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Minnesota Geological Survey
Harvey Thorleifson, Director

 
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MINNESOTA SOIL, TILL, AND GROUND-WATER GEOCHEMICAL DATA

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R.S. Lively and L.H. Thorleifson
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Minnesota Geological Survey
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Open File Report OFR-09-02

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Recommended citation: Lively, R.S., and Thorleifson, L.H., 2009, Minnesota soil, till, and ground-water geochemical data. Minnesota Geological Survey Open File Report OFR-09-02, 19 p., 1 poster, 69atlas pages, 8 digital tables, 1 geodatabase.

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2009 by the Regents of the University of Minnesota
All rights reserved

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Associated files on the Link site:

Data Tables -- data_tables.zip--Excel files and explanatory material to supplement the data plots and geodatabase information.

Geochemical Atlas of Minnesota -- Single page plots of individual elements for each medium sampled, soil, till and ground water. The folder element plots contains pdf documents for each element or other variable analyzed. Some pages have data for a single medium only. The pdf file entitled Mn_Geochemical_Atlas_maps is a single document that contains all of the map pages. This is a large file (approx. 360 megabytes).

Geochemical Landscape of Minnesota -- PDF poster(42 in. wide x 50 in. long) that shows landscape features with overviews of element distribution patterns in soil, till and ground water.

Geodatabase -- geodatabase.zip--ESRI file geodatabase containing separate shapefiles of point data for soil, till, and ground water, used to create the geochemical maps; also contains a polygon file of Minnesota counties. Unzips to: statewide_geochem.gdb.

Metadata -- Folder containing metadata about the soil, till and ground-water plots.

Readme -- Brief summary of the files on the link site.

Report_geochem_Mn-- PDF summary of the project and outcome.


 

ABSTRACT

The rocks and soils that are the foundation of our environment leave an imprint on the chemistry of our water and our lives. This chemical landscape reflects a combination of natural history and cumulative human impacts, and it influences biodiversity and human health. Geochemical mapping thus is needed to clarify elemental variations, and to support assessment of the natural and human-influenced factors that dictate these variations. The Minnesota Geological Survey (MGS) and the Minnesota Pollution Control Agency (MPCA), in cooperation with the United States Geological Survey (USGS), therefore have assembled three geochemical data sets for soil and water as a basis for an atlas that will provide an overview of geochemical patterns, and a reference that will place more thorough environmental geochemical surveys into a context. Data contributed to the project were derived from soil, soil parent material, and well water samples analyzed following USGS, Geological Survey of Canada, and Environmental Protection Agency protocols, respectively. The soil data include stream sediments largely in the western part of the state, and the soil parent material data are from sites underlain by till. The well water samples were from multiple aquifers utilized for drinking water, at greatly varying depth and geology. The analyzed fraction for soils was <150 microns, for soil parent materials it was <63 microns, and both employed a multi-acid near-total digestion. Soil geochemistry data, provided by the USGS, were derived from 1,352 samples. Maps were prepared by averaging the results from soil in the top 0.2 meter and at about 0.5 meter depth from the same sample site. The stream sediment data included in the soil maps were from west-central and western Minnesota, and a few additional samples in other parts of the state. Soil and some stream sediments were collected in 2004 and 2005. Most stream sediments were collected in 1979, under the National Uranium Resource Evaluation program, and were reanalyzed by the USGS in 2005. Results for soil parent material were from 250 till samples collected at 1 to 2 meters depth that were analyzed as part of an indicator mineral survey conducted in 2004. The ground-water data provided by the MPCA was based on 954 water well samples collected between 1993 and 1996. The water well sampling was conducted in a nine square mile cell on 11-mile centers, within which one sample was collected from each identified aquifer used as a source of drinking water. Atlas pages were prepared for each variable, with maps for each sampling medium on a single page, along with a generalized explanation. Symbol categories were based on natural groupings in the data using the natural breaks method; values below detection were set to half the detection limit, or an arbitrary value in the case of the ground-water data. The data tables for each medium are available as Excel tables and as an ESRI geodatabase. Selected element maps and general landscape information are also presented as a poster to give an overview of the geochemical landscape and a basis for its interpretation in relation to geology. Together, the tables and database components provide a regional reference for environmental management and exploration that will typically rely on more detailed sampling. Construction of the atlas was funded by the Minnesota Minerals Coordinating Committee. The maps, poster, and data are available from the Minnesota Geological Survey web site, and additional information may be obtained from the MPCA and the USGS.



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Figure 1. Direction of ice flow and provenance of glacial sediments in Minnesota.

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Figure 2. Typical soil sampling conditions.

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Figure 3. Location of soil (black circles) and stream sediment (red squares) sites.

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Figure 4. Typical till sampling conditions.

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Figure 5. Location of till sample sites.

Figure 6. Location of well water sampling sites.

Figure 7. Two depictions indicating the 3D nature and varying geologic context of the well water data, using manganese as an example. The upper figure is a 3D oblique statewide view looking from the southwest; the lower figure shows all data projected onto a south to north section view

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