Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

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Vantage to Pomona Heights Chapter 2 230 kV Transmission Line Project FEIS Proposed Action and Alternatives PAGE 2-12 Design Options (e.g., steel single pole, wood single pole, steel H-frame, wood H-frame, undergrounding) are discussed in each of the resource sections in Chapter 4.2 through 4.16. The Overhead Design Option is common to all Action Alternatives presented in this FEIS and is described in Section 2.2.2. The Underground Design Option, a project feature not common to all Action Alternatives, was analyzed for two discrete route segments of the NNR Alternative and is described in Section 2.2.5. Disturbance assumptions, design, construction, operation, and maintenance characteristics of the NNR Alternative - Overhead Design Option are detailed in Sections 2.2.2 through 2.2.4. Disturbance assumptions, design, construction, operation, and maintenance characteristics of the NNR Alternative - Underground Design Option are detailed in Section 2.2.5. 2.2.2 Overhead Transmission Line Design Specifications This section describes the typical characteristics of the proposed Project facilities common to all Action Alternatives. The typical overhead design features and characteristics of the 230 kV transmission line are presented in Table 2-2. The components of the proposed transmission line are described below, including structure types, foundations, conductors, insulators, and associated hardware and overhead groundwire. 2.2.2.1 Structures The structures for the proposed 230 kV transmission line would be either single-circuit H-frame wood or steel poles, or single wood or steel poles depending on location. H-frame wood pole structures are proposed for most of the transmission line located in open terrain. The H-frame tangent structures would be between 65 and 90 feet tall and spaced approximately 650 to 1,000 feet apart depending on terrain. In developed, agricultural, or constrained areas, single wood or steel pole tangent structures would be used. The single pole tangent structures would be between 70 and 110 feet tall and spaced between 400 to 700 feet apart. Angle and dead-end structures would be guyed to ground anchors. The 2,800-foot Columbia River crossing would utilize approximately 200-foot tall steel lattice structures. The exact height of and distance between structures would be dictated by topographic and land use characteristics and safety requirements for conductor clearances. Structure design characteristics are identified on Table 2-2 and illustrated in Figures 2-4 and 2-5. 2.2.2.2 Foundations Direct Embedded-Wood/Steel Structures Poles would be placed in augured holes, directly embedded into the ground and typically do not require concrete foundations. The embedment depth for poles up to 95 feet tall is typically 10 percent of the pole length plus two feet; for poles 100 feet and taller, 10 percent of the pole length plus three feet. Embedment depth is expected to be between 9 and 15 feet based on the structure heights proposed for the Project. The actual depth would depend on load and soil characteristics. No foundations would be required for the wood pole structures except where necessary due to local terrain conditions, areas of uplift, and at transmission angle points. The diameter of the hole excavated for embedment is typically the pole diameter plus 18 inches. When a pole is placed in a hole, native or select backfill would be used to fill the voids around the perimeter of the hole.