There was a dirt road to our truck garage and when I was a kid, I would go out with buckets and have to sloush oil with a scooper all over the road, you would fling it, to keep the dust down. There were trees on both sides and grass and a field on the downside. I never in 25 years saw the oil kill the trees, damage the grass or the field where rain washed off into. I think the oil contaiminated soil thing as hazardous waste is a big money making gimmick. The City boro would come out actually spray the fairgrounds with used oil, again no side effects whatsoever. I am one that experienced this , not read about the impacts. Did not do a thing. About the mower deck, I think the decks are made of better metal now, its been a long time since I seen one rust out, I think if you clean it out ever time, scrape the grass off, you will get sick of the mower before it rusts out.