In today’s Academic Minute, Dr. Emily Elliott of the University of Pittsburgh explores aging sewer systems and reveals the threat they pose to the environment.
Emily Elliott is an assistant professor in the Department of Geology and Planetary Science at the University of Pittsburgh. Her research seeks to trace fluxes of reactive nitrogen through atmospheric, terrestrial, and hydrologic systems using isotope geochemistry. She earned her Ph.D. at Johns Hopkins University.
Dr. Emily Elliott – Environmental Risk from Aging Sewers
If you look at city landscapes with a critical eye, you may notice that urban streams are often piped underground so we can build on top of them. Sewers are also placed underground. The proximity of sewers and streams in these kinds of situations can create problems, particularly as sewers in urban centers age and begin leaking. These leaky sewers can contribute multiple pathogenic, chemical, and nutrient contaminants to the ground and surface waters in urban areas. There are 500,000 miles of sewer lines in the U.S., and many sewer systems are close to a hundred years old. This is potentially a large problem in urban areas; however we don’t have a good idea of how much the sewers actually leak.
Led by Marion Divers, a PhD candidate conducting her dissertation research in my laboratory, this study aimed to quantify how much nitrogen contamination was leaking from sewer pipes, ultimately affecting urban streamwater. The research was conducted in Nine Mile Run, a stream located in Pittsburgh, Pennsylvania that drains a 6-square-mile watershed. Nine Mile Run, like many urban streams, is largely buried in storm drains.
Our results suggest that sewers are constantly contributing nitrogen to streamwater during dry weather. They also send a mix of nitrate from sewage and other sources to streams during storms. In fact, calculations indicate that between 10 to 20 tons of nitrogen are contributed yearly to the Monongahela River from this small urban watershed. When you consider that all urban areas may contribute similar amounts of nitrogen, the potential cumulative effect from cities on water quality is enormous.
Pittsburgh is currently under a consent decree with the US EPA to eliminate sewage that is sent into streams during rain storms. However, because our data shows significant nitrogen consistently in streams during dry weather, eliminating nitrogen during wet weather events may not have the desired effect on river water quality.
The problem of leaking sewers is only going to get worse as our infrastructure ages.