Deer Island Water Treatment Plant

On Tuesday the 8th of August, I had the opportunity to tour the waste water treatment plant on Deer Island.  This is a tour that is available to anyone who wants to go (after a security clearance) and I happened to be lucky enough to join a group put together by the Metropolitan Area Planning Council.


Security checkpoint for entry into the water treatment plant


Beautiful views back towards Boston from Deer Island.

So warning – this is going to be TLDR for most people.

I had caught a reference to Deer Island on the whale watching tour day – I was on the top deck in the wind so I caught “something-something-something essential harbour clean-up something-something-something” and looked it up a bit later to find out that there’s a whopping great water treatment plant on Deer Island that’s treating a whole bunch of the sewerage (and some storm water) from across a large chunk of greater Boston. It’s managed by the Metropolitan Water Resource Authority (MWRA).

Deer Island is connected to the mainland by a very narrow strip of land that according to Wikipedia, was deposited in the channel during a hurricane in 1938. In the rather marvellous scale-model of Boston circa 1900 it is a distinct island.


Model of Boston and surrounds, circa 1900. Displayed at the Paris World’s Fair in 1900. Sorry for the lack of oomph – we weren’t supposed to be taking photos inside at all, but this was too cool to not sneak out the camera.

There’s been a water treatment plant of some description on Deer Island since the late 1800’s. There’s also been a hospital and a prison.  A ‘modern’ water treatment plant was built in the 1960’s. By modern, I mean they were dumping primary processed sewerage directly into the harbour for nearly 30 years and by all accounts the harbour looked and behaved like an ecosystem that was getting a couple of million people’s worth of barely processed sewage dumped in it. The diagram of the old plant make it look like the outfall pipes were maybe 400m long (Wikipedia says 30 feet). I have to assume that falling into the harbour was a guaranteed trip to hospital and that no-one in their right mind would swim or paddle in it.  And yes, prior to this, it was raw sewerage going directly into the harbour. But you know – with the outgoing tide!  So there’s that.

Side-note – apparently the lobster catch in the Harbour fell off in the mid-1990’s. Eww.

The legislative history of the water treatment plant is really interesting to me and I’d love to have a bit more time (or to find the book that has undoubtedly already been written) about the process of developing and implementing the 1972 Clean Water Act and how on earth they managed to fund it.  This is a nice summary of the law, but the story behind it remains opaque to me.

Of course, the 1990’s facility at Deer Island was not constructed with Federal Funding.  According to the tour, Boston applied for waivers when the Act first went through – I guess because the treatment plant was only a few years old.  But they were still not complying with compulsory secondary treatment more than a decade later and sludge finally stopped being dumped in the harbour 19 years after the Clean Water Act went through.

The MWRA came into existence pretty much perfectly in time to get smashed with a lawsuit regarding compliance with the Act. There are a number of plaques around the island commemorating Judge David Mazzone, who ruled in 1985 that the Water Treatment Plant had to comply with the Clean Water Act. He then oversaw the Boston Harbor Project for nearly 20 years.  As someone who has spent a chunk of the summer swimming on the beaches and watching the wildlife in the harbour – thanks Judge!


Judge Mazzone. A pretty cool dude.

This treatment plant is apparently the second largest in the USA. There’s one in Chicago(? or Detroit?) that’s bigger, but this one is almost unimaginably huge. They average more than 1 gigalitre of sewerage per _day_. And given that they take the storm water from Cambridge and Somerville as well, their max capacity is over 4 gigalitres per day and very occasionally in big storms, they can’t keep up with the volume coming through.

Interestingly, the volume of water coming through the system continues to drop and there are now and will likely continue to be difficulties with there being sufficient flow in the system. So somewhere under the city right now there is probably a stagnant lake of raw sewerage that’s just getting larger over summer.  Eww. Sorry for that.

Distraction – a couple of older people in the group were like ‘AHA! AND THAT IS WHY GREYWATER RECYCLING IS A STUPID IDEA!” which… what? I mean, I understand how their thought processes went, but personally went to ‘Are we gonna have to replumb the city or encourage excess water use? How much is this going to cost us?’

And given what was said about the delicacy/touchiness of the hydraulic balance of the system through Cambridge and Somerville, at some point there may have to be some consideration of putting tertiary treated water back through the system to keep things moving, given that it will probably be much cheaper and less disruptive to do that than to try and put a new sewerage system in (my thoughts, not thoughts from the MWRA).

