A ballasting system for an on-site sewage treatment and disposal system for areas having a ground water level above a minimum depth below grade. A perimeter barrier is arranged around a selected subterraneal volume within a ground area. The perimeter barrier has a circumference and a closed end closest to atmosphere. A pump having a gas intake and a discharge side which discharges gas at a pressure greater than atmospheric pressure is also provided. The discharge side of the pump is in fluid communication with the selected subterraneal volume to lower the ground water level within the perimeter barrier to a level at or below the minimum depth below grade. A flexible membrane is located adjacent the perimeter barrier end and within the ground area. The flexible membrane extends over substantially the entire circumference of the perimeter barrier. A plurality of ballasting beams is located above the flexible membrane and within the ground area. Each of the beams extends across the circumference of the perimeter barrier. Each end of the beams is anchored within the ground area by an anchor.