Plumbing issues - two different backflow valves failing!

[Joe P.]

One of my properties is in a combined sewer system. Whenever it has rained, and it has rained extensively here in PA/NJ, the original backflow valve installed was failing.

I had my plumber who I trust install a new backflow valve; they removed all the old pipe, brought in new PVC and checkvalve (installed right over the sump pump by the edge of the basement). This was Monday.

My tenant came home today after a few days away and some terrible rain, and said the basement was worse than ever. He said its now leaking by the newly installed backflow valve.

I'm lost on this one. My plumber mentioned it could be a city problem, but there has to be some recourse to prevent this, no?

Any help would be appreciated.