Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS Reconstruction of Mt. Adams Orchard Diversion The replacement of the water supply diversion would take place after the dam has been breached, but prior to the commencement of the spring irrigation season. As part of the replacement, a pipeline and intake would be constructed at a location that allows reliable access and operation. Sediment and erosion control for the disturbed upland areas associated with pipeline and intake installation would be addressed under BMPs as described in the Project Description (PacifiCorp 2004). It is likely that instream work would be required to install the diversion structure. Similar to the instream work associated with the Northwestern Lake Bridge, fine grained sediments would be suspended in the water surrounding the intake structure, potentially increasing turbidity during installation. Alternatively, the possibility of changing the surface water appropriation to a groundwater appropriation would be investigated. If the change can be approved in time, that may become the preferred approach. If that change occurred, there would be no direct effects on surface waters. Effects on groundwater would be negligible. Haul Roads Soil, rock and vegetation would be removed from the road sites as part of road widening for the new or upgraded access roads and staging areas as described in the Project Description (PacifiCorp 2004). Although most of the project work areas would be accessible by existing roads, new or improved roadways would be required, such as former (now overgrown) reservoir access roads along the east side of the lake, and road extensions necessary to access proposed work areas (such as access to the lower portion of the dam). Access roads have been identified as being required for the dam decommissioning project: AR-2 Powerhouse Road to dam existing AR-3 Access road to dam and SA-3 existing and new AR-4 Powerhouse Road to SA-3 existing and new AR-5 Powerhouse Road to dam (lower) and to Flowline (upper) existing and new AR-7 Powerhouse Road to surge tank, flowline (lower) & penstock (upper) new AR-9 Access road for penstock removal (lower) existing AR-11 Access road for tailrace grading existing and new AR-12 Access road to substation existing AR-13 Access road from Powerhouse to SA-5 existing and new AR-14 Graves Road to lake existing AR-15 Cabin Road to lower lake existing and new AR-16 Cabin Road to lower lake existing and new Segments of all roads are relatively steep (8 percent or greater). New construction would require clearing, excavation and fill along the designated rights-of-way. Existing roads may be realigned and upgraded, but would require significantly less right-of-way preparations. During construction, access roads would be vulnerable to rainfall, prior to placement of roadway surfacing and installation of cut/fill slope protection. Vehicle use on gravel access roads would generate sediment, and stormwater runoff may increase and would carry sediment. Access roads within the current reservoir area would require fill materials to be placed on the sediment. 4.2-6
Condit Dam Hydroelectric Project Final Supplemental EIS BMPs would be implemented to minimize erosion and thus turbidity, as described in the Upland Stormwater and Erosion Control Plan (PacifiCorp 2004). Applicable BMPs should be effective for reducing the coarser grained sediment through even the small sand grain sizes. However, colloidal materials would not be removed and runoff would be turbid. If stormwater events occur during the construction phase, stormwater flows to the lake and to the White Salmon River would locally contribute suspended solids to the receiving water bodies. Because of the size of the receiving water bodies and the timing of construction (normally a dry period in most years), the impact of stormwater total suspended solids (TSS) from the construction areas is considered to be less than significant. Preparation of Staging Areas and Disposal Sites Prior to removal of the dam, the staging areas would be prepared for the concrete storage (perhaps for several years) and disposal (SA-3) and for temporary storage of the decommissioned wood stave pipe materials (SA-5). Other staging areas (SA-1, SA-2, and SA-5) would be temporary through the decommissioning work, but would be revegetated at the end of the decommissioning project. Except for SA-5 and SA-4, all sites that would be cleared of native vegetation are grass-covered. SA-5 has been cleared of apple trees recently (in transition to a pear orchard). A stand of deciduous trees covers part of SA-4. Staging areas would be converted from natural vegetation and residential uses to a gravel pad. Disposal sites would be cleared of vegetation and topsoil. During site preparation of all staging areas, standard BMPs, as described in the Upland Stormwater and Erosion Control Plan (PacifiCorp 2004) would be employed to prevent sediment from being carried by stormwater to Northwestern Lake. BMPs also would be employed to minimize soil from the staging area being deposited on access roads, where stormwater could carry accumulated sediment into Northwestern Lake. The grades on the staging areas and disposal sites are generally less than the steeper grades associated with the roads, and therefore the degree of erosion and increased levels of TSS in stormwater is considered to be less than significant. Preparation of Work Areas A total of seven work areas would be utilized for this project. Preparation of each work area would be nearly identical to preparation of staging areas, and the same BMPs would be implemented to control erosion and minimize turbidity in stormwater runoff. As a result, the amount of sediment that stormwater could transport to the receiving waters is considered to be less than significant. Petroleum Products and Hazardous Materials Potential impacts related to the use and storage of petroleum products include contamination of stormwater runoff or surface water by accidental petroleum product spills associated with fueling or the potential rupture of a small tank or drum that may contain petroleum products. Petroleum hydrocarbons (such as diesel fuel) would be the most likely contaminants. Large volumes of petroleum hydrocarbons would be stored in double-wall tanks/tractor-trailer with secondary containment, making high volume spills unlikely. 4.2-7
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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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Condit Dam Removal Condit Dam Removal - Access Washington

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