Assuming there's not too much iron and steel in the land fill, it's might be possible he could find it with a sensitive enough magnetometer at 1 meter, maybe mo

Assuming there's not too much iron and steel in the land fill, it's might be possible he could find it with a sensitive enough magnetometer at 1 meter, maybe more so if you built a motor to move it around rapidly. I think the field strength at 1 meter might be something like 1 milliGauss, which should definitely be detectable. Walking the field and recording the magnetic fields might be possible, you'd at least know the range you needed. Secondly, any recent dated arial photos could maybe be used to determine a better approximation of depth, i.e. looking for a marker in the actual photo, then going to dig to find that marker, record the depth.