Most natural gas processing plants will have to start reporting on toxic chemicals they release  under regulations the Environmental Protection Agency plans to enact.

The rulemaking process, which is expected to take up to two years to complete, will affect many of the 551 gas processing plants in the US, including 20 in California. The EPA specifically rejected imposing the reporting requirements on oil and gas wells, compressor stations and pipelines.

The processing plants will be required to disclose emissions of benzene, formaldehyde, hexane, xylene and 20 other chemicals listed in the federal Toxic Release Inventory (TRI) database.

The reports will have to be submitted annually, rather than every three years as is now required for many TRI emissions. The information will also be provided to state regulators. Processing plants with fewer than 10 employees are exempt from the requirement.

The EPA decision followed a petition filed in 2012 by the Environmental Integrity Project and 17 other environmental groups, and a lawsuit the groups filed against the agency early in 2015.

Environmentalists had sought to have a range of other energy-related facilities included in the new rule. But the EPA said it saw not need to change its 1996 decision that excludes oil and gas wells, compressor stations, pipelines and other upstream infrastructure from TRI reporting.