Trained Eye

 
 
 

Sewer Collapse & Excavation

Question:

I hope you will be able to help with this question.

My sister's sewer line collapsed somewhere outside her home. This was either at the junction of the inner/outer wall in the basement or further out under the front steps, depending on what the city's diagrams show. My question relates to a recent excavation job that occurred at her neighbour's home, last fall, about 10 feet across her back door. This job required digging around their chimney. I understand that there were various pieces of equipment, including Bobcats, coming through my sister's front yard and sidewalk.

My sister has had problems with her sewer line in the past due to tree roots, but nothing to this extent. We had three different companies come to try and unblock the sewer line, including calling the City, and all have said the break is somewhere close to the house and out approximately 10-12 feet from the inside sewer trap. None of the recommended excavators/construction companies that bothered to show up are too keen to fix this problem now, and I understand the reluctance, but it is not a problem that can wait till nicer weather.

Is there a way to determine if the sewer break/collapse is related to the recent excavation job next door?

Answer:

Blockage and damage to old sewer lines is quite common, especially in older areas with large trees. Replacement is often the only way to permanently prevent further blockage and can be quite costly. Determining whether the neighbour’s recent excavation was partially responsible may be impossible to determine and would only be a matter of speculation. I will address the damage and blockage issue and offer my opinion on the possible effects of the work next door.

Underground sewer piping, connected to the drains in older homes was quite high quality and durable but does not have an unlimited life expectancy. Many drains have been functioning well for fifty years, or longer, but will eventually wear out. The durability is often a function of the amount of soil movement and vegetation around the home. If there is considerable erosion and shifting, the old pipe sections may become disconnected and slightly misaligned. Once this occurs, clay and debris can easily run into the drains and block them up. Also, small cracks or holes in the pipes may allow fine tree roots to enter the pipe as they search for water. This is normally more of a problem in the winter, as the roots go deeper into the unfrozen soil in search of moisture.

If the openings in the pipe are small, regular clearing by a “Rooter” technician or plumber may allow these to drain fairly well for many years. When these openings become big enough, large roots may enter the drain, often causing them to split apart or become weak enough so that they eventually collapse. When this happens, as in your sister’s case, there is no alternative other than to replace the damage sewer pipes. If the damage is entirely on her property, it is her responsibility to pay for the complete upgrade or repair. If the damage is on the City’s property, the repair cost may be covered under a program from the City of Winnipeg which requires only a nominal deductible to be paid by the homeowner. Check with the City Water & Waste to determine your sister’s eligibility.

If the damaged sewer is not underneath the basement floor slab in the home, as you have stated, replacement of the damaged sewer is done outside the home. A city approved sewer contractor will dig at least one hole in the front yard of the home, cut the existing drain pipes where damaged, and replace them with new plastic piping. If the damage is more extensive, at least one more hole will be dug in the front street to access the drain connection to the main sewer underneath. The old pipes will be removed from the sewer main line and a new hole bored deep in the ground, all the way through to the opening in the front yard, near the broken pipe. New piping sections will be pushed through the bored hole and connections made to the undamaged old drains near the house and under the road. Once complete, the holes will be backfilled and the house drains will once again flow to the main sewer.

There is a small possibility that the excavation work and heavy equipment did exacerbate the situation, but it is not responsible for the deterioration to the old drain. The old pipe, which is buried at least a metre or more below the ground, would have to be very badly corroded, cracked, or partially collapsed to be affected by vibrations from nearby equipment. The fact that your sister has had previous partial blockages is proof that there was some damage to the drain pipes that allowed tree roots to gain access. The collapse of the piping may have been speeded up by the recent work next door, but it was likely inevitable. Also, the work was done several months before the problems occurred and I would have expected immediate sewer blockage if the work caused the pipes to collapse. Regardless, proving that there was any connection would be next to impossible and highly speculative, at best.