Depending on the types of waste at the site, landfill gas sampling may be necessary to determine gas concentrations and lateral gas migration for the purpose of scoping enforcement and remedial work for referral to the local Air Quality Management District.

Typically, landfill gas constituents contain, by volume:

  • 38-58 percent methane gas
  • 0.2-1 percent oxygen
  • 2-10 percent nitrogen
  • 30-48 percent carbon dioxide
  • 0-1 percent hydrogen
  • <1 percent nonmethane organic carbons (NMOC)

A landfill gas characterization study performed by the CalRecycle indicated that the most common NMOCs for landfill gas include:

  • Benzene
  • Ethyl benzene
  • Toluene
  • Vinyl Chloride
  • Dichloromethane
  • Trichloroethylene
  • 1,2, -cis-Dichloroethylene
  • Tetrachloroethylene
  • Collection of landfill gas samples should be performed in accordance with standardized landfill gas sampling procedures

An example of a typical gas investigation work plan prepared by the CIWMB, (now CalRecycle) is the Newport Terrace Landfill Gas Sampling and Analysis Plan.

A table listing site investigations completed by the CalRecycle is also available. The investigations are listed alphabetically by site name and include: Solid Waste Information System (SWIS) number, type of plan or report produced, investigation type, types of operations, and whether the site is located in a rural or urban setting. The table identifies site investigations during which geophysical survey operations were utilized. A publication entitled “Landfill Gas Investigations at Former Landfills and Disposal Sites” is available that provides case studies on landfill gas investigations conducted with LEAs across the state.

Continuous monitoring for structures is a critical component to landfill gas investigations, particularly where structures are located on or within 1000 feet of a disposal site. The continuous monitoring web page provides general information and example work plans to assist LEAs and consultants performing these types of investigations.

You can also check the combined SWRCB/CIWMB regulations, Division 2, Title 27 (Subchapter 4, Article 6) for information on gas control at closed and active sites.