In this post, we will have look at common failure causes and acceptable methods of preventive maintenance for sanitary sewage systems.
Common Causes of Sanitary Sewage System Failure
In general, there are four main causes for sanitary sewage system overflow and failure:
- Infiltration of groundwater through broken piping and defective joints
- Inflow of stormwater during heavy rainfalls into the system
- Blockage of sewer lines
- Lift station pump malfunction
Sanitary System Preventive Maintenance
The activities around maintenance of the sanitary sewage systems can be performed in three steps:
- Sanitary system Assessment
- System Cleaning
- System Monitoring/Re-assessment
Step 1: Sanitary System Assessment
The first step in preventive maintenance of sewage systems is overall system assessment to find the problem areas within the system that require more frequent attention/cleaning. Following activities should be performed as part of the system assessment:
System Flow & Rainfall Monitoring
- Flow meters shall be utilized to capture flow depth and velocity data at sample points across the sewage system. Collected data shall be used to establish a baseline for Inflow volumes. A typical flow meter used in sewage systems is Mag Master which is an insertable electromagnetic flowmeter sensor. A Flowmeter sensor is typically installed in a manhole for ease of access. A cellular modem is also attached to the manhole and sends signals to a data collecting server.
- Rainfall monitoring instruments are also being to obtain accurate data on the inflow into the system
Following techniques are traditionally being used to inspect sewer lines:
- Closed-Circuit Television (CCTV) – Also known as Remote Video Inspection (RVI)
- Zoom Camera Technology
- Lamping Inspection
- Visual Inspection by a Technician
- Smoke Testing
Among the above options, CCTV is the most cost-effective and commonly used inspection tool for sewage systems. Other methods are either tend to be limited in terms of length of pipe to be assessed per each inspection (Lamping inspection and visual inspection) or failing to provide a comprehensive picture of the inner piping (Camera inspection).
Closed-Circuit Television (CCTV)
CCTV inspections are performed for each pipe segment (manhole to manhole) separately. A camera is inserted into the piping in the manhole location. The camera then moves downward as the speed of 30 ft/minute until a significant defect is observed. Then, the camera should be stopped to provide a clear picture of the suspected area. It also should be noted that if the water level inside the piping is more than 20% of the pipeline diameter, the video recording should be stopped and resumed once the flow level is reduced. In this circumstance, either crew should involve inflow reduction activity to reach the desired water level inside piping or wait for the dry season where the water level is lower than 20% of the pipeline diameter. The recorded videos of this inspection can be used as a reference for future inspections.
Once the suspected areas of the sanitary sewage system are known through CCTV inspection, Smoke testing can be performed to further narrow down sources of deficiencies inside the system. Smoke testing is primarily used in inspecting of laterals. In this method, a portion of the piping system (from one manhole to another one) is being blocked and then high-velocity smoke is being pumped in one of the manholes using a blower. If the system is in good condition, smoke will leave through the other manhole lid. If there is any piping defect, smoke will exit through any cracks along the line in the system downstream of the manhole. Equipment needed for this test include Blowers and smoke candles/fluids.
In recent years, some new technologies have been introduced to the underground piping inspection market that can be combined with or replace traditional CCTV technology to provide more accurate inspection results. These new technologies include but are not limited to:
- Acoustic techniques: acoustic sensors are being used to detect any defect in piping.
- Sonar/CTV: This method combines the use of sonar for inspection of the portion of the line that is below the water level and CCTV to inspect the pipe portion above the waterline.
- Ground Penetrating Radar
- Sewer Scanners and Evaluation Technology (SSET): Produces high-definition 2D images. More accurate than CCTV as it provides multi-source data by scanning the entire pipe circumference.
- Laser Pipe profiling: Using Laser scanning method, a 3D model of the sewage system can be built.
- Drone technology – Drone can use laser beams, sonar or high-definition CCTV to scan pipes and produce a 3D model of the sewer system.
- Infrared thermography – As the water entering the sewage system (through infiltration) is usually at a lower temperature than the sewage itself, this thermal method can help in quickly identifying groundwater infiltration to the sanitary sewage system.
Using these emerging technologies will enable the system owner to rely more on the software-generated data rather than the subjective opinion of the technician performing the test and have more accurate mapping of the sewage system.
Step 2: System Cleaning
Depending on the application, sewage piping size and type of deposits expected in the sewage system, different methods are being utilized for cleaning of sewage lines. Following are some of the common cleaning methods used in industry for cleaning sewage lines (1):
- Balling: Most effective for cleaning pipe sizes in the range of 5-24 inches, commonly used for removing grease built-up.
- Jetting: Efficient for cleaning of small diameter pipe sizes
- Flushing: Normally used in combination with mechanical methods such as rodding or bucket machine to remove floatable and sand.
- Rodding: Commonly used for lines up to 12 inches in size
- Bucket Machine: effective in removing larger solid wastes, sand and gravel. Rarely used because of being time-consuming and potential for damage to pipe.
Given the Base Plant site condition, a combination of hydraulic (hydro-jetting) and mechanical (rodding if needed) methods would be the most effective option.
Step 3: System Monitoring/Re-assessment
System flow monitoring and Inspection (ex. CCTV and smoke testing) should be conducted as an ongoing process to constantly re-assess the condition of the sanitary system piping and manholes and to update the system hot spots lists if any change in the sewage system overflow patterns is being observed.
Frequency of Inspection and Cleaning
Currently, there is no standard regarding the minimum requirement for frequency of cleaning and inspection of the sanitary sewage lines, but a general guideline by the American Society of Civil Engineers is suggesting the following frequency for maintenance activities (2):
It should be noted that the above numbers are just to provide a guideline and are not universally accepted, for example, City of Placentia, CA has a guideline to perform CCTV inspections for 10% of the sewage system per year (3).
As per this guideline, as an example, roughly around 30% of the entire sanitary sewage system in the base plant should be cleaned per year. However, quarterly or even more frequent cleaning is required for hot spots that have been detected to cause overflow problems based on system historical monitoring data.
A common practice adopted by some municipalities in California (3) is to clean collection lines based on size:
- 12 inches in size or less at least once every 18 months
- More than 12 inches in size every 5 years
CCTV Inspection and Smoke Testing Certification/Training Requirements
Some of Canadian municipalities made it mandatory for all technicians performing CCTV inspection and smoke testing to be certified through National Association of Sewer Service Companies (NASSCO PACP). Alberta has not made this certification mandatory yet for private sewer systems, however, only trained and competent personnel should conduct this inspection and using NASSCO PACP certified technicians is strongly recommended.
If you are looking for an experienced team of experienced engineers and trade professionals to look after maintenance of sewage system at your site, feel free to reach out to us for a free consultation session.
- Arbour, R and K. Kerri, 1997. Collection Systems: Methods for Evaluating and improving performances, Prepared for EPA office of wastewater management by the California State University, Sacramento, CA
- Black & Veatch, 1998, Optimization of Collection System Maintenance Frequencies and System performance, prepared for the EPA Office of Wastewater management under a cooperative agreement with American Society of Civil Engineers
- City of Placentia Sanitary Sewer Preventive Maintenance Program