Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
All three types of activities would include blasting. Blasting noise is considered an impulse
noise because of its rapid onset and decay. It can cause temporary and permanent shifts in the
threshold of hearing depending on the decibel level. The U.S. Occupational Safety and Health
Administration (OSHA) standards do not allow employees to be exposed to an impulse noise
that exceeds 140 dB. Studies conducted by the U.S. Army also indicate that no hearing
protection is required for single blasts with peak levels below 140 dB. Blast charges are
typically sized so as to produce peak acoustical overpressures below 122 dBPeak (C-weighted)
(the threshold of annoyance for blasts recommended by the U.S. Army) at any sensitive land
uses.
URS assumes the blast charges would be sized to produce peak acoustical overpressures below
122 dBPeak (C-weighted) at 1/4 mile from the Proposed Action, i.e., the distance from Condit
Dam to the nearest residential property (sensitive land use), because:
• Pre-dam removal activities would require blasting of only the final 15 feet of
concrete on the upstream water-face of the dam.
• The intent of blasting for dam breaching and removal activities would be to fracture
the residual concrete of the dam for removal rather than blast it out of place.
• The intent of blasting for post-removal management activities would be only to
dislodge woody debris causing unstable slope conditions or adversely affecting fish
passage.
Several residences (i.e., sensitive noise receptors) are located near the dam, the concrete
disposal site, and the roads along which trucks and construction equipment would travel during
the Proposed Action. Intermittently, construction noise levels at these residences would
significantly exceed the modeled noise levels. The noise levels at these sensitive receptors due
to construction activities do not exceed state or local noise standards due to exemptions for
construction in the Klickitat County, Skamania County, and State of Washington noise
regulations. However, construction noise impacts to adjacent residential properties would be
significant due to the duration and intensity of noise that would be received.
4.8.3 Mitigation Measures
Recommended mitigation measures for the Proposed Action include:
• Construction activities should not be conducted within ¼ mile (1,320 feet) of an
occupied dwelling on weekends, legal holidays, or between 10 pm and 7 am on
other days
• All construction equipment should be required to be equipped with noise control
devices no less effective than those provided on the original equipment
• Operation of equipment with unmuffled exhaust systems should not be allowed
• Noise reduction measures should be required during construction, including
turning off idling equipment and using the quietest effective back up alarms
4.8-10