The slab was poured far too low to the water table, and there was significant ground water in the area (even though this property was NOT in a flood zone).

I suppose that at least solved the mystery of how the water was coming in and at least it means its not from the blocks filling up with ground water (drain tile not failing) - lol.

That area needs addressing, but it will be tricky to know if that is the issue, or if it comes from groundwater/waterproofing below.

IF oil works through this collapse and returns to more recent levels, and IF farmers actually have groundwater this year, Bakersfield could be the appreciation story of California.

A big empty vessel sitting in the ground will move, especially when it rains in the winter and the groundwater puts pressure on the pool shell.

However, if there are some cracks or penetrations in the slab groundwater infiltration could be a concern...For sure it sounds like you should at least have someone familiar with foundations take a look...

However, high ground water levels, like those after heavy rain, can submerge leach fields, causing "over saturation" and system failure, leading to potential septic backup in the home and, if Santa Cruz County Environmental Health is notified, could trigger a ATD upgrade requirement.

. :) 400 GPM will run a small city LOL.. maybe you meant 40 gpm :)   having dealt with wells and septics my entire career  one would need to do some good due diligence on this stuff.. if trucking in water is allowed then I guess thats the fix when the well dries up.. if the ground water is not recharging you certainly could have a lot  of dry holes.

I have seen old septic systems consist of an old car body for the tank and field all rolled into one (BTW cars rust away and the whole thing caves in - also provides zero treatment and discharges raw sewage to the groundwater) Proximity to a well is important.

He probably has a leak, we're at the top of the Palisades so groundwater is unlikely.