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 . Our Mission.View Sewer Overlay Diagram

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One third of the District's land (12,478 Acres) are served by a combined sewer system. These sewers carry both sanitary waste and stormwater runoff in the same pipe system and during rain events once they reach capacity will discharge sewer effluent directly into the Anacostia, Potomac, and Rock Creek Watersheds. There are 60 such combined sewer overflow outfalls in the District and are shown in graphic to the left. On an average year there are typically 73 rain events that trigger these discharges and on average over 334 million gallons of unprocessed sewage flows directly into our receiving waters.

DC WASA (Water and Sanitary Authority) will be collecting over $1.2 billion from the District's residents to correct this problem so, that they are in compliance with the EPA's clean water act and to reduce the number of CSO's. However, in the preparation of WASA's LTCP (Long Term Control Plan) they mention that the most effective way to reduce them amount of stormwater runoff would be to implement a system wide alternative low impact development policy that would include "greenroof" retrofits. They mention that greenroof are a highly effective and economical form of in flow source control and that if 20% of the roofs were retrofitted with vegetated systems they could reduce the citywide runoff by 1.2% but reduce the number of CSO's by 13%. If the District could implement a policy that provided direct incentives to land owners to install these systems on all buildings over 28% of the CSO's could be prevented.

There are a number of regulations and incentives that could be enacted to help pay into a revolving "green roof fund". The first would be to enact a combined sewer overlay district which could have new projects pay into the fund and would help to offset the costs for homeowners wishing to install a greenroof by obtaining a grant or low interest loan. You could also create a "split waste water" tax credit that would allow property owners to disconnect their downspouts from the storm sewer and could be administered by WASA. Also, you could enact programs that provide "FAR or density bonuses" for developers that install greenroofs.


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