Superfund

# Calculating Waste Characteristics

When the most hazardous substance at the site is determined, its combined factor value is calculated, and the HWQ factor value calculated, the Waste Characteristic (WC) factor is calculated using the HRS Rule, Section 2.4.3, page 51592.

The combined factor value for the most hazardous substance at the site is multiplied by the HWQ factor value. Based on this product, a Waste Characteristics factor category value is assigned to the pathway using Table 2-7. The assignment structure of Table 2-7 prevents the Waste Characteristics factor category from dominating the HRS score which could otherwise occur due to the wide range of hazardous substance toxicities, the large degree of uncertainty about waste quantities at a site, and the extreme variation in waste quantity between sites. Table 2-7 compresses the WC factor category value so that it does not range over several orders of magnitude. In addition, the WC factor category value is subject to a maximum of 100, except when the bioaccumulation potential factor value (BPFV) is considered in two of the surface water pathway threats. In this case, the procedure for determining the WC factor value is a bit more complex and the maximum value is 1,000.

Here is an example using the Ground Water pathway:

1. It has been determined that the most hazardous substance at the site for the ground water pathway is arsenic (from SCDM, Toxicity = 10,000 and Mobility = 1).

2. Multiply Toxicity x Mobility = 10,000. This is the combined factor value.

3. It has also been determined that the HWQ factor value for the pathway is 100 (from Table 2-6).

4. Multiply the combined factor value (10,000) x HWQ factor value (100) = 1,000,000.

5. Waste characteristics factor value = 32 (from Table 2-7).

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