That's nothing. Should I ever be able to afford building on a vacant lot, one of the rules not to be broken is no coral and no "topsoil". Coral and "topsoil" are the reasons why I deal with salt contamination, pH problems, as well as elemental toxicities in residential landscapes. Ground coral is an easy material for the builder to compact to spec for foundations. Topsoil is a nice way of describing the subsoil dug out of another building site so that several inches of ground coral can be brought in.