How to build on "junk fill"?

[Mark Beekman]

I recently purchased a vacant residential lot on which there was previously a single family home that was foreclosed on and then demolished. The house had "sinking" issues which rendered it unsafe. Supposedly about 100 years ago they dug a test pit looking for iron ore. When they didn't find any, the pit was then used as a dump for construction debris and then covered over.

I just got a hold of the geo-engineering report ordered by the Township, complete with borings, which basically says that there's uncompacted, junk fill down to 30 feet, with bedrock at 45-65 feet.

What is the best approach for building on a lot such as this? The geo report mentions replacing the fill and properly compacting it. The lot is 14,000sq/ft, so I'd imagine that would be a big to-do, unless only the soil under the house footprint would need replaced. I've been reading up on helical piers and am wondering if that may be an option.

I'll be talking to some experts in the coming weeks, but I'd like to get some education from BPers before I do.

[Wayne Brooks]

Helical piers need to be installed in sound soils.  As far as I know, you can't install in rock though.  Here there would be either excavate and replace, yes a big to do, or drilling/installing concrete pilings (square 8-12") but then that means "beam" foundation construction, on the piers.