Wooden ties leach the oily creosote, a carcinogen, their whole life, especially at the beginning. Even the vapors from fresh ties are nauseating. After 30+ years I assume less than 50% of the creosote remains. What I don't know is how much creosote dissolves in water (probably not much), and if there are any soil bacteria that break it down over time.
Where I live we have only wooden ties on three (at times 4) tracks that go right down the middle of the city, yet our water supply exceeds EWG standards, which are stricter than the federal government's standards.
So I think you are right in that not much creosote dissolves in water.
