Background/Objectives: The phased remedial investigation (RI) performed at the Berry's Creek Study Area (BCSA) in Bergen County, NJ, required high-resolution sediment coring and geochronology to achieve several objectives.
These included (i) estimation of short- and long-term sediment deposition rates to support both conceptual and quantitative models of the site sediment budget and (ii) evaluation of natural recovery patterns for multiple constituents of potential concern (COPCs). A variety of physical settings and ancillary challenges necessitated a flexible and continually refined method of data collection. The site included approximately seven miles of waterways (both primary stems and tributaries) and 760 acres of Phragmites marshes; differing geotechnical conditions required equipment with the precision and flexibility to support low- and high-resolution sampling in a variety of physical settings.
Approach/Activities: 78 total sediment cores were advanced for geochronology and COPC characterization. Customized sampling methods were developed and refined over the course of the RI/FS to improve sampling depth control and improve overall data quality by consolidating sample collection into a single core. Characterization included analyses for the radioisotopes 137Cs, 210Pb, and 7Be; COPCs; and geotechnical parameters. Data interpretation focused on the identification and quantification of sediment deposition rates using the highest-confidence lines of evidence, i.e. certain 137Cs-derived results. Additional deposition rate estimates were derived from ancillary results from 137Cs analysis as well as 210Pb analyses performed over multiple horizons.
Results/Lessons Learned: The coring effort successfully characterized the range of sediment deposition histories and varying degrees of natural recovery of COPCs in sediment. The results clearly underscore the marked differences in behavior between marsh and waterway habitats. Marshes showed consistent records of sediment deposition and robust patterns of natural recovery, with precise peaks of 137Cs and COPC concentrations, indicative of peak COPC loading in the middle of the 20th century. Long-term sediment deposition rates for tidal marsh areas averaged 0.40 cm/yr.
Waterway coring results differed considerably from those of marshes and also showed notable variability within the waterway system. Differences in profiles for radioisotopes and COPCs among cores reflect the historically dynamic patterns of sediment deposition and differences in depositional behavior among specific morphologic features. Based on deposition rates derived with the highest confidence, waterway deposition rates are typically in the range of 0.5 – 2.0 cm/yr. Deposition patterns showed variations among broad study segments, but little variation was attributed to morphology classes. Most waterway cores demonstrated long-term depositional histories since the 1960s and reduction/recovery of COPC concentrations continuing to the present.