Engineers Australia

Hydraulic Containment at Landfill Sites

Kane Mitchell, Environmental Scientist, Environ Australia Pty Ltd, Hunter Valley

A hydraulic containment system of some description is commonly required to abate the offsite migration of leachate and/or contaminated groundwater at landfill sites, and to a lesser extent other contaminated sites (i.e. industrial facilities). In Australia, these systems typically comprise pumping leachate/groundwater from a series of extraction bores to maintain an inward hydraulic gradient, with the extracted leachate/groundwater transferred to a treatment plant, or to sewer. The construction of a cut-off wall may be a more appropriate approach where saltwater intrusion is an issue, subsurface conditions are not favourable for groundwater extraction (i.e. low hydraulic conductivity aquifer) or a high level of certainty is required regarding the containment of the targeted groundwater/leachate due to site sensitivity. The lecture will provide a brief background on the application and limitations of cut-off walls in groundwater remediation projects (landfill and other contaminated sites) as well as a case study of a groundwater remediation project conducted at a 40Ha former landfill site situated adjacent to a canal in the Sydney metropolitan area, including discussion of: the design and construction of a soil/bentonite cut-off wall (1.5km in length, 0.8m wide, max. depth 15m) and associated leachate collection/treatment system; the usefulness of a full scale pilot test conducted prior to full commitment to the soil/bentonite slurry approach; the development of an innovative means of validating the performance of cut-off walls in tidal groundwater systems; The demonstrated performance of the wall to date.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.