Paper No. 278-9
Presentation Time: 10:05 AM
GEOCHEMICAL AND HYDROGEOLOGICAL CONTROLS ON RADIUM AND BARIUM IN DEEP SANDSTONE AQUIFERS OF ILLINOIS (Invited Presentation)
The deep Cambrian-Ordovician sandstone aquifers in Illinois and the upper Midwest are heavily used for water supply, but they can have elevated concentrations of naturally occurring radium and barium. In the Chicago region in northeastern Illinois, many public water supplies have been dealing with these water quality issues for many years. We recently sampled 33 wells in the central part of Illinois southwest of the Chicago region to better understand the regional water quality of the deep sandstone aquifers. Both 226Ra and 228Ra were detected in all samples, though 226Ra tended to be the dominant isotope. 222Rn, a daughter of 226Ra, generally had a positive relationship with 226Ra although it typically had concentrations one to two orders of magnitude higher than 226Ra. This suggests the presence of significant amounts of 226Ra on the aquifer matrix. Dissolved 238U, the parent of 226Ra, did not appear to be correlated with 226Ra concentrations. Barium concentrations were generally not as high as observed in some parts of northeastern Illinois, and sulfate (barite) clearly controls its solubility. On the other hand, sulfate concentrations do not appear to be controlling radium concentrations. In some areas of central Illinois, there is a significant amount of Pleistocene recharge, as evidenced by relatively negative values of δD and δ18O. In general, the greater the amount of Pleistocene recharge detected, the lower the radium concentration.