Stabilization

What Is Stabilization?
Stabilization refers to a group of cleanup methods that prevent or slow the release of harmful chemicals from wastes such as contaminated soil, sediment, and sludge.¹

These methods usually do not destroy the contaminants. Instead, they keep them from “leaching” into the surrounding environment at unsafe levels. The process of leaching occurs when water from rain or other sources dissolves contaminants and carries them downward into groundwater or over land into lakes and streams.

What is the Purpose of Stabilization?
It causes a chemical reaction that makes contaminants less likely to leach into the environment.

Stabilization is often used together with solidification (see SOLIDIFICATION) to prevent people and wildlife from being exposed to contaminants, particularly metals and radioactive contaminants.

How Does Stabilization Work?
Similar to solidification, stabilization also involves mixing wastes with binding agents. However, unlike solidification which encases the contaminants, binding agents used in stabilization cause a chemical reaction with contaminants to make them less likely to be released into the environment. For example, when soil contaminated with some metals is mixed with water and lime (a white powder produced from limestone) the reaction changes the metals into a form that does not dissolve in water.¹

Binding agents can be mixed into the waste while still in the ground (often referred to as “in situ”). This usually involves drilling holes using large mixers or augers that inject the additives underground and mix them with the waste.

The number of holes needed depends on the size of the augers and the contaminated area. Dozens of holes may have to be drilled.

When the waste is shallow enough, the contaminated soil or waste is excavated and additives are mixed with it above ground (often referred to as “ex-situ”). The waste is either mixed using backhoes and front end loaders or placed in machines called “pug mills” which can grind and mix materials at the same time.

How Long Does the Stabilization Process Take?
Stabilization may take weeks or months to complete with the actual time being dependent on several factors:

• Size and depth of the contaminated area.
• Soil’s density or rocky matrix making it more difficult to mix with the binding agent.
• Mixing occurring above ground which requires the extra step of excavation.
• Extreme cold or rainfall delaying treatment.

Is Stabilization Safe?
The additives used in stabilization are materials often used safely in construction and other activities. When properly handled, these materials do not pose a threat to workers or the community.¹

To ensure safety, water or foam can be sprayed on the ground to make sure that dust and contaminants are not released to the air during mixing. If necessary, the waste can be mixed inside tanks, or the mixing area can be covered to minimize dust and vapors.

The final stabilized product is tested to ensure that contaminants do not leach. The strength and durability of the stabilized materials are also tested.

Does Stabilization Have a Good Track Record?
Stabilization provides a relatively quick and lower-cost way to prevent exposure to contaminants, particularly metals and radioactive contaminants. Solidification and stabilization have been selected or are being used in cleanups at over 250 Superfund sites across the country.

References

1. A Citizen’s Guide to Solidification and Stabilization, EPA, www.epa.gov, retrieved October 16, 2014