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Gowanus Canal CAG Meeting
Tuesday, January 22, 2019
Mary Star of the Sea Senior Apartments, 41 1st Street


Katia Kelly and Brad Vogel opened the meeting at 6:35 p.m.

Project Updates: Kevin Clarke, New York City Department of Environmental Protection

NYC Department of Environmental Protection: Presentation on Gowanus CSO Storage Tunnel Alternative to Proposed Gowanus CSO Tanks.

In lieu of the Combined Sewer Overflow (CSO) storage tanks. The city has to build two tanks: an 8-million gallon tank at the Head End (RH-34), and a 4-million gallon tank at the Owls Head site to abate OH-007.

DEP has met all the EPA Superfund milestones and will continue to do so.

The tunnel idea came out of a discussion about other water bodies, Flushing Bay and Newtown Creek, where DEP is pursuing tunnels under those bodies for stormwater, so when looking at those, it occurred to DEP to explore the potential to use a tunnel for Gowanus as well. The tunnel would be a 16-million-gallon, soft-ground tunnel to follow the alignment of the canal.

There are assets on the water side, like the pumping station, many built more than a hundred years ago. Very expensive, but built to last. We have to make the right decision when building this kind of thing. At a minimum, the tunnel would hold 16 million gallons – four million more than the capacity of the two tanks – this would give the same solids capture. Reduces CSO RH-34 outfall from about 6 discharges to 4.  At Owls Head, it goes from 4 to zero. The tunnel is easier to construct, and has less construction impact. The headhouse would be about the same size as the lot at the RH site. There is no longer above-ground facilities so we can be more flexible with the design of the open space. The cost is estimated at $1.2 billion.

The City has already acquired the necessary parcels  The timeline would be a little bit longer and the schedule is more aggressive. The tunnel provides a scalable system – we can extend the tunnel further than the alternatives we looked at, and will continue to look at, including following down Second Ave and fixing drainage in Red Hook and Park Slope.

The timeframe for completion could be 2030. This follows the rezoning; everyone knows the area is ripe for development. This would help plan for population growth and resiliency. There is street flooding, and occasionally sewer backups. As sea level rises, it is harder to get sufficient flow – the tunnel makes that easier and protects against rising sea level.

Project Milestones completed to date:

EIS:   February 2018

ULURP: April 2018

CP1: June 2017 on time

CP2: excavation and substructures underway April 2019

CP3: aboveground work EPA Sept 19 (on target)

Completed site acquisition in October of 2018.

Completing the tunnel program schedule would incorporate the work that has happened already. The EIS should only require a supplemental to continue with the tunnel. ULURP and land acquisition is out of the way.

Facility Changes:

Odor – as the tunnel fills it displaces air – that air needs to be vented and goes through odor control strategy – in the DEP operating bureau the strategy will remain the same but may need some updating.

Same with the grit management.

Pumping station and headhouse layout – the operating bureau is doing a lot of work on that.

The flow diversion influent and design – the diversion structures will be similar; instead of a tank they’ll go to a shaft.

The headhouse at RH-34 will be a similar size. That visioning work needs Public Design Commission approval.

No changes are required in the already completed site prep or demo for CP1 for a change to the tunnel.

The supportive excavation strategy – slurry wall to bedrock – is the same as would be used for the tank.

We heard the tunnel sounded crazy – there have actually been a lot of soft ground tunnels – especially some of the river crossings – work previously done by hand using steel cans is now done by a boring machine. The Gowanus flushing tunnel was built using a shield; it wasn’t a cut and cover. The flushing tunnel brings water from Buttermilk Channel to the head of the canal – constructed using a shield – under compressed air – CAG Member noted in the 1970s, the City secured $478 million for the Red Hook Waste Water Treatment Plant.

Soft-ground tunnels opposed to rock tunnels – all of NYC tunnels are in hard rock, several hundred feet underground. Two main types of tunnel-boring machines – earth-pressure balance and slurry-pressure balance machine – material is removed with an Archimedes screw and dumped on a conveyor.

Slurry – you’re pumping in clay and water to assist with how much material is being moved – makes it more pumpable. This kind of system is more pumpable – stuff is removed with a pipe backup.

