Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
4.7.2 Impacts
Pre-Dam Removal Activities
There are no existing regulated emission sources at the project site, and any temporary or
permanent new sources associated with dam removal are not expected to cause significant
adverse air quality impacts. Pre-dam removal impacts could result from drilling the tunnel
that would be used to drain the reservoir. Assuming liberal use of water during concrete
drilling, little or no concrete dust should be made airborne during this activity. PacifiCorp
project mitigation documents (dust control, etc.) do not speak to the potential to create dust
during tunnel drilling. The final 15 feet of concrete would be blasted; however, the rush of
water into the tunnel should negate that impact to the air.
Road building would be necessary to gain access to the various areas of demolition. Road
construction companies are familiar with regulations to minimize fugitive dust emissions,
and use water and chemical binders during dry periods. Since much of the work would be
during the wet season, road construction emissions are unlikely to present a problem.
Ecology provides a number of pamphlets to assist construction companies to comply with
fugitive dust rules, such as Windblown Dust (Publication #04-02-009); Building and
Construction Projects (Publication 95-1004); and Outdoor Burning (Publication 92-04).
Dam Breaching and Removal
Temporary and intermittent dust would be created by the combination of concrete cutting and
blasting used in the dam demolition. During blasting operations, blasting compounds
sometimes create very localized hazardous and/or toxic emissions. These emissions would
be of concern to workers during demolition activities. Blasting emissions are very
intermittent and are not regulated by the agencies as a source. Demolition contractors will
control safety of blasting operations and report to industrial oversight agencies.
Post-Removal Management
Post-demolition concerns are probably greatest for the sediments deposited in the reservoir.
Some of these sediments would be fine particles capable of becoming airborne during dry
weather with high winds. Since winds are channeled up and down the river valley, the
potential to impact visibility in the Gorge would be a potential concern. PacifiCorp has
scheduled the dam breaching for the typical beginning of the wet season and has taken care
to provide dust control plans and characterize the sediments. Stabilization and revegetation
is important for a number of reasons, including maintaining good air quality in the vicinity.
Toxic chemicals such as pesticides were reported in only one sediment sample in the
sediments, so it is assumed that the sediments are not a hazardous or toxic air pollutant
concern. Wood debris exposed by draining the reservoir are unlikely to be of a fine enough
grain size to become airborne off site, causing public exposure.
4.7.3 Mitigation Measures
Mitigation measures are detailed in the dust control and revegetation plans (PacifiCorp
2004). PacifiCorp will implement all of the BMPs for dust control and revegetation of the
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