Slurry cutoff walls are constructed by excavating narrow trenches under bentonite slurry and then backfilling (displacing) the slurry with higher gravity impermeable material to create subsurface barriers that prevent the lateral flow of groundwater. They are used to contain the migration of contaminated groundwater; reduce the permeability of storage impoundments such as tailings dams, ash ponds, or wastewater treatment ponds; and to prevent under seepage in levee and dam construction. Great Lakes E&I has constructed more than 21 million square feet of slurry cutoff walls, placing us at the forefront of the industry with regard to capability and experience in this type of construction. Design permeability and strength requirements as well as native soil and groundwater conditions influence the composition of the engineered slurry backfill. Great Lakes E&I’s slurry wall construction capabilities include the ability to design and construct soil-bentonite, soil-attapulgite, soil-cement, soil- cement-bentonite, cement-bentonite, and slag-cement-bentonite cutoff walls. Additional expertise includes the installation of biopolymer collection trenches and permeable reactive barriers (PRBs).
Biopolymer collection trenches are used to extract or intercept groundwater. They are used to contain the migration of contaminated groundwater or to dewater areas for construction or excavation. During installation, the trenches are supported by a biopolymer (e.g., guar gum) slurry, eliminating the need for shoring. The trench is then backfilled with sand or porous media and the biopolymer degraded either naturally or by the addition of enzymes. The native soil and groundwater conditions influence the type and concentration of biopolymer slurry used to maintain the trench. Additional expertise includes the installation of slurry walls and permeable reactive barriers (PRBs).
Permeable reactive barriers (PRBs) are in-situ treatment zones constructed to treat groundwater as it flows through them. The treatment can include sorption/precipitation, chemical reduction or oxidation, and/or biological degradation, allowing PRBs to be specifically designed around the contaminants of concern. Common reactive materials include activated carbon, zero valent iron, limestone, and organic substrates. Often slurry walls are used to direct groundwater flow through PRBs, reducing the size (and cost) to treat a contaminated groundwater plume. Great Lakes E&I has experience with the installation of PRBs using biopolymer trenching, mandrel placement, and deep soil mixing. Additional expertise includes the installation of biopolymer collection trenches and slurry walls.
NATOMAS CROSS CANAL LEVEE IMPROVEMENT PROGRAM
Great Lakes E&I continued a history of award-winning performance, receiving the American Society of Civil Engineers (ASCE) 2010 Outstanding Project of the Year Award for the Natomas Levee Improvement Program. The Natomas Basin is part of the Sacramento River Flood Control Project (SRFCP), an integrated system of levees, nearby bass channels and dams, constructed to protect communities in the Sacramento Valley from flooding. The levees were constructed with unsuitable materials that proved to be extremely porous when subjected to sustained high flows.