As sewer system networks age, the risk of deterioration, blockages, and collapses becomes a major concern. As a result, municipalities worldwide are taking proactive measures to improve performance levels of their sewer systems. Non-emergency sewer line cleaning and inspecting sewer lines are essential to maintaining the capacity of the sewer and maintaining a properly functioning system; these activities further a community’s reinvestment into its wastewater infrastructure. In many systems the sewer lines have low flow between midnight and 5 AM, or many of the sewer lines can be temporarily plugged during this time frame.
Inspection programs are required to determine current sewer conditions and to aid in planning a maintenance strategy. Ideally, sewer line inspections need to take place during low flow conditions. If the flow conditions can potentially overtop the camera, then the inspection should be performed during low flow to reduce the flow.
Most sewer lines are inspected using one or more of the following techniques:
• Closed-circuit television (CCTV)
• Visual inspection
• Lamping inspection.
Television (TV) inspections are the most frequently used, most cost efficient in the long term, and most effective method to inspect the internal condition of a sewer. CCTV inspections are recommended for sewer lines with diameters of 4 – 48 inches. The CCTV camera must be assembled to keep the lens as close as possible to the center of the pipe.
In larger sewers, the camera and lights are attached to a raft, which is floated through the sewer from one manhole to the next. To see details of the sewer walls, the camera and lights swivel both vertically and horizontally. In smaller sewers, the cable and camera are attached to a sled, to which a parachute or drogue is attached and floated from one manhole to the next.
Documentation of inspections is very critical to a successful operation and maintenance (O&M) program. CCTV inspections produce a video record of the inspection that can be used for future reference.
In larger sewers where the surface access points are more than 1000 linear feet apart, camera inspections are commonly performed. This technique involves a raft-mounted film camera and strobe light. This method requires less power than the CCTV, so the power cable is smaller and more manageable. Inspections using a camera are documented on polaroid still photographs that are referenced in a log book according to date, time, and location.
Visual inspections are vital in fully understanding the condition of a sewer system. Visual inspections of manholes and pipelines are comprised of surface and internal inspections. Operators should pay specific attention to sunken areas in the groundcover above a sewer line and areas with ponding water. In addition, inspectors should thoroughly check the physical conditions of stream crossings, the conditions of manhole frames and covers or any exposed brickwork, and the visibility of manholes and other structures.
For large sewer lines, a walk-through or internal inspection is recommended. This inspection requires the operator to enter a manhole, the channel, and the pipeline, and assess the condition of the manhole frame, cover, and chimney, and the sewer walls above the flow line.
When entering a manhole or sewer line, it is very important to observe the latest Occupational Safety and Health Administration confined space regulations. If entering the manhole is not feasible, mirrors can be used. Mirrors are usually placed at two adjacent manholes to reflect the interior of the sewer line.
Lamping inspections may be used in low priority pipes, which tend to be pipes that are less than 20 years old. Lamping is used on projects where funds are extremely limited. In the lamping technique, a camera is inserted and lowered into a maintenance hole and then positioned at the center of the junction of a manhole frame and the sewer. This technique is very limited in the amount of pipe that can be inspected and is seldom used anymore.