Cement-Based Stabilization of Lead Contaminated Soil
Situated in the heart of the Victoria, Dockside Green is being built on fifteen acres of former industrial land adjacent to the Upper Harbour and downtown, between the Johnson and Bay Street bridges. With a planned total of 1.3 million square feet of mixed residential, office, retail and commercial space, Dockside Green represents the largest development of city land in Victoria’s history. The developers are Vancity and Windmill Developments, who are thoroughly committed to the triple bottom line (TBL) approach to development. In other words, they embrace their responsibility to balance profits with environmental and social dividends. Dockside is committed to achieving the highest level of certification under the LEED® green building rating system. This will be the first entire development ever to target this goal.
Before construction began, a pocket of lead contamination that exceeded the BCHazardous Waste Leachate Standard was discovered on the site. This contamination had to be treated in a cost-effective and efficient manner if the project was to continue.
The Quantum Environmental Group chose cement-based
solidification/stabilization to address the contamination. They treated 10 tonnes of lead contaminated soil using Portland cement which was incorporated into the soil on site by using an excavator bucket. No specialized equipment was required.
After the Portland cement was thoroughly mixed into the earth at the site, an environmental consultant sampled soil for leachable metals. Analytical soil results showed that the cement-based solidification/stabilization had rendered the soil non-hazardous so this area of Dockside Green could continue to be redeveloped. Cement-based solidification/stabilization has helped this project achieve its sustainability and triple bottom line goals by addressing the lead contamination in a cost-effective and complete manner.
What is Cement-Based S/S?
Solidification/stabilization (S/S) is a widely used treatment for the management and disposal of a broad range of contaminated materials and wastes – particularly those contaminated with substances classified as hazardous in the United States. The treatment involves mixing a binding reagent into the contaminated substance. This process protects human health and the environment by immobilizing contaminants within the treated material, preventing them from migrating to plants, animals and humans.
S/S treatment has been used to treat radioactive wastes since the 1950s and hazardous wastes since the 1970s. S/S continues as a cornerstone treatment technology for the management of radioactive and hazardous wastes, as well as site remediation and Brownfield redevelopment. The U.S. Environmental Protection Agency (EPA) considers S/S an established treatment technology. EPA has selected S/S treatment for 24% of its Superfund source-control remedial actions.
How S/S Works
S/S treatment involves mixing a binding reagent into the contaminated substance. Although the terms solidification and stabilization sound similar, they describe different effects that the binding reagents create to immobilize hazardous constituents. Solidification describes changes in the physical properties of a contaminated substance. The desired changes usually include an increase in compressive strength, a decrease in permeability, and encapsulation of hazardous constituents. Stabilization refers to chemical changes of the hazardous constituents in the treated substance. The desired changes include converting the constituents into a form that is less soluble, mobile, or toxic.
Effects of Binding Reagents on Waste – Inorganic & Organic
Commonly used binding reagents include Portland cement, cement kiln dust (CKD), and a number of proprietary reagents. Portland cement is a generic material principally used in concrete for construction. This material is also a versatile S/S binding reagent with the ability to both solidify and stabilize a wide variety of wastes. Portland cement-based mix designs have been the most popular S/S treatments and have been applied to a greater variety of wastes than any other S/S binding reagent.
Cement is frequently selected for the reagent’s ability to:
- chemically bind free liquids
- reduce the permeability of the waste form
- encapsulate waste particles, surrounding them with an impermeable coating
- chemically fix hazardous constituents by reducing their solubility
- help reduce the toxicity of some contaminants
This is accomplished by bringing about physical changes to the waste form and, often, chemical changes to the hazardous constituents themselves. Cement-based S/S has been used to treat wastes that have either or both inorganic and organic hazardous constituents.
Due to the great variation of waste constituents and media, a mix of reagents should be designed specifically for each waste that is to be treated. Mix designs often include by-products or additives in addition to Portland cement. Fly ash is often used to capitalize on the pozzolanic effect of this material when mixed with hydrating Portland cement. CKD and slag have minor cementitious properties and are sometimes used for economy. Lime can be used to adjust pH or to drive off water utilizing the high heat of hydration produced by these S/S binders.
|Developer||Dockside Green Limited Partnership|
|Contractor||Quantum Environmental Group|