SGM-SF_2017with 12/20 Revisions

21 SGM-SF SGM-SF Discussion Table A-3: Recommended Post-mitigation Monitoring Events For Chemical Vapor Intrusion A-3: Monitoring Events and Stewardship A-3.1 Monitoring events A-3.2 Initial post-mitigation testing A-3.3 Initial seasonal verification A-3.4 Ongoing stewardship A-3.5 Decommissioning Systems Appendix Table A-3 and subsequent guidance illustrates monitoring events that are in accordance with the consensus of the SGM-SF committee . Once baselines are established, ongoing monitoring and stewardship activities can be better defined. A-3.3.3 Discussion: Surrogate testing methods, including radon gas Surrogate methods to monitor continued effectiveness of mitigation are commonly employed in lieu of an ardent regimen of indoor testing. PFE testing is the most common example. Indoor measurements of soil gases other than the chemical(s) of concern can also be an effective supplement. Radon is also well suited for evaluating continued reduction of soil gas entry. Testing for radon before and after mitigation can establish a baseline for surrogate correlation by comparing results with other indoor measurements. Naturally occurring radon is found everywhere on earth regardless of what survey maps might suggest. Initial indoor measurements as low as 2.5 pCi/L are common anywhere and can provide evidence for a difference between pre- and post-mitigation. Concentrations of 4 pCi/L or greater are even more helpful for estimating percentages of reduced soil gas entry and evidence of enhanced benefits to occupants. A-3.3.4 Indoor air testing When possible, testing should be made under reproducible conditions.