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Questions and Answers

At the Site Inspection (SI), does it make sense to put an air sampling station on the outside portion of the distance ring?

No.   Air sampling stations should be placed on the inside boundary of a distance ring in order to maximize the chance of detecting an air release while also maximizing possible actual contamination targets.   This distance ring is determined by the likelihood of detecting the air release.

If an observed release cannot be documented, how are the targets evaluated?

The targets are evaluated as potentially contaminated.

What is the level of contamination (Level I, II, or potential) for release samples A, B, and C, given the substance-specific background level and benchmarks?

  • A = 35 mg/kg.   Potential: the concentration is not significantly above the background level.   No observed release = no actual contamination.

  • B = 60 mg/kg.   Potential: the concentration is above a benchmark, but is not three times background.   No observed release = no actual contamination.

  • C = 100 mg/kg.   Level I: the concentration is above a benchmark and also meets observed release criteria.

  • The applicable benchmark is Benchmark 1 (55 mg/kg).   Benchmark 2 plays no role in this evaluation.

What is the level of contamination for this well?

Level I (based on the I index, which is greater than one).

What is necessary to establish actual contamination?

In order to establish actual contamination, you must first establish that there has been an observed release at a target location.

What is necessary to establish Level I contamination?

To move from Level II to Level I, the target must be subject to concentrations above a health-based benchmark.

For the ground water pathway, 2,4­dimethyl phenol has a benchmark of 0.7 mg/L. It was detected in a monitoring well at 0.7 mg/L. What level of contamination does this document?

None.   Even though it is at or above a benchmark, there are no targets associated with the monitoring well.

What can you do to establish Level I concentration if your samples results are not above a benchmark for any given substance?

Try the I and J indices for all the substances in each target sample.


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