There is a fresh breeze blowing in Washington, DC and it will whistle through more trees, bushes, flowers and shrubs. Tens of millions of dollars more.
The additional plantings will be accomplished through a landmark modification of a Consent Decree that was just agreed to by DC Water, the District of Columbia government, the United States Environmental Protection Agency and the US Department of Justice. DC Water will build a bit less tunnel to capture stormwater, opting instead to capture stormwater at the surface in our city, before it can get to a drain and contribute to flooding.
I have written before about the benefits of using green infrastructure to manage stormwater and the big question in Washington, DC has been whether we could reopen the existing Consent Decree that mandates a more traditional tunneling remedy to realize any of these advantages. The big news, after six years of effort, is that the answer is YES!
Elements of this accomplishment are groundbreaking and worthy of thoughtful explanation and discussion. I plan to write about this exciting arrangement in six parts:
Part 1 (below): Background
Part 2: Equivalence
Part 3: Timing
Part 4: Green Jobs
Part 5: Affordability
Part 6: Public Participation
The US Department of Justice lodged with the federal court a modification request to the existing Consent Decree that governs the remedy to the problems associated with combined sewer overflows (cso). Combined sewers take sanitary flow and stormwater flow into the same sewer pipe – hence the “combined” notation. This system was a vast improvement over what existed before in Civil War era Washington – sewage was conveyed untreated to the Potomac through an open sewage canal that flowed along the current route of Constitution Avenue.
Yet what was a remarkable step forward over a century ago is now a huge problem. These sewers fill up with stormwater during rainfall events and then, by design, allow overflows to our Rivers to relieve the pressure. Without the overflows, the sewers would become pressurized just like a water main – and would push this nasty combination of sewage and stormwater back up into homes and businesses, and up out of manholes onto city streets. In fact, that is exactly what happened four times in the Bloomingdale neighborhood in 2012. So much rainwater flowed into the Northeast Boundary sewer that it filled, became pressurized, and then pushed this concoction onto city streets and into basements.
Allowing overflows relieves this pressure and allows new to continue into the sewers even during the biggest storms. Yet these overflows – to the Potomac, Rock Creek and Anacostia River – cause immediate and significant water quality problems. And Washington, DC is not alone – More than 750 communities in our fair country have combined sewer systems as well, all designed to overflow to the ocean, or our rivers and streams during major storm events.
The principle challenge then is to reduce the quantity of stormwater flooding into the combined sewers. One way is to divert the stormflow down enormous shafts that connect to mammoth underground tunnels. These tunnels can either hold the overflow until the storm surge passes and there is capacity in the combined sewers to convey the flow for treatment, or the tunnels can take the storm flow directly to the treatment facility. These remedies for combined sewer challenges are popularly called “grey” solutions – because they rely on concrete sewers and associated hard infrastructure.
The Consent Decree that was entered with the court in 2005 directed DC Water to solve the CSO problem with a grey solution. We are currently on-schedule and on-budget to reach the mandated solution – and are building huge tunnels that will capture 98% of the overflow that would otherwise flood into the Anacostia River. Under the current consent decree, we have two additional tunnels planned for the Potomac and Rock Creek.
The great strength of the grey tunnel solution is that its performance is very clear – the volume of the tunnel; and the maintenance limited. Since stormwater does not flow into the tunnel except in major flooding events, the tunnel is empty most of the time. The tunnel itself has almost no moving parts and can be constructed with an expected useful life of a minimum of a century (and probably far longer). The strengths are clear: performance, low maintenance, long-lasting.
The challenges are equally impressive. Building huge underground tunnels is incredibly expensive – rarely can a city get away with a tunnel remedy for less than a billion dollars, and in our case in DC, $2.6 billion plus. And in comparison to a whopping bill to be borne by our customers, it is a remedy that will never been seen. Our customers in the District will be funding the largest public works project in the era since Metro, yet will never actually see it work directly. And as already mentioned, most of the time the tunnels will be empty.
DC Water, and many water utilities across the country, are concerned that presenting a huge bill to a customer base that will not see what they are paying for, and which will be empty most of the time, creates the risk that we will lose the support of the people we need to complete the work. And if public agencies are not able to raise rates sufficiently to cover the costs – work to solve combined sewer overflows will continue because it is mandated under the Clean Water Act. Other work will be postponed or cancelled to make sure the tunnels are built. This potential consequence makes much, much worse the greatest already-existing risk to our water systems – which is deferred capital maintenance on critical systems.
The reality of this risk compelled DC Water to consider green infrastructure. GI captures stormwater that would otherwise overflow existing sewers – so it achieves the same outcome as the tunnels. Except GI, built at the surface, is connected to the lives of our customers and work during every rainstorm – no matter what the size. Moreover, the benefits are multiple – stormwater management (the primary goal), water quality improvements, habitat creation, reduction in ground level heat islands, improved air quality and reduction of greenhouse gases.
Who does not prefer to walk down a beautiful shaded street in the hot summer, surrounded with lush plantings near the sidewalk?
So in 2009 we embarked on an assessment of how to incorporate GI into our Consent Decree. We decided at the onset that we would not change the remedy for the Anacostia. The larger volumes of overflow are discharged to the Anacostia, which is a slow moving tidal River. As a result, any contaminants tend to stay in the River for long periods, and often settle down into the sediments. For these reasons, and the practical reality that our building schedule has us building the Anacostia tunnels now – and therefore makes it much harder to propose an alternative – we decided to focus on the Potomac and Rock Creek Tunnels.
Up next: Equivalent Performance