Soil Vapor Extraction Endstate Tool (SVEET)

Soil vapor extraction (SVE) is a prevalent remediation approach for volatile contaminants in the vadose zone. A diminishing rate of contaminant extraction over time is typically observed due to 1) diminishing contaminant mass, and/or 2) slow rates of removal for contamination in low-permeability zones. After a SVE system begins to show indications of diminishing contaminant removal rate, SVE performance needs to be evaluated to determine whether the system should be optimized, terminated, or transitioned to another technology to replace or augment SVE. This guidance specifically addresses the elements of this type of performance assessment. While not specifically presented, the approach and analyses in this guidance could also be applied at the onset of remediation selection for a site as a way to evaluate current or future impacts to groundwater from vadose zone contamination. The guidance presented here builds from existing guidance for SVE design, operation, optimization, and closure from the U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and the Air Force Center for Engineering and the Environment. The purpose of the material herein is to clarify and focus on the specific actions and decisions related to SVE optimization, transition, and/or closure. The process of gathering information and performing evaluations to support SVE remedy decisions is presented in this guidance document in a stepwise approach. Steps start with revisiting the conceptual site model after SVE has operated for a period of time. The guidance also describes information that needs to be considered in terms of the environmental impact and compliance context for optimization, transition, and closure decisions. While these elements of the remediation goal may have been considered at the onset of remediation, they should also be revisited at the time of key remediation decisions. Quantitative approaches are provided to evaluate the impact or remaining vadose zone contaminant sources on groundwater in support of optimization, transition, and closure decisions. This material highlights relatively recent advances in use of mass flux/discharge approaches and includes a calculation tool to facilitate the evaluation process. The material in these initial steps is then synthesized using a decision logic approach to optimization, transition, and closure decisions.