Scenario: You are the “on-call” person for after-hours responses to sewage calls. It’s Sunday afternoon during a four-day holiday weekend when many people have overnight guests and of course they’ve enjoyed a large traditional meal. You are dispatched to a call across town where a slow draining and gurgling toilet complaint has been called in to your municipality. You respond immediately and drive directly to the address. When you arrive, the resident tells you that for the past few days the toilet has been making gurgling sounds when it was flushed, except for the last time, when there was no gurgle and the water didn’t go down.
Fortunately, the sanitary sewer main is in the front of the property and you quickly begin your investigation. You open the nearest sewage manhole to find the direction of the flow of water. The nearest manhole is the first downstream manhole from the residence and you find a lower than normal flow level of water. Then you walk to the next upstream manhole, open it, and discover the manhole is filling with raw sewage. This condition indicates a blockage. You’ve learned to clear blockages from the closest downstream manhole jetting upstream to prevent flooding and possibly more damage to the residence.
First Step – Restore Flow
The first crucial step in line maintenance is to restore flow to a line that is completely blocked to prevent a sanitary sewer overflow (SSO). Suggested nozzles for this job would be a wedge-shaped penetrator, elongated penetrator, or some type of nozzle with a forward-facing jet or jets and a strong traction characteristic (traction characteristics being defined as a tight jet pattern providing maximum thrust against the pipe wall to ensure that the nozzle is propelled up the line). Penetrating nozzles are designed with one goal; find a blockage, go through it, and return some flow to the pipeline. Typically, the forward jet or jets, (wedge or cylindrical shape) will provide the means for the nozzle to penetrate the clog, and rear facing thrust jets will provide the power for the nozzle to push through the clog and/or move debris down the line. When practical, the debris comprising the clog should be removed from the line to prevent the formation of other clogs downstream.
Too often operators think that once flow has been established their job is finished. That is not the case.
Intermediate Step – Assessment
After some flow has been restored to the pipeline, an intermediated step should be taken, namely, assessment of the problem. Too often operators conclude that a blockage is caused by roots, or grease, or some other problem common to their area. Often, a careful inspection of the debris being removed from the line will give an indication of the true problem. In today’s world of pan and tilt crawler cameras, almost all operators have access to some kind of closed circuit television (CCTV) system to assess line problems. It is highly recommended that once flow is restored, a camera system be used to pinpoint problems. In the event that debris still clogs a line, it may be necessary to go to Step 2 before doing the initial camera assessment.
Second Step – Fully Clean the Line
The uninitiated might wonder why cleaning a line is always the next step in the process of restoring flow, even though the initial assessment might indicate hardened grease or mineral deposits, or a large root mass is causing the blockage and seems to indicate the use of a chain cutter or milling head is in order. Two issues are of concern here: 1) the operator wants to know for sure what is the cause of the blockage, and if there are other conditions (bellies, sags, lateral bores) contributing to the lack of flow. In many cases, a thorough cleaning with the proper nozzle may remove the remainder of the blockage and eliminate the need to use other equipment, and 2) even if the blockage can’t be removed by a thorough cleaning, root saws, milling heads, and even rotational nozzles and other tools do not perform their functions, such as root or scale removal, properly if working in dirty lines or partially submerged in water. Most root saws and rotational nozzles will lose revolutions per minute (RPM), require maintenance and rebuilding, or stop spinning completely over time if used in pipes that are not clean and/or dewatered.
Intermediate Step – Assessment
A thorough CCTV inspection after cleaning is recommended before moving to the next or final steps. Due to the power and efficiency of many of today’s nozzles and cleaning tools, blockages may be removed by simply cleaning the lines. If this is not the case, and a cutter, chain flail, etc. is needed, the assessment can indicate how extensive the problem is, where the operator should begin, and any conditions that might make the removal more difficult.
Third Step – Perform Other Cleaning as Required
Most nozzle companies provide a rotational 360° cleaning nozzle to provide final grease removal. The camera and sewer cleaning operators should note, however, that if the pipe’s video assessment shows the pipe to be clean except for the telltale white “streaks” on the pipe walls, these streaks are deposits of grease left in the line. This grease residue is often the “adhesive strip” for new clogs and obstructions to begin.
Summary
Always speak to the person who called in the complaint to verify the problem.
Determine the flow direction.
Clear the blockage from nearest downstream manhole traveling upstream towards the blockage.
Use a “penetrator” type nozzle to establish flow. Always jet through the blockage to the next upstream manhole.
Assess the blockage with CCTV to see if more cleaning is necessary. If blockage is due to roots, select a chain-flail or milling head nozzle or a root saw to clear the roots. If blockage is due to grease or mineral deposits, select a rotational nozzle to clean.
Assess the blockage again with CCTV to verify if more cleaning is necessary.
If necessary, clean again with a rotational cleaning nozzle.
Verify with CCTV that the blockage has been completely removed.
This scenario is not based on an actual event, but it can, and does happen in many OMAG municipalities every year. All sanitary sewer overflow events do not fit this scenario. It is meant to illustrate that no single sanitary sewer cleaning nozzle works for every situation. Different types of nozzles are designed for specific purposes. Check with your equipment supplier for nozzles that are designed for the cleaning situation(s) you are dealing with.
