We were commissioned by a large residential home builder in South Florida to identify the source of an intermittent odor occurring in a large residential home.
During an odor event, we collected samples of the air inside the home using a SUMMA canister, an evacuated canister the size of a propane cylinder. Analysis of the sample revealed a high level of methane gas. It was found that the odor occurred within a few hours of major rain events. Temporary piezometers (well points) installed around the house found that the odor events were associated with elevated groundwater levels following rain events. Investigation of construction records found that the home had been built on fill over an organic muck. These findings allowed us to determine that the odor was coming from decaying vegetation under the slab and that the rain was forcing the gas through plumbing fixture openings in the slab.
Remediation of the problem required sealing of all cracks in the slab, and installation of a sub-slab de-pressurization system, similar to systems used for radon remediation to keep the gas from entering the home. Sub-slab de-pressurization is required until all organic material under the slab have completed decomposition.