If I were to suggest something to the SPTC, Prior to covering with the sand I'd recommend scarfing up the top layer of the old dump site and "cart" that material over for disposal at the main site. The residues from low temperature combustion of plastics are pretty damned nasty (dioxins)...not much can be done about the leachate that has already occurred. However, additional leaching of those compounds into the ground water could be precluded by disposing of the top layers of soil at the main dump which was built with a "liner"to preclude ground water contamination.