Moutain Home Builders (MHB) is a residential real estate developer. MHB purchased a 50 acre parcel of land from a rancher for residential development. MHB undertook soil studies as part of development and fond that the soil was contaminated with arsenic and lead from silver mining operations that had taken place many years ago. The site was cleaned up by the EPA using superfund monies and MHB held liable for the cleanup costs. Does MHB have a valid defense? Explain.