Microscopic organisms remove nitrogen from Arlington's waste water at the Water Pollution Control Plant in South Arlington.
Since the 1930s, Arlington County has operated the Water Pollution Control Plant along the northern edge of Four Mile Run, a stream that forms part of the county's southern border.
But something's changed this year. The plant has something new: nitrogen-eating bacteria as part of its waste water treatment system. In a conference room at the plant, operations manager Frank Corsoro shows how the level of nitrogen that's discharged into the river has declined.
"These are the total maximum daily loads but on a annual basis in pounds per year," he says. Moving his finger across the graph, he shows a blue line that peaks at 12 pounds per year then dips down to 1.4 -- well below new guidelines released last week by the Environmental Protection Agency.
"I would find it hard to believe that, right now, anybody is lower than us," Corsoro says. "I would be very surprised."
That's because Arlington County has invested more than $500 million into this plant over the last decade.
Past the aeration tanks, beyond something called a sludge digester, Corsoro comes to the new facility.
"It doesn't look like much. But this is really is what's allowing us to get down to these very, very low total nitrogen levels," he says.
Fairfax County doesn't have one of these. Neither does Alexandria. That means that they'll have to find some way to cope with the new standards.
That's an especially difficult problem for Alexandria, where raw sewage is dumped into the river during heavy rains. Alexandria officials declined to answer questions about the new standards, but the situation is different in Arlington.
"There's a lot of competition for the dollars that are out there, and the county, I think, wisely chose to get in the queue first and develop their plan well in advance of when the requirement was going to kick in," Corsoro says.
As to whether Arlington's leading the region in this area, Corsoro says, "I don't think there's any question."
Stripping nitrogen from waste water doesn't come cheap, and other local governments in the D.C. area are facing the potential of following in Arlington's footsteps -- by investing hundreds of millions of dollars into reducing the amount of pollution headed to the Chesapeake Bay.