The GoodFlow concrete leach field chambers are made of concrete and are H-20 rated so they can withstand a load of 10,000 psf (pound per square foot).  Most plastic chambers are not H-20 rated and can be crushed under the backfill and/or heavy equipment.  Plastic chambers, including H-20 rated plastic chambers, also ‘knife’ into the ground.  This happens when there is pressure on the chamber from the backfill or heavy equipment and the sides of the chamber knife into the ground because of the thin walls on the side of the chambers.  When a chamber is knifed into the ground it decreases the liquid storage capacity and increases the chance of failure with septic backup into the house or leakage into the topsoil.  The GoodFlow system has thicker sides and does not ‘knife’ into the ground.