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Highlight 8-32, page 263 of the HRS Guidance Manual

Scoring Intakes Subject to Actual Contamination

The level of contamination must be determined to score the nearest intake and population factors and may affect the minimum value for the hazardous waste quantity factor. Once the level of contamination has been established for each intake within the TDL, score these targets as shown in Highlight 8-32. Section 8.8 provides detailed instructions for scoring nearest intake and population factors for intakes subject to actual contamination.

HIGHLIGHT 8­32
COMPARISON OF SCORING LEVEL I, LEVEL II
AND POTENTIAL CONTAMINATION

Level of Contamination Nearest Intake Factor Value Population Factor Value Minimum HWQ Factor Valuea
Actual — Level I 50 10 x number of people 100
Actual — Level II 45 1 x number of people 100
Potential (dilution weight) x 20 0.1 x dilution­weighted population 10b

a Minimum hazardous waste quantity factor values apply if Tier A is not adequately determined for all sources.

b May be 100 in certain cases when there has been a removal action; see HRS section 2.4.2.2 and EPA's removal policy fact sheet.

TIPS AND REMINDERS

  • Actual contamination cannot be established without an observed release to surface water, but an observed release to surface water is not necessarily sufficient to document actual contamination of a drinking water intake.

  • Benthic tissue and sediment samples cannot be used to establish Level I concentrations for the drinking water threat, but can be used to establish Level II concentrations. Only analytical data from surface water samples can be used to establish Level I concentrations.

  • To use multiple hazardous substances to establish Level I concentrations using the I or J index, all hazardous substance concentrations must be from the same sample or comparable samples. Comparable samples are samples taken at essentially the same location and at essentially the same time, and analyzed by equivalent methods.

  • The area of actual contamination and the level of actual contamination within that area can vary for each of the three surface water threats.

  • Intakes at sites that consist solely of contaminated sediments with an unknown source cannot be evaluated at Level I, regardless of surface water concentrations at the intake.

 

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