Fixing Water Pollution at the Sewer Source
By Sumner Brown
Sewer leaks get fixed only by physical work on sewer pipes by people with tools. For years Belmont has been lining leaking sewer pipes in the streets, to keep sewage out of our streams. The down-and-dirty of sewer work has been described in this newsletter (“How do Sewers Get Relined?”, BCF Newsletter July/August 2007), a counterpart to former BCF director Anne-Marie Lambert’s articles on the top-down issues of environmental motivation, legal pressure, schedules, progress, and costs.
Many of the leaks in streets have been repaired, according to Glenn Clancy, director of Community Development. However, repeated water sampling still finds evidence of leakage in our stormwater runoff. Identifying these sources entails tracing the sewer lines back to the laterals; pipes that connect the sewer pipes under the street to the individual homes. The town’s Engineering Division is now fixing these leaking laterals. This is trickier and more difficult than lining the sewer in the street because there are no manholes for access at the lateral endpoints under the street.
Figure 1. The mother camera has treads for propulsion through the main sewer. The daughter camera extends from the mother and can explore laterals at angles off the main line. (Sumner Brown photo)
If your home’s lateral leaks sewage into a storm drain, your sewage ends up in a stream. The present town program fixes your laterals and makes it a pain-free experience for you. The town will notify you if they suspect your home may have a leaking lateral. To check for leaks, a dye will be washed down your lateral. That is one of two interruptions you will experience. If the dye introduced from your house shows up in a storm drain, you will be told at a later date to not use much water, such as showering or washing clothes, for two hours or so on a certain day. Then your lateral is fixed. No one has spent more than perhaps five minutes in your house. That was for the dye test. Your yard has not been dug up. Your lateral is now as good as new.
Out in the street, a roughly four-person crew has been working, with access through manholes but without people going into the manholes. They use remote video cameras to locate where the leaking lateral enters the main sewer, inspect the lateral to make sure it is sound enough for lining, measure the lateral, and guide tools that clean the lateral and place the lining into the lateral. The cameras are fantastic.
Earlier-version cameras could be placed into a sewer and moved in a straight line to see things of interest inside the sewer, but they could not make a turn into a connecting pipe. The cameras used for lateral work are actually dual cameras. The mother camera is self-propelled. When it comes to a lateral, it can release a daughter camera to enter a lateral at a right angle from the main line, and then push the daughter camera through the lateral to inspect and measure the length of the lateral.
Figure 1 shows the mother camera with her daughter sticking out and up about a foot. The main camera points straight ahead, mostly hidden between side plates that protect the camera while it is dropped into manholes. The treads on the mother are for propulsion in the main sewer. The range of the mother camera is limited by traction of the treads on the sewer interior and friction of the cables that must be dragged by the mother behind her. The range is hundreds of feet. Once the daughter is ready to enter a lateral, the mother flips open and pushes the daughter at an appropriate angle to enter the lateral, then pushes the daughter’s cable. The first hundred feet or so of the daughter’s cable is wrapped by a spiral of spring steel, so that it is flexible but it can be pushed hard. The amount of daughter cable the mother has pushed out is a measure of the lateral, so the lining can be cut to the correct length.
Figure 2. Crew member Chris Gouveia leads two camera cables into a manhole on Hoitt Road from the National Water Main Cleaning Company camera truck. Inside the truck, the crew foreman runs the mother camera. (Sumner Brown photo)
Figure 2 shows National Water Main crew member Chris Gouveia leading two camera cables into a manhole on Hoitt Road. One cable is for the mother camera and the other is for the daughter camera. Chris stands behind a National Water Main Cleaning Company camera truck, inside which the crew foreman runs the mother camera. Another National Water Main truck has a water trailer for cleaning the lateral, and a third, the lining truck, carries the fabric and chemicals for the liner, and the steam curing equipment. The water trailer and lining truck are shown in Figure 3.
Figure 3. The lining truck carries the fabric and chemicals for the liner, as well as the steam curing equipment. The water trailer in front is for cleaning the lateral. (Sumner Brown photo)
To clean a lateral, a high-pressure hose with a back-pointing spray head is pushed into the sewer with its water supply turned off. The hose is about as thick as a garden hose. The very tip of this hose is slightly bent sidewards. A crew member pushes the cleaning hose with his hands; the mother camera shows him where the tip is relative to the lateral, and whether its bent tip is pointing in the correct direction. The camera can nudge the cleaning hose tip. The person pushing the hose can feel if the tip starts into the lateral. When that happens, he turns on the water and cleaning begins. The high pressure water leaving the hose points backward, which pushes the hose forward while cleaning the lateral. When the hose reaches the end of the lateral, the water is turned off and the hose is pulled out.
Next the lining gets prepared. The fabric that will be part of the lining is cut to the length needed, and the epoxy chemicals are measured, mixed, and applied to the fabric. The liner enters the sewer inside out. At the sewer main junction the liner is anchored to the lateral, and is then blown into the lateral with gas pressure. Once in place, steam is used to heat and thus cure the lining, a process which takes about an hour and a half.
Costs to the town have two components. Belmont’s contract with National Water Main specifies availability, so when the town requests a lateral relining, the work occurs within a specified time period. The second component involves how much work is needed for each lateral lined. Longer laterals cost more. The cost of lining each lateral is covered by the town budget. If a homeowner pays for a lateral relining, the cost is in the ballpark of $10,000.
Sumner Brown is a director of the Belmont Citizens Forum.
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