There used to be a pool in my backyard. Here’s what I learned by the way my dad did it.
– Get a permit. If not the city will think you have a pool forever. Even with a permit, they will still have it in some of their databases.
– The basic process is drilling big holes in the side and bottom so that it can drain when it rains. Then filling it up with big stuff… In my dad’s case he was also removing some of the old hardscape patio around the pool to get a rectangular (vs kidney shaped) garden. He tossed all the concrete from the patio and coping and the first few feet of the sides of the pool, into the bottom.
– He then got the free mulch from the dump and filled it up… truckful by truckful. He rented a compactor and ran that over it in 8″ lifts. Rinse and repeat over many days.
– Then he put weed killer over the whole thing – since the free mulch has lots of weed seeds. Waited 2 weeks for new sprouts and retreated.
– finally he filled the top 18″ with a combination of clean fill and top soil.
My dad did it DIY style with some hired handyman help for the hauling of the free mulch.
There’s an entire subculture on moving around fill dirt in San Diego. Contractors are always looking for places to get fill dirt, or to dump fill dirt. Craigslist can be your friend if you’re willing to do the work. Make friends with a pool contractor – they are ALWAYS looking for places to dump fill dirt.