Three years after a leak of radioactive tritium focused attention on the Vermont Yankee nuclear plant, the state Health Department says radiation levels are declining
That’s the good news. But state officials are also worried that detecting new leaks may be difficult because the groundwater monitoring wells are already contaminated.
The contamination came to light in late 2009, when a plume of radioactive water was discovered flowing underground from Yankee east toward the Connecticut River.
The source of the radioactive tritium was later traced to leaking underground pipes – pipes that Yankee officials had first said did not exist.
Bill Irwin is the state’s radiological health chief.
He told the Fish, Wildlife and Water Resources Committee recently that the tritium levels have declined, as measured in picocurries per liter.
"The highest levels of tritium in the groundwater there has gone from about 2.5 million picocurries per liter to about 88,000 picocurries per liter," Irwin said.
Irwin handed out a map showing where the wells are located on the plant grounds. He said 12 wells still show tritium, with some exceeding the Environmental Protection Agency’s safety standard for drinking water.
"Now these are monitoring water wells not drinking water wells, so someone would not be doing the appropriate thing by drinking from these wells," he said. "But it does give you an indication that the highest levels are four times the EPA drinking water level guidance for tritium at this time."
After the tritium was discovered, plant technicians sealed many of the pipes to prevent future breaks. But Irwin said the current contamination makes detecting new leaks difficult.
"The groundwater remains contaminated and leaves us without any means of detecting new leaks," he said. "Obviously, if you’re looking for something new leaking – with a low concentration – if the groundwater already has much greater concentrations in it we will have a difficult time detecting that. So we genuinely have to rely on other methods of detecting tritium leaks at the plant."
Those other methods are carried out by Yankee personnel under the supervision of the Nuclear Regulatory Commission. They include inspecting plant systems for any sign of new leaks and examining sumps and other areas where water collects.
Still, Irwin said pinpointing future leaks will be a challenge.
"We’re left with a groundwater monitoring program that’s crippled by the fact that essentially the gauges are contaminated," he said.
Irwin and other scientists have also studied fish caught in the Connecticut River and elsewhere in the region. He said the research indicates that the strontium 90 and other isotopes found in the fish did not come from Vermont Yankee.
There’s little difference in radiation levels between fish caught near Vermont Yankee, and those found far from any nuclear power plant. Irwin said that indicates the source of the radioactivity in the environment was probably above ground nuclear testing that ended in the early 1960s.