D.C.’s wastewater system dates back to 1810 and includes 1,800 miles of sanitary and combined sewers—a longer distance than from D.C. to Denver. The system includes 16 stormwater stations, 75,000 catch basins and manholes, and 9 wastewater pumping stations. The advanced treatment system at Blue Plains is the largest of its type in the world, in-taking on average 330 million gallons per day (MGD), including from outlying counties, with a capacity of 384 MGD, the equivalent of 560 Olympic swimming pools. A third of the city is served by combined sewers, which can result in sewage overflows into the region’s rivers during high rain events. DC Water’s Clean Rivers Project, planned in the early 2000s and in construction since 2011, is working to reduce such overflows by, among other things, building 18 miles of new tunnels to store water during high rain events.