USING CHLOROFLUOROCARBONS AND TRITIUM TO DATE GROUNDWATER FROM THE JORDAN AQUIFER IN RICE COUNTY, MINNESOTA

The Jordan Aquifer, a sandstone unit that is confined by roughly 100 meters of glacial sediment to the west of the Cannon River, and by several strata of shaley limestone to the east, has recently become the primary well source for private landowners across Rice County, Minnesota due to recent increases in nitrate pollution among other groundwater sources. Although little nitrate has been found in the water of the Jordan aquifer, and other hydrologic models indicate groundwater in the Jordan Aquifer should be hundreds to thousands of years old, well water from 10 sites tested for chlorofluorocarbon (CFC) and tritium concentrations show recharge dates are actually on a decadal scale. Furthermore, the variability of the local stratigraphy suggests that not all groundwater is being protected to the same degree; in some regions as little as 25 meters of sediment are all that separates the top of the Jordan from surface runoff. Fracture flow, which in this case occurs when younger water travels horizontally through fractures into neighboring Jordan wells, is one available explanation for the short recharge time within the Jordan aquifer. Rough calculations of vertical hydraulic conductivity of surface water moving down into the Jordan interpreted from the bore hole stratigraphy of some wells indicate that without fracture flow, water should take anywhere from 1,000 to 2,500 years to recharge the Jordan. Well water was further tested with an ICP-MS for trace elements that could indicate anthropogenic contamination such as Lead, Cadmium, and Arsenic, and chloride content which indicates that there has been recent surface runoff from road salt. This study should inform concerned professionals as well as the general public about the importance of keeping pollutants from entering rivers and other surface water reservoirs in order to keep groundwater healthy.