Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
The potential project-generated traffic volumes were distributed onto the surrounding
roadway network for the beginning and ending trips per day because most of the internal
trips are on private or local roadways. Peak hour traffic volumes that include the proposed
project (a total of 34 vehicle trips) were developed.
A peak hour LOS analysis for the roadway segments in the project area was undertaken. The
results show that the small increase in traffic traveling to the study area as well as the
intersection of SR 141/Powerhouse Road would cause little or no perceptible change to
operations. As stated above, the maximum change would involve the addition of 9 truck
trips and 25 vehicle trips (employees) traveling to the project site during the am and pm peak
hours. This increase in truck and vehicle traffic only changes the operations minimally for
any vehicle turning from Powerhouse Road onto SR 141 (the worst-case scenario).
If concrete recycling occurs, the location of the recycling would be off-site, assumed to be
within 30 miles. Under this scenario, the approximately 30,000 cubic yards of concrete
would require 3,000 truck loads, assuming 10 yards per load. If that is distributed evenly
over the 8-month deconstruction period, it would be less than 3 loads per hour entering SR
141. The same number of empty trucks would return to the site. Those truck trips would be
added to the vehicle trips noted above expected to travel on Powerhouse Road, SR 141 and
SR 14. Under this scenario, the truck traffic would increase from 9 to 12 per hour. This
change would not reduce the LOS on roadways and at intersections throughout the day. The
additional trucks would slightly increase the potential for accidents.
Parking/Staging
Parking and staging areas would be necessary. Primary sites for staging are adjacent to
Powerhouse Road next to the dam. These sites include an area occupied by a private
residence (which would have to be purchased) and by a shed owned by PacifiCorp. There
are additional small flat areas adjacent to access roads that would also be used as staging
areas and parking areas. Areas would require the removal of existing buildings, clearing of
vegetation, grading and gravelling (where necessary).
Alternative Access Roads
It is anticipated that alternative access roads would need to be constructed to allow access to
different parts of the dam demolition. The project vehicle trip generation would be the same
as described above. The building of alternative access points would still need to intersect
Powerhouse Road or SR 141 at some point.
An alternative access road for removal of the demolished dam materials would result in the
same trip generation. It is anticipated that most truck trips would be from the dam site to a
few thousand feet upstream, the proposed concrete disposal site.
Post-Removal Management
Due to the demolition of the dam, stability concerns concerning the Northwestern Lake Road
bridge have been raised in a report by DCI Engineers (2004). Sediment around the H-piles
would be washed away, resulting in a decrease in lateral load capacity and a decrease in axial
load buckling strength, possibly resulting in a collapse of the bridge. Erosion of the banks
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