A USGS model published in 2017 predicts 2.1 million people in the United States drink well water containing arsenic above the EPA Maximum Contaminant Level of 10 ug/L. The map above shows the probability of finding arsenic greater than 10 ug/L in wells across the continental United States. In states like Maine and New Hampshire, wells are usually drilled into hard crystalline bedrock, which tends to increase the likelihood of high arsenic. Maine and New Hampshire also have among the highest per capita reliance on private wells for drinking water in the United States (ME: 56% and NH: 46%), yet testing rates are low.