This post provides an overview of the methods used to evaluate sewer systems along with common techniques and key considerations for sewer pipe rehabilitation and repair.
Communities across the Midwest and beyond face evolving challenges associated with aging sewer infrastructure.
“Generally speaking, many Midwest sewer systems were installed between the 1940s and early 70s, and the average design life of a sewer pipe is 50 years,” shares Wes Farrand, PE, Civil Engineer for Snyder & Associates. “Deterioration is unavoidable and complete reconstruction can be costly and time consuming. However, a variety of sewer rehabilitation techniques exist to address defects and concerns while extending service life.”
The cause of sewer system deterioration ranges from structural fatigue to general damage and chemical corrosion along with old age and other issues. Knowledge of what’s causing pipes to go bad helps guide informed decision-making for rehabilitation.
Depending on the severity of deterioration or defect and the type of rehabilitation used, Farrand says the design life of a pipe can often be extended up to 50 years.
Evaluating Your Sewer System
To ensure smooth operation and maintenance of your sewer collection system, an evaluation of current conditions with a focus on sewer mains, manholes, laterals, and pump stations is essential.
“A sewer system evaluation is the first step of proactive sewer system maintenance and repair,” states Farrand. “It allows a community to address issues early on before they lead to bigger problems that are more expensive to fix.”
For Wes and his colleagues, sewer system evaluations are also helpful in determining which rehabilitation techniques are optimal for a given set of circumstances. With the purpose of rehab defined, a plan to address the most critical issues first can be developed and implemented in phases to maximize the use of available funds.
Sewer System Inspections
Sewer system evaluations use various methods of inspection or televising with a camera or other technology to provide a glimpse of what’s going on within a sewer system. Use of the NAASCO Pipeline Assessment Certification Program (PACP), which is the industry standard for coding on system conditions and defects, helps maintain evaluation consistency over time.
In addition to traditional televising, other sewer system inspection techniques include:
Acoustic Blockage Detection (Sewer Line-Rapid Assessment Tool or SL-RAT)
Acoustic blockage detection can be a cost-effective way to get a preliminary report on the condition of your sewer system. Using an acoustic transmitter and signal receiver, sound waves are sent through sewer pipes in rapid succession to gather information on pipe conditions.
While it doesn’t pick up small defects or provide information on the specific type of issue present in a pipe, it does help determine potential areas of concern for further inspection.
“It’s a relatively new, quick, and easy to use technology that’s worth considering, especially if funding is limited,” Farrand says.
Televising equipment that extends a second camera up lateral services from the main sewer to evaluate the condition of service lines is also available. Service laterals can be a significant source of infiltration that can easily go unnoticed or unaddressed in rehabilitation plans.
Multi-Sensor Inspection (MSI)
For larger collection systems such as the Des Moines Metro’s WRA Interceptor Sewers, MSI is advantageous for instances where higher flows prevent televising using a standard crawler-based equipment. Floating through a sewer pipe, MSI gathers HDTV, laser, and sonar data on system conditions.
“Sonar provides information on debris located below the water level. The laser will tell you if there’s voids or corrosion above the water level, and the camera provides a high definition visual inside the pipe,” he explains.
Prioritizing Sewer System Rehabilitation
Armed with knowledge of current sewer system conditions, the next step is to establish goals for rehabilitation. Naturally, serious defects or deterioration should take priority over less serious issues. However, it’s important to keep in mind that there could be more going on than what meets the eye.
“Whether your goal is to repair structural damage, reduce I/I [inflow and infiltration], improve capacity, or a combination of everything, you’ll want to carefully review all system concerns,” notes Farrand. “Minor defects can lead to much bigger problems and things can escalate quickly.”
Sewer Rehab: Common Methods & Key Considerations
Sewer rehabilitation can take many forms depending on the cause of deterioration or defect, the severity of the issues observed, available budget, and other aspects.
“Selecting the correct way to rehabilitate your sewer system requires careful thought and analysis,” shares Farrand. “Will service interruptions be required? What’s your budget? What kind of access do we have to the area of concern? These are the types of questions you’ll want to address before you move forward.”
Constant innovation within the industry has led to an extensive array of sewer rehabilitation techniques. Working with a skilled team of professionals will help guide informed decisions for successful sewer rehab. Some common, tried and true methods of sewer rehab to consider include:
Use of a chemical grout for sewer system rehab is a relatively low-cost option with a great deal of flexibility, making it applicable in many situations.
