Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
The possibility of spills during fueling of the cranes or other equipment could impact surface
water. The largest quantity of potential pollutants without secondary containment would be
contained in a 55-gallon drum or in fuel tanks of large machinery. Therefore, a potential release
would not be expected to exceed 55 gallons. Prevention of releases of hazardous substances and
responses to releases, if they were to occur, would be mitigated in accordance with procedures
outlined in the Spill Prevention and Containment Plan (PacifiCorp 2004). With proper planning
and implementation of the Spill Prevention and Containment Plan, the potential for a release of
petroleum products or hazardous substance that would cause a significant water quality impact is
considered to be low.
Dam Breaching and Removal
Dam breaching and removal would result in water quality impacts in the White Salmon River.
Management of the concrete from the dam would include stockpiling and/or disposal of the
concrete debris on the 8-acre site owned by PacifiCorp (SA-3) (Figure 3-4). Potential surface
water and groundwater quality impacts include increased sediment load and changes to pH.
Impacts from storage of petroleum products and fueling of equipment would be similar to those
described above.
Drain Tunnel Construction and Dam Removal
Concrete debris from drain tunnel construction and dam removal may alter surface water quality
downstream of the dam. Squier Associates performed a bench-scale test of the alkalinity effects
from pulverized concrete on behalf of PacifiCorp (Squier Associates 1998). Four concrete core
samples collected from the dam were pulverized and fine sand size and smaller fragments (less
than 0.25 millimeter diameter) were mixed into solution with river water samples at
concentrations from 0 grams per liter (g/L) to 100 g/L. The samples were held at a stable
temperature and pH values were recorded periodically over 30 days. At the end of the test
period, solutions of 5.0, 10.0, 25.0, and 100.0 g/L concrete fragments demonstrated pH values of
greater than 10 standard units. The maximum pH values recorded during the test typically
occurred between 7 and 16 days. Squier Associates estimated that the majority of surface water
impact from pH would occur as a result of the initial creation of the lake drainage tunnel through
the dam. According to PacifiCorp, the discharge from the lake would be approximately 10,000
cfs for a period of approximately 6 hours. Based on the discharge volume and estimated volume
of concrete pulverized during the final blasting of the tunnel, Squier Associates (1998) estimated
that the river water pH immediately downstream of the dam would immediately increase to
approximately 11.4 standard units, then decrease to a slightly elevated level within 5 hours. A
check of the assumptions used by Squier Associates and recalculation revealed that any spike in
pH is likely to be diluted to less than lethal levels in less than a minute and be near normal in 15
minutes or less. This impact is considered to be a very localized and short-term effect that would
not extend very far downstream and would not, for example, be likely to reach the Bonneville
pool on the Columbia River.
Water used in drilling into the dam to develop the drain tunnel will be collected and removed
from the site. Larger blocks of concrete in the stream will also be removed. As part of the
Sediment Assessment and Management Plan (PacifiCorp 2004), pH levels will be monitored
continuously at the powerhouse downstream of the dam and compared to background pH levels
to observe potential effects from the concrete cutting and blasting.
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