Reactive mineral coatings play an important role in contaminant transformation. This research focuses on identifying and studying redox transition zones where reactive mineral coatings are expected to be significant. To accomplish this study, a 60-foot core was collected from an area of concern at the Chambers Works Site in NJ. With stainless steel liners, 2-foot sub-sections of the core were obtained, protected with argon-purged PVC tubes, and stored at 4<sup>o</sup>C. The cores were jacked in a glove box into a total of 225 2-inch subsamples preserved with triple-layer protection to prevent oxygen permeation and organic interactions with the container. A suite of analytical tools was used on each sample including X-ray fluorescence (XRF) for composition, soil pH, redox potential (ORP), and volatile organic carbon (VOC) concentration in the headspace. From XRF results, iron and sulfur were among the dominant elements present with gradients observed throughout the core. Iron concentrations peaked at multiple depths with the most significant gradients observed from 32’ to 38’ and 49’ to 50’. Sulfur concentrations peak as well at depths consistent with Fe trends and gradients spanning five orders of magnitude; the increases in the S and Fe concentrations are consistent with sulfide precipitation. Over the 60 feet, soil pH ranged from 3.74 to 8.03. Steep gradients in the oxidation-reduction potential included -141.4 – 651.0 mV. VOCs were detected using the photo-ionization detection and reported as chlorobenzene; readings ranged from below detection limit to 6.4 ppm. As a result of this screening process, a number of redox transition zones were identified and include depths 21.0’-22.8’, 31.0’-34.3’ and 39.0’-43.0’. Other analyses that have corroborated the importance of the zones being studied involve evaluating bacteria abundance and contaminants of concern found in groundwater. A more detailed study is being conducted in four of the transition zones. <br/>

Identifying redox transition zones in the subsurface

254th National Meeting (2017)

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