Milwaukee’s sorry “Deep Tunnel” story

Milwaukee was one of the first cities to commission a deep tunnel to capture combined sewage/rainwater sewer overflows.  It was designed and built by the American engineering firm behind the Thames Tideway Tunnel project.

After the programme was launched in 1977, the tunnel was eventually commissioned in 1993/4 at an initial capital cost of nearly US$3bn.

Out of capacity a decade after being built: time to shell out for a 2nd tunnel

A decade later, after dumping a record breaking 4.6 billion US gallons of wastewater into Lake Michigan in a single storm event in early 2004, the deep tunnel had to be shored up with a second tunnel for close to another US$1bn[1].

While the $3 billion Deep Tunnel project was supposed to cure Milwaukee’s sewerage ills, as the court noted, it has not done the job. Since the Deep Tunnel went on line the sewerage district has dumped an estimated 18 billion gallons of untreated sewage into the lake [as of 2004]
Handwriting’s on the wall for MMSD’s Deep Tunnel, the Journal Times, 5-Sept-2004

Needless to say, the city’s electorate was rather dismayed to have to cough up so much more money after the substantial price tag of the ineffective first instalment.  But that’s precisely the risk with large engineering, once committed, they become a sunk cost (literally) and it’s very difficult to admit it was all a mistake, so more money gets committed.

Despite the additional capacity, the two tunnels were again reported to be dumping vast amounts of sewage into water courses by 2011.  Indeed one of the local beaches is ranked 2nd dirtiest in the US.

It’s now clear the tunnels cannot do the job and that addressing the root cause of the problem, diffuse pollution caused by stormwater runoff, rather than its mere symptom – sewers overflowing – is the way to go if one cares for a long term solution rather than a temporary workaround which, due to its finite capacity, just cannot cope with increasingly common extreme weather events.


Milwaukee’s tunnels also provide well for the legal profession as they continue to be the subject of a seemingly never ending string of lawsuits, even 20 years after commissioning.  Read for example: Court ruling has MMSD scrambling for solution to leaks (Milwaukee Journal Sentinel, 18-Jul-2013). This paints a rather bleak picture: beside still not properly preventing sewage overflows, the deep tunnel is also causing severe subsidence in the city centre because groundwater seeps into it.  This appears to be caused by a poor design which resulted in cracks; rather devilish to fix 300ft below ground.

MMSD had argued that work in even one mile of the tunnel would require it to shut down the entire tunnel system for a year or more and cost tens of millions of dollars. Closing the entire tunnel system for a year would allow unchecked overflows of sewage into Milwaukee’s rivers and Lake Michigan.

Reported in Milwaukee Journal Sentinel, 18-Jul-2013

The above statement raises a critical issue: whenever a tunnel is taken offline for mjor maintenance (planned every 10 years in the TTT’s case), the tonnes of sewage/rainwater mixture have nowhere to go and would wreck havoc with the improved river/lake ecology[2].

This experience could well be the reason Thames Water have sought a UK taxpayer-backed blank cheque in the form of the Water Industry (Financial Assistance) Act 2012, to guarantee all contingent liability on their tunnel project.  [3]

Learning from hindsight and others’ experience…

To be fair, this was a few years before Philadelphia XXX:link started thinking outside the box and demonstrated what can actually be achieved with Green Infrastructure.  So maybe Milwaukee didn’t have a choice.  London, on the other hand, just like New York or Washington DC, does have the benefit of Philly’s and Milwaukee’s experience.

No wonder the president of Milwaukee Common Council recently stated that with the benefit of hindsight, a tunnel would come last on his list of measures to remediate the combined sewer overflows issue. He would favour an actual solution – rather than a workaround – to the problem:

Stopping rainwater from entering sewers by disconnecting pipes, known as downspouts, and setting up rain gardens and green roof initiatives.
Alderman Willie Hines, president of Milwaukee Common Council

Time for a change in strategy…

With the ruinous tunnel strategy having demonstrably failed, Milwaukee recognised the need for a shift in strategy. Since being forced to cough up a second time in 2002, it has undertaken a programme of mitigation of stormwater flooding by tackling the problem at its source rather then continue to bury yet more good money after bad; having realised that no matter how big, a tunnel will never manage to absorb all the rainwater that mother nature, aided by climate change, will throw at us.

Milwaukee now scores 5/6 on the National Resource Defence Center Emerald Cities index.

  1. [1] the dramatic failure of the deep tunnel, on which the Thames Tideway Tunnel is modelled, is well documented in this extensive report by the Wisconsin Policy Research Institute
  2. [2] Once again, it’s common sense that addressing the cause of the issue – rainwater gushing down combined sewers – rather than its symptom, sewer overflowing due to excess rainwater – is evidently the superior solution.  Distributed Green Infrastructure can be maintained on a piecemeal basis, which besides not threatening the environment, is also obviously cheaper, not to mention much easier.
  3. [3] This way, any issue with the tunnel, including any resulting from “savings” TW and/or their contractors will have made while constructing it – as was the case in Milwaukee, where only part of the tunnel was lined – will have to be borne by the UK taxpayer – see section 2.7 in our mythbuster for more info.