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Subslab Soil Gas Sampling Using Various Installation Methods, Sampling Durations, and Sample Volumes: A Case Study
Citation:
Buckley, G., V. Boyd, C. Lutes, L. Levy, E. Ross, T. Walker, R. Truesdale, J. Zimmerman, A. Williams, AND B. Schumacher. Subslab Soil Gas Sampling Using Various Installation Methods, Sampling Durations, and Sample Volumes: A Case Study. 12th International Conference on Remediation of Chlorinated Solvents and Recalcitrant Compounds, Palm Springs, CA, May 22 - 26, 2022.
Impact/Purpose:
SSSG data obtained from the grab samples analyzed with the GC-ECD show that, in most cases, the variations over durations comparable to existing time-integrated sampling techniques, such as sorbent tube samples, are limited. For instance, less than a quarter of the SSSG sampling locations exhibit relative standard deviations over a one-month period greater than 30%. In those cases, the results of a conventional sample collected over 15 minutes would be expected to be similar to a time-integrated sample collected for a day or a month; these results would likely lead to the same conclusions in a VI assessment and the same site management decisions. In a few cases, however, concentration changes of as much as an order of magnitude were observed. This presentation will also provide recommendations for best sampling practices.
Description:
There is relatively inconsistent information in vapor intrusion (VI) guidance and field operating procedures regarding the preferred purging and sampling duration, flow rate, and volume for collecting subslab soil gas (SSSG) samples, as well as limited research to demonstrate whether these factors significantly affect the usability of the data in a VI assessment. There is also limited information about the potential influence of SSSG probe construction on data, and limited consensus on the effect of certain meteorological parameters. At an industrial warehouse-type building, a controlled research sampling event was conducted during summer months to evaluate several factors that may yield variable analytical results, including SSSG probe construction, sample containers, and seasonal and meteorological influences. This presentation will focus on a comparison of analytical results of SSSG samples collected concurrently and consecutively using various probe installation methods, different sampling containers, durations and volumes, and under various meteorological influences, with the objective of determining whether different sampling approaches may affect the VI assessment.
