Utility lines are usually installed prior to any new construction. If the land is graded, leveled, or reshaped in any other way, this will change the depth of any underground utility lines. Natural ground settling will also change the depth. If you need to dig near the locate marks, hand-dig (use a hand implement, like a shovel) or soft-dig (use air or water pressure) within 24 inches of either side of the markings to avoid damage.