Two property owners asked the City Council’s Finance Committee on Thursday night to come up with more ways to lessen the blow of a proposed stormwater fee that could take effect in 2016.

The proposed fee is designed to provide funding for $170 million in projects over the next 15 years to reduce polluted runoff from entering waterways such as Back Cove and Casco Bay.

The new fee would be assessed on the amount of hard surfaces such as pavement, compacted gravel or rooftops on a property. Roughly 85 percent of the city’s property owners would be charged $6 to $18 a month, while seeing reductions in their sewer bills.

Ian Houseal, the city’s sustainability coordinator, said the proposed fee is designed to spread the cost of upgrading the stormwater system to comply with state and federal environmental regulations, including the Clean Water Act.

Current funding mechanisms, such as property taxes and sewer fees, would exempt a significant number of properties, placing a greater burden on residential property owners.

“This would bring in more properties that would be paying,” Houseal said, citing nonprofits that don’t pay property taxes and parking lot owners, who don’t have sewer accounts.

Among the property owners faced with some of the largest fees are Unum Corp. and L.L. Bean. Unum would have to pay roughly $7,000 a month, or $80,000 a year, for two properties it owns on Congress Street, while L.L. Bean would pay $9,882 a month, or $118,584, for three properties it owns on Northport Drive.

Roads and island communities that are part of Portland, except Peaks Island, would be exempt from the fee, but city-owned buildings and schools would be subject to the fees. Houseal said that is expected to cost $400,000 a year.

Houseal said the city will offer credits to property owners who try to reduce runoff by building rain gardens, dry wells or retention ponds. “It is possible to eliminate this fee entirely if you are motivated,” he said.

The Finance Committee held a public hearing in October, and has discussed the proposed fee at neighborhood meetings. The committee must approve the proposal if it is to be taken up by the council. No date was set for that vote.

Although a dozen people attended Thursday’s public hearing, only two property owners spoke.

James Grattelo, president and co-owner of Joker’s Family Fun and Games on Warren Avenue, said he anticipates $17,000 a year in new fees. He criticized the road exemption, because downtown merchants, whose customers park on the street, would not have to shoulder any costs. “I understand we need to clean up Casco Bay, but I think someone needs to go back to the drawing board and they need to be able to spread this fee throughout the city,” he said, noting that he maintains a 300-car parking lot.

Grattelo asked the city to consider providing no-interest loans to property owners who want to upgrade their property to eliminate stormwater runoff altogether. He estimated a retention pond would cost $50,000 to construct.

Paul Pappas, who represented Pende Associates Inc., which owns property on Riverside, said the company could be charged $10,000 a year even though not contributing to the stormwater problem. The properties get their water from a well, have a septic system, and stormwater flows to a grassy 10-acre parcel, he said.

City officials said they would work with concerned property owners.

Stormwater fees are not new to Maine or the United States, but have been contentious. City officials already have recommended setting aside $50,000 to cover potential legal challenges.

The city has set up a website, www.cleangrowthcleanwater.com/calculator, that will allow property owners to see how many “monthly billing units” staff have estimated for each property.