Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS may cause settlement and collapse of the abutments and bridge piers. DCI Engineers has proposed a scheme to protect the four bridge piers and approach pavements. 4.6.3 Cumulative Impacts The proposed project would create approximately 25 full-time jobs and an estimated 200 vehicle trips per day from the dam removal site. If the majority of trips being located on-site (removal of debris to areas approximately 1,000 feet upstream of the dam), the small increase in trips on local roads associated with the proposed project is not anticipated to create traffic congestion or a diminution of the LOS at any affected intersection. If concrete recycling occurs, there would be an increase in trips on local roads. This would result in some increase in traffic congestion and a slight increase in accident risk, particularly at intersections. Other approved projects in the area are not anticipated to have overlapping construction and/or demolition periods. It is anticipated that construction/demolition vehicles for these overlapping projects traveling into or out of Washington State would be via SR 14 and not result in cumulative impacts on SR 141 or Powerhouse Road. 4.6.4 Mitigation Measures This section discusses the proposed mitigation measures that would be implemented to reduce project-related impacts to traffic circulation in the project area. Construction safety: Provide traffic safety signs during the 8-month peak demolition period warning vehicles traveling along SR 141, SR 14, and Powerhouse Road of upcoming truck access points. Traffic and Parking: Promote ride-share and vanpool programs during the 8-month peak construction period for construction workers to reduce vehicle trips. Access Roadways: Continued monitoring of access roadways constructed for this project to minimize erosion and stabilization problems. All access roadways should minimize alteration of existing native vegetation. If concrete recycling occurs, coordinate increased truck traffic on Powerhouse Road, SR 141, and SR 14 with WSDOT and local agencies. A traffic management plan would be developed and coordinated with the agencies. If needed, repave or resurface roadway surfaces along Powerhouse Road, SR 141, SR 14 and other local roadways that may experience increased loading and volumes. Northwestern Lake Road (Bridge): Implement the mitigation measures listed in the report by DCI Engineers (2004), including: • Drive steel sheet pile to refusal at bedrock depth around the two central piers in a semi-circular pattern to create two separate cofferdams bounding the river channel. 4.6-10
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
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Condit Dam Removal Final SEPA Suppl
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March 23, 2007 Dear interested part
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Condit Dam Hydroelectric Project Fi
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Appendix A Memorandum of Agreement
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Appendix C Supplemental Aquatic Res
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Agency and Organization Letters and
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Agency and Organization Letters Con
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Contents Public Meetings Response P
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Contents Individuals Individuals A-
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