NIAGARA FALLS – Repair costs at the city’s sewage treatment plant from a fierce July rainstorm are slowly surging beyond the $2 million estimate unveiled last month.

The last of the Buffalo Avenue plant’s four main pumps returned to operation Tuesday morning, plant officials said, but damage to the facility went beyond what was initially thought.

While the facility as a whole is up and running, there’s still a lot of fine-tuning to do, said Paul J. Drof, the Niagara Falls Water Board’s executive director.

Also, some of the ancillary systems remain off-line and are in need of repairs, Drof said.

“The reliability is something we’re not at all comfortable with yet,” he said.

Those ancillary systems include the meters that indicate how much material is flowing through various phases of treatment at the plant.

There are also some problems cropping up now that did not appear right away after the storm.

Some parts of the electrical system are beginning to corrode from water damage, said Richard Roll, technical and regulatory services director for the Water Board.

Plant officials estimate that when the storm forced the plant to shut down because of flooding, at least 125 million to 150 million gallons of untreated sewage were released into the lower Niagara River.

Officials said they do not have an updated estimate of repair costs.

Temporary pumps installed in the wake of the storm remain in place as a backup system. Those temporary pumps have been in place longer than anticipated, contributing to the higher repair costs.