AUBURN — Auburn Sewerage District trustees approved a nearly 29 percent rate hike Tuesday night, raising residential customers’ monthly bills by about $4.70 beginning Feb. 1.

The rate will go from $2.45 per 100 cubic feet to $3.16 per 100 cubic feet and will apply to residential and commercial users.

“This option gives consumers the most control over their bill and rewards conservation,” Superintendent Sid Hazelton said. 

The rate increase will boost revenue by 15 percent, or $574,000, this year. It’s needed to meet requirements of the federal Environmental Protection Agency Clean Water Act and because of a revenue shortfall last year when overall sewer volume was down, Hazelton said. 

“Unless sewer rates are raised, our operating cash would fall below acceptable levels,” according to a district information sheet.

At Tuesday night’s public hearing at the Auburn Public Library, some ratepayers were upset by the increase because the rate was raised 9 percent on Dec. 1, 2014.

Hazelton said the district has spent nearly $18 million over the past 15 years to fix the combined sewage overflow problem. Another $2.6 million is needed over the next five years, he said.

The district is required by federal law to address combined sewage overflow discharges that could pollute the Androscoggin and Little Androscoggin rivers.

Asked why trustees didn’t take out a bond or a loan, Hazelton said that would increase Auburn’s debt, putting the burden on all city residents, not just sewer users.