Wondering if anyone has experience setting one of the large black water tanks up to collect rainwater?
Mostly I want to know about protecting the tank from tree roots. My idea is to dig down some and put some sand at the bottom and then do a ring of earthbags maybe 2 high around the perimeter so as to keep earth from being directly against the tank. Also if the tank ever needs to be lifted up this should make that easier. So the tank is about 8 feet high and this will put about 2-3 feet of it below grade. This tank will pump into my off grid house and also run downhill to the garden. Already have the tank and looking to set up and connect to gutters in the next couple of weeks.
Check with an engineer to get the correct back fill material for your soil conditions.
Buy a tank that is pre-stressed for direct burial.
2500 gals x 8.5 lbs/gallon @70 F = 21,250 pounds when filled.
MAKE SURE YOU COMPACT THE SOIL UNDER THE TANK PROPERLY (use <6" LIFTS, with compactor, not just tires.)
Having no leaks in the tank will eliminate any problem with tree roots. Proper compaction prevents holes.
Back fill all the pipes & walls carefully to prevent damage from settling.
As with any foundation, provide unimpeded surface drainage away from the foundation.
From other threads, I see you'll need a "first flush" tank to keep bird poop & dust out of your cistern. Look up how to use them.
If you need to lift the tank, you'll have to excavate even a foot of back fill. Use whatever the local engineer calls for a direct burial tank.
If you plan to have water delivered to the same tank, make sure your tank is lower than the delivery truck, (pumping costs extra).
My experience is in soil testing for foundations. The tank manufacturer, if known, should have specs for foundations & back filling.
Consider elevating the tank for a gravity feed to your house?
Consider using two tanks, one near the elevation of the greenhouse, so you have the potential of a closed micro-hydro water battery:
Using excess solar/wind power to pump water from the lower greenhouse tank to the 2500 gal tank as power is available.
Allowing that water to flow to the down hill tank, diverting the flow of water to the greenhouse tank thru turbine driven generator:
Provides reliable back-up power, (and drinking water when you need it...)!
The sizing of the tanks depends on your total power loads, and the excess daytime power that you can generate.