Ammonium nitrate is about 18.6 cubic feet per (American 2000#) ton.
That would be just over 5000 cubic feet, or a 10' X 10' building 50' high.
That's enough volume and weight to go bang.
Based on that information, lets assume that the WHITE building in the picture is their office building. The car spots are there. The building due west of it, the gray one, is therefore the Ammonium Nitrate storage facility. Large rectangular building - just what we would store a large volume of bags of fertilizer in.
Just west of the building like they said.