IS THE OKC MEMORIAL A DECORATIVE VERSION OF THE DOME ON RUNIT ISLAND?

This is how the United States dealt with the radioactive soil produced in some of their nuclear tests conducted in the Pacific Ocean. The radioactive soil was collected, buried and capped with concrete. 

This is the OKC Memorial. It was creatively graded and decorated with plenty of concrete structures in order to hide the residual left over radioactive soils at the site. Most of the wreckage of the Murrah Building was hauled to a guarded landfill. 

These two photos give you a sense of the grading that has taken place at the bombing site. The grassy hills slope up from the reflecting pool. I would say there is probably a 15 to 20 foot difference in elevation from pool level to the top of the hill. The construction of the site took place in such a way that all radioactive debris could be hauled off and the left overs could be buried beneath the concrete or the beneath the slope of the lawn.