The Virginia Department of Environmental Equality has approved the city and Alexandria Renew Enterprises’ plan to remediate its four outfalls.

The plan, developed jointly by the city and AlexRenew, outlines a plan to remediate the outfalls, a portion of Alexandria’s 19th-century sewer system, by the commonwealth’s mandated deadline of July 1, 2025.

The plan calls for the construction of an approximately two-mile-long tunnel system that would connect to the existing sewer system. The plan also includes improvements on AlexRenew’s Water Resource Recovery Facility to pump and treat wastewater collected in the tunnels.

A city news release estimates the plan would reduce the number of times the four outfalls overflow into the Potomac River from 60 times per year to less than four times per year.

AlexRenew, as part of the plan, would serve as the central site of construction for the proposed tunnel system. City council approved the plan in April and also voted to transfer ownership of the outfalls from the city to AlexRenew.

The plan will now enter its design stage, which a city news release said would include an outreach program to the community.

The new plan follows a 2017 bill signed by former Gov. Terry McAuliffe that mandated that the city fix its outfalls by 2025.