Mystery solved!

Our construction project started slowly because shortly after we got the temporary fencing set up we got some very heavy rain and a backed-up sewer. Our contractor proposed sending out a plumber to investigate, which seemed like an ideal solution. Only the plumber didn’t show for day and then weeks. In the meantime sewage was pouring out of the downspouts and into the area around the foundation of the garage.

It was gross, of course, but it became a hazard when the workers started to dig out the foundation in order to install a larger footing. So we called a plumber on our own who came to investigate. He was initially confused about the way the sewer pipes were installed. Like almost everyone who knows something about sewer lines, he assumed it drained out to the street in front. But the city sewer runs down the alley in the back.

Once he’d sorted that out, he sent down a camera to take a look. Typically sewer lines get clogged when tree roots break through clay pipes. But the first thing the plumber noticed was that our pipes are ABS, which is a plastic that roots can’t penetrate. After pushing the camera down a bit, he hit a block. It wasn’t a block he could push though, but a total obstruction in the line. it wasn’t far from the downspout that ought not, but does, go to the sewer, but that wasn’t the problem.

While trying to locate the obstruction, he saw something shiny. Then he measured the distance and hit upon a theory. He noticed the temporary fence had a pole going into the ground near where the sewer was obstructed. And sure enough, that post was the problem. Here’s a picture of the hole it punched though the sewer:

Our contractor said he’d never heard of such a thing and it’s hard to know why the fence people kept driving the post after it hit the sewer line. But now that we’ve figured it out, the contractor is going to replace the pipe and disconnect the downspout.