Hey, there! Log in / Register

Rain overwhelms sewer system; raw sewage released into Charles, Mystic, Boston Harbor

Maps showing where raw sewage flowed into the Charles, Mystic and harbor.

Brown indicates raw sewage, blue means treated sewage, green means no sewage released.

The MWRA and the Boston Water and Sewer Commission are reporting that "combined sewer outfalls" dumped raw and treated sewage, along with lots of rainwater, into area waterways overnight because of all the rain - but that the flow means people didn't have to worry about sewage backing up into their homes and businesses.

The MWRA explains:

A combined sewer overflow (CSO) occurs when a large storm overwhelms the sewage system causing rainwater to mix with wastewater and discharge to a nearby water body. This relief measure prevents sewage backups into homes and businesses.

The first overflow started at 6:55 p.m. on Wednesday at a pipe into the Mystic in Somerville.

On the off chance you were thinking of going for a swim in one of the rivers or the harbor, the MWRA advises: Don't. At least not for a couple of days.

The MWRA says it's too early yet to say just how much sewage was released into the Charles and Mystic rivers, Alewife Brook and directly into Boston Harbor. It adds that it only tracks releases from its own pipes; Boston, Chelsea, Cambridge and Somerville have their own outfall pipes as well.

BWSC reports most of its CSOs, along Boston Harbor and the Muddy River released sewage into the waterways as well (gold or red on the map indicates overflows):

BWSC overflows

Via Tom.


Like the job UHub is doing? Consider a contribution. Thanks!



Voting closed 33

Damned if you, damned if you don't here - sewage into the river or sewage into people's homes and businesses. As bad as this is, Boston and the metro area are in a better position than other major coastal cities (hello NYC) because we've maintained our storm water and sewer infrastructure very well, mostly because they are run by professionals and not politicians here.

Voting closed 6

Maintained? Perhaps. But most municipalities are dealing with systems that were built in a time when downpours were infrequent, not common.

Your characterization of "in the river or in the street" is a false dichotomy, too. That's not how CSOs work. The problem is that we combine storm water with sewage for a number of historical and logistic reasons. Stormwater overruns the sewage system and that's why it is vented to the rivers. If the sewage ran in its own pipes, it wouldn't be an issue. Some communities have storm overflows that are not bearing sewage.


Because we live in an already humid summer climate and because warmer air holds more water, there has already been a 71% increase in downpour events in the Northeast since the 1950s (source: 2014 National Climate Assessment). Increases in frequency and intensity of downpours mean that our cities and towns are experiencing more flooding not associated with rivers and streams, and seeking state money to study and upgrade their systems.

At least we live in a state that believes in climate change and is doing something about these local and regional issues. Check out how many local MVP Action Grant Projects are dealing with street flooding, discharges, and sewers.

Voting closed 5

It may be worth noting that code now says you can't route your gutters and drains directly into the sewer system. In this picture, the down spout combines with the building sewer connection. That's a no no now.

Many old houses still do that, until they are found out.

Now the gutters and drains are supposed to go out on the lawn and be absorbed into the soil (good luck with that) or eventually into a separate sewer for runoff.

Right now the water table is very high here. Even though the rain last night was much less than expected. you'll be seeing a lot of water in basements, because the water table is getting all the way up to the basements.

As Swirly points out, this may be one of the rainiest summers in Boston history (more rainfall so far this year than in all of 2020), but that may the future we're looking at here.

Voting closed 35

Now the gutters and drains are supposed to go out on the lawn and be absorbed into the soil

This is an example of why “one size fits all” regulation is so annoying. My house, like pretty much everyone else’s in my neighborhood, is built right to the lot line on 3 sides and has a 10 foot setback in the rear. The soil in my area is a hard, high clay aggregate with all the absorbency of concrete. A drywell is impossible. Disconnecting my rear downspout from the sewer connection and dumping the runoff onto the ground would flood my downhill neighbor. Disconnecting my front downspout from the sewer and dumping the runoff onto the sidewalk would probably bring me technically into compliance, but the water would simply run 10 yards down the hill and into the storm drain, where it would end up right back in the sewer. My street doesn’t have a separate storm sewer.

Voting closed 24

Thanks to our watershed organizations and environmental and health equity groups and legislators, we now have a law that makes the state publicize these events and post signage.


This is also another reminder: DO NOT PLAY IN THE FLOOD WATER. If you don't have to come in contact with it, stay out of it. Do not let your kids or pets play in flood water, either. Even where there are no CSOs or sewers, septic tanks contribute their share.

Voting closed 5

In the city of Boston, I was under the impression that most storm drains (on the street) drain in a system that is normally separate from the sewage coming from peoples houses. As I understood it, they get combined when there is too much storm water, but normally they are kept separate. Is this false?

Voting closed 18

BWSC is systematically separating the systems, but they are not quite done yet:

The Sewer System
The City is served by two types of wastewater collection systems: separated and combined.

A separated sewer system is comprised of sanitary sewers and storm drains. Sanitary sewers are designed to transport only sanitary flow, whereas storm drains are designed to transport stormwater flows

A combined system performs the dual function of transporting sanitary flow as well as stormwater runoff in one conduit identified as a combined sewer. This type of system is common in older cities

Currently, BWSC’s Engineering Department replaces combined sewers with sanitary sewers and storm drains each year to reduce the amount of combined sewer pipe in the system.

Note that the MWRA discharges are largely regional in nature - they have to do with overflow in regional infrastructure carrying combined sewer and stormwater from all the MWRA communities, not just Boston.

Source: https://www.bwsc.org/environment-education/water-sewer-and-stormwater/se...

Voting closed 35

All of Greater Boston has had work ongoing to separate the storm sewers and the sanitary sewers. And it's worked really well! The number and severity of CSOs has decreased dramatically! That's a big reason why the Harbor and Rivers are generally pretty clean now. Not everything has been separated though, so when we get large rain events (like a hurricane) the sanitary system can still be overwhelmed.

Voting closed 28

Note that cities and towns are in the midst of a multi-decade project to address this problem. The typical scheme is to separate the sewers and storm drains. It’s a huge expense and disruption, involving digging up every street in a neighborhood for months.

Another scheme involves underground holding tanks that can contain storm water until the sewer system is able to handle it.

All this effort is worth it. There are just a fraction of the outfall pipes compared to the early 80s, and the remaining ones have overflow events much less often.

Voting closed 40

Yep! Deer Island got the most attention, but the Sludge Judge also made the state (eventually, the MWRA) do something about these CSOs; in turn the MRWA made its cities and towns fix their own CSOs. Boston's done a ton of work to end raw sewage flowing into the Charles and the harbor (most notably from Stony Brook).

Voting closed 27

Magoo went for a paddle up the mystic this morning after the rain. This report explains to Magoo what Magoo thought he saw were bebe alligators. Turns out what Magoo saw were hoo-man turdigators. Magoo.

Voting closed 19

And you were expecting . . .

Voting closed 8

The system works as designed and installed. Next you'll be complaining about road salt runoff.

Voting closed 3