7. Significant Environmental Impacts and Mitigation

We examine, first, the project action alternatives identified in the EIS and, second, the alternative components additionally analyzed by the Commission's Energy Division.

7.1. Impacts by Project Action Alternative

All of the project action alternatives analyzed in the EIS (Alternatives 1, 2, 3 and 6) would have significant and unavoidable adverse impacts on air resources, cultural resources and visual resources. The significant environmental effects on other resources can be reduced to less than significant with mitigation.

7.1.1. Air Resources

All of the project action alternatives would have similar significant and unavoidable impacts on air resources.

Construction activities and associated vehicle traffic would generate emissions of criteria pollutants and hazardous air pollutants. Daily construction-related emissions for all of the action Alternatives 1, 2, and 3 would exceed South Coast Air Quality Management District regional emissions significance thresholds for reactive organic compounds, nitrogen oxides, carbon monoxide, Particulate Matter (PM) 10 and PM 2.5. Alternative six would have similar impacts on air emissions as the action alternatives.

Operational emissions would involve vehicle travel by Solar Farm employees or other employees conducting periodic inspections or maintenance activity along the Gen-Tie Line or at the Red Bluff Substation.

Decommissioning emissions would be comparable in type and magnitude, but likely lower than, the construction emissions.

7.1.2. Cultural Resources

All of the project action alternatives would have similar significant and unavoidable impacts on cultural resources.

Construction of Alternative 1 would directly impact at least 57 sites within the footprint of the project components. Twenty of the sites are potentially eligible for the California Register of Historical Resources (CRHR). In addition, construction would directly impact the potential Desert Training Center/ California-Arizona Maneuver Area Historic District and the North Chuckwalla Petroglyph District. Construction would indirectly impact the historic landscapes of the Colorado River Aqueduct, the North Chuckwalla Mountains Quarry District, and a prehistoric site by constructing modern elements that would disturb the historic setting of these resources.

Construction of Alternative 2 would directly impact 42 sites within the footprint of the project components. Twenty-one of the sites are potentially eligible for the CRHR and assumed to be eligible for the National Register of Historic Places and thirteen are believed to be associated with the potential Desert Training Center/California-Arizona Maneuver Area Historic District. All project components would have direct audible and visual impacts on the historic landscapes of the Colorado River Aqueduct, the North Chuckwalla Mountains Quarry District, and a prehistoric site by constructing modern elements that would disturb the historic setting of these resources.

Construction of Alternative 3 would directly impact 41 sites within the footprint of the project components, as well as the potential Desert Training Center/California-Arizona Maneuver Area Historic District and the North Chuckwalla Petroglyph District. Fourteen of the sites are potentially eligible for the CRHR, nine of these are believed to be associated with the Desert Training Center, and one is a contributing, National Register of Historic Places-listed site in the North Chuckwalla Petroglyph District. All project components would indirectly impact the historic landscapes of the Colorado River Aqueduct, the North Chuckwalla Mountains Quarry District, and a prehistoric site by constructing modern elements that would disturb the historic setting of these resources.

Construction of Alternative 6 would have similar impacts to cultural resources as construction of Alternative 1.

Native American consultation is on-going at this time and may find that sacred sites, traditional cultural properties, or traditional use areas are present within or near the construction area of all of the action alternatives, which may directly disturb Native American resources, impede access to these areas, or otherwise disrupt traditional practices.

Operation of all of the project action alternatives would have similar impacts. Operations would primarily have indirect impacts on the historic landscapes of five resources and possibly an unknown number of Native American resources, stemming from new construction within these landscapes that would not be in keeping with the historic nature and setting of the resources. The presence of project components may exclude Native American access to resources of traditional significance or detract from the viewshed of a sacred site, traditional use area, or traditional cultural property.

Decommissioning of all of the action alternatives would have similar impacts. Decommissioning would restore historic landscapes and viewsheds of, and access to, some, but not all, impacted cultural resources.

7.1.3. Visual Resources

All of the project action alternatives would have similar significant and unavoidable impacts on visual resources.

Construction would result in the permanent disturbance of approximately 3000 to 4000 acres. Construction and operations would be visible and changes to the characteristic landscape would alter visual resources. For three of the most critical viewpoints (or key observation points), the strong degree of contrast would not comply with interim visual resource management Class II and III objectives.

Decommissioning (which would not occur until the end of the project lifespan, which could be greater than 50 years) would restore the natural visual resources, but would likely take decades after decommissioning for the landscape to resemble the existing conditions.

7.2. Impacts by Component Alternatives

7.2.1. Red Bluff Substation Alternatives

All of the Red Bluff Substation alternatives would have significant and unavoidable impacts to cultural resources, with Substation A and Access Road 1 causing the most impacts, and Substation B causing the fewest impacts.

All of the Red Bluff Substation alternatives would have comparable significant and unavoidable impacts to air resources and visual resources.

7.2.2. Gen-Tie Line Alternatives

All of the Gen-Tie alternatives would have significant and unavoidable impacts to cultural resources. Based on the surveys conducted, GT-A-2 appears to have substantially fewer impacts (two potentially eligible CRHR sites and impacts to two additional archeological resources) than either GT-A-1 (six potentially eligible CRHR sites and impacts to 13 additional archeological resources) or GT-B-2 (six potentially eligible CRHR sites and impacts to 17 additional archeological resources). However, full-coverage surveys for the GT-A-2 corridor were not available, and additional resources likely exist which could be affected by construction of GT-A-2.

All of the Gen-Tie Line alternatives would have significant and unavoidable impacts to visual resources. However, GT-A-2 would have the least impact because it would be collocated with an existing transmission line for the majority of its length, while GT-A-1 and GT-B-2 would both require new transmission corridors with similar impacts.

7.2.3. Solar Farm Layout Alternatives

Both Solar Farm layouts would have significant and unavoidable impacts on air resources, cultural resources, and visual resources. Solar Farm Layout B would have 550 MW of power output and would permanently disturb 3912 acres of ground, as compared to Solar Farm Layout C which would have 314 MW of power output and would permanently disturb 3045 acres of ground. Solar Farm Layout C would have the fewest short-term impacts to environmental resources overall. However, by more greatly contributing to California's Renewable Portfolio Standard goals, Solar Farm Layout B would have fewer long-term indirect environmental impacts to special status plants and wildlife. Solar Farm Layout B and Solar Farm Layout C are therefore considered to be environmentally equal.