Gradient scientists analyze surface and subsurface data using Geographic Information Systems (GIS) technology to assess the sources and extent of observed contaminants. Evaluating historical and contemporary land cover and land use provides important clues to contaminant source identification. Comparing site-specific environmental sampling data to changes in land cover demonstrates the timing and variability of human or ecological exposure to chemicals of concern. Layering sampling data, imagery, and other geographic data together in a GIS database facilitates innovative modeling. Gradient utilizes GIS analyses to characterize groundwater and surface water systems, and create powerful visualizations of contaminant sources and their fate and transport history.
Contaminant Release and Migration Conceptual Model Development
Gradient reviewed historical environmental investigations, aerial imagery, and other records dating back to the 1940s to assist in the development of a conceptual model of contaminant release and migration in groundwater. We incorporated a comprehensive set of groundwater quality data into a database and developed maps illustrating plume signature and evolution over time. Our analysis included aerial images dating back to the 1930s and an evaluation of changes in land cover and use.
Geospatial Analyses for Sediment Cost Allocation
For a heavily impacted urban water body, Gradient developed a comprehensive multimedia database from multiple data sources to identify potential upland sources and impacts to sediments. We performed geospatial analyses, including interpolating sediment core log data and evaluating spatial variability, to identify sources and allocate sediment volumes that had been impacted by those sources.
Geospatial Analysis to Evaluate Exposure
For a toxic tort case in California, Gradient performed geospatial analyses to support the evaluation of potential plaintiff exposures. Using a GIS and customized automation routine, we mapped chromium and trichloroethylene (TCE) concentrations in groundwater and air relative to dozens of plaintiff residence locations over multiple exposure periods.
Land Use and Land Cover Analysis to Identify Historical Features and Changes Over Time
Gradient performed interpretation and analysis of aerial and satellite imagery near a historical dump site. We reviewed information collected during previous environmental investigations, and evaluated landform and land cover changes at the site from the 1940s to the present day. We also collected GPS locations for pertinent site features, using a mobile GIS application.
Analysis of Aerial Photographs and Topography to Identify Alternative Sources of Contamination
To assess the extent of change in land cover and identify potential sources of contamination, Gradient analyzed aerial photographs dating back to the 1930s at a site and in its vicinity. We evaluated topographic information and documented historical flooding events to identify areas potentially impacted by the redistribution of soil contamination.
Technical Evaluation to Determine Jurisdictional Status Under the Navigable Waters Protection Rule “Definition of ‘Waters of the United States'”
Gradient applied a holistic, weight-of-evidence approach to determine the jurisdictional status of several surface water features at a site. We relied on historical and contemporary aerial photography; property surveys and field data; regulatory documents; and local, regional, and national GIS data in our approach. The results of our analysis helped the landowners to make decisions about the future use of their land.