Formatted Title:

World History (Cold War to Present) Preserved in the Sediment Record at an Industrial Facility

Background/Objectives:

Understanding the relative age of contaminated sediments in comparison to potential historical releases can enhance the conceptual site model for a sediment remediation project by providing insight to differentiation, delineation, and allocation of sources. Determination of when and whether sediments and contamination were deposited can be conducted through a variety of methods, including radiometric dating, chemical analysis, bathymetric comparison, and lithologic evaluations.

Approach/Activities:

As part of a feasibility study investigation, multiple cores were collected throughout a creek and associated tributaries. Notably, one core advanced contained newspaper fragments dating back to 1945 parallel to an adjacent core containing known fill material. Select boring locations advanced were evaluated for radiometric analytes, including Pb-210, Cs-137, and Be-7. Radiometric results were evaluated using a constant flux, constant sedimentation model. Sediment depositional environment strength was calculated from these results. Additionally, bathymetric surveys, completed along same or like transects in 2017 and 2022, were compared to identify areas of recent deposition or scour, helping to understand geomorphological processes in the waterbody.

Results/Lessons Learned:

Sediment depositional studies can benefit from coordinated parallel approaches. The combination of radiometric dating, chemical analyses of sediments, lithologic evaluations, and careful field observations provides a robust methodology for evaluating sediment depositional and chemical discharge histories. In this case, a 1945-time horizon was established in sediment by the fortuitous recovery of newspaper fragments referencing events exclusive to 1945: release of movies (You Came Along and A Tree Grows in Brooklyn) and events of World War II (Operation Herring and specific bombing raids in Europe). These fragments establish the 1945 time-horizon at a depth of 3.125 feet below sediment surface (ft-bss), which corresponds to non-detect results for Cs-137. After 1945, atmospheric nuclear testing resulted in the fallout and deposition of Cs-137, which peaked in 1963. A corresponding concentration profile of Cs-137 is preserved in sediments with peak concentration measured at 1.375 ft-bss (1963), then declining in concentration toward the sediment surface (present day). The inclusion of comparative bathymetric data allowed for identification of areas of deposition (addition to sediment record) and scour (erasure of the sediment record and future disconformity). Sediment profile imaging and comparative bathymetry suggest net sediment deposition at the confluence of three water bodies, which was validated by Cs-137 data indicating positive rate and strength of deposition compared to a reference location.

Nathan Stevens

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World History (Cold War to Present) Preserved in the Sediment Record at an Industrial Facility