Evaluating the Efficacy of a Low-Impact Delivery System for In Situ Treatment of Sediments Contaminated with Methylmercury and Other Hydrophobic Chemicals

Dr. Charles Menzie | Exponent Inc.

ER-200835

Objectives of the Demonstration

Environmental Restoration Project ER-200835 involved field demonstrations of in-situ treatment of sediment contamination with activated carbon (AC) delivered using the SediMite® delivery system. While ER-200835 focused on Canal Creek at the Aberdeen Proving Ground (APG) in Maryland, data from two other sites—Bailey Creek at Ft. Eustis, Virginia, and Berrys Creek in the Hackensack Meadowlands of New Jersey—are incorporated, to broaden the assessment and enable the evaluation of performance for various types of habitats. Collectively, the report provides information on the treatment efficacy of activated carbon delivered by SediMite® for two wetland/marsh environments and two tidal creeks. Contaminants present in sediments and/or wetland soils at one or more of these sites include polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and related degradation products (DDx), and mercury.

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Technology Description

The treatment material—SediMite®—is agglomerate that is composed of the treatment agent (AC in this case), a weighting agent, and an inert binder. The agglomerate is manufactured as pellets that can be easily handled and dispersed. The product is delivered using either blower-type devices (Vortex) or spreaders. An application of SediMite® by tele-belt has also been performed for Mirror Lake in Delaware. Once the pellets are distributed on sediments or wetland soils, the SediMite® pellets disaggregate and release the active treatment agents.

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Implementation Issues

The projects demonstrated that:

  • SediMite® pellets were effectively delivered to wetland soils and aqueous sediments using either the Vortex blower system or the TurfTiger spreader system.
  • Most of the applied AC was retained in wetland/marsh systems over the duration of the demonstration.
  • Retention and/or AC concentrations for subaqueous applications varied over time. These variations are thought to reflect edge effects in the case of Bailey’s Creek, and possible storm effects on resuspension or burial in the case of Canal Creek.
  • Mixing of SediMite®-applied AC into sediments occurred throughout the targeted biologically active zone for applications to subaqueous sediments. Vertical mixing of SediMite®-applied AC into wetland/marsh sediments was slower and to less depth than that observed for subaqueous sediments.
  • Based on field-collected sediments or wetland soils, SediMite®-applied AC significantly reduced the bioavailability for PCBs and DDx over the period of study.
  • Results for mercury are considered equivocal, in part because the applied activated carbon did not remain in the treatment area.
  • Applications of AC via SediMite® had negligible adverse effects on native benthic invertebrate communities in Bailey and Berrys Creeks.

Implementation Issues

  • SediMite® can be effectively applied topically to wetland and open-water environments.
  • The physical fate of applied AC varied among environments due to variations in physical and biological conditions. These processes should be better understood and planned for as a part of designing full-scale implementations.

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Points of Contact

Principal Investigator

Dr. Charles Menzie

Exponent Inc.

Phone: 571-214-3648

Fax: 410-987-8700

Program Manager

Environmental Restoration

SERDP and ESTCP

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