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.土壤蒸汽提取（Soil vapor extraction, SVE）是针对包气带（vadose zone）内挥发性污染物的主流污染修复技术。实际应用中通常可观测到污染物提取速率随时间逐渐降低的现象，其成因主要包括两点：一是污染物总量持续减少，二是低渗透区域内污染物的去除速率缓慢。当土壤蒸汽提取系统出现污染物去除速率下降的迹象后，需对系统性能开展评估，以确定应对方案：对系统进行优化、终止其运行，或是转换为其他技术以替代或增强土壤蒸汽提取系统的功能。本指南专门针对此类性能评估的各环节展开说明。尽管未作专门阐述，本指南中的方法与分析框架也可应用于场地修复方案选型的初期阶段，用于评估包气带污染物对地下水当前及未来的潜在影响。 本指南基于美国环境保护署（U.S. Environmental Protection Agency）、美国陆军工程兵团（U.S. Army Corps of Engineers）以及空军工程与环境中心（Air Force Center for Engineering and the Environment）已发布的土壤蒸汽提取设计、运行、优化与关停相关指南编制而成。本文档的核心目的在于明确并聚焦于与土壤蒸汽提取系统优化、转换及关停相关的具体操作与决策事项。 本指南以分步流程的形式，阐述了为支撑土壤蒸汽提取修复决策所需开展的信息收集与评估工作。流程的第一步为：在土壤蒸汽提取系统运行一段时间后，重新审视场地概念模型。本指南还说明了在制定优化、转换及关停决策时，需结合环境影响与合规要求考量的各类信息。尽管修复目标的相关要素可能已在修复启动初期被纳入考量，但在关键修复决策节点仍需重新审视。 本指南提供了定量分析方法，用于评估包气带中残留污染物源对地下水的影响，以支撑优化、转换及关停决策。本文重点介绍了质量通量/排放法应用的最新研究进展，并附带一款可简化评估流程的计算工具。随后，本文将通过决策逻辑方法整合上述前期步骤的相关内容，为优化、转换及关停决策提供支撑。