Dirt floor of 3 sided pole barn

[Pgw]

Am housing my chickens and geese in a 3 sided pole barn with dirt floor. It was once used for horses and tractor storage. My concern is the soil. Should I be concerned about contaminants and how to remedy.? I plan on using pine and other hardwood chips on floor of run only and hemp inside coops.
I built a 20x10 ft run that will house 2
coups. They will also have a 50 ft x30 ft area to free range. Thanks!

 

[aart]

Tractors might have spilled oil and/or gas.
Would have to replace ~6" of dirt to reduce risk.