When does a river qualify as impaired?

VOLUNTEERS FOR THE Addison County River Watch Collaborative on May 1 sample the Lemon Fair River, a tributary to the Otter Creek, for phosphorus, nitrogen, E. coli and turbidity. The Collaborative’s data is used to educate towns about the quality of nearby streams and rivers, and it is sometimes used in the Tactical Basin Planning process.

ADDISON COUNTY — At 7:15 a.m. on May 1, a member of the Addison County River Watch Collaborative stretched a long pole with a plastic cylinder into the water of the Lemon Fair River, a tributary to the Otter Creek that runs through Orwell, Shoreham, Cornwall and Weybridge.
Later that day, the sample was sent off to a lab, where it was tested for concentrations of phosphorus, nitrogen, E. coli and turbidity.
The collaborative samples the Otter Creek and its tributaries on the first day of every month, excluding winter. Their water quality data is the some of the most consistent and thorough in the area, dating back to 1997, and is often the catalyst for clean water projects.
Every two years, based on a rotation, the collaborative chooses a “focus watershed,” where the data collection process becomes more intensive. For 2018-2019, they are focusing on the Lemon Fair.
Director Matt Witten, who splits his time between the collaborative and a teaching job at The Lake Champlain Maritime Museum, presents the data to interested members of the public at “water quality chats,” which are usually hosted by local conservation commissions.
In April, Witten gave a chat at the Middlebury Conservation Commission. He discussed the status of each river in the area, starting with the Lemon Fair. Almost all of the land surrounding the river is farmland, and the soils are thick with clay, which attracts phosphorus like a magnet, he said.
The collaborative wants to see concentrations of phosphorus that are below 27 micrograms per liter, the state-wide standard for the amount of phosphorus that should exist in any body of water that does not have a prescribed TMDL. 
But in the Lemon Fair, phosphorus readings consistently range from 100 to 300 micrograms per liter. 
“The Lemon Fair blows the standard entirely out of the water,” Witten told the crowd in Middlebury. “There’s way too much phosphorus in the Lemon Fair, no matter how you look at it.”
But the Lemon Fair is not on the state’s official list of impaired waters. When a body of water is listed, it requires its own TMDL, which is a step toward remediating its quality.
Basin planners Angie Allen and Ethan Swift have seen this data, but according to Swift, it’s not enough to list the river.
It’s naturally silty, and though its brown current looks polluted, it was likely just as brown centuries ago, Witten says. That type of river can handle a higher level of phosphorus while supporting a healthy ecosystem.
“We actually have some streams in Vermont that may exceed the phosphorus criteria, but the other nutrient response variables would indicate that the stream is still meeting standards, and it may still be supporting the critters that live there,” Swift said. “So far, the data has not been compelling enough for us to consider the Lemon Fair as impaired.”
But Swift admits, even though the Lemon Fair can support its ecosystem, its phosphorus still flows into the Otter Creek, which flows into Lake Champlain. For now, Allen and Swift are watching the river closely and encouraging best management practices for the landowners who live on its banks.

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