Floating Spatial Domain Averaging in Surface Soil Remediation

Abstract

Cleanup plans for contaminated surface soil are frequently developed with the goal of ensuring that regulatory criteria for risk exposure are met after remediation. Currently, some of the plans for Superfund sites are based on the premise that a concentration equal to the average goal or based on a confidence level expression of the concentration measurements is not to be exceeded (NTE). However, in cases of widespread low-level contamination, the NTE constraint may result in lowering risk well below the regulatory criteria and substantially increasing remediation costs. Alternative methods based on spatial averaging are developed and explored in this paper. Floating spatial domain averaging (FSDA) is a multi-criteria decisionmaking tool in which concentrations or risk factors are averaged over domains that represent exposure areas. The domains are variable in space. The averaging domain floats over the surface in increments representative of the sample or cells spatially interpolated raster units. This allows for the incorporation of domain-wide topological information into the averaging operation around each cell. Floating domain averaging can be done manually or with the aid of geographical information systems (GIS). Additional marginal cost or cleanup objectives can be incorporated into the model and linear programming solutions used as a multi-objective decision-making tool. IntroductionThe Environmental Protection Agency (EPA) is responsible for the development of cleanup goals and remediation plans at waste sites in the United States (1). These plans are intended to ensure that regulatory criteria that protect public health and the environment are met at the sites after remediation.Remediation plans are commonly based upon the premise that a certain concentration is not to be exceeded anywhere at the site, which is referred to as the "not to exceed" (NTE) approach. However, soil screening levels (SSLs) developed by the EPA for screening potential surface soil remediation areas are based on an areal or spatial domain averaged risk (2). Consequently, alternative cleanup plans that are based on spatial averaging may be appropriate.Spatial domain averaging techniques are of particular interest in areas of widespread low level contamination, where full-site remediation based on the NTE approach might reduce average risk well below the EPA SSL criteria with associated significant increases in costs (3). If contamination at a site is not randomly distributed, then spatial interactions and relationships are important considerations in spatial domain averaging techniques. The floating spatial domain method in surface soil remediation planning, which is introduced here, is a multi-criteria decision-making tool by which some spatial topology and interactions are considered over exposure areas for future land uses. This method is evaluated herein for a site where one contaminant or risk factor is being targeted for remediation. The contamination is not distributed randomly over the site, and its levels are within an ...

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