Final Site Information Package for National Remedy Review Board ...

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