Variations of well water radon in Virginia and Maryland.

In north-central Virginia and south-central Maryland, municipal water supplies obtained from reservoirs provide radon-free potable water. However, about 10 percent of the population consumes well water. Radon in drinking water from some wells exceeds 4,000 pCi/L. Only about 30% of the radon is lost between the well storage tanks and the homes. The average radon concentration is about 2,000 pCi/L, which greatly exceeds the U.S. Environmental Protection Agency's recommended Maximum Contamination Level of 300 pCi/L. In this study of a geologically diverse area, the well water comes from granite (radon averages about 3,000 pCi,/L), schist and phyllite (about 2,000 pCi/L), sandstone (about 1,500 pCi/L), and quartzite (about 1,100 pCi/L). Aeration experiments on well water in storage tanks indicated that about 60-70% can be removed using a splash box with an exhaust fan on the storage tank, and about 60-70% can be removed using bubble aeration. About 90% of the radon can be removed by the simultaneous use of bubble aeration, splash box, and an exhaust fan. However, this combination does not become less efficient through time. Passing the water through tanks of activated charcoal can remove about 90% of the radon, though the charcoal becomes less efficient over an interval of a few months.