The maximum depth a tree stump and its roots should be ground down to remove it properly is 6 feet below the surrounding surface soil. Any deeper than that is excessive and puts plumbing pipes, gas lines, and electrical lines at risk. It also puts landscaping, pools, decks, patios, and other non-biodegradable materials at risk. In rare cases, deeper stump grinding may be necessary at a higher cost depending on the specific type of tree, health, and age.