Cement-Based Stabilization of Lead Contaminated Soil
During a routine hydrocarbon excavation in Glacier National Park, British Columbia, a crew from the Quantum Environmental Group uncovered an unusual layer of yellow soil. Testing showed that the soil was contaminated with lead, and the yellow colouring came from road paint that had been deposited there over many years. A construction deadline was fast approaching and Quantum wanted a quick and reliable solution for this unexpected problem. They chose cement-based solidification/stabilization.
Quantum treated approximately 250 tonnes of hazardous (leachable for lead) contaminated soil with 8% type GU Portland cement.
The lead contamination was treated in a quick, cost-effective manner and construction schedules were not impeded. Retesting the affected soil revealed that the lead was now non-leachable and therefore stabilized. Quantum’s project was completed on time and on budget.
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.
|Owner||Public Works and Government Services Canada|
|Engineer||Golder Associates Ltd.|
|Contractor||Quantum Environmental Group|