Effective Remediation Strategies Focus on Contamination Risk

Posted by geologixaus on February 12th, 2020

Can a contaminated site ever be restored to pre-development conditions? Not usually as full restoration is not only very expensive, it may not even be necessary. In order to work out appropriate clean-up goals, environmental consultants will determine a site’s contamination profile and assess whether there is a potential risk of harm to humans or the environment. If there’s a risk to either, effective remediation solutions will focus on removing or mitigating the identified risks.

Adverse health effects are present when there’s a connection between a contaminant and anyone or anything that is present on the site (ie. the receptor). If there is no connection between a contaminant and a receptor then there is no risk of adverse effects. For example, if a receptor can’t inhale, ingest or touch a contaminant, there is no exposure link, and remediation isn’t required for safe use of the site.

Tier 1 Criteria

Government regulations determine the contamination limits for water, air, and soil. These are called Tier 1 criteria and based on conservative assumptions of receptor exposure. If contamination is detected at these levels, this indicates that a site has a low and acceptable risk. Consequently, if contaminant testing results fall well below Tier 1 criteria, there’s a negligible risk to humans or the environment.

When Tier 1 Criteria are Used Incorrectly

Sometimes Tier 1 criteria are employed as a default clean up levels. This can increase development costs if it leads to remediation that simply isn’t required. When a contaminant is present at a level higher than the Tier 1 criteria, an investigation should follow to determine whether a receptor is actually exposed and at risk of harm.

Why does a Tier 1 exceedance not automatically imply a risk to health or environmental receptors? As exposure to a contaminant can occur through direct contact, inhalation, or ingestion, a non-existent or blocked pathway to a receptor does not present contamination risk so remediation may not be required. If, however, there is a potential exposure pathway, a more detailed Tier 2 or Tier 3 assessment can be undertaken to consider site specific factors and model exposure pathways that don’t rely on the generic assumptions of Tier 1 criteria. Site specific assessments can deliver more targeted remediation or enable appropriate risk management options.

Tier 2 and 3 Risk Assessment

A Tier 2 or 3 investigation requires the calculation of site-specific safety criteria and clean-up goals (if relevant). It could also conclude that the contamination presents an unacceptable risk for the proposed or existing land use. The value of a Tier 2 or 3 risk assessment is that it may demonstrate that remediation is not required or justify a reduced scope of works in order to make a site suitable for its proposed use.

A Tier 2 / 3 assessment will take account of the contaminant toxicity and behaviour in relation to specific site features as well as the proposed land use. Land features, onsite buildings / infrastructure, the time that someone may be exposed, and other site specific elements may create or mitigate exposure risk. When clean-up goals are devised they can then be tailored to address any unacceptable risks either by removing or mitigating any exposure links. 

Remediation or Further Investigation?

When a potential contamination risk is identified by a Tier 1 risk assessment, a decision is needed on whether to perform a more site-specific assessment or head straight into remediation. This decision can impact development costs and needs to consider the extent of contamination in light of the land’s proposed use. A decision will often come down to the experience of the environmental consultant, however, a good decision hinges on the quality of the initial contamination assessment.

Site Investigation

A useful site investigation characterises the nature and extent of any potential contamination. The first step considers historical information about the site (also called a Phase 1 assessment). A Phase 2 site assessment will  obtain greater detail on the potential sources, types, and distribution of contaminants. This involves collecting soil, air, biota and / or water samples which are tested at a lab and analysed against Tier 1 criteria.

The Importance of Experience

Many landowners (and environmental consultants) take a ‘dig and dump’ approach to remediation following Tier 1 contaminant exceedances. As well as increasing costs, this can be harmful to the environment. Expert experience and advice is pivotal in assessing a site and providing sustainable and cost-effective remediation solutions. It is also important to meet all regulatory requirements to avoid project delays and additional expenses.

Geo-Logix is highly experienced in risk assessments and remediation projects. We are trusted many of Australia’s largest property developers and can provide the help you need. For expert advice on your project, contact Ben Pearce at bpearce@geo-logix.com.au.