For the project that went out to bid in 2019, the city included the toxic remediation specifications for the remediation project that ended in 2011. It's a long document, but if you are interested in what was done to remove the ash pit waste from the long ago dump that existed before Watson Park became a park, you can read the details here.
The first section of this pdf is for the 2019 construction, but keep paging through and you will see the previous specs.
The plans are also linked below.
specification file is over 900 pages!
and here are the plans