An Overview of the National Priorities List Site Boundary Polygon Validation Project

Author: William Douglas Henriques
Organization: Agency for Toxic Substances and Disease Registry

1600 Clifton Road, NE
Atlanta, GA 30333
USA

The Agency for Toxic Substances and Disease Registry (ATSDR) routinely characterizes populations surrounding hazardous waste sites for exposure mitigation and health education purposes. An initiative to ensure the accuracy of polygons that depict the National Priorities List (NPL or Superfund) hazardous waste site boundaries in the ATSDR database began in the fall of 1998 in response to a request from the public regarding the proximity of schools to these sites. The objectives of this initiative were to validate, edit, or create polygons representing NPL sites that were of sufficient resolution to analyze features within one-quarter mile of the site and to update or collect metadata for each polygon. The site boundary metadata provides supporting documentation of the source information that was used for the creation of the polygon, and its uses and limitations. This information is required of federal agencies as a result of the executive order signed in 1996.

To validate an NPL site boundary polygon, TIGER/Line 97 files for streets, rivers, and railroads were entered as themes into ArcView GIS 3.1. When available, aerial photographs, typically USGS orthophoto quads downloaded from TerraServer, were entered into the GIS and registered to apparent features in TIGER/Line files using the ArcView Image Analysis extension. Documents containing site maps and site description (ATSDR Public Health Assessments or documents developed through EPA contracts on Superfund sites) were reviewed for descriptive information or maps that clearly depict the site boundary, and the polygon was validated. For sites requiring update or creation of a boundary polygon, the site polygon was digitized on the screen using imagery and TIGER files for reference. The file was then added as a theme into the project and metadata were gathered using an Avenue script developed in house. As a final step to the validation process, the polygon and supporting documents were forwarded to the Environmental Protection Agency (EPA) and a map server application was developed for review by the regional site managers. In a pilot study of 60 NPL sites using the methods described herein, 58 sites (97%) were validated. Of the sites validated, 19 (32.7%) did not require editing and of the 19, three were validated based on existing metadata. Thirty-eight sites (65.5%) required editing, and one site (1.7%) was created. Of those sites requiring editing, the written site description was used in 13 of the sites (13%), maps were used in 32 of the sites (84%), and aerial photographs were used in 23 of the sites (61%).