Pathways
An HRS score for a site is determined by evaluating four pathways:
- Ground water migration (HRS Section 3.0);
- Surface water migration (HRS Section 4.0);
- Soil exposure (HRS Section 5.0); and the
- Air migration (HRS Section 6.0).
The surface water migration pathway is composed of two migration components; overland/flood and ground water to surface water, reflecting migration of contaminants above ground and below ground from a site into surface waters. The HRS surface water pathway score is based on the higher of these two component scores. Also, three different "threats" are evaluated for the surface water pathway: drinking water, human food chain, and environmental, reflecting the different types of threats posed by contaminated surface water. Two different "threats" are also evaluated in the soil exposure pathway: resident population threat and nearby population threat. In general, threats scores are summed in pathway calculations.
Pathway scoresheets are provided for each pathway in the HRS rule:
- Ground water migration pathway (HRS rule, Table 3-1, page 51595)
-
Surface water migration pathway
(HRS rule, Table 4-1, page 51608 and
Table 4-25, page 51628)
- Drinking water migration pathway
- Human food chain threat
- Environmental threat
-
Soil exposure pathway
(HRS rule, Table 5-1, page 51646)
- Resident population threat
- Nearby population threat
- Air migration pathway (HRS rule, Table 6-1, page 51651)
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