Check for 'seepage' in the basement.
the 'seepage' of water
gas/oil 'seepages'
(..) You ever tried that before? -How much is it? -Costly. Well, our oil sits right up on top of the ground. I believe that's called seepage. Doesn't necessarily mean there's anything underneath. -What would you give us for it? -I don't know. -Something you don't know. (..)2007 There Will Be Blood