What are the potential pitfalls with 6+ family rehabs?

[Andy Kurtz]

I've found a potential deal, but I don't know what I don't know when it comes to investing in 6+ unit buildings. Found a bank owned 6 family in a rural C+ area in New Hampshire. Property is boarded up, and needs massive rehab. Electrical and roof are newer, which is a nice plus. The bank recently dropped the price by 50%, to $50k. Assuming a rehab of $20k/unit, the rents in the area would make this a cash cow, as the units could each fetch $750 with ease. My concern is, I'm afraid there's a hidden surprise that would only be uncovered by performing an expensive environmental cert. My questions are twofold - #1 - what are the worst possible pitfalls that are typically missed by the naked eye? #2 - is there a way to tell, through public records, if there's something buried underground that would cause a problem? Thanks for your input.