Lauren Wellborn and Amber Greune (North Carolina) Presented at the 2017 ASCE North Carolina Section 2017 Spring Technical Conference held at Duke University's Fitzpatrick Center in Durham, North Carolina on April 28, 2017.
ASCE North Carolina members come from all disciplines of civil engineering, from all types of backgrounds, and from all corners of the state. Benefits are geared to meet the high standards of the profession and keep engineers on the cutting edge of industry technology.
Title: Sediment Coring and Geochronology to Evaluate Sediment Deposition Patterns and Natural Recovery Occurrence
CoAuthors: Peter de Haven, P.E., Jedidiah Sirk, P.E., Scott Compston,
Geosyntec Consultants; Todd Martin, Integral Consulting
Background/Objectives: A phased remedial investigation (RI) 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, 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; an additional study area upstream of a tide gate indicated much lower (average 0.13 cm/yr) deposition rates due to limitations of sediment supply.
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. Multiple possible sediment deposition interpretations can be derived from a waterway sediment core. 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 recovery of COPC concentrations; overall, despite waterway variability, approximately 80% of waterway locations show moderate to strong evidence of natural recovery.
Title: The Role of Bromide in Trihalomethane Formation
Discipline: Water Resources
Drinking water treatment processes must be optimized to control disinfection byproduct formation while meeting disinfection requirements for pathogen inactivation. The presence of bromide in the water can complicate these conflicting treatment goals. The role of bromide in the formation of disinfection byproducts is clear in controlled studies, but remains clouded at full scale. A more robust understanding of brominated disinfection byproduct formation could help guide EPA's proposed effluent limitations for bromide.
For more information regarding the event, visit: The 2017 ASCE NC Spring Technical Conference
To learn more about Lauren see her profile at: https://www.linkedin.com/in/lauren-wellborn-p-e-5660499/
To learn more about Amber see her profile at: https://www.linkedin.com/in/amber-greune-6355247/