This document was prepared by the Missouri Department of Natural Resources’ Solid Waste Management Program (SWMP) to provide guidance on how to properly sample for methane gases in enclosed spaces.
Proper selection of sampling equipment to be used for monitoring buildings is critical to make proper public safety assessments. While explosimeter-type instruments are appropriate for measuring methane in most monitoring in buildings, be aware that some meters burn the sample to analyze it. In an oxygen-free environment, this type of meter is not reliable and can give methane readings that are falsely low. For monitoring of spaces that may be oxygen-free, such as manholes and underground utility vaults, oxygen levels should also be sampled for worker safety and to make certain the methane monitoring equipment being used is appropriate to measure in these conditions. Detection instruments selected for monitoring buildings must have a detection threshold below 1.25% methane.
To properly assess a building, samples should be collected from:
- Around the walls of the building and near electrical sockets
- Closets or other enclosed wall spaces
- Cracks in cement floors
- Ceiling areas
- Crawl spaces and basements
- Areas where underground utilities enter the building
- Any other confined area
- Floor drains
Step 1 - Make sure the instrument has been properly calibrated to methane. (Some instruments of this type are calibrated to hexane or propane, which have different combustible limits than methane).
Step 2 - Prepare the instrument for sampling by allowing it to properly warm up per the manufacturer’s instructions.
Step 3 - Attach the hose to the instrument and begin sampling. Some instruments have wands that can be attached to the plastic hose to collect air samples. You must sample at each location for a long enough duration that the instrument will respond if methane is present. Each instrument should have a response time designated by the manufacturer that should be followed so that results are valid.
Step 4 - If methane is detected by the instrument in any concentration it should be recorded and reported to the department.
The times chosen to monitor methane gas are almost as important as the procedures used to collect the sample. If possible, sample collection should occur when landfill gases are most likely to migrate. Scientific evidence indicates weather and soil conditions influence when gas will migrate. For these reasons sampling should be considered when:
- Barometric pressure is low
- Soils are saturated
- The ground surface is frozen, snow- and/or ice-covered.
The Missouri Solid Waste Management Regulations [ 10 CSR 80-3.010(14) and 10 CSR 80-4.010(14) ] require owners of sanitary landfills in operation after Jan. 1, 1994, and owners of demolition landfills in operation after July 30, 1997, conduct quarterly monitoring of all buildings located within the landfill’s permitted boundary. Owners of the landfills must implement a methane monitoring program to make sure regulatory limits for methane are not exceeded - 1.25% (25% of the lower explosive limit) by volume in buildings on-site. Samples must be collected at least quarterly and the results must be submitted to SWMP in an electronic format within a week of collection. The information to be included in the data submission and the format by which to submit the data is described in SWMP’s guidance document, “Guidance for Submitting Landfill Gas Monitoring Data.”
Corrective Action / Emergency Response
If methane gas concentrations in the structure exceed regulatory limits or are an obvious public safety threat, the landfill owner/operator must do the following:
- Immediately evacuate the structure and take all necessary steps to protect public health and safety.
- Notify the following:
- Local fire department
- Other appropriate emergency management or public health and safety authorities
- The department
- Owners of underground utilities within 1,000 feet of the affected structure
- Take appropriate action to mitigate the effects of the methane accumulation in the affected structures until a permanent remediation is completed.
- Follow the instructions of the fire department or emergency management or public health and safety authorities. This may include:
- Ventilating the affected structure
- Inspecting the affected structure and sampling for methane or installing methane detectors inside the structure
- Sealing methane intrusion pathways into the affected structure
- Implement corrective actions as necessary.
Missouri has stringent regulations governing methane gas migration. Landfill gases that migrate into buildings present a threat to public safety. It is the responsibility of the landfill owner/operator to take any and all steps to protect landfill employees, contract workers, visitors and the general public from migrating landfill gases.
Farquhar, Grahame, Monitoring and Controlling Methane Gas Migration, course notes presented at April 1993 Sanitary Landfill Design and Management training, offered by the University of Wisconsin-Madison, College of Engineering.
SCS Engineers, Inc., April 1989, Procedural Guidance Manual For Sanitary Landfills, Volume II: Landfill Gas Monitoring and Control Systems, prepared for the California Waste Management Board. United States Environmental Protection Agency, November 1993, Solid Waste Disposal Facility Criteria, Technical Manual, EPA 530-R-93-017.