USGS study examines levels of metals in native soils in Iowa

A common misconception among purchasers of commercial real estate is that the only good environmental due diligence result is one in which no contamination is found in soil samples taken as part of a Phase II audit. This ignores the fact that soils in Iowa have trace amounts of metals which are byproducts of the degradation and erosion of native rock and glacial till.

As an example, lets assume that during a Phase II inspection of a site that a laboratory reports that soil extracted from a soil boring contains lead. A common reaction among buyers is to assume that by finding lead in the soil that a pending sale will have to be called off because the site is “contaminated.” That reaction may well be totally misguided. Soils in many areas of Iowa naturally contain background levels of various metals, including lead. In some parts of northeast Iowa, including Dubuque, the alluvial soil has very high levels of lead that exceed most state and federal standards. In some cases, geologists attribute the lead in alluvial soil to lead that has migrated to those soils through erosion of local lead-bearing rock. Galena, Illinois has been a national producer of lead and lies just on the other side of the Mississippi from Iowa. The Mines of Spain area south of Dubuque has been mined for lead as far back as the late 1700s.

Until recently, there was no comprehensive information on the metals content in Iowa soils. That situation has now, gratefully, changed.

The Iowa Department of Natural Resources has recently has produced a document with the unfortunately vague title of “The Iowa State-Wide Trace Element Soil Sampling Project: Design and Implementation.”

This Iowa study was conducted by a joint venture between the Eastern Mineral Resources Group (EMRG) of the United States Geological Survey (USGS) and the Iowa Geological and Water Survey (IGWS) of the Iowa Department of Natural Resources (IDNR). The major goals of the Iowa study were to “determine baseline, or at least background concentrations of naturally occurring chemical elements across Iowa based on soil samples, and to use the resulting data set to provide context for a number of geological and environmental studies.” Id. at 16. The samples were taken from soil, as opposed to stream sediment. The shallow samples were from 0-8 inches deep and the “deep” samples were taken from 12-24 inches below the surface. I assume that the focus on such shallow soil samples was to try to correlate the results to USGS sampling of stream sediments in other states. Regardless of the motivation, taking soil samples from such a shallow depth is likely to understate the trace metals in native soils for those metals that can be transported by water, leach, or which can migrate into deeper soils as the soils are disturbed by agricultural activity. Lead is one example of a metal that has demonstrated a propensity to migrate to a lower depth due to its density.

Still, the results are very interesting for anybody with an interest in understanding background levels of metals in Iowa soil.

Lead was found in 100% of all samples across the state, with a mean of 20.86 ppm. However, a very high concentration of lead was found in deep samples in and around the Danbury, Iowa area in Woodbury and surrounding counties.

It is worth noting that arsenic was found in 100% of all soil samples with elevated levels found in southern and central Harrison, Shelby, Audubon and Guthrie Counties and northern Pottawattamie, Cass and Adair counties. One sample in Audubon County was more than 19 ppm of Arsenic. The statewide mean concentration was 9.19 ppm. The geologist who authored the report attribute the arsenic to the breakdown of pyrite and glacial till and rock parent material. Id. at page 72. The report also noted that 48% of rural drinking water wells in Iowa contain arsenic above the USEPA’s maximum contaminate level (MCL) of 10.0 ppb for public water supplies. Iowa has a human health criterion for arsenic at 0.18 ppb. This means that it is nearly impossible to comply with Iowa law unless you import or distill your water supply.

On page 32 of the report, Barium was found at elevated levels in all of the Counties along the Missouri River south of Woodbury County, Iowa, with a band running across the state along State Highway 92.

Chromium, Mercury, were also found in many of the samples from around the state. Mercury was found in 96.99% of all samples with a mean sample result of 0.03 ppb. The highest result was 0.40 ppb.

The United States Geological Survey (USGS) and the Iowa Geological and Water Survey (IGWS) of the Iowa Department of Natural Resources should be congratulated for getting consistent data in what appears to be a scientifically sound effort.

About James Pray

Attorney with BrownWinick Law Firm in Des Moines, Iowa.
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