Engineering and Construction: Construction Begins on M-29 Outfall Improvements for Four Mile Run

This $3.6 million investment will extend the useful life of the outfall, reduce river flow entering the combined sewer system, and begin to reduce backups from the river into the Run neighborhood.
A 14-foot diameter arched pipe makes up the 100+ year old M-29 outfall. A 14-foot diameter arched pipe makes up the 100+ year old M-29 outfall.

Across about 75 percent of Pittsburgh, stormwater and sewage are collected in the same pipes. This combined sewer system was designed more than 150 years ago to discharge sewage directly to the rivers. When the Allegheny County Sanitary Authority (ALCOSAN) wastewater treatment plant was built in the 1950s, the combined sewers were modified to carry sewage to the plant during dry weather. However, stormwater from heavy rains can still overwhelm the pipe capacity, causing combined sewer overflows (CSOs) of sewage and stormwater at outfalls along the rivers.

The M-29 outfall is the 29th combined sewer outfall along the Monongahela River, as counted from the Point. This outfall collects stormwater and sewage from the Four Mile Run watershed, which encompasses Schenley Park and several Pittsburgh neighborhoods including Greenfield, Hazelwood, Oakland, Squirrel Hill, and the Run.

In early June, we began construction at the Hazelwood Green site to rehabilitate the 100+ year old M-29 outfall. Our contractors, Independent Enterprises and Allison Park Contractors, are working together to address a structural issue first. Allison Park Contractors will then continue the repairs by lining 450 feet of the 14-foot diameter sewer outfall, installing a new end wall and flap gate on the river, and refurbishing portions of the sewer chamber under Second Avenue. 

M-29 outfall project area between Second Avenue and the Monongahela River at the Hazelwood Green site. M-29 outfall project area between Second Avenue and the Monongahela River at the Hazelwood Green site.

You may see crews in the area as they work above ground, below ground, and on the river itself. There will be a daily lane closure during the week on Second Avenue with limited detours on nights and weekends. Construction is expected to be complete in fall 2021.

This $3.6 million investment in Pittsburgh’s sewer system will extend the useful life of the outfall, reduce river flow entering the combined sewer system, and begin to reduce backups from the river into the Run neighborhood. The project is partially funded by ALCOSAN. 

The M-29 outfall work is part of the larger Four Mile Run Stormwater Project, which proposes to slow the flow of stormwater in Panther Hollow Lake and Junction Hollow and construct separate storm sewer pipes from the Run neighborhood to the Monongahela River.

Learn more at Pgh2o.com/m29outfall.