Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
• A well could substitute for withdrawal from the river and eliminate those impacts.
Wells are generally considered preferable to surface water withdrawals. Since a
change in the point of diversion would be required, a well would be strongly
considered.
Post-Removal Management
• To assess the effectiveness of the Sediment Management and Revegetation Plans
(PacifiCorp 2004), long-term water quality monitoring is proposed.
• Monitoring of applicable water quality parameters, including turbidity, total
suspended solids, and pH, as well as observation and documentation of banks and fish
passage, will continue from the commencement of dam removal activities until such
time that performance criteria are met (PacifiCorp 2004). Infrequent, short-term
turbidity spikes are expected to continue for three to five years, and the monitoring
would continue at least as long as the reservoir sediment-induced turbidity spikes are
still evident.
• If on-site disposal of the concrete debris is selected as the preferred disposal option,
shallow groundwater monitoring downgradient of the concrete disposal site would be
performed to confirm that groundwater quality meets applicable standards.
• Periodic water quality analyses are performed as part of normal public water supply
well requirements at the City of White Salmon production well to document water
quality and track changes to water chemistry over time. Impacts are not anticipated;
therefore, additional sampling or mitigation is not recommended.
4.2.4 Significant Unavoidable Adverse Impacts
Significant unavoidable adverse impacts identified with respect to surface water include massive
turbidity and sediment transport as part of the dam breaching and removal. Total suspended
solids in the White Salmon River within the six hours after the dam breach could range from
100,000 to 250,000 ppm and turbidity values could range from 50,000 to 127,000 NTUs.
Elevated turbidity levels also are expected in the Bonneville pool, where the water of the
Columbia River and the White Salmon River mixes. Clay particles will likely remain suspended
in the Columbia River, thus increasing turbidity, all the way to the mouth of the Columbia River.
Decreasingly frequent episodes of elevated TSS and NTUs are expected through the first year
following the dam breach, as bank and river channel stabilization occurs. These turbidity spikes
are predicted to return to near background levels within three to five years.
Significant unavoidable adverse impacts were not identified with respect to groundwater.
4.2-13