Civil Engineering November 2022 | Vol 30 No 10

T he Plettenberg Bay Landfill was a licensed landfill for garden waste and building rubble, classified as GSB+, i.e. General Waste: Communal (small landfill): Site Water Balance Positive (significant leachate produced). Upgraded in 2000, the works comprised the shaping of the existing waste, capping it, constructing a lined primary cell on top and provision of stormwater and leachate management systems. The development plan required that a further cell be developed after the first primary cell had reached capacity. Ultimately, at the end of the site’s lifespan, four cells would have been constructed. It was important that the cells, which entailed excavating into the bank of the southern slope, be developed expertly as it would both ensure the required airspace and provide the material for ongoing covering of waste. However, the landfill was not properly operated in accordance with the develop- ment plan and the site reached capacity much earlier than planned, with the result that the height was measured to be ap- proximately 15 m higher than the design height, while the slopes of the landfill were in the order of 1:1.5. The landfill was closed for receiving waste on 15 December 2018 and a variation waste management licence was issued to extend the closure and decom- missioning licence. REHABILITATION AND CLOSURE Rehabilitation measures included pulling back existing waste to reshape the slopes, followed by capping of the area with a geosynthetic clay liner and covering it with topsoil to allow for the growth of vegetation. Other features of the closure design were upgraded stormwater and leachate systems together with ground- water and landfill gas monitoring plans. The pre-construction top level of the landfill was measured in some places at approximately 108 m above mean sea level (MSL). The decommissioning licence requirements stipulated a height restric- tion of 102 m above MSL. To achieve this, major earthmoving activities had to take place to reshape the existing waste body within the restrictions of the existing site boundaries. Furthermore, the aim was to obtain final side slopes of between 1:2.6 to ideally 1:3. The capping and closure designs were mainly based on the fact that the only evidence found of any type of bottom liner was for one cell that was developed near the centre of the landfill. But there were no records available of the cell design or its operation. Another consideration in the design was the waste composition. Significant settlement of the landfill could also be expected and had to be addressed in the design. Zutari recommended that the exten- sion of the footprint would assist in flat- tening the side slopes of the waste body and accommodating the volume of waste that had to be handled. SUCCESSFUL REHABILITATION A landfill facility that caused great con- cern for the Bitou Municipality, as well as an eyesore to the surrounding upmarket residential areas, has been transformed over the course of the rehabilitation project. The entire area will be hydroseeded and eventually disappear into the surrounding landscape. The municipality has already had enquiries from various groups interested in utilising the completed site or parts of it. The Plettenberg Bay Landfill can be considered a textbook example of how landfill rehabilitation should be ap- proached and conducted.  SANRAL SA I CE 2022 Nat i onal Awards Category: Techn i cal Excellence FINALIST Technical Excellence category (Sponsored by SKI Civil and Structural Engineers) KEY PLAYERS Client: Bitou Local Municipality Consultant: Zutari Contractor: SC Housing and Civils Construction of the Decommissioning Works for the Plettenberg Bay Landfill 18 November 2022  Civil Engineering The Plettenberg Bay Landfill reached capacity much earlier than planned The landfill was capped with a geosynthetic clay liner and covered with topsoil to allow vegetation growth