Large-Scale Physical Models of Thermal Remediation of DNAPL Source Zones in Aquitards

Abstract

Prescribed by ANSI Std Z39-18 This report was prepared under contract to the Department of Defense Strategic Environmental Research and Development Program (SERDP). The publication of this report does not indicate endorsement by the Department of Defense, nor should the contents be construed as reflecting the official policy or position of the Department of Defense. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the Department of Defense.

Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

“…8g and h). Condensation of gas-phase VOC, which has been described in other studies of thermal technologies (e.g., Baker and Hiester, 2009) and would be significant at the field scale, is expected to have occurred in the colder zone of Experiment D and likely contributed to the upward mobilization of DNAPL. Any DNAPL that condensed after being transported away from dyed DNAPL, and was colorless, could not be identified using the light transmission method in these experiments.…”

“…Although each of these mechanisms contributes to DNAPL removal, gas capture of vaporized VOCs is the dominant mechanism of removal during a thermal remediation application (e.g., Baker and Hiester, 2009;Beyke and Fleming, 2005;Heron et al, 2005Heron et al, , 2006Heron et al, , 2013Vermeulen and McGee, 2000). As such, the effectiveness of ISTT requires that temperatures are high enough within the treatment volume to vaporize VOCs and establish connected gas transport pathways to soil vapor or multiphase extraction points (e.g., Baker and Hiester, 2009;Heron et al, 2006;McGee et al, 2004). In other words, the application of heat makes conditions more favorable for removal, but most thermal methods are still extraction techniques (e.g., Beyke and Fleming, 2005;Stroo et al, 2012).…”

“…Previous studies have highlighted the importance of establishing connected gas channels for advective transport between the DNAPL source zone and extraction points (e.g., Heron et al, 1998;Martin and Kueper, 2011) and that subsurface temperatures should be increased to the boiling point of groundwater to facilitate the formation of steam conduits (e.g., Baker and Hiester, 2009;Heron et al, 2006). Martin and Kueper (2011) further exemplified this in the presence of low-permeability layers, where the absence of steam conduits resulted in local accumulation and lateral migration of co-boiled vapor leading to reduced mass removal.…”

“…Condensation in these colder zones prior to vapor extraction can be detrimental to performance. For example, Baker and Hiester (2009) observed both the partial collapse of a steam front due to increased groundwater flux during thermal conductive heating (TCH) experiments, as well as DNAPL condensation at the steam front as it propagated through colder zones. The risk of condensation and subsequent dissolution of DNAPL following buoyant transport of discontinuous gas clusters (i.e., as opposed to continuous gas channels) into colder zones was also identified by McGee et al (2004) and Krol et al (2011a).…”

In Situ Thermal Remediation of DNAPL Source Zones

“…The combination of heating and in situ chemical oxidation are also examined, using persulfate as the model oxidant, are also examined. This project was carried out in conjunction with several other thermal projects (in particular, SERDP ER-1423 (Baker & Hiester, 2009) and SERDP ER-1419 (Pennell et al, 2009)) and was intended to complement those other approaches by focusing on ERH and processes occurring at the centimeters to meters scales and at less than 100 o C.…”