Anyway, so that is an enormous enormous, enormous amount of sewerage to be dealing with everyday.  There are headworks at Nut Island in Quincy and also on Deer Island and in a few other places, but all of the primary and secondary treatment for more than 2.5 million people is done on Deer Island.

We weren’t allowed to take photos inside the facility, sadly, or I would love to show you the piping galleries with the markings for all the various things that are being piped around. I really thought that Rachel W would have loved it. Pipes and valves and chains hanging from valves everywhere, along with a fairly standard set of re-use of waste products. It looked neat and pretty to me, but I would have appreciated an expert piping opinion!

They’re using anaerobic digestion for primary treatment, then piping that primary sludge (back under the harbour) to a plant in Quincy that makes Baystate Fertilizer.  The methane is collected and goes to a heating plant that both generates some of their power and acts as a water heating device – the water is then used to manipulate the temperature of the digester feeds and incidentally as the emergency showers and eye-wash stations.


Huge egg-shaped digesters. The digesters themselves are quite a bit smaller and perched inside and partially below these shells>

Attached to the whole system is an odour control system that grabs the sulphides through some base chemical supplies (can’t remember what now) and then uses pretty standard carbon scrubbing methods to grab the post-digestion asphalt-y smell.


Odour control – code pink 🙂

Then it’s off to the secondary processing for an aerobic treatment with pure oxygen. The pure oxygen is also made on site in a cryogenic facility. Then clarifiers, chlorination and dechlorination and into the outfall pipe to head 15km out to sea for diffusion in Massachusetts Bay.


Oxygen input into the secondary processing system, which consists of fully enclosed double-stacked tanks underneath us.



Chlorinate the little bastards to death! 15 minutes by regulation. Wind turbine in the background is a test-model.


Seafloor diffuser. Obviously not on the seafloor. They have to maintain enough flow through these things that shellfish don’t decide to start growing in them (which they would, because there’s still yummy stuff in the processed water).

Another side-note – there is a memorial to the people who died while digging the tunnel. Our guide wasn’t entirely sure if 3 or 4 people had been killed on the job, but noted that the rate was substantially lower than the average tunnelling deaths in the USA, which is approximately one person dying per mile of tunnel constructed. I have no idea how this compares to tunnelling deaths in Australia (or indeed around the world), but that seems ridiculously, unreasonably high to me. Surely we have learned how to do this better.  Surely.


Memorial plaque on the diffuser.

They get about 90% of the stuff out of the sewerage before release and the water is clear and seaweed and suchlike are growing quite cheerfully in the outlets. They test for bacteria, though I don’t think that anything would stop if bacteria levels were breached. Maybe they could pipe it around again to the chlorination tanks (I’m not sure, as I didn’t get a chance to ask). They track the Nitrogen and Phosphorus levels but are not required to do anything about them at this point in time.



And away she goes into the outfall tunnel.

The Deer Island site is absolutely packed. They haven’t needed to build one of the secondary reactor and clarifier modules, so they have a little space to move.  They are clearly anticipating that at some point the EPA will require tertiary processing of sewerage and they’ve decided not to try and unlink the storm and sewerage system in the north-of-the-Charles section of the system, as there’s a good chance that storm water will at some point in the near future be subject to at least some treatment requirements.

The overview of the plant and the tour took about 2.5 hours, with an hour of that being a gallop (and seriously it was a gallop) around the site itself. I think at least another 45 minutes needs to go into the actual site tour, but they did give us the Program Manager of Process Operations for the session, so that may be a bit too much of an ask for that length of time.

I found it really interesting and I would recommend anyone who is vaguely interested in how their city works to come and have a look.  I would have loved to have had a chat with MWRA strategic planners about what regulatory changes they are expecting and what changes they want. MWRA is a rates-funded organisation and I don’t know what formula is used to determine how rates are set and that would also be of interest to me.

You can have a giant roam around the MWRA website here – There compliance conditions include a whole range of transparency measures for monitoring and public reporting on bacteria etc, more detail on the Harbour Project and a whole bunch of stuff around water supply that I’ve yet to read in any detail.  Should you be the kind of nerd that I am and think that sort of thing is fun.


Tour group on the trot.


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