Bioremediation in Wetland Areas, Standard Chlorine of Delaware Inc. Superfund Site, Delaware City, Delaware

Science Center Objects

Major releases of chlorinated benzenes and benzene are known to have occurred at the Standard Chlorine of Delaware Inc. Superfund Site from 1966-2002, resulting in contamination of the groundwater underlying the site and the wetlands surrounding Red Lion Creek.

Although installation of a groundwater interception and treatment system has been completed around the main facility, wetland and sediment areas impacted by contaminated groundwater discharge and past surficial spills remain outside this containment area.

Implementation of in situ bioremediation was identified for the wetland areas under the selected remediation alternative during the Feasibility Study.

Background

Major releases of chlorinated benzenes and benzene are known to have occurred at the Standard Chlorine of Delaware Inc. Superfund Site from 1966-2002, resulting in contamination of the groundwater underlying the site and the wetlands surrounding Red Lion Creek. Although installation of a groundwater interception and treatment system has been completed around the main facility, wetland and sediment areas impacted by contaminated groundwater discharge and past surficial spills remain outside this containment area.

Implementation of in situ bioremediation was identified for the wetland areas under the selected remediation alternative for the SCD site during the Feasibility Study, and a laboratory treatability investigation of bioremediation of wetland sediments was completed in 1993 (Roy F. Weston, 1993, AR308120). This feasibility investigation, however, was inconclusive on the potential bioremediation technologies that could be used to enhance degradation and their effectiveness in the wetland areas.

Objectives

Characterization of contaminant extent in wetland area,
Seasonal natural attenuation monitoring in low to moderately contaminated areas,
Column studies for permeable, reactive cap in moderately contaminated area,
Laboratory tests for evaluation of treatment of highly contaminated sediment.
Strategy and Approach:

Wetland characterization includes installation and sampling of passive diffusion bags (PDBs) and dialysis samplers, piezometer and peeper installation and sampling, thermal infrared (TIR) surveys of potential seepage areas
Investigation of natural attenuation processes and application of bioremediation includes
In situ microcosms (MICRO-Tracs, or biotraps) with unamended and amended treatments (biostimulation, addition of WBC-2 culture, 13C-labeled parent compounds); includes assessment of geochemistry and microbial populations.
Laboratory microcosms and column experiments are also underway to further assess degradation pathways and rates for trichlorobenzene and dichlorobenze isomers and monochlorobenzene under different conditions in the wetland sediment, and the ability of the anaerobic WBC-2 culture to degrade these compounds.

Peeper and PDB samples showed greatly different redox conditions and groundwater contaminant concentrations in two areas of the wetland

  • In situ microcosm experiments were conducted in October-December 2009 and October-December 2010. Both natural and enhanced (biostimulation and/or bioaugmentation) degradation were observed under both aerobic/slightly reducing conditions and anaerobic conditions
  • A thermal infrared helicopter survey, completed February 16, 2011, with cooperation from the U.S. Army, Aberdeen Test Center, showed some hotspots; an additional flyover is planned using UAVs