Sanitary sewer overflows (SSOs) in Baltimore have been in decline for five consecutive years, falling 31 percent since Fiscal Year 2012, according to a review by the Baltimore City Department of Public Works (DPW).

In the fiscal year concluded June 30, 2017, Baltimore recorded 464 SSOs. That is down from 670 SSOs in Fiscal 2012.

SSOs happen when sewage escapes from a sanitary sewer pipe because 1) the sewage flow exceeds the pipe capacity, or 2) obstructions or blockages in the pipe such as tree roots or FOG (Fats, Oils, and Grease).

The first type of overflows typically occurs during and after rain events, when storm water enters the sanitary pipes through illicit storm-drain connections.  These are referred to as “wet weather” overflows, and have historically been less common than “dry weather” overflows, typically caused by obstructions or blockages in the line.

A more aggressive, proactive approach to clearing and preventing clogged sewer lines has dramatically reduced the number of dry weather overflows. DPW Director Rudolph S. Chow, P.E., established the Office of Asset Management in part to determine where the most significant sewer line blockages were occurring and to provide corrections wherever possible.

“We need to keep working to reduce sanitary sewer overflows, but I’m gratified to see our efforts being reflected in cleaner streets and streams,” said Director Chow. “Baltimore’s residents, and everyone who cares about public health and a clean environment, should feel good about this reduction in SSOs.”

Root control treatment, FOG education and abatement, correcting broken or sagging sewer lines, and other measures have reduced by 64 percent the number of dry weather overflows, from 524 in Fiscal 2012 to just 188 in Fiscal 2017. In the last two fiscal years alone, repeat dry weather overflows (those occurring in the same location) have been cut nearly in half, from 193 in Fiscal 2015 to 107 in Fiscal 2017.

Reports of wet weather overflows have increased during the same period, rising from 146 in Fiscal 2012 to 276 in Fiscal 2017. DPW began construction earlier this year on the Headworks project at the Back River Wastewater Treatment Plant, which when finished by the end of 2020 will restore the capacity of the sewer main leading to the plant and eliminate more than 80 percent of the volume of wet weather overflows.

Future improvements will include increasing the size of the pipes in some sections of the sewer collection system in order to increase capacity and reduce overflows. DPW is also working to identify and eliminate illegal connections that allow thousands of gallons of stormwater to enter the sanitary sewers, contributing to the overflows.