Passive Soil Vapor Extraction - GSI Environmental Inc.

5.1 Decision Framework for Selection of PSVE TechnologiesSRNL-STI-2009-00571Rev. 1In the absence of a technology specific decision framework and process documentation,it may still prove difficult to reliably demonstrate to a regulator or a stakeholder thatPSVE is sufficient to meet some or all MNA requirements within an acceptabletimeframe.Recently, the ITRC (2008) published a document titled “Enhanced Attenuation:Chlorinated Organics” that includes and explains a decision framework to assess theattenuation capacity of a chlorinated solvent site. The enhanced attenuation strategyrelies on an evaluation of the contaminant mass balance to help identify and quantifyattenuation processes occurring at the site. The basic premise of EA is that for somesites, source mass flux reductions due to natural attenuation processes may not besufficient to meet regulatory criteria, causing MNA alone to be an unacceptabletreatment option. However, implementation of a suitable technology or a combination oftechnologies could reduce the source mass flux and/or increase the rate of naturalattenuation to an extent that ensures that the site meets MNA requirements. Thus, asite-specific contaminant mass balance could be the basis for determining whichremedial technologies are capable of bridging the gap between current site conditionsand MNA requirements at the site.A typical EA assessment entails• An evaluation of the degree of enhancement in the rate of source fluxreductions/natural attenuation that would be needed to create conditions suitablefor an MNA application (e.g., a stable or shrinking plume), and;• Identification of the class of technologies that would most effectively meet siteobjectives in a timely fashion. Source strength reduction technologies such asSVE, source excavation and infiltration barriers reduce source mass and/orreduce mass flux from the source zone. Attenuation capacity enhancementtechnologies such as permeable reactive barriers and bioremediation increasethe contaminant attenuation rate by promoting abiotic or biological transformationwithin the plume.For ease of use, the decision process is presented in flowchart format (Figure 5.1) and isintended to be an iterative process for a smooth, efficient and defensible transition toMNA.33 Enhanced Attenuation TechnologiesPassive Soil Vapor Extraction