Dense Nonaqueous Phase Liquids (DNAPLs)
- Policy and Guidance
- Chemistry and Behavior
- Environmental Occurrence
- Detection and Site Characterization
- Treatment Technologies
- Conferences and Seminars
- Additional Resources
"Treatment train" approaches represent a practical means to address difficult remediation problems, such as pure or dissolved-phase DNAPL contamination in soil and groundwater. The optimal remedial action at a given site often requires the use of multiple technologies that can be used either sequentially or concurrently. A single remedial technology is rarely the most cost-effective approach throughout the life cycle of a cleanup project.
Sequential technology implementation over time allows specific technologies to be used for particular phases of the cleanup. Performance objectives trigger the transition to the next phase of the treatment train and can be used to make that transition occur at the optimum time to prevent a technology from operating beyond the point of diminishing returns.
Simultaneous technology implementation of multiple unit processes in a single treatment system allows specific technologies to be used for particular contaminants of concern that otherwise would not be appropriate or cost-effective for all contaminants. As site conditions change, it may not be necessary or cost-effective to continue using all unit processes of the treatment train. Performance objectives can be used to trigger the modification of the treatment train at the optimal time to prevent a unit process from being used beyond the point that it is necessary or cost-effective (ERT2 2007).
Three primary strategies that can be used separately or as components of a remediation treatment train include contaminant extraction or separation from environmental media, destruction or alteration, and immobilization. A treatment train for a DNAPL groundwater problem might begin with in situ thermal treatment via electrical resistance heating, followed by in situ biological treatment as a polishing step. Treatment train approaches require active management of the overall remediation strategy, i.e., making process control decisions for individual treatment components while remediation is underway, and also deciding when to switch from one component to the next (Triad website).
For treatment technologies that might be used in a treatment train but are not addressed individually in these DNAPL pages, Technology Focus provides information on the following methods:
- Ground-Water Circulating Wells
- Natural Attenuation
- Soil Washing
- Solvent Extraction
Information on applications of treatment trains specific to a chemical class can be found in the class subsections listed to the right. The examples include the implementation of both conventional and innovative technologies to achieve cleanup.