Costs and Benefits of a Contaminated Sediment Toxicity Testing Program. L. Williams and G. Braun, Foster Wheeler Environmental Corporation
Decisions to cleanup contaminated sediments are often based solely on comparisons of sediment chemistry with risk-based sediment screening values. Further evaluation of contamination through toxicity testing is often dismissed because of the perceived expense of additional study in comparison with the practicality of an engineered solution (e.g., capping). However, this conventional wisdom is rarely challenged with analysis of the actual costs of the engineered solution in comparison with the benefits of sediment toxicity testing. Consequently, a cost-benefit approach was developed for sediments contaminated with polycyclic aromatic hydrocarbons (PAH) in the vicinity of a former manufactured gas plant. The cost-benefit analysis was developed for a range of total PAH concentrations in sediments. The screening level concentration (NOAA’s ER-L) was selected as a lower threshold below which testing would not be conducted because toxicity is not expected. The upper threshold concentration represents the level above which sediments could be considered toxic and, therefore, would be presumptively capped without further testing. The upper threshold value was based two factors: 1) the probability of passing a toxicity test, and 2) the net economic benefit of toxicity testing. Net economic benefit was defined as the savings gained (i.e. costs avoided) for areas that would not be capped, minus the costs of conducting toxicity tests and capping those areas where the tests failed. The results of this analysis show that there is a net benefit to toxicity testing even at a high threshold sediment concentration that has a low probability of passing the test. Avoiding capping costs for only a few dredge management areas that pass a test at relatively high threshold levels could compensate for the costs of testing at sites that failed. Based on a 20 to 40 percent probability of passing the test, benefits could range from about $100,000 to $325,000.
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