Mid Coast Hospital will break ground on a $21 million addition with a ceremony at 11:30 a.m. Wednesday.

The expansion will allow the emergency department to add treatment rooms and improve patient flow. The redesign will also improve diagnostics and provide better waiting and administrative space, hospital officials said.

In addition, 18 private inpatient rooms will be added to the medical surgical unit. The diagnostics department will add more rooms for changing, preparation, counseling and recovery after treatment.

Midcoast opened its new facility near Cook's Corner in 2001.

Brenda Harvey, Maine's commissioner of health and human services, cleared the way for the expansion when she signed the final approval of Mid Coast's Certificate of Need application on Aug. 7.