All, just wanted to pass some information along about our experience with our backflow preventers (BFPs) and the most recent flooding. Through conversations with neighbors it sounds like there is some confusion and misinformation around, so here is our experience.
We have two backflow preventers installed in the front of our house. One is inside in the front of our house on our main sewer line. The other is outside in our basement door well on the combined line for the external floor drain and front downspout.
We are on the 100 block of RI Ave NW in the heart of the flooding and the water level this time nearly breached our front steps for the first time in all four of these floods. The BFPs absolutely did prevent us from getting sewage backup through our toilet and backup through our front floor drain which in the past rises to two feet and breaches through the front of the basement resulting in flooding. Again, the BFPs prevented both of these vulnerable spots from flooding our house in the most recent incident of Sept 2. In fact our front basement door well was nearly dry.
And here is the BUT.
Our rear downspout which captures all of the roof run-off (400 gallons per inch of rain for our 800 sq foot roof on a 40'x20' row house) runs directly down into one of the main line pipes (either combined or sewer, I'm not sure), both of which have the BFP engaged to prevent sewage backup. So the result is all the roof run off rain water fills the pipes, it cannot escape and it runs backwards to find vulnerable spots to eject. The result is a lot of rain water (not sewage) coming up through our toilet and up through the rear external floor drain which eventually breaches the house as it rises above the sandbags in front of our door. I bailed this water constantly for over an hour and it was all clear, so it was definitely rain water.
So our BFPs successfully prevent sewage backup. But they do create a new problem of rain water run off flooding. So our next step is going to have to be diverting our rear downspout to run into an 80 gallon rain barrel with an overflow pipe. If you recall the 400 gallon per 1" of rainfall, obviously the 80 gallon barrel will fill quickly and then be spouting overflow into the only place we can run it - our yard. The way our houses are set up, there is no alley access or street access to pump this water. The best hope is for the ground to absorb it. The challenge is, what happens when/if all 10 houses on our block on RI Ave and the 10 behind us on Seaton Place NW all run our roof run off to the backyards? That's 80,000 gallons per 1" of rain.
We understand we are trading one potential problem for another, but we really have little other option at this point.
If you can find the physical room for one, and the $1,400 it costs, there is a 650 gallon "water wall" to collect run off - but it is 7 feet wide, 7 feet tall and 30 inches deep. That is a big apparatus to fit in the back of a small row house yard.
So that is our current reality with the BFPs installed. No sewage, a definite plus. Rain run-off, a work in progress with potential problems down the road depending on severity of rain. I thought this information may be valuable to those on the fence on BFPs, for those who have not been able to anticipate new problems created as old ones are solved, and for DC to know that people will find solutions individually to protect their homes. If there is to be a collective solution found, DC better get moving on it before all of our individual solutions create a bigger problem then what exists now.