What is Immobilisation?
Hazardous waste comes in many forms, but all with a commonality that the contaminants of concern present, have harmful effects on human health and/or the environment. In most cases, due to the high levels of toxic elements in hazardous waste, it is not usually safe to dispose of in landfills, risking soil and groundwater pollution.
There are various remediation techniques that can be utilised to treat and contain hazardous waste, one of these techniques is known as immobilisation. Immobilisation can be achieved in several ways – either natural, chemical fixation or micro- or macro-encapsulation – is the process of restricting movement of hazardous compounds in these wastes so that they do not leach from the source material and continue to harm the environment and/or human health.
What is Leachability?
Soil becomes contaminated when waste or unwanted compounds seep in and disrupt its natural state. Factors leading to this could range from industrial activity, inappropriate disposal of waste, use of pesticides or fertilizers, oil spills to even leisure activities including rifle ranges and gun clubs.
Leaching takes place when these contaminants in soil dissolve and leach out when they come in contact with water. Leachability tests measure the soluble contaminants in the soil. There are several different testing methods available, depending on the environment the material will be subjected to.
Leachability tests are critical when it comes to understanding the environmental risk of hazardous wastes, especially in the case of soils impacted by heavy metals.
Heavy Metal Contamination and Leaching
When the soil is contaminated with heavy metals (e.g. lead, zinc, cadmium) it is known as heavy metal contamination. Exposing such soil to varying pH conditions such as rain, waterlogged environments, and other human-influenced conditions, encourage physiochemical changes to occur across the soil horizon. This causes the soil to expel contaminants into a liquified medium (leachate), where it can travel across a project site.
Effective containment or immobilisation can halt this process, thus reducing the risk posed by the heavy metal impacted soils and the environment around it.
The Immobilisation Process
Immobilisation is an active process where contaminated soils are mixed with suitable binders or reagents which influence pH, create new compounds and/or change the structural properties of the soil. Heavy metal solubility may be reduced through adsorption, ion exchange, and/or precipitation of pollutants.
The mobility of heavy metals in soils is very dependant on the soil characteristics – the organic matter content, grain size and distribution, and pH of the soil. Heavy metals are more soluble and have more mobility in acidic environments.
Immobilisation helps reduce the capacity of soil contaminants to leach, and this method is a particularly popular application for heavy metal contamination across a broad spectrum of waste streams.
The types of immobilisation methods that we use at Enviropacific are:
1. Chemical immobilisation: This is the most common method where chemicals are used to stabilise the contaminants.
2. Encapsulation with physical boundaries: In this method, a physical barrier is placed between the contaminated waste and the surrounding landfill environment.
The aim of immobilisation method validation trials is to determine the optimum ratio and the type of additive/reagents necessary to blend with the heavy metal impacted waste stream that complies with end goal disposal criteria. These criteria are set by the Environment Protection Authority (EPA) and the practical and financial outcomes are outlined to the relevant stakeholders involved (the client).
The process is largely influenced by the occupational health and safety measures necessary in handling both the heavy metal impacted waste product destined for treatment (immobilisation) and the risk associated with the practical application of required reagents.
Evolving industry practice and the associated technology and science enabling the changing processes by which immobilisation works are undertaken is a key focus area for Enviropacific. While fostering a keen interest in innovation we also recognise well established immobilisation techniques that can be applied to certain waste streams where general and specific immobilisation approvals can be sought from the EPA.
In any project, we are legally and ethically obliged to remain compliant with regulations and potential harm to the environment. Identification of soil contamination that exceeds the relevant EPA thresholds is influential in the disposal process, which significantly affects the bottom-line cost of any given project.
Enviropacific recently delivered two successful yet distinctly different waste stream heavy metal immobilisation projects. Click here to read how our team treated the lead-impacted soil in the former shooting area at Truganina.
Another successful immobilisation project involved the testing and subsequent treatment and disposal of a prescribed industrial waste stream, click here to read more.
Our project teams are uniquely positioned to promote and discuss the advantages of exploring the benefits of heavy metal immobilization treatment works supported by a robust data driven assessment and risk management process. These considerations are important as they drive the outcomes that assist us in managing our client’s contamination risks.
Benefits of Working with Enviropacific
We work in a way that our immobilisation treatment methodologies allow for transparency, robustness, and repeatability.
Our in-house testing, analysis, and standing operating procedures ensure that any treatment trial works we undertake are monitored and clearly communicated to our clients. Our service package includes – staging site mobilisation events, correct dosing of reagents, and validation sampling
We can competitively price and manage hazardous waste treatment and mitigate risk for our clients through a thorough investigation of sites, careful project planning, resourcing, and clear communication.