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.

[George W.]

Combined sewer is having sanitary waste and storm water being served by the same waste piping system. if you have a check valve installed on the sewer main it's only going to stop water from flowing back from the street. So if the city sewer is backed up and full of water, the flap on the check valve will not open and let water from the house side drain. Kinda confusing how you mentioned the sump pump, if your sump pump is draining into the house side of the sewer (behind check valve). Then when the city side is backed up that sump pump water has no where to go besides the lowest fixture. Sump pumps should not be installed on a sewer main. Also see if you're rain leaders go into your house on some old buildings with combined sewers they did. So when the streets backed up and it's raining hard the flap on check valve won't open and all the rain water could still be trying to drain through your lowest fixture.