Thanks for the responses. Time for an update:
Since the first post I have talked to Daybreak, Rio Tinto, Kennecott, South Jordan City, and the Landfill. I have received pretty reliable information. It appears to be the mulching facility operated by the landfill, not the landfill itself. The landfill is responding and taking steps to try to resolve the problem. I hope it works.
Laura, you may want to be more informed before you lecture. Not sure where you live, but we live on the west side of the lake and we get the smell during the warmer months about twice a week. The last few cold months, maybe every week, or other week. We are closer to the mulching facility, and we may get different wind patterns from the west than other areas of Daybreak. Most neighbors here have also commented. (not always in a positive fashion) We all hope it gets resolved.

But what about the people who are already living there?

I live here. Never smelt it.