PORTLAND — Owners of large properties with expansive roofs, paved parking lots and other impervious surfaces will bear the economic brunt of a proposed plan to fund storm-water treatment efforts in the city.

By January 2016, residents and business owners could be assessed a $6-per-month fee for each 1,200 square feet of impervious surface. The plan, introduced to the City Council Finance Committee on Aug. 21, will require council approval to be enacted.

As drafted by the 12-member Sustainable Stormwater Task Force, which includes Casco Baykeeper Joe Payne; Fred Dillon, who also serves as storm water coordinator in South Portland, and Bill Bennett of Oakhurst Dairy, the plan will reduce sewer fees by $1.50 per hundred cubic feet, to $8.20.

As outlined on the city website, the proposed service charge is viewed as a way to assess the cost of continued sewer separation and storm-water treatment projects more equitably, while assuring the city complies with state and federal clean water regulations.

Property owners could get credits against the fee by reducing impervious surface, adding rain gardens or detention ponds, or taking other steps to reduce the flow of storm water.

The charge would be assessed to all private and municipally owned properties, while exempting all Casco Bay islands except Peaks, and all properties of 400 square feet or less. Municipal roads, railroad tracks and the Portland Jetport runways would not be assessed the service charge.

If the service charge is approved, property owners will be directly billed by the city, as opposed to the current inclusion of fees in waste-water billing by the Portland Water District. The city will use aerial photographs of properties and round up to the nearest increment of 1,200 square feet to calculate the fees.

The task force estimated 400 million gallons of combined sewage and runoff was dumped into local streams and Casco Bay in 2011, frequently because storm and waste-water flows through the same sewers to the PWD treatment plant near East End Beach and can overwhelm the system during heavy storms.

Projects to redirect storm water directly to Back Cove or Casco Bay are ongoing, and included last year’s extensive work along Baxter Boulevard. In the next year, sewer separation projects are planned for East Bayside near Anderson and Fox streets.

The city has 133 miles of combined sewer pipes and 62 miles of sanitary sewer pipes, and the task force estimated sewage pollution of Casco Bay and other waterways has been reduced by 42 percent since 1993. About 20 miles of combined sewer pipes have been replaced, but future demands remain expensive.

An estimated $15 million to $20 million is spent annually to maintain and upgrade waste water systems, according to the task force. But city officials forecast that $60 million will be needed by 2030.

Planned upgrades include expansion of the treatment plant on East End Beach, constructing facilities at Back Cove and on the west side of the peninsula “to store 15 million gallons of polluted runoff for treatment,” and repair and expansion of catch basins, detention ponds and manholes throughout the city.

Storm-water fees have been assessed throughout the country since 1974, according to the Ellicott City, Maryland-based nonprofit Center for Watershed Protection.

The first was instituted in Washington state. A storm water fee was enacted for the 10 most populous cities and counties in Maryland in 2012.

David Harry can be reached at 781-3661 ext. 110 or [email protected]. Follow him on Twitter: @DavidHarry8.

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