Philadelphia’s “green” stormwater infrastructure management under fire as sewer overflows increase

(UI) – Philadelphia's "Green City, Clean Waters" program, launched in 2011, aimed to manage stormwater primarily through green infrastructure like rain gardens and porous pavements. This approach positioned the city as a leader in urban stormwater management, particularly as climate change has made heavy rainfall more common, according to Yale Environment 360.

However, with the increasing intensity of storms, critics argue that Philadelphia's reliance on green infrastructure alone is proving insufficient. Despite the initiative, sewer overflows have increased, with an average of 14 billion gallons of polluted stormwater being released annually.

In contrast, cities like Milwaukee, Boston, and Alexandria are adopting a more balanced approach, combining green infrastructure with traditional gray infrastructure, such as underground pipes, tunnels, and holding tanks.

Milwaukee’s Metropolitan Sewerage District, for example, uses both systems, but its gray infrastructure, including storage tunnels and tanks, has been most effective in reducing overflows into Lake Michigan. These stormwater systems can handle up to three inches of rain, whereas green infrastructure can only manage about half an inch.

Boston is gradually separating stormwater from sewage lines to reduce overflows into local waterways. The city is also using partial treatment facilities to screen and disinfect stormwater before it’s discharged. Currently, the city is revising its long-term control plan to reflect projected increases in rainfall by 2050.

In Alexandria, Virginia, a new $615 million underground wastewater tunnel is being constructed to reduce sewage overflows into the Potomac River. This tunnel, designed to handle future increases in rainfall, will significantly cut the number of annual overflows from 70 to just four once completed.

Washington, D.C., is also making significant investments in stormwater management, with an 18-mile underground tunnel network under construction to hold 249 million gallons of stormwater and sewage. This $3.29 billion project, which incorporates a small amount of green infrastructure, aims to reduce overflows by 96% once completed later this decade.

Philadelphia’s Water Department acknowledges the growing challenges posed by climate change, projecting a 9.5% increase in annual rainfall by 2050. However, the department is hesitant to adjust its Green City, Clean Waters plan until more long-term data is available.

This story was originally reported by Yale Environment 360. 

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