He told me the residents have now received a "consultation paper" re the new runway and this refers exclusively to a new runway, NW of the airport, heading toward Datchet.
http://www.heathrowairport.com/stati...tion_FINAL.pdf
The M25 will go in a tunnel and a reservoir will be filled in.
I suspect you may be thinking of the former gravel pits just to the SW of the M4/M25 junction.
They would certainly be under the proposed runway and need to be filled in, but neither the original nor the revised NW runway proposal go anywhere near either the Queen Mary or Wraysbury reservoirs:
