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Exploration geochemical methods developed and used by the petroleum industry can be invaluable for environmental site characterizations. Many of these methods are not used because they are unfamiliar to environmental scientists and to most regulatory agencies. The rule-of-thumb methods of site characterization (randomly placed monitoring wells, EPA method analyses for target compounds, and the like) are rarely adequate to fully delineate and explain the nature and distribution of subsurface contamination.

The Austin, Texas, case study demonstrates how a phased assessment approach can be used to accurately define petroleum contamination in a study area. Various unconventional methods and techniques (standard for the petroleum industry, but not for the EPA), including forensic geochemistry, were used to better delineate the areal and vertical extents of subsurface contamination.

Prior to this study, more than 400 boreholes, monitoring wells, and temporary monitoring wells were installed on six former storage and distribution terminals and pipeline properties and adjacent private and public properties in the east Austin area. The assessments performed included standard regulatory methodologies (borehole drilling, monitoring-well installation, EPA method BTEX and TPH laboratory analyses, and the like), with the goal of characterizing individual properties. The migration of contaminants off the terminal properties, however, was unresolved and unreported.

The scope of work for this study included documentation of historical hydrocarbon releases; collection of soil-vapor, soil-core, and groundwater samples; and analyses of these samples obtained in close proximity to and down-gradient of the terminal and pipeline properties. Geochemical analytical methods were used to determine the different types of products released and the distribution of these petroleum products (contaminants) in vadosezone soils and groundwater. The data collected during this study were integrated with all available data previously collected.

Geologic cross sections and soil-vapor, soil, and groundwater isoconcentration maps were constructed using the data collected during this study. The maps and sections and forensic geochemistry techniques were used to delineate and demonstrate the areal and vertical extents of petroleum hydrocarbon impact on private and public properties located down-gradient of the six former fuel storage and distribution terminals and product pipeline properties in the east Austin area.

The sources of the vapor, soil, and groundwater contamination were multiple releases on the terminal and pipeline properties, based on historical records and assessment data. Contamination resulting from these releases has reached groundwater and subsequently has migrated off-site onto public and private properties. Based on the results of the work performed, it is obvious that the use of soil-vapor studies and other geochemical methods was essential to economically assess off-site migration of petroleum contaminants from the terminal and pipeline properties.

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