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Ecological Risk Assessment

Frequently Asked Questions

Media Considerations

  1. How should I evaluate subsurface soils?
  2. Do I need to evaluate subsurface sediments in the ecological risk assessment?
  3. When do I consider my receiving waters freshwater and when do I consider them saltwater?

1. How should I evaluate subsurface soils?

Subsurface soils should be evaluated in the risk assessment unless it can be demonstrated that there is no contamination, no prey, or no receptors at this depth. In any event, the subsurface soil media should be discussed in the uncertainty section of the ecological risk assessment. For sites where the sampling has already been completed there may be no need to collect additional data. The available subsurface soil data, if any, can be handled either quantitatively or qualitatively as appropriate (e.g., two to six foot composite samples may only need to be evaluated qualitatively). A Region 3 BTAG representative should be consulted on a site specific basis in these situations.

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2. Do I need to evaluate subsurface sediments in the ecological risk assessment?

The depth interval of sediment that must be evaluated in the ecological risk assessment is dependent on the site-specific conceptual model. However, during the initial phases of sampling and risk assessment, depths of sediment samples can generally be restricted to the 0 - 6" interval. Deeper sediments will be assessed in the nature and extent of contamination phase as either excavation or storm events could expose sediments with concentrations of contaminants that would adversely effect ecological receptors. The evaluation of potential impacts of contaminated groundwater discharge to sediment / surface water should be addressed on a site-specific basis.

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3. When do I consider my receiving waters freshwater and when do I consider them saltwater?

Salinity must be determined at the time of sampling. Receiving waters with salinity values less than 1 part per thousand (ppt) should be considered freshwater and evaluated using freshwater criteria or benchmarks. Those with salinity values between 1 ppt and 10 ppt should be considered brackish and evaluated using the more conservative of the freshwater and marine benchmarks. Receiving waters with salinity values equal to or greater than 10 ppt are considered marine and should be evaluated using marine criteria.

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