Water comes up both sink after garbage disposal - Freezing and Pressure Vacuum Break

[BluePlane44]

Hello,

It is unseasonably cold down here in Houston and yesterday, and since I forgot to winterize my system, my sprinkler system pressure vacuum breaker (FEBCO 765) broke so I had to shut off the first valve (inflow) to it.

http://www.febcoonline.com/Products/765



Today, after I use the garbage disposal, I note the following:

As the disposal is running, the sink that has the disposal drains rapidly as usual, but the opposite sink spits up dirty black water (it doesn't spurt or jet upwards like a geyser, more like bubbling slowly).

As soon as I turn the disposal off, the opposite sink stops building up water but does not drain either. And if I run water into the disposal sink, the disposal sink won't drain until I turn on the disposal, but then the opposite sink starts building up with that dirty black water, too.

All the other sinks and toilets in the house flush normally without backflow.

I think this backflow in the garbage disposal may be related to the inflow shut off of my pressure/backflow system for my sprinklers, but I am not sure. I tried every configuration of opening/closing the two valves that I could, but I couldn't get the disposal to behave.

My questions are:

1- is the backflow in the kitchen sink indeed related to the sprinkler system? (Are any of you familiar with similar setups?)
2 - will this resolve on its own when the weather behaves itself and the ice in the pipes melts, or do I need to fix the pressure vacuum breaker for this to resolve?
3 - what is backing up - in other words, is it just from the garbage disposal or is it other toxic sewage?
4- is the kitchen sink water unsafe to drink because of this ( i don't think that's the case)?
5 - I recently unclogged my dishwasher's drainage pipe and put in a new air gap because it as previously leaking out onto the kitchen counter; so now while Ihave my garbage disposal backed up I should not run my dishwasher, right?

Thank you for your advice in advance.

[hj]

The sink drain is clogged, but it has absolutely nothing to do with the Febco PVB breaking, although it is possible, but not likely, that the drain is also frozen. As long as you do not drink the black water in the sink, it is safe to use the water out of the faucet.