You bring up an interesting point. If the pipe is really 1-1/2" as I stated, and I really pushed it 3/4" into the concrete, as I also stated, then it would be right at the point of being trapped in the concrete. It really is 1-1/2" pipe, but it's nowhere near being pushed into the concrete past the midway point, so my channel is going to be quite a bit shallower than 3/4". That's what comes from trying to estimate something which I couldn't see well instead of figuring it by the very simple arithmetic involved. Thanks.