Sienna Solar Final Environmental Impact Report

99MT 8ME, LLC is the applicant for the Sienna Solar and Storage Project, a utility-scale solar photovoltaic facility located on approximately 1,854 acres in Lucerne Valley, San Bernardino County, California. The project is designed to produce up to 525 MW of solar power and include 525 MW of battery energy storage capacity, generating approximately 1,175 GWh of electricity annually over a 30-year operational lifetime. The generated energy will be transmitted to the Southern California Edison electric grid via the proposed Calcite Substation. The project was approved by San Bernardino County on October 23, 2025, with a Notice of Determination filed on October 27, 2025. The project's environmental compliance is managed through a Final Environmental Impact Report and a Mitigation Monitoring and Reporting Program, both prepared in accordance with the California Environmental Quality Act and California Public Resources Code Section 21081.6. Construction of the main project is estimated to take between 12 and 24 months, while the Calcite Substation construction is scheduled from February 2026 to June 2027. Key operational requirements include the implementation of a Paleontological Worker Environmental Awareness Program led by qualified professionals, adherence to final geotechnical engineering reports approved by the County Land Use Services Department, and specific traffic management protocols to minimize congestion during construction.