Technicians seeking the source of a leak of radioactive tritium at the Vermont Yankee nuclear plant have found concentrations in groundwater there that were three times higher than what was discovered last week, a plant spokesman said Monday.

Tritium was measured at 70,500 picocuries per liter, which the spokesman, Rob Williams, characterized as a low level. The highest level discovered so far “does not present a risk to public health or safety whatsoever,” he said in a statement.

But it does put Vermont Yankee over the threshold at which it is obligated to make a report to federal regulators within 30 days, and say what it will do about the problem. The limit, 30,000 picocuries, was crossed on Sunday.

The Nuclear Regulatory Commission has already been at the site to study the problem, and Vermont Yankee is well into an attempt to find the leak and map the pollution.