The areas I work in are primarily brownfields and remediation related to organic contaminants. The state in Canada, and around the world for that matter, is that there are easy sites to clean up, and those easy sites have been cleaned up. These are sites with contaminants near the ground's surface in nice, permeable, sandy soils. There are a number of different technologies available to clean up those kinds of sites.
At the other end of the spectrum, you get into contaminants in fractured rock at great depths, and you have contaminants like PCBs or heavy metals that are very difficult to remove. That's still a challenging area for remediation scientists.