snedat1 = Import["/Users/robertcaldwell/Desktop/BRAZIL\ 2012/Materials/tmp.dat"];

(* best fit is χ^2 = 562.25 *)

ListContourPlot[snedat1,Contours->{562.25+2.3,562.25+6,562.25+9.2},ColorFunction->"Warm",ContourStyle->{{Black,Thick},{Black,Thick},{Black,Thick}}]