O27 Site
Site overview
The O27 site is located at the end of Westhall Street in Pittsburgh and is one of the most complex and critical sites in the Ohio River Tunnel system. Deep underground, the main Ohio River Tunnel, the Chartiers Creek Branch Tunnel and the dewatering tunnel will converge at this location, making O27 a major hub within the tunnel system.
The dewatering tunnel will transport captured combined sewage from the tunnel system to the new Wet Weather Pump Station, where it will ultimately be sent to the treatment plant for processing.
Construction at O27 will include a large vertical shaft approximately 50 feet wide and 170 feet deep, along with flow-control equipment and modifications to the existing outfall.
Once construction is complete, a small above-ground control building will remain at the site. One of only two control buildings planned for the entire Ohio River Tunnel project, it will house equipment used to manage and control flows through the tunnel system.
Westhall Street, Pittsburgh Directions: Google Maps Apple Maps
Beneath the surface
Go beyond the construction fence and explore the O27 site.
Underground Cross Section
Cross-section illustration of the Ohio River Tunnel facilities underneath the O27 site located at the end of Westhall Street, not far from the ALCOSAN wastewater treatment plant in Marshall Shadeland. An existing sewer connects to a regulator that directs overflow into a vertical drop shaft approximately 170 feet deep and 50 feet in diameter. The drop shaft connects the Chartiers Creek Tunnel and the Ohio River Tunnel to a dewatering tunnel. The image also shows a large manhole, a gate control building located at the site, two tunnel vent locations, and a modified outfall. Surface buildings, bridges, railroads, streets, the Three Rivers Heritage Trail, trees, and subsurface soil and bedrock layers are displayed to illustrate the local context.
Aerial Site Plan
Aerial site plan showing the location of the Ohio River Tunnel (ORT) facilities underneath the O27 site at the end of Westhall Street near the ALCOSAN wastewater treatment plant. A manhole and a regulator connect to a drop shaft. The ORT and the Chartiers Creek Tunnel, which crosses under the Ohio River, also connect to the drop shaft. Finally, a dewatering tunnel connects the drop shaft to the new wet weather pump station, which is being constructed as part of a separate project. The plan also shows a modified outfall, tunnel vents, and a gate control building. A shaded area indicates the primary limits of construction, with buildings, streets, the Three Rivers Heritage Trail, and the Ohio River providing context for the construction site location.
What to expect during construction
Residents should also be aware that Westhall Street and the Three Rivers Heritage trailhead will be closed shortly after the start of construction and remain closed for the entire duration of the project. The Three Rivers Heritage Trail trailhead will be temporarily relocated to Doerr Street during construction. An alternate bike path has been installed on Doerr Street and on Preble Avenue between Doerr and Eckert in coordination with the City of Pittsburgh.
Nearby businesses will likely experience construction impacts, such as intermittent noise during shaft excavation, potential noise from authorized night work, and increased truck traffic during specific phases of the project. ALCOSAN is committed to working with residents and businesses to minimize disruption and will keep stakeholders inform of what to expect during each phase of the project.
Permitted work hours at this site will be:
General work hours*
- 6:00 a.m. to 8:00 p.m., Monday through Friday
- 7:00 a.m. to 8:00 p.m. on Saturday and Sunday
*Impact-producing construction activities, such as pile driving and jackhammering, are limited to 8:00 a.m. to 6:00 p.m., Monday through Saturday. Controlled blasting activities are limited to 7:00 a.m. to 7:00 p.m., Monday through Friday, and 9:00 a.m. to 5:00 p.m. on Saturdays. Work hours exclude legal holidays; limited exceptions, including emergencies, may apply.
Extended hours for specific activities
Certain activities at the O27 site will occur outside of the general work hours. These include:
- Chartiers Creek Tunnel construction: Tunneling activities and associated work may continue during extended hours.
- Authorized underground work and support activities: Certain underground construction and support activities may occur outside of general work hours.
- • Surface activities: Any authorized surface activities occurring during extended hours will be limited to on-site work.
What's happening at O27
Closures, public meetings and construction updates for the O27 site.
