You are here:
GIS Analysis to Assess where Shallow Ground Water Supplies in the United States are Vulnerable to Contamination by Releases of Motor Fuel from Underground Storage Tanks
Citation:
EARLE, R. C., J. T. WILSON, F. KREMER, AND J. W. WEAVER. GIS Analysis to Assess where Shallow Ground Water Supplies in the United States are Vulnerable to Contamination by Releases of Motor Fuel from Underground Storage Tanks . U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-11/108, 2012.
Impact/Purpose:
EPA Report for publication.
Description:
Data reported on the long form of the 1990 United State Census were used to identify the number of households in each census block group that obtained water from a private source. A data file was purchased form ESRI Business Solutions (ESRI, 2009) that contained the latitude and longitude of active retail gasoline service stations in the United States. Using Geographical Information System tools (GIS tools) and geo-referenced GIS coverage files on each census block group, the latitude and longitude of each active service station was used to assign the service station to a census block group. Then the number of service stations in each census block group was summed. A simple probability analysis was performed based on the distribution of service stations and the distribution of the households that obtained water from a private supply. Specifically, GIS was used to compare: (1) the relative possibility that an individual household that obtains its water from a private source will be impacted by a release from any service station in the immediate neighborhood; (2) the relative possibility that a release from an individual service station will impact any household in the immediate neighborhood that obtains water from a private source; and (3) the relative possibility for a given surface area of land that there will be an impact from any service station to any household that obtains its water from a private source. The possibilities of an impact were described by vulnerability indices. Vulnerability Index 1 is simply the density of service stations in each census block group. It describes the consumer’s risk of having his water supply impacted. Vulnerability Index 2 is simply the density of household in each census block group that obtain water from a private source. It describes the risk to the service station owner that a release from his station will impact someone’s private water supply. To describe the risk to the entire community that obtains ground water from shallow sources, the index that describes the possibility that a single household might be impacted was multiplied by the number of households that are at risk. Vulnerability Index 3 was calculated by multiplying Vulnerability Index 1 for each block group by the number of households in each block group that obtain water from a private source. Vulnerability Index 3 describes the resource manager’s risk that a release from a gasoline service station in their geographic area will impact the private water supply of a household in their geographic area. The appendices contain maps that depict the distribution of each of the Vulnerability Indices. Maps are provided showing the distribution of block groups with values for the Indices that are in the upper 30%, upper 10%, upper 3%, and upper 1% of all block groups in the map. Maps are provided for the 48 contiguous United States as a whole, and for those contiguous States that are contained within each EPA Region.