Published in October 2019 Focus on the Environment Newsletter
The Michigan Department of Environment, Great Lakes, and Energy (EGLE), Remediation and Redevelopment Division (RRD) recently published the Soil Background and Use of the 2005 Michigan Background Soil Survey Resource Materials. The document outlines procedures for determining whether concentrations of metals in soils at a site can be attributed to naturally occurring sources and incorporates their 2015 update to the Michigan Background Soil Survey.
Most remedial programs, including those in Michigan, do not require cleanup or due care obligations if contamination is due to natural conditions, even when concentrations exceed risk-based generic cleanup values. This scenario is most commonly encountered with certain metals in soil. To determine if concentrations of metals at a site result from a release or from natural conditions, it is common to perform site-specific background studies. These studies seek to identify soils in the vicinity of a potential release that would be unaffected by any release and have similar origins.
In areas with long industrial histories, it is often difficult to find appropriate soils to conduct background studies. At the same time, it can be redundant for every site to have its own background investigation. In these situations, it is often useful and beneficial to have regional values that can be used as screening levels at a site without immediately going to the time and expense of a site-specific study. The new Michigan guidance provides such a study.
Included in the Michigan guidance are tables of generic background concentrations that can be applied at a site. To use these tables, one must first determine which of four former glacial lobes advanced across the site. As the glaciers advanced across Michigan, they scraped up pieces of bedrock. Different types of bedrock have different concentrations of metals, so each glacial lobe that advanced in a different direction across different bedrock types is expected to have unique metals concentrations relative to other lobes.
The tables are also organized by generic soil types – topsoil, sand, and clay. After the glaciers are gone, how the deposited materials weather and soils are formed can have a significant effect on the concentrations of metals that remain in the soil. Knowing the glacial lobe and soil type, tables in the guidance can be used to determine whether a release may have occurred, or if metals concentrations are likely a result of natural conditions.
If you have a site where you are trying to differentiate between a release and natural conditions, please reach out to us. We authored an Evaluation of Background Metal Concentrations in Ohio Soils for Ohio EPA in 1996 and have continued to work with our clients to ensure they don’t unnecessarily address naturally occurring concentrations. In 2018, we published another study identifying sources and influencing factors of background concentrations of arsenic in Ohio soils . In the process of these investigations, we have compiled a very large database of background concentrations of metals in soil, sediment, and groundwater throughout the United States. This information may be the difference between no further action and additional investigation or the potential cleanup of metals at your site.
Nate Wanner is a Cox-Colvin Senior Scientist with over 15 years of experience leading and completing environmental projects, in addition to six years as an educator and IT director. He holds a BS in Geology: Water Resources from Ohio University and a Masters in Geographic Information Systems from Penn State University. His areas of expertise include brownfields, underground storage tanks, due diligence and database services. Nate is an Ohio EPA VAP Certified Professional (CP), a Certified Professional Geologist (CPG) with the American Institute of Professional Geologists (AIPG) and is a registered Professional Geologist (PG) in Kentucky.