Retail Warehouse Landfill Gas Mitigation

Farallon conducted a detailed evaluation of methane gas mitigation at a property under consideration for development as a retail warehouse. Because of the property’s location adjacent to a former Seattle landfill, Farallon designed and implemented a monitoring program that involved installation of two landfill gas monitoring probes to assess the current impact of the landfill on the property. Monitoring results indicated that the landfill was still producing gas and that measurable levels of methane was migrating onto the property. To protect the new warehouse from methane gas infiltration, Farallon designed an active gas collection system that was incorporated into the design of the building foundation. An air-sweep system consisting of perforated polyvinyl chloride and high density polyethylene collector lines was placed beneath the building’s concrete slab, with the collector lines attached to a low-vacuum blower. A second set of perforated lines placed between the vacuum lines distribute fresh air beneath the concrete slab. The system allows both distribution of fresh air through the gravel beneath the concrete slab and collection of methane that may be migrating under the slab.