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If a spill occurs, approximately 67; 1,815; and 744 barrels of product would be released under three
<br />probable release scenarios: (1) active leak detection lower limit of 1 percent of pipeline flow (i.e., about
<br />32 barrels per hour (bph)), (2) complete rupture and maximum release of 3,200 bph, and (3) small leak
<br />rate of 1 bph detected after 30 days. In the case of scenarios 1 and 2, the leak or spill would be detected
<br />within 30 minutes through loss of pressure in the pipe. A small leak may only be detected by a static test.
<br />A hazardous spills clean-up team would be required as a conservation measure to respond to any spills
<br />within 1 hour, and the project proponent would be required to maintain all equipment and materials
<br />necessary for site clean up.
<br />Two different spill scenarios were analyzed: Ridges Basin Reservoir at full capacity (120,000 acre-feet)
<br />and Ridges Basin Reservoir at minimum pool (30,000 acre-feet). These two scenarios are discussed in
<br />the following paragraphs.
<br />At 120,000 acre-feet (full capacity), Ridges Basin Reservoir would be approximately 9,000 feet at its
<br />widest point, and 17,010 feet at its longest point. At a spread rate of 1,969 feet/h, refined petroleum
<br />would spread across the reservoir (9,000 feet) in approximately 4.5 hours, and would spread the entire
<br />length of the reservoir (17,010 feet) in approximately 8.5 hours. At a spread rate of 1,969 feet/h, the
<br />volume of water affected in the first hour after the petroleum product contacts the water is approximately
<br />2,516 acre-feet, and the entire reservoir (120,000 acre-feet) would be affected in approximately 8.5 h.
<br />To determine potential toxicity of a petroleum product spill, the most toxic component of the product is
<br />used. Benzene is considered the most toxic fraction of petroleum product because of the low
<br />concentration at which toxic effects occur. Benzene is selected as the key indicator for toxicity of
<br />petroleum product because other fractions are less toxic. Benzene comprises about 2.2 percent of the
<br />volume of refined petroleum product (e.g., gasoline). Acute and chronic toxicity thresholds for rainbow
<br />trout exposed to benzene are 7.4 mg/L and 1.4 mg/L, respectively (USEPA 1998). Rainbow trout would
<br />probably be used as the principal fishery for Ridges Basin Reservoir and are the most effective indicator
<br />of toxicity to aquatic organisms for this project.
<br />For a large spill (i.e., complete rupture and release of 1,815 barrels), benzene is estimated to be acutely
<br />toxic at a water volume of up to about 0.70 acre-feet, and chronically toxic up to a water volume of 3.68
<br />acre-feet. (see table B-2). In the case of Ridges Basin Reservoir, the greatest risk of toxicity would occur
<br />within the first hour at a spread rate of 1,969 feet/hr.
<br />By the end of the first hour following contact of the petroleum product with water in the reservoir, the
<br />concentration of benzene from a large spill (1,677 gallons) would be about 0.002 mg/L; thereafter, the
<br />concentration of benzene would be less than 0.001 mg/L, which is far below toxicity levels (see table B-
<br />3). Hence, block values at each end of Ridges Basin would prevent release of petroleum product of
<br />sufficient magnitude to be toxic to aquatic life or bald eagles.
<br />The worst possible case scenario for a petroleum leak or spill in Ridges Basin Reservoir would be during
<br />winter when bald eagles are likely to be present; when low air temperatures would slow evaporation of
<br />petroleum product components, such as benzene; and with the reservoir at minimum allowable pool of
<br />30,000 acre-feet. Under this scenario, toxicity levels of benzene during a large spill (1,677 gallons),
<br />would be the same as with the full pool volume of 120,000 acre-feet; i.e., 0.002 mg/L in the first hour and
<br />0.004 mg/L thereafter. The lower volume of Ridges Basin Reservoir would still provide sufficient
<br />dilution to eliminate toxic effects of benzene. These spill scenarios assume little or no evaporation of
<br />benzene, and so the concentrations provided would be maximum.
<br />B-13 Weetninuche Construction Authority
<br />P.O. Box AA - Towaoc, CO 813,134
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