Seepage Analyses of Soil-Bentonite Slurry Cutoff Wall through Landfill

Abstract

Slurry cutoff walls have been used as vertical barriers to mitigate seepage of subsurface contaminant and to permit safe reuse of existing sites without extensive clean-up. The objective of the paper is to presents seepage analyses of soil bentonite (SB) cutoff walls that are part of the Dallas Floodway Extension project. The finite element program SEEP was utilized for the analyses. This flood control project in Dallas, Texas includes construction of wetlands for environmental mitigation purposes. The alignment of one of the wetland cells, Cell F, goes through the Linfield and UPRR landfills, requiring excavation of 1M yd 3 of landfill materials. Due to the presence of water in these landfills, migration leachate from the landfills into the wetland cell could occur over time. To mitigate migration of leachate into the wetland cell, two SB slurry cutoff walls are being constructed parallel to the longitudinal axis of Cell F. This paper presents the numerical modeling of the cutoff walls for three different wall configurations. The lowest factor of safety for the under seepage analyses of all three wall configurations was more than 1.2, required by the regulatory agency.