Geologic controls on the occurrence of dissolved radon in ground water in New York State.

摘要

The goal of this research is to develop effective methods to identify areas of potentially high dissolved radon concentration values to prioritize sampling of drinking water for dissolved radon concentration in demographic and geologic areas of New York State. Dissolved radon (radon-222) naturally occurs in all ground water to some extent from the radioactive decay of radium-226 in soils and bedrock. The health risk associated with dissolved radon is not from ingestion, but its addition to indoor air radon by degassing into the home from water use activities, such as showering and laundering.; The three digital, mappable geologic maps used for the investigation of dissolved radon concentration values were the geological bedrock maps at two different scales, 250000 and 25000, and the aquifers of New York State map. In the areas underlain by the metamorphic bedrock of the Reading Prong in western Orange County, a 1/4 mile grid overlying the Real Property database was used to identify homes utilizing well water to sample for dissolved radon concentration in this area. This method identified four areas requiring further detailed investigations.; The area of the Franklin Marble formation was selected for a more detailed study. The well water with the highest dissolved radon concentration showed an increase in the total dissolved uranium concentration from 38 pCi/L, sampled during the 1997 ground water recharge, to 3400 pCi/L sampled at the end of the summer ground water recession. Exploration of the area showed the source of the uranium was caused by intruding uraniferous sills into the marble, a calcium carbonate rich environment. Chemical and physical analysis of the water was completed for one full year to determine the cause of the temporal increase in dissolved uranium concentration during the ground water recession. The results show the elevated uranium concentrations are due to the well accessing a lower effective permeability fracture set in the dry years of 1997–1999 after the upper fractures enlarged by solution features are pumped dry. In 2000 with the increases in rainfall these upper fracture sets did not go dry and the total uranium concentration remained at the 38 pCi/L for the entire water year.; In the metamorphic bedrock the distribution of uranium is spotty and unpredictable. The geological bedrock maps are marginally useful at any scale to predict the location of uranium. The gridded map at 1/4-mile intervals over the spatially located New York State Real Property data to sample for dissolved radon concentration proved to be the most robust method in identifying areas for more detailed investigation. In the more detailed investigation on the Franklin Marble formation, field work combined with water sampling was the most effective method to identify the areas most impacted by high dissolved radon and uranium concentrations.