Archive, Infrastructure

How Green Can You Go?


We continue to gain very positive media attention for our deep tunnel project to nearly eliminate combined sewer overflows (CSOs) in the rivers of Washington, DC. This article and graphics, in USA Today, focuses on the issue more broadly – considering there are 750+ cities that have this issue across the country – and uses our Lady Bird Tunnel Boring Machine as an example. Take a look – the video is one of the best I have seen at explaining the problem.

But not the best! I think my favorite video about the issue is our own “A Drop’s Life!” If you don’t remember, take a look here.

Finally, one of the issues referenced in this article and discussed at some length in many places is the role of Green Infrastructure (GI).  I am a huge fan of GI and am trying to integrate a significant investment in GI into our Clean Rivers Project (the name of our plan to respond to CSOs).  A comparison is often made to a very ambitious and impressive GI program in Philadelphia – and why many other cities, like Washington, DC and Northeast Ohio among others – have not also developed a plan with a similar scale of GI investment.

Philadelphia’s plan (Green City, Clean Waters), costing more than $1 billion, relies mostly on GI.  Cleveland (Project Clean Lake) and Washington rely mostly on “gray” tunnels and are using GI as a supplemental approach in a hybrid solution – and have $3.0 billion and $2.6 billion dollar price tags respectively.

The answer is fairly simple.  Which remedy is selected, and how much GI it includes, is almost entirely driven by the percentage of capture of the overflows that must be met.  For both Cleveland (overflows to the Great Lakes) and Washington, DC (overflows to the Chesapeake) – the capture percentages are very, very high – 98 and 96% respectively.  We have both realized that it is difficult to retain that much flow in large storms without deploying the tunnels, and are using GI as a supportive technique.  For Philadelphia, the capture percentage target is lower, so they can rely more broadly on GI.  I admire Philadelphia’s plan and believe the city will be transformed by its implementation.  But it is not on the table in DC because a comparative version will simply not attain the capture percentage of the total overflows that we must meet.

All these approaches are excellent.  I support the maximum use of GI that is possible within an agreed-upon budget combined with an agreed-upon capture target.  For Washington, DC, we are still seeking to attain 96% capture, which means we need the scale of capture that tunnels provide, supplemented (we hope) by a nearly $100 million investment in GI.

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