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A Spatial Environmental Risk Assessment Methodology for Risk-Based Decision Making at Large, Complex Facilities

By Lesley Hay Wilson, Randall J. Charbeneau, and David R. Maidment

ABSTRACT

Spatial Environmental Risk Assessment (SERA) methodology is the integration of geographic information systems (GIS), (i.e., spatial databases), relational databases and environmental models to practically implement environmental risk assessment. The SERA methodology was developed to facilitate evaluation of multiple source areas and exposure pathways that are typical at large, complex facilities. The methodology includes spatial and tabular databases for the site conceptual model, integrated exposure pathway analysis through linkages between the site conceptual model database and fate and transport models. The methodology includes both deterministic and probabilistic calculations. First order uncertainty analysis is used for determining variance in exposure pathway ending concentrations using confidence intervals for modeling input parameters developed based on site data, reference information and judgments about parameter variability.

The impacts of multiple sources at one receptor location are analyzed through a process of segmentation of the exposure pathways, so that parallel and serial exposure pathway segments can be analyzed. The relationships between the exposure pathway segments and the source areas, the model scenario data and the results are managed in the site conceptual model database. Spreadsheets linked to the site conceptual model database are used to calculate attenuation factors using fate and transport models. For the deterministic calculations, the exposure pathway completeness is determined based on comparison of ending concentrations to target levels. For the probabilistic calculations, the exposure pathway completeness is determined based on the probability that the ending concentration is below the target level and the coefficient of variation in the ending concentration is used to determine the value of additional information.

The SERA methodology was implemented using PC-based software and examples from a case study are presented. The case study example results are used to illustrate the visualization benefits of the GIS implementation and the use of the uncertainty results to support decision making. The case study examples illustrated the applicability of the SERA methodology for groups of exposure pathways impacting single receptor locations and the data management benefits were demonstrated for the site conceptual model.

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