The Metropolitan St. Louis Sewer District says the lining has been completed in the past several weeks on its $150 million Deer Creek Sanitary Tunnel project.

“The tunnel, itself, is basically done,” said Sean Stone, a spokesman for the utility.

Plenty more work is needed before the 4.3-mile tunnel begins operation. Still on track for its targeted completion in late 2022, the project features a tunnel 19 feet in diameter that stretches from Clayton to Interstate 44. Crews finished boring the tunnel early last year, churning through rock 150 to 250 feet below ground with a tunnel boring machine nicknamed “Mrs. Nancy.”