The pit is done (at least in the short term). Several days of shovelling dirt from the dirt piles in the back yard into the wheelbarrow and then dumping it into the pit has both eliminated the dirt piles, and filled in the pit.
The dirt in the dirt piles was what I saved from digging out the pit (and other parts of the yard). Mostly it would then be the heavy clay that is native to this area. But it also includes some amount of sandy loam that some contractor would have brought in, and some amount of better, composted soil that we brought in later. But still the bulk of the dirt is not very good. So to improve the soil quality, I mixed in 32 bags of leaves, and about 30 bags of "organic humus".
The "organic humus" is the least expensive soil additive from Lowe's. It's mostly semi-composted wood products. It looks like pine needles plus other stuff. The leaves were from the neighbors. It being Fall, lots of people rake up their leaves, put them in bags and leave them on the curb for the City to pick up. I picked up some of these bags and brought them home.
As I was breaking up the dirt piles and shovelling it into the wheelbarrow, I mixed both the leaves and the humus into the soil. The theory is that this will add organic compounds to the soil, and make it better soil. It certainly makes it lighter and airier. I expect it to settle quite a bit over time in the pit.
The two spots in the back yard where the dirt used to be piled are now just barren dirt spots.
I've tried to spread some grass seed and put down a layer of organic humus on the top of each area. If we were to get any rain, the grass might grow and help keep the dirt in place. If this doesn't work, I'll try something else next Spring.
I have receipts for 30 bags of the humus from Lowe's this month $46.76, plus there were probably a dozen from a previous purchase. In addition, it was taking days to move the dirt from the piles into the pit, so, since time was of the essence at this time of the year, I hired a day laborer to help with shovelling. $80 for a days work. This allowed me to finish up the digging in one day.