Denver International Airport completed the capping of 64 oil and gas wells and removal of 38 tank batteries on the airport property on Aug. 12, part of a $12.5 million program to support the airport’s mission to become “one of the greenest airports in the world.”

Airport authorities said the wells once produced a positive financial return for the airport, but when Kerr-McGee Gathering closed the gathering lines serving the airport property and the surrounding area in May 2018, DIA officials decided to start the process of closing its wells permanently, according to DIA spokesperson Jose Salas.

Airport authorities said it cost nearly $500,000 yearly to maintain the infrastructure and stay in compliance with Colorado’s oil and gas regulations.

“The wells at DEN were the only wells located within Denver and this closure effectively ceases all oil and gas activities in our city,” Denver Mayor Mike Johnston said in the release. “This work aligns with our unwavering commitment to climate-aligned, sustainable policies and action to ensure Denver remains a top place to live.”

The $4.8 billion airport opened in 1995 as a replacement for the embattled Stapleton International Airport, which was shut down due to noise and pollution complaints from residential neighborhoods that sprang up around the airport as Denver expanded.

The scheduled opening date of Denver International Airport was delayed four times because of design changes and automated baggage handling system problems. Only parts of the automated baggage system were functional when the airport opened, and it came in more than $1 billion over budget, according to the federal General Accountability Office.

“We are immensely proud of the work and dedication from our teams to achieve this milestone, which symbolizes our commitment to sustainability and responsible practices,” said Denver International Airport CEO Phil Washington. “This accomplishment underscores our dedication to being a leader in airport sustainability, setting an example for others to follow.”

Washington made sustainability a key component of Vision 100, the strategic plan designed to enable the airport to serve 100 million annual passengers.

Authorities said the capping and decommissioning process required extensive coordination within the airport and with oil industry engineers, contractors, and state regulatory agencies. They added that, with the final closure of the wells, the land would now be turned over to tenant farmers and others to “repurpose and rejuvenate.”

Denver International Airport, one of the busiest airports in the world, generates more than $36 billion for the region annually.