Impermeable subsurface barriers contain or modify 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 contamination down gradient. Methods used by Moretrench to create subsurface barriers include slurry trenching techniques, including vibrating beam, grouting, and ground freezing.
Slurry trenches are narrow excavations typically keyed into an underlying impermeable stratum and backfilled with a low permeability bentonite/soil mix to create hydraulic barriers that prevent the migration of contaminated groundwater. They are typically constructed with either soil-bentonite or cement-bentonite backfill. Soil-bentonite barriers are the most common, are less costly to install and are typically used for long term solutions. Cement-bentonite construction is used when higher strengths are required, backfill cannot practically be mixed locally, or when certain groundwater chemistry conditions warrant.
Slurry trenches offer several practical and economic advantages over structural vertical barriers such as steel sheeting, secant pile walls or diaphragm walls. The backfill can be engineered to specific project requirements and visually and physically monitored during installation. Excessive noise or vibration are eliminated. The installation is rapid and the completed wall is free of joints.
Permeation Grouting may be used to provide permanent in situ containment of a contaminant plume to prevent migration from its current location. Containment can take the form of the creation of a watertight curtain to surround the contaminated zone or by grouting all of the contaminated soil within a targeted region. Permeation grouting can also be used to install a perimeter cut-off to exclude contaminants on environmental sites.
Jet Grouting can be used by jet grouting contractors for the in situ encapsulation of contaminated soils, as was the case at a former manufactured gas plant, or to provide a hydraulic barrier for contaminated groundwater.
Ground Freezing. The excavation and disposal of contaminated soils may be effectively accomplished with a temporary perimeter barrier wall. Installation of a frozen perimeter cut-off wall around the zone to be excavated provides both excavation support and groundwater control. Ground freezing is minimally invasive and results in minimal solid waste that must be disposed of. Also, there is negligible change in the groundwater regime outside the confined area following thawing of the freeze.