I have the following file.grd with the content shown below. This file is an output of the program CALPOST, which reads the outputs of the program CALPUFF. I can read the file.grd using R and raster:
I wonder if I understand your question well. You could use your grd file (or dat file as Calpost allows) as input for the Surfer program from Golden Software (time limited trial version). Or stay in the R sphere and try gdalUtils, or perhaps PuffR. You might have to edit your output file.