Table of Contents

Metals occur naturally in soils, but their spatial distribution is influenced by the soil’s parent material as well as human influence such as different types of land use. Identifying and quantifying metals in soil and water is important because some metals are toxic. The RSC property has seen a variety of uses in recent history, including some that involved the use of fertilizers, pesticides, and fungicides which often contain metals.

The goal of this study was to obtain baseline data for metals concentrations in soil and water samples at the RSC. This pilot survey tested for the concentration of select metals of interest (Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, and Zn) in soil and water samples from several areas at the site.

Most of the metal concentrations had unimodal distributions, many of which were positively skewed due to a few high concentration samples as seen in the following histograms.

To understand these results in the context of the region, the soil sample results were compared to data from the United States Geological Survey (USGS). The USGS collected soil samples from locations East of Sabin, MN (Site MN6361) and near Rollag, MN (Site MN2265) in September 2009. Data from these locations offer comparison values and baseline metal concentrations for the region. The USGS published maps of the conterminous United States with interpolated values between sampling sites, from these maps a predicted range was determined for the location of the RSC.

Values were also compared to the Soil Reference Values (SRVs) from the Minnesota Pollution Control Agency (MPCA) which are a screening tool used to evaluate potential human health risks from exposure to contaminated soil. See the following table.

Some of the metals had average concentrations that matched expected concentrations for the region, and many had average concentrations below what was expected for the region. The USGS data came from analysis done using a total digestion technique while the RSC data from this study came from analysis done using a partial digestion technique. This may explain why some metals had average concentrations much lower than expected for the region. Why Cu, Fe, K, Mg, Mn, and Zn had concentrations below the expected range while Cd, Cr, and Pb had concentrations in the expected range was unclear. The chosen digestion technique was likely more effective at freeing Cd, Cr, and Pb from the soil matrix and less effective at freeing Cu, Fe, K, Mg, Mn, and Zn from the soil matrix.

Graduated symbol maps were created in ArcGIS Pro with data grouped into 5 classes based on the Jenks Natural Breaks method. This provided a qualitative picture of which locations had higher or lower metal concentrations.

These preliminary investigations of the spatial distribution identified areas of interest for continued study, i.e. areas of high concentration.

Since ArcGIS Online maps cannot be embedded, I have included a Google MyMaps showcasing the data in a graduated colors map. Click the icon in the upper left to see the various layers.