As organic material decomposes in a landfill, it produces a byproduct known as landfill gas. Landfill gas is about 50% methane, with the remainder being mostly carbon dioxide. It also contains small amounts of nitrogen, oxygen, water vapor, and other non-methane organic compounds (NMOCs).
The Landfill Gas System at Freshkills Park collects and controls gas emissions through a network of wells. Those wells are connected by pipes below the surface that convey the gas through a vacuum. Once collected, the gas is processed to pipeline quality at an on-site Landfill Gas Purification Plant. Gas emissions, NMOCs, and other hazardous pollutants are reduced by almost 100%, and landfill gas and its odor are prevented from entering the atmosphere.
In addition to this active gas collection and recovery system, an additional safety system is in place to prevent the migration of gas off site. When portions of the gas treatment system need to be repaired, gas is sent to one of three flare stations, where the gas is burned off in a controlled environment.
New York State Department of Environmental Conservation (NYSDEC) requires that the City of New York Department of Sanitation (DSNY) conduct quarterly monitoring to ensure that the landfill gas collection system is working as designed to prevent the release of methane. Installed with the landfill gas collection system are a series of landfill gas monitoring wells that DSNY monitors for methane on a quarterly basis. DSNY also conducts periodic surface monitoring that includes measuring surface methane concentrations and well head pressures at the extraction wells.
In the future, little or no landfill gas will be generated by the site, and the active extraction system will no longer be necessary. When NYSDEC allows DSNY to turn the active extraction system off, landfill gas will be passively vented through gooseneck pipes that have been installed at the site.