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Questions and Answers

Would a photograph of a source inundated during a flood establish an observed release to the surface water?

Yes, if the source was documented to contain hazardous substances.

What kind of information could you use to show that sediment samples are similar?

Sampling location (depth, position in stream, etc.), grain size, sampling date, etc.

Do the two background samples adequately address attribution?

Yes, because the background samples are placed between the suspected source and any alternative sources, which may exist further upstream. Thus, in judging whether the release sample is significantly elevated above background, the background measurement will already account for the contribution of any alternative sources. This allows the scorer to isolate the impact of the suspected source in attributing it to any contamination.

Do the two background samples still adequately address attribution?

No, because the background samples are no longer placed between the suspected source and the alternative source. Thus, in judging whether the release sample is significantly elevated above background, the background measurement will not account for any possible contribution of the alternative source. This prevents the scorer from isolating the impact of the suspected source in attributing it to any contamination.

Can an observed release be documented for the source at the bottom site?

No. An attribution sample located between the two sources is needed because it is not possible to determine ground water flow from two points. Because of possible subterranean obstructions, the flow depicted on this graphic may only be a component vector of the actual flow.

What information is needed in order to document an observed release from a site?

  • Recorded information documenting that a substance attributable to the site has been entering the media of concern (Direct Observation); or

  • The detection in the media of one or more hazardous substances attributable to the site with concentrations significantly above background levels. The "significant increase" has to be at least partially attributable to the site.

If an observed release cannot be documented, how will it affect the site score?

Because the maximum value for potential to release is 500 and an observed release is assigned a factor value of 550, potential to release will always have a lower score. Also, because actually contaminated (Level I or II) targets cannot be evaluated without an observed release, the target values will also be significantly lower.

How does the HRS define significance above background for documenting an observed release?

If the background is non-detect, any release sample above the detection limit qualifies as a significant increase above background. If the substance is detected in the background sample, the release sample concentration must be at least three times greater than the background level.

When might attribution samples be needed?

Attribution samples may be needed when there is a possible alternative source of the same hazardous substance being examined at the site.

 

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