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Vantage to Pomona Heights Chapter 4 230 kV Transmission Line Project FEIS Environmental Consequences PAGE 4-8 4.2.2 Impact Levels (High, Moderate, Low, No Identifiable Impact) Impact levels are based on vegetation types that occur along the assumed transmission line centerline. Impact levels are assigned based on resource sensitivity (e.g., special status plant or sensitive habitat), resource quality (the existing condition of the resource), resource quantity (the amount of the resource potentially affected), and the type and duration of impact (short- or long-term). These criteria were applied to develop impact level categories of high, moderate, low, and no identifiable. High – A high level of impact would result if the construction, operation, or maintenance of the proposed Project would potentially cause a substantial adverse change or stress to vegetation resources that have a high sensitivity. Moderate – A moderate level of impact would result if the construction, operation, or maintenance of the proposed Project would potentially cause some change or stress (ranging between substantial and insubstantial) to vegetation resources that have moderate sensitivity. Low - A low level of impact would result if the construction, operation, or maintenance of the proposed Project would potentially cause an insubstantial or minor change or stress to vegetation resources that have low sensitivity. No Identifiable - No identifiable impact would be indicated where no measurable impact would occur to vegetation resources. 4.2.3 Impacts Common to All Route Segments 4.2.3.1 General Vegetation This section presents information on impacts common to all route segments for overhead transmission line construction. To assess impacts to vegetation resources, a 150-foot wide survey corridor was analyzed. Impacts to vegetation resources from the NNR Alternative - Underground Design Option are discussed individually in Section 4.2.4 for Route Segments NNR-4u and NNR-6u. The proposed Project would directly affect vegetation communities through the temporary trampling of herbaceous vegetation, the partial removal of above-ground plant cover, and the complete removal of vegetation due to construction of the transmission line, access roads, and temporary work spaces. Vegetation would be permanently removed and disturbed at structure bases and along permanent access roads. Vegetation removal could have a variety of effects on vegetation communities including changes in community structure and composition. The degree of impact depends on the type and amount of vegetation affected and the rate at which vegetation would regenerate after construction. In addition, removal of vegetation can reduce or change the functional qualities of vegetation for wildlife habitat (see Section 4.3 Wildlife and Special Status Wildlife Species). Within the Project area, the recovery of vegetation would vary by plant community type following construction. Grasslands and herbaceous wetlands would generally recover within five to seven years while shrublands, including sagebrush (Artemisia sp.) and rabbitbrush (Chrysothamnus viscidiflorus and Ericameria nauseosa), may require 30 to 50 years (Olson et al. 2000; Lesica et al. 2005). RDFs would be implemented during construction and operation and are anticipated to be effective at minimizing the amount of vegetation that would be impacted (refer to Section 2.3 - Required Design Features Common to Action Alternatives). RDFs include: minimizing the blading of native plant communities during construction, operation, and maintenance consistent with safe construction practices; utilizing existing roads to the extent possible; and reseeding disturbed areas with certified weed-free native or other acceptable species as detailed in the Reclamation, Revegetation, and Monitoring Plan in the Plan of Development (POD).