Sewer System Evaluation Survey

Project Update - March 6, 2023

From March 6, smoke testing will occur in the Downtown Durham area (south of Holloway Street between S. Alston Avenue and Fayetteville Street), as noted in the maps below. Work will take place from 7 a.m. to 6 p.m. Smoke testing work involves blowing smoke into the wastewater pipes to look for broken pipes and leaks.

Project Update - February 13, 2023

From February 13 through February 24, smoke testing will occur in the Downtown Durham area, as noted in the maps below. Work will take place from 7 a.m. to 6 p.m. Smoke testing work involves blowing smoke into the wastewater pipes to look for broken pipes and leaks.

The smoke is white to grey in color, nearly odorless, and is non-toxic and non-staining. The smoke will not leave residue or create a fire hazard.

The smoke should escape through vent stacks on the roof of buildings which is a sign that the structure’s plumbing is properly installed. Crews will not enter a home or business. Smoke should not enter a home or business. If it does, it is an indicator that the structure’s plumbing is not properly vented. It is recommended that residents run 1-2 gallons of water through all drains inside a home or business to ensure that drain taps are not dry. This should help prevent smoke from entering your structure.

Project Information
The Department of Water Management (DWM) has contracted with CDM Smith, Inc. to perform a Sewer System Evaluation Survey (SSES), which includes conducting sanitary sewer and manhole inspections at various locations throughout the City’s sewer service area beginning in spring 2022 for a period of approximately one year. In addition, crews will be smoke testing to look for broken pipes and leaks.

The work will include:

195,000 linear feet of Closed Circuit Television (CCTV) inspection
1,000 manhole inspections
195,000 linear feet of smoke testing

Sewer and manhole inspections are among tasks performed in-house by the City; however, there are sewer mains in locations that are difficult or impossible to access with equipment and vehicles used by City staff. This contract will clean and inspect roughly 20 miles of mains and manholes in busy City streets or those located off-road and alongside creeks and wetlands.

During this project, crews will access the sewers through existing manholes located in streets, right-of-ways, and easements. No disruptions to sewer service are anticipated during cleaning and inspection; however, it is recommended that residents leave their toilet seats down when not being used, in the improbable event that back pressure from the cleaning causes toilets to bubble.

A map showing the anticipated cleaning and inspection schedule is provided. Door hangers in English and Spanish will be distributed seven days prior to any work anticipated in your area.

Sewer System Evaluation Survey Project Map

FAQ

WHY IS CLEANING AND INSPECTION NECESSARY ?

The City owns and maintains approximately 1,200 miles of sanitary sewer mains. Cleaning and inspection of these mains are vital tools in maintaining and evaluating the City’s sewer collection system. Condition assessment enhances the ability of the City to make technically sound judgments regarding management of these assets. Sewer cleaning is also a requirement for compliance with the City’s wastewater collection permit issued by the North Carolina Department of Environmental Quality (NCDEQ).

WHAT DOES SEWER CLEANING AND INSPECTION WORK ENTAIL?

Sewer cleaning is primarily conducted through hydro-jetting. Hydro-jetting is a sewer cleaning process that utilizes a low volume of water under high pressure. This is a standard industry approach designed to scour the walls of underground pipes, removing potential obstructions (e.g., grease, roots, sediment) from the interior of the pipe. Mechanical cleaning equipment is used as needed if hydro-jetting is not sufficient to properly clear the sewer line.

Once the sewer pipe segments have been cleaned, a robotic camera is sent underground for video inspection of each pipe segment. Crews observe the inside of the sewer pipes making digital notes via computer attached to the camera to assess and rate each segment's condition. This inspection data is then entered into the City’s asset management system with a "score" based on the condition, which allows the City to schedule pipe maintenance, repairs and replacements as necessary. The assessments are made consistent using the Pipeline Assessment Certification Program (PACP) rating system, which is standard practice in the industry.

WHAT DOES SMOKE TESTING ENTAIL?

Smoke testing work involves blowing smoke into the wastewater pipes to look for broken pipes and leaks. The smoke is white to grey in color, nearly odorless, and is non-toxic and non-staining. The smoke will not leave residue or create a fire hazard. The smoke should escape through vent stacks on the roof of buildings which is a sign that the structure’s plumbing is properly installed. Crews will not enter a home or business. Smoke should not enter a home or business. If it does, it is an indicator that the structure’s plumbing is not properly vented. It is recommended that residents run 1-2 gallons of water through all drains inside a home or business to ensure that drain taps are not dry. This should help prevent smoke from entering your structure.

The areas we are addressing with these SSES services were identified utilizing the North Basin sewer hydraulic model. The modeling results indicated that these area are experiencing higher levels of inflow and infiltration and should be prioritized for rehabilitation. The SSES investigations will allow us to pinpoint where rehab efforts need to be focused and what type of rehab is most appropriate.

HOW LONG DOES IT TAKE?

Cleaning and video inspection each pipe segment can take from a few hours to a few days. Parking and traffic impacts will be minimal in the area, with appropriate controls and signage in place. Door hangers in English and Spanish will be distributed seven days prior to any work anticipated in your area.