I'm off riverdale and Glassell, right down the street from where you used to live. small world.
The soil is sandy because of the santa ana river bed.
Naw, no toxic problems at all. I'm doing it because I've already fixed three under-slab leaks over the past two years and now I have another. I'm tired of busting holes in the slab and then trying to match tiles.
All the leaks have been on the hot water lines, which I've been told is normal. The hot water is sposed to develop pin hole leaks 3 times as fast as the cold unless someone is BS'n me. The copper pipe is thin wall, they went cheap when they built the house.
No recirculation system, just a hot water heater in the garage.
I've ran new pipes up in the attic on 1/3 of the house already (built in 1969) but because I have a breeze way twixt the garage and the house it's a PITA to run all of them in the attic. The main line comes in from the front of the house, all the way to the garage which is in back around the corner, then back to the house again. Not easy access to get the pipes in the attic there.
The epoxy is sposed to seal all pin hole leaks and prevent future leaks without having to rip up all the walls and stuff.
I plan on living there for 10 more years, then I retire to Utah or Idaho or someplace cold.
Here'as a picture of the garage