First thing to do to build soft-ground tunnel is a pumping station and mining shaft. Hydromill is how you would dump concrete in, and construct the wall. Once constructed, you lower the boring machine. As it is moving and removing materials, the machine erects precast segmented liners and forms the finished tunnel, and is ejected behind the tunnel liner.

Hatch Mott MacDonald Tunnel Boring Video ( Muck and supply train takes the muck out – holes in the face of the cap, mixing chamber, belt conveyor, basically important to see how the machine moves forward and how the liner is erected. DEP estimates it will tunnel 50 feet a day. Last segment to go in is the key, there are gaskets around each segment – bolts that lock the pieces in – pumps grout through the holes around the tunnels – the machine would be assembled on-site from parts made elsewhere.

DEP isn’t the only one thinking about storm and CSO soft-ground or rock tunnels. Cleveland, DC, Portland, Boston, Flushing Bay (has been proposed and Long-Term Control Plan was approved), Rochester started construction in late 1970s, different lengths and diameters.

Gowanus is only half a mile – it does increase the diameter in order to meet the gallons from the head of the canal to the Salt Lot. In order to meet the solids reduction we expect to meet with the tanks, we had to increase the diameter.

NYC can benefit from decades of national and international advances and lessons learned about soft-ground tunnels. DEP has been spending a lot of time researching and looking at lessons learned – how the facility is operated. As the tunnel is filling, do they let it in and remove it, that’s the stuff DEP wants to figure out. On soft ground, the schedule has been a big concern – spend a lot of time validating schedule, lessons learned. Have looked a lot at the DC Clean Rivers Project tunnel alternative, which is a system where some of the tunnels have been completed, some will be completed, freeways, etc. Private homes, facilities, century-old homes, they have tunneled under and adjacent to the Anacostia and Potomac Rivers. Take a look at Theirs are 18 to 20 feet across, and include 18 miles of tunnel. Also, the Thames Tideway in London – 23.5 ft depth, 66 to 2013 feet, bulk of tunnel is 15.5. Tunnels all under the River Thames – another segment was constructed in chalk using a slurry tunnel boring program, which is essentially the same, even though it isn’t soft ground, it was chalk

With the Gowanus Canal:

Our alignment – Head End site: snowman or a figure-8 shaft follows the alignment of the canal to minimize impacts on private property, wouldn’t require ULURP or easements, would end up at DSNY property. 65-foot shaft to retrieve the machine there. Bar screens maybe, venting, small footprint, way smaller than the tank. During rain, the RH-34 outfall would fill at same time, but the air in the tunnel gets displaced and odor controlled.

Soil profile and stratigraphy. Shallow end is Owls Head. Roughly 125-150 feet below the surface – sloping toward the Red Hook site. Would want all the flow – staying in soft ground – 50 to 60 feet below the National Grid barrier wall.

Questions & Answers

CAG: What if it fills up too fast?
DEP: It won’t, anything in excess would flow to the canal

CAG: What about contamination at the depth of the tunnel – we know there will be coal tar in some locations.
DEP: We conducted deep borings and found contamination at Red Hook site and Owls Head – don’t have them at the depth, but do have much shallower ones. DEP will have to conduct geotechnical environmental boring program. That will be shared with the contractors. Might dictate what type of machine DEP will use.

There are many examples of soft-ground and rock tunnels – asbestos and heavy metals, benzene – stuff that would be similar to Los Angeles’s La Brea Tar Pits. On each of the contaminated soil tunnel sites, there was success. There is always the potential for settlement to occur. The tunnel boring machine has limited ground loss – standard is 0.5% – DEP thinks less than half an inch. Seattle, DC, LA have all constructed tunnels under existing buildings without damaging them. Zone of influence of the tunnel – if the settlement reaction that occurs is directly over the tunnel, it is another reason they’re selecting under the canal/in alignment with it – estimating less than half an inch. As you move diagonally, the deep foundations like the support walls along the canal will become outside the zone of influence. Other measures for settlement mitigation – pressure sensors, control room, lots of information that goes in – how fast, how much material, what is the pressure, how much grout – gets checked in real time and alerts for precaution. Some machines have a slurry or foam injection – that gets tested before.

