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ADVISORY — ACTIVE SOIL GAS INVESTIGATIONS trenches, utility corridors, drains, sewer lines, clarifiers, septic systems, piping, ASTs, USTs and waste management units, and surrounding land uses; CSM (see Section 2.3.2); SAP (see Section 2.3.3); A statement of the investigation objectives relative to the site-specific DQ0s; A statement as to whether permanent or temporary soil gas wells or sub-slab probes are to be installed.' See DTSC's Vapor Intrusion Guidance concerning the need for the installation of permanent soil gas wells; A statement as to whether a mobile and/or stationary laboratory will be used, and the rationale for making this decision; A geological cross-section of the site showing the major lithologic units and zones for vapor monitoring; Procedures to properly decommission soil gas wells to effectively prevent cross- contamination in the subsurface; A project-specific quality assurance project plan (QAPP) for the project if no existing approved QAPP is applicable; Procedures for handling and disposing of investigation-derived waste in accordance with federal, state and local agency requirements; and A site-specific Health and Safety Plan. 2.3.2 Conceptual Site Model A CSM is an integral part of all site investigations. The purpose of a CSM is to provide a conceptual understanding of the potential for exposure to hazardous contaminants at a site based on: Sources of contamination; Release mechanisms; Transport media; Exposure pathways; and Potential receptors. The CSM also aids in the justification for the number, location and frequency of samples. The CSM should consist of descriptive text and diagrammatic or schematic figures relating the sources of contamination to receptors and the environment. The 3 The term "vapor probe", "soil gas probe", "soil gas monitoring well", and "soil vapor well" are considered equivalent and are used interchangeably within this Advisory. July 2015 4