An expansion at the city’s Clinton Water Treatment Plant will cost about $4 million more than expected, causing city leaders to look at whether water rates will have to increase more than planned.

City staff members said they were optimistic that residents’ water and sewer bills would not need to increase any more than what city commissioners already have approved, but they said they couldn’t yet rule out that possibility.

“What we’ve been able to gather so far is there might be some shifting that we can do to avoid a rate increase,” Assistant City Manager Debbie Van Saun said. “But we can’t speak definitively to that until we get a little further along.”

Water rates have been increasing by about 4 percent per year since commissioners approved a five-year rate plan in 2004. Sewer bills have been rising even more, at about 9 percent per year.

New estimates for the plant expansion now call for the project to cost $19.1 million, up from an estimate of $15.4 million. The approximately

$4 million cost increase for the water plant expansion is related to everything from trash to safety improvements, Van Saun said.

She said the city is now budgeting $500,000 to remove solid waste from the site. The site was used as a city dump in the early to mid 1900s, city leaders said.

Van Saun said the city was aware of the dump, but was unable to estimate how much it may cost to remove the soil from the site until more tests were completed. Those tests now have been completed, she said.

“There’s nothing really dangerous there, but it is not your basic digging in a greenfield out there,” Van Saun said.

Chris Stewart, the city’s interim director of utilities, said additional safety improvements to the site that were not anticipated will cost another $500,000. Stewart said he’s recommending that the city use a new treatment system that relies on a liquid form of chlorine. Currently, the plant uses a gas form of chlorine that is stored under pressure in 1-ton tanks.

Stewart said if those tanks were to ever rupture or leak, it could cause significant concerns for workers and neighborhoods surrounding the plant being exposed to the chlorine gas.

“Chlorine gas itself is a pretty dangerous product,” Stewart said. “You have to be real careful when you are dealing with it. We spend a lot of time training all our employees about it.

“I think it is absolutely worth the $500,000 increase. It will pay dividends because we’ll have a safer product.”

Other causes for the cost increase, according to city staff members, include:

¢ $600,000 increase in steel prices used for construction of the plant.

¢ $200,000 increase in site work related to widening the roads on the property to create easier access for trucks that enter the site.

¢ An inflation rate of about 7 percent for labor costs related to construction of the plant.

Van Saun said city leaders won’t have a definite answer on the rate question until they receive bids for the plant. Bids are expected to be received in either March or April. Construction would start shortly thereafter. The project would be substantially completed by July 2008.

Stewart said the expansion would increase capacity by about 15 million gallons per day at the plant, located southwest of Bob Billings Parkway and Wakarusa Drive. Stewart said the plant – one of two in the city – is expected to meet the city’s water capacity needs through at least 2015.

City commissioners will review plans for the plant at their 6:35 p.m. meeting on Tuesday at City Hall, Sixth and Massachusetts streets.