An auger was used at a former manufactured gas plant site to mix cement into 103,000 cubic yards of contaminated soil to a depth of 22 feet.

A large number of sites throughout the country are contaminated with hazardous substances, a legacy of careless or inadequate handling of industrial chemicals and wastes. With a lack of regulation, awareness of their toxicity, and adequate disposal services, chemicals of all sorts were released into the soil and water. Many sites have been since been abandoned. The so-called “Superfund” program was established under CERCLA, Comprehensive, Environmental Response, Compensation and Liability Act to address clean up of contaminated sites. It collected a tax from petroleum and chemical manufacturers as well as potentially responsible parties and set a threshold of complete and permanent clean up. Tremendous progress has been made in the last couple of decades in both developing remediation technologies and working through the liability issues to start the clean up process and remove the contamination. One negative consequence of such a thorough and costly program was a fear among developers of having anything to do with former industrial lands. This, among other factors, helped drive development out into farmland and open space, leaving dilapidated properties, which no one wanted to touch, in urban areas. The term ‘brownfields’ refers to these properties that either are or even might be contaminated in some way. New programs were developed to facilitate cooperation between the EPA, and state and local authorities, to help assess these properties (over a third were found to have either no contamination or levels below concern), and support their remediation and redevelopment. This effort has sparked many urban revitalization and redevelopment projects that have brought properties back into productive use, improving not only the environment, but the local economy as well.

 

S/S treatment improved the soil structure for the proposed redevelopment, as well as treating the contamination.

Portland cement, often combined with other materials such as cement kiln dust, lime, lime kiln dust, limestone, fly ash are used as binding reagents to change the physical and chemical properties of a wide range of contaminants. The process is called Solidification/Stabilization, or S/S and it has been successfully applied to both in situ and ex situ (on and off site) remediation projects. In the context of brownfield development, in situ treatment has the added benefit of often improving the soil’s structural properties for redevelopment. Solidification refers to the process of changing the physical properties of the material, while stabilization refers to a chemical transformation. Hazardous constituents are generally bound or encapsulated by the S/S process. This keeps them from moving around (e.g. heavy metals leaching into ground water) and being taken up by plants, animals and humans. The challenge with in situ S/S is mixing the binding reagents with the soil to fully lock up the contaminants.