They shall be free of all structures except historic buildings, stone
walls, and structures related to conservation uses. The City may grant
approval of structures and improvements required for storm drainage,
sewage treatment and water supply within the conservation areas, provided
that such facilities would not be detrimental to said conservation
areas (and that the acreage of areas required for such uses is not
credited towards minimum conservation acreage requirements for the
tract, unless the land they occupy is appropriate for passive recreational
use). The City may also grant permission to construct modest buildings
for recreational uses, such as shelters for the use of ice skaters,
etc., provided they are located within unconstrained parts of the
conservation areas (i.e., not wetland, floodprone, or slopes greater
than 20%).