Soil Testing

does it cost a lot to get it tested? I'd give it a shot before you start in on figuring out raised beds. if you get it tested and everything is normal, chances are you're not having ground-seepage issues and can go ahead and plant in your garden proper. otherwise, construct some beds, or head to ikea for some cheap alternatives.

The book they use to teach the master class at the BBG is called "Teaming With Microbes: A Gardener's Guide To The Food Soil Web" and you can check it out at their library (but not the BPL, I already checked.)

There's a $9, less info test through UMass. So you could afford more samples.
(I just went to urban dirt class at the BBG last weekend. Who knew concrete makes soil alkaline?)

There was a soil mapping project that they rec'd, if you're really into it
http://www.nycswcd.net/soil_survey.cfm

This is obvious, but they recommended paying attention to the nutrients/pH/CEC profile as well as lead or arsenic (leached from pressure treated wood) and other contaminants.

Since you've got 3' of loamy topsoil, perhaps your building has a good history and there was a garden there before.
I lived one place that revealed a buried fridge and all kinds of other crap, so went for container gardening only. Where I am now, I know the history (Italians gardening, not burying lead paint, leaving me a figs) and I wouldn't be that worried about it -- unless I had small kids.

One strategy - especially if you're in a minimal risk situation - is to plant cover crops/things that draw the bad stuff out of the soil for a couple of years, and recondition with compost (which binds with stuff like lead and makes it unavailable to move into your fruits. The other thing I learned was leaves and stems are more risky on the contaminant front, and the long the growing season, the more contamination. So greens are less of a good idea than tomato and berries.

Subject: Rutgers soil testing

I had my soil tested at Rutgers:
http://njaes.rutgers.edu/soiltestinglab/

It's pricey -- $100 but incredibly thorough. I tested 3 areas of my yard which actually varied in acidity before planting some trees and shrubs.

Then later I sent in some plant samples for different trees that were suffering from some vermin. They sent me back a lot of detailed info with a correct ID on the spider mites and powdery mildew. The spider mite ID allowed me to finally get the right non-toxic spray:
gardensalive.com

and i may have saved the 2 junipers.