I live in a brand new home (finished building in May 2009) and moved in September 2009. There has been a faint smell of sewege gas in and near my kitchen sink and up in my shower since the day right after I moved in to this home. Recently, the smell coming in from under my kitchen sink has gotten much worse (it's pretty bad when you open the cabinet door). As added information, my sink is part of an island in the middle of the kitchen.

The house is under warranty, so the plumbers have already checked/fixed several things including the following:
- p-trap - according to them there is nothing wrong with it
- there are three pipes coming out of the wall under the sink that are completely sealed off (can't remember the name of them) but, supposedly, they are for to the sewage lines. The plumbers re-capped them and re-sealed them
- replaced the disposal
- used bleach to clean out the drain in the bathroom upstairs

Even after all of these repairs/fixes, the sewage smell is still there. Is there anyway the sewage leak could be coming from a broken pipe either in the island or underneath the slab (my house is built on slab)? If not, what else could be causing this problem?

Island sink venting can be tricky. Its really up to the plumber that installed the plumbing to find and fix this problem. Can you show us a picture of the plumbing under the sink.

Sink in an island got my attention. Can you post a picture of how the vented this drain> If they used an AAV it may be malfunctioning.