CCTV - Benefits and Limitations
By Jose L. Villalobos, P.E.
and Derek M. Wurst, P.E.
V&A has found two effective methods of evaluating sanitary sewers; Closed Circuit Television (CCTV) inspections and physical entries. This article will review the benefits and limitations of using CCTV and physical entries to assess the condition of sanitary sewers.
Closed Circuit Television Inspections
Closed Circuit Television can be used in sanitary sewers with diameters ranging from 4 inches to 120 inches depending on the camera equipment. The distance that the camera can travel inside a pipeline ranges from 200 feet for small cameras to a maximum of 1,000 feet for larger cameras. The camera can be mounted on a skid, floatable raft system, or tractor-like wheels in order to traverse the pipeline. The following photos show some of the conditions encountered during CCTV inspections.
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| Photo 1. Broken vitrified clay pipe in a sanitary sewer. | Photo 2. Groundwater infiltration at a pipe joint. |
Photo 1 shows a shattered vitrified clay pipe in a sanitary sewer pipeline. Photo 2 shows a residential lateral connection with extensive groundwater infiltration entering the pipeline through an ungrouted joint. CCTV inspections are beneficial because they can document the condition of a pipe using a video camera. The video camera’s distance counter provides the approximate locations of defects within the pipeline. CCTV is useful in small diameter pipelines where physical entries are not possible.
Some of the limitations of CCTV include the inability to measure the size of defects, limitations of distances traveled by the equipment, insufficient lighting, or too much water flow in large diameter pipelines. The identification of pipe defects vary among CCTV inspectors however, until recently, the National Association of Sanitary Sewer Companies (NASSCO) created the Pipeline Assessment and Certification Program (PACP). The PACP program provides standards for evaluation, defect labeling, and data exchange for CCTV inspections.
Physical Man Entries – An Alternative to CCTV Inspections
Unlike CCTV inspections, physical entries into sanitary sewers are classified as confined space entries and safety procedures must be implemented prior to entering the pipeline. Confined space entries usually require more manpower than a CCTV inspection. The ability of an entrant to physically traverse upstream and downstream in a pipeline depends on the atmospheric environment. If the gas monitoring system indicates a high level of hydrogen sulfide or a low oxygen concentration in the air, the entrant must wear a Self Contained Breathing Apparatus (SCBA) while in the pipeline conducting the investigation. The SCBA can be an oxygen tank attached to the back of the entrant or it can be a hose that supplies air to the entrant through a sealed mask. Photos 3 and 4 show SCBA equipment.
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| Photo 3. Entrant wears a fall protection harness, escape bottle and sealed mask. | Photo 4. Practice entry into a manhole using an air supply hose. |
One of the advantages of doing a physical entry as opposed to a CCTV inspection, is the ability to take physical measurements and conduct testing. As long as the wastewater flow in the pipe is not too high and other safety precautions are taken, a physical entry inspection can be done. Some examples of pipeline defects found during physical entries are shown in Photos 5 and 6.
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| Photo 5. Measurement of damaged concrete taken during a physical entry. | Photo 6. Concrete sample collection near the wastewater line (view looking down). |
V&A’s Experience with CCTV and Physical Entries
V&A does not conduct CCTV inspections, however V&A has engineers certified by the National Association of Sewer Service Companies (NASSCO) for assisting CCTV subcontractors and reviewing video tapes. Due to safety concerns, V&A does not perform man entry confined space inspections in sanitary sewers with live flows unless they are larger than 48 inches in diameter. Without live flows, V&A can conduct confined space inspections in pipelines that are 24 inches or larger in diameter. Contact V&A at the number below if any further information or guidance is needed with respect to these services.
V&A Consulting Engineers
1999 Harrison Street, Suite 975, Oakland, CA 94612
Phone 510-903-6600 Fax 510-903-6601
One Riverway, Suite 1700, Houston, TX 77056
Phone 713-840-6490
www.vaengr.com
Copyright 2005
Winter 2006
Case History
