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Benchmarks and Levels of Contamination

  • Environmental benchmarks (freshwater and saltwater) are found in SCDM.

    • For each sampling point that meets observed release criteria, determine whether it is Level I or Level II by comparing the concentration of those substances that meet the observed release criteria against the appropriate benchmark for the sampling point.

  • QUESTION: If the average tidal cycle chloride content at a sampling point is 1,500 mg/l, should you use the freshwater or the saltwater benchmark? (For definitions of freshwater, brackish water, and saltwater, see pages 229 - 230 in the HRS Guidance Manual.)

  • ANSWERThe zone of Level I concentrations extends from the PPE to the most downstream (or farthest) sampling point that meets the criteria for Level I.

    • Look at the formula at the top of the middle column of HRS page 51625 or press here:

      HRS rule, page 51625

    • Sum all the wetland frontage within the zone of Level I concentrations and assign that frontage a value from HRS Table 4-24, page 51625.

    • Sum the values for all the listed sensitive environments on HRS Table 4-23 that lie within the zone of Level I concentrations.

    • Sum the values for wetlands and listed sensitive environments. This sum is multiplied by 10 for Level I concentrations. Enter the product in HRS Table 4-1, page 51608.

  • The zone of Level II concentrations, if any, extends downstream (or beyond) to the farthest sampling point that documents an observed release but has no substances in the release that meet or exceed an environmental benchmark.

    • The formula and the procedure for assigning a value are the same as for Level I except the multiplier for Level II is 1 rather than 10.

  • The zone of potential contamination, if any, extends from the most downstream (or farthest) sampling point which documents actual contamination to the TDL and no farther.

    • Within this zone of potential contamination, analyze separately for each dilution range. Within each dilution range, add the value assigned to wetland frontage in that range to the sum of the values of sensitive environments within that range. Multiply the resulting sum by the appropriate dilution weight from HRS Table 4-13, page 51613.

    • Sum the dilution-weighted values for environmental targets (wetlands plus sensitive environments) and multiply the sum by 1/10 for potential. Enter this value for potential contamination in HRS Table 4-1, page 51608.

EXERCISE: The PPE from the site is on a small stream with a streamflow of 25 cfs. The stream discharges into a large stream within about a mile from the site. The large stream has a streamflow of 250 cfs.

Three samples document observed releases to the small stream. The nearest sample is Level I and the next two are Level II.

There is wetland frontage along both the small and the large stream and habitats known to be used by two Federal designated endangered species are collocated with the wetlands.

The wetland frontage by zone of contamination is approximately:

Level I 100 feet
Level II 1400 feet
Potential (25 cfs) 3000 feet
Potential (250 cfs) 800 feet

What is the score for environmental targets?

Listed Sensitive Environments and Wetlands


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