Geology and Ground-Water Condition in the Chisholm-Dewey Lake Area, St. Louis County, Minnesota

Document
Description
The Chisholm-Dewey Lake area is in St. Louis County, northeastern Minnesota, and is about 175 miles north of Minneapolis and St. Paul. Included at the south edge of the 105 square mile project area is the city of Chisholm (1960 population, 7,144) which is situated at about the midpoint of the north-eastward-trending Mesabi Range, the major iron ore producing district in the United States. The are is in the Superior Upland physiographic province. A high ridge of Giants Range Granite forms the Laurentian Continental Divide and crosses the lower southeast quarter of the area. Several water and wind gaps dissect this granite ridge; the broadest is at Chisholm where a gap is about 1 1/2 miles wide. North and South of the granite ridge the surface is characteristic of glaciated terrain. It contains numerous swamps and lakes and many knobs and ridges which consist largely of sand, gravel, and boulders. Altitudes within the area range from 1,796 feet above m.s.1. (mean sea level) atop of the divide in the southeast to 1,365 feet at the surface of Shannon Lake in the Northwest. The surficial deposits in the Chisholm-Dewey Lake area consist of glacial clay, silt, sand, gravel, and boulders of Quaternary (Pleistocene) age and organic (peat) deposits and alluvium of Recent age. The bedrock is of Precambrian age and consists of igneous and sedimentary rocks that have been slightly metamorphosed. Some water is obtainable from every formation in the Chisholm-Dewey Lake area; however, the major aquifers occur in the oxidized zones of the Biwabik Iron-Formation and the sand and gravel (outwash) deposits in the glacial drift. Although the Biwabik Iron-Formation yields large quantities of water, the power costs required to lift the water more than 200 feet, as compared with lifts of 20 feet in glacial drift aquifers, and the constant threat of interruption by mining operations prevent selection of the iron-formation as a dependable source of water supply at Chisholm. A Chisholm muncipal well completed in a glacial outwash deposit that occurs in a bedrock channel on the north edge of the city has been pumped at 1,200 gpm *gallons per minute) for 8-10 hours with 14 feet of drawdown in the well. Another city well, presumably completed in outwash material that occurs between 55 and 74 feet below land surface, was pumped at 125 gpm with 52 feet of drawdown. A pumping test made of a sand and gravel aquifer underlying an area in the northwest corner of Chisholm showed a coefficient of transmissibility (T) of 15,000 gpd (gallons per day) per foot and a coefficient of storage (S) of 0.0003. Ground-water recharge, which derived from local precipitation, occurs mainly after the spring thaw and during heavy, prolonged rainstroms in the summer and early fall. An average annual estimate of total precipitation during 1952-59 on 90.67 square miles of the Chisholm-Dewey Lake area included in the Sturgeon River drainage basin amount to 45 billion gallons. For the same period an estimated 34 billion gallons of water per year was lost through evapotranspiration; 11 billion gallons per year flowed in streams out of the area; and 0.2 billion gallons per year was withdrawn by pumping. Thirteen comprehensice chemical analyses and reports from well owners show that iron and manganese are the most troublesome dissolved mineral constituents in ground water in the Chisholm-Dewey Lake area. The combined concentration of iron and manganese ranges from 0.04 to 14 ppm (parts per million). The combined concentrations are greater in ground water from aquifers adjacent to or underlying swamp areas than they are in ground water from bedrock and drift aquifers along the slopes of bedrock hills and ridges. Dissolved-solids contents of all water samples analyzed range from 108 to 360 ppm which is below the 500 ppm recommended limit of the U.S. Public Health Service (1961) for public water supplies.
Date Issued
1970
Number of Pages
72
Decade
Publisher
U.S. Geological Survey
Body of Water
County
Rights Holder
Minnesota Water Research Digital Library
Rights Management
Creative Commons