In regards to mitigation measures for the redevelopment of brownfield sites, the two design options that I am most familiar with, is to install a 40mil impervious linear and or install 3′ of clean fill.
The basic concept is that you are capping the areas of contaminated soils with a liner or with soil.
In regards to the impervious liner, determine the proposed grades throughout the site and then install the linear at the bottom of your excavation (base of the driveway/road base).
In regards to installing the 3′ of clean fill, determine the proposed grades throughout the site and then excavate 3′ below this and install 3’ of clean fill.
Installing the 3′ of clean fill, allows for the greatest flexibility in your design and the use of the site, but will greatly increase your construction cost.
Can you create landforms on the site that will allow you to fill portions of the site so that you can leave the contaminated soils on site?
In the areas of lawn and plantings is the loam contaminated? If so your options are to use the contaminated loam and fence in the areas so there is no skin contact or install the clean fill and loam seed and install plantings.