Remediation of contaminated sites with cement, also called solidification/stabilization with cement (S/S with cement) is a common method for the safe environmental remediation of

contaminated Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...

land with

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

. The cement solidifies the contaminated

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

and prevents

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

s from moving, such as

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...

causing leaching of pollutants into the

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

or being carried into streams by rain or

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many par ...

. Developed in the 1950s, the technology is widely used today to treat industrial hazardous waste and contaminated material at

brownfield In urban planning, brownfield land is any previously developed land that is not currently in use. It may be potentially contaminated, but this is not required for the area to be considered brownfield. The term is also used to describe land prev ...

sites i.e. abandoned or underutilized properties that are not being redeveloped because of fears that they may be contaminated with hazardous waste. S/S provides an economically viable means of treating contaminated sites. This technology treats and contains contaminated soil on site thereby reducing the need for landfills.

Process

The Solidification/Stabilization method utilizes chemically reactive formulations that form stable solids that are non-hazardous or less-hazardous than the original materials. Solidification refers to the physical changes in the contaminated material when a certain binding agent is added. These changes include an increase in compressive strength, a decrease in permeability, and condensing of hazardous materials. Stabilization refers to the chemical changes between the stabilizing agent (binding agent) and the hazardous constituent. These changes should include a less soluble, less toxic constituent with hindered mobility.4.20 solidification/stabilization.
(n.d.). Common bonding agents include, but are not limited to,

portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th ...

, lime,

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, fly ash, slag,

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

, and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...

. Because of the vast types of hazardous materials, each agent should be tested on the site before a full-scale project is put under way. Most binding agents used are a blend of various single binding agents, depending on the hazardous material it will be used on. Portland cement has been used to treat more contaminated material than any other S/S binding agent because of its ability to bind free liquids, reduce permeability, encapsulate hazardous materials, and reduce the toxicity of certain contaminants. Lime can be used to adjust the pH of the substance of drive off water by using high heats of hydration. Limestone can also be used to adjust pH levels. Slag is often used for economical purposes because of its low cost.

Different methods

In situ

In situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...

is a Latin phrase meaning “in the place”. When referred to chemistry or chemical reactions it means “in the reaction mixture”. In situ S/S, accounting for 20% of S/S projects from 1982–2005, is used to mix binding agents into the contaminated material while remaining on the site. Outside benefits of in situ mixing include conserving transportation costs, no landfill usage, and lesser risk to surrounding communities to be exposed to the hazardous materials while in transport. In-situ mixing treatments can also have the added benefit of improving soil conditions on the site.Solidification/stabilization.
(n.d.). Portland Cement Association

Ex situ

Ex situ is a Latin phrase meaning “off site”. In ex situ mixing, the hazardous materials are excavated, then machine-mixed with a certain bonding agent. This new, less-hazardous material is then deposited in a designated area, or reused on the initial site.
(2002, June). From 1982–2005, ex-situ S/S technologies have accounted for 80% of the 217 projects that were completed.

Limitations and concerns

Prolonged use of the treated site and environmental and weather conditions may cause the materials used to stabilize the contaminants to erode, limiting the effect of the stabilization on the hazardous materials. Because of this, continuous monitoring of the site is required in order to ensure the contaminants have not re-assembled. Environmental factors such as freezing–thawing and wetting–drying were the focus of many studies dealing with the strength of S/S. It was found that freezing and thawing had the most adverse effects on the durability of the treated materials. When dealing with a radioactive contaminant, the solidification process may be interfered by various other types of hazardous waste. Most S/S processes have little or limited effects on organics and pesticides. Only by destroying these wastes by heating at very high temperatures will organics and pesticides be immobilized. Prior to performing the process to these types of sites, treatability studies need to be conducted in order to conclude if the solidification/stabilization process will be beneficial. These cement processes can result in major volume changes to the site, often up to double its original volume.

Projects

Sydney Tar Ponds

The governments of Canada and the province of Nova Scotia agreed in January 2007 to clean up the infamous

Sydney Tar Ponds The Sydney Tar Ponds were a hazardous waste site on Cape Breton Island in Nova Scotia, Canada. Located on the eastern shore of Sydney Harbour in the former city of Sydney (now amalgamated into the Cape Breton Regional Municipality), the Tar Ponds ...

contaminated site using S/S technology. Cement was mixed into the contaminated waste to solidify and stabilize it. When the S/S process was complete, the solidified areas were covered with an engineered cap consisting of a clay, followed by layers of gravel and soil. Finally, the surface was planted with grass and other vegetation.Tar ponds solidification/stabilization.
(n.d.).

Former wood treating facility in Port Newark, New Jersey

S/S technologies were used to treat a contaminated former wood treating facility in Port Newark, New Jersey. Approximately of soil was contaminated by wood with arsenic, chromium, and

polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...

s. 8% of Portland cement was used by wet weight of contaminated soil. Both in situ and ex situ processes were utilized to treat over 35,000 cubic meters of contaminated soil. The ex situ treated soil was mixed with Portland cement by a

pugmill A pugmill or pug mill is a machine in which clay or other materials are mixed into a plastic state or a similar machine for the trituration of ore. Industrial applications are found in pottery, bricks, cement and some parts of the concrete and asp ...

then placed on top of the in situ treated soil. This created an excellent base for pavement to be placed over the site. The proposed use for the treated site is a shipping container storage area. Wilk, C. M. (n.d.)
Applying solidification/stabilization for sustainable redevelopment of contaminated property.
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Former electric generating station in Boston, Massachusetts

Abandoned warehouses in Boston, Massachusetts are being renovated or torn down in order to build new structures. On this site is the former Central Power System, built in 1890. When built, this power station was considered to be the biggest electric generating plant in the world. This building has been abandoned since the 1950s and has not produced electricity in over 90 years. In the early 90s, renovations were started but were quickly shut down when free-floating oil was discovered in the sewers. Cleanup efforts were unsuccessful as they brought more oil onto the site. In 1999, cement-based S/S treatments were utilized to treat 2,100 cubic meters of contaminated materials. Lead and Petroleum contaminated soils were managed and treated successfully at this site.

Dockside Green in Victoria British Columbia

A complex of mixed residential, office, retail and commercial space is being built on of former industrial land in downtown Victoria that was contaminated by lead. 10 tonnes of soil was treated with cement, which was mixed into the soil on site simply by using an excavator bucket. The soil was thus rendered completely safe as was shown by tests on soil samples.

Former battery breaking site in Brandon, Manitoba

A 10,000 square metre lot formerly occupied by the Brandon Scrap Metal and Iron Company was chosen by the City of Brandon for the site for its new fire and police headquarters. For many years, lead cell batteries were destroyed there and the lead was extracted, leaving the untreated cases on site. An environmental assessment showed that the site was contaminated due to the presence of heavy metals, lead and hydrocarbon pollution. Cement based S/S was employed to successfully remediate 600 tonnes of contaminated soil.

Skeet shooting range near St. Catharines, Ontario

A vacant 5-hectare property near the Welland Canal in St. Catharines had surface soil containing dangerous concentrations of lead and polycyclic aromatic hydrocarbons (PAHs) to a depth up to 0.4 m due to the past operations of an adjacent skeet shooting range. About 26,000 tonnes of soil were treated using S/S to bring the contamination levels below the Ontario Land Disposal Regulations criteria.Soil Remediation- Surplus Seaway Property- St. Catharines, Ontario
Canadian Environmental Assessment Agency

References

External links

A Citizen’s Guide to Solidification/Stabilization
* Technical References from U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and U.K Environment Agency: https://web.archive.org/web/20110317002710/http://www.cetco.com/ccs/Literature.aspx {{DEFAULTSORT:Solidification Stabilization (S S) With Cement Waste treatment technology