Yes. Most drainfields (such as rock and pipe, chamber system, etc.) are constructed in open lawn areas and are not designed to handle vehicles or heavy equipment driving on them. The weight of vehicles and heavy equipment compacts the soil, which can damage pipes. Impermeable materials, such as concrete and asphalt, should not be laid on top of a drainfield because they reduce evaporation and the supply of oxygen to the soil. Oxygen is critical to the healthy bacteria in your septic system and the proper breakdown of sewage by soil microorganisms.