Some of these areas of construction waste have been present for some time. The last photo shows an area that is recently filled (about 1 month). I thought initially they were trying to fill the fishponds but access to the area appears to have been blocked so dumping has stopped at this site.
The area to the west of the buffalo fields (highlighted on your map) has been undergoing a lot of this sort of activity - it looks like the abandoned fishponds here (which were dry and overgrown) have been filled in.
