While redoing the landscaping in the backyard my partner and I noticed some concrete under where we were looking to plant a shrub. Decided to see just how big this piece of concrete is and now we are a bit worried.
We found the edge of it and started to dig. It looks like someone put plywood, pavers, and a bucket to “seal” the void. After removing those items we found a cavity that is ~ 4ft deep and ~6ft wide (forwards and backwards). There are stones that look to be purposefully arranged as a boarder around it although it the stones look weird almost like someone mixed concrete with large aggregate and then broke it up.
There are two iron pipes that are heavily corroded and one looks to still have water running through it even though out main water line is on the complete opposite side of the house (opposite corner and opposite side). Looking at our basement and crawl space I dont see any pipes that could come through and we have no sinks/bathrooms on that side of the house. There is another larger pipe, 4-6inch ID, that isnt capped.
Link to images: https://imgur.com/a/ZIkxfNP
How should we proceed?