San Gabriel Trench Grade Separation Project

Beginning in 2008, SWCA prepared cultural, paleontological, and natural resources compliance documentation in support of the proposed San Gabriel Trench Grade Separation Project, in the City of San Gabriel, Los Angeles County, California for the Alameda Corridor – East Construction Authority. The project is located along a 2.5-mile segment of Union Pacific Railroad immediately south of historic Mission San Gabriel Arcángel, founded in 1771, and included construction of a below-grade railroad trench.

SWCA conducted technical studies and prepared Environmental Impact Report sections for compliance with state and federal statutes, particularly CEQA and NEPA, for review by the California Department of Transportation (Caltrans), the lead agency. Cultural resources work included archaeological and architectural history surveys and evaluation studies, which were prepared in compliance with Section 106 of the National Historic Preservation Act (NHPA) and Caltrans standards. SWCA completed eight technical studies and reports, including multiple phases of archaeological and built environment resources identification and evaluation. This work culminated in SWCA’s successful preparation of a Finding of Adverse Effect and a Memorandum of Agreement with Treatment Plan, the key documents that have guided subsequent mitigation efforts. All of these documents were well-received and approved by Caltrans and the State Historic Preservation Office with minimal comments.

From 2010 to 2018, SWCA oversaw the mitigation of adverse effects to the National Register of Historic Places and California Register of Historical Resources listed San Gabriel Mission site and nearby historic properties, including multiple archaeological data recovery phases, the preparation of Historic American Buildings Survey (HABS) and Historic American Engineering Record (HAER) documents for architectural features, extensive public outreach, and the relocation and preservation of the historic Chapman’s Millrace, one of the earliest expressions of the Industrial Revolution on the West Coast. SWCA also provided construction phase support services, including archaeological monitoring and data recovery.

The quality of SWCA’s work on the project was recognized in 2013 by the City of San Gabriel with a San Gabriel Martin E. Weil Award for Historic Preservation/Conservation, and in 2019 the San Gabriel Trench was named Project of the Year by the California Transportation Foundation.