I'm curious how common this is and what would actually need to be wrong (if anything) on the city-side of plumbing for storm water to back up into residential sewer pipes at ground level. I suspect a 6-8 foot cast iron pipe section extends from the back of the house at an angle and joins a perpendicular clay sewer pipe that continues on and joins the main city sewer pipe. Either the cast iron pipe or the clay sewer pipe on the property could have a hole in it. Given the direction of the leak, I suspect the cast iron pipe. How common are storm water leaks in sewer pipes?