There are four basic kinds of septic systems: Cesspools: They are constructed of concrete with drainage holes along the side and is open to the sand below. Trench’s: They include drainpipe laid in 1 1/2″ Rock, Gravel less Pipe and Chambers. Pressure Beds: They are small pipes with small holes (orifices) in them laid in rock. Wastewater is sprayed into rock under pressure to distribute it evenly across the whole bed area. Mounds: They are a constructed sand hill with a pressure bed system in it. Then covered with dirt and topsoil. A ISTS Designer will make the determination which system type that is needed from the site evaluation that was completed prior to designing your new system.