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Historic Downtown Response and Recovery

1/4/2021
Sonia Allman, 615-862-4494

Inspection of underground sewer infrastructure

Today Metro Water Services’ Contractor, Ace Pipe Cleaning, Inc. began inspection of the underground sewer infrastructure in the area of the Christmas Day tragedy. The sewer line in 2nd Avenue North is a combination of clay pipe, concrete pipe and unknown material (most likely clay). The clay portion of the pipe is 10-inch and 12-inch in diameter and dates to 1903. It is possible that these clay pipes 5 feet to 8 feet underground may have been damaged due to the blast’s impact and vibration.

Ace Pipe Cleaning, Inc., will use CCTV equipment to visually inspect the sewer lines. The CCTV camera, connected to a crawler with a flexible cable, is lowered into a sewer manhole. The technician can control the movement of the crawler as well as the camera and see a real time view of the pipe on a monitor. Video footage of the inspection will be used by Metro Water Services personnel to assess the condition of the pipes.

The inspection perimeter is Union Street to Broadway and 4th Avenue North to the River. The inspection will begin at Union Street and move toward 2nd Avenue North to make sure that there is no damage to the sewers where buildings will be occupied first.

In some areas it may be necessary to clean the sewer line in order to inspect it. This will be done using a large jet vac which utilizes a strong jet of water to dislodge debris and a vacuum to draw it out of the pipe.

Ace Pipe Cleaning, Inc. will inspect 12,000 feet of sewer line ranging in size from 8 inches to 30 inches.

  • Clay, approximately 3300 feet
  • Unknown, approximately 5300 feet
  • Concrete, approximately 1800 feet
  • Brick, approximately 450 feet, some lined

The inspection (and potential cleaning) cost is estimated to be $75,000.

Based on the condition of the pipe, Water Service engineers will determine if repair or replacement is necessary. We will not have additional information until we are able to complete the inspections.

Currently, we do not believe there was any damage to the public water system. The overall water and sewer systems are functioning normally.

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We have over 3,100 miles of sewer main in our system and 58% of it is over 40 years old.

Much of system in the downtown area is a combined sewer system meaning a single pipe conveys both sanitary sewage and stormwater. Combined sewer systems are common in cities that developed in the 19th century. Since there were no facilities for treating wastewater in that era, it was common practice that sewage and stormwater were both discharged directly to the rivers and streams.

In 1958, the Central Wastewater Treatment plant was completed, and the combined pipes now convey both the sewage and the stormwater to the wastewater treatment plant.