Services
ENVIRONMENTAL REMEDIATION
DFI/CSCE 13th Annual Geotechnical Seminar: Earth Slope Engineering
September 17th, 2010
Dam Safety 2010
September 19th, 2010
The 10th International Workshop on Micropiles
September 22nd, 2010
Barrier Techniques (Cut-off and Exclusion)
Impermeable subsurface barriers contain or inhibit the flow of groundwater. They may be installed down gradient of a known contaminant source, such as a landfill, to prevent the migration of contaminated water off site, or up gradient of a contaminated zone to prevent the flow of clean groundwater down gradient. Geotechnical methods used by Moretrench to create subsurface barriers include slurry trenching techniques and grouting systems.
Subsurface Barriers using Slurry Trenching Techniques
In material that can be readily excavated, slurry trenching techniques are frequently used for environmental containment or cut-off. Slurry trenching involves the excavation of a narrow aperture, generally two to five feet wide, that is typically keyed into an underlying aquitard or acquiclude to form a complete barrier to horizontal or vertical groundwater flow. Excavation is by backhoe or clamshell, depending on design depth, and is accomplished under thixotropic slurry to maintain trench sidewall stability. Engineered backfill of low hydraulic conductivity is placed in the trench as excavation progresses to form the continuous cut-off.
Soil-Bentonite and Cement-Bentonite Trenches: Soil-Bentonite (S-B) is the most commonly used backfill mixture. Where backfill strength is also required, a soil-cement-bentonite (S-C-B) or cement-bentonite (C-B) mixture may be used.
Permeable Reactive Walls are passive systems that allow groundwater to flow through specified treatment media. Contaminants in the groundwater react with the medium and are degraded, precipitated or absorbed.
Subsurface Barriers Using Other Techniques
Jet Grout Curtain Walls are effective in preventing the flow of contaminated groundwater or contaminant plumes. Curtain wall installation can be pinpointed to a specific subsurface stratum.
Permeation Grouting can be used to sufficiently reduce the hydraulic conductivity of soils and thus prevent contaminant migration. Grouting may take the form of creating a watertight barrier around the zone of contamination or by grouting all of the contaminated soil within a targeted region.
Ground Freezing, which is accomplished with negligible subsurface disturbance, may be used to provide perimeter earth support and groundwater control for the excavation and disposal of contaminated soils or to isolate an area from the surrounding hydrological regime and thus minimize the volume of contaminated groundwater to be pumped and treated.
Hydrodynamic Barriers using Dewatering Techniques
Hydrodynamic Barriers are designed to prevent the migration of contaminants down gradient. They are formed by the creation of a trough or depression in the water table using dewatering techniques. The contaminant is captured within the depression and pumped away for treatment. This method is suitable for aquifers of low transmissivity and where the natural groundwater gradient is relatively flat.