Mitigation of Soil Toxins through Earthen Floors

Hello all, this is my first post to this site. Curious if anyone has any thoughts with my current situation. I’m planning a project where the building site is a vacant city parcel with buried rubble and a foundation from the existing building that was demolished about 10 years ago. When they demolished the building they caved in the walls and buried everything within the CMU basement walls. I've begun the process of excavating to locate the perimeter of the foundation and can say the CMU walls are still in great shape. I’m planning on building a new small building (probably strawbale) atop the foundation walls. What I’m not certain of is if I should plan to do a raised floor with a crawl space to avoid potentially mitigation from toxins like lead that may be present from the buried building rubble. The only other concern would be cracking of the earthen floor from differential settlement (as over time the rubble decomposes). Since the building has been there for over ten years though I’m not too worried about anything settling more than an inch or two. I’m hoping to save time and money by not excavating 8’ down and sending all of it to the landfill AND avoid the extra expense of a raised floor system. If I place a vapor barrier in my earthen floor system my hope would be that I would have plenty of barrier to prevent mitigation from toxins. Thinking further though I’m also wondering if even if I do a raised floor system would those toxins still radiate through the air barrier of a crawl space even if I vent it? And my main goal is to develop a model for redevelopment of these vacant parcels that doesn’t involve using heavy machinery, hence my efforts to avoid serious excavation. Thanks in advanced for any ideas!