Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

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Vantage to Pomona Heights Executive Summary 230 kV Transmission Line Project FEIS October 2016 PAGE ES-viii Subroute has the lowest number of miles of no identifiable impacts (30.0 miles), Alternative H has the highest number of miles of no identifiable impacts (54.1 miles), NNR Alternative – Overhead and Underground Options have the lowest number of miles with low impacts (8.2), and Alternatives E and G have the highest number of miles of low impacts (13.2 miles). No moderate or high impacts to water resources are anticipated for any of the Action Alternatives. Geology and Soils No long-term disturbance to geologic and soil resources would occur with the construction of any of the Action Alternatives. Overall impact levels are similar for all of the Action Alternatives with overhead construction, with the majority of the impacts categorized as moderate to low. However, the NNR Alternative – Underground Design Option would create more moderate impacts as compared to other NNR Alternative options (including the Agency Preferred Alternative) due to the displacement of greater volumes of soil as a result of excavated areas. Alternative F would have the highest amount of moderate impacts (19.6 miles) and Alternative B would have the highest amount of impacts characterized as high (7.9 miles). While geotechnical investigations are included in the RDFs, a more comprehensive geotechnical investigation would be required along the entire NNR Alternative – Underground Design Option as compared to the Action Alternatives with an overhead construction design. Geology and soil impacts resulting from open cut trenching are expected to be greater than those that would occur from an overhead design option as the area that would be disturbed is larger. It is estimated that approximately 215,000 cubic yards of soil and bedrock would need to be excavated for the NNR Alternative – Underground Design Option. This is approximately equal to 13,400 standard, double-axle dump truck loads (assuming 16 cubic yards per load). In addition to the impact caused by trenching, excavated soil and bedrock must be stockpiled and/or transported during construction. The risk of electric transmission service disruption as a result of seismic activity or landslides would be substantially greater with the NNR Alternative – Underground Design Option than any of the other Action Alternatives due to the inability to span discovered geologic faults.