Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
• Build concrete wing walls and a crib structure, tying the existing bridge
abutments to the new sheet pile cofferdams with circumferential galvanized
cables near the top of the cofferdam wall.
• If embedment depth of piles into the bedrock cannot be ascertained by a
geotechnical engineer, excavate the soil and dewater inside the cofferdam to an
elevation near the bottom tip of the sheet piles. Provide temporary bracing to the
existing piers and sheet pile walls in stages as required for temporary construction
stability while the cofferdam soil is removed.
• Install reinforced concrete grade ties from the existing concrete pile caps to the
new concrete wing walls to increase the lateral strength and stability of the pile
caps. Anchor wing walls to the bedrock above the river channel with high
strength grouted Dywidag Threadbar rock anchors.
• Backfill the cofferdam and concrete crib structure with granular structural fill to
finish grade elevations.
• Provide riprap along river revetment slopes on both sides to protect shore from
high velocity flow.
• Include provisions for navigational markers and, if necessary, signage on the
bridge in accordance with accepted design standards.
4.6.5 Significant Unavoidable Adverse Impacts
With the implementation of the mitigation measures identified above, no significant
unavoidable adverse impacts are expected to occur to transportation or traffic.
4.6-11