Thanks for the nice terrains!  I was just playing around with the tile sets, and I noticed a slight oddity about the "sewer" tiles:  the other terrain types can be combined in two ways to make them look either "raised" or "sunken".  This, however, does not work for the sewer tiles, because the three tiles starting at pixel (5 * 32, 14 * 32) are a bit too tall.  I decreased their height to 16 pixels (instead of 32) and then they line up nicely with the corrners just above them, allowing for "sunken" as well as "raised" "sewers".