How Litter Enters Your Ocean: A Sewage Journey

San Francisco’s sewage and stormwater are treated together in a combined sewer system made up of over 1,000 miles of underground pipes. Combined sewer systems are rare, there are only 772 left in the United States, and they exist mainly in America’s oldest cities. San Francisco is one of two cities in California and is the only coastal city with such a system. San Francisco’s pipes are over one hundred years old and many sections are built of bricks that are fragile and in need of repair.

Aside from the potential problems summarized in San Francisco’s 2030 Sewer System Master Plan, the combined sewer system captures 90% of the sewer and stormwater on an average (non-rainy) day. This ends up being about 80 million gallons of wastewater per day. The wastewater is treated at two water treatment plants that pump the treated wastewater offshore from outfall pipe off the beach.  The California Regional Water Quality Control Board (Water Board) sets requirements for pollutant levels discharged into California waters. Through this process, the wastewater is filtered, meaning trash is removed prior to discharge.

Larger problems arise on rainy days when the combined sewer system, which can handle close to 500 million gallons per day, is stressed by large quantities of rainwater. Several stormwater holding tanks are located around the City that when pressed on rainy days will overflow directly into the Bay and ocean, carrying pollutants and litter.

An obvious technique to control the situation is to reduce stormwater entering the system. Surfrider’s Plant Don’t Pave Project encourages locals to replace non-permeable surfaces, mostly concrete with permeable surfaces. San Francisco Surfrider partners with the Friends of the Urban Forest on expanding efforts to grow native plants in areas that were once covered in concrete. Simply, if runoff and water use is reduced, less wastewater will be in the system hopefully prolonging and reducing overflow times, meaning less trash would flow out to the oceanic gyres.

Specifically, 10% of San Francisco’s stormwater is not pumped into the combine sewer system and covered under another Water Board permit. Because California does not yet have a state-wide limit for trash entering water bodies, trash particles that may be entering the ocean from these storm drains are not monitored, which is true in many coastal cities. On a positive note, 77 of San Francisco Bay’s municipalities are included in an impressive permit requiring trash levels entering the Bay through storm drains be reduced to zero by 2022. There are similar requirements on the L.A. River where trash reductions are required. The hope is state-wide policy requiring trash reductions will become reality in the next couple of years.

Until then, efforts that continue to show that beach litter is a significant problem will help support the needed state-wide policy to limit trash entering our oceans. Last Saturday, over 70 volunteers at the Baker Beach Cleanup were the first to log litter as part of our new effort to catalog  trash at our monthly beach cleanups. The test-run found students and families interested in participating in “community science ” and hundreds of extremely small pieces of styrofoam and over 500 cigarette butts were picked up by the group.

Carolynn Box, San Francisco Surfrider

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