AZTEC — The Aztec City Commission approved spending an additional $72,000 in unexpected costs to upgrade its 1960s-era water treatment plant Tuesday evening.

But paying the surprise bill was made easier because the bid for the project to replace and upgrade control, power and valve systems was nearly $100,000 under what had been budgeted.

That means the project still will be roughly $20,000 under budget.

The city commission had approved spending nearly $400,000 to update and automate the outdated water plant earlier this month. Pillar Innovations was awarded the design-build contract to upgrade one of the plant's four water treatment systems.

"We knew this could happen," said Mike Huber, city engineer and public works director. "Part of the design process involves discovery. In this case, disassembling very old electrical parts that reveal the degree of disrepair or decay involved."

The modified project approved Tuesday included additional items that will need to be added to the water plant's work order include a new river-pump flow meter, a power feed from a transformer, electrical conduits, and plumbing for the chemical pumps.

"We thought originally that we could go in and retrofit a lot of the equipment in a cost-effective way, but going through we found that there were enough pieces in sorry shape that made replacement the best option," Huber said.

Some of the part upgrades for the plant were news to the city engineer.

"Some of the equipment upgrades, I wasn't even aware existed," Huber said. "As we went through the plant, the contractor brought up brand new technology like arc-flash protection additions that are smart investments for the facility."

Also added to the bill is a catwalk cabling system to incorporate new wiring loads.

The plant's ongoing upgrade work is still on schedule to be completed by the end of April, Huber said. Upgrades and automation to the plant's disinfection systems are scheduled to begin in May.

"As we move forward and look forward to future expenses, we want to automate and the water plant is an example of that," Mayor Sally Burbridge said. "The fact that our personnel have kept these aging facilities going this long to be able to make life-extending improvements is remarkable."

City commissioners approved the additional funding with a unanimous vote.