Use of Compound-Specific Stable Isotope Analysis to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs - CSIA Protocol for Vapor Intrusion Investigations

Compound-specific stable isotope analysis (CSIA) can be used as a building-specific vapor intrusion investigation tool to augment data from other investigation methods. The primary utility is to provide an independent line of evidence to distinguish between vapor intrusion and indoor sources of VOCs. This CSIA protocol is not a standalone investigation approach. It involves collection of subsurface source (i.e., groundwater) and indoor air samples. Concentrations of target VOCs from these media must be known or estimated to develop CSIA sampling parameters (e.g., sample collection time). This document i) describes the applicability of CSIA for vapor intrusion investigations (Section 2.0), ii) provides a step-by-step procedure for sample collection (Section 3.0), and iii) includes guidelines for data interpretation (Section 4.0). Prepared in collaboration with the University of Oklahoma, Norman