How can a creosote-treated railway tie retaining wall be replaced safely?
Taking down and replacing that kind of wall can be a huge, expensive job requiring the services of a professional (especially if the cottage foundation is nearby) and, if the ties being replaced are below the high waterline, you’ll need approval from Fisheries and Oceans Canada and possibly other bureaus depending on which province your cottage is in.
Although having creosote-treated wood near the water isn’t ideal and should be avoided in a new installation, the disruption caused by taking out an old wall and replacing it will do more environmental damage than leaving it in place. The chemicals will have penetrated deep into the wood cells and won’t leach out into the soil or water to any appreciable degree. Unlike creosote itself, creosote-treated wood doesn’t pose a risk to humans as long as frequent direct physical contact is avoided (so don’t sit on the wall, for example). However, Health Canada should be consulted for updates on health hazards associated with the use of creosotes in wood.