Use of On-Site GC/MS Analysis to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs

Distinguishing between vapor intrusion (VI) and indoor sources of volatile organic compounds (VOCs) is a significant challenge in site assessments, greatly increasing the cost and complexity of investigations. Rapid on-site analysis of indoor air samples using a portable GC/MS allows the users to understand the distribution of VOCs in real-time, supporting identification of the source while in still the field. The overall objective of the demonstration was to develop and validate a step-wise investigation procedure using commercially-available off the shelf (COTS) on-site GC/MS analysis with real-time decision making as a tool to distinguish between vapor intrusion and indoor sources of VOCs. Use of on-site GC/MS analysis to distinguish between vapor intrusion and indoor sources of VOCs requires a field-portable analytical instrument with sufficient sensitivity to measure VOC concentrations in indoor air within the concentration range of regulatory concern (i.e., as low as 1 g/m3). A high degree of precision is also required because the protocol relies on measuring concentration gradients inside a building to identify sources of VOCs. For the demonstration, we utilized a HAPSITE portable GC/MS instrument. Although specific procedures in the investigation protocol were developed using the HAPSITE, any on-site instrument with sufficient sensitivity and precision may be used in the protocol. The field investigation program included application of the on-site GC/MS analysis protocol at four Department of Defense (DoD) sites. To evaluate the validity of this investigation approach, we also conducted conventional vapor intrusion and compound-specific stable isotope analysis (CSIA; ESTCP Project ER-201025) investigations concurrently at the study sites. Results from the three investigation methods were compared to evaluate the relative effectiveness of the different investigation approaches. This report presents the results from a total of seven demonstration buildings. Prpeared in collaboration with Hill Air Force Base, UT, and GSI Environmental Inc., Houston, TX.