The U.S. Geological Survey has begun a survey of private wells in New England to determine how many contain dangerous levels of uranium.

John Colman is leading the investigation, working with the Massachusetts departments of public health and environmental protection, The Boston Globe reported Friday. Next week, 1,600 residents of three counties in eastern Massachusetts will get letters with two plastic bottles asking for samples of their water.

"It's easy, it's free, and you learn something about your water," Colman said.

Colman said the homeowners were selected to give a full sample of the rock layers in the area.

Since states began monitoring public water systems for uranium about five years ago, 70 have been found in Massachusetts, Connecticut and New Hampshire with levels exceeding those deemed safe by federal standards. The new study is the first to look at private water supplies, which serve about 500,000 people in the region.