Magnitude and Variability of Biogenic Interference in Cold Regions Soils

In organic soils commonly found in cold regions, many compounds with similar characteristics are found in petroleum contamination and natural organic material (NOM). These similarities make it difficult to distinguish between natural compounds and true contamination using standard test methods. “Biogenic interference” is the term used to describe the NOM quantified as “petroleum” during a standard test for soil contamination. The inability to differentiate between biogenic interference and soil contamination is of concern because it can cause cleanup standards to be set at lower limits than the actual contamination warrants. This paper presents the results from over 200 uncontaminated soil samples that were analyzed to determine the magnitude and variability of biogenic interference in soils from cold regions. Studies were conducted to evaluate the correlation between fundamental physical∕chemical properties of soil and extractable NOM levels. Samples were also collected and analyzed to evaluate spatial (vertical and horizontal) variations in background extractable NOM at one site. A final set of samples was analyzed to determine the range of background extractable NOM levels at uncontaminated sites throughout Alaska. The results show that uncontaminated soil from across Alaska can contain several hundred to several thousand mg∕kg of extractable naturally occurring diesel and residual range organics. A high degree of variability was observed in the amount of extractable NOM at different sites across Alaska and within a single site.