When you purchased the property in the new developement you purchased its entirety from its topsoil all the way down unless there were exclusions for minerals below ground in the grant deed to you. If there was nothing in the purchase agreement excluding the mounds of the topsoil from the purchase agreeemnt, you bought the land and all of the mounds of topsoil when you closed escrow.If the contractor is claiming ownership of the mounds of topsoil on your property, he or she will have a very difficult time proving his ownership to this dirt since it came with the property that you now own. You should ask him or her for the factual and legal basis for his or her claim to this soil.Good luck.