R3 PM Application of Spatially Explicit Techniques in Ecological Risk Assessment
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in Ballroom 3

(SAM-1117-133201) Developing Spatial Averages for Discontinuous Chemical Contamination.

Samuelian, J.¹, Alsop, W.², ¹ AMEC Earth & Environmental, Portland, ME, USA² AMEC Earth & Environmental, Westford, MA, USA

ABSTRACT- The determination of the representative soil concentration of a chemical contaminant (Exposure Point Concentration; EPC) is integral to the evaluation of potential ecological or human health risks at chemical waste sites. EPA has developed guidance for using the upper 95th confidence limit (95UCL) of the mean concentration for deterministic risk assessments as well as the supporting software ProUCL. These methods do not account for the spatial representativeness of the samples. Although geostatistical tools, such as splining or kriging, are available that account for the spatial distribution of the chemical results, many of these methods have an underlying assumption that a continuous distribution of chemicals is present at the site. In the case of particulate contamination, such as explosives, the sample results can have a discontinuous distribution at the site. We will demonstrate some alternate approaches to developing an appropriate spatially representative mean and 95UCL for such data sets. Furthermore, we will also discuss how composite samples have been used to develop spatial averages for risk assessments that better represent the average concentrations of chemical contaminant when compared to discrete samples.

Key words: Ecological Risk Assessments, Risk Management, Decision-Making