The Portland City Council voted unanimously Wednesday to charge property owners for the size of their rooftops and driveways.

The new stormwater fee, effective in January 2016, will be used to fund projects costing $170 million over the next 15 years to meet federal mandates to reduce the amount of polluted runoff that enters waterways such as Back Cove and Casco Bay.

The council also approved a $292,000 investment to hire five people to launch the program.

“I think this is one of the more forward-thinking policies we have put together in a while,” said Councilor David Marshall. “It’s a big step in the right direction.”

All six people who spoke during the public hearing supported the proposal.

The new fees are intended to spread the cost among the largest number of property owners possible. Other funding mechanisms available to the city, such as property taxes and sewer user fees, would put the burden more on homeowners.

Much of the polluted runoff comes from large parking lots, which typically don’t have sewer accounts – or bills – while nonprofit organizations do not pay property taxes.

The upgrades are needed to bring the city into compliance with the federal Clean Water Act.

The city has several systems that handle both sewage and stormwater. During heavy rainfall, those systems are overwhelmed so water containing raw sewage and other pollution from the runoff, such as motor oil and anti-freeze, is discharged into nearby water bodies.

Sarah Lakeman of the Natural Resources Council of Maine said the upgrades are important to protect the health of residents, wildlife and waterways. To address the issue, the program must reduce the amount of stormwater while providing funding for needed upgrades, she said.

By enacting the proposal after years of discussion, Portland joined Lewiston, Bangor and several dozen cities across the country that are using stormwater fees to pay to upgrade aging or inadequate infrastructure. While the program is new in Bangor, Lewiston has been collecting stormwater fees for more than six years.

Portland will offer credits to property owners who take steps to reduce or eliminate runoff by building rain gardens, dry wells or retention ponds.

“This is a well-designed proposal that will address the problem in a fair and equitable way,” Lakeman said.

While the average homeowner would pay an estimated increase of $4.50 a month, Councilor Nicholas Mavodones Jr., who chairs the council’s Finance Committee, said some commercial and industrial businesses could see substantial increases.

Among the property owners faced with the largest fees are Unum Corp. and L.L. Bean. Unum would have to pay roughly $7,000 a month for two properties it owns on Congress Street, while L.L. Bean would pay $9,882 a month for three properties it owns on Northport Drive.

Chris O’Neil, a municipal lobbyist for the Portland Community Chamber, said many in the business community were “incredulous” when the fee was first proposed in 2012, but the city’s process has allowed businesses to “take this large and bitter pill and get it down.”

O’Neil asked city officials to closely monitor the program, while seeking financial help from the federal government. “This is a (federal) mandate and an unfunded one,” he said.

The city has set up a website – www.cleangrowthcleanwater.com/calculator – that will allow property owners to see how many “monthly billing units” the city’s staff has estimated for each property based on impervious area – rooftops and pavement. Each billing unit is equivalent to $6, so a property with 3 billing units would be assessed $18 a month in fees.