Comparing the Tunnel and the Tanks

The tunnel would result in less disruption and a smaller footprint than the tank construction. Once the staging happens to construct and put the machine in, there is little on the surface, then the odor control area.  With the Second Avenue Subway – trucks had to pull into one end of a transfer shed – directly under buildings – lots of mitigation strategies exist.

Design flexibility – can maybe shave off 5 or 10 percent – more flexibility because the front is different.

Tunnel facilities would have to be rehabilitated for the future – the intention may be more shade trees.

There is more design flexibility with the tunnel than the tank.

Cost: Tanks are $1.2 billion, the tunnel is $50 million more – operations costs estimate.

Scalability: want to explore where that tank can go.

Schedule: the tunnel could be done by 2030 – a little later than the tanks, with the Head End by 2029, and Owls Head by July 2030 – the tunnel would be December 2030.

Capacity: 16 million gallon capacity.  8-million-gallon tank at RH and 4-million-gallon tank at Owls Head, and that’s CSO volume reduction and those tanks are flow-through – the 9 million gallons – would receive some treatment – the flow from the tunnel is screened – that flow also settles from the front to the end, results in lower solids discharge at the back end – in order to meet the solids performance – you have to make the tunnel a flow-through facility – could say they’re proposing a 12-million-gallon tunnel. 58% to 74% reduction is what is mandated – the tanks meet 90% solids reduction – so that creates fewer CSOs. Reduction in CSO events. RH-34 – with tanks 6 gets reduced to 4; at OH-007, instead of 4 events that goes to zero.

Questions and Answers

CAG: Safety and CSOs – this tank is going to be 100 feet below ground? Nervous about our guys, what’s the evacuation like? How do we get stuff out? It sounds scary.
DEP: The only place anybody would have to enter on a regular basis would be from the shaft at the Head End, isolated from the tunnel – people won’t be in the tunnel on a regular basis. They’ll go in there once every 5 to 10 years for cleaning or inspection.

CAG: Putrescible materials the majority of time plus an air layer – CS4 and carbon bubbling though the water – is it always going to be full of water? Lots of anaerobic materials go with the air.
DEP: Tunnel is sloped to provide self-cleaning velocities – the wet-weather events and then it gets dewatered – that flow is pumped out – the self-cleaning removes everything from the tunnel – similar to what was planned for the tank – sewage and then odor control 24/7, 365 – any gas will be removed right then.

CAG: Given some settlement can occur, wouldn’t it be better to do the tunnel first and the capping later, the cone of influence through the tunnel wall – EPA not here to speak to that.
DEP: There is some settlement addressed in National Grid’s design for the cap and there won’t be a breach.

CAG: In light of the lack of planning foresight with the Brooklyn Bridge Park and Brooklyn-Queens Expressway, $1.2 billion is a lot of money, but are we thinking too small? The economies of scale in this, the canal is 1.8 miles – just because we met the mandate it is 0.5 miles. With global warming accelerating, are we thinking far enough along?
DEP: Understand, but don’t have the answer.

CAG: 25 years ago was told it was too complicated – climate change biggest problem – between more frequent storms and elevated sea level – how is this being addressed in all of the plans – I’m 36 feet above sea-level – if that goes, may as well say goodbye.
DEP: Can always increase the size, been hearing about a barrier on Hamilton Avenue to move it.

CAG: To build on resiliency, we need upgraded catch basins and infrastructure, is DEP thinking about increasing gray infrastructure?
DEP: Yes, obviously green goes a long way, but we’ve been looking at increasing micro tunnels 30 to 40 feet below ground, to relieve some of the chokepoints to the canal or the tunnel. The tunnel would have to be constructed first.

CAG: If the tunnel follows the line of the canal, why does it have to be so deep?
DEP: Soft-ground tunnels – CSO and stormwater wants to be more shallow – the deeper you go, the harder it is to pump out materials, not just from energy use but would have to change the design – the three things determining it: depth of the barrier wall – want distance between it; the structures below the canal (the deeper you go, the less you’ll impact those), and then we’re limited the other way, because toward the south end rock starts to come up – we want to protect the barrier wall but not so deep we hit rock.

