Climate and Weather Driven Temporal Variability of Vapour (Vapor) Intrusion under Natural and Mitigated Conditions: Implications for Sampling and Mitigation Strategies
Vapor/vapour intrusion (VI) is the migration of volatile organic chemicals (VOCs) from contaminated subsurface sources to indoor air. Exposure to VOCs via VI is typically evaluated using multiple lines of evidence, with indoor air samples being the most heavily weighted. However, changing meteorological forces produce temporal variability in indoor air concentrations on multiple time scales. This critical review summarizes and contextualizes papers that:
•determine the degree of temporal variability in VOCs and radon in indoor air under documented meteorological conditions at a variety of time scales;
•apply multiple graphical and mathematical techniques to elucidate the relationship between indicators and tracers of VI and indoor air concentrations;
•develop and assess optimized sampling and monitoring strategies; and
•evaluate the use of applied vacuums for diagnostic and management purposes, including the building pressure cycling method, mitigation through sub-slab depressurization, and remediation with soil vapor extraction.
The inadequacy of a simple stack-effect¬–based “winter worst” conceptual understanding of VI temporal variability is shown. A more nuanced understanding of individual building characteristics—including the degree of weatherization and the occupant’s seasonal ventilation practices—is needed to schedule targeted, economical sampling during reasonable worst-case conditions. This review demonstrates the potential for false negative assessments when small numbers of random or convenience-based short duration indoor air samples are used as the basis for VI decision making. Radon as a tracer generally provides the single best currently available guide to VOC VI sample timing.
