The purpose of the project is to provide a new access point to the Red Line at Alewife Station. The MBTA Red Line subway northwest of the Charles River operates in a below grade tunnel. Maintenance access is four miles from Alewife Station at the First Street gate. The existing tunnel is over 25-ft below ground surface near Alewife. This Project will complete final design and construction to create the new access point to the Red Line Tunnel in Cambridge, MA near Alewife Station. The Base Technical Concept (“BTC”) consists of a 15-ft wide paved access road, approximately 150 feet in length, followed by a boat section ramp approximately 130-ft long that provides below-grade access to a new tunnel that ties into the existing Red Line tunnel approximately 150-ft from the end of the boat section ramp. The BTC includes constructing the new tunnel structure and boat section ramp within a support of excavation system (SOE). The proposed SOE system includes sheet piling walls, internal bracing, and a working base slab over a jet grout bottom plug. Soil within the excavation area is contaminated. A Final Release Abatement Measure (RAM) needs to be developed that follows the methods described in the Draft RAM plan submitted to the Massachusetts Department of Environmental Protection (MassDEP) in August 2024 or the Public Involvement Plan (PIP) process needs to be re-initiated. Dewatering will also be required as part of the excavation and water needs to be properly discharged. The tunnel and boat section ramp structures are detailed for conventional form and pour concrete methods starting with the base slab and progressing upward to the top of the boat walls and the tunnel roof slab. The final grading and tree planting plan needs to be in accordance with the Order of Conditions issued by the Cambridge Conservation Commission on January 6, 2025 (MassDEP File #123-0325), otherwise the process to receive a new Order of Conditions needs to be re-initiated. To provide access to the existing Red Line Tunnel, two openings approximately 14-ft high x 40-ft wide are included in the BTC into the side of the existing tunnel to connect the new Access Tunnel. This operation will include the partial demolition of the existing Red Line Tunnel slurry walls. Truck pads are included in the BTC within the existing Red Line Tunnel at each of the two openings to provide a designated “on-track” entrance point and “off-track” exit point for equipment and hi-rail vehicles. The BTC equips the new tunnel with a manually operated flood door to prevent unauthorized personnel from accessing the tunnel and to prevent water ingress. The proposed electrical scope of work includes new security devices, lighting within the new tunnel, and electrical modifications within the existing Red Line tunnel.