CAG: What about the energy pumping the water up?
DEP: Luckily they don’t run all the time; basically around the rain events, about 40 a year.

CAG: Is it multiple pumps?
DEP: Yes,

CAG: Noise reduction?
DEP: Yes

CAG: Power?
DEP: Would be ConEd

CAG: How can you limit trucks, traffic during construction?
DEP: Red Hook Site – we will continue to look at that – should be a little less than the sites we acquired – 24-hour muck system – one way to reduce truck traffic is longer hours, we are providing a little more volume, reducing size of slurry wall, might be like a snowman-type shaft – shouldn’t be a big difference with construction traffic – much smaller impact at Owls Head site with tunnel rather than tanks.

CAG: What about barges?
DEP: Looking into it, but the canal is very narrow for that.

CAG: Longevity of the tunnel and how it operates, what is the lifespan?
DEP: A hundred years – in London the tunnel was 200-year span.

CAG: What is the safety record, any unsafe tunnels or unsuccessful ones? Failures?
DEP: Increased settlements, no explosions, biggest failure I’m aware of in the US – tunnel boring machine itself was over 57ft in diameter in Seattle, part of Alaska Way Viaduct – big machine failure, so they had to dig down to the tunnel and repair that – it was a way, way bigger tunnel. The size of this tunnel is so much smaller it decreases the risk.

CAG: Does the tunnel itself have to be taken down, and what happens if there’s a CSO event then?
DEP: Continuing to look at that – different places go at different times – will likely be every 5 to 10 years – cleaning cycle isn’t a hundred percent – increases ventilation, isolate and go in. Might bring in small material.

CAG: Why would you decide to go one way rather than the other way?
DEP: The larger outfall and the pumping station is there already – the pumping station takes a short cut.

CAG: At the former site there was opportunity for public space once project was done, is that still the case?
DEP: Below ground portions wouldn’t be there, so there is additional flexibility because no access points would be there.

CAG: What do we mean by scalability for us? We’re already interested in scaling these projects up.
DEP: The goals of the Record of Decision – as part of the planning, we’re looking at several alternatives mostly looking south – maybe down Second Avenue, maybe continuing to follow the canal – provides additional stormwater outlets and CSO mitigations – we need to continue to look at the range.

CAG: Let’s say we went ahead and did this 16 million gallons and then the mayor said let’s go 20 million more – how would that happen?
DEP: Go back into the shaft [with the tunnel boring machine] and connect [the tunnels].

CAG: Why are we supposed to believe this after NYC tried to deny it had responsibility to do this, then to say 7 million gallons was enough, so now why all of a sudden with more time because of private land instead of the park, why should we trust DEP, the project has just gotten more expensive and now it will be 2030 before there’s any relief from raw sewage, and on top of that the Gowanus could be lined with new buildings before this even happens.
DEP: We’ve met every milestone to date and are on track to meet the next ones. This was probably the fastest EIS, fastest ULURP, fastest land acquisition – taken it very seriously – because of the size of the investment – $200 million for land acquisition. Pivoting to a tunnel is a better down payment. We are pursuing tunnels for Flushing Bay, 2.5 to 3 miles at $1.6 billion, and construction dates are much longer. Newtown Creek, the rock is higher so it will be rock, but it is much larger and will be implemented over a longer timeframe – not crazy, lots of municipalities are constructing them.

CAG: To quicken the process, could you have two machines and meet in the middle?
DEP: Would have to put another shaft in the middle and that’s not possible in soft ground.

CAG: How many times you replace the pumps is less than spectacular?
DEP: We do have experience with pumps of this size – like the North River Plant – I think that’s over 100 feet.

CAG: 2030 to me is a long time, if you’re going to do this, you’re going to spend $1.2 billion, don’t you think it could be done faster? How did you come up with 2030?
DEP: All the work to date has been conceptual, as a side task under the contract for the tank design. There was language in our contract that allowed us to take alternatives. But we need to continue the detailed facility planning and design plus the geotechnical/environmental boring and design. DEP has started this – the city procurement takes a while to put contracts into place. Trying to speed that up – giving ourselves a year to procure that contract – January 2020, and then four years to do detailed planning and design including the boring. Then a year to get the contractors, and then, construction begins.

CAG: I think you downplayed surface subsidence – and think you need to do more research for your contracts and drilling – in other things I was reading was soft rock.

CAG: How much has been spent on the tank design to date?
DEP: About $30 million; the amount is on the order.

CAG: When will the CAG see plans for the Salt Lot tank? Until EPA shifts to accepting the tunnel, that will still move forward, right?
DEP: The design has to be done under a separate procurement, working on it.

CAG: Surprised that the soft tunneling examples didn’t include from head of the canal to Hanson Place, that’s part of the history of tunneling – Gowanus. My question is the advantage to this is that it is expandable. Expandability would be helpful – the whole plan of the tunnel is based on the tank footprints – carrying things upland/inland based on a 30-inch diameter pipe in the tunnel so you’re transferring everything as planned – the sewage would flow down Bond.
DEP: It does not go down Bond.

CAG: Okay then how do you plan on transferring with the 30-inch pump? It seems shoehorned into the tank and not the best for the tunnel.
DEP: A new force main at 33-inch diameter, new pump, can accept 30 million gallons per day – pumps that flow into the force main and takes a shortcut into the Red Hook interceptor on Columbia Street – reduces a lot of pressure – average dry-weather flows at the station are at 6 or 7 million gallons so they do the dewatering at night when flows are lower – not taking advantage of a burdened system.

CAG: What about the Brown Tsunami?
DEP: Gowanus Pumping station – only going to be 30 million gallons a day – rain events like that will always create overflows. We design for an average year. We’re never going to create something for that storm – one like that hasn’t happened since 2011. You try to capture the small storms but the big peaking storms are impossible.

CAG: In an event with multiple big storms?
DEP: 85% of the storms we see are less than three inches; DEP tries to capture the majority of the storms.

CAG: There are a number of blackouts – what is the redundancy of the power, or do they not function when Con Ed doesn’t function?
DEP: There’s emergency power via diesel fuel at the Gowanus pumping station, but the flushing tunnel shuts down. To divert the flow for Owls Head/Head End it is set by weirs, don’t have to open/close, won’t pump out until power is back on.

CAG: Are the shafts under the canal, south of it?
DEP: Conceptually, the headhouses are directly over the shafts.

CAG: Conceptually, would it be possible or desirable to put it on the land where you were going to build the tank, or would you use the Eastern Effects lot?
DEP: Looking into that, as with any construction, the more staging the better.

CAG: The timeline with the 4-year geotechnical – is that going to push back any capping or dredging?
DEP: No, that will take about a year and half – will take a couple months.

CAG: Appreciate more public-space options, but will the city commit to keeping that public space?
DEP: As the owners of parcels 6 &7, we don’t want to give it up, it is our intention to keep it and have it be public space. Need property to support the project.

Community Member: Timeline of the dredging and a timeline of the staging?
DEP: We don’t really have that.

Community Member: Can this connect to Butler? Right now it just says employee parking – is that possible? With more space, there’s an empty lot Con Ed bought, do you know how tall the walls will be?
DEP: Maybe 50 feet (high walls).

Community Member: How much did the city pay for that land?
DEP: Allotted something like $90 million for 50,000 square feet.

Community Member: Am I wrong to assume there will be no CSO capture for 2030 if we go with the tunnel?
DEP: No, that’s right, but it’s the same for the tanks – only one will be ready for 2029.

Community Member: Does the density in the community affect how large anything will be?
DEP: No, more about water projections. Some areas will be up-zoned, those are the end goals – like quality of life is more important than number of people.

Community Member: Newtown Creek 2017 figure $600 million and then 2014 inflation figure. This is less than half the size and about the same cost.
DEP: They might just be providing the base cost.

Community Member: Why would DEP give some communities numbers that are so far off?
DEP: $1.6 billion for a 25-million-gallon tank.

CAG: DC has 18 miles of storm capture – the swamp was already drained. Build canals, not walls. DEP has a presentation in Harlem on January 31 for the Flushing Bay tunnel, right? Could you give a little preview?
DEP: Not familiar with Newtown Creek, and they are advancing a planning-only contract because they have more work to do. Flushing Bay is 18 to 20 feet diameter, 2.5 miles long, and right now the intention is to site the tunnel on property owned by NYC, leased to PANYNJ, and the intention there is to divert BB006 and BB008, and they’re adjacent to each other and then will go to Bowery Bay. That tunnel does conveyance at a similar depth, soft, and instead of adjacent to a pump it is adjacent to the waste water treatment plant. If the City can’t use that land because of lease issues, they will have to acquire land. Flushing Bay plan was approved in early 2017. Now trying to procure facility planning.

Resolutions & Committee Reports

It was affirmed that a quorum of members is present.

Admin Committee

  • Report on the two new members:
    • Kelsey: A member of the Gowanus Dredgers, lives in Prospect Heights, wants to be more involved in Brooklyn – would be an at-large member for meetings, wants to join the Water Quality committee, lives in same sewer shed as Gowanus.
    • Richard – on a journey – interested in conservation and how it comes together – Gowanus has all these surprises, from the first battlefield to guns from mafia hits, retired senior executive and wants to give back – gone to a couple Newtown Creek meetings, Archaeology and Water Quality committee meetings. Interested in liaising with Newtown Creek and Gowanus.

Both new members approved to join.

Archaeology Committee

Resolution: Retention of Existing Marine Bollards from Public Place Site


There are existing bollards the committee voted to make sure the PRPs retain and save so they are put along the canal – taking into account some of Terri’s issues, like couldn’t be put right back in same place so they aren’t put right on the retaining wall.

Could we acknowledge that there will be work done (EPA) with the CAG to find an appropriate home in a historically authentic manner?

We should cc: National Grid and Gowanus Green Developer Team

Yes, all agree, amended.

Should cc: NYC Department of Housing Preservation and Development as well.


The resolution was adopted.

Resolution: Saving Full Gowanus Station Building if CSO Tunnel Plan Adopted


The tunnel map currently shows it being on top, move the “snowman” south. If EPA accepts DEP’s tunnel plan.

The resolution was adopted.

Resolution: Regarding 4th Street Turning Basin Archaeological Artifacts and the need for a MOA/Programmatic Agreement


This came out of Archaeology committee – the gist is to find a home for the artifacts, and call on the EPA saying we need a Memorandum of Agreement or we’ll keep having this lack of protocol for what happens when things are found. The Gowanus Trust has allowed items to hang out – Brooklyn Historical Society and several other places. Who will actually put them out – moving to have them warehoused? We need a site not only that will take these but display them.

The resolution was adopted.

Resolution: Protecting Historic S.W. Bowne Grain Storehouse and Preventing Navigational Hazards from Impacting the Cleanup


Owner has not done anything with this property now – resolution calls on a number of city agencies to do this. Remove paragraph about the Fire Department – asking them to investigate it is like so what – why are we broadening it this much – it is a problem but it might not be in the purview – should we take this to CB6? Purpose of this tonight, I’m not voting unless we take the paragraph out – CB6 part two – if we include this won’t it be more ammo for CB6? They can come after any city agency, the CAG can’t.

It isn’t our mission. There is a Land Use Committee for CB6 and that’s where to take it.

The CB isn’t an authority either. The purpose of the CB6 liaison (Hildegaard) is to take this.

Is it possible to move this ahead without the FDNY paragraph?

Strike and vote, yes, agree. In the future, we’ll see if there’s any capability there.

Have the District Manager of Community Board 6 put some pressure on this.

The resolution was adopted as amended.

The meeting adjourned at 9:05 PM.

CAG Members Present

Janet Aitchison
Jerry Armer
David Briggs
Marlene Donnelly
George Fiala
Katia Kelly
Louis Kleinman
Hildegaard Link
Linda Mariano
Andrea Parker
Peter Reich
Chrissy Remein
Buddy Scotto
Brad Vogel
Sue Wolfe (alternate for Sabine Aronowsky)
Maryann Young (alternate for Rita Miller)
Susan Yung

Others Present

Kevin Clarke, Portfolio Manager, New York City Department of Environmental Protection
Alicia West,, Public Affairs, NYCDEP
Ted Timbers Public Affairs, NYCDEP
Terri Thomson, National Grid

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