In 1984 a superior court judge gave the state of Massachusetts a choice: commit to cleaning up Boston Harbor by modernizing an outdated sewer system or the Metropolitan District Commission (now known as the Department of Conservation and Recreation), which oversaw the Metropolitan Sewerage System (MSS), would be placed in receivership, under control of the federal government. Really, it wasn’t a choice so much as a threat. Regardless, it worked.
State lawmakers grudgingly created the Massachusetts Water Resources Authority (MWRA) that same year and gave the new agency a mandate of fixing the nation’s oldest sewer system to help bring the famously polluted Boston Harbor into compliance with federal water quality standards. Under court supervision, the MWRA developed a long-term plan to get Boston’s pipes in order. One of the primary targets was combined sewer overflows or CSOs.
When they were built during the late 1800s, Boston’s sewers were state-of-the-art. A unified maze of underground pipes collected wastewater from homes and businesses, and stormwater from street drains and directed it to Moon Island where it was released into the harbor during outgoing tides. As Boston’s population boomed in the early 1990s, this system quickly became a liability. Dumping untreated sewage into the harbor proved disastrous for local fisheries and shellfish beds, and the much of the waste came back up the Charles River (which had not yet been dammed) when tides came back in, causing significant public health problems.
As a remedy, several sewage treatment plants were built in the 1950s. But Boston’s extensive single-stream sewer system, once the envy of other major cities, proved to be a major hinderance. With wastewater and stormwater coming through the same set of pipes, treatment plants were frequently overwhelmed by unmanageable amounts of water, especially during storms and snowmelt.
CSOs were created to relieve the pressure on Boston’s sewers. CSOs are pipes that direct excess sewage to nearby waterways to prevent raw sewage from flowing backwards into residences and up storm drains. By 1987 there were 84 CSOs in the metropolitan Boston area, most of them along the Charles and Mystic Rivers. With an ever-growing population, the CSOs were in constant use, dumping over 7 billion gallons of untreated waste into local rivers in some years.
Getting CSOs under control in improving the capacity of treatment plants, officials hoped, would benefit the entire water system from the rivers all the way out to the harbor. The long-term control plan developed during the formation of the MWRA included 35 CSO improvement projects ranging from minor repairs to the development of new treatment facilities and storage tanks. A deadline of 2015 was set for completing them. 31 of those projects are now finished. According to David Kubiak, who manages the MWRA’s CSO program, three more are currently under construction and the final project is in development.
By nearly any measure, the program has been a major success. The amount of CSO discharges has been reduced nearly 84% and water quality has improved dramatically in the harbor and in other local waters. Yet even when the CSO plan is complete, Boston’s single-stream sewers mean that CSOs will likely remain part of the equation for the foreseeable future.