MONACA — Shell Chemical has been granted an air quality permit for a proposed petrochemical plant in Western Pennsylvania, a step the company called “a critical milestone” as it decides whether to build the multibillion-dollar project along the Ohio River.

The state Department of Environmental Protection announced Monday that it had approved the company’s air quality plan and several water-related permits for the site in Potter Township, Beaver County.

Shell bought the former zinc plant this year but said it is still evaluating whether to build the so-called “ethane cracker” about 25 miles northwest of Pittsburgh. The plant would convert ethane from Marcellus Shale natural gas liquids into chemicals used to make plastics, tires and even antifreeze.

Local officials hope the plant will bring hundreds of jobs and thousands of related jobs to the region.

Pennsylvania in 2012 signed off on lucrative tax breaks as it competed for the project with other states

“The receipt of the air permit is a critical milestone for the project,” the company said in a statement Monday. “However, it does not mean we have made a final decision to build the project.”

The permits follow a public hearing last month that included concerns raised by the Philadelphia-based Clean Air Council. The environmental group said local officials, union leaders and residents should push for better air quality monitoring and safety guarantees if they support the plant and the permitting process continues.

“It will be a major source of pollution,” executive director Joseph Minnot said Monday. “If they make a decision that it’s worth it for economic development reasons ... they can make some demands of the company, to make it safer.”