My basement has a foul smell that occurs after it has rained or the air is damp outside. The problem is the worst in the Spring and Fall. Last Spring the smell was strong around the sump pump lid which is located in a corner in the back of the basement. This lid has been sealed and the smell is not noticeable in this location now. The smell is centralized to the front section of my basement. The odor is very strange. It does not smell musty and it does not smell like sewage. It is a gassy smell. Reminds me of rotten eggs. I do not have any water problems in my basement. One person told me that the smell is related to decaying tree roots under my house. I think the wet ground is forcing a vapor into my house but I do not know how to solve the problem?? Any ideas on how to solve this problem?