Hazard Analysis - doe-std-1120-2-20050033

DOE-STD-1120-2005/Vol. 2

HAZARD ANALYSIS

Example 5:

Final Hazard Categorization of Environmental Restoration Activity

A former active disposal site that was operated from 1943 to 1970 is currently planned for soil excavation

and offsite disposal. The area consists of 15 acres. Burning and disposal of debris, including radioactive

wastes from Y-12 are known to have occurred within unlined trenches that were eventually covered with

soil.

Soil and groundwater sample results from remedial and field investigations were used to estimate a 95

percent upper confidence level of radioactive material inventory. A preliminary hazard categorization

was performed in accordance with DOE-STD-1027-92 and considered the sum of multiple radionuclide

fractions to their respective threshold quantity values. This concluded that inventory was 49 times higher

than the threshold for Hazard Category 3 (HC3) and 90% of the Hazard Category 2 thresholds.

Therefore, the site was initially categorized as HC3.

A simple hazard evaluation was prepared and documented, which considered the presence of available

energy sources (e.g., fires, vehicle collisions, impacts from aircraft crash, high winds, localized flooding).

No dispersive mechanisms were identified to exist, except when material was exhumed in preparation for

transport via dump trucks which exposed material to several release mechanisms. The maximum quantity

of material expected to be removed at any one time was limited because of excavation capabilities and the

number of dump trucks that could physically transport materials.

The credible release fractions for each event were determined using DOE-HDBK-3010-94. These values

were then compared with the bounding release fraction from DOE-STD-1027-92, which is 1E-3, and a

ratio of the two numbers calculated. The release fraction of 1E-3 is used as a basis for Hazard Category 2

determinations in DOE-STD-1027-02 for non-volatile solids, powders and liquids, and was also

confirmed to be the baseline value in EPA Technical Background document that supported Hazard

Category 3 threshold quantities. Any decrease in this release fraction will result in an increase in the

DOE-STD-1027 TQ value, proportional to the ratio mentioned above.

The most limiting release fraction was associated with a vehicle accident and was modeled after a free-

fall spill of powder in accordance with DOE-HDBK-3010 (Airborne Release Fraction of 2E-03 and

Respirable Fraction of 0.3). This value is 60% of the baseline value, and for the sum of all isotopes in

question results in a total adjusted HC3 TQ of approximately 7.0 curies. The inventory of one dump

truck is estimated at 0.074 Ci (20yd3) of mixed isotopes. Over 90 dump trucks would need to

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