Treatment of dissolved-phase chlorinated ethenes in groundwater using in situ bioremediation (ISB) is an established technology; however, its use for DNAPL source zones is an emerging application. This training course supports the ITRC Technical and Regulatory Guidance document In Situ Bioremediation of Chlorinated Ethene: DNAPL Source Zones (BioDNAPL-3, 2008). This document provides the regulatory community, stakeholders, and practitioners with the general steps practitioners and regulators can use to objectively assess, monitor, and optimize ISB treatment of DNAPL source zones. The objective is to provide adequate technology background for the user to understand the general and key aspects of ISB for treatment of chlorinated ethene DNAPL source zones. It is not intended to be a step-by-step instruction manual for remedial design, but describes technology-specific considerations for application of ISB of DNAPL source zones.
For this training and guidance document, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" that accumulate above confining units. The DNAPL source zone includes regions that have come into contact with DNAPL and may be storing contaminant mass as a result of diffusion of DNAPL into the soil matrix. Even though DNAPLs may be present in both the unsaturated and saturated zones, the discussion of ISB of DNAPL source zones in this training and guidance document focuses on treatment of DNAPL source zones within the saturated zone.
Two goals of any DNAPL source treatment technology are to 1) reduce the mass of contaminants within the source area and 2) prevent migration of contaminants above unacceptable levels. The enhanced ISB technology reduces source mass and controls flux through the enhanced dissolution and desorption of DNAPL constituents into the aqueous phase, and subsequent microbially mediated degradation processes. Although enhanced ISB of DNAPL source zones has been demonstrated in the field at a few chlorinated solvent sites, expectations for rapid depletion of the source zone must be realistic. This training and guidance provide detailed requirements necessary to support the realistic determination of goals for ISB of a DNAPL source zone.
To get the most out of this training, before the class, please review the associated document, the ITRC Technical and Regulatory Guidance document In Situ Bioremediation of Chlorinated Ethene: DNAPL Source Zones (BioDNAPL-3, 2008).