i'd have to agree with catmando. I say put a couple in it and watch the magic.... or demise.... it could go either way obiviously but i sure would jump at the chance to try it. could be some of the most fertile soil you've ever grown in. i wouldnt worry too much about chemicals and what not..
how 'bout some grower's mix, with perlite, EWC and lime.
the Grande is filthy. using some pond muck as part of your mix is okay. it will certainly be alive....lol. just make sure it drains well. no more than a 1/4 of the whole mix, imo. i use peat, perlite, and poop as a base soil. cheap as .....dirt 1:1:1 i lime it, and amend it.