ANDERSON — Another step was completed Thursday in the process of raising city residents’ sewer rates by about $15 a month to pay for the largest public works project the city ever has undertaken.

The Anderson City Council preliminarily approved an ordinance establishing sewer rates that will help pay for the first five years of a 20-year project that will significantly reduce the city’s combined sewer overflow, also called CSOs, events into the White River.

The ordinance, if approved on its third reading next month, would set the rates at $6.15 per 100 cubic feet for metered residences and $63.71 a month for unmetered users. The increase will result in about a $15 increase per month for the average user and an $11 increase for the minimum user, said John Skomp, a financial consultant with Crowe Horwath LLP.

Commercial rates would be $5.37 per metered 100 cubic feet, and industrial rates would be $5.12 per metered 100 cubic feet.

CSO events occur when rainfall combines with sewage and overflows the city’s water treatment capacity, being released into the White River. Now, Anderson sees about 600 CSO events a year, but a federal mandate affecting cities across the Midwest will require the city to decrease the events to 84 a year.

“Anytime it rains here over a quarter of an inch, we’re running to the river,” Board of Public Works Chairman Greg Graham said.

Skomp said the rate increases will pay for the first five years of the project, estimated at $54 million of the total $161 million project, and the city hopes to attract enough development in that time to offset future rate increases.

Water Pollution Control Superintendent Nara Manor said her department had applied for federal stimulus money to pay for parts of the project. It submitted about $30 million worth of shovel-ready projects and hopes to see grant money or low-interest loans.

“We feel we have a really good chance to get that money,” Manor said. “We’re trying to look at it from all directions.”

The council also preliminarily approved an ordinance that would bring up the towns of Edgewood and Chesterfield to Anderson residential sewer rates. The towns now use Anderson’s wastewater treatment facility and pay wholesale rates according to an earlier agreement that expired in December.

Rates would gradually be increased until 2011, when they would reach the $6.15 per 100 cubic feet rate of Anderson residential users.

Public hearings on both the Anderson rate increase and the Edgewood and Chesterfield rates will be in April, before the ordinances receive their third reading, city attorney Tim Lanane said.

Contact Aleasha Sandley: 640-4805, aleasha.sandley@heraldbulletin.com.