Bentonite slurry walls are constructed by mixing the excavated soils with the bentonite slurry and gradually backfilling the trench. Backfilling begins by lowering the fill into the bottom of one end of the trench using a clamshell. When the mound of backfill reaches the surface, the remainder of the trench is filed by pushing fill down the slope of the mound into the trench using a bulldozer. Operators gradually move down the trench until the entire trench is backfilled. The ideal soil for bentonite wall is silty sand. Chunks of clay, rocks bigger than 6 inches and roots, or other organic material must be removed from the soil before mixing with the bentonite slurry. Installation of bentonite slurry wall requires level ground and a large work area to mix the soil with the bentonite slurry. These walls are susceptible to attack by incompatible chemicals.