The website describes the method of burial like this:
A file clerk from the burial crew recorded the information before the bodies were stacked in the trenches – without coffins, lying on their sides, and as close together as possible. After filling, each grave was marked with a narrow wooden strip bearing the deceased's registration number.
And as you say, they were "row graves". So while the bodies were laid "as close together as possible", they were still sufficiently separate to put down gravemarkers for each one. We see that in one of the photos. I don't think this is very comparable to the story of Treblinka. Maybe as a sanity check.
The aerial photos show that large sections of woods around this area had been deforested, but none of these are mentioned in the text or marked on the map, so they are not mass graves. If I only count the white rectangle, the approximate rectangle where the mass graves are supposed to be, including walking paths, I get
~6,400 square meters.
If I take the map from their PDF file and strictly count only the area of the graves marked 1 and 2, by using a color histogram, I get
~8,900 square meters. This number is probably more accurate since the aerial photo is rough and obscured by trees. I
think this sounds right for the 11,500 bodies.
As for the ash grave, marked on the map in the PDF as number 3, it is about as small as reported by Irving. Where Irving estimated it at 25 x 16 ft, I estimate it at 32 x 15 ft. As Leif
touched on in the debate thread, this would barely be enough space for the ashes of 6,865 people. If we assume a grave depth of 6 ft and we use the rates given
by Callafangers:
25 ft x 16 ft x 6 ft = ~68 cubic meters of space.
6,865 bodies x 0.008 cubic meters ash per body = ~54 cubic meters of human ash.
6,865 bodies x 0.078 cubic meters wood ash per body = ~535 cubic meters of wood ash.
So much material put into such a small space would make a sizable mound. For the sake of argument, let's try maximizing the grave space. My largest estimate of the area came from using a color histogram, at 66 square meters. If we assume a depth of 2 meters:
66 square meters x 2 meters depth = ~132 cubic meters of space.
There is still a big discrepancy. I have to suppose that a substantial part of the ash was removed in some way that was undocumented. Perhaps much of it was lost to wind and rain, or it blew off the top of the trucks, or it was trucked away to multiple locations. If not that, something else in the assumptions has to be fixed. Perhaps the pit is deeper than I assume, or the pit's dimensions were reduced after the war.