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.
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|
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.