Hawaii Department of Health, Pearl City, HI. 291 pp, 2017

A sampling method study was conducted at a former dry cleaner site. Previous investigations based on traditional passive and active soil vapor sampling methods that identified PCE vapors beneath the building slab provided inconsistent results in terms of the magnitude and extent of the vapor plume. This inconsistency was attributed in part to random, small-scale variability of PCE concentrations within the vapor plume and the small volume of vapor represented by single discrete vapor sample points (e.g., one liter). Small-scale heterogeneity within subsurface vapor plumes is well documented and was not investigated in detail as part of this study. The study instead focused on innovative approaches to both acknowledge and address this heterogeneity and provide more reliable data for assessment of vapor intrusion risks at sites where existing buildings overlie VOC-contaminated soil or groundwater. Two approaches were investigated: 1) high-density deployment and combination of passive samplers for identification of large-scale VOC patterns beneath a building slab, and 2) large-volume purge methods for collection of samples representative of very large, risk-based volumes of vapors under slabs to form an assessment of potential vapor intrusion risks. http://eha-web.doh.hawaii.gov/eha-cma/Downloads/HEER/LVPFieldStudyHDOHJuly2017.pdf