria could result in unnecessary remediation and significantly increased development costs.
Exceedance of a Tier 1 criteria does not imply a risk to human or environmental health. What it does trigger is further investigation and assessment on the ways a receptor may be exposed to contamination. Exposure pathways include inhalation, ingestion or direct contact. If there are no complete exposure pathways between a receptor and a contaminant, there is no risk and the site can be considered fit for use without remediation.
If a potentially complete exposure pathway is present based on exceedance of Tier 1 criteria, environmental consultants are required to take a site-specific risk-based approach that involves a more detailed ‘Tier 2 or Tier 3’ assessment. Alternatively, appropriate risk management options can be implemented.
Tier 2 and Tier 3 Risk Assessment
Site specific Tier 2 and Tier 3 risk assessment can involve the calculation of site-specific safety criteria, site specific clean-up goals, or the determination of whether existing site contamination presents an unacceptable risk under that site’s proposed or existing land use. Tier 2 and Tier 3 risk assessment takes into account site specific factors such as the contaminant behaviour, building construction type, the duration someone may be exposed and other site features that may impact exposure risk.
The value in a Tier 2 or Tier 3 risk assessment is that it may demonstrate a site does not require contamination remediation, or may greatly reduce the degree of remediation required to make the site suitable for a proposed use.
The Fork in the Road
The fork in the road comes when there is a potential risk identified at the Tier 1 risk assessment level. Do you enter straight into remediation and management, or undertake a more site-specific risk assessment (Tier 2 and Tier 3)? This decision can depend on a number of factors including the proposed development or existing land use, and the degree or extent of contamination.
Knowing whether to enter into remediation or site-specific risk assessment (which can impact project costs) comes down to the experience and expertise of the environmental consultant. However, this decision hinges on the quality of the initial contamination investigations.
Site characterisation is essential in establishing the nature and extent of contamination. The first stage is to collate site history information to gain an understanding of the type and potential extent of contamination on a site (the Phase 1 assessment) . Based on the findings of the site history, a more detailed Phase 2 assessment will collate scientific data from air, water, soil, or biota to determine the types, sources and distribution of contaminants.
Without a meaningful dataset an environmental consultant will be unable to provide reliable advice. This could lead to unexpected finds when remediation works are carried out or inappropriate and overly expensive remediation strategies.
Tier 1 contamination exceedances are often met with a dig and dump approach which can be unnecessarily expensive and generate other environmental impacts. To ensure the most appropriate and cost-effective solutions to site contamination you should seek an experienced environmental consultant and seek a scope of works that meets EPA guidelines.
Geo-Logix has performed hundreds of risk assessments and remediation projects for some of Australia’s biggest property developers. If you would like information or advice about assessing, managing or remediating site contamination please contact Geo-Logix or email Ben Pearce at email@example.com.