I want to buy a house and would like to gain insight as to what I'm dealing with in the yard. A Cistern? Cesspool? Any ideas?

Three facts:

1) Back yard has concrete mass 18" diameter bulging out of ground about 20' from rear of house. I assume this is a capped well; the city has no record of a well on grounds and house uses municipal water.

2) There's also a broken 4" pvc pipe sticking vertically out of ground. This is located about 18-20' from rear of house and 12' from the concrete mass. Pipe is very very deep; at least 10 feet.

3) Further back in the yard, 30' or so, theres a simple fence sectioning off the remaining 18' of lot. Beyond this fence are holes 1' deep spread over a 6-7' radius plus or minus a few additional holes punched here and there roughly 1.5' in diameter. Holes could be caved in areas but it also looks similar to what would be if small plants had been dug out. A little bit of debris is back there as well. There's shingles probably from when garage was done and a carpet.


Any ideas on what this layout suggests?
thanks