Characterization of Groundwater from Rice County, Minnesota, using CFC dating, Hydrogen and Oxygen Isotope Analysis, and Ion Concentrations
Kathryn Stalker,Karla Knudso, Travis Ruthenburg, Alexandra Schmitt, Kristen James, Brandon Murphy, and Bereket Haileab, Dept. of Geology, Carleton College, Northfield, MN 55057
March 2004 (This abstract was presented at the GSA meeting in Minneapolis, Minnesota)
Abstract
An initial investigation was performed to examine isotope, CFC, and ion presence in the groundwater of Rice County, Minnesota. The groundwater displays d18O ranging from -8.67 to -9.80 and d D ranging from -54.00 to -75.00, consistent with regional meteoric recharge. CFC-determined recharge dates range from 1940 for water samples from the Jordan Formation aquifer to 1970 for the Shakopee Formation, while shallow wells show recharge within the last 2-3 years. Major ion concentrations indicate a likely anthropogenic input of chloride and, more importantly, nitrate, in the shallow wells. Nitrate concentrations show a direct correlation with the recharge dates, with many recently sourced wells showing nitrate concentrations above the EPA standard for drinking water. Potassium was found in low concentrations except for one anomalously high value of 89.62 mg/L. Ammonium was only found in two wells, with concentrations of 2.06 and 0.27 mg/L.
Key words: CFC, groundwater, oxygen, hydrogen, isotope