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Using Green Infrastructure To Manage Combined Sewer Overflow (CSO)

Learn how governments and municipalities are striving to reduce the CSO discharges to local bodies of water using green infrastructure.
Combined Sewer Overflow

It is safe to say that engineering design standards for routine rainfall events are adequate.  City populations are growing and the demand for pollution mitigation and effective infrastructure are begging the question – how do we prevent future environmental and infrastructure disaster? WGI explores using green infrastructure to manage Combined Sewer Overflow (CSO).

American cities have experienced major storm events resulting in infrastructure malfunctions and water quality snafus for combined sewer systems.  Combined sewer overflow (CSO) is the “discharge from a combined sewer system that is caused by snowmelt of storm water runoff” (DECNY, 2016).  Governments and municipalities are striving to reduce the CSO discharges to local waterbodies.

Why all the fuss over CSO discharges?  “Treatment plants are unable to handle flows that are more than twice design capacity… when this occurs, a mix of storm water and untreated wastewater discharges directly into the City’s waterways” (NYCEP, 2016).  I hope my audience agrees, but I certainly hope to keep local waterways as clean and protected as possible.

How does this affect America’s fastest growing cities?  It is imperative that infrastructure keeps up with population growth.  As a new generation that prides itself on environmental awareness, we must consider steps to implement new infrastructure to prevent the adverse effects of CSOs.  Ultimately, this will improve water quality and associated environmental conditions of our local waterbodies.

What can be done to avoid future conundrums?   The implementation of green infrastructure can be used to prevent storm water from entering a City’s sewer systems.  Green infrastructure examples include bio-swales, green roofs, and rain gardens.  Other options include upgrades in wastewater treatment facilities, storm sewer expansion, and CSO retention tanks to mitigate future pollution.  These types of green and conventional source controls act to “detain or retain storm water runoff though capture and release, infiltration into the ground, vegetative uptake and evapotranspiration” (NYCEP, 2016).  Upfront, green infrastructure can reduce the need for storm water storage and treatment systems – which is a plus for “afterthought” or “uh-oh” costs (both environmental and monetary).

Mother Nature will take its course and human nature is a challenge to influence; by changing the nature of how we adapt our infrastructure solutions, we can avoid environmental problems caused by CSOs.


  1. Combined Sewer Overflow (CSO). http://www.dec.ny.gov/chemical/48595.html: DECNY, March 29, 2016
  2. Combined Sewer Overflows (CSOs) http://www.nyc.gov/html/dep/html/stormwater/combined_sewer_overflow.shtml: NYCEP, March 29, 2016

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