I have Indian Hawthorne hedges growing on both sides of my driveway facing the street. One side has just started dying from about six feet from the driveway and outward on either side. Half the hedge is now gone, and, I need advice before I replant. My bathroom drains both flow into the pipe that runs under the center of the problem, but, having had a blockage cleared between the access point and the street main, I no there is no blockage. Any ideas?