A remediation type of activity can happen a few ways.
You can remediate by dealing with the contaminant on the site. I won't even try to get into any kind of scientific explanation of the process there, but you can deal with it on the site, or you can dispose of it.
Then there are also risk mitigation activities to block off the site or make it somehow inaccessible. There are other types of risk mitigation activities that could be undertaken.
I don't know whether Mr. Sattar has a few more examples, but there are multiple ways to deal with this.