By Sabri Ben-Achour
D.C. holds its wastewater treatment plant up as the largest and most advanced in the world.
And it pumps out millions of pounds of nutrient pollution into the bay, but that's changing.
Blue Plains, as it's called, can process a billion gallons of wastewater in a day.
It's a lot of water, and it has to go back into the Potomac from where it came.
But with it goes nitrogen -- 8.5 million pounds of it every year.
Nitrogen is one of the nutrients that causes algae blooms and dead zones in the Bay where nothing can live.
And this one plant is responsible for more than 3% of the nitrogen runoff in the entire bay.
But the EPA is setting a new limit for the plant, it'll need to cut it's nitrogen pollution by half, down to just under 4 million pounds a year by 2014.
The plant is well on track to do that, it's already started upgrades and is ahead of schedule.
In total, it's upgrades - including a revamp of the city's sewer systems - will cost nearly $4 billion, shared between Maryland, D.C., Virginia, and the Federal Government. This upgrade itself - to reduce nutrient pollution - will cost $900 million.