The web-based guidance designed to help state regulators and other practitioners understand, evaluate, and select ASCTs to support site conceptual site model and remedial strategy development and refinement. The document describes site characterization tools that can quickly deliver semi-quantitative or qualitative data to identify locations and depths where quantitative data should be collected. These same tools typically aid in visualizing and understanding the physical and environmental characteristics of a site.  Such capabilities help target investigations and remedial actions, potentially reducing characterization and monitoring costs while improving results. ASCTs designed to provide contaminant-related data are often used in combined to bolster one another. The combination of ASCTs promotes a better understanding of the relationship between contamination mass and site geology. This understanding enhances the conceptual site model development and assists in selecting more effective remedial strategies. ASCTs in this document are divided into four general categories: direct sensing tools, downhole geophysical tools, surface geophysical tools, and remote sensing tools. An interactive ASCTs Selection Tool is provided to identify appropriate tools and information for collecting geologic, hydrologic, and chemical data. Once one or more prospective tools have been identified, more detailed information about a tool can be obtained by reviewing the description of the tool in the web-based document and the Tool Summary Tables, Case Studies, and Checklists. The Tool Summary Tables, Case Studies, and Checklists can be downloaded from the ASCT webpage in a printable format (PDF).

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