One thing that has been grossly overlooked in this discussion is that coal ash is not like soil.
Just because it may have similar amounts of contaminants (or maybe even less) than some acceptable soil, one must account that soil has had thousands of years of rain to rinse out whatever AVAILABLE free toxins it has. That which remains will be mechanically or chemically bonded to a significant extent. Coal ash has had no such "long washing" and thus has a far higher rate of leaching chemicals.
Read my disclaimer under the link before ranting http://action.sierraclub.org/site/DocServer/coalashrule_MythFactSheetMay10.pdf?docID=5283
It starts with:
"Myth #1: Coal ash is like dirt."
It is from what some consider a fairly extreme group but it does use references, it isn't just a "pull it out of my..." opinion.
Knee jerk reaction folks won't even consider such words that don't fit their preconceptions. Others will believe everything and those in between may think.
It also (as do most coal hazard articles) uses information from the most common coal used. Quality anthracite is far too expensive for most power generation. However, the accelerated leaching or "available contaminants" is clearly true for any ash.
Quality anthracite (if one knows they actually are getting that) is far cleaner to start with than what is used in most power plants.
As stated before, I am in the middle of the road. I do use my ash but won't trust it's high chemical release rates anywhere near my produce nor would I endanger a well if I had one in fairly porous soil.
To each their own, but don't compare soil contaminant quantity with that of ash which has much higher available contaminants.