"Large-Scale Physical Models of Thermal Remediation of DNAPL Source Zones in Aquitards
"Focus and objectives of the research project. In-Situ Thermal Remediation (ISTR) technologies are receiving increasing attention for remediation of dense non-aqueous phase liquid (DNAPL) source zones in soil and groundwater (GW), and are the subject of a number of related current projects funded by the Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP). A clear understanding of the primary mechanisms of ISTR is crucial for the U.S. Department of Defense (DoD) and Department of Energy (DOE) to be able to select appropriate sites and effective ISTR technologies for DNAPL source zone remediation. This project in particular was proposed in response to SERDP Statement of Need (SON) for FY 2005
CUSON-05-04 dated November 6, 2003, which sought “fundamental or applied studies to improve our understanding of:
(1) the mechanisms of removal and destruction of free phase and residual dense nonaqueous phase liquids (DNAPLs) during in situ thermal treatment, including the reductions in plume loading and plume longevity; and
(2) the impact of varying subsurface conditions on overall removal and destruction efficiency during thermal treatment.”
It is noteworthy that a more recent SERDP and ESTCP Expert Panel Workshop identified development of treatment approaches for flow-limited portions of DNAPL source zones as a critical research need (SERDP and ESTCP 2006). An ESTCP SON released in 2008 focused further attention on remediation of aquitards.
Thermal conductive heating (TCH) is an ISTR technology that takes advantage of the invariance of thermal conductivity across a wide range of soil types to effect treatment of DNAPL above and below the water table, particularly in lower-permeability and heterogeneous formations. TCH thereby can complement steam enhanced extraction (SEE), which is generally more applicable to higher-permeability formations below the water table.
The objectives of this project (ER-1423) were to:
1. determine the relative significance of the various contaminant removal mechanisms below the water table (e.g. steam generation, steam stripping, volatilization);
2. assess the DNAPL source removal efficiency and accompanying change in water saturation at various treatment temperatures/durations through boiling; and
3. evaluate the potential for DNAPL mobilization, either through volatilization and recondensation, and/or pool mobilization outside of the target treatment zone (TTZ) during heating.