“Because it’s a chemical grout, there’s a tremendous amount of variability in the different chemicals that can be used to solve different issues depending on the desired result,” explains Farrand. “There are grouts that set in five seconds and others that set in 12 hours. Some that like water and some that don’t. It all depends on the needs and goals of each unique situation.”
Acrylamide and polyurethane grout are just two of many grout variations and types. Working with an experienced professional is essential to select the appropriate grout for your specific sewer system issues.
Ideal grout applications include open joints, small holes, leaks, I/I reduction, manholes, and lateral infiltration. Grouting can also work well with other rehabilitation methods that provide structural improvements, which grout can’t on its own. For lateral cracking, large voids, or areas with continuing soil movement, the effectiveness of grout can be limited. With the right application and the correct grout, the average service life expectancy of chemical grouting for sewer system rehabilitation can be 20-25 years.
Cured-in-Place-Pipe (CIPP) Lining
CIPP lining has been around since the 70s and has become a common means of sewer pipe rehabilitation. It utilizes a textile liner that’s impregnated with liquid resin before being inverted into an existing pipe with air pressure. Next, steam or hot water is used to cure the liner, creating a new, corrosion-resistant pipe wall with an expected service life of 50 years.
Minor to moderate structural defects, offsets, protrusions, cracks, root intrusions, and some I/I reduction are optimal applications for CIPP lining. However, if water is seeping in at a service tap, CIPP lining won’t be effective in reducing I/I due to the opening made in the liner at the service tap location. In terms of I/I, CIPP lining is better suited for addressing issues with joints and cracks. Depending on system conditions, grouting or root removal may be necessary before CIPP lining can occur.
Additional considerations to keep in mind for CIPP lining include:
- Adding end seals at manholes to prevent water traveling between the old pipe and new pipe from entering structures
- Pre-lining work may be necessary to stop heavy infiltration
- Service taps will need to be reopened
- Future service taps should connect to the liner, not the host pipe
- Lateral I/I requires additional rehabilitation methods
- Curing methods can make a difference
- Uncommon chemicals in sewer flows can affect the liner curing process
CIPP Point Repair
Using similar technology as CIPP lining, CIPP point repair corrects a single defect in an otherwise structurally sound pipe. However, if more than two point repairs need to be made in the same sewer line, Farrand says it’s often more cost-effective to line the entire pipe.
Less Common Methods to Consider
Other methods of sewer system rehabilitation that are less common or rarely used but applicable to unique circumstances include:
- Pipe Bursting
- Centrifugally Cast Mortar Lining
- Other Cementitious Coatings
- Polymer Coatings
- Fold & Form
- Pipe Eating
- Spiral Wound Sliplining
Record Keeping & GIS Asset Management
Regardless of the methods used to evaluate, maintain, and repair your sewer system, Farrand says keeping records up-to-date and ongoing monitoring of your sewer system is paramount.
He encourages communities to get paper copies of any sewer system evaluation report along with copies of any video or photos taken during the evaluation. Providing duplicate records of everything to public works staff, city hall, and city engineers helps ensure data is available when needed. However, as more communities move away from traditional record-keeping systems in favor of electronic record keeping, geographic information systems (GIS) and asset management systems are quickly becoming the norm.
“GIS and asset management systems take record keeping to the next level by linking and logging data in one central location,” states Farrand. “There’s a lot you can do with GIS and it’s scalable for each individual community.”
How often ongoing monitoring and inspection should be done depends on the client, system, and community budget. Some suggest televising every five to seven years, but with limited budgets, Farrand feels every ten years can be sufficient.
“It really depends on your system. If you have a lot of issues, you’ll need to monitor more often,” he shares. “Older systems should be watched more closely than newer ones, and in some instances, only a portion of your system may need to be monitored more frequently.”
Proactive Sewer Rehab in Your Community
Sewer system rehabilitation can be an overwhelming task to undertake, especially as financial resources become increasingly strained. However, through proper planning and ongoing monitoring, rehabilitation remains a highly cost-effective way to maintain sewer system infrastructure long-term.
“The best way to avoid costly repairs and service interruptions is to put a proactive plan of action in place. Taking a proactive approach allows us to phase the monetary burden of rehabilitation to fit within a community’s annual operating budget,” he says. “In the end, unaddressed, deteriorating pipes create bigger problems and ultimately cost more money.”