Final Site Information Package for National Remedy Review Board ...
Final Site Information Package for National Remedy Review Board ...
Final Site Information Package for National Remedy Review Board ...
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SITE INFORMATION PACKAGE FOR NATIONAL REMEDY REVIEW BOARD<br />
PART B, SECTION 14: COST INFORMATION<br />
In reality, the existing protective barriers installed to protect human health will need to be<br />
maintained into perpetuity to meet the CERCLA threshold criteria. The existing remedies<br />
have already been in place <strong>for</strong> nearly 15 years in some areas of the Upper Basin.<br />
Furthermore, the design life of the remedy protection projects implemented under<br />
Alternative RP-2 would be expected to be greater than 30 years.<br />
14.2.1 Alternative RP-1: No Further Action (Post-Event Response)<br />
Alternative RP-1 does not include actions to reduce the potential risk of damage to the<br />
existing selected human health remedies, but instead relies on cleanup and re-remediation<br />
of damage to the existing selected remedies after the damage occurs. The expected costs to<br />
repair existing protective barriers and re-remediate previously clean areas, based on the<br />
modeling results, are the costs associated with Alternative RP-1.<br />
A methodology <strong>for</strong> evaluating the long-term damage to the existing selected remedies that<br />
would be expected from storm events in the Upper Basin was developed to complete the<br />
NPV cost analysis <strong>for</strong> Alternative RP-1 (CH2M HILL, 2009e). The methodology used risk<br />
analysis principles developed by the U.S. Army Corps of Engineers (1989, 1996) to evaluate<br />
flood control projects. Basic probability theory suggests that the “expected” annual damage<br />
from extreme weather events can be stated as the sum of all such events, with each of the<br />
expected damages multiplied by its probability of occurrence.<br />
The risks posed to the existing selected remedies under Alternative RP-1 are a product of<br />
the probability of damage occurring and the consequence, or magnitude, of the damage. The<br />
probability of damage is higher <strong>for</strong> more frequent, smaller storm events. However, the<br />
consequence of damage is higher <strong>for</strong> less frequent, larger storm events. The probability of<br />
damage and consequence, or magnitude and damage together make up the risk posed to the<br />
existing selected remedies. The evaluation included an analysis of 5-, 25-, and 50-year storm<br />
events. The model results from each of these storm events provided a total area that would<br />
require re-remediation and/or cleanup following the given storm event.<br />
The probability of damage occurring was based on the probability of occurrence of all<br />
different storm events. In any given year, the selected remedies are at risk <strong>for</strong> damage from<br />
storm events of all sizes and frequencies. In a single year, there is a 2 percent probability of<br />
experiencing damage from a 50-year storm event. There is also a 20 percent probability of<br />
experiencing damage from a 5-year event, added to the probability of the occurrence of the<br />
50-year event. It is this cumulative probability and consequence that is the annual expected<br />
damage to the remedy.<br />
Using the methodology described above, the annual expected cost of damage to the selected<br />
remedies was calculated based on the potential area of damage estimated by the hydrologic<br />
and hydraulic model outputs of the 5-, 25-, and 50-year storm events, and the probability of<br />
these floods occurring. The 30-year NPV life-cycle cost was then calculated as the present<br />
value of the expected annual damage over the 30-year time horizon. The estimated total cost<br />
(30-year NPV) <strong>for</strong> Alternative RP-1 <strong>for</strong> the eight Upper Basin communities where detailed<br />
analyses were conducted is $50.1 million, including the side gulches.<br />
As discussed in Part B, Section 8, the side gulches were not evaluated to the same level of<br />
detail as the eight Upper Basin communities. The portion of the estimated total cost (30-year<br />
NPV) <strong>for</strong> Alternative RP-1 directly related to the side gulches is approximately $16.3<br />
B14-3