Harvard Square Station marks the first use of slurry walls as part of a permanent transit structure. Due to the historic buildings of Harvard University abutting the new station slurry walls and the extent of the open excavation up against the many commercial buildings surrounding Harvard Square, an extensive instrumentation program was implemented to monitor the buildings and the slurry walls for ground deformations throughout construction. Eldon Abbott, PE served as the supervising engineer for the construction monitoring program which involved field measurements of ground and wall movements, monitoring loads on tiebacks, tilt meters on buildings, and groundwater wells during station construction to give advance warning of conditions that might damage nearby buildings. Eldon also served as a geotechnical engineer for the design of the station, including evaluation of subsurface environment for slurry wall excavation, preparation of a geotechnical design summary report, and specifications and programs for building protection during construction.