MARSHALL — Keeping Marshall’s water treatment facilities up-to-date has been a long, ongoing process. But plans to improve the city wastewater treatment plant took another step forward at Tuesday’s city council meeting.

Council members approved an agreement with the engineering firm of Bolton & Menk, for design and bidding services on upgrades to the wastewater plant.

It’s time to refurbish or replace several parts of the plant, Marshall wastewater superintendent Bob VanMoer told council members. Most of the equipment that will be upgraded is more than 20 years old, city staff said.

“We’re really hitting the critical stage for a lot of this equipment,” VanMoer said.

Back in March, the council had approved a wastewater facilities plan drafted by Bolton & Menk. The plan proposed two major phases of work. First, aging parts of the plant would be refurbished or replaced, and systems used for turning waste into fertilizer safe for application on farm fields would be expanded. The second phase of the facilities plan would only start if Marshall is ever required to limit the nitrogen allowed to be discharged in wastewater.

Under the agreement approved Tuesday, Bolton & Menk would design upgrades to several parts of the Marshall wastewater plant, including pumps and clarifiers, which are used to settle solid waste out of wastewater. City staff estimated that they would receive bids for the project in June.

Marshall needs to have contract documents ready for the Minnesota Pollution Control Agency to review in March, city staff said.

The upgrades to the wastewater plant are a separate project from plans to pre-soften Marshall Municipal Utilities’ raw water. However, the wastewater plant still plays an important role in helping to keep pollutants from being released into the Redwood River.