RADIONUCLIDES IN GROUNDWATER FROM IGNEOUS AND METAMORPHIC ROCK AQUIFERS: CAN LONG-TERM PUMPING REDUCE THE CONCENTRATIONS AND RELATED GROSS ALPHA?

Groundwater produced from igneous and metamorphic rock aquifers of the southern Piedmont/Blue Ridge locally contain naturally occurring concentrations of uranium, thorium, radon, and radium that exceed the federal EPA and state EPD drinking water standards. Commonly, wells that have concentrations or gross alpha particle activity that exceed the regulatory limits are abandoned because of the potentially high costs associated with treatment. However, with the growing demand on surface water, many municipalities and industries are exploring for, and developing groundwater as an alternative to surface water or to augment surface water supplies. Uranium and thorium, and their associated daughter products, are generally naturally occurring and may be concentrated in rock types, such as granites, granitic-gneisses, and granitic pegmatites. Cities and towns with subsurface geology which favors high radionuclide concentrations need alternatives to test-well abandonment.

A recently drilled well in granitic biotite gneiss cross cut by large granitic pegmatites has an estimated yield of 150,000 gallons per day. However, uranium concentrations measured in the water extracted from this well exceed the State°¦s regulatory limit of 30ƒÝg/l. The client is in desperate need of additional water supplies. As an alternative to abandoning the well, we have conducted a two-week (820-hour) pumping test to see what, if any, effects pumping will have on the concentration of naturally occurring radionuclides. The results of this test are presented.