Closure/Postclosure of Disposal Facilities

Case Study: Colma Landfill Warehouse Retail Store

Closed landfills can be utilized in a variety of ways involving large buildings such as business parks, parking facilities and retail locations such as malls or retail stores.

Colma Landfill (41-AA-000) is a closed, major solid waste landfill upon which a warehouse retail store has been built. The landfill is generating large volumes of landfill gas caused by the decomposing waste, and is also subsiding dramatically as the waste mass compresses and reduces. The landfill is located in a developed area of Colma as shown in this photo.

To accommodate both of these circumstances, the project architects developed means to address these two problems:

Active gas collection: The closed landfill has been generating significant amounts of flammable and dangerous landfill gas as the waste decomposes. To mediate the large volumes and dangers, from fire, of the landfill gas, an active gas collection system was installed. Consisting of a network of flexible PVC pipe, the gas collection system draws the gas in by means of a negative pressure system that draws the gas from the waste mass, into the perforated collection wells, through pipes placed within the waste to a flare. The flare combusts the gas, which reduces the “greenhouse” effect as well as odor and danger of fire.

Structural features: Articulated ramps and floor support of the structure allow continued use of the retail store during the postclosure use of the site. As the waste in the landfill decomposes, its volume reduces and the surface of the landfill subsides. This subsidence can be irregular, settling at different rates in different places throughout the landfill.

The structure is constructed on concrete support piles, which are driven down to underlying bedrock directly below the store. The structure is constructed on these pilings and will then subside minimally.

Large access ramps for the store were constructed to provide uninterrupted access to the structure. As the landfill wastes decompose, the surface drops, unevenly. The articulated or hinged ramps, connected to the structure, will lower with the falling ground surface, allowing continual access by customers into the store.

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Last updated: April 18, 2008