Advances in Field Measurement, Sampling and Sensor Technologies for Quantifying Confidence in Representing Vapor Intrusion Exposures

Advances in Field Sampling, Measurement, and Sensor Technologies
Oral Presentation

Prepared by H. Schuver1, B. Schumacher2, J. Zimmerman3, C. Lutes4, C. Holton5, R. Truesdale6
1 - US EPA, US EPA - OLEM - ORCR, 1200 Penn. Ave. NW (MC-5303P), Washington, DC, 20460, United States
2 - US EPA - ORD, , Las Vegas, Nevada, United States
3 - US EPA - ORD, , Durham, NC, United States
4 - Jacobs, , Cary, NC, United States
5 - Geosyntec, , Denver, Colorado, United States
6 - RTI International, , Durham, NC, United States


Contact Information: schuver.henry@epa.gov; 703-308-8656


ABSTRACT

Vapor intrusion exposures are a result of a complex integration of an apparently-endless list of subsurface source/media, building/occupant and atmospheric (weather) factors. Vapor intrusion exposures are not predictable even with complex, building-specific models using detailed temporal/spatial inputs. Only indoor-air target-chemical concentrations can represent and integrate all the factors involved. However, indoor chemical concentrations due to VI, have been found to be highly-variable across both buildings and time. This makes deciding where and when to sample to represent the ‘elevated’ exposures of most concern for site-wide decision making, very challenging.
New technologies make practical the nearly-continuous measurement of supplemental (non-target-chemical) metrics that are less-disruptive to building occupants and lower-cost, i.e., allowing a sufficient-number/frequency of samples to provide improved understanding and confidence for when, and where, to sample indoor air. Documentation of measurement devices, sampling protocols and procedures, as well as statistical-testing the associations between these metrics and target-chemical concentrations, can quantify the confidence in representing exposure levels of concern from either regularly-scheduled/occasional short-term indoor ‘grab-sample’ sampling efforts, or as ‘trigger-points’ for automated sampling by sensor technologies
We’ve studied three supplemental metrics for improving our sampling for chemical vapor intrusion (e.g., differential-Temperature and Pressure, and indoor Radon). With the evidence from buildings to-date we have found indoor Radon levels can reflect the effects of both Temperature and Pressure as well as the effects of wind and all near-building subsurface-media, building/occupant and weather factors (but not variation in the deep-chemical-vapor source-term). Despite some differences, Radon and chemical-vapors in soil gas have been found to move in measurably- similar ways/together as a Tracer of each other’s intrusion into indoor air. The quality and integrity of the evidence for this association will be presented, along with the outline of a possible-future SW-846 method effort to fully document measurement devices, sensor technologies, sampling protocols and procedures.