Environmental Services is preparing to repair about 3,700 feet of the 112-year-old brick Taggart Outfall sewer tunnel. Measuring from 64 to 118 inches in diameter and 20 to 65 feet deep, the large Outfall is showing signs of significant deterioration requiring repairs. The Taggart Outfall drains a large area of Southeast Portland and conveys overflows from the combined sewer system to the Willamette River during rain events. A structural failure of the Outfall would have profound impacts on this area, potentially flooding numerous businesses and residences and resulting in many millions of dollars of property damage and disruption. Repairs will allow the Outfall sewer to properly perform its role in protecting public health, water quality, and the environment.
The contractor for this project, James W. Fowler Co., will conduct closed circuit television (CCTV) inspections of the Outfall tunnel in the fall of 2018, which will allow the City to confirm existing conditions and then order the materials needed to repair the Outfall. This CCTV work will take about three weeks to complete.
Crews will mobilize to begin repairs in April or May of 2019 when weather will permit them to work safely inside the tunnel. Depending on the weather, construction may require two summers of work.
Construction activities will be concentrated at existing manhole access locations along the Taggart Outfall. Work zones will move as project segments are completed.
Approved 24/7 Work Schedule
The Portland Noise Office approved the city's request for a Noise Variance. To take advantage of Portland's dry season to complete these urgent repairs, Environmental Services is planning to work all hours and all days in the industrial area between SE Grand Avenue and SE 16th Avenue adjacent to light rail. Work in the other, more residential areas will be completed during regular daytime construction hours from 7 a.m. to 6 p.m. Monday through Friday, and Saturday if needed.
The Outfall will be repaired using construction methods that can be completed from inside the sewer line and will require minimal work aboveground in the roadway. Crews can safely work in the Outfall pipes only on dry days when there will be no flow in the pipes from rain or other parts of the sewer system.
Work at each manhole west of the light rail tracks may last several months, while work on manholes in SE 16th Avenue and in SE Tibbetts Street should be less than a month at each location. Crews may be working at multiple locations at the same time.
The Taggart Outfall is a large-diameter and deep sewer pipe. It is between 5 to 10 feet wide and 20 to 65 feet below the surface. Safety requires that crews will only be able to work in the Outfall pipes on dry days when there will be no flow from either rain or other parts of the sewer system. The primary construction method to repair the Taggart Outfall will be Tunnel Liner Plate. Of all the construction methods Environmental Services analyzed, this method will most effectively reinforce the Outfall pipe and cause the least impact and disruption to the neighborhood. This method will minimize traffic impacts and noise. All access to the sewer will be through existing manholes with no excavation required.
Crews will enter the sewer through existing manholes, as illustrated in the project map. Inside the sewer, crews will essentially construct a new tunnel inside the old brick sewer. They will assemble the new steel liner plates in place inside the sewer and then fill the space between the liner and the old brick sewer with grout.
The vast majority of construction time will be the installation of the tunnel liner plate. The liner plate will be delivered to the access points on flatbed trucks and off loaded using fork lifts. The liner plate will then be lowered into manholes and assembled underground in the sewer. In some areas, vactor trucks may be used to remove sediment from sewer prior to installation of the liner plate; however, there is a very limited amount of sediment in the sewer. This activity will be limited in duration.
Once the liner plate is installed in each section, the space between the brick sewer and the liner plate will be grouted; this operation will be of short duration and take significantly less time than the installation of the liner plate. Grout pumps located on the surface near the access manholes will pump the grout into the sewer.
Once sections of grouted liner plate are completed, cementitious material will be installed on the inside face of the liner plate in the industrial area only. Cement pumps will be located on the surface by the access manholes. This is a short duration activity. Generators on the surface, near the access manholes, will be required for the pumps and other equipment used in construction. All generators and compressors will be silenced.
Noise Mitigation Measures
The major sources of noise will be the grout pumps, generators, and unloading of the liner plates. The contractor will be required, by contract, to use quiet generators. The other major source of noise will be the delivery and unloading of the liner plate. Mitigation measures are incorporated into the construction contract. These mitigation measures are the following:
- Night and weekend work is only proposed for industrial areas where there are no residences within 200 feet.
- All compressors and generators will be silenced. Noise levels for quiet generators are around 69 dBa.
- Backup alarms on all trucks will be turned off and spotters will be used instead.
- Vactor truck use and any required saw-cutting will not be allowed from 10 p.m.-7 a.m.
- Lighting will be adjusted to the lowest levels to limit overshooting the work site and impacts to the immediate community.
- City inspectors will be on site during work hours to enforce contract restrictions on noise.
Potential Traffic Impacts
Accessing the sewer line through manholes will require lane closures, which will require traffic control and construction signage. When lanes are closed in a work zone, they will be closed 24/7 for the duration of construction in that area, including at night and on weekends. Where needed, traffic will be routed around the work zones.
Traffic controls will be implemented at the following locations:
- Lane closures to enable safe access to manholes
- Temporary removal of on-street parking in and near the work zones
- Traffic restrictions along SE 10th Avenue from SE Gideon to SE Woodward
- Minor lane restrictions for a day or two at SE Milwaukie and SE Woodward
- Lane restrictions for short periods of time near SE 16th and SE Pershing, SE 16th and SE Center, and SE Tibbetts and SE 19th