Hello All,
Sorry for not getting back quickly. I wanted to post so everyone could use this as a lessons learned. To recap, I was getting major amounts of iron or dirty water coming out of the house faucets/fixtures..etc after the sprinklers were ran. We're on a community well and my neighbors do not have the same problem, though they only have water softners. It took forever to narrow it down to this. I had my incoming feed line cleaned out about a month ago and there was a significant amount of iron that was rinsed out. I did not run my sprinklers for a while because it was rainy. Well, it did not fix the problem. It did help with the incoming water supply quality to the house after the sprinklers were ran; it wasn't as bad. However, I still had just really dirty water after the iron filter and water softner. So, I put my sprinklers to run for 1 minute each zone and ran all 10-11 zones. I went down in the basement and sat by the tanks. I could hear a little sloshing going on in the iron filter and noticed that the pre-filter started to get cloudy after about the first 3 or 4 zones; I was not running any water in the house. After everything was done, I had to regen the iron filter and softner again. I noticed some real fine sediment also in the prefilter; it looked like BIRM.
To sum it up, the CHECK VALVE WORKED! It isolated the house plumbing from the irrigation system. The big water demand of the sprinklers caused a pressure drop on the main line and forced water in the reverse direction, maybe not much, but it had to be fast as it stirred things up. I ran the sprinklers 4 times in a row (all zones for a minute a piece) without any problems. I could tell the check valve was locked down right when the first zone ran. It just sounded differently....there was no noise around/in my water conditioning system. Also, I found out that it is code to have isolation on my house plumbing in my area.
Thanks for everyone's help. I appreciate it!!!