ABSTRACT

The default subslab soil gas (SSSG)-to-indoor air attenuation factor (AF) of 0.03 to assess the vapor intrusion (VI) pathway and generate VI screening levels for SSSG was developed by the United States Environmental Protection Agency (EPA) based on chlorinated volatile organic compound (VOC) indoor air and SSSG data collected in residential buildings and compiled in EPA’s 2012 VI database. In their VI guidance published in 2015, EPA recognized that this default AF may be overly conservative for nonresidential buildings. In 2015, the Department of Defense (DoD) began developing a first-of-its-kind VI database to assess AFs at commercial and industrial buildings at DoD installations and support the development of alternative generic AF values. This database was expanded in 2019 to include 76 buildings at 22 DoD installations across the United States and is comparable in size to EPA’s VI database. The DoD database includes chlorinated VOC data from SSSG and indoor air samples collected from multiple sampling zones within these buildings. Empirical SSSG-to-indoor air AFs were calculated using the same screening methods employed by EPA to filter out potential background source contributions unrelated to VI, including a source strength screen. Analysis of indoor air–SSSG data pairs found that there is substantially more attenuation occurring from SSSG to indoor air in DoD commercial and industrial buildings relative to residential buildings, and that the DoD buildings’ AFs are one to three orders of magnitude lower than EPA’s residential-based default of 0.03. The results support the use of a generic SSSG-to-indoor air AF of 10⁻³ (0.001) to support VI assessment and develop SSSG screening levels at large commercial and industrial buildings as an alternative to the residential default AF.

Implications: The use of subslab soil gas (SSSG)-to-indoor air attenuation factors (AFs) is a key component of vapor intrusion (VI) pathway assessments and VI screening level development for SSSG. Currently, the United States Environmental Protection Agency (EPA) and many state regulatory agencies use a default AF of 0.03 based on chlorinated volatile organic compound (VOC) data collected in residential buildings. VI assessment data collected at Department of Defense (DoD) installations indicate that there is significantly more SSSG-to-indoor air attenuation occurring at DoD commercial and industrial buildings. For that reason, the default AF of 0.03 results in SSSG screening levels that are overestimating VI-related risks in these types of building. The DoD data support the use of a generic SSSG-to-indoor air AF of 10⁻³ (0.001) for conducting VI assessment and developing SSSG screening levels at large commercial and industrial buildings as an alternative to the residential default AF.

摘要

用于评估蒸汽侵入 (VI) 路径并生成 SSSG 的 VI 筛选水平的默认底板土壤气体 (SSSG) 至室内空气衰减因子 (AF) 为 0.03，由美国环境保护署 (EPA) 基于在住宅建筑中收集并编入 EPA 2012 VI 数据库的氯化挥发性有机化合物 (VOC) 室内空气和 SSSG 数据。在 2015 年发布的 VI 指南中，EPA 认识到这种默认 AF 对非住宅建筑可能过于保守。2015 年，国防部 (DoD) 开始开发同类首创的 VI 数据库，以评估国防部设施中商业和工业建筑的 AF，并支持开发替代通用 AF 值。该数据库在 2019 年进行了扩展，包括美国 22 个国防部设施中的 76 座建筑物，其规模与 EPA 的 VI 数据库相当。DoD 数据库包括来自 SSSG 的氯化 VOC 数据和从这些建筑物内的多个采样区收集的室内空气样本。使用 EPA 使用的相同筛选方法来计算经验 SSSG 到室内空气 AF，以过滤掉与 VI 无关的潜在背景源贡献，包括源强度筛选。对室内空气-SSSG 数据对的分析发现，与住宅建筑相比，国防部商业和工业建筑中从 SSSG 到室内空气的衰减要大得多，而且国防部建筑的 AF 比 EPA 的住宅低一到三个数量级- 基于默认值 0.03。⁻³ (0.001) 支持 VI 评估并在大型商业和工业建筑中开发 SSSG 筛选水平，作为住宅默认 AF 的替代方案。

影响：使用底层土壤气体 (SSSG) 到室内空气衰减因子 (AF) 是蒸汽侵入 (VI) 路径评估和 SSSG 的 VI 筛选水平开发的关键组成部分。目前，美国环境保护署 (EPA) 和许多州监管机构根据在住宅建筑中收集的氯化挥发性有机化合物 (VOC) 数据，使用 0.03 的默认 AF。在国防部 (DoD) 设施收集的 VI 评估数据表明，在国防部商业和工业建筑中发生的 SSSG 到室内空气衰减明显更多。因此，0.03 的默认 AF 导致 SSSG 筛选水平高估了这些类型建筑中与 VI 相关的风险。DoD 数据支持使用通用的 SSSG 到室内空气 AF 为 10^-3 (0.001) 用于在大型商业和工业建筑中进行 VI 评估和开发 SSSG 筛选水平，作为住宅默认 AF 的替代方案。