Slurry Wall Construction Technology and Information

Slurry wall construction consists of subsurface barriers of vertically excavated trenches filled with slurry. The slurry, usually a mixture of bentonite and water, hydraulically shores the trench to prevent collapse and retards ground water flow.

Slurry wall construction is used to contain contaminated ground water, divert contaminated ground water from the drinking water intake, divert uncontaminated ground water flow, and/or provide a barrier for the ground water treatment system.

These subsurface barriers consist of a vertically excavated trench that is filled with a slurry. The slurry hydraulically shores the trench to prevent collapse and forms a filter cake to reduce ground water flow. Slurry walls often are used where the waste mass is too large for treatment and where soluble and mobile constituents pose an imminent threat to a source of drinking water.

Slurry walls are a full-scale technology that have been used for decades as long-term solutions for controlling seepage. They are often used in conjunction with capping. The technology has demonstrated its effectiveness in containing greater than 95% of the uncontaminated ground water.

Many of these walls are constructed as a soil bentonite slurry wall, and water mixture. The bentonite is used primarily for soil stabilization during trench excavation. A soil-bentonite backfill material is then placed into the trench (displacing the material) to create the hydraulic cut off wall. This composition provides a barrier with low permeability and chemical resistance at low cost. Other compositions, such as cement/bentonite, pozzolan/bentonite, attapulgite, organically modified bentonite, or geomembrane composite, may be used if greater structural strength is required or if chemical incompatibilities between bentonite and site contaminants exist.

Typically placed at depths up to 30 meters (100 feet) and are generally 0.6 to 1.2 meters (2 to 4 feet) in thickness. Installation depths over 30 m (100 ft) are implementable using clam shell bucket excavation, but the cost perunit area increases by about a factor of three. The most effective application of this for site remediation or pollution control is to base (or key) at 0.6 to 0.9 meters (2 to 3 feet) into a low permeability layer such as clay or bedrock, as shown in this figure. This "keying-in" provides for an effective foundation with minimum leakage potential. An alternate configuration for installation is a "hanging" wall in which the wall projects into the ground water table to block the movement of lower density or floating contaminants such as oils, fuels, or gases. Hanging installations are used less frequently than keyed-in installations.