A.  Cracks in concrete slabs
B.  Spaces behind brick veneer walls that rest on uncapped hollow-block foundations
C.  Pores and cracks in concrete blocks
D.  Floor-wall joints

E.  Exposed soil, as in a sump or crawl space
F.  Weeping (drain) tile, if drained to an open sump
G.  Mortar joints
H.  Loose fitting pipe penetrations
I.  Open tops of block walls
J.  Building materials: brick, concrete, rock
K.  Well water (not commonly a major source in Minnesota homes)