What causes magnetic fields in houses?

The following diagram explains what causes AC magnetic fields in the houses that are near underground electrical cables.
In the drawing there are two cases:
1) the ideal case when all the currents return through the same cable;
2) the real situation - which causes the magnetic fields - when some currents return through earth.
The point 2) is "preffered" I guess for economical reasons, because it saves the neutral wire. Probably, logically, if all the currents return through the same cable, the neutral wire should be three times thicker.
However, this real configuration produces "net currents" ([2]) - in the diagram denoted Ig1 and Ig2 with red paths. Through this configuration the currents do not cancel within the same cable => the cable produces magnetic fields proportional to the currents within.

What are the health effects of these AC magnetic fields?
One can read in [1] that it depends of the field intensity, of course.
And this also depends on the distance from the house to the cable.
But, as many houses are near the underground cables, the situation cannot be neglected.

What are the maximum permanent allowed magnetic field intensities in a house?
These values as written in [1], are presented in [3].


[1] http://magneticsciences.com/EMF-health
[2] https://www.emfs.info/sources/distribution/uk/
[3] https://www.baubiologie.de/downloads/english/richtwerte_2008_englisch.pdf