This report presents the results of a Determination of Effects assessment undertaken for the proposed Amtrak Zoo to Paoli Electrification Transmission Line Project. The proposed modernization project includes the replacement of approximately 325 80- to 100-year-old catenary structures, transmission lines, signal power lines, and the 100-year-old Bryn Mawr Substation building at the Bryn Mawr switching station. The proposed work is located within the right-of-way (ROW) of a 20-mile section of Amtrak’s Keystone Corridor, between the Philadelphia Zoo in Philadelphia and the substation at Paoli, and extends through portions of Philadelphia, Montgomery, Delaware, and Chester counties. The existing overhead catenary system of wires that extends between the structures will not be replaced and instead will be moved from the old catenary structures to the new catenary structures.