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ADVISORY - ACTIVE SOIL GAS INVESTIGATIONS 1.0 INTRODUCTION The Advisory — Active Soil Gas Investigations (ASGI or Advisory) provides technically defensible and consistent approaches for collecting and analyzing soil gas samples. This Advisory applies to both subsurface soil gas samples and soil gas samples collected in sub-slab areas under buildings. The Advisory is not a regulation. It does not impose any requirements or obligations on the regulated community. Rather, it provides a technical framework and reference for addressing soil gas sample collection and analysis. It is not intended to determine the need for soil gas samples, but rather to serve as a guide once a decision has been made to collect soil gas samples. Other technically equivalent procedures may exist. This Advisory is not intended to exclude alternative approaches or methodologies. The Advisory is a compilation of available information, knowledge, experience and best practices regarding soil gas sampling. The mention of trade names or commercial products in this Advisory is for illustrative purposes only, and does not constitute an endorsement or exclusive recommendation by the contributing government agencies. Active soil gas sampling and analysis refers to the methods utilized to collect vapor phase data at sites potentially affected by volatile organic compounds (VOCs), chlorinated solvents, petroleum hydrocarbons, methane, hydrogen sulfide and semi- volatile organic compounds (SVOCs). The data obtained from a soil gas investigation can be used to identify the source and spatial distribution of contamination at a site or to estimate contaminant indoor air concentrations for risk assessment purposes. For sub- slab sampling, evaluating risk associated with vapor intrusion to indoor air, cleanup and mitigation approaches, along with the public outreach associated with vapor intrusion investigations, mitigations and remediations, consult the following DTSC documents: Final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (October 2011) VIG [http://www.dtsc.ca.gov/AssessingRisk/upload/Final_VIG_Oct_2011.pdf] Vapor Intrusion Mitigation Advisory Final Revision 1 (October 2011) VIMA [http://www.dtsc.ca.gov/SiteCleanup/upload/VIMA_Final_Oct_20111.pdf] Vapor Intrusion Public Participation Advisory Final (March 2012) VIPPA [http://www.dtsc.ca.gov/SiteCleanup/uploadNIPPA_Final_03_05_12.pdf] Proven Technologies and Remedies Guidance — Remediation of Chlorinated Volatile Organic Compounds in Vadose Zone Soil (April 2010) PTR [http://www.dtsc.ca.gov/SiteCleanup/upload/cVOC_040110.pdf] The ASGI, along with the above-referenced documents, represents a "compendium" of guidance documents available to stakeholders for the evaluation of all aspects of vapor intrusion. This document supersedes the 2012 and 2003 Advisory— Active Soil Gas Investigations (Cal/EPA, 2003) and 1997 LARWQCB Interim Guidance for Active Soil Gas Investigations (CRWQCB, 1997). It is the opinion of Cal/EPA that active soil gas investigations should be performed in accordance with this document. However, as noted above, other technically equivalent procedures may exist, and this Advisory is not intended to exclude alternative approaches or methodologies. July 2015 1