I have several bags of soil that were contaminated with residue from oil paint and thinners. The painters cleaned their supplies back behind the garage right over the roots of a large tree, so I removed what I could and planned to take the soil to the city's disposal center. Is there a safe way to reclaim the soil myself with organic amendments? Should I treat the remaining soil around the tree roots?

Since you already dug up the soil, I would spread it out to let the thinners evaporate. Then put it back where it came from with some molasses and organic fertilizer like alfalfa or corn meal.

In addition to what was already suggested, don't forget that lots of homemade compost also will supply plenty of beneficial and cleansing microbes to help the soil "contamination" issue too.

Good point. I usually don't suggest compost but this is one place where I do like the application.

Don't forget humate, deactivated charcoal and zeolite. They work too.
Humate is inexpensive and generally available. The other two can be a little more difficult to come by.

Kathe

A little d-limonene or orange oil added to Garret Juice will help too.
Remember it only hurts when it gets on green tissue in solutions that are stronger than they should be. Definitely put the soil back after it has had time to let some of the contaminants burn off.

A thought - your tree would benefit from the sick tree treatment to deal with anything it has already absorbed.

Kathe