MASTECH MS6818 Located underground concrete pipe at 1.4 meter depth

Using the "MASTECH MS6818", I located underground concrete pipe at 1.4 meter depth and at 20 meters of length. I used a wire with an copper area of 0.7mm^2 and a plastic isolation. (1.1 meter is only the entry depth, the pipe is actually located at 1.4 meter)