Doug Siglin

Yesterday I wrote about World Water Day and DC's underground tunnel project to reduce untreated sewage overflows to the Anacostia. The sewage tunnel project isn't the only nationally significant thing going on in DC to improve our rivers and streams, so I'm treating myself to another bite. It is surely still World Water Day somewhere.

Innovation is essential in all sectors, including water. The big sewage storage tunnel is interesting and significant, but quite a traditional way of doing things. In terms of innovation, there’s something more important going on in DC.


Water engineers love this word, and it shows up with increasing frequency in everyday language, although very few people know what it means.  I’m happy to provide a translation for the rest of us: runoff.

Here’s the story. Rain or snow runoff is a serious pollution problem in urban areas. Hard surfaces like asphalt, concrete and roofing accumulate pollution from the air and many other ways. Rain or snowmelt washes the pollution off into streams and rivers, usually without any treatment. If you need a visual, think about what a pristine downtown snowpile looks like after a few days. During heavy rains, runoff can also cause massive stream erosion when it forcefully blasts out of underground pipes. IN DC, runoff is responsible for carrying trash to the Anacostia and the Potomac, which is unattractive but not terribly dangerous, and for carrying less visible things like polycyclic aromatic hydrocarbons, which are linked to cancer, cardiovascular disease and developmental impacts at high concentration levels.

Towns and cities around the world have a hard time figuring out what to do to prevent polluted runoff. Obviously, it's not possible to stop the rain or snow, eliminate all sources of pollution, or abolish hard surfaces.  It also is tough to capture and treat all runoff before it enters the streams and rivers. Progress is definitely possible, but it is slow and expensive.

For the past twenty years or so, the prevailing notion in urban areas in the US and elsewhere has been to retain rain or snowmelt "on site" – close to where it falls – and either infiltrate it into the ground or give it some basic filtering treatment through natural or mechanical means. Green (or vegetated) roofs on buildings are a good example, as are “rain gardens”. With natural methods, microbial action breaks down the pollutants over time.

The DC region has been a global leader in this work for more than a decade.

But here’s the innovative thing. The District has raised the bar significantly by creating a Stormwater Retention Credit system. My old friend Ben Grumbles, who has a way with words and happens to be Maryland’s Secretary of Environment, calls the District's system “catch and trade.” In a positive way.

DC passed regulations in 2013 requiring all new DC buildings, and all "major substantial improvements" of older buildings, to build in the means to capture and infiltrate, evaporate, or treat a volume of rainwater related to the size of the building's footprint. But instead of retaining 100% of the volume obligation on site, owners can choose to buy Stormwater Retention Credits for up to 50% of their requirement from other landowners in DC who voluntarily capture runoff through certified management practices.

The reason this is innovative and important is because not all stormwater is created equal. Runoff from a relatively clean surface like a rooftop is less polluting than stormwater running off, say, a parking lot or alley covered with trash, oil, and rust particles. Runoff flowing directly into the Potomac causes no erosion while stormwater blasting into a small tributary does real damage. Runoff that creates flooding in homes and businesses needs to be a priority for redirection and infiltration.

Moreover, in DC, the central third of the city is served by the Combined Sewer System, which I wrote about yesterday. When the new storage tunnels are finished (starting this week) most runoff in the central part of the city, however contaminated, is going to go to Blue Plains for treatment. But in the other 2/3 of the District, it will continue to go right into the nearest creek or river with all that it carries.

This is the critical point: the Stormwater Retention Credit system allows moving required runoff management investments from places that do less good for people and the environment to places that do more good. That’s huge.

Of course, for the system to work, there have to be landowners in the most critical areas willing to build certified stormwater management systems that produce credits and sell those credits to willing buyers.

The District’s innovation has caught the attention of water engineers and policymakers around the world. Many are waiting to see if it works. So far, the jury’s out: it’s great in concept but somewhat less than perfect in operation. A new, innovative, and partially market-based credit system like this has to really struggle to produce both supply and demand. The most important needs are abundant information, and active persuasion, to get producers and purchasers through the initial stages of ignorance, confusion and risk-aversion. The system probably also has to somehow provide investment capital and technical assistance to help landowners in the highest value runoff management areas to design and implement the projects to produce credits. The critical public policy goal is participation in the system by landowners in specific, high impact places, not just those with easy access to dollars and design engineers. That's the only way to maximize impact. 

Like the District itself, the staff and board of the Anacostia Waterfront Trust have been working on this since 2013. With the support of the National Fish and Wildlife Foundation and the Keith Campbell Foundation for the Environment, we designed a program called “RainPay” (get it?) to act as an intermediary or broker. Our idea is to provide the upfront capital and technical assistance to landowners in the most important places in exchange for a split of the eventual credit sales revenue. We have had a strong preference for working with churches and other nonprofits, so as to provide them with an income stream for their good works, and moreover, to provide operations and maintenance work to people who can most benefit from it. It’s been a real slog to get all the pieces in place, but we persist. You can read about the first project here. Our second project, at Ward 7’s East Washington Heights Baptist Church, is about to break ground.

The District of Columbia’s Stormwater Retention Credit system is a new way of addressing an old problem for urban areas. That’s what we need, of course. It will play a huge role in cleaning up the Anacostia, Rock Creek, the Potomac, and other DC streams if it can break out of its formative stage and become a robust marketplace. If it does, it will be an innovative and successful model for the world in how to manage polluted runoff and transform urban rivers into safe recreational and economic assets.

For more information on the Trust's RainPay program, visit