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W Minnesota Pollution Control Agency Baseline Water Quality of Minnesota's Principal Aquifers Ground Water /May 1998 In March 1998, the Minnesota Pollution Control Agency (MPCA) released a report, "Baseline Water Quality of Minnesota's Principal Aquifers," that provides data about the quality of the state's ground water resources. This fact sheet summarizes the study and provides contacts for more information. What is the baseline study? The baseline study is an assessment of ground water quality in Minnesota's principal aquifers. The objectives of the study were to determine background water quality of the state's principal aquifers and identify factors that affect ground water quality. How was the study conducted? Samples were collected from domestic wells using a statewide grid, with a distance of 11 miles between each grid node. Each aquifer identified at a grid node was sampled. Sampling included 47 inorganic chemicals and five field parameters, volatile organic compounds (VOCs), and some sampling for tritium (a radioactive isotope) and pesticides. A total of 954 wells were sampled statewide. What information did the study generate? Summary statistics were generated for each chemical in Minnesota's principal aquifers. This includes mean, median, maximum, minimum, 95th percentile, and 95th percent confidence limit concentrations. For aquifers with more than 15 samples, these data serve as background concentrations. Factors affecting water quality were identified for each chemical and aquifer. Some of the more important conclusions are listed below. • Water quality in glacial drift aquifers was generally good but varied widely, with arsenic, manganese, iron, and nitrate concentrations locally being at high concentrations. • Water quality in Cambrian and Ordovician aquifers of southeast Minnesota was good, except in those areas where the aquifers appeared to be poorly protected by overlying glacial deposits. • Water quality in the Cretaceous and Sioux Quartzite aquifers generally was poor due to high concentrations of sulfates, boron, dissolved solids (including hardness), and, in some cases, nitrate and manganese. • Water quality in Precambrian aquifers depends on the type of soil or bedrock and ranged from poor in North Shore Volcanics (high boron, manganese, and beryllium concentrations) to good in crystalline bedrock aquifers. Concentrations of most chemicals were higher in the western part of the state. This reflects increased time that the water has been in the ground, decreased recharge, and differences in parent material toward the west. Similar but less significant relationships were observed in the southern part of the state. Nitrate, iron, manganese, arsenic, and boron were among the chemicals most strongly correlated with oxidation - reduction potential (redox) conditions in Minnesota Pollution Control Agency, 520 Lafayette Road North, St. Paul, MN 55155 -4194 (612) 296 -6300, toll -free (800) 657 -3864, TDD (612) 282 -5332 This material can be made available in alternative formats for people with disabilities Printed on recycled paper containing 100 percent fibers from paper recycled by consumers