Baltimore’s Sewage Problem and its Effect on Local Waterways

Gabriel Watson
Common Syndicate
Published in
5 min readJan 21, 2020


When heavy rains fall in Baltimore, the City’s antiquated sewage system causes overflows into residents’ homes and contaminated waterways across the city. Using data from Blue Water Baltimore (BWB), Maryland Department of the Environment (MDE), US Geological Survey (USGS), and the National Oceanic and Atmospheric Administration (NOAA), we can follow the story from raindrop to overflow and beyond.

Precipitation daily total, Baltimore Washington International Airport, July 8th 2018 — Aug 6th 2018, NOAA. Created by Chesapeake Commons.

In 2018, from July 16th to August 1st, Baltimore Washington International Airport’s rain gauge recorded an incredible 16 inches of precipitation, representing 22% of 2018’s record breaking rainfall (71.82 inches). The USGS Jones Falls outlet monitoring station (home to Baltimore’s beloved Mr. Trash Wheel) recorded an average discharge rate of 262 CF/s (cubic feet per second) for the month of July, more than double the yearly mean of 102 CF/s. Impervious surfaces such as parking lots and rooftops do little to delay the onslaught of water. While precipitation rapidly sweeps lawn fertilizer and motor oil into Baltimore harbor tributaries, it also infiltrates sewage infrastructure through cracks and broken pipes. The intense influx of stormwater into the sewage system exceeds Baltimore’s processing capacity, causing sanitary sewage overflows (SSOs).

Daily Sanitary Sewage Overflows (SSOs) across Baltimore — displayed month by month, Maryland Department of Environment. Created by Chesapeake Commons.
SSO daily total, Baltimore City, July 8th 2018 — Aug 6th 2018, Maryland Department of the Environment. Created by Chesapeake Commons.

During the same 21 day period, data from Baltimore City shows the dilapidated sewer system overflowed an estimated 85 million gallons. Over 128 Olympic-size swimming pools worth of sewage and stormwater backed up into residents’ homes, flooded through manhole covers, and poured into streams via structured overflow mechanisms. With the contaminated stormwater came potential disease-causing bacteria like E Coli, and Enterococcus.

SSO in Baltimore — Aug 2018,

Contact with water containing over 150 CFU/100ml (colony-forming units per 100 milliliters) of Enterococcus is considered high risk by the State of Maryland and can cause a variety of illnesses, including West Nile Virus, gastrointestinal infections, and Staphylococcus. Public health researchers in Massachusetts found an association between emergency room admittance for gastrointestinal illness and the number of SSOs that occurred 14 days prior. Using water quality monitoring data, we can begin to understand the relationship between precipitation intensity, SSOs, and bacteria forming colonies.

Between July 16th and August 1st, BWB collected 19 samples, eight of which had measurements of Enterococcus greater than 130 CFU/100ml — a moderate risk exposure threshold used by BWB. Six of these samples measured 2,400 CFU/100ml, more than 18 times the contact threshold. Surprisingly, just a week later on August 7th, all tested monitoring sites showed levels well below the 130 CFU/100ml threshold.

Percent of Stations Over 130 Enterococcus CFU/100ml (weekly average), July 12th 2018 — Aug 7th 2018, Blue Water Baltimore. Created by Chesapeake Commons.

This rise and fall in CFUs is indicative of bacteria’s complex and understudied lifecycle in our urban waterways. Capturing these relatively short spikes in bacteria levels with monthly or bi-weekly data is difficult. Increasing data granularity with daily water quality monitoring would help researchers to better understand these relationships. Additionally, data on SSOs from Baltimore is significantly underreported and generally unreliable. Without quality data, researchers are unable to fully understand the mechanisms at play. Recent research has shown promise in predicting bacteria levels using analytical techniques like Bayesian Belief Networks and regression analysis. These techniques can help public health officials preemptively alert residents to dangerous levels of bacteria before contamination.

Efforts to stem the flow of sewage have been underway since 2002, when the EPA and the Maryland Department of the Environment sued the City of Baltimore for severely neglecting its one-hundred-year-old system. The resulting consent decree forces Baltimore to increase its combined sewage and stormwater processing capacity via the $430 million Back River Waste Treatment Plant Headworks Project.

Back River Wastewater Treatment Plant, Baltimore City.

The project aims at fixing a miles-long sewage backup emanating from the Back River Wastewater Treatment plant. The upgrade in capacity is estimated to stem 80% of overflows. Additionally, the City will replace clogged and broken pipes, close structured overflow sites, and reimburse residents for costs associated with overflows. Baltimore City was given a deadline of 2016 along with mandatory reporting guidelines and fines of up to $10,000 for overflowed sewage. The City failed on multiple counts to meet the goals laid out in the 2002 consent decree, and an updated consent decree was written in 2016 with a Phase 1 deadline of 2021 and Phase 2 completion by 2030.

Modified Consent Decree Timeline, Baltimore City.

Following the story of rainfall through Baltimore’s urban ecosystem elucidates the challenges faced by city officials, public health professionals, and conservationists. Baltimore’s once state-of-the-art sewage system has succumbed to the tenacity of nature and the consequences of poor public policy. Progress is underway; however, further data collection and research is necessary to better understand the complex social-environmental relationship between public works infrastructure and our natural waterways.

In the graphic below, click and drag the time slider to show precipitation, SSOs, and bacteria at the same time. For example, select the timeframe between July 1st, 2018 and September 1st, 2018 and examine the close relationship between precipitation and SSOs and the lagged response in bacteria levels. You can also select the timeframe using the three metrics; however, the selected metric will remain fixed in time. To reset, click the whitespace in your chosen metric.

Precipitation, NOAA | SSO, Maryland Department of Environment | Enterococcus CFU/100ml, Blue Water Baltimore, Jan 1st 2016 — December 31st 2018. Created by Chesapeake Commons.

Interested in more? Check out these resources:

Chesapeake Common’s SSO map 2016-2018.

Blue Water Baltimore’s Baltimore Water Watch.

Environmental Integrity Project’s SSO map tool 2011-2015.

Baltimore City’s SSO map.