Seattle next year will begin a much more aggressive street-cleaning program as it attempts to keep more pollutants out of Puget Sound.

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Copper, zinc, phosphorous and other pollutants build up on Seattle’s streets before rain washes them into storm drains and waterways that lead to Puget Sound. During heavy rains, the sewer system fills up and the problem can worsen.

As a solution, the city plans to double the coverage of its street-cleaning program, hoping to scour at least 40 additional tons of pollutants from roadways each year before they can reach the Sound.

The $800,000 street-cleaning expansion — meant to help satisfy a consent agreement with state and federal authorities to rein in combined sewage overflows — also is the frugal way to go, officials said.

“If you can remove the pollutant before it gets into water, it’s cheaper,” said street-cleaning program manager Shelly Basketfield. “Once the pollutant is in the water, you have to treat all the water.”

This expansion would bring the number of annual miles covered from 10,000 to 20,000, with the goal of increasing the collection of pollutants from about 100 tons to 140 tons a year or more.

The program cost $1 million for 2015, according to Seattle Public Utilities (SPU) spokesman Andy Ryan. Expanding it will bring that expense to $1.8 million for next year.

The project won’t start until January, Basketfield said. This gives SPU and the Seattle Department of Public Transportation, who partner on the program, enough time to plan the new routes, hire more operators and get new equipment.

“One of the big things we’re working on right now with the program is developing routes so that each route … will be swept in the most cost-effective way,” Basketfield said.

Focus on arterials

The street-cleaning program focuses its efforts on arterials: city streets that have a high volume of traffic, such as Aurora and Rainier avenues and Martin Luther King Jr. Way. Most of the sweeping work is done at night.

Under a consent agreement by the city with the Environmental Protection Agency and the Washington state Department of Ecology, Seattle must control 34 out of 86 outfalls that discharge to waterways, Ryan said.

According to the release, street-cleanup programs can cost four to 10 times less than conventional water treatment.

The city started its street cleaning as a pilot program in 2011. Since then, SPU and SDOT have collected data on its effect on removing pollutants from water.

“We have been able to show definitively that street sweeping is one of the most cost-effective measures we can use to protect our waterways,” Basketfield said.

The cleaning program is just one aspect of the greater Protect Seattle’s Waterways plan, approved by City Council last month. The $600 million, 15-year plan aims to reduce the amount of pollutants flowing onto Seattle’s bodies of water to comply with state regulations and the federal Clean Water Act.

Funding for Protect Seattle’s Waterways is scheduled for discussion by City Council next week, Ryan said. SPU is proposing to fund it through an increase in drainage and sewer rates. If approved, average monthly residential bills would increase by 6.4 percent in 2016, according to an SPU release.

The program falls under SPU’s business plan that the council approved last year, which aims to bring the average rates of all SPU services to an annual average of 4.6 percent through 2020. Average combined rates will jump from 2.9 percent this year to 4.1 percent in 2016, Ryan said.

Other projects under Protect Seattle’s Waterways include a sewage-overflow storage facility that will start construction in 2018. The project is 2.7 miles long and will be located between Fremont and Ballard, on the north side of the ship canal, according to an SPU release.

Seattle Public Utilities has spent $130 million in combined sewer overflow reduction since 2010, according to an April presentation to the Seattle Public Utilities and Neighborhoods Committee.

Sewage overflows have been an issue for Seattle and King County since the turn of the decade. Past reports by The Seattle Times have questioned whether sewage overflows are the biggest source of pollution for Seattle’s bodies of water.

Source under debate

The Puget Sound Partnership, the state agency charged with cleaning up and restoring Puget Sound, in 2011 said surface runoff, not sewage overflow, is the biggest source of pollution to the Sound. The city’s projects are additional to King County’s own individual combined-sewer overflow (CSO) projects.

Ryan said the story led SPU to focus on cleaning land surfaces rather than later treating water.

“Is spending all these hundreds of millions of dollars on CSO cleanup as effective as possibly affecting stormwater? The answer is complicated,” he said.