Improving the sustainability of source removal


Abstract:There is a growing recognition of the importance of making hazardous waste remediation more sustainable, and thereby minimizing its economic, environmental and social impacts. The attention of sustainable remediation practitioners has thus far been focused on remediation of lower concentration targets, such as dissolved plumes, where reliance on green techniques that mimic naturally occurring processes such as bioremediation may be particularly effective. There has been less attention, however, on source removal, such as of dense non-aqueous phase liquid (DNAPL) source areas. At sites where achievement of stringent remedial goals is necessary in a short timeframe, aggressive source remediation is required. Among the various methods of “aggressive” (but efficient) source remediation / removal that are currently available, many require excavation, which can be highly energy-intensive (at deep sites or if the distance to offsite treatment or disposal is relatively far) and tends to strongly impact neighborhoods. In situ technologies such as soil vapor extraction (SVE), multiphase extraction and in situ chemical oxidation are less disruptive than excavation but frequently produce diminishing returns due to diffusion-limited mass transport in the subsurface. Life Cycle Analyses (LCAs) were conducted for four sites in Germany (Hiester et al. 2003; Hiester and Schrenk 2005) where SVE was later followed by In Situ Thermal Remediation
(ISTR), and at one site in Denmark (Pfeilschifter et al. 2007), where SVE and ISTR were compared with excavation/off-site treatment, and SVE was again followed by ISTR.

Though site specific conditions such as volume, contaminants and depth below subsurface differed widely, each of the LCAs calculated for those site-specific conditions showed that SVE consumed more energy, produced more waste and generated more greenhouse gases than ISTR, while requiring a lengthy or even indefinite period of time to remove sufficient contaminant mass to achieve site closure. Whether or not excavation compares well with ISTR in an LCA depended primarily on the transport distance to a suitable disposal or treatment site. ISTR offers the reduced neighborhood impacts of an
in situ remedy combined with the ability to achieve predictable, timely site closure. ISTR has restored impaired properties enabling beneficial reuse, even to residential standards in a number of cases. It also has produced results consistent with restoration of groundwater, an increasingly scarce resource. An effective robust source removal technology such as ISTR that minimizes environmental, economic and social impacts on a life-cycle basis can thus turn out to be the most sustainable source removal solution for such sites, and should be considered during remedy selection.

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