Unique Long-Term Study Finds Sewer Overflows, Stormwater BMPs Have Greatest Water Quality Impacts in Gwynns Falls Watershed

Baltimore Sun article (2018-04-16) reported on a recently released study quantifying pollution sources and clean-up efforts in the Baltimore City and Baltimore Count Gwynns Falls watershed. The study was compiled by the United States Geological Survey (USGS), in partnership with Blue Water Baltimore and the Cary Institute of Ecosystem Studies. The study tracked water quality in the 171 square kilometer watershed from 1998 to 2016.

Source: USGS

The study is unusual in that it was able to analyze 20 years of water quality data for an urban area (something that does not exist for many urban environments areas) and pinpoint both water pollution sources leading to watershed degradation as well as the positive effects of various kinds of watershed restoration projects. The study factored in climate change and the increased precipitation the watershed has received over time.

The study found that a major contributor to watershed degradation was sewer overflows while the installation of stormwater best management practices (BMPs) likely have a positive effect on water quality. From the study:

However, sanitary sewer overflows and best management practices, are factors that appear to affect the water quality at Carroll Park, the most downstream location monitored in the Gwynns Falls watershed. The increasing duration of sanitary sewer overflows was related to increasing loads and concentrations of nutrients; sanitary sewer overflow volume was related to total coliform levels. In contrast, installation of  structural best management practices appears to be related to declines in phosphorus. These outcomes, while preliminary, indicate that current efforts and investments in gray and green infrastructure improvements likely positively affect the water quality of the Gwynns Falls watershed. Further, this study has established a framework to evaluate the effect of future gray infrastructure repairs in accordance with the Baltimore City and County Consent Decrees and green infrastructure installation.

Additional comments provided by the Sun article:

“We’ve known a long time, sewage bad, stormwater projects good,” said Alice Volpitta, water quality manager for Blue Water. “Now we can say with scientific certainty that that is the case, and that carries a lot of weight.” …

“This is the first time with statistical accuracy we can say sewage is really detrimental to water quality,” Volpitta said.

Peter Groffman, professor at the City University of New York Advanced Science Research Center and a senior research fellow at the Cary Institute of Ecosystem Studies in New York, said long-term data “is the only way to know for sure whether our investments in clean water infrastructure are working.”

“Even with 20 years of water quality data, we are just beginning to see the long-term effects of sewage overflows and water main breaks, along with the stormwater projects that are designed to address polluted runoff,” Groffman said.

Useful Links

USGS 2018 Report: Factors Affecting Long-Term Trends in Surface Water Quality in Gwynn Falls Watershed