They've already done soil testing in several areas and no contamination has ever been found.

As others have said, request a walk-through with the landlord prior to move-out.Commonly overlooked spots: damage behind doors, kitchen cupboards not wiped clean and occasionally items left in the deep reaches of the cupboards, refrigerator seal folds not clean, window tracks not clean, stove top dirty underneath (most lift up), range bottom drawer dirty and/or items left inside, door stoppers missing, loose towel rods, dusty light fixtures, plumbing fixtures not entirely clean, outside lights and mailbox dirty, tops of door trim and tops of baseboard dirty, light switches dirty, refrigerator drip pan dirty and back of refrigerator dusty.BTW, to clean the range burner bowls, soak them overnight in ammonia and then scrub.

I prefer a house without carpet but I'll still buy one that has it since the cost to replace it with laminate or paint the hardwood underneath is pretty low and requires less maintenanceI will usually leave the carpet there until it is destroyed which is usually after 1 or 2 tenants

Fortunately, the place was habitable and sanitary since there was concrete underneath so I had the right to continue charging rent.

@Jerry K.Thanks for sharing. invest in raw land has so much opportunities if you know what to look for the different components, like soil, vegetation , mineral rights, water source...etc.In your case is the billboard.

As a rehabber and wholesaler myself I can say that that kind of behavior is frowned upon and can soil your reputation.As a rehabber I have a rule when dealing with wholesalers (as most rehabbers do): I go through the wholesaler or I don't do the deal at all.

. - I am assuming that normally carpeted stairs are wood underneath? 

In my situation the seller had owned the property free and clear so it was a pretty smooth transaction, it sounds like there is still a bank mortgage attached to yours and that is what you Are looking to get from underneath so your situation might be a little more detailed.

Then sadly in that 2 weeks the inspection supposedly came back with ground water/soil contamination.

Yeah I have this same problem.Make sure you spend an extra couple bucks per tube and get the good stuff.It will be waterproof tight and the good silicone stays pliable and flexes when expands.This keeps the seal 100% tight.The cheap crap won't flex and then will start cracking and allow water behind it in certain spots.Will slow the leak down but not get rid of it completely.I would take this time to make sure where the ceiling is soft that there is no leaks coming from the tub drain,shower diverter,or shower head pipe behind the wall.Also it's not always the tub leaking.The toilet is usually close by to the shower.The seal at the toilet to the floor for sewer or the bolts from the tank to bowl could be bad or the seal for the flush between the tank and the bowl.The water can slowly run down the outside of the back of the tank under the sub floor.When you take the drywall off and look at the sub floor underneath you should see darker areas where the leak is more prominent.You can also use a moisture meter to determine the first point of entry for the leak.Make sure control valve and diverter are snug to the wall and sealed properly.Water can get behind there while taking a shower and cause a slow drip.