While not a new technology in conventional construction, excavation under slurry is not a commonly used remedial strategy. However, in addition to the benefits afforded by excavation under slurry in stabilizing the excavation sidewalls and adjacent buildings, the cement slurry also chemically binds to contaminants, rendering them inert, and substantially reduced the volume of excavated material requiring disposal. It also eliminated the need to control groundwater during the project.
St. John's University
The innovation is the process of excavating contaminated areas of land through the use of slurry. This excavation process cleans out the contaminated substance(s) that are underground, prevents water from rushing in, and supports the underground trench walls from collapsing. This process eventually leads to the land being uncontaminated and foundations for any buildings would then be able to be built upon that land. The goal of the cleanup action for the site is to achieve cleanup levels that protect public health and the environment.
The initially proposed remedy of excavating the site to remove contaminated material was technically feasible but had drawbacks. These included the need to remove and treat groundwater within the excavation, additional engineering design and construction for the support of excavation sidewalls and adjacent buildings, and a larger volume of material for disposal. When the remedy was re-evaluated in consideration of other innovative remedial alternatives, the benefits of excavation under slurry became clear.
This innovation was created by a small team of employees from ConEdison. The individual that we interviewed, who wished to not have their name disclosed, played a key role in the creation too.
Excavations under slurry and slurry wall construction, first developed in Europe, have been used in the United States since the 1940s. The process involves excavating a trench and filling it with a cement and bentonite clay slurry to exert hydraulic pressure on the sides. It stabilizes the surrounding soils and supports further excavation. Cement and clay are also excellent at absorbing and binding contaminants. When solidified, the slurry chemically stabilizes contaminated soil making it inert. The application of this technology in the remediation of contaminated soil is infrequently used over conventional techniques such as excavation and capping of contaminated sites because it is innovative and not as widely understood. Both environmental engineers and environmental regulators don’t often propose it or consider it as part of a remedial alternatives analysis for these reasons.
The New York State Department of Environmental Conservation required that the site be cleaned up. This was ConEdison’s responsibility since it inherited the operations and liabilities of the company that used to operate this MGP site.
“The initially approved design was to sheet the road, excavate, and fill with clean soil. When we went to the field and we did the investigation, we found out that the utilities under the road were in a very bad shape (gas, sewer, water, electric), sinkholes in the road, and the foundation of the 100 year old two story building next to the site was at risk. During the excavation, the tremendous vibration would impact both - the building could collapse because of too much stress and utility lines could break (which would lead to gas leaks, sewer line breaks and water leaks). In our business if contaminated soil will come in contact with contaminated water, then you have to collect and treat it which is a very expensive proposal. Because of these problems with the conventional process we looked for a solution and found this innovative way to save our customers a lot of money. That’s why when I started thinking out of the box, I came up with excavation below slurry.”
The typical way of excavating contaminated soil, or water, is collecting it through pumps, putting it in the storage tanks, and then hauling those storage tanks to the treatment facilities. However, even though this may be effective, the entire process is quite expensive. There needed to be a way to find innovations in the remediation process to look for cost savings. The role of environmental regulators in this case is to enforce that ConEdison as the responsible party cleans up the site and protects public health. The person we interviewed was then a part of a team that used this innovative technology called excavation under slurry. This eliminated the additional costs and it also did not jeopardize the utilities in the area or any adjacent buildings that may have had been compromised during the course of the project.
Prior to the innovative process being used, there was about 1/4 of an acre of land was contaminated with MGP (manufactured gas plant) products. Landowners can not develop in those areas so the contaminated soil needs to be attended to before the site can be returned to productive use. This is where the use of innovative technology comes into play in order to remedy the polluted areas. This impacts the environment in a positive way because the pollution was removed and rendered inert. The cleanup levels also protected public health and the environment overall. In addition, landowners could go ahead and develop the land and put any new building foundations down as they see fit. This impacts society because now more usable land will increase the tax base for the town and help to redevelop a waterfront area along the Hudson River. This proves to be beneficial for the property owner, the public, and also the government. A property owner will profit from those living in the building, the future tenants can live in a clean residential property, and the government has a right to collect taxes on this higher value land.
The following link leads to an article describing a remediation project done by ConEdison (https://peekskillherald.com/3678/environment/toxic-tar-from-20th-century-gas-lighting-subject-of-waterfront-cleanup/) and it expands on what we have discussed already. The person we interviewed played an integral part in this Peekskill Cleanup Project since the innovation was used here.
“This is not of their concern. They do not care how long this is gonna take and how much money this is gonna cost. That's our concern.”
“So rather than going with this conventional excavation method and jeopardizing the utilities in the area or the adjacent buildings that had shaky foundations, we found this innovative technology called excavation under slurry.”
The innovation helped in eliminating miscellaneous and additional costs in engineering and construction support that are typically being incurred during the normal site remediation processes. It also enabled ConEdison employees to utilize a remediation process without damaging any gas lines or utilities in the general area, or comprising the structural stability of adjacent buildings.
There were many societal and environmental benefits. Firstly, the innovation enabled ConEdison employees to remove pollution that impacted the surrounding environment, including the Hudson River. This allowed the land to then be developed upon since you could not do so previously. This could benefit society as the foundation for a future store, business, or even residential area. Taxpayers also benefited from this innovation since it is their money that funds most of ConEdison’s projects for the government. Overall, this innovation was beneficial for society and the environment and it will carry on with doing so for years to come.
., Project Manager, Environmental Health and Safety Remediation Group
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