A Lesson for London from Milwaukee
Posted by Richard Conniff on October 2, 2011
London’s Mayor Boris Johnson says his city is lapsing back to the Great Stink of 1858. The city’s sewerage system, built for a city of 2.5 million people, cannot handle the present population of 8 million, and every time the skies add in just two millimeters–less than a tenth of an inch–of rain, the”Bazalgette Interceptors” break open and raw sewage pours into the river. Johnson writes:
In one of the crimes for which we are truly all guilty, society is now discharging an awful 50 million tons of raw sewage into the river in London alone, and unless we are bold in our plans, that figure will rise to 70 million tons in 10 years…
When Bazalgette designed his interceptors, in response to the Great Stink of 1858, he assumed that they would only kick into action in emergencies – truly torrential downpours of a kind that happen once or twice a year.
Now it happens 50 times a year, basically once a week. Johnson says the answer is massive infrastructure improvements, conceived and built with “neo-Victorian boldness”:
That is why it is time to recognise that we can no longer rely on Victorian capital, and why Thames Water is right to be consulting on its proposed super-sewer, known as the Thames Tideway Tunnel.
Of course, it must construct this cloaca maxima in a way that minimises hassle for local people and avoids damage to riparian beauty spots. But the basic idea is excellent, and essential. At a depth of 75 metres – below the Tube and other excavations – and with a bore the width of three buses, this huge tunnel will run winding beneath the course of the Thames from Richmond to a series of vastly improved and upgraded East End sewage works … It is a breathtakingly ambitious project, on a scale that would have attracted the approval of Brunel and Bazalgette themselves.
But here’s the lesson London needs to learn from Milwaukee: What Johnson, an Oxford man, calls the “cloaca maxima” approach doesn’t work, no matter how big you build it. It may be necessary, but it’s not enough. Instead of neo-Victorian thinking, what’s needed is a little post-industrial creativity, to keep the rainwater from getting into the sewerage system in the first place. Here’s what I wrote about it, sometime last year:
Planting trees might seem at first like an improbable tool for dealing with combined sewer overflows (CSOs)—a common problem in older cities where domestic wastes and stormwater run through the same pipes. Many cities now face federal deadlines—and huge construction costs—to stop such systems from spilling raw sewage into basements and waterways during rainstorms. The conventional engineered, or “gray,” remedy is to build massive deep tunnels capable of retaining overflow, to be released gradually through municipal water treatment plants after the rain stops falling. But cities are now also pushing to prevent the water from getting into the system in the first place by using trees, green roofs and permeable pavements to sponge it up where rain falls.
In one typical case, the Milwaukee Metropolitan Sewerage District has spent $4 billion over the past two decades on gray remedies, adding 494 million gallons of deep-tunnel storage. But when a major rainstorm hit late on a Saturday afternoon in June 2008, the runoff was on track to fill the entire system in just 56 minutes.District managers had to divert combined wastes into area waterways and reserve the deep tunnels to retain separated household wastes, which also overflowed as the storm continued over the next three days. To prevent that kind of mess in the future, the district is now spending $300 million to preserve open space along local waterways. It also recently paid market prices to remove 75 homes in a downtown neighborhood, adding the land to a city park that doubles as a flood retention pond.
Likewise in Philadelphia, a 2009 study compared gray CSO prevention measures (adding more deep tunnels) with a green infrastructure approach that aimed to halve the runoff from existing impervious surfaces at roughly the same cost. Stratus Consulting, based in Boulder, Colo., estimated that the gray approach would produce $122 million in benefits over 40 years after subtracting construction costs. For the green alternative, the net benefits added up to $2.8 billion—more than 20 times as much—including improved property values, increased recreational opportunities and avoided heat-stress deaths.
Those kinds of numbers have attracted widespread interest. For instance, an innovative proposal from the Center for Neighborhood Technology in Chicago would fund tree planting and other green infrastructure programs with municipal bonds based on the projected increase in real estate values and tax revenues such programs produce. But there has been only cautious interest so far because it’s unclear whether enforcement officials at the Environmental Protection Agency will accept green infrastructure as a tool for CSO prevention. Even so, Philadelphia recently launched the largest green infrastructure program in the country to transform the city over the next 20 years at a cost of $1.6 billion. The city is also adjusting its water and sewer fee structure so that commercial users pay, in part, based on a property’s impervious surface area—a measure of stormwater runoff. Howard Neukrug, director of the city’s Office of Watersheds, described the program as an attempt to “break down some of the barriers against nature and deal with rainwater where it lands.” Despite reservations about the cost, The Philadelphia Inquirer summed up neighborhood response this way: “What’s not to like about cleaner air, cooler houses and prettier streets?”