I moved into my house a couple of years ago. The lawn was horrible so I put in new sod. A small portion of the yard quickly died. I then tried seeding this area with no luck. Being new to lawn care I thought I did something wrong, however upon speaking with some of my neighbors I learned that the previous owner was an elderly man and died while fertilizing his yard! Apparently an entire bag of fertilizer was dropped on this area and was left on the yard for years which my neighbors say is why nothing in this area will grow. Of course I have watered and watered and watered again to try to wash this away. Any suggestions?
I could agree with replacing the soil if this had been in the last few years. But since you say "was left on the yard for years" I am not so sure. Fertilizer leaches out over time and you say you have watered thoroughly. I would take a sample to your local county extension agent for a soil test, explain this particular concern, and find out for sure what the problem is. You may still have to remove the soil, or some other tactic, but at least you won't be "parts swapping" as my dad used to call some mechanics.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!