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Rey Farve, Project Leader

For a detailed (technical) description/documentation of the Web application and the datasets used see the White Paper that was developed by the contractor (NorthStar, Inc.). The discussion below is intended as a general (nontechnical) description of the datasets used in the application.

Data Sources

The statistical dataset used in the applications are:

USGS soil samples shapefile. A shapefile (ngs.zip) produced by the USGS is available from the National Geochemical Survey Database Web site; it contains soil sample data from 74,408 locations nationwide.

EPA Level III EcoRegions. A shapefile of the EPA Level III EcoRegions of the continental United States is available at the U.S. EPA’s Western Ecology Division Web site (USEPA 2005).

Ecological Soil Screening Levels (SSL). The proposer (Michael Crump) developed a dataset (table) for use in the application that is based on the EPA Ecological Soil Screening Levels Guidance. The Ecological SSL Guidance is a tool that was developed by EPA to help standardize and accelerate the evaluation and cleanup of contaminated soils at sites on the National Priorities List where future residential land use is anticipated. The information in the table is a summary of contaminants that have a toxic effect on living organisms and the concentration levels (in parts per million) at which effects are noticed. (For more details see the White Paper, appendix B.)

Dataset Compilation

Using Geographic Information Systems (GIS) software, the USGS soil samples shapefile was intersected with the EPA’s EcoRegion shapefile. This dataset was then exported to an Excel spreadsheet for further processing. (Data manipulation to ensure data consistency is described in section II of the White Paper.)

An Excel spreadsheet was used to group the data by Level III EcoRegion and to produce various statistics for each element by EcoRegion. These statistics include:

• Number of samples within each EcoRegion.
• Number of samples per EcoRegion for which a value was reported for each element.
• Number of samples for which a precise value was reported for each element.
• Number of samples for which an imprecise value was reported for each element.
• Number of samples for which no value was reported for each element.
• Minimum and maximum concentrations reported for each element per EcoRegion.
• Average concentration of each element and its standard deviation.
• First, second, and third statistical quartiles (percentiles) for each of the elements.

The statistical data generated in the Excel spreadsheet was then exported as a tab-delimited ASCII text file for use by the Web application. The Ecological SSLs also were exported and formatted for use by the application.