Protection from Methane Gas Infiltration

Farallon designed a methane gas mitigation system to protect a large retail warehouse located over layers of methane-generating organic silts deposited on an ancient lake bed in South Ogden, Utah. To protect the new building from methane gas infiltration, Farallon designed an active air-sweep system that was incorporated into the building foundation design. This system comprises 3- to 6-inch-diameter perforated PVC collector pipes beneath the building slab, attached to a low-vacuum blower. A second set of perforated pipes placed between the vacuum pipes distribute fresh air beneath the slab. A high-density polyethylene membrane beneath the slab and above the pipes provides further building protection. A geonet composite layer provides a flow path for fresh air to sweep from the distribution pipes to the collector pipes while accumulating methane that may have migrated under the slab. The system operates at a low vacuum that prevents drawing large volumes of methane from a distance. Farallon continues to provide assistance in periodic monitoring